In many parts of the world, the mosquitoes responsible for
transmitting malaria are specialist feeders on humans and often rest
within human houses. Cattle sheds are often next to, and sometimes even connected by,
a shared wall to human houses, yet current control efforts are
restricted to domestic dwellings only.
The goal of eliminating malaria in countries like India could be more
achievable if mosquito-control efforts take into account the
relationship between mosquitoes and cattle, according to an
international team of researchers.
‘The goal of eliminating malaria in countries like India could be more achievable if mosquito-control efforts take into account the relationship between mosquitoes and cattle.’
Matthew Thomas, professor of entomology, Penn
State, said, "We found that in an area of India that has a high burden of
malaria, most of the mosquitoes that are known to transmit malaria rest
in cattle sheds and feed on both cows and humans. Given this cattle-shed 'refuge' for mosquitoes, focusing only on
humans with regard to malaria control is a bit like treating the tip of
The researchers determined the importance of cows in the
malaria-control problem by capturing adult mosquitoes in different
habitats within six villages in Odisha state - which has the highest
number of malaria cases in the country - and noting where the
mosquitoes had been resting. The team then used molecular techniques to
determine which species they were and which hosts they had been feeding
The scientists collected a total of 1,774 Anopheles culicifacies
and 169 Anopheles fluviatilis
mosquitoes across all study sites. They found that both species were
denser in cattle sheds than in human dwellings, and both were feeding on
humans and cattle.
Next, the researchers used their field-collected data to help build a
computer model that simulated the life of an adult mosquito. They used
the model to explore how best to control the mosquitoes to have maximum
impact on malaria transmission in these villages.
"Our model analysis suggests that conventional control tools - such
as insecticide-treated bed nets and indoor insecticide sprays - are
less effective when mosquitoes exhibit 'zoophilic' behaviors (having an
attraction to nonhuman animals)," said Thomas. "However, extending
controls to better target the zoophilic mosquitoes - for example, by
broadening coverage of non-repellant insecticide sprays to include
cattle sheds - could help reduce transmission dramatically."
Waite added that the model suggests very little cattle-based vector
control effort would be required to drive malaria transmission in the
region to elimination.
"We show that directing even modest amounts of effort to
specifically increase mosquito mortality associated with zoophilic
behavior can shift the balance towards elimination," she said.
The findings appear in Scientific Reports
"Understanding the dynamic between humans, cattle and mosquitoes
could have major implications for malaria control policy and practice,
not only in India, but in other areas where transmission is sustained by
zoophilic vectors," said Thomas. "Specifically, optimizing use of
existing tools will be essential to achieving the ambitious 2030
elimination target set by the World Health Organization, which aims to
decrease malaria cases globally by 90% compared to 2015 levels
and eliminate malaria in at least 35 additional countries, by 2030."