Filariasis B74.8

Infections with filariae or nematodes , which parasitize extraintestinally. Their larvae are called microfilariae and are usually transmitted to humans by bloodsucking arthropods. They cause a range of specific and non-specific symptoms.

Major human pathogenic Filariidae:

• Wuchereria bancrofti, Bruga malayi, Brugia timori (different filariae, clinical symptoms similar)

• Loa loa

• Onchocerca volvulus
• rarely: Mansonella spp., Dirofilaria immitis, B. pahangi, W. kalimantani.

Dirofilariosis, cutaneous:

• Pathogen: Dirofilaria repens
• Vector: Mosquitoes

Loiasis:

• Pathogen: Loa loa
• Vector: flies (Chrysops)

Lymphatic filariasis:

• Pathogen: Wuchereria bancrofti, Brugia malayi, Brugia timori
• Vector: mosquitoes (Aedes, Anopheles, Culex, Mansonia)

Onchocerciasis:

• Pathogen: Onchocerca volvulus
• Vector: Black flies (Simulium)

• Onchocerciasis: Worldwide prevalence: approx.18 million infected. Occurring 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.

Vectors transmit infective worm larvae (L3) during a blood meal, 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, among others. 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.

• Onchocerciasis: Leading symptoms: Onchocercoma.
  • localized form (Sowda)
  • generalized form: onchodermatitis; ocular changes (river blindness).
• Lymphatic filariasis:
  • acute
  • chronic: elephantiasis, hydrocele, chyluria, tropical pulmonary eosinophilia.
• Loiasis:
  • Calabar swelling
  • Glottic edema
  • Tissue irritation of conjunctiva and eyelids.

• Serum antibodies against filarial crude antigen
• Blood filtration
• Skin Snips (from superficial skin biopsies, which are placed in physiological saline solution, up to 1 dozen microfilariae migrate in a few minutes and can be seen under the microscope)
• determination of eosinophil granulocytes in blood; DEC provocation test
• depending on the form:
  • opthalmological examination
  • extirpation of a suspicious skin nodule with hsitological examination
  • extraction of a medina worm.

• Ivermectin, albendazole and diethylcarbamazine (DEC not for onchocerciasis), usually as a combination treatment. Followed by 6 weeks of treatment with doxycycline 100 mg/day.

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. Taylor MJ (2003) Wolbachia in the inflammatory pathogenesis of human filariasis. Ann NY Acad Sci 990: 444-449