LeAnne M. Fox

Infectious Agent

Onchocerciasis, also known as river blindness, is caused by the filarial nematode, Onchocerca volvulus.

Mode of Transmission

Infection occurs through vector-borne transmission by the bite of female blackflies of the genus Simulium, that bite during the day and are found near rapidly flowing rivers and streams.

Occurrence

• Onchocerciasis is endemic in more than 25 nations located in a broad band across the central part of Africa. Small endemic foci are also present in the Arabian Peninsula (Yemen) and in the Americas (Brazil, Colombia, Ecuador, Guatemala, southern Mexico, and Venezuela).
• An estimated 17 million people are infected worldwide.

Risk for Travelers

• Short-term travelers to endemic areas are at low risk for this infection.
• Travelers who visit endemic areas for extended periods of time (generally greater than 3 months) and live or work near blackfly habitats are at greater risk for infection.
• Most infections seen in the United States occur in expatriate groups, such as missionaries, field scientists, and Peace Corps volunteers.

Clinical Presentation

• Infection with O. volvulus can result in a 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.
• Immigrants from endemic areas may present with skin and/or ocular disease.

Diagnosis

• Diagnosis is made by finding either the 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 in specific groups, such as expatriates with a brief exposure history, when microfilariae are not identifiable. Determination of serum antifilarial immunoglobulin (IgG) is available through the Parasitic Diseases Laboratory at the National Institutes of Health (NIH) or through the Division of Parasitic Diseases, CDC.

Treatment

• Ivermectin (150–200 μg/kg orally, once or twice per year) is the drug of choice for onchocerciasis. Repeated annual or semiannual doses may be required, because the drug kills the microfilariae but not the adult worms, which can live for many years.
• Antibiotic trials, with doxycycline (100 mg orally per day), directed against Wolbachia, an endosymbiont of O. volvulus, have demonstrated a decrease in onchocercal microfiladermia with 6 weeks of therapy.
• Diethylcarbamazine (DEC) is contraindicated in onchocerciasis, as it has been associated with severe and fatal post-treatment reactions.
• Any subcutaneous nodules should be excised if their anatomic location allows it to be done safely.
• To ensure correct diagnosis and treatment, travelers should be advised to consult with an infectious diseases or tropical medicine specialist.

Preventive Measures for Travelers

• No vaccine is available.
• No drugs for preventing infection are available.
• Protective measures include avoidance of blackfly habitats and the use of personal protection measures against biting insects (see the Protection Against Mosquitoes, Ticks, and Other Insects and Arthropods section in Chapter 2).

References

1. Burnham G. Onchocerciasis. Lancet. 1998;351:1341–6.
2. Drugs for parasitic infections. Med Lett Drugs Ther. 2007;5(Suppl):e1–15.
3. World Health Organization. Onchocerciasis and its control. Report of a WHO Expert Committee on Onchocerciasis Control. World Health Organ Tech Rep Ser. 1995;852:1–104.
4. Murdoch ME, Asuzu MC, Hagan M, et al. Onchocerciasis: the clinical and epidemiological burden of skin disease in Africa. Ann Trop Med Parasitol. 2002;96:283–96.
5. Albiez EJ, Büttner DW, Duke BO. Diagnosis and extirpation of nodules in human onchocerciasis. Trop Med Parasitol. 1988;39(Suppl 4):331–46.
6. Abiose A. Onchocercal eye disease and the impact of Mectizan treatment. Ann Trop Med Parasitol. 1998;92(Suppl 1):S11–22.
7. Brieger WR, Awedoba AK, Eneanya CI, et al. The effects of ivermectin on onchocercal skin disease and severe itching: results of a multicentre trial. Trop Med Int Health. 1998;3:951–61.
8. Tielsch JM, Beeche A. Impact of ivermectin on illness and disability associated with onchocerciasis. Trop Med Int Health. 2004;9(4):A45–56.
9. Hoerauf H, Mand S, Adjei O, et al. Depletion of Wolbachia endobacteria in Onchocerca volvulus by doxycycline and microfilaridermia after ivermectin treatment. Lancet. 2001;357:1415–6.