Differentiation of Filarial Endoparasites
Filaria! These nematodes cause (and carry) some of the most disfiguring, debilitating, and widespread parasitic diseases. Transmitted by Diptera, Culicinae, and a few other blood-sucking arthropods throughout the equatorial belt, the infestation of humans by these roundworms has been largely ignored since the end of colonization and abandonment of the majority of the impoverished areas where they’re endemic.
Currently, several organizations are working together to eradicate the filaria who have humans as their sole reservoir, but there’s still a long way to go. The fact that some of these parasites leave patients with life-long disabilities requiring support makes allocating resources purely for eradication much more difficult.
In this image you can see four separate nematodes, each causing a very different type of infection:
- Mf. Bancrofti = Wuchereria bancrofti. Causes elephantiasis [note: it’s NOT elephantitis, which literally means “swollen elephant”. Elephantiasis means, misleadingly, “caused by an elephant”, after its elephantine appearance.] Transmitted by several species of mosquito. Originally endemic to the equatorial regions of the Old World, brought to the New World by the slave trade. 120 million people infected worldwide.
- Mf. perstans = Mansonella perstans. Causes serous cavity filariasis, which is relatively minor compared to other filarial infestation. However, the infestation can cause a general malaise (decreasing work ability) and is very difficult to treat, as other anti-filarial drugs are ineffective. Around 114 million people in Sub-Saharan Africa and South America are known to be infected, but the non-specificity of symptoms and infection make exact figures impossible.
- Mf. loa = Loa loa. Causes loa loa. This is the one with “that worm that crawls across your eye”. Loa loa also causes Calabar swellings, which are dense, goose-egg sized, non-specific swellings, just below the surface of the skin. This parasite is co-endemic with Onchocerca volvus (the cause of river blindness, also a filarial worm), causing problems during eradication attempts of the latter: Loa loa can cause encephalitis when it’s killed off by ivermectin, which is the primary way to eliminate O. volvus.
- Mf. demarquaii = Mansonella ozzardi. Causes serous cavity filariasis, but is restricted to the New World. Mexico and Argentina are the primary areas where one would contract this worm.
Significant species not included in this image are Onchocerca volvus, which causes river blindness, Brugia malayi and Brugia timori, which cause lymphatic filariasis, and Mansonia streptocerca, which causes subcutaneous filariasis. Dracunculus medinensis (Guinea worm)is also not included, but that nematode has a significantly different life cycle and infectious mechanism than the others.
[Source: A Treatise on Tropical Diseases: A Manual of the Diseases of Warm Climates. Sir Patrick Manson, 1919.]