Biology Reference
In-Depth Information
needs in malaria control and that malaria research remain an ongoing part
of control/elimination programs.
8.1. Anti-transmission Vaccine
The smallest number of malaria parasites occurs when gametocytes from the
blood develop into oocysts in the mosquito gut. Killing the relatively few
parasites within the mosquito would block transmission at what is thought
to be the parasite's most evolutionarily vulnerable point ( Polley et al., 2004 ).
Although this can be done with primaquine, an anti-transmission vaccine
has been sought based on natural immunity to vivax showing blocking
of mosquito infection in man in a variety of Asian and American settings
( Kappe et al., 2010 ; Plowe et al., 2009 ). Because anti-transmission measures
are aimed at a population and not an individual, there has been little interest
until recently in what has been called an altruistic vaccine . Antigens have been
identified, which have been successfully used in vitro and in animal models.
Initial clinical testing of a combined falciparum and vivax transmission-
blocking vaccine has occurred indicating that such vaccines are safe and
immunogenic. One can be hopeful that transmission-blocking vaccines will
progress further towards field trials, however, it should be remembered that
the supposedly simple blood stage vaccine RTS,S has been in development
for more than 20 years as an indication of how difficult it is to field test vac-
cines against tropical diseases ( Vogel and Roberts, 2011 ).
8.2. Improved Anti-mosquito Measures
Anopheline mosquitoes are fully capable of evolving insecticide resistance
and may also change their behaviour in ways to make them less exposed
to ITN. The future prospects for new insecticide compounds, especially
any completely new chemical entities, are not good as their development
largely depends on agricultural needs and not human health. The evolution
of mosquito enzymes capable of imparting insecticide resistance has been
documented in many field situations, particularly in Africa where the main
concern is falciparum malaria, but resistance threatens all malaria control
programs regardless of species ( Abilio et al., 2011 ). Particularly worrying
are malaria programs that doubly depend on pyrethroid compounds both
to impregnate bed nets and also spray house walls as this provides multiple
opportunities for mosquito evolution of insecticide resistance ( Kaiser et al.,
2010 ). IRS with DDT, particularly in Southern Africa, has been used as an
alternative to pyrethroids; despite environmental concerns, the limited use
of DDT for human health as opposed to agricultural production is safe
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