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Dangue

Introduction

One of the most important resurgent tropical infectious disease is dengue. Dengue Fever and Dengue Hemorrhagic Fever (DHF) are acute fevers caused by four antigenically related but distinct dengue virus serotypes (DEN 1,2,3 and 4) transmitted by the infected mosquitoes, Aedes aegypti. The disease is marked by the onset of sudden high fever, severe headache and pain behind eye eyeballs, pain in muscles and joints; so the disease is also called “break bone fever”. The illness lasts for 6-7 days. Other signs and symptoms, are laboratory criteria are given below.

Clinical Criteria
Fever
Positive Tourniquet Test
Petechiae or ecchymosis
Maculopapular rashes
Arthalgia, Myalgia
Gastrointestinal Bleeding
Shock in Hemorrhagic Shock Syndrome

Laboratory Criteria
Isolation of the dengue virus in serum or autopsy
Increased IgM or Igm antibodies titresDengue antigen detection by immunohistochemistry, immunofluorescence, ELISA.
PCR
Leukopenia, and Thrombocytopenia (100,000 cells/mm3 or less)

Burden of Disease

Dengue is a disease of the tropics and is one of the most important emerging diseases affecting nearly half of the world’s population. It is estimated that there are between 50 and 100 million cases off dengue fever and about 500,000 cases of dengue hemorrhagic fever that require hospitalization each year. The World Health Assembly passed a resolution in 1994 which urged Member states to strengthen their national and local programme for the control of DF/DHF.

Dengue outbreaks have been reported from urban areas from all states. All the four serotypes of dengue virus (1,2,3 and 4) exist in India. The Vector Aedes Aegypti breed in peridomestic fresh water collections and is found in both urban and rural areas. Analysis of available data from 54 dengue outbreaks between 1954 and 1995 indicate that:

1. Dengue outbreaks occurs both in urban and rural areas; and
2. Over the years there has been an increase in reported cases of dengue fever, dengue hemorrhagic fever and dangue shock syndrome. There are many reasons for resurgence of dengue.
a) unplanned and uncontrolled urbanization.
b) inadequate waste management and water supply.
c) increased distribution and densities of vector mosquitoes.
d) lack of effective mosquito control.
e) Increased spread of dengue viruses, and
f) deterioration of public health infrastructure and surveillance system.

Diagnostic tests for dengue virus are not readily available in most parts of the country. At present, there is no mechanism for monitoring and surveillance for dengue. Following reasons were found to be the cause of epidemic;

1. Breeding conditions for the vector in these areas as in the other parts of India posing a constant threat of Dengue in India.
2. Desert coolers, water storage tanks and utensils, leaking water supplies, wells and fountains, rain water collections and water bodies, tyre dumps, junk cans, rain-soaked and un-cleared garbage, dumps, etc. provide an excellent substrate for Acedes breeding.
3. No Acdes control programme is in existence in India. There is no surveillance of Aedes densities. Dengue is not a notifiable disease in India.
4. The National Apical Advisory Committee on surveillance and response to district just set up by the government following outbreak of plague that must have included Dengue as a priority item for surveillance. An emergency plan should be prepared.

Strategy

1. Surveillance for disease and outbreaks
2. Early diagnosis and prompt case management
3. Vector control through community participation and social mobilization
4. Capacity building

There is no separate programme for this however, resources of NAMP are utilized.

Comments

Public understanding and community involvement are the keys to the success of vector control. The steps are:

a) Vector control through community participation and social mobilization.
b) All efforts of control should be directed against the Aedes aegypti mosquitoes. Steps should be taken to eliminate the mosquitoes and the breeding places of mosquitoes if possible. Small household collections of water should be properly disposed off.
c) Prevent mosquito bites.
d) Educate the public for environment hygiene and preventive measures required for vector control.
e) There is no specific medicine for the treatment of the disease. Only symptomatic treatment is given. Antipyretics-salicylates (E.g. Aspirin) should never be used in Dengue fever as it act as antiplatelets that increases the bleeding tendency. Paracetamol can be given safely. Fluid and electrolyte balance should be maintained. In some cases platelets, plasma or whole blood may be required. The mosquito control environmental manipulations is required for proper sanitation.

Tucson may be part of the Sonoran Desert, but to the mosquito Aedes aegypti, it’s a tropical paradise. Unlike other mosquito species, this one survives in small—very small—amounts of water in a cup, in a watering can, in dishes under potted plants, or in trash left around the yard that accumulates water during the monsoon season. But more threatening than a nasty bite, this mosquito transmits dengue fever, a virus endemic to more than 100 countries around the world (see sidebar). Although Tucson has never had an outbreak of dengue, it does support year-round populations of A. aegypti that are able to carry the virus from person to person.
“This particular mosquito is a significant medical threat to Tucson,” says Henry Hagedorn, a professor of entomology at the University of Arizona. “It lives around humans, breeds in our back yards, and in our homes. Controlling the mosquito is a matter of controlling the backyard breeding sites.” To be a threat to public health in Arizona, both the mosquito and the virus must be present. So far, Tucson has high numbers of A. aegypti, but no dengue fever.
Hagedorn, along with research associate Frank Ramberg and a team of undergraduate students, is studying the ecology of this mosquito to find out if it’s going to be an important vector of dengue in Tucson. To do this they have had to devise a series of tests to analyze parts of the insect’s life cycle and its feeding habits. So far they have focused on the mosquito’s egg-laying behavior, the frequency of its blood meals, and how often it bites animals other than humans. Also under study are the various ways people make their homes and back yards attractive habitats for the insect.
egg-laying behavior
Hagedorn began the study in the Sam Hughes region of central Tucson. Within that neighborhood’s network of alleyways, students set out 36 oviposition, or egg-laying traps—one-

quart mason jars painted black with a piece of paper inside. The jar is filled with water that attracts mosquitoes to lay their eggs on the paper. For four months in 2000 the research team checked the jars for eggs twice a week across a seven-block area. Each time, they counted the A. aegypti eggs. Most eggs were found in July, August and September, which correlated with rainfall occurrence during the
“We got about 20,000 eggs in those four months, which means there were about 300 females producing about 60 eggs after each blood meal,” Hagedorn says.” So now we know they are here in the largest numbers during that time, but actually, they are here all year.” Why? Because the eggs can dry out and remain dry for months and then hatch when water is available. This mosquito originally lived in tree-holes or rock pools in Africa that dried out regularly so it evolved to survive periodic dryness.
Vectoring Ability
To be a good disease vector (carrier), a mosquito must take a blood meal from a person infected with the virus and then live for 10 to 14 days. During this time the mosquito may take several other blood meals while the virus multiplies in its body. By the time the third blood meal is taken, Hagedorn says the
mosquito has enough virus inside it to transmit to someone when it feeds again. The researchers wanted to find out if the mosquitoes that were coming to bite people had already bitten somebody else, and could potentially transmit the virus.
Offering herself as a potential victim, a visiting undergraduate student from Switzerland, Paquita Hoeck, went to the test neighborhood over a three-month period in 2000, stood in the alleys, and waited for mosquitoes to land on her. When they did, she caught them before they bit her and took them back to the lab where she dissected them and looked at the ovaries to see if they were dilated, which is evidence that they had taken blood meals and produced eggs.
On the average, 40 percent of the mosquitoes coming to bite her had taken a previous blood meal and had developed a batch of eggs. “Surprisingly, this is the same average the Aedes aegypti mosquito shows in Thailand and Puerto Rico, where dengue is endemic,” Hagedorn says.
What Did They Feed On?
The next step was to find out if the mosquitoes had recently fed on humans or on animals. Although they prefer humans, and only transmit dengue from one human to another, they will also bite dogs or other pets if they have no other choice.
Sam Merrill, an undergraduate student in molecular biology, began collecting A. aegypti mosquito samples in May, 2001 to test what animals the mosquitoes bite. His research is part of the UA’s Undergraduate Biology Research Program (UBRP) which enables students to receive funding for research and earn either academic credit or a salary. In research that is still underway, Merrill catches mosquitoes, grinds them up in the lab, and runs them through a test that that uses antibodies to detect blood types of different animals. Preliminary results are running fifty-fifty, for human and nonhuman antibodies, indicating that only 50 percent of the mosquitoes have bitten humans. If this is confirmed, the threat of dengue transmission would be reduced.
Human Ecology
“The human link in all of this is that we create the conditions the mosquito larvae can breed in, and we provide shelter for the adults, which need protection from the heat of the day,” Hagedorn says. “The best way to avoid dengue fever is to reduce the access the mosquito may have to you.” The homeowner should focus on environments in and around the
monsoons. Tracking The Mosquito’s Behavior
Each step of the research has raised more questions regarding the mosquito’s blood feeding habits over its lifetime, how long it lives, and how far it flies between meals, all important factor in determining the vector ability of A. aegypti. Merrill is developing a method of taking “genetic fingerprints” of A. aegypti that can be used to follow individual mosquitoes throughout their life spans, to determine how long they live, how often they take blood meals, and how large the mating populations are.“We need to find out how the population in Tucson is related to those in Phoenix and other cities in Arizona, Texas, and Mexico,” Hagedorn says. Since the mosquito prefers living inareas with moisture, the adult insects can’t survive flying across long stretches of empty desert. So how are they moving? And how fast are they moving? Hagedorn believes it’s possible that the mosquitoes in Phoenix may have arrived there not by flying from Tucson, but by hitching rides in cars or trucks.

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