Scientists at the Liverpool School of Tropical Medicine, working with colleagues at the University of Dundee, have discovered how the tiny sand fly spreads one of the world's most deadly tropical diseases - Leishmaniasis.
Their discovery, which has been published in the magazine Nature, has been welcomed as the sort of fundamental breakthrough which could eventually lead to a vaccine being developed against the parasitic disease which can cause severe illness and even death.
Leishmaniasis affects about 12 million people worldwide at any one time, with about 2 million new cases every year. Humans catch it when bitten by sand flies carrying the single-celled organism Leishmania. However, many things about the transmission of Leishmaniasis have remained a mystery such as the dosage of parasite in each sand-fly bite required to cause disease, and the identity of shadowy 'virulence factors' thought to enhance the infection.
Working with colleagues at the University of Dundee, Liverpool researchers Dr Paul Bates and Matt Rogers have worked out how the Leishmania parasite has manipulated the sand fly as the perfect transmission system for itself.
Their research reveals the size of the infectious dose, the underlying mechanism of parasite delivery by regurgitation, and the novel contribution made to infection by filamentous proteophosphoglycan (fPPG), a component of a parasite-secreted gel that is co-injected with the parasite when the sand-fly bites its victim. Their findings - the result of four years research - shows that this gel greatly enhances the infectivity of the parasite.
As Dr Bates points out: “Scientists have known for many years that if you get bitten by a sand-fly you may catch Leischmaniasis. But what we didn’t understand was the actual mechanics of it.
"There are three players - the person or animal affected, the sand fly itself and the parasite living in the sand-fly and then in the human/animal that gets bitten. To understand the transmission of the disease we have had to look at the three players together and in doing so have discovered something completely new about the transmission - namely that the gel that the parasite manufactures itself and which the sand-fly carries actually causes more disease. This is because the gel is sticky and stops the sand fly being able to feed properly on its victim’s blood. This means that it gets more and more frustrated, causing it to bite again and again, which means more likelihood of infection.