Control methods for phlebotomine sand flies

Bruce Alexander

Molecular & Biochemical Parasitology GroupLiverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UNITED KINGDOM

Types of vector control

• Chemical

• Biological/Microbial

• Genetic modification

• Environmental manipulation

Personal protection methods

• Repellents

• Protective clothing

• Mosquito nets/curtains

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

Spraying house with residual pyrethroid insecticide

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

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?

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

budget

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?

Fluorescent powders for mark-release-recapture studies

Mark-release-recapture procedure

1. Catch sand flies by direct aspiration (e.g. in Shannon trap or on host)

2. Count and introduce into container with fluorescent dust

3. Release at site

4. Attempt to recapture by various methods in following days

Mark-release-recapture procedure – information that can be gained

1. Gives some idea of distance that can be potentially travelled (4km in Central Asia, 2.2km in Brazil, 1km in Colombia)

2. Gives some idea of age sand flies can reach in nature – 3 weeks in France

3. Host loyalty?

Mark-release-recapture procedure – limitations

1. Area to be reviewed increases considerably with distance from release point, requiring more times, traps and/or personnel

2. Species, age and physiological status of insects at release not known (lab-reared flies may not behave in same way)

3. Recapture rate generally low (about 1%)4. Insects stressed by capture and marking?

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

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

Insecticide-impregnated mosquito net

Curtains/Sand fly-proofing house – Impossible??!!

ITNs the only solution here!

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

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??

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

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

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 upgradedBUT- Never tested in the field (yet!)

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

“Nopikex”, a repellent soap containing DEET and permethrin

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

Scalibor® - Insecticidal dog collars

Advantages - disadvantages

• 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

Larval breeding sites usually difficult to find – but P. argentipes breeds in cattle shelters.

Bt or neem leaves could be tried

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

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