MMA course work - PSM part 1:Dengue

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WHAT IS DENGUE?

Dengue fever and dengue hemorrhagic fever (DHF) are acute febrile diseases, found in the tropics and Africa,

and caused by four closely related virus serotypes of the genusFlavivirus, family Flaviviridae.It is also known

as breakbone fever. The geographical spread is similar to malaria, but unlike malaria, dengue is often found in

urban areas of tropical nations, including Puerto Rico, Singapore, Malaysia, Taiwan, Thailand, Indonesia,

Philippines, Pakistan, India, Brazil, Vietnam, Guyana, Venezuela and Bangladesh. Each serotype is sufficiently

different that there is no cross-protection and epidemics caused by multiple serotypes (hyperendemicity) can

occur. Dengue is transmitted to humans by theAedes aegypti(rarelyAedes albopictus) mosquito, which feeds

during the day.

In 1779-1780, the first reported outbreak of dengue fever (DF) occurred almost simultaneously in Asia, North

America, and Africa. This indicates that the virus and its vector have a worldwide distribution in the tropical

regions of the world. The clinical presentation of dengue infection involves a wide spectrum of findings, from

asymptomatic or mild self-limiting infection of dengue fever to potentially fatal hemorrhage and shock (dengue

hemorrhagic fever [DHF], dengue shock syndrome [DSS]).

Each year, an estimated 50-100 million cases of dengue fever and several hundred thousand cases of dengue

hemorrhagic fever occur. As many as 3 billion people live in areas where dengue is endemic.

Dengue fever is typically a self-limiting disease with a mortality rate of less then 1%.

When treated, dengue hemorrhagic fever has a mortality rate of 5%. Untreated, dengue hemorrhagicfever has a mortality rate as high as 50%.

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The disease is distributed worldwide in tropical areas.

Incidence is equal in males and females.

Persons of all ages can be infected and develop dengue fever. However, children younger than 15 years typicallypresent with only a nonspecific, self-limited, febrile illness.

In Southeast Asia, dengue hemorrhagic fever is primarily an illness of children and is the leading cause of death

and hospitalization in that population. Elsewhere, the disease affects all ages.

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CAUSES AND RISK FACTORS

Living in endemic areas of the tropics (or warm moist climates such as the southern United States)where the vector mosquito thrives is an important risk factor for infection.

Poorly planned urbanization combined with explosive global population growth brings the mosquito

and the human host into close proximity. Increased air travel easily transports infectious diseases between populations.

The most widely used mosquito-control technique, spraying cities to kill adult mosquitoes, is noteffective. Efforts should target the larval phase with larvicides and cleaning up larvae habitats (eg,garbage, areas that accumulate stagnant water).

Poor sanitation and poor refuse control provide excellent conditions for mosquito larvae to grow.

Lack of immunity to the virus serotypes contributes to infection rates in a population.

Hurricanes and other natural disasters increase the habitat for mosquito growth in urban areas byincreasing rubble and garbage, which act as water reservoirs.

Potential Breeding Sites

The usual sites:

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The unusual sites:

PREVENTIONVaccine development

There is no commercially available vaccine for the dengue flavivirus. However, one of the many ongoingvaccine development programs by doctors is the Pediatric Dengue Vaccine Initiative which was set up in 2003with the aim of accelerating the development and introduction of dengue vaccine(s) that are affordable andaccessible to poor children in endemic countries. Thai researchers are testing a dengue fever vaccine on 3,0005,000 human volunteers after having successfully conducted tests on animals and a small group of humanvolunteers. A number of other vaccine candidates are enteringphase IorII testing.

Mosquito control the primary prevention.

All doctors should be aware of the preventions while treating the patients of dengue fever. They should notifyand advise the patients to take several measurements to avoid getting the disease again.

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There are two primary methods: larval control and adult mosquito control. In urban areas, Aedes mosquitosbreed on water collections in artificial containers such as plastic cups, used tires, broken bottles, flower pots, etc.Continued and sustained artificial container reduction or periodic draining of artificial containers is the mosteffective way of reducing the larva and thereby theAedes mosquito load in the community.Larvicide treatmentis another effective way of control the vector larvae but the larvicide chosen should be long-lasting and

preferably have World Health Organization clearance for use in drinking water. There are some very effectiveinsect growth regulators (IGR's) available which are both safe and long-lasting (e.g. pyriproxyfen). Forreducing the adult mosquito load, fogging with insecticide is somewhat effective.

The guidelines below will give you an overview of how you can prevent theAedes mosquito from breeding.

At all times : Turn pails and watering cans over and store them under shelter. Remove water from plant pot plates. Clean and scrub the plates thoroughly to remove mosquito eggs.

Avoid the use of plant pot plates, if possible. Loosen soil from potted plants to prevent the accumulation of stagnant water on the surface of the

hardened soil. Do not block the flow of water in scupper drains along common corridors in HDB estates. Avoid

placing potted plants and other paraphernalia over the scupper drains. Cover rarely used gully traps. Replace the gully trap with non-perforated ones and install anti-mosquito

valves. Cover bamboo pole holders after use. Rainwater can potentially accumulate in these bamboo pole

holders if they are uncovered and create a habitat. No tray or receptacles should be placed beneath and/or on top or any air-conditioning unit so as not to

create a condition favourable for mosquito breeding.

Every other day : Change water in flower vases. Clean and scrub the inner vases. Wash roots and flowers of plants

thoroughly as mosquito eggs can stick to them easily.

Once a week : Clear fallen leaves and stagnant water in your scupper drains and garden. These leaves could collect

water and cause blockage to the drains, thus resulting in the buildup of stagnant water.

Clear any stagnant water in your air-cooler unit.

Once a month : Add prescribed amounts of sand granular insecticides into vases, gully traps and roof gutters even if

they are dry. Clear away fallen leaves in roof gutters and apron drain. If structurally feasible, remove the roof gutters.

Common insect repellents include:

DEET. This pesticide has long been the insect repellent of choice in the United States. DEET blocks amosquito's ability to find people who've applied it.

Apply repellent with a 10 percent to 30 percent concentration of DEET to your skin and clothing.Choose the concentration based on the hours of protection you need the higher the concentration of

DEET, the longer you are protected. A 10 percent concentration protects you for about two hours. Keepin mind that chemical repellents can be toxic, and use only the amount needed for the time you'll beoutdoors. Don't use DEET on the hands of young children or on infants younger than age 2 months.

Picaridin. This repellant, also called KBR 3023, offers protection that's comparable to DEET at similarconcentrations. It also blocks a mosquito's ability to find people who've applied it. Picaridin is nearlyodorless, which may make it a good alternative if you're sensitive to the smells of insect repellents.

Oil of lemon eucalyptus. This plant-based chemical may offer protection that's comparable to lowconcentrations of DEET. Don't use this product on children younger than 3 years.

Others. Shorter acting repellents generally containing plant-based oils such as oil of geranium,cedar, lemon grass, soy or citronella may offer limited protection.

Secondary prevention

Prevention of mosquito bites is another way of preventing disease. This can be achieved either by personalprotection or by using mosquito nets.

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Protective clothing:

Wear long-sleeved shirts.

Wear socks.

Wear long pants and consider tucking your pants into your socks.

Wear light-colored clothing, since mosquitoes are more attracted to darker colors.

Apply permethrin-containing mosquito repellent to your clothing, shoes, and camping gear and bednetting. You can also buy clothing made with permethrin already in it.

Wear a full-brimmed hat to protect your head and neck or a baseball cap with a fold-out flap to protectthe back of your neck.

Consider wearing a mosquito net to cover your head and face or torso.

Potential antiviral approaches

The yellow fever vaccine(YF-17D) is a vaccine for a related Flavivirus, suggesting that laboratory-basedmodification of YF-17D to target the Dengue virus (viachimeric replacement) instead has been discussed

extensively in the scientific literature. To date, however, no full scale studies have been conducted.

In 2006, a group of Argentine scientists discovered the molecular replication mechanism of the virus, whichcould be attacked by disruption of the polymerase's work. Incell cultureand murineexperiments,morpholinoantisense oligos have shown specific activity against Dengue virus.

Educational approaches

Posters

Banners

An example of Chinese New Year prevention banner

Pamphlets/booklets

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relies on reports by lcal physicians who often do not consider dengue in their differential diagnoses. Asa result, an epidemic has often reached or passed its peak before it is recognized.

Increased travel by airplane provide the ideal mechanism for infected human transport of dengueviruses within population centers of the tropics, resulting in a frequent exchange of dengue viruses and

other pathogens.

Lastly, effective mosquito control is virtually nonexistent in most dengue-endemic countries.Considerable emphasis in the past has been placed on ultra-low-volume insecticide space sprays foradult mosquito control, a relatively ineffective approach for controllingAe. aegypti.