Treating dogs with a systemic insecticide, that is, penetrating the blood, would considerably reduce the transmission of visceral leishmaniasis to humans, according to a study led by the Institute of Global Health (ISGlobal) in Barcelona.
The results of the study, published in the journal 'Plos Neglected Tropical Diseases', will help define the type of insecticide and how to apply it to achieve maximum effectiveness. Visceral 'zoonotic' leishmaniasis, caused by the parasite Leishmania infantum, can be fatal and is transmitted to humans by the bite of sandfly females, which feed on infected mammals, particularly dogs. In Brazil, where the prevalence of the disease is high (more than 3,000 cases per year), the sacrifice of infected dogs has proved ineffective in slowing the transmission of the parasite.
Treating dogs in the community with systemic insecticides could be another alternative, although at the moment there are no systemic insecticides registered in the market for use against sandflies. In this study, the research team developed a mathematical model to estimate the impact of the use of systemic insecticides in dogs on the number of human infections caused by L. infantum in an endemic area of Brazil.
They took into account different combinations of insecticide efficacy, percentage of treated dogs, and duration of the insecticidal effect.
The model revealed that, for reducing the number of new cases by half, it would be necessary to treat 70% of the dogs in the community with an insecticide whose initial efficacy is 80% and that does not go below 65% for six months. "Our model predicts that, at the community level, the use of systemic insecticides in the 'canine' reservoir of the parasite could significantly reduce human infections with L. infantum," explained Albert Picado, an ISGlobal researcher and coordinator of the study.
According to Picado, treated baits or chewable tablets could be used to facilitate the administration of the insecticide. The study points to the possibility of developing new products or adapting existing ones to be used as a public health intervention to control visceral zoonotic leishmaniasis in endemic regions.