Malaria time bomb began ticking in ’07?

Mumbai: The BMC’s latest Environment Status Report (ESR) reveals that the malaria menace in the city has been growing for the past three years with a constant rise in the disease’s positivity rate. Health experts are blaming climate change as one of the key reasons for this steady rise in Malaria. The world over, a changing climate scenario has affected the opening and shortening of the transmission window, altering the life-cycle of the malaria parasite, experts said. “What has happened is that the incubation period—the rate at which the parasite multiplies—is varying because of the city’s temperature. This is one of the reasons why Mumbai, with its extreme temperatures, climate and rainfall, has been witnessing a rise in the positivity rates,’’ said a health expert.
    Besides climate change, heavy construction activity and large slum populations in Byculla, Elphinstone, Dadar, Parel, Matunga, Ghatkopar, Andheri (E) and Kurla are cited as major reasons for the large number of cases.
    According to the report, in 2007-08, the number of blood samples that the public health machinery collected was 6.9 lakh and the percentage that tested positive was 3.72; the number of malaria deaths that year was 122 and the worst-affected ward was Elphinstone with the rate touching a staggering 7.44%. The next year, too, there was a rise in the number of people who tested positive, and 99 deaths were recorded. Once again, the area in and around Elphinstone emerged as a mosquito hotbed.
    BMC health officials said greater surveillance has meant that more samples are being collected and therefore, the positivity rate has climbed. In 2009-10, the number of samples collected were close to the 9 lakh mark and the positivity rate climbed to 4.57, says the report. The large number of samples collected was cited as a factor for the rise in positivity. “This was made possible by deploying more staff at the worst affected areas,’’ said an official.
    This year, the corporation has declared the seven worst affected wards that have witnessed nearly two-thirds of all the reported malaria cases.
Monsoon-related diseases claim 3 lives
Three deaths were registered in the city due to monsoonrelated diseases on Friday and Saturday, taking the death toll to 13 in the first week of August. A 16-year-old boy, a resident of Grant Road, and a 40-year-old man from Dharavi succumbed to malaria on Friday and Saturday. Malaria has claimed 10 lives this month. Dengue, too, has claimed its second victim this month, an 18-year-old boy from Worli. Meanwhile nine people, including two children, tested positive for the H1N1 virus on Saturday. — Pratibha Masand

VIRUS VS PARASITE

Dengue loses deadly sting to malaria

Mumbai: Have you ever wondered why Mumbai, which is seeing a proliferation of malaria cases, is not being plagued by dengue even though both diseases have mosquitoes acting as the vector? Since the onset of the monsoon, there have been 7,140 reported cases of malaria and the death toll is 33. On the other hand, only 135 citizens were admitted to civic hospitals for dengue and three succumbed to the disease. The answer to this disparity lies in the fact that these diseases are spread by two different types of mosquitoes.
    Both are female, but it is only the malaria-spreading anopheles mosquito that thrives on stagnant water—which explains the municipal corporation’s sudden interest in construction sites. But the dengue-causing mosquito, the female aedes, needs a steady supply for fresh water. “Anopheles mosquitoes need large water bodies to breed in. Stagnant water and excess humidity are favourable conditions. The aedes on the other hand, does not need excess water, and can breed in small containers, tyres and flower pots. In fact, we find that dengue cases rise during intermittent spells of rainfall in the months of August, September and October,’’ said Dr Daksha Shah, head of the civic epidemiology cell.
    The breeding patterns of the two female mosquitoes
are different, with the anopheles emerging as the more proliferating survivor of the two. The aedes can lay eggs approximately three times in its lifetime, producing 100 eggs in each sitting. On the other hand, the anopheles has a regular breeding pattern: till it dies, the female can lay 30 to 150 eggs every two to three days. You do the math.
    Given the growing number of construction sites that are home to stagnant pools of water, this year, it is the anopheles’ sting that is becoming deadlier.
    City doctors said there is a third reason for why malaria is spreading so rapidly; it boils down to the differences between a parasite and a virus. Physician Dr Hemant Thacker, who consults in many private hospitals, explains that malaria is caused by a parasite called plasmodium, while dengue is caused by a virus.
    “While the lifespan of a virus is not more than five to 15 days, a plasmodium can stay active in a body—if undetected—for six months to a year,” he said.
    Even if a person is immune to the plasmodium, he can carry the parasite, which has a greater chance of latching itself on the next anopheles mosquito that bites him. “That mosquito will transmit it to other human beings. But the dengue virus may not live long enough to be transmitted from the infected person to another human being by a mosquito.”