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USAID

USAID's NTD Program
USAID's NTD Program

Lymphatic Filariasis

Diagnosis

Diagnosis of LF is achieved through a combination of sound epidemiological history, clinical findings, and laboratory tests.

In endemic areas, lymphedema of the limbs or disease of the male genitalia in an individual more than 15 years old is likely due to a filarial infection in the absence of other obvious causes such as congestive heart failure or trauma to the lymphatic system.

The definitive diagnostic can be difficult because it is made only by detection of the worm. Indeed, adult parasites localized in lymphatic vessels or nodes are mostly inaccessible. However, high frequency ultrasound coupled with Doppler techniques may identify motile adult worms in the scrotum (up to 80 percent of infected men) and in the female breast.1 This technique of diagnosis is very expensive and not suitable for mass or routine diagnostics in developing countries.

Microfilariae can be found through laboratory examination of nocturnal blood. However, many infected individuals do not have microfilaremia, and definitive diagnosis may be difficult.

Assays for circulating antigens of W. bancrofti allow the diagnosis of microfilaremic and cryptic infection. Two tests are currently available: the enzyme-linked immunosorbent assay2 test and the immunochromatographic card test.3 The two tests have sensitivity that range from 96 to 100 percent and a specificity of 99 percent.

An antibody-based assay (dipstick test) for diagnosing Brugian filarial infection has been developed for use in Brugian filariasis-endemic areas.4

Because disease may persist in individuals with burned-out infections, it is impossible to exclude a diagnosis of filarial-induced disease in the absence of circulating antigens or parasites. This situation may occur in persons with multiple courses of treatment or who have left the endemic areas.

Learn more about lymphatic filariasis:

 

References

  1. Dryer G, Santos A, Noroes J, et al: Amicrofilaraemic carriers of adult Wuchereria bancrofti. Trans R Soc Trop Med Hyg 90:288-289, 1996.
  2. More SJ, Copeman DB: A highly specific and sensitive monoclonal antibody-based ELISA for detection of circulating antigen in bancroftian filariasis. Trop Med Parasitol 41:403-406, 1990.
  3. Weil GJ, Lammie PJ, Weiss N: The ICT Filriasis Test: A rapid-format antigen test for diagnosis of bancroftian filariasis. Parasitol Today 13:401-404, 1997.
  4. Rahmah N, Taniawati S, Shenoy RK, et al: Specificity and sensitivity of a rapid dipstick test (Brugia Rapid) in the detection of Brugia malayi infection. Trans R Soc Trop Med Hyg 95:601-604, 2001.