Filariidae

Jean-Nicolas Demarquay (1863); Otto Wucherer (1866); Timothy Lewis (1872); Joseph Bancroft (1876); Patrick Manson (1877).

The family Filariidae belongs to the class of nematodes (threadworms). The Filariidae, the fialria or nematodes (from Latin filum = thread), are very thin 2.0-50cm long parasites whose larvae, produced by the millions, are called microfilariae. Microfilariae circulate in the blood of the host (human) and are usually transmitted by blood-sucking arthropods to other humans. Here they in turn cause the specific and non-specific symptoms of filariasis.

Loa loa (Central Africa; vector: Chrysops; infestation of the conjunctiva, skin swelling)

Wuchereria bancrofti (Asia, Africa, South America; vector: Anopheles; elephatiasis)

Bruga malayi (Southeast Asia; vector: Anopheles; elephantiasis)

Brugia timori (Indonesia; vector: Anopheles; elephantiasis)

Onchocerca volvulus (Central and South America, Africa; vector: blackfly; river blindness, dermatitis)

The distribution of filariae depends on the distribution area of the respective vectors. Most filariases are transmitted by insects in tropical countries. It is estimated that approximately 100 to 200 million people worldwide are infected with filariae. The population in developing countries is particularly affected.

During a blood meal, vectors transmit microfilariae (L3) capable of infection, which develop into adult worms in the course of 3-20 months, depending on the species. These live for 10-15 years in the case of onchocerciasis and 8-9 years in the case of Wucheria bancrofti, among others. During this time, the female worms constantly produce millions of microfilariae, which enter the blood where they are ingested by mosquitoes.

Most filariae harbor bacterial endosymbionts of the genus Wolbachia (related to Rickettsia). These are significant for the immunology of the filariae themselves and for their embryogenesis and, on the other hand, induce disease symptoms in the macrohost (e.g. they are held responsible for corneal opacities). Antibiotic elimination (doxycycline) of Wolbachia leads to a complete inhibition of embryogenesis and thus to sterility of the worms.

In lymphatic filiariasis, immunological processes are in the foreground at the beginning of the infection in order to ward off the infection. Nonspecific allergic reactions, fever, headache, arthralgias, as well as lymphangitis and lymphadenitis. Later, the different stages of lymphatic congestion become apparent. Elephantiasis may be complicated by bacterial overgrowth. Onchocerca volvolus leads to painless nodules in the skin where the adult worms collect in clusters in the subcutaneous tissue. Eye infestation results in blindness (river blindness). Loa Loa is a migratory filarial worm that migrates through the subcutaneous connective tissue of the host. The migration of the worm leads to chicken-sized inflammatory nodules, usually of the lower limb (cameroon bump), which disappear after a few days. If the worm migrates into the eye, it can be seen there (eye worm).

Onchocerciasis: Worldwide prevalence: about 18 million infected. Occurs mainly in tropical Africa, Yemen, Central and South America.

Lymphatic filariasis: About 80 million infected, of which about 2/3 in China, India and Indonesia, furthermore in humid regions of Africa.

Loiasis: Occurring in rainforest areas of Africa. Prevalence in endemic areas: 3-30% of the population is infected.

The diagnosis of filariasis is made by the clinical picture. A particular phenomenon is that the microfilariae have adopted the biting habits of their vectors. They emerge periodically either during the day (diurnal periodicity) or at night (nocturnal periodicity) in the peripheral blood of the infected person. During the rest of the time, they reside in the central blood vessels of internal organs.

Furthermore:

• Serum antibodies against filarial crude antigen.
• Blood filtration
• Skin Snips (skin biopsies stored in saline solution. Microfilariae migrate from these within a short time and are detectable by microscopy).
• Determination of blood eosinophils, DEC provocation test

See below the individual clinical pictures

Preventive measures are primarily of an exposure-prophylactic nature (mosquito nets, repellents, skin-covering clothing).

1. Bockarie MJ et al (2002) Mass treatment to eliminate filariasis in Papua New Guinea. N Engl J Med 347: 1841-1848
2. Hoerauf A et al (2001): Depletion of wolbachia enterobacteria in onchocerca vólvulus by doxcycline and microfilaridermia after ivermectin therapy. Lancet 357: 1415-1416
3. Rajendran R et al (2003) Mass treatment of filariasis in New Guinea. N Engl J Med 348: 1179-1181
4. Santosh T et al (2017) Incidental cytodiagnosis of microfilaria from subcutaneous nodule. Natl Med J India 30:241.
5. Taylor MJ (2003) Wolbachia in the inflammatory pathogenesis of human filariasis. Ann NY Acad Sci 990: 444-449.