How sand fly mating habits are helping tackle tropical disease in £2.5 million project

The tropical disease Leishmaniasis is being tackled by catching female sand flies who carry the parasite that causes the disease.

Scientists led by Professors Orin Courtenay of Warwick University and Gordon Hamilton of Lancaster University, developed the concept as part of a £2.5M project funded by The Wellcome Trust and published in PLOS Neglected Tropical Diseases.

There are now plans to commercialise the research which involves using male pheromones to attract female sand flies towards insecticide-treated areas.

Globally over 350 million people are at risk of infection from Leishmaniasis, with an estimated 300,000 cases annually, and approximately 4,500 deaths each year in Brazil alone. Children under the age of 15 are disproportionately affected.

Visceral Leishmaniasis, affects the internal organs and is fatal if untreated as there is no human vaccine for the disease. In Latin America, Europe, and parts of central and East Asia, the Leishmaniasis parasite is transmitted from infected dogs by sand flies when they bite people.

In Brazil, dogs are euthanized if they are found to be infected, but which has not impacted on controlling transmission. Insecticide-impregnated dog collars is an alternative to protect the dogs but these are too expensive for many people and protective coverage is patchy.

The beneficial effects of this "lure-and-kill" method reduced female sand flies by 49% compared with 43% for the insecticide-collar only.

The method works as the male sand fly vector produces a pheromone that attracts blood-seek females to mating aggregations. We developed a synthetic copy of the pheromone which was put into slow-release dispensers and co-located with pyrethroid insecticide outside resident houses, which kill the parasite transmitting vectors.

The insecticide-collars have been shown by the Warwick researchers to reduce human visceral Leishmaniasis by 50%

Professor Orin Courtenay from the School of Life Sciences and Zeeman Institute at the University of Warwick comments:

"The beneficial effects of the lure-and-kill method were most noticeable by reducing confirmed infection incidence and clinical parasite loads in dogs by about 50%, and in reducing sand fly abundance.

"Our approach will be a lot less expensive and gives just as good a result as the insecticide collar."

Professor Hamilton said: "We wanted to develop a less costly method to trap large amounts of sand flies to reduce the number of infected dogs which in turn act as a source of infection for people."

The researchers introduced a sachet of the male sand fly pheromone to attract female flies to chicken sheds already sprayed with insecticide.

"This killed a large number of the sand flies".

The next stage is to work with industry to synthesize the pheromone in bulk ready for use in affected areas.

Credit: 
University of Warwick