Kerala - Thiruvananthapuram   

Mosquito eggs pose an epidemic threat

Thiruvananthapuram: The focus of vector-control activities being undertaken during the pre-epidemic period should be on intensive anti-larval activities in the first 10 days of the rains, says an expert.

This is because the possibility of a new epidemic caused trans-ovarially — from the virus-infected eggs laid by Aedes mosquitoes at the end of their active period in the last breeding season — cannot be discounted, says K. Raju Kumar, adviser on vector control for the Epidemic Cell of the Indian Medical Association.

The State government has charted an action plan for prevention of chikungunya this year, which focuses on source reduction as well as complementary activities, such as fogging and garbage clearance.

While these measures are certainly effective for preventing a new epidemic, attention should be paid to the fact that millions of virus-laden eggs deposited by mosquitoes during the last rainy season would be already there in the soil, just waiting for the first showers to come alive again, cautions Dr. Raju Kumar.

“It is the breeding habits of the Aedes species which makes this mosquito virtually indestructible. The female mosquitoes lay the eggs on any wet surface; it does not really require a lot of water to breed. These eggs have the capacity to stay alive for up to a year or more, even in dry conditions. If the virus-infected eggs come alive due to flooding or rain, the emerging adult mosquitoes could initiate the human-mosquito-human cycle again even during the inter-epidemic period,” he says.

However, an article published in the November 2006 issue of Indian Journal of Medical Research says though there is evidence of transovarial transmission (TOT) of dengue virus, “earlier studies have failed to demonstrate the TOT of chikungunya in Aedes species.”

Dr. Raju Kumar suggests that while organising awareness campaigns on effective and sustainable vector control, the message should stress on this critical 10-day window period during which the eggs of the Aedes mosquitoes hatch and develop into adults.

Chemical as well as biological anti-larval measures should be adopted during this period. Chemical spraying should be done in all water-logged areas where there are fewer human activities, while biological control measures, such as introducing larvae-feeding fish, should be adopted in water sources, such as wells or ponds.

Other control measures such as clearing trash from around houses, where rainwater can pool, observing “dry day,” spraying, fogging and keeping the environment clean should also be carried out regularly during the entire rainy season, it is advocated.

It has also been suggested that residents’ associations form vector control squads to make house visits in their respective localities every three days to ensure that there is no water-logging or that there are no potential vector-breeding sites.

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