Epidemiology and Prevention of Wuchereria Bancrofti Infection - Mosquito Bourne Illness

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Experts always say that prevention is better than cure. This is very true when epidemiologists are dealing with how to eradicate the prevalence of microfilaremia and elephantiasis in various areas. Even if doctors are able to cure infected people using drugs and surgical methods but infection of other people is still continuous, the problem is not solved. The best way is to look at the roots of the problem – the mosquitoes that transmit W. bancrofti microfilariae to humans.

Epidemiology of Wuchereria bancrofti Infection

Parasitologists have identified at least 77 species and subspecies of mosquitoes that are capable of supporting the development of W. bancrofti; these species and subspecies belong to the genera Anopheles, Culex, Aedes and Mansonia. They claim that only few of these species are actively involved in transmitting W. bancrofti to human populations. The vector mosquitoes have a high preference for human blood and usually breed near human habitation. Because they prefer human blood over animal blood, they can transmit to humans whatever parasites are contained in them; examples of parasites are the Plasmodium protozoans and Dengue virus (carried specifically by Aedes mosquito).

Most mosquitoes that carry W. bancrofti microfilariae (juvenile stage) are night feeders. They usually feed on human blood between 10pm to 2am because this is the period when microfilariae are concentrated in blood vessels of the peripheral tissues which the mosquitoes’ proboscises can reach. Beyond this period, microfilariae move to blood vessels in deep tissues which coincide to the non feeding period of the mosquitoes. The presence of microflariae within a specific period is termed periodicity. If epidemiologists could determine what species of mosquitoes feed during the period when microfilariae are concentrated in the human peripheral blood vessels, they could design effective control methods.

The conditions for the transmission of W. bancrofti differ from locality to locality and country to country. Epidemiologists should independently consider each case within the framework of the biology of a specific vector and host, harnessing technical and economic resources that are available to the best advantage.

Unique in the animal kingdom, humans seems to be the only animal naturally infected by W. bancrofti; there is no other existing organism that serves as reservoir (bank, storage, etc) for the parasite. (Gutierrez 2000)

Prevention of Wuchereria bancrofti Infection

Environmental factors in tropical regions favor the growth and development of vector mosquitoes. In some areas, controlling the population of mosquitoes is difficult or almost impossible. It is because the mosquitoes lay their eggs in areas that are not noticeable or cannot be destroyed easily like tree holes and hollows at bases of palm fronds. Furthermore, coconuts with holes filled with enough water become a conducive place for the development of mosquito larvae. These coconuts must be burnt to destroy the larvae and to restrain further deposition of mosquito eggs. Any material or place that can be filled with water and open for egg deposition must be monitored from time to time. Remove the water they contain and if possible prevent water from filling in them.

People visiting areas where elephantiasis and related diseases are prevalent must take the extra care to avoid acquiring the parasites. They can apply insect repellants in their skins, use mosquito nets when they sleep especially at night, and do any other preventive methods recommended by experts. Administering chemotherapeutic drugs to indigenous people is effective to eradicate parasites in their blood. If all the W. bancrofti juvenile and adult worms are completely eradicated in their blood, there would be no more parasites that mosquitoes acquire every time they feed on human blood. (Gutierrez 2000)

Educating the people on W. bancrofti and the infections that it causes is still the best preventive method. Teach them to use mosquito nets when they sleep as well as destroying the places where mosquito larvae thrive. In a research conducted by Eberhard and colleagues (1996) shows that less than 50% of an affected population heard of elephantiasis and only 6% knew it was transmitted by vector mosquitoes. This was observed in a community in Haiti. When these Haitians learned something about the disease, the cases of elephantiasis and related illnesses greatly declined.

References

Eberhard ML, Walker EM, Addiss DG, and PJ Lamie. 1996. A survey of knowledge, attitudes, and perceptions (KAPS) of lymphatic filariasis, elephantiasis and hydrocoele among residents in an endemic area in Haiti. Am J. Trop. Med. Hyg. 54:299-303.

Guttierrez, Yezid. 2000. Diagnostic Pathology of Parasitic Infections : With Clinical Correlations. Oxford University Press.