Nepal | February 24, 2020

Integrated approach needed to fight dengue threat: Experts

Sabitri Dhakal

Kathmandu, September

Researchers and health practitioners have said that if a mass awareness campaign is not conducted, it will be difficult to prevent dengue from spreading.

They say mosquito eggs can survive for years before hatching. Experts, therefore, say mosquito eggs and larvae must be searched and destroyed to prevent dengue infection.

“The adult female Aedes Aegypti mosquito lays eggs on the wet surface of any container above the waterline. It generally lays 100 to 200 eggs at a time.  These eggs are hardy, stick to the walls of the container and can survive dry conditions for up to a year,” said Ishan Gautam, associate professor of entomology.

“Mosquito eggs are resistant to desiccation, allowing them to survive unfavourable conditions,” said Dayaram Bhusal, associate professor at Central Department of Zoology, Tribhuvan University. “These dengue causing mosquitoes can spread to new areas when dormant eggs are transported along with materials such as tyres, plant pots and bamboo,” added Gautam.

The eggs have the capacity to resist desiccation and can survive in unfavourable environments for up to over a year.
Once the eggs find favourable humidity, temperature and water they will develop into larvae,” said Gautam.

Mosquito eggs hatch at 14 to 30 degrees Celsius, but it takes time for them to hatch when the temperature drops to below 10 degrees Celsius. After resisting the winter season the same eggs can hatch upon arrival of the summer season, Gautam added.

“Such quiescent eggs constitute a significant problem for vector control because they can directly contribute to increasing the mosquito population. This quality of the eggs also facilitates their transportation and establishment of new mosquito populations in various areas,” said Anup Bastola, chief consultant and tropical medicine physician at Sukraraj Infectious Disease Hospital, Teku.

“The same could have happened with regard to the spread of dengue in Kathmandu. Last year, dengue cases were reported in Sano Bharyang.

The eggs might have remained resistant during winter and hatched as the temperature rose, but a thorough study should be carried out,” said Bastola.

“The Aedes Aegypti mosquito does not lay eggs in a single place. If it is disturbed while laying eggs, it goes to a new place and lays eggs. This is how the mosquito population rises in new areas,” added Gautam.

According to Epidemiology and Disease Control Division 7,370 dengue cases were reported across the country till Wednesday, up from 5,095 on September 10. Within a period of a few months, dengue has spread to 67 districts.

“Integrated vector management, including vector control, search and destroy drives and education of the public is extremely important for controlling dengue,” said Bastola.

A version of this article appears in print on September 22, 2019 of The Himalayan Times.

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