LeAnne M. Fox

Infectious Agent

Lymphatic filariasis is caused by the filarial nematodes Wuchereria bancrofti and Brugia malayi.

Mode of Transmission

Vector-borne transmission occurs through the bite of infected Aedes, Culex, Anopheles, and Mansonia mosquito species.

Occurrence

• Lymphatic filariasis affects an estimated 120 million persons in tropical areas of the world.
• Lymphatic filariasis is found in sub-Saharan Africa, Egypt, southern Asia, the western Pacific islands, the northeastern coast of Brazil, Guyana, Haiti, and the Dominican Republic.
• Since most infections are asymptomatic, many go unrecognized.

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 longer than 3 months) and who are intensively exposed to infected mosquitoes are at greater risk of infection.
• Most infections seen in the United States are in immigrants from endemic countries.
• A recent report from the GeoSentinel Surveillance Network showed only 0.62% (N=271 of 43,722) of medical conditions reported during 1995–2004 were caused by any filarial infection, and only 101 (25% of the total) were caused by W. bancrofti. Lymphatic filariasis caused by W. bancrofti was acquired worldwide, with 32% from South America, 12% from sub-Saharan Africa, 22% from South Central Asia, and 14% from the Caribbean. As expected, the majority of cases (62%) were seen in immigrants or refugees. In the few nonresident visitors with a known trip duration who acquired W. bancrofti, the stay was >180 days.

Clinical Presentation

• Most infections are asymptomatic, but living adult worms cause progressive lymphatic vessel dilation and dysfunction. 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.
• Tropical pulmonary eosinophilia is a potentially serious progressive lung disease that presents with nocturnal cough, wheezing, and fever, resulting from immune hyperresponsiveness to microfilariae in the pulmonary capillaries.

Diagnosis

• The standard for diagnosis is microscopic detection of microfilariae on a thick blood film. In most endemic areas, the highest concentration of microfilariae in the peripheral blood occurs at night; therefore, blood specimens should be collected between 10 pm and 2 am.
• Determination of serum antifilarial immunoglobulin (IgG) is also a diagnostically useful test. This assay is available through the Parasitic Diseases Laboratory at the National Institutes of Health (NIH) or through CDC’s Division of Parasitic Diseases.

Treatment

• The drug of choice for treatment of travelers with W. bancrofti or B. malayi infection is diethylcarbamazine (DEC). DEC, which is available to physicians licensed in the United States for this purpose, can be obtained from the CDC Parasitic Disease Drug Service at 404-639-3670 under an Investigational New Drug protocol (see www.cdc.gov/ncidod/srp/drugs/drug-service.html). DEC kills circulating microfilariae and is partially effective against the adult worms. DEC is also used to treat tropical pulmonary eosinophilia.
• Although ivermectin kills microfilariae, it does not kill the adult worms.
• 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.
• To ensure correct diagnosis and treatment, travelers should be advised to consult an infectious disease or tropical medicine specialist.

Preventive Measures for Travelers

• No vaccine is available.
• No drugs for preventing infection are available.
• Protective measures include avoidance of mosquito bites through 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. Nutman TB, editor. Lymphatic Filariasis. London: Imperial College Press; 2000.
2. Abramowicz M, editor. The Medical Letter Report on Drugs for Parasitic Infections. New Rochelle, NY: The Medical Letter; 2007.
3. Michael E, Bundy DA, Grenfell BT. Re-assessing the global prevalence and distribution of lymphatic filariasis. Parasitology. 1996;112(Pt 4):409–28.
4. Dreyer G, Addiss D, Roberts J, et al. Progression of lymphatic vessel dilatation in the presence of living adult Wuchereria bancrofti. Trans R Soc Trop Med Hyg. 2002;96(2):157–61.
5. Dreyer G, Medeiros Z, Netto MJ, et al. 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(4):413–7.
6. Shenoy RK, Suma TK, Rajan K, et al. 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(5):587–94.
7. Ottesen EA. Efficacy of diethylcarbamazine in eradicating infection with lymphatic-dwelling filariae in humans. Rev Infect Dis. 1985;7(3):341–56.
8. Dreyer G, Addiss D, Noroes J, et al. Ultrasonographic assessment of the adulticidal efficacy of repeat high-dose ivermectin in bancroftian filariasis. Trop Med Int Health. 1996;1(4):427–32.
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(4):977–1010.
11. Lipner EM, Law MA, Barnett E, et al; GeoSentinel Surveillance Network. Filariasis in travelers presenting to the GeoSentinel Surveillance Network. PLoS Negl Trop Dis. 2007;1(3):e88.