Prevention and control of leishmaniasis

Leishmaniasis has been listed as one of the eight major neglected tropical parasitic diseases and one of the most difficult to control due to zoonotic nature and the large species and genetic diversity of parasites and vectors. In Sri Lanka, this disease is spreading throughout the dry zone areas.    

According to WHO, early diagnosis and effective case management, vector control, effective disease surveillance, control of reservoir hosts and social mobilization and strengthening partnerships are the key strategies for prevention of leishmaniasis. Early diagnosis and effective case management is essential to reduce the prevalence of the disease and prevent disabilities and death. There are no available vaccines or drugs to provide immunity to the infection. Therefore, the most effective way to prevent infection is prevention of sand fly bites by safety and vector control measures.

Sand flies are mostly active during night time, especially from dusk to dawn. Therefore, outdoor activities during this time should be avoided and the amount of exposed skin should be minimized by using long sleeved shirts and long pants and socks when possible. Insect repellents can be applied to exposed parts of the skin. Insecticides can be sprayed in living or sleeping areas of houses and bed nets, screens, curtains, and clothing can be soaked with Pyrethroid containing insecticides to prevent indoor bites. Reservoir hosts on the other hand are also need to be controlled in order to reduce the risk of infection. However, this is a complex task and the control measures should be modified to suit local conditions

Control of the sand fly vectors mainly based on chemicals and environmental management However, as in many other diseases integrative vector control is strongly recommended for leishmaniasis. Use of insecticides though indoor residual spraying or use of insecticide treated curtains, bed nets with the proper environment management reducing sand fly human contact and sand fly populations could help reduce the transmission of the disease. But these intervention methods are not as easy as they seem to be due to practical considerations. Thus biological control methods are proven to be more promising.

Biological control

Biological control methods mainly involves the use of transformed or naturally occurring bacteria to kill larval stage, arrest the egg development or to kill the parasite within the vector. Successful killing of sand fly larvae using Bacillus thuringiensis under laboratory condition has been demonstrated by some studies were able to reduce sand fly populations using bacteria Bacillus sphaericus in Kenya. Same group of researchers have also reported the possibility of using the same species of bacteria in order to inhibit the development of sand fly eggs.

A gut of a paratransgenic sand fly with B.subtilis under fluorescence microscope

Paratransgenic strategies are proven to be a very effective way in control of insect vectors by several studies Studies reports successful survival of transformed bacteria Bacillus subtilis within the gut of Phlebotomus argentipes mid gut until the adulthood through metamorphosis under laboratory conditions. This is the only study conducted so far to assess the feasibility of paratransgenic control of leishmaniasis. However, further studies will give enough information and may pave the way for more effective control of the disease.

Tharaka Wijerathna

References

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