In the past eight days, 53 persons tested positive for dengue in the city.

According to the Chennai Corporation, since October 1, 74 persons in the city have tested positive for the infection. The health department has urged civic agencies to take precautionary measures.

Four different types of dengue are spread by the Aedes aegypti mosquito — DEN V1, DEN V2, DEN V3 and DEN V4. When a person is infected by one kind of virus, he acquires immunity for that serotype, but it does not ensure protection against the other three types of dengue viruses.

Someone who has high fever for three to 14 days with head ache, myalgias, body ache, rashes and low white blood cell count, is considered to have the classic dengue fever called ‘break bone fever’. The patient may complain of weakness and nausea, too. Various tests are conducted to check for the infection. The first line of treatment is to relieve symptoms of pain and control fever. Even during high fever, the patients must be administered fluids and directed to avoid non-steroidal, anti-inflammatory medications to prevent risk of haemorrhage. According to Corporation health officials, testing kits are available that can confirm if persons suspected with dengue have the infection.

Although doctors rely on clinical symptoms to initiate treatment, even those with uncharacteristic manifestation of the disease are subjected to serological tests, so a dengue haemorrhagic fever is not confused with classic dengue fever, said K. Selvarajan, joint director, blood safety, Tansacs.

He said awareness programmes were needed to sensitise doctors, too, about the infection. ADGP (prisons) J.K. Tripathi said steps were taken to prevent mosquito breeding in Central prisons across Tamil Nadu. So far, no case of dengue had been reported, he said.

The Aedes aegypti mosquito spreads four strains of the disease

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