Issue 719 - Page 30

Malaria mosquito bites

Scientists discover they feed in shifts some during day , and some at night

By Agencies & Independent Reporter

Malaria cases and deaths have been slowing down in sub-Saharan Africa in the last few years . This is because of a steady drop in incidence rate of the disease for decades prior due to mass deployment of insecticide-treated nets ( ITN ), researchers have pointed out .

But , researchers have pointed out ; the rate of the decrease in cases and deaths has been slowing down . The question is why ? That is what a group of researchers set out to study , with interesting findings .
The researchers found that each species of mosquitoes has two populations : One that bites during the day and the other at night .
Most biting events occurred indoors between dusk and dawn , the analysis showed .
Major malaria vectors Anopheles gambiae , Anopheles coluzzii , Anopheles funestus and Anopheles pharoensis , however , also substantially took to daytime feeding inside human dwellings , the study found .
This feeding behaviour is scattered throughout the day , the researchers highlighted . Routine surveys miss this , they pointed out .
And that there is no difference in the infectivity of the two groups , said Carlo Costantini from the French National Research Institute for Sustainable Development , University of Montpellier , and one of the authors of the study .
There are , however , some unresolved questions : Did Anopheles mosquitoes recently take to daytime feeding to evade control measures or was the behaviour prevalent but undetected ?
There is a lack of sufficient past data , Costantini explained .
“ There is some evidence that in Africa ’ s Benin and Senegal , a recent change in behaviour occurred in response to ITNs ,” he said .
The researchers found that around 20-30 per cent of mosquitoes that carry malaria-causing parasites bite during the day inside human dwellings .
According to them , this means authorities should re-evaluate malaria control measures , which tend to focus on reducing exposure to mosquitoes at night .
Their study is published in the journal Proceedings of the National Academy of Sciences ( PNAS ), one of the world ’ s most-cited and comprehensive multidisciplinary scientific journals . The peer reviewed journal is part of the National Academy of Sciences ( NAS ).
The study looked at eight species of Anopheles mosquitoes that spread malaria to humans in Central African Republic . These mosquitoes typically bite people at night , previous studies found .
Researchers have neglected daytime biting activity in anopheles mosquitoes , said Costantini .
Costantini and his colleagues wondered if this was because malaria mosquitoes were hunting during the day as ITNs reduced their chances of securing a meal .
The team collected 7,982 Anopheles mosquitoes from eight species , including
Anopheles gambiae , Anopheles coluzzii and Anopheles funestus — the most important malaria vectors in tropical Africa .
The team collected these mosquitoes over 48-hour cycles for an entire year at four sites in Bangui , the capital of Central African Republic .
They studied the biting behaviour of these species across the day to compare how biting times were spread out between mosquitoes biting indoors and outdoors .
Around 18 per cent of Anopheles funestus mosquitoes were biting during the day , a 1970 study recorded . In the current study , the estimate is 28 per cent .
This suggests that the baseline ( past ) level of biting was already high for this species , and it may have increased since then , he explained .
The scientists plan to extend the study to other areas across Africa . They also want to find out what makes the mosquitoes bite at a particular time of the day and if daytime-bit-
28 May . 20 -26 2022