River Blindness

Filarial Infection (Filariae, Family Filarioidea)
1. Onchocerca is in the family Filarioidea and is considered a filarial infection
2. Filaria are blood and tissue Nematodes transmitted by Arthropod Bite
3. Adult filariae, living in the Lymphatic System, birth prelarval microfilariae
4. Microfilariae invade tissue and circulate in blood and lymph
  1. Microfilariae are transmitted between human hosts via Arthropod Bite
5. Filariae are hosts to an endosymbiotic, Rickettsial-like Bacteria, Wolbachia
  1. Killing Wolbachia (e.g. doxycyline) decreases microfilaria and renders adult worms sterile
Onchocerca Volvulus (Onchocerciasis , River Blindness)
1. Transmitted via Black Fly bite (near rivers and streams in Africa, Central America and South America)
2. Adult Onchocerca mate and produce microfilariae
3. Microfilariae invade the Dermis and connective tissue

Fibrous skin and and Subcutaneous Nodules
1. Papules and Nodules contain curled up adult worms
Thickened, dry, scaly skin may appear lizard-like
1. Host response to microfilariae Skin Infection
2. Associated with Pruritus, Hyperpigmentation and intraepithelial Granulomas
Ocular involvement
1. Results in blindness ("River Blindness")
2. Microfilariae infect the Cornea and anterior chamber
  1. May be seen on Slit Lamp exam of anterior chamber

Skin biopsy
1. Superficial biopsy with microfilariae
2. Incising skin Nodules may identify curled-up adult worms

Ivermectin (weight >15 kg): 150 mcg/kg for 1 dose (may be repeated every 3-12 months as needed)

Ideal target for eradication, as humans are the only host (similar to Small Pox)
Ongoing eradication program (WHO)
1. https://www.who.int/teams/control-of-neglected-tropical-diseases/onchocerciasis/prevention-control-and-elimination
2. Vector control projects (e.g. black fly Insecticides in endemic regions)
3. Broad use of scheduled Ivermectin (twice yearly) in endemic regions