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Dengue fever is caused by the Aedes egypti mosquito. Culex and Anophelesmosquitoes (which cause diseases like malaria and filaria) are nocturnal — that is, they emerge and bite at night. They can be effectively kept at bay by using mosquito nets while sleeping at night. Aedes egypti, however, is a daytime urban insect. It cannot live above 1,220m or fly more than a hundred metres. It is easily identifiable — its body is striped like that of a tiger. It lives in houses and breeds in stagnant water. This could be in flower vases, old tyres, upturned bottle caps, and even water that collects on leaves and plants.
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Eradication of their breeding grounds is, therefore, a Herculean task, which cannot be achieved by the government alone. Citizens need to do their bit, awaken their civic sense and keep their neighbourhood garbage free. At home, flower vases, water cooler trays, and all sorts of open containers — including broken mugs and bottle caps — should be emptied.
The government often uses frogs or sprays of insecticides to reduce the population of Aedes egypti in populated areas. The sprays need to be used every eight to 10 days to interrupt the cycle of virus transmission. Also, people must leave their doors and windows open so that the insecticide can penetrate indoors, into the nooks and crannies where the mosquitoes rest. We often close all openings to prevent the “harmful chemicals” from entering inside. This negates the effects of spraying.
Once an infected mosquito bites, there is an asymptomatic incubation period of five to six days. After this, dengue sets in abruptly with headache and high fever. There is pain behind the eyes and on moving the eyes. Severe body ache makes it difficult for the person to move, giving dengue the nickname “back breaking” fever. There may be rashes on the skin and inside the mouth. There may also be bleeding into the conjunctiva of the eyes, making them appear blood shot.
After three or four days, the temperature returns to normal. But this is only a temporary respite; the fever returns a few days later with all the previous symptoms but in a milder form. Dengue is, therefore, also called “saddle back” fever.
Unfortunately, there is no specific treatment for dengue. There is no vaccination (as yet) to prevent infection or specific antiviral medication to combat the condition. Affected persons have to ride out the disease with supportive treatment, hoping for the best. Treatment is symptomatic with paracetamol for lowering the fever and fluids for hydration. Aspirin and non-steroidal anti-inflammatory agents like brufen must be avoided. Blood transfusions may have to be given if there is bleeding and shock.
The first attack of dengue usually takes a few weeks to completely recover from. Overall, the disease has a five per cent mortality. It is especially dangerous in children. The dangerous form, called dengue haemorrhagic fever, which is accompanied by shock and bleeding, occurs with subsequent infections with the virus, especially if they are of a different “serotype”.
Humans are infective during the first three days when the virus is multiplying in the blood. During this period, it’s important they lie inside a mosquito net all day and night. This is to prevent them from infecting other members of the household.
The diagnosis is made by excluding other causes of fever. Blood tests may show a low white cell count and platelets. There are, however, some confirmatory tests, like complement fixation, Elisa and an increasing number of antibodies.
Dengue is a self-limited disease. The severity of the symptoms depends on the serotype of the virus, immunological status of the host and, to some extent, genetics.
Herbal products — such as fresh leaves and extracts of neem and tulasi — are being investigated for their anti viral and immune boosting properties. The results are not conclusive. Claims and counterclaims about the efficacy of herbal products are difficult to evaluate. Double blind control studies have not yet been done to prove or disprove their efficacy.
One can prevent mosquito bites to a certain extent by wearing long-sleeved clothing, sleeping inside a mosquito net, and using mosquito meshes for windows and doors. Water should not be allowed to stagnate in containers in and around residential areas. Adding a handful of rock salt or pouring kerosene into stagnant water prevents mosquitoes from breeding.
Remember, no vaccine or specific treatment exists — the only way to escape dengue is to prevent being stung by these pesky insects.
Source: The Telegraph (Kolkata, India)