DISEASE TRANSMISSION AT THE WILDLIFE-HUMAN INTERFACE STAN FENWICK REGIONAL TECHNICAL ADVISOR USAID-ONE HEALTH WORKFORCE TUFTS UNIVERSITY-UNIVERSITY OF MINNESOTA
DISEASE TRANSMISSION AT THE WILDLIFE-HUMAN INTERFACE
STAN FENWICK
REGIONAL TECHNICAL ADVISOR USAID-ONE HEALTH WORKFORCE
TUFTS UNIVERSITY-UNIVERSITY OF MINNESOTA
Course Outline
Ecosystems and human health
Ecosystem change and increasing human wildlife contact
Wildlife and disease emergence
Ecosystems, Ecosystem Health and Conservation
Medicine – General Concepts
Definitions
An Ecosystem is a biological community of interacting organisms and their physical environment
Ecology is the biological discipline that deals with the interaction of organisms with the environment, and impacts on all aspects of human and animal health
Biodiversity is the variability among living organisms from all sources, including terrestrial, marine and other ecosystems and ecological complexes of which they are a part
Ecosystem health is a trans-disciplinary concept that bridges the natural, social and health sciences. It can incorporate human values and perceptions that are important in the
management of disease
A healthy ecosystem is defined as a socio-ecological unit that is stable and sustainable, maintaining its character in
composition, organization and function over time while remaining economically viable and sustaining human
communities
Definitions
vet.tufts.edu
Conservation medicine strives to understand health in an
ecological context (identifying the environmental determinants
of health) and uses that understanding to develop preventive or corrective
approaches and to maintain the health of all species in a
sustainable fashion
Central Hypothesis
Climate change and vulnerable ecosystems are leading to an increase in emerging and re-emerging diseases
Economic, social, political and behavioral factors can influence the environment and affect health
SIGNS OF ECOSYSTEM STRESS
• Appearance of emerging infectious diseases
• Loss of habitat and biodiversity
• Increase in “generalist” opportunist species over “specialists”
e.g. seagulls, sparrows, pigeons, rats and mice versus more
specialized animal species
• Decline in species necessary for plant pollination
• Decline in natural predators of pest organisms
• Proliferation of algal blooms along coastlines and waterways
Vietnam News, July 2015
• Biodiversity inhibits population explosions of pest species
• Reduction in biodiversity can lead to closer contact between animal diseases and people – an example is Lyme Disease and white-footed mice, increasing due to a decrease in predators and habitat restructuring, efficient maintenance host for ticks
IMPACT OF BIODIVERSITY ON HEALTH
http://www.alleghenyfront.org/sites/default/files/styles/slideshow_medium_626/public/MouseWithTicks.jpg?itok=F-9pktIb
Human-Livestock-Wildlife Interface
Land Use Change & Human Population
Growth
Increased Contact Between Humans,
Livestock, & Wildlife
Enhanced Flow of Pathogens
Health Risks to Humans, Livestock, & Wildlife
Livelihood Impacts & Economic
Pressures
ENVIRONMENTAL CHANGES INFLUENCING HUMAN AND WILDLIFE CONTACT
Deforestation: removes habitats, predisposes to floods and landslides, habitat fragmentation, changes in vector and reservoir habitats
Changes in surface water availability: increased animal and vector ranges
Bangkok Post July 2015
Overpopulation: expansion into previously uninhabited areas, increased synanthropic animal species (those species ecologically associated with humans)
ENVIRONMENTAL CHANGES INFLUENCING HUMAN AND WILDLIFE CONTACT
Road building: allows access to wildlife and wilderness areas
Climate change
Affects food production and
population nutrition
Can lead to an increase in range
of pathogen reservoirs and
vectors
Contributes to a loss of biodiversity
ENVIRONMENTAL CHANGES INFLUENCING HUMAN AND WILDLIFE CONTACT
Example of Hantavirus transmission in the US
Local enzootic transmission; Sin
Nombre reservoir is deer mice; many
hantaviruses each has a single rodent host
Mild winters and summer rain lead to large increases in rodent numbers;
crowding leads to many infections; mice may enter homes; humans inhale virus or come into contact with urine, faeces or nests; cats, dogs, coyotes can be infected
but do not transmit CDC
Intensive farming practices: result in monocultures, e.g. palm oil plantations impinging on orangutan habitats; impact on vector and reservoir species, e.g. bats and fruit trees
ENVIRONMENTAL CHANGES INFLUENCING HUMAN AND WILDLIFE CONTACT
Increased temperatures
Increase in natural disasters
e.g. floods, rats and leptospirosis
Flooding in Hanoi http://i.telegraph.co.uk
Flooding in Manila news.bbc.co.uk
ENVIRONMENTAL CHANGES INFLUENCING HUMAN AND WILDLIFE CONTACT
Anthropogenic change, wildlife trade, tourism bushmeat consumption etc. all result in closer
contact between humans and other animal species
OTHER EXAMPLES OF HUMAN AND WILDLIFE CONTACT
WILDLIFE AND DISEASE EMERGENCE
• Emerging diseases are those caused by ‘new’ agents or by previously known organisms appearing in places or in species in which the disease was previously unknown
• Includes new animal diseases with an unknown host spectrum, many are zoonotic
• Wildlife reservoirs represent a more frequent source of ‘new’ agents
WHO/FAO/OIE DEFINITION
“An emerging zoonosis is a zoonosis that is newly recognised or newly evolved, or that has occurred previously but shows an increase in
incidence or expansion in geographical, host or vector range”
So, emerging infectious diseases can be -
A known agent appearing in a new geographic area
(e.g. West Nile Virus)
A known agent or its close relative occurring in a hitherto unsusceptible species
(e.g. Avian influenza)
A previously unknown agent detected for the first time
(e.g. SARS coronavirus)
WHY IS THE RATE of ZOONOTIC DISEASE EMERGENCE INCREASING?
…..because the number of high-risk interfaces for disease transmission is increasing, especially
in developing countries
Emerging zoonoses
Approximately 60% of human EIDs are zoonoses (868/1415)
Approximately 72% originate in wildlife
54.3% caused by bacteria (includes rickettsiae) 25.4% by viruses or prions
10.7% by protozoa 6.3% by fungi
3.3% by helminths
IMPORTANCE OF ZOONOSES
Public health
Economic impact
Impact on vulnerable communities
Political impact
24
Principles: Disease Ecology
Pathogen flow and drivers at the
human-livestock-wildlife
interface
The arrows indicate direct,
indirect or vector-borne
pathogen flow. Each box
represents a driver
Jones et al, 2013
The “spillover theory” and drivers of spillover
• Spillover theory – humans constantly challenged with pathogens from animals, only a small proportion invade and fewer still succeed in causing disease
• Can also be used for spillover from wildlife to domestic animals, or
from humans and domestic animals to wildlife • Environmental and climate change • Socio-economic, demographic and political drivers
– Agricultural intensification – Livestock keeping – Bushmeat hunting
Spillover and Disease Emergence
Animal Amplification
C
A
S
E
S
TIME
Human Cases
Wild Animal
Domestic Animal
N.B. spillback to wildlife can also occur
Is relatedness more important than contact for spillover (or spillback)?
Phylogenetic distance from
humans
# o
f sh
ared
pat
hogen
s
Probability of contact with
humans
# o
f sh
ared
pat
hogen
s
Contact rate and spillover risk
Henipaviruses
Lyssaviruses
Flaviviruses
Bunyaviruses
Many ways (direct and indirect) to be exposed to wildlife diseases….
Handling contaminated materials Ingesting infected meat, water Bites or scratches from infected wildlife Inhaling contaminated air, materials Bites from infected insects which have
bitten wildlife
Viral diversity in the host and disease emergence
Hepatitis viruses
SIV/HIV
….a “pool of pathogens”
Known viruses, corrected for number of species & sampling effort per Order
0 5 10 15 20 25 30 35 40
ARTIODACTYLA
CARNIVORA
CHIROPTERA
LAGOMORPHA
NON-HUMAN PRIMATES
PERISSODACTYLA
RODENTIA
Viruses identified per species
Host diversity exposure and disease emergence
photo: C. Gomes Köndgen et. al. Current Biology 2008
Pandemic Human Viruses Cause Decline of
Endangered Great Apes (HMPV, RSV)
Human Metapneumovirus Respiratory syncitial virus
Date Community Symptoms Morbidity Mortality Causative pathogen
March 1999 North
Respiratory
32 (all)
8/32
Streptococcus pneumoniae (a), RSV B
March – December
2001
Middle
Chronic respiratory
1/12
1/12
Non detected
March 2004
South
Respiratory
41 (all)
9/41
S. pneumoniae (b), Pasteurella multocida, HMPV
Haemophilus influenzae
August 2005
South Respiratory 32 (all) 2/32 RSV B
February 2006
South Respiratory 34 (all) 1/34 S. pneumoniae (b) RSV B
February 2006
East Respiratory ? 3/? S. pneumoniae (a) RSV B
Chi et al. 2007, J. Bact.; Köndgen et al. 2008, Curr. Biol.
Pandemic Human Viruses Cause Decline of Endangered Great Apes (HMPV, RSV)
Zoonotic Agent Families in Wildlife
• Rhabdoviridae (Rabies, ABL) • Paramyxoviridae (Nipah, Hendra) • Retroviridae (SIV/HIV) • Flaviviridae (West Nile) • Togaviridae (WEV/EEV/VEV) • Herpesviridae (Herpes B) • Filoviridae (Ebola, Marburg) • Coronaviridae (SARS) • Bunyaviridae (Hantaviruses,
RVFV) • Orthomyxoviridae (H1N1, H5N1
influenza) • Others?????????????
J. Epstein copyright 2006
37
Kock 2014
Estimated global mortality from selected wildlife zoonoses
Log scale
Five stages have been proposed for the evolutionary transformation of an animal pathogen
Stage 1: Pathogen only in animals Stage 2: Pathogen moves occasionally from
animals to humans (‘primary infection’) Stages 3/4: ‘Secondary infections’ increasing
transmission from animal to humans and humans to humans
Stage 5: Pathogen exclusive to humans
EVOLUTION OF INFECTIOUS DISEASES
Action, events or circumstances which may trigger a wildlife disease event
Human-wildlife
interactions
Livestock-wildlife
interactions
Wildlife management
actions
Climatic events
Can result in the introduction of disease or alters the manner in which an existing disease occurs
Individual effect
Population effect
Ecosystem effect
Host-parasite ecological continuum and disease emergence
• Few diseases affect only one group • Complex relationships set scene for disease emergence
• Arrows show factors driving disease emergence
Daszak et al., 2000. Science; 287
Canine distemper
Lyme disease
Taeniasis
Rabies
Population growth and urbanisation
Technology and industry
Travel and trade
Wars and social disruption
Ecological changes due to economic development and
land use
Microbial adaptation
Emerging Infectious Diseases Some factors contributing to infectious disease emergence
Human vulnerability (drugs, alcohol, immunosuppression)
Climate and weather Changing ecosystems
Poverty and social inequality Breakdown of public health measures
Lack of political will Intent to harm
Increases in numbers of unregulated companion animals, synanthropic animals and birds and arthropod vectors
Concentrated populations of wild and domestic animals outside cities expose people to zoonotic agents by direct or indirect contact
Growing population of drug and alcohol impaired and immuno-suppressed people worldwide are at higher risk of zoonoses
SOME RECENTLY EMERGED ZOONOSES
Human immunodeficiency virus (HIV)
Haemorrhagic fevers (Ebola, Marburg)
Henipaviruses
Highly Pathogenic Avian Influenza (HPAI)
Severe Acute Respiratory Syndrome (SARS/MERS)
Bat Diseases
Bats have become one of the most significant reservoirs for emerging zoonotic diseases over the past 2 decades • Lyssavirus (Australia) • Rabies (world wide distribution) • Hendra (Australia) • Nipah (Malaysia, S. Asia) • Menangle (Australia) • SARS (Asia & world wide spread) • Ebola, Marburg (Africa) • Paramyxoviruses (possibly mumps) (worldwide)
Fruit bats a major reservoir
Family Filoviridae – Genus Filovirus EBOLA VIRUS
• First recognised in 1976 in Sudan and DRC (near Ebola river) • Average case fatality rate of ~50% • First outbreaks in remote villages of Central Africa near rainforests,
recent outbreak has spread to urban areas • 5 species – Zaire, Bundibugyo, Sudan, Tai Forest (all from Africa)
and Reston (non-pathogenic, from Philippines) • Pteropid bats thought to be the natural hosts although natural
reservoir not confirmed • Primates, antelope and porcupines can be infected and die
humans handle or eat carcass of dead primate or duiker human infection occurs
Suspected Ebola transmission in Africa
Bat Wild primate Duiker
In 2003, 114/128 people infected with Ebola in Congo/Gabon died – and an estimated 6-800
gorillas!
www.cdc..gov
Total cases in the 3 worst affected West African countries, 2014-15 (Sierra Leone, Liberia, Guinea)
In the recent Ebola outbreak, which started in 2014, there have been around 24,000 cases
with 14,000 deaths, over 58% mortality
Control of emerging diseases from wildlife or to wildlife – requires a One
Health approach
Animal
Amplification
C
A
S
E
S
TIME
Wildlife ecologists
Some of the ‘characters’ in One Health
Conservationists
Veterinarians
Behavioral Scientists Field Epidemiologists
Diagnosticians
Medical and Public Health Practitioners
Many difficulties in dealing with wildlife diseases…
Hard to sample wildlife; hard to detect diseased animals and carcasses rarely found
Few diagnostic tests for wild animals Knowledge of wildlife diseases, transmission and cycles
lacking People very protective of wildlife
Few interventions used for livestock can be used in wildlife,
e.g. culling
Although when such interventions are used a lack of ecological understanding can lead to unforeseen problems
..should have involved wildlife ecologists in the planning
SMART surveillance
Strategic selection of geographic locations for surveillance
Strategic selection of species for surveillance
Animal
Amplification
C
A
S
E
S
TIME
Human Cases
Wild Animals
Domestic Animals
Early Detection and Control
Opportunities
Wildlife Surveillance and Forecasting
This enables interventions or surveillance to be targeted
DAY
CA
SES
Current Outbreak Detection and Response
Adapted from J. Davis, Climate Adaptation Workshop, Nov. 2003
First Case
Detection & Reporting
Laboratory Confirmation
Response
Opportunity for control
DAY
CA
SES
First Case Detection & Reporting
Lab Confirmation
Response
However, if we have effective early warning systems in place
Surveillance, Observations
and Monitoring Information
Adapted from J. Davis, Climate Adaptation Workshop, Nov. 2003
Opportunity for control
What’s Next?
• Recently a number of new avian influenza virus strains have infected humans, the most serious being H7N9
• A new coronavirus, MERS, has been identified in the Middle East, closely related to SARS virus and reservoir probably bats; humans most likely infected via contact with camels
• Most recently an epidemic of Ebola virus has occurred in West Africa, probably linked to initial bush meat consumption (bats, primates)
http://virologydownunder.blogspot.com.au/
From March 2013 – May 2015 there have been 665 confirmed cases of human H7N9 infection, with 229 deaths = 34.4% mortality rate. Most cases in China, few in travellers (HK,
Taiwan, Malaysia)
Middle East Respiratory Syndrome (MERS) is a viral respiratory illness that is new to humans. It was first reported in Saudi Arabia in 2012 and has since spread to several other countries, including the United States. Most people infected with MERS-CoV developed severe acute respiratory illness, many of them have died. Camels and bats are believed to be linked to the epidemiology of the disease To June 2015 there have been 1329 cases, with 525 deaths (39% mortality)
MERS in South Korea
An outbreak of MERS was reported in South Korea in
May 2015, in a traveller returning from Saudi
Arabia. The outbreak was poorly contained by
hospitals
Since June 29th there have been 182 confirmed cases (1
in China) with 32 deaths, 17.6% mortality,
considerably lower than in Saudi Arabia (44%)
In Conclusion
•The occurrence of emerging zoonotic diseases is multifactorial, and is affected by many causal factors, including ecological conditions
•Overpopulation has stressed the environment and resulted in closer contact between people and wild animals
•Environmental stability and biodiversity are important for ecological, human and animal health
•Control of new emerging diseases needs to take into account related environmental factors
The Final Word From SEAOHUN (again)!!