II. Pathophysiology
- Filarial Infection (Filariae, Family Filarioidea)
- Onchocerca is in the family Filarioidea and is considered a filarial infection
- Filaria are blood and tissue Nematodes transmitted by Arthropod Bite
- Adult filariae, living in the Lymphatic System, birth prelarval microfilariae
- Microfilariae invade tissue and circulate in blood and lymph
- Microfilariae are transmitted between human hosts via Arthropod Bite
- Filariae are hosts to an endosymbiotic, Rickettsial-like Bacteria, Wolbachia
- Killing Wolbachia (e.g. doxycyline) decreases microfilaria and renders adult worms sterile
- Onchocerca Volvulus (Onchocerciasis , River Blindness)
III. Findings
- Fibrous skin and and Subcutaneous Nodules
- Thickened, dry, scaly skin may appear lizard-like
- Host response to microfilariae Skin Infection
- Associated with Pruritus, Hyperpigmentation and intraepithelial Granulomas
- Ocular involvement
IV. Labs
- Skin biopsy
- Superficial biopsy with microfilariae
- Incising skin Nodules may identify curled-up adult worms
V. Management
- Ivermectin (weight >15 kg): 150 mcg/kg for 1 dose (may be repeated every 3-12 months as needed)
VI. Prevention
- Ideal target for eradication, as humans are the only host (similar to Small Pox)
- Ongoing eradication program (WHO)
- https://www.who.int/teams/control-of-neglected-tropical-diseases/onchocerciasis/prevention-control-and-elimination
- Vector control projects (e.g. black fly Insecticides in endemic regions)
- Broad use of scheduled Ivermectin (twice yearly) in endemic regions
VII. References
- Gladwin, Trattler and Mahan (2014) Clinical Microbiology, Medmaster, Fl, p. 366