SM NAJMUS SAKIB
Experts found that October rains in Bangladesh this year has helped the dengue virus vector, Aedes aegypti, lay eggs for a longer period than usual, stirring worries that the prevalence of the disease may prolong to December in the country.
Moreover, they said the mosquitoes can now bite after daytime if there is enough light in the households as the temperature in Bangladesh does not fall as much as the other countries, which has more intense winters.
"Dengue mosquitoes can't survive after temperatures fall below 18 degrees Celcius, but the eggs still survive," Virologist Dr. Mushtaq Hussain told the FE, mentioning that dengue has now became a yearlong public health crisis in Bangladesh.
Dr Mushtaq is in the team of experts who since last year are researching on the vector led by Prof Kabirul Bashar, an entomologist and zoology teacher at Jahangirnagar University. They are examining climate change and adaptation and soon will file their research for a peer-reviewed scientific journal.
Entomologists, climate change experts, and virologists feared a worsening dengue situation with the number of Aedes larvae likely to increase in next two months as temperature drop and rains occurs and temperature falls down after the October rains.
At least 286 people died and over 59,420 hospitalisations were reported due to the dengue infection from January till October 29, according to the Directorate General of Health Services (DGHS).
"We have been observing changing behaviour in the dengue mosquito since last year, certainly about its life cycle. An adult dengue mosquito usually survives 20-25 days but it survives up to 40 days in winter (November and December)," Prof Kabirul Bashar said.
"This change is attributed to dengue adaptation towards climate change," he added.
"We generally know dengue outbreak comes in control during the winter season but due to the long life, the probability of mosquito bites and higher density we fear that the worsening condition continues during this winter," he explained.
"Dengue mosquitoes won't survive in a higher temperature above 35. During the summer and rainy seasons adult dengue mosquitoes usually survive 20-25 days," he added.
"Meanwhile, rains in October helped the mosquitoes have a good environment for breeding. And, as long as the surrounding environments have higher mosquito density, the dengue situation won't improve."
"From egg larvae to adult dengue -it's an about 50-60 days journey. So, due to the rains in October, the new dengue mosquitoes would survive till December. Since there are more mosquitoes, there are more mosquito bites," he elaborated.
In Bangladesh, July to September is considered as the dengue outbreak period, according to the WHO. However, due to the changing weather, dengue mosquitoes are now well survived till November.
Virologist Dr. Mushtaq Hussain told the FE that it takes up to 1.5-2 months to complete its life cycle after dengue laid eggs after rains ended. So, the dengue situation prevails until the end of this year as we see rains in October.
Ahmad Kamruzzaman Majumder, professor at the Department of Environmental Science, Stamford University, explained that the temperature and humidity are considered as friendly environments for dengue, which was mostly found in June and July.
"But now we see mosquitoes get friendly weather even after the end of the rainy season. We reported rains in November last year," he told the FE.
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