Vampires Zapped: Orally Administered Drug Suggests New Approach in Malaria Prevention

Vampires Zapped: Orally Administered Drug Suggests New Approach in Malaria Prevention

By Siwei Zhang

Malaria prevention in under-developed regions, such as Sub-Saharan Africa, has been demonstrated to be both resource-demanding as well as labor intensive. Currently, the methods of prevention mainly focus on the elimination of Anopheles, the definitive host of Plasmodium falciparum, thus breaking the life cycle of the parasitic protozoa. This prevention strategy, albeit being proven effective in many countries such as China and Thailand, requires a large amount of initial cost that sometimes far-exceeds the capacity of Sub-Saharan countries. For example, an estimation suggests that establishing an initial framework for mosquito control and elimination would cost approximately 1/5 of the total GDP in Tanzania, which is clearly both financially and practically unacceptable. In addition, the application of insecticides during the procedure involves the use of DDT and pyrethroids. This generates not only environmental concerns but, more importantly, insecticide resistance that requires periodical rotation of different insecticides that complicates any prevention project further by adding extra logistic factors. To make the situation more difficult, there is currently no effective vaccine available against Plasmodium. Hence, the prevention of malaria heavily relies on the use of insecticides as well as the distribution of mosquito nets in local communities, a working mechanism that has not changed much in the last 50 years.

Recently, a research group at Colorado State University, Fort Collins, teamed up scientists in Burkina Faso and suggested that ivermectin, a 30-year-old anti-parasitic drug that just won the Nobel Prize of Physiology or Medicine this year, may still possess some new tricks that allows it to be used for malaria prevention. It has been known that in addition to its well-established role as an anti-roundworm drug that fights against river blindness and elephantiasis, ivermectin, a member of the avermectin family, is also toxic to Diphtheria insects if ingested. However, the obvious problem that prevents the drug to be used as an insecticide is that it needs to be ingested to be effective, in contrast to other popular insecticides such as DDT that kill on contact. The research indicates that, if there is a sufficient level of ivermectin present in the blood, it will be able to weaken or kill the feeding mosquitoes upon ingestion. Interestingly, since ivermectin functions by interacting with glutamate-gated chloride channels, an invertebrate-specific ion channel on the membrane of neural cells, it does not have significant effects on mammals and also does not readily cross the blood-brain barrier. Even the mass administration of ivermectin is considered safe for human. In addition, whilst maintaining a steady supply of ivermectin may also present logical problems for remote Sub-Saharan regions, it is much less labor demanding in comparison to traditional methods of insecticide-based mosquito control and elimination.

Such a discovery may inspire a new direction of pharmaceutical R&D for both human and veterinary use: Will it be possible to design orally-administered drugs to kill exoparasites? Until now, the elimination of exoparasites, such as mice, lice, and bed bugs, are still restrained to the use of externally-applied drugs such as ointments and sprays. Due to the high resistance of parasite eggs against these drugs, recurrence is very common during the treatment of exoparasites. The ivermectin case may only be a beginning, with the full potential of orally-administered anti-parasites and insecticides waiting to be unleashed.

Further Readings:

The effect of ivermectin in seven strains of Aedes aegypti (Diptera: Culicidae) including a genetically diverse laboratory strain and three permethrin resistant strains. Deus KM et al., J Med Entomol. 2012 Mar;49(2):356-63.

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