Control methods for phlebotomine sand flies

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Control methods for phlebotomine sand flies

• Bruce Alexander
• Molecular Biochemical Parasitology Group
• Liverpool School of Tropical Medicine, Pembroke
  Place, Liverpool L3 5QA, UNITED KINGDOM

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Types of vector control

• Chemical
• Biological/Microbial
• Genetic modification
• Environmental manipulation

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Personal protection methods

• Repellents
• Protective clothing
• Mosquito nets/curtains

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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

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Spraying house with residual pyrethroid
insecticide
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Cone test determining whether the residual
insecticide on a wall still kills sand flies
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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?

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

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Fluorescent powders for mark-release-recapture
studies
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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

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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?

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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?

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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

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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

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Insecticide-impregnated mosquito net
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Curtains/Sand fly-proofing house Impossible??!!
ITNs the only solution here!
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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

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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??

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Painting tree trunk with whitewash to make it
unsuitable as a sand fly resting site
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Virtual barrier zone -1

• Create cordon sanitaire around village
• Resting site trees treated with whitewash (not
  residual insecticide) to make them unsuitable
• Doesnt kill sand flies but makes them stay
  further away from village less chance of
  man-vector contact

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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!)

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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

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Nopikex, a repellent soap containing DEET and
permethrin
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Tested in the field by the Colombian army
unfortunately soap found to have no residual
effect if rinsed off
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Scalibor - Insecticidal dog collars
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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

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

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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