Parasites make dogs smell enticing to infectious sand flies

In a new study from Lancaster University, researchers have demonstrated that the parasite Leishmania infantum can alter the scent of its host. The experts report that dogs infected with the parasite smell more attractive to female sand flies than males.

In Brazil, the parasite Leishmania infantum is transmitted by the bite of infected female Lutzomyia longipalpis sand flies. There are up to 300,000 new cases of leishmaniasis every year. 

Leishmania parasites are transmitted from infected dogs to people by sand flies when they bite. Visceral leishmaniasis affects the internal organs and can be fatal. In Brazil alone, approximately 4,500 people die each year from the visceral form of the disease.

“In this study we showed that infected dog odor is much more attractive than uninfected dog odor to the female sand flies. Only the females can transmit the pathogen and male sand flies, which do not transmit the parasite, are not affected by the changed odor,” said study lead author Professor Gordon Hamilton. 

“This clear-cut difference in attraction of female and male sand flies suggests that the females are preferentially attracted by parasite infected hosts and this could lead to enhanced infection and transmission opportunities for the parasite.”

The Lancaster team had previously determined that dogs infected with Leishmania parasites smelled different than uninfected dogs.

“Domestic dogs are the reservoir of infection, therefore understanding how the infection affects the attractiveness of dogs to the insect vector is important in understanding the epidemiology of the disease and offers opportunities for new control and diagnostic methodologies,” explained Professor Hamilton.

The researchers collected odors from infected and uninfected dogs in a Brazilian city. The study revealed that female sand flies were more attracted to the odor of infected dogs compared to uninfected dogs. 

According to the study authors, the findings provide strong evidence that parasites manipulate the odor of their hosts, potentially enhancing infection and transmission opportunities for the pathogen.

“This demonstration of the parasite’s manipulation of its host’s odor, to potentially improve its transmission opportunity, will help us to understand the epidemiology of the disease, improve existing control strategies as well as develop new methodologies for control and diagnosis,” wrote the researchers.

The study is published in the journal PLOS Pathogens.

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By Chrissy Sexton, Earth.com Staff Writer