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EFFECTS OF CLIMATE CHANGE ON THE EPIDEMIOLOGY OF VECTOR BORNE
ZOONOSES IN DEVELOPING COUNTRIES
(A case study of Rift Valley Fever in Kenya)
1. INTRODUCTION
1.1 Preamble.
Volatility of infectious diseases may be one of the earliest biological expressions of
climate instability (Epstein P, 2008).
Changes in climatic patterns and in seasonal conditions may affect disease behaviour in
terms of spread pattern, diffusion range, amplification and persistence in novel habitats
(Martin et al, 2008). Vector-borne and zoonotic diseases, such as, Lyme disease, West
Nile virus, Malaria, Rift Valley Fever (RVF), Plague, Hantavirus pulmonary syndrome,
and Dengue fever have been shown to have a distinct seasonal pattern, and in some
instances their frequency has been shown to be weather sensitive. Because of the
sensitivities of the vectors and animal hosts of these diseases to climatic factors, climate
change-driven ecological changes, such as variations in rainfall and temperature, could
significantly alter the range, seasonality, and human incidence of many zoonotic and
vector-borne diseases (FAO/IAEA, 2010).
Rift Valley Fever is a vector borne zoonotic disease of importance in Kenya. It is a
peracute or acute disease of domestic ruminants caused by a mosquito borne virus and
characterized by necrotic hepatitis and a hemorrhagic state. Humans become infected
from contact with tissues of infected animals or mosquito bite. Infection in humans is
usually associated with mild to moderately severe influenza-like illness, but severe
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complications such as ocular sequelae, encephalitis and hemorrhagic disease, occur in
some patients. Outbreaks of the disease occur when particularly heavy rains favour the
breeding of mosquito vectors (Swanepoel and Coetzer, 2003).
Climate change is likely to affect the epidemiology of RVF owing to its effect on the
frequency of extreme weather patterns like droughts and floods hence the effect on the
population of the mosquitoes and other biting insects which are the main vectors.
Ironically, the countries that have contributed least to global warming mainly the
developing countries are the most vulnerable to its impact especially from diseases that
higher temperatures can bring (FAO/IAEA, 2010). This is because they lack not only the
technology, but also the financial resources and the public-health infrastructure. (Barnhill
H, 2008).
Rift Valley fever (RVF) disease was first reported in Kenyan livestock in 1912 and the
country has reported the most frequent epidemics of the disease involving both humans
and livestock (Murithi et al, 2010).Although low-level RVF virus transmission likely
occurs within enzootic regions each year, the emergence of virus activity in large
epizootic-epidemic cycles is periodic and associated with abnormally high rainfall events
that allow for the abundant emergence ofAedes species floodwater mosquitoes
transovarially infected with RVF virus and secondary vectors ( Bird et al, 2008).
This project seeks to analyze the change in weather patterns (specifically temperature and
rainfall) and its relationship with RVF outbreaks in Kenya in the last 15 years. This will
help to give a general understanding on how the epidemiology of vector borne zoonotic
diseases is likely to change as a result of climate change and suggest ways in which
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Kenya and other developing countries can constitute public health modalities by which to
deal with the resulting health challenges.
1.2.Problem statement.
Climate change is emerging as one of the main challenges that humankind will have to
face for many years to come. Human and animal health issues are only two of many
concerns, albeit quite crucial. Climate change could also become a major threat to world
food security, as it has a strong impact on food production, access and distribution.
Abnormal changes in air temperature and rainfall and the increasing frequency and
intensity of drought and floods have long-term implications for the viability and
productivity of world agro-ecosystems (Martin et al, 2008).
While the implications of future climate change are complex and difficult to assess, it is
certain that infectious zoonotic diseases will have an increased impact on global health
issues and their control will be a major factor in social wellbeing. If vulnerable
communities can be helped by significant investments in health services and improved
management of climate-sensitive diseases in the immediate future, then humans will at
least face the potential impacts of climate change with a lower baseline of infections
(Martin et al, 2008).
Based on the problem stated, this study seeks to analyze the periodic prevalence of RVF
in the last 15 years versus the climatic trend(rainfall and temperature) in this period and
in this way show how climate change is likely to affect the epidemiology and the
resultant socioeconomic impacts of RVF and the steps that should be taken in terms of
early prediction, prevention and control, in order to minimize or eradicate the negative
impacts of this disease as well as other vector borne zoonoses.
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1.3. Objectives
1. To determine how many outbreaks of Rift Valley Fever have occurred in Kenya between
1995 and 2009.
2. To assess the climatic trend between 1995 and 2009 using rainfall, temperature and
humidity.
3. To assess the relationship between Rift Valley Fever outbreaks and climate (rainfall and
temperature) between 1995 and 2009.
4. To study the trend of average annual temperatures in a representative district of each
province between 1995 and2009 to ascertain if temperatures have generally been
increasing or decreasing.
1.4. Justification
Climate change has far reaching consequences that go beyond health and touch on all
life-support systems. It is therefore a factor that should be rated high among those that
affect human health and survival (Githeko et al, 2000).
Studying how climate change impacts the epidemiology of RVF in Kenya helps us use
this as a model to project the expected changes in epidemiology of vector borne zoonotic
diseases in developing countries in general. Greenhouse gas emissions which are the
major culprits of global warming are bound to be on the increase as the country aims to
transform itself into a newly industrializing, Middle-income country providing a high
quality life to all its citizens by the year 2030. To combat poverty, Kenya is expected to
raise income in agriculture, livestock and fisheries even as the industrial production and
the service sector expand. The country plans to implement 4-5 disease free zones and
livestock processing factories to enable Kenyan meat, hides and skins to meet
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international standards (Government of the Republic of Kenya, 2007). It also aims at
having a sustainable environment and reducing losses attributed to environment related
disasters. To do this, Kenya seeks to enhance disaster preparedness in all disaster prone
areas and improve capacity for adaptation to global climate change. Incorporating or
integrating adaptation to climate change into planning processes is a necessary strategy
for sustainable development over the long term (Government of the Republic of Kenya,
2007).
This study will help come up with solutions that will bring the country one step closer to
realizing its vision 2030 goals as well as implementing changes that will benefit the
developing countries in general to be in line with the Millennium Development Goals
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2. LITERATURE REVIEW: CLIMATE CHANGE AND VECTOR BORNE ZOONOSES.
2.1 CLIMATE CHANGE
2.1.1 What is climate change?
As defined by the Encyclopedia of Climate Change and Global Warming complied by Prof. S.
George Philander, climate change is commonly used to describe any systematic alteration or
statistically significant variation in either the average state of climate elements such as
precipitation, temperature, winds, or pressure; or in its variability, sustained over a finite time
period (decades or longer). (Nsikak Benson, 2008).
2.1.2 Causes of climate change
The earths main source of energy is the sun, but this planet would be far too cold for
most of its inhabitants were it not for its atmosphere, the thin veil of transparent gases
that covers the globe. The atmosphere serves as a parasol that reflects sunlight, thus
keeping the planet cool, and as a blanket that traps heat from the Earths surface, thus
keeping us warm. The blanket is the greenhouse effect, which depends not on the two
gases nitrogen and oxygen that are most abundant, but on trace gases that account for
only a tiny part of the atmosphere. These gases warm the air in their interior mainly by
blocking convective mixing with the outside (Philander ,2008) .They include carbon
dioxide, methane and nitrous oxide, along with water vapor and are known as the Green
House Gases (GHGs) as the working principle is the same as that of a greenhouse. Just as
the glass of the greenhouse prevents the radiation of excess energy, this gas blanket
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absorbs some of the energy emitted by the earth and keeps temperature levels intact
(Shrivastava, 2001).
The earths temperature is controlled by the balance between input energy from the sun
and its loss back into space. Green house gases are critical to this temperature balance in
that the energy received from the sun is in the form of short-wave radiation that warms
the earths surface and as a result emits long-wave infrared radiation. The greenhouse
gases trap and re-emit some of this long-wave radiation, and warm the atmosphere. On
average, one-third is reflected back into space and two-thirds warms the planet and drives
its weather engine.
This warming takes place through a shield known as the ozone layer that limits the loss of
heat from the Earths surface and increases the average global temperature by 33 oC,
without which the Earth would be frozen and life on the planet would cease.
It is a well established fact that the emission of greenhouse gases that produce greenhouse
effect; most notably carbon dioxide (CO2), nitrous oxide (N2O), chlorofluorocarbons
(CFCs), methane (CH4), and ozone (O3), are increasing in the atmosphere and thereby
deflecting more long-wave infra-red solar radiation back to Earth, hence global warming
and the ongoing climate changes. This is threatening the survival of many plants and
animals as well as the well being of people around the world. The industrial revolution in
the19th century saw the large use of fossil fuels for industrial activities (Shrivastava,
2001). These industries created jobs and over the years there has been urban migration, a
trend that continues to date. More and more land that was covered with vegetation has
been cleared to make way for houses. Natural resources are being used extensively for
construction, industries, transport and consumption. In its 2007 report, the
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Intergovernmental Panel on Climate Change (IPCC,2007), a large International panel of
scientists, all experts on the Earths climate, concluded that human activities, specifically
those that cause an increase in the atmospheric concentration of carbon dioxide, have
started affecting the Earths climate. The panel further predicted that far more significant
climate changes are imminent (Shrivastava, 2001).
2.1.3 Effects of climate change
According to Wikipedia, the following are some of the effects of climate change.
Glacier retreat and disappearance
This widespread decrease in glaciers and ice caps has contributed to observed sea level rise. With
very high confidence, IPCC (IPCC, 2007) made the following projections relating to future
changes in glaciers:
In Polar Regions, there will be reductions in glacier extent and thickness.
More than one-sixth of the world's population is supplied by meltwater from major
mountain ranges. Changes in glaciers and snow cover are expected to reduce water
availability for these populations.
a) Oceans
Global warming is projected to have a number of effects on the oceans. Ongoing effects
include rising sea levels due to thermal expansion and melting of glaciers and ice sheets,
and warming of the ocean surface, leading to increased temperature stratification. Other
possible effects include large-scale changes in ocean circulation. The oceans serve as a
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sink for carbon dioxide, taking up much that would otherwise remain in the atmosphere,
but increased levels of CO2 have led to ocean acidification (Wikipedia).
b) Extreme weather
Climate change is likely to change the frequency of extreme weather events, such as tropical
cyclones, floods, droughts, heatwaves and hurricanes, and may destabilize and weaken the
ecosystem services upon which human society depends.
c) Health
Climate change is also expected to affect animal, human and plant health via indirect pathways.
It is likely that the geography of infectious diseases and pests will be altered, including the
distribution of vector borne zoonotic diseases such as RVF, which are highly sensitive to
climatic conditions.
2.1.4 Adaptation to effects of climate change
Africa is the most vulnerable region to climate change, due to the extreme poverty of many
africans, frequent natural disasters such as droughts and floods, and agricultural systems heavily
dependent on rainfall(IPCC, 2001).
It is, therefore, essential for these countries to prepare themselves for coping with or, one can
say, adapting to such adverse impacts and to ensure that such adaptation measures and policies
are built-in to their existing national and sectoral development activities (Chowdhury, 2003).
Climate change has the potential to undermine sustainable development, increase poverty and
delay or prevent the realization of the MDGs. An effective way to address the impacts of climate
change is by integrating adaptation measures into sustainable development strategies so as to
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reduce the pressure on natural resources, improve environmental risk management, and increase
the social well-being of the poor (United Nations Framework Convention on Climate
Change,2006).
The public health and medical community have made enormous strides in control of infectious
diseases during the past half-century. Widespread availability of antimicrobial drugs, vector-
control systems, diagnostics, vaccines, and increasingly sophisticated predictive models
represent a powerful set of tools to protect public health from emerging diseases (Rosenthal,
2010).
2.2 VECTOR BORNE ZOONOSES
According to the World Health Organization, zoonoses are diseases naturally transmitted to
people from non-human vertebrates e.g. dogs, raccoons, etc as well as invertebrates e.g.
arthropods.
From the perspective of infectious diseases, vectors are the transmitters of disease-causing
organisms that carry the pathogens from one host to another. By common usage, vectors are
considered to be invertebrate animals, usually arthropods. Technically, however, vertebrates can
also act as vectors, including foxes, raccoons, and skunks, which can all transmit the rabies virus
to humans via a bite.
Arthropods account for over 85 percent of all known animal species, and they are the most
important disease vectors. Arthropods may affect human health either directly by bites, stings, or
infestation of tissues, or indirectly through disease transmission.. The most significant mode of
vector-borne disease transmission is by biological transmission by blood-feeding arthropods. The
pathogen multiplies within the arthropod vector, and the pathogen is transmitted when the
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arthropod takes a blood meal. Mechanical transmission of disease agents may also occur when
arthropods physically carry pathogens from one place or host to another, usually on body parts.
The transmission of vector-borne diseases to humans depends on three different factors: the
pathologic agent; the arthropod vector; and the human host.
A majority of vector-borne diseases survive in nature by utilizing animals as their vertebrate
hosts, and are therefore zoonoses.There are different patterns of vector-borne disease occurrence;
parasitic and bacterial diseases, such as malaria and Lyme disease, tend to produce a high disease
incidence but do not cause major epidemics. In contrast, many vector viral diseases, such as
Yellow Fever, Rift Valley Fever, dengue, and Japanese encephalitis, commonly cause major
epidemics. (enotes.www.enotes.com)
Globalization and climate change have had an unprecedented worldwide impact on emerging and
re-emerging animal diseases and zoonoses. Climate change is disrupting natural ecosystems by
providing more suitable environments for infectious diseases allowing disease-causing bacteria,
viruses, and fungi to move into new areas where they may harm wild life and domestic species,
as well as humans. Diseases that were previously limited only to tropical areas are now spreading
to other previously cooler areas e.g. malaria. Pathogens that were restricted by seasonal weather
patterns can invade new areas and find new susceptible species as the climate warms and/or the
winters get milder. There is evidence that the increasing occurrence of tropical infectious
diseases in the mid latitudes is linked to global warming. (FAO/IAEA, 2010).
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2.3 RIFT VALLEY FEVER
2.3.1 Introduction
Rift Valley Fever (RVF) is a peracute or acute disease of domestic ruminants caused by a
mosquito-borne virus and characterized by necrotic hepatitis and a hemorrhagic state, but
infections are frequently inapparent or mild. The aetiologic agent is a mosquito-borne, RNA
virus of the family Bunyaviridae, genus Phlebovirus (Swanepoel and Coetzer, 2003). The
disease is most severe in sheep, cattle and goats, producing high mortality in newborn animals
and abortion in pregnant animals. It is a zoonosis and humans get infected from contact with
tissues of infected animals or mosquito bites. Outbreaks of the disease occur when particularly
heavy rains favour the breeding of the mosquito vectors (Swanepoel and Coetzer, 2003).
2.3.2 Clinical Findings
a) The disease in animals
Signs of the disease in domestic ruminants tend to be non-specific, rendering it difficult to
recognize individual cases of RVF. During epidemics however, the simultaneous occurrence of
numerous cases of abortion and disease in ruminants, together with disease of humans, tends to
be characteristic of RVF (Swanepoel and Coetzer, 2003).
In the peracute disease animals die suddenly without exhibiting noteworthy signs of illness.
Under field conditions, most animals develop the acute disease. Following an incubation period
of 24-72 hours, there is fever of up to 42oC that lasts for 24-96 hours, anorexia, weakness,
listlessness and an increased respiratory rate. Some animals may regurgitate ingesta, and develop
melaena or foetid diarrhea and a blood tinged, mucopurulent nasal discharge. A few animals may
be icteric (Swanepoel and Coetzer, 2003).
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Pregnant animals may abort at any stage as a result of the febrile reaction and/ or infection of the
fetus. Aborted fetuses are usually autolysed. Although there is no evidence that infertility is
impaired after abortion, this is possible in instances where retained placenta and purulent metritis
occur as complications to abortion, particularly if there is also salpingitis (Swanepoel and
Coetzer, 2003).
b) The disease in humans
Humans acquire RVF through bites from infected mosquitoes and through exposure to blood,
body fluids, or tissues of infected animals. Direct exposure to infected animals can occur during
handling and slaughter or through veterinary and obstetric procedures. Laboratory technicians
are at risk of acquiring disease by inhalation of infectious aerosols generated from specimens.
(Anyangu et al, 2010).
Human RVF outbreaks are primarily characterized by mild, acute febrile illness with
spontaneous recovery, although in a few cases (< 8%) the disease can be associated with severe
jaundice, rhinitis, encephalitis and hemorrhagic manifestations, hence fatal (Mohammed et al,
2010).
2.3.3Mosquitoes as RVF vectors
Laboratory studies indicate that numerous species of mosquitoes and sand flies are susceptible to
oral infection, some of which are able to transmit RVF virus by bite to domestic animals
including sheep, goats, cattle and camels, as well as human beings (Sang et al, 2010).
The Aedine mosquitoes are the main vectors of the virus though other species, as explained in
the later in this section, are involved in the spread of the disease. The virus is also present in
milk, feces and aborted fetuses (Turell et al, 1984).
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Following the ingestion of an infective blood meal by a susceptible mosquito, there is an
extrinsic incubation period of approximately one to two weeks before transmission can occur.
During this time RVF virus replicates in the cells of the midgut, escapes to the haemocoel and is
disseminated via the haemolymph to replicate in the salivary glands and other organs, but in a
proportion of some mosquitoes infection is confined to the midgut, implying that there is a
mesenteroneal barrier to spread of infection (Swanepoel and Coetzer, 2003).
In Aedine mosquitoes, transovarial transmission of virions occurs from the female mosquito to
her progeny, and females of the next generation can transmit the virus orally without having
become infected by a prior blood meal. It is obligatory for Aedine eggs to be subjected to a
period of drying as the water recedes before being wetted again next time the dambo floods.
Dambos are topographic depressions which suddenly flood during heavy rains causing the eggs
of dormant RVF virus-infected floodwater Aedes spp. mosquitoes to hatch. Aedine eggs can
survive for long periods in dried mud, possibly for several seasons if the dambo remains dry.
Moreover, only a proportion of eggs hatch at each successive flooding, which clearly represents
a survival mechanism to prevent the mosquito population from being lost when precipitation has
been inadequate to sustain breeding. Dams with shallows that are subject to periodic drying and
flooding also provide suitable habitat for floodwater breeding Aedines (Swanepoel and Coetzer,
2003).
These mosquitoes maintain RVF virus through transovarial transmission and transmit it to
domestic and wild ungulates that come to the dambos for water, functioning as enzootic vectors.
As amplification ensues, epizootic vectors such as Culex theileri become important in
transmission to domestic livestock. A variety of mosquitoes have been associated with RVF
virus, including Culex pipens in the Egyptian outbreak. Rift Valley Fever virus has also been
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isolated from Culex zombaensis and Mansonia africana in Kenya (Swanepoel and Coetzer,
2003).
In the proportion of mosquitoes in which theres infection, internal dissemination of infection
and transmission of the virus occur, and the duration of the extrinsic incubation period tends to
be characteristic for each vector species and does not appear to be influenced by the strain of
RVF virus, but by increased doses of virus, and higher ambient temperatures during extrinsic
incubation which produce disseminated infection in a greater proportion of mosquitoes and
shorter extrinsic periods (Turell et al, 1985).
Thus, apart from favoring the breeding of vectors, warm weather may be an accessory factor in
precipitating outbreaks of RVF through increasing vector efficiency (Swanepoel and Coetzer,
1994).
2.3.4 Epidemiology of Rift Valley Fever.
According to the American Journal of Tropical Medicine and Hygiene, vol. 83(2), outbreaks are
associated with unusually heavy rainfall, leading to flooding and a synchronous generation of a
large number of infected mosquitoes (Anyangu et al, 2010). These are thought to occur when
topographic depressions called dambos suddenly flood, causing the eggs of dormant RVF
virus-infected floodwaterAedes spp. mosquitoes to hatch.
In the interepidemic period the virus is maintained within the eggs ofAedes mosquitoes
embedded in soils where previous RVF outbreaks have occurred. Other findings suggest that the
virus may also be maintained by cryptic cycling between domestic livestock or wild herbivores
and mosquitoes. During the epizootics, heavy rainfall and flooding provide an environment for
Aedes mosquitoes to rapidly multiply and become the predominant mosquito population, which
results in extensive livestock transmission and amplification of the virus. After an initial burst of
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transmission, other mosquito species (e.g. Culex, Anopheles, Mansonia, etc) and biting insects
can become infected and transmit the virus among animals and from animals to human beings
(Mohamed et al, 2010).
The flooding of dambos and the humid weather conditions prevailing in epidemics favour the
breeding not only of the Aedine maintenance vectors, and the non-aedine mosquitoes which
serve as epidemic vectors, but also of other biting insects which are potential mechanical
transmitters of RVFV (Swanepoel and Coetzer, 2003).
Eggs of species which breed in water, other than aedine mosquitoes, cannot survive dry
conditions and these insects re-colonize flooded dambos from suitably close rivers and dams, so
that a succession of vector species occurs once flooding takes place. Infected livestock circulate
high levels of virus and mechanical transmission of infection by mosquitoes, midges,
phlebotomids, stomoxids, simulids and other biting flies is thought to play a significant role in
epidemics (Logan et al, 1991).
Infected animals appear to be more attractive to mosquitoes, and by implication other biting flies,
than non-infected animals and it has been shown that probing for blood and feeding proceed
more rapidly and efficiently on viraemic hosts. (Bailey, 1981)
Factors which determine the morbidity and mortality associated with outbreaks of RVF include
the virulence of the strain of virus and the susceptibility of the vertebrates involved (Anderson &
Peters, 1988).
The RVF epizootics and epidemics are closely linked to the occurrence of the warm phase of the
El Nino / Southern Oscillation phenomenon and elevated Indian Ocean temperatures that lead to
heavy rainfall and flooding of habitats suitable for the production ofAedes and Culex mosquitoes
that serve as the primary RVF virus vectors in East Africa. El Nino-Southern Oscillation events
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are a combined ocean atmosphere phenomenon, involving changes in the temperatures of surface
waters in the tropical Pacific and in its closely linked atmospheric counterpart, the Southern
Oscillation. El Nino-Southern Oscillation events involve a large exchange of heat between the
ocean and the atmosphere, and affect:
Global mean temperature
Trade winds
Tropical circulation
Precipitation.
Such events occur about once every three to seven years (Martin et al, 2008).
2.3.5. Rift Valley Fever in Kenya.
An acute and highly fatal disease to lambs associated with heavy rains and accompanied by
reports of illness in humans was first recognized in the Rift Valley in Kenya at the turn of the
century, but the causative agent was not isolated until 1930. Major outbreaks of the disease
affecting sheep and cattle were recorded in Kenya in 1930-31, 1968, 1978-79, 1997-98, 2006-07
and lesser outbreaks at irregular intervals during intervening years (Davies et al, 1985).
The 1997-98 epidemic which started in Garissa district, North Eastern Kenya and adjacent parts
of Somalia in October 1997, occurred in an essentially arid area following exceptionally heavy
rains (Woods et al, 2002).
In mid-December 2006, the Ministry of Health in Kenya received reports of fatal cases of a
febrile haemorrhagic illness of unknown aetiology among people living in Garissa district in the
North eastern province, after unusually heavy rains and flooding in the area as shown in figure 2.
The RVF virus was isolated and Immunoglobulin M (IgM) antibodies to RVFV were detected in
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clinical specimens from affected patients and animals. During the next 4 months, approximately
700 suspected cases of RVF with 272 confirmed and 120 probable cases were reported in 18
districts within six of eight provinces in Kenya. During this period, RVF outbreaks were also
reported in Somalia and Tanzania (Amwayi et al, 2007).
2.3.6 Impact of climate change on RVF
At present, the world climate is in a warming phase. In 1996, The Intergovernmental Panel on
Climate Change (IPCC) concluded that, the balance of evidence suggests a discernible human
influence on global climate (IPCC, 1996). Indeed, evidence suggests that human activities
contribute to warming the planet and climate models predict an increase in global mean
temperatures of between 1 C and 3.5 C during the 21st century, with large differences in trends
between locations.
Temperature changes are one of the most obvious and easily measured changes in climate, but
atmospheric moisture, precipitation and atmospheric circulation also change as the whole system
is affected. These effects alter the hydrological cycle, especially the characteristics of
precipitation/rainfall (amount, frequency, intensity, duration, type) (Trenberth et al. (2007).
Finally, it is anticipated that global climate change will induce changes in the magnitude and
frequency of extreme events and have significant effects on the geographical range and seasonal
activity of many vector species (McMichael et al, 1996).
It is therefore expected that global climate change will alter the distribution and increase the risk
of some vector-borne zoonoses, including Rift Valley fever (RVF), leading to significant
changes in the geographical distribution and frequency of RVF epidemics.
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As mentioned in the IPCC report ( IPCC, 1996), heavy rainfall events are likely to become much
more frequent in years to come and extremes of the hydrological cycle, such as floods and
drought will invariably be enhanced with global warming. In fact, the increase in rainfall in East
Africa, extending into the Horn of Africa, is robust across the entirety of the models surveyed in
the IPCC report. Thus, it may be assumed that the frequency and severity of RVF outbreaks on
this part of the continent will increase. This could also affect other countries that import animals
from Africa, such as some islands in the Indian Ocean.
Climate changes may also affect the three fundamental components of the epidemiological cycle
of RVF, namely: vectors, hosts and virus. The consequences of global warming on vectors, in
particular, may be many. The greenhouse effect, through changes to temperatures and the pattern
of seasonal and geographical variation in rainfall, will alter the prevalence of mosquito vector
populations. Temperature has a direct effect on mosquitoes. It leads to increased activity,
increased reproduction and therefore increased frequency of blood meals and faster digestion of
blood (Martin et al, 2008).
Pathogens harboured by mosquitoes also mature faster. Increased water temperature cause
mosquito larvae to develop faster also increasing overall vector capacity (Reiter, 2008).
The effect of precipitation on vectors is indirect. Increased precipitation creates more potential
breeding sites for mosquitoes. The vegetation is dense after rainfalls and this provides shelter and
resting grounds for vectors (Githeko et al, 2000).
Heavy rainfalls are predicted for East Africa and therefore more RVF outbreaks. In turn, this
may affect the potential for transmission of Rift Valley Fever.
As far as hosts are concerned, climate changes may induce modifications in their distribution and
density, as well as their migratory pathways. Historically, the dissemination of RVF has been
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attributed in part to nomadic herds: the modification of migratory pathways could introduce the
virus into previously virus-free areas. Climate modification may also result in the selection of a
strain that is either more or less virulent (Martin et al, 2008).
2.3.7. Prevention and control.
a) Vectors
The viability of mosquito eggs in dambo soil can be reduced by burning of the grass cover, and
strategically timed application of larvicides can be used to suppress mosquito breeding (Logan et
al, 1990). Other measures such as chemical control of adult vectors, movement of stock from
low-lying areas to well-drained and wind-swept pastures at higher altitudes, or confining of
animals to mosquito proof stables, are usually impractical, instituted too late and at best
palliative in the face of a RVF epidemic (Swanepoel and Coetzer, 2003).
b) Immunization
Immunization remains the only effective way of protecting livestock. Two vaccines are
currently available for vaccination of animals against RVF. The first being, formalin inactivated
vaccine available in South Africa and Egypt. This vaccine safe in pregnant ewes, but is poorly
immunogenic, thus requiring a booster dose to achieve immunity and regular revaccination to
maintain immunity. The second is a live vaccine based on the attenuated Smithburn strain. This
vaccine is widely used in Africa and the Middle East. It is more immunogenic than the formalin
inactivated alternative, but may cause abortion and foetal teratogenicity when ewes are
vaccinated during pregnancy. A live Clone 13 RVF vaccine has recently been registered for use
in cattle, sheep and goats in South Africa. The vaccine is based on a natural RVF virus mutant
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with a large deletion in the NSs gene. Evidence so far indicates that the vaccine is highly
immunogenic, and does not cause abortion or foetal teratogenicity in ewes vaccinated during
pregnancy. The risk of reversion to virulence is believed to be negligible given the substantial
genetic deletion present in the vaccine virus. The Clone 13 RVF vaccine therefore seems to be a
safer and more effective alternative to RVF vaccines currently being used to protect livestock in
Kenya. (GALV Med, 2010)
Epidemics of RVF tend to occur at irregular intervals of many years and it is usually difficult to
persuade farmers to vaccinate livestock during the long inter-epidemic periods. The occurrence
of epidemics is usually difficult to predict as they usually have a very sudden onset. Hence it is
advisable in African countries with large sheep and goat populations to immunize the offspring
of vaccinated ewes and nannies on a regular basis (at six months of age), when colostral
immunity has waned, with a single dose of the modified live Smithburn vaccine. This should
offer life-long protection (Assad et al, 1983). Lambs and kids of susceptible dams can be
immunized at any age.
On the other hand, veterinarians and others engaged in the livestock industry should be made
aware of the potential dangers of exposure to zoonotic agents in handling tissues of diseased
animals, and precautions should be increased during RVF epidemics. A formalin-inactivated cell
culture vaccine produced in the USA is used on an experimental basis to immunize persons such
as laboratory and field workers who are regularly exposed to RVF infection (Eddy, et al 1981).
c) Technology use
Advancing technologies are creating exciting possibilities for prevention and control of emerging
diseases. They include: far-reaching and constantly improving communication tools, including
use of mobile text messaging resulting in improved surveillance approaches, and state-of-the-art
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satellite imagery and mapping capacity to forecast and detect ecologic changes and climate
anomalies relevant to disease prevalence (Ford, et al, 2009).
In addition, monitoring of animal and insect vector motility and geographic distributions and,
development of highly sensitive diagnostic tools for use in human, animal and vector
surveillance are enhancing the ability to detect new` pathogens or changes in reservoir patterns
for known pathogens. These new capacities will dramatically improve the ability to detect early
and, ultimately to forecast in advance, the emergence of disease threats so that effective
measures can be taken to avert or minimize the public health impact (Breiman et al, 2010).
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3. METHODOLOGY
3.1 Research Design
This will be a retrospective cross-sectional study that will utilize quantitative
techniques of data collection, on the prevalence of RVF versus the weather
patterns; specifically temperature and rainfall between the years 1995 and 2010.
This will meet the outlined objectives in chapter 1 in a bid to show the
relationship between climate and RVF outbreaks in order to project the likely
effects of climate change on its epidemiology in terms of increased frequency of
outbreaks.
3.2 Study areas and data collected
By the year 2007, six of the eight provinces in Kenya had reported outbreaks of
RVF i.e. Rift Valley, Eastern, Central, North Eastern, Coast and Nairobi
provinces.
In each of these provinces data will be obtained on the year when outbreaks
occurred within the years 1995-2010.
Because heavy rains and flooding have been associated with RVF epizootics,
rainfall data as well as the prevailing temperatures between the years 1995-2010
available will be examined.
Annual rainfall data and prevailing temperatures from one representative station
will be reported in each of the six provinces between 1995 and 2010.
In the six provinces where RVF outbreaks have been reported, the representative
stations will be those closest to the districts reporting RVF; i.e. Nakuru station
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(Rift Valley province), Garissa station (Northeastern province), Meru station
(Eastern province), Malindi station (Coast province), Thika station (Central
province), and Wilson airport station (Nairobi province). Though Western and
Nyanza provinces have never reported RVF, they will be part of this study and the
representative stations will be Kakamega and Kisumu respectively.
3.3 Data collection procedures
This will entail:
a) Collection of recorded cases of RVF in Kenya from The Central Veterinary Research
Laboratories, the Kenya Medical Research Institute, Nairobi, Kenya and the Department
of Disease Surveillance, Ministry of Health, for the period between 1995 and 2010.
b) Collection of recorded weather patterns i.e., temperature and rainfall from the Kenya
Meteorological Department for the period between 1995 and 2010.
c) Study of published and unpublished material as well as relevant case studies sourced
from the internet, including all support documentation and articles unavailable locally,
graphic representations in form of photographs and drawings of relevance to climate
change and its effect on RVF epidemiology.
d) Data collected will be entered in data collection sheets.
3.4 Data analysis.
This will be analyzed as follows:
i. Tabulation of data and calculation of averages for annual temperature and rainfall in
1995-2009 for the representative districts in the 8 provinces using Microsoft Excel.
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ii. Tabulation of administrative districts that reported cases of rift valley fever during the
1997-98 and 2006-07 outbreaks showing percentages and bar graphs to show proportion
of the country involved in the two outbreaks.
iii. Graphical representation of annual temperature, and rainfall in 1995-2009for the
representative districts in the 8 provinces as well as the magnitude of both outbreaks
(1997/1998 & 2006/2007) in terms of the number of districts involved in the province
expressed as a percentage of total administrative districts in the same province. For the
purpose of uniformity the administrative districts used are based on the geographic
boundaries of the eight provinces and 69 administrative districts in place in 1999 as the
number and size of districts have recently been restructured.
iv. Graphical representation of average annual temperatures per province between 1995 and
2009 using Microsoft Excel and using the trend line to study the trend of average annual
temperatures in each representative district.
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DATA ANALYSIS
INTRODUCTION
A total of 38/69 (55%) administrative districts in the country had reported RVF epizootics by the
end of 2007. The Western and Nyanza provinces, located on the southwestern region of the
country, had never reported RVF infections by 2007 (Murithi et al, 2010). As shown below, the
2006/2007 outbreak involved 36/69 administrative districts (52.2%) compared to the 1997/1998
outbreak which involved 22/69 administrative districts (31.8%).
DISTRICTS PER PROVINCETHAT REPORTED RVF IN 1997/1998 OUTBREAK AND
THE 2006/2007 OUTBREAK
1997/1998 0UTBREAK (22/69 DISTRICTS- 31.8%)
1. Rift Valley Province: West Pokot, Uasin Gishu, Trans Nzoia, Narok, Nakuru, Laikipia,
Kajiado.
2. Eastern Province: Isiolo, Makueni, Marsabit, Machakos.
3. North Eastern Province: Garissa, Mandera, Wajir.
4. Coast: Kilifi, Kwale, Tana River.
5. Central: Kiambu, Maragua, Nyeri, Thika.
6. Nairobi
7. Western Province: None.
8. Nyanza Province: None.
2006/2007 OUTBREAK (36 DISTRICTS- 52.2%)
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1. Rift Valley Province: West Pokot, Uasin Gishu, Nakuru, Laikipia, Kajiado,
Baringo, Samburu, Marakwet, Kericho.
2. Eastern Province: Isiolo, Makueni, Machakos, Mbeere, Embu, Moyale, Meru
Central, Meru North, Meru South, Mwingi, Kitui.
3. North Eastern Province: Garissa, Mandera, Wajir, Ijara.
4. Coast: Kilifi, Kwale, Tana River, Taita Taveta, Lamu, Malindi.
5. Central: Kiambu, Maragua, Thika, Muranga, Kirinyaga.
6. Nairobi.
7. Western Province: None.
8. Nyanza Province: None.
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PROVINCE TOTAL NUMBER
OF
ADMINISTRATIVE
DISTRICTS
DISTRICTS
INVOLVED IN
1997/1998
0UTBREAK (%)
DISTRICTS
INVOLVED IN
2006/2007
OUTBREAK (%)
Rift Valley 18 7 (39%) 9 (50%)
Eastern 12 4 (33%) 11 (92%)
North Eastern 4 3 (75%) 4 (100%)
Coast 7 3 (43%) 7(100%)
Central 7 4 (57%) 5 (71%)
Nairobi 8 - -
Nyanza 12 0 (0%) 0 (0%)
Western 8 0 (0%) 0 (0%)
1. RIFT VALLEY PROVINCE
Nakuru
R 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
FALL 59.5 72.7 93.7 95.8 55.79 50.83 101.85 83.24 94.67 80.9777.1
6
PERATURE 18.57 18.14 18.56 18.72 18.85 19.32 18.69 18.87 18.77 18.7418.7
7
BREAKS 0 0 39% 39% 0 0 0 0 0 0 0
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2. NORH EASTERN PROVINCE
Garissa
R 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
NFALL 34.21 11.76 79.2 53.25 25.09 13.44 21.68 46.71 33.2 15.4
PERATU
28.92 28.99 28.62 28.71 28.57 28.84 29.05 28.91
TBREAKS 0 0 75% 75% 0 0 0 0 0 0
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3. EASTERN PROVINCE
Meru
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2
NFALL
126.9
8 81.15
184.9
9
127.5
2 84.67 49.85
101.4
4 152.1
127.5
5
118.1
4 68
PERATU
18.42 18.54 18.55 18.31 18.24 18.58 18.47 18.34 18.93 19
TBREAKS 0 33 33 0 0 0 0 0 0 0
4. COAST PROVINCE
Malindi
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2
NFALL 65.21 87.47
177.9
2
117.9
2
103.8
2 85.05 81.55 89.5 89.35 75.1 72
PERATU
26.28 27.45 26.45 27.01 26.5 26.43 26.66 26.84 27.2 26.97
TBREAKS 0 0 48 48 0 0 0 0 0 0
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5. CENTRAL PROVINCE
Thika
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2
NFALL 63.33 66.7
116.6
7 115 75 29.1 66.7 108.3 58.3 63
PERATU
14.09 14.03 15.29 14.63 13.97 14.31 15.27 15.04 14.07 14.93 15
TBREAKS 0 0 57 57 0 0 0 0 0 0
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6. NAIROBI PROVINCE
RS 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2
NFALL 73.56 56.61 81.94 117.5 62.75 44.1 120.1 79.35 78 70.56 60
PERATU
18.98 18.35 20.39 19.38 19.45 19.71 19.56 19.89 19.8 19.73 19
7. WESTERN PROVINCE
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Kakamega
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2
NFALL
167.2
5
174.6
3 134.9
159.2
5 145.8
117.8
5
185.5
6
178.7
8
175.8
5 129.5
13
PERATU
20.56 20.61 21.1 20.81 20.45 20.91 20.76 21.05 21.34 21.24 21
TBREAKS O 0 0 0 0 0 0 0 0 0
8. NYANZA PROVINCE
Kisumu
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2
NFALL
120.9
8
128.3
5 134.2
104.7
3
128.6
6
101.2
4
124.2
9
134.8
7
104.3
6
115.9
9 9
PERATU
23.5 23.28 23.85 23.87 23.25 23.6 23.31 23.66 23.67 24
TBREAKS 0 0 0 0 0 0 0 0 0 0
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GRAPHICAL REPRESENTATION OF AVERAGE ANNUAL
TEMPERATURES PER PROVINCE BETWEEN 1995 AND 2009
1. RIFT VALLEY PROVINCE
Nakuru
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2. NORTH EASTERN PROVINCE
Garissa
3. EASTERN PROVINCE
Meru
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4. COAST PROVINCE
Malindi
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5. CENTRAL PROVINCE
Thika
6. NAIROBI PROVINCE
Nairobi
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7. NYANZA PROVINCE
Kisumu
8. WESTERN PROVINCE
Kakamega
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SUMMARY
The purpose of this project was to study the climatic trends in terms of rainfall and temperature
between 1995 and 2009 and how the epidemiology of RVF has changed over the same period.
Findings of the study are summarized below;
1. There have been two major outbreaks between 1995 and 2009, i.e. 1997/1998.
2. These outbreaks occur when the affected regions record extremely high rainfall having
been preceded by a relatively dry period. E.g. as seen in the 1997/98 outbreak, Garissa
went from 11.7mm in 1996 to 79.2mm in 1997 and Thika from 66.7mm in 1996 to
116.67mm in 1997.
3. Comparison of the two outbreaks shows that the 2006/2007 one was more extensive,
involving 52.2% of the country as compared to that of 1997/1998 that only involved
38.1% of the country.
4. From the graphical analysis of average annual temperatures per province it is clear from
the trend line in the graphs that the temperatures have been gradually increasing during
this period.
DISCUSSION
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The challenges of climate change and development in Africa are closely linked. But we
urgently need to improve our understanding of how climate change will affect Africa
Beckett (2004).
This study reveals that temperatures have been gradually increasing and that the
magnitude in terms of number of regions involved in the outbreak has increased. This
may partly be explained by what is in chapter 2 of this report under the subtopic on
effects of climate change on RVF (2.3.7) which states that it is therefore expected that
global climate change will alter the distribution and increase the risk of some vector-
borne zoonoses, including Rift Valley fever (RVF), leading to significant changes in the
geographical distribution and frequency of RVF epidemics. This is further explained by
the fact that temperature has a direct effect on mosquitoes, the principal vectors of RVF
virus. It leads to increased activity, increased reproduction and therefore increased
frequency of blood meals and faster digestion of blood (Martin et al, 2008). Pathogens
harboured by mosquitoes also mature faster. Increased water temperature cause mosquito
larvae to develop faster also increasing overall vector capacity (Reiter, 2008).
If this trend goes unchecked, RVF may further extend to involve more regions and this
will be detrimental to Kenya as a developing country. By 2100 it is estimated that
average global temperatures will have risen by 1.03.5 oC, increasing the likelihood of
many vector-borne diseases in new areas. Human settlement patterns in the different
regions will influence disease trends in that this will lead to introduction of pathogens to
new areas and due to global warming which accompanies climate change, these
pathogens and their vectors thrive and cause disease since the climatic conditions are now
conducive (Githeko et al, 2000).
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RVF has negative socioeconomic impacts which retard development. Outbreaks result in
substantial hardship, directly through illness and through direct economic impact (as a
result of animal deaths and abortions, and because of a variety of commercial bans.).
Specifically hard hit by the latest outbreak were the pastoral communities of the north
eastern (NE) part of Kenya. In this region, livestock serve an important livelihood
function for pastoralists, with livestock trade representing over 90% of pastoral incomes
(Mutunga, 2010). Moreover, NE Kenya has the highest incidence of poverty within
Kenya, with poverty rates of approximately 70% in 2004 (Society for International
Development, 2010).
It is important to note that RVF does not just affect producers, but also impacts a host of
other service providers within the livestock supply chain and other parts of the larger
economy. Beyond livestock producers in the affected areas, traders, slaughter-house
workers, butchers, transporters, and a range of small-scale businesses, such as operators
of food kiosks who served these workers, all incurred losses. It was reported that
significant numbers of livestock traders and butchers were unable to resume their
business activities after the bans on livestock movement and slaughter were lifted
because of depletion of capital. Cumulatively, these downstream impacts can often dwarf
the impacts of the disease at the farm level (Rich et al, 2010). This shows that there is
increasing need for us as a country to adapt ways in which we can mitigate climate
change and to adapt to its impacts especially when it comes to health.
RECOMMENDATIONS
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1. As the world embraces the one health initiative, there should be better
coordination between veterinary epidemiologists, medical epidemiologists and
environmentalists and through the combination of their different areas of expertise
study the new trend of diseases, especially vector borne diseases as a result of
climate change and therefore come up with better methods of surveillance,
prevention and control of such diseases.
2. Veterinary and medical experts, through extension services should educate and
create awareness to the public, especially in marginalized areas where poverty and
illiteracy is at its highest, on what climate change is and the effects we are likely
to experience. We should enlighten them on coping strategies which might
include educating people in areas solely dependent on livestock for their
livelihood on alternative sources of income.
3. It is our responsibility as veterinary extension officers to educate people on the
importance of livestock insurance as most insurance companies nowadays insure
animals against losses due to epidemics.
4. We cannot ignore the fact that we have started experiencing effects of climate
change on epidemiology of most diseases, among many others. It would be
advisable to introduce studies on global warming and climate change into the
curriculum in both veterinary and medical schools so that we are well equipped to
deal with some of the unexpected changes seen in terms of disease epidemiology
e.g. whereby a while ago wed disregard the likelihood of a certain disease
occurring in a certain area based on the fact that the environment wasnt
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conducive for the causative agent to thrive and cause disease. This is bound to
change and it would be quite costly to be ignorant on such issues.
5. REFERENCES
1. Paul Epstein (2008) Climate change and infectious disease: stormy weather ahead?
Epidemiology13(4), pg 373-375.
2. Joint FAO/IAEA Program (2010) Climate change & the Expansion of Animal &
Zoonotic Diseases.
3. V. Martin, V. Chevalier, and others (2008) Impact of Climate Change on the
epidemiology and control of RVF,Revue Scientifique technique Office international
Epizooties, 27 (2):413-426.
4. GithekoA K, Lindsay S W, Confalonieri U E and Patz J A (2000) Climate change and
vector-borne diseases: a regional analysis.Bulletin of the World Health Organization,
78 (9): 1143.
5. Anthony Nyong (2005); Key Vulnerabilities to Climate Change in Africa
7/30/2019 efffects of climate change on epidemiology of vector borne zoonotic diseases
44/45
6. United Nations Framework Convention on Climate Change, (2007) Climate
change: Impacts, vulnerabilities and adaptations in developing countries, pg 29-52
7. Mohammed M, Fausta Mosha, Janeth Mghamba, Sherif Zaki and others (2010).
Epidemiologic and clinical aspects of Rift Valley Fever Outbreak in Humans in
Tanzania, 2007.AmericanJournal of Tropical Medicine and Hygiene, 83(2): 22
8. Rosemary Sang, Elizabeth Kioko, Joel Lutomiah and others (2010). RVF Epidemic in
Kenya, 2006/2007: The Entomologic Investigations. AmericanJournal of Tropical
Medicine and Hygiene, 83(2):28
9.Bailey, C.L, (1981). U.S. Army Medical Research Institute for infectious diseases, Fort
Detrick, Maryland. Personal communication
10.Anderson, G.W. & Peters, C.J. (1988) Viral determinants of virulence for RVF in rats.
Microbial Pathogenesis2: 283-293
11.Davies, F.G. (1985) Rainfall and epizootic Rift Valley Fever, Bulletin of the World
Health Organization, 63:941-943.
12.Woods, C.W, Karpati A.M and others (2002).An outbreak of Rift Valley Fever in
northeastern Kenya, 1997-98.Emerging Infectious Diseases, 8:138-144.
13.Amwayi S and others (2007). Risk factors for severe Rift Valley Fever Infection in
Kenya. The American journal of tropical medicine and hygiene, 83; 14-21.
14.Reiter P (2008) Climate change and mosquito-borne disease: knowing the horse before
hitching the cart. Revue Scientifique technique Office international Epizooties
27(2):383-398.
7/30/2019 efffects of climate change on epidemiology of vector borne zoonotic diseases
45/45
15.Assad, F., Davies F.G. & Eddy G.A. (1983). The use of veterinary vaccines for
prevention and control of Rift Valley Fever. Bulletin of the World Health Organization,
61:261-268).
16.Robert F Breiman, Bruno Minajauw and others (2010).Rift Valley fever: Scientific
Pathways toward Public Health Prevention and Response. The American Journal of
Tropical Medicine and Hygiene, 83:1-4.
17.Government of the Republic of Kenya (2007). Vision 2030.
18.Logan T.M and others (1991). Mosquito species collected from a marsh in western
Kenya during the long rains. Journal of the American Mosquito Control Association,
7:395-399.
19.R. M. Murithi , P. Munyua, P.M. Ithondeka, J.M. Macharia, A. Hightower, E. T.
Luman, R. F. Breiman & M. Kariuki Njenga (2010) Rift Valley fever in Kenya: history
of epizootics and identification of vulnerable districts. Epidemiology, pg 1-9.
20.Swanepoel Rand Jaw Coetzer, (2004) Infectious Diseases of Livestock volume two
(2nd Edition).
21.Prof. S. George Philander, (2008) Encyclopaedia of climate change and global
warming.
22.Shrivastava, A.K, (2001) Global warming.
23.Anthony E Castro (1992) Veterinary Diagnostic virology.
24.Global Alliance Livestock Vet Medicine (GALVmed) (2010), Safety and efficacy of
OBP clone 13 Rift Valley fever vaccine in sheep, goats and cattle under Kenyan field
conditions, Study protocol.