Malaria makes its host smell better to mosquitoes

"Mosquitoes wouldn't opt to carry the malaria parasite because it isn't good for the mosquito," says Consuelo De Moraes. "Probably the parasite is not only manipulating the mice to alter their scent, but the mosquitoes to be more attracted to the infected scent." (Credit: Martin Grimm/Flickr)

Malaria parasites can change their host’s scent to attract mosquitoes and spread their offspring, report researchers, who say the scent change could be used as a diagnostic tool.

“Malaria-infected mice are more attractive to mosquitoes than uninfected mice,” says Mark Mescher, associate professor of entomology at Penn State. “They are the most attractive to these mosquito vectors when the disease is most transmissible.”

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Parasites, spread by mosquitoes, cause malaria in humans and animals. The disease can be spread only by an insect vector, a mosquito.

The mosquito ingests the parasite with a blood meal, and the parasite creates the next generation in the mosquito’s gut. These nascent parasites travel to the mosquito’s salivary glands and are passed to the host during the next meal.

“We were most interested in individuals that are infected with the malaria parasite but are asymptomatic,” says Consuelo De Moraes, professor of entomology. “Asymptomatic people can still transmit the disease unless they are treated, so if we can identify them we may be able to better control the disease.”

Not good for the mosquito

As reported in the Proceedings of the National Academy of Sciences, when the researchers used a mouse malaria model, the mosquitoes were more attracted to infected mice, even when the mice were otherwise asymptomatic. The study also showed that several individual compounds whose concentrations were altered by malaria infection contributed to the increase in attractiveness to mosquitoes.

To eliminate other factors such as carbon dioxide production and body temperature as an attractant, the researchers extracted the body scent from the mice and showed that the changes in the scent alone altered the attraction of mosquitoes.

“Mosquitoes wouldn’t opt to carry the malaria parasite because it isn’t good for the mosquito,” De Moraes says. “Probably the parasite is not only manipulating the mice to alter their scent, but the mosquitoes to be more attracted to the infected scent.”

Useful for screening humans

While the mosquitoes were not attracted to mice that had acute malaria symptoms, they were particularly attracted to mice during a period of recovery when the transmissible stage of the malaria parasite was present at high levels.

In regions where malaria is prevalent, significant numbers of people harbor asymptomatic infections but remain able to transmit the disease to others. The researchers hope this altered scent profile might help to identify those needing treatment.

“If this holds true in humans, we may be able to screen humans for the chemical scent profile using this biomarker to identify carriers,” Mescher says.

The Bill and Melinda Gates Foundation Grand Challenges Exploration supported this work.

Source: Penn State