Skip to main content

Vector Control for Visceral and Cutaneous Leishmaniasis

Final Report Summary - VCVCL (Vector control for visceral and cutaneous leishmaniasis)

The main project objectives were to determine if a sex pheromone is used by either P. papatasi and/or P. perniciosus in their mating ecology. Specifically we wished to determine in laboratory experiments if males of either species might be attractive to females or if females might be attractive to males. We then also wished to establish the age of the adult males or females that produced pheromone and the age of sand flies that were most responsive to sex pheromone to help us understand more of the biology of the sex pheromone and to help devise appropriate strategies for its practical use. We also wished to determine the site of pheromone production and to establish the distance over which it might be attractive.

All of the work described in the objectives has been carried out for Phlebotomus papatasi and clearly demonstrated that a sex pheromone is produced by males. A similar scheme of work for P. perniciosus showed that a sex pheromone is not produced by that species.

We have demonstrated clearly and unambiguously through behavioural assays carried out both in the laboratory and in the field in Tunisia that male P. papatasi produce a sex pheromone that is attractive to females. We showed that the sex pheromone is produced by young males (1-3 days old) and is attractive to young (1-3 day old) females. Old males (4 - 6 days old) are not attractive to young or old females (4 - 6 days old) and old females are not responsive to either young or old males. In addition we found that females are not attractive to males and in that males are not attractive to other males. We have also shown that females are highly sensitive to concentration of the male produced sex pheromone. Small groups of males (or males + females, n=5 or 10) are attractive large groups of males (or males + females, n=30 or 60) are repellent. Our laboratory experiments were conducted over a distance of up to 20 cm. Experiments carried out in the field in Tunisia confirmed the results of the laboratory experiments and we were able to attract female P. papatasi to traps baited with small numbers of live males and females and repel females from traps baited with larger numbers of live males and females. These results also indicated that the sex pheromone is operative over at least 3 m. Together these observations form the basis for progressing with the chemical identification of the sex pheromone over the next few years.

Extensive SEM and TEM studies failed to conclusively identify potential sites for pheromone production in males. Clearly the sites of sex pheromone production are not as extensive or as obvious as in Lutzomyia longipalpis and suggest that they are few in number and may be hidden. We therefore carried out an extensive study on male/female mating interactions to reveal the precise sequence of events and interaction of both partners during courtship and mating. Analysis of this behaviour revealed that male P. papatasi swing their abdomens slowly from side to during courtship males that do not do this do not mate. This behaviour reveals the inter-segmental membranes which may be a possible site of pheromone producing glandular tissue.

The study has clearly demonstrated the presence of a sex pheromone in P. papatasi an important vector of cutaneous leishmaniasis in European, Middle Eastern and Southern Mediterranean countries. Cutaneous leishmaniasis may cause facial disfigurement, and is more likely to affect children under 15 years old in European, Asian and Southern Mediterranean countries resulting in severe social towards those affected. Precise figures are not available but reports suggest that between 36,000 & 65,000 cases may occur in endemic Mediterranean (including European) countries annually.

The field study element of the project so far is particularly important as it demonstrates that wild populations of P. papatasi can be significantly manipulated by the sex pheromone. This project will now lead to the isolation and chemical characterisation of the pheromone, its eventual synthesis and exploitation for vector control. We are optimistic that the use of a sex pheromone and other semiochemicals as part of a vector control strategy will play an important part in reducing the impact of leishmaniasis.