Chapter 3Infectious Diseases Related To Travel

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 the bite of female blackflies of the genus Simulium, which bite during the day and are found near rapidly flowing rivers and streams.

EPIDEMIOLOGY

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.

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

A recent report from the GeoSentinel Surveillance Network showed only 0.6% (271 of 43,722) of medical conditions reported from 1995 through 2004 were caused by any filarial infection, and only 101 (37% of the total) were caused by O. volvulus. Most (95%) of those who acquired onchocerciasis did so in sub-Saharan Africa; 3 infections were acquired elsewhere. As expected, most cases (62%) were seen in immigrants or refugees. Nevertheless, in this study, 7 travelers from nonendemic regions who acquired onchocerciasis did so during trips of ≤31 days.

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 or ocular disease.

DIAGNOSIS

Onchocerciasis is diagnosed by finding 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 IgG is available through the National Institutes of Health (301-496-5398) or the CDC’s Division of Parasitic Diseases and Malaria (404-718-4745; parasites@cdc.gov).

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. Therefore, some experts recommend treating patients with 1 dose of ivermectin followed by 6 weeks of doxycycline.

Diethylcarbamazine (DEC) is contraindicated in onchocerciasis, because it has been associated with severe and fatal posttreatment 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 or drug to prevent infection is available. Protective measures include avoiding blackfly habitats and the use of personal protection measures against biting insects (see Chapter 2, Protection against Mosquitoes, Ticks, and Other Insects and Arthropods).

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