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Dog fleas, not just sandflies, may be transmitting the potentially fatal disease leishmaniasis, say scientists.

Leishmaniasis, a common but neglected disease in tropical and subtropical areas, is caused by a parasite transmitted by sandflies to humans.

The disease ranges from a mild form, in which skin lesions heal by themselves, to a fatal form that invades internal organs.

Dogs harbour some species of Leishmania parasite and represent the largest urban reservoir of the disease, write Brazilian scientists in a Veterinary Parasitology paper published last month (October).

"Canine visceral leishmaniasis — the form that affects dogs — is a problem worldwide because dogs are asymptomatic [lack symptoms] and have parasites on their skin that can infect humans," Valéria Marçal Felix de Lima of Brazil's Paulista State University and an author of the study, told SciDev.Net.

But leishmaniasis is increasing in parts of Brazil even though sandflies show low rates of infection with the parasite. This suggests other vectors must be transmitting the parasite between dogs.

So de Lima's team tested dog fleas. They mashed up fleas from 22 leishmaniasis-infected dogs, and injected them into 22 hamsters.

Four months later, a fifth of the hamsters were carrying Leishmania parasites.

"Dog fleas could be important in transmitting the disease from dog to dog," says de Lima. Sandflies can then transmit this reservoir of infection to humans, she explains.

De Lima concedes the research does not show that fleas can directly transmit leishmaniasis between dogs, but this should be investigated.

If dog fleas are proven to play a role in leishmaniasis transmission, "it will be necessary to change the control methods in dogs to include new strategies to control fleas", says de Lima.

Oscar Daniel Salomón, of Argentina's National Program of Leishmaniasis, says: "The article only shows that fleas who fed from infected dogs had parasites in their stomach, just like a dirty syringe could have them".

More studies are needed to prove if these findings make epidemiological sense," he adds.

Link to abstract in Veterinary Parasitology

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