Control methods for
phlebotomine sand flies
Bruce Alexander
Molecular & Biochemical Parasitology Group
Liverpool School of Tropical Medicine, Pembroke Place,
Liverpool L3 5QA, UNITED KINGDOM
Types of vector control
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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 markrelease-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
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?
1.
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
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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!)
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 wellcared 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