Description

Lymphatic filariasis is caused by adult worms (filariae) that live in the lymphatic vessels. The female worms release microfilariae that circulate in the peripheral blood and are ingested by mosquitoes; thus, infected mosquitoes transmit the infection from person to person. The two major species of filariae that cause lymphatic disease in humans are Wuchereria bancrofti and Brugia malayi.

Occurrence

Lymphatic filariasis affects an estimated 120 million persons in tropical areas of the world, including sub-Saharan Africa, Egypt, southern Asia, the western Pacific islands, the northeastern coast of Brazil, Guyana, and the Caribbean island of Hispaniola (1). Because most infections are asymptomatic, many go unrecognized. On average, 16 cases are diagnosed, reported to CDC, and treated annually in the United States.

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 and who are intensively exposed to infected mosquitoes can become infected. Most infections seen in the United States are in immigrants from endemic countries.

Clinical Presentation

Most infections are asymptomatic, but the living adult worm causes progressive lymphatic vessel dilation and dysfunction (2). Lymphatic dysfunction may lead to lymphedema of the leg, scrotum, penis, arm, or breast, which can increase in severity as a result of recurrent secondary bacterial infections (3,4). Tropical pulmonary eosinophilia is a potentially serious progressive lung disease with nocturnal cough, wheezing, and fever, resulting from immune hyperresponsiveness to microfilariae in the pulmonary capillaries.

Prevention

No vaccine is available, nor has the effectiveness of chemoprophylaxis been well documented. Protective measures include avoidance of mosquito bites through the use of personal protection measures (see Chapter 2).

Treatment

The drug of choice for treatment of travelers with W. bancrofti or B. malayi infections is diethylcarbamazine (DEC). DEC, which is available to U.S.-licensed physicians for this purpose, can be obtained from the CDC Parasitic Diseases Drug Service at 404-639-3670 under an Investigational New Drug protocol. (See http://www.cdc.gov/ncidod/srp/drugs/drug-service.html.) DEC kills circulating microfilariae and is partially effective against the adult worms and tropical pulmonary eosinophilia (5). Ivermectin does not kill the adult worms (6). Two potential alternative drugs being investigated are albendazole (7) and doxycycline (8). Many patients with lymphedema are no longer infected with the filarial parasite and do not benefit from antifilarial drug treatment. For chronic manifestations of lymphatic filariasis, such as lymphedema and hydrocele, specific lymphedema treatment (including hygiene, skin care, physiotherapy, and in some cases, antibiotics) and surgical repair, respectively, are recommended (9). To ensure correct diagnosis (10) and treatment, travelers should be advised to consult an infectious disease or tropical medicine specialist.

References

1. Michael E, Bundy DAP, Grenfell BT. Re-assessing the global prevalence and distribution of lymphatic filariasis. Parasitology. 1996;112:409-28.
2. Dreyer G, Addiss D, Roberts J, Noroes J. Progression of lymphatic vessel dilatation in the presence of living adult Wuchereria bancrofti. Trans R Soc Trop Med Hyg. 2002;96:157-61.
3. Dreyer G, Medeiros Z, Netto MJ, Leal NC, de Castro LG, Piessens WF. Acute attacks in the extremities of persons living in an area endemic for bancroftian filariasis: differentiation of two syndromes. Trans R Soc Trop Med Hyg. 1999;93:413-7.
4. Shenoy RK, Suma TK, Rajan K, Kumaraswami V. Prevention of acute adenolymphangitis in brugian filariasis: comparison of the efficacy of ivermectin and diethylcarbamazine, each combined with local treatment of the affected limb. Ann Trop Med Parasitol. 1998;92:587-94.
5. Ottesen EA. Efficacy of diethylcarbamazine in eradicating infection with lymphatic-dwelling filariae in humans. Rev Infect Dis. 1985;7:341-56.
6. Dreyer G, Addiss D, Norões J, Amaral F, Rocha A, Coutinho A. Ultrasonographic assessment of the adulticidal efficacy of repeat high-dose ivermectin in bancroftian filariasis. Trop Med Internat Health. 1996;1:427-32.
7. Jayakody RL, DeSilva CSS, Weerasinghe WI. Treatment of bancroftian filariasis with albendazole: evaluation of efficacy and adverse reactions. Trop Biomedicine. 1993;10:19-24.
8. Taylor MJ, Makunde WH, McGarry HF, Turner JD, Mand S, Hoerauf A. Macrofilaricidal activity after doxycycline treatment of Wuchereria bancrofti: a double-blind, randomised placebo-controlled trial. Lancet. 2005;365:2116-21.
9. Dreyer G, Addiss D, Dreyer P, Noroes J. Basic lymphoedema management: Treatment and prevention of problems associated with lymphatic filariasis. Hollis, NH: Hollis Publishing Co.; 2002.
10. Eberhard ML, Lammie PJ. Laboratory diagnosis of filariasis. Clin Lab Med. 1991;11:977-1010.