Aedes breeding not confined to your home

In Delhi, which has about 40 lakh households, mosqui to control workers carried out a staggering 2.9 crore home visits this year checking for breeding of dengue or chikungunya-carrying mosquitoes, according to data put out by Delhi's three municipal corporations. That works out to an astonishing eight visits for each household till September.

The corporations' data also shows that this year mosquito larva breeding was found in about 1.2 lakh households. As a share of the total number of visits made, this is a puny 0.4% or about one in 250.

If this data is accurate, it raises the question whether this whole strategy of fighting dengue and chikungunya focused on in-house breeding is valid and workable.The ongoing outbreak of these two diseases means mosquitoes of the Aedes species have bred in large numbers.Where were these mosquitoes breeding?

If the figures are valid each and every household was under constant supervision. It is possible that between two consecutive visits to any house, mosquitoes could have laid eggs, developed to adulthood and flown away ­ it takes just six days for this cycle at an optimum temperature of 32 degrees Celsius, according to Gautam Aditya, a vector expert from Calcutta University .

TOI spoke to several municipal corporation officers, who insisted on anonymity , while saying that the Capital's 3,500 `domestic breeding checkers' and other field workers were hard-pressed to cover the ground. Many residents of Delhi asserted that checkers had visited once or twice, if at all. That raises doubts about the data.

But it is also likely that mosquitoes are breeding in large numbers outside of homes. Areas in the immediate vicinity of homes are also the responsibility of the mosquito control workers. But how much can the man do, considering that he is visiting 50 houses every day , including climbing on to the roof to check overhead tanks?

“Focusing only on indoor breeding grounds of aedes is not adequate as the vector mosquitoes have been reported to breed in peridomestic habitats like junk material, discarded tyres in open, bird feeding earthen pots, outdoor water containers beneath shrubby places, etc.“ Ramesh Chand Dhiman, senior scientist at the National Institute of Malaria Research, New Delhi, told TOI. There are other breeding places for aedes mosquitoes, according to Aditya. Research has shown that this highly adaptable species lays eggs in sewage drains, septic tanks and even in brackish water. This is contrary to the given wisdom that aedes breeds only in fresh water.

“One of the biggest bree ding grounds for aedes is discarded plastic containers like bottles, cups, bags etc.Rainwater collects in them and the aedes female will quickly lay eggs in even a small amount of water. So, garbage dumps in cities like Delhi are prime breeding grounds,“ he told TOI.

Solid waste management is a growing and urgent problem in most Indian cities.And this garbage contains a lot of plastic that can hold a few inches of water. Delhi generates about 9,000 metric tonnes of garbage every day and it is common to see garbage piled up in dhalaos in colonies.Besides community participation, “proper management of waste disposal“ is essential to check breeding of mosquito vectors, says Dhiman.

(TOI)