Control methods for phlebotomine sand flies

1. Control methods for phlebotomine sand flies Bruce Alexander Molecular & Biochemical Parasitology Group Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UNITED KINGDOM

2. Types of vector control • Chemical • Biological/Microbial • Genetic modification • Environmental manipulation

3. Personal protection methods • Repellents • Protective clothing • Mosquito nets/curtains

4. Chemical control • Many New World foci of CL associated with forested areas, control of sand flies not considered practical • In urban areas spraying programmes may be carried out using residual insecticides • Sand flies susceptible to all major groups of insecticides but pyrethroids normally used

5. Spraying house with residual pyrethroid insecticide

6. Cone test – determining whether the residual insecticide on a wall still kills sand flies

7. Limitations of chemical control • Costly to carry out spraying programmes, especially when other vector-borne diseases need to be controlled in same area (e.g. dengue) • Resistance to insecticides not a problem, except in India (DDT resistance in P. argentipes) • Where to spray – animal shelters? Within 200m radius of cases?

8. Arrival of dengue in South America – now 2 urban vector-borne diseases competing for public health budget

9. Chicken houses - to spray or not to spray? • Not spraying chicken houses would save money and deflect all infected sand flies towards chickens, reducing number of infective bites(?) • Use chicken houses as foci of control measures?

10. Fluorescent powders for mark-release-recapture studies

11. Mark-release-recapture procedure • Catch sand flies by direct aspiration (e.g. in Shannon trap or on host) • Count and introduce into container with fluorescent dust • Release at site • Attempt to recapture by various methods in following days

12. Mark-release-recapture procedure – information that can be gained • Gives some idea of distance that can be potentially travelled (4km in Central Asia, 2.2km in Brazil, 1km in Colombia) • Gives some idea of age sand flies can reach in nature – 3 weeks in France • Host loyalty?

13. Mark-release-recapture procedure – limitations 1. Area to be reviewed increases considerably with distance from release point, requiring more times, traps and/or personnel • Species, age and physiological status of insects at release not known (lab-reared flies may not behave in same way) • Recapture rate generally low (about 1%) • Insects stressed by capture and marking?

14. Alternatives to institutionalised spraying programmes –individual or community-based control • Mosquito nets (personal protection) • Insecticide-treated nets (control?) • Long-lasting, ready-impregnated nets (more sustainable?) • Environmental manipulation

15. Mosquito nets - Considerations • Untreated nets require very fine mesh to keep out sand flies (owner discomfort/claustrophobia) • Treating nets at community level requires investment in insecticide, regular re-treatment, adequate disposal of waste chemical • Long-lasting, ready-impregnated nets more expensive – useless after 20 washes • Insecticide resistance already in mosquitoes and bedbugs

16. Insecticide-impregnated mosquito net

17. Curtains/Sand fly-proofing house – Impossible??!! ITNs the only solution here!

18. Environmental manipulation - barrier zones • Chop down all trees (potential sand fly resting sites) within 200m radius of village • Kill any potential reservoir species • Apply insecticide to cleared area - Esterre et al., (1986) in French Guiana

19. Barrier zones - the drawbacks • Cleared land will be used to build houses or grow crops….and will have to be extended outwards • Who pays for insecticides? Where and when are these applied? • And by whom??

20. Painting tree trunk with whitewash to make it unsuitable as a sand fly resting site

21. Virtual barrier zone-1 • Create “cordon sanitaire” around village • Resting site trees treated with whitewash (not residual insecticide) to make them unsuitable • Doesn’t kill sand flies but makes them stay further away from village – less chance of man-vector contact

22. Virtual barrier zone - 2 • Whitewash cheap and safe • Anybody can apply it • Already widely used to deter leaf-cutter ants • Establishes boundaries of village • No trees cut down – continue to provide fruit, shade • Easy to see when needs to be upgraded BUT • Never tested in the field (yet!)

23. Repellents • Stop sand flies biting • Based on diethyltoluamide • (DEET), citronella or other plant extracts • Expensive, short term – only for temporary exposure (soldiers, tourists) • Neurotoxic effects (DEET), skin problems • May react with plastics

24. “Nopikex”, a repellent soap containing DEET and permethrin

25. Tested in the field by the Colombian army – unfortunately soap found to have no residual effect if rinsed off

26. Scalibor® - Insecticidal dog collars

27. Treated with deltamethrin Repel and kill sand flies under controlled conditions Spread over entire skin in 48h Only effective for 6 months (must be replaced) Effective for well-cared for pets, useless for stray dogs Relatively expensive Advantages - disadvantages

28. Larval breeding sites usually difficult to find – but P. argentipes breeds in cattle shelters. Bt or neem leaves could be tried

29. Summary-1 • Sand flies susceptible to all major insecticide groups • Larval breeding sites difficult to locate - control by larvicides generally not an option (but see P. argentipes) • Adults move by hopping across surfaces prior to biting so vulnerable to residual (contact) insecticides • VL (sand fly) control may have been unexpected consequence of anti-malaria programmes

30. Summary-2 • Few indications of insecticide resistance (yet) • Mosquito nets offer personal protection or control at community/individual level • Environmental manipulation should be considered in many situations