Through female blackflies (genus Simulium), which typically bite during the day and near rapidly flowing rivers and streams.
Endemic in central Africa. Small endemic foci are also present in the Arabian Peninsula (Yemen) and in the Americas (Brazil, Colombia, Ecuador, Guatemala, southern Mexico, and Venezuela). Most infections, outside those in endemic populations, occur in expatriate groups, such as missionaries, field scientists, and Peace Corps volunteers.
Highly pruritic, papular dermatitis; subcutaneous nodules; lymphadenitis; and ocular lesions, which can progress to visual loss and blindness. Symptoms in travelers are primarily dermatologic and may occur months to years after departure from endemic areas.
Presence of microfilariae in superficial skin shavings or punch biopsy, adult worms in histologic sections of excised nodules, or characteristic eye lesions. Serologic testing is most useful for detecting infection when microfilariae are not identifiable. Determination of serum antifilarial IgG is available through the National Institutes of Health (301-496-5398) or CDC (www.dpd.cdc.gov/dpdx; 404-718-4745; firstname.lastname@example.org).
Ivermectin is the drug of choice. Repeated annual or semiannual doses may be required, as the drug kills the microfilariae but not the adult worms. Some experts recommend treating patients with 1 dose of ivermectin followed by 6 weeks of doxycycline. Diethylcarbamazine is contraindicated in onchocerciasis, because it has been associated with severe and fatal post-treatment reactions. An expert in tropical medicine should be consulted to help manage these patients.