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Lymphatic filariasis
Diagnosis

Diagnostic methods

Parasitological diagnosis
Microfilariae may be found in the peripheral blood between 10 p.m. and 2 a.m. for most species and subspecies. Microfilariae can be differentiated after staining of thick haemolysed blood films or after concentration of citrated blood (e.g. on polycarbonate membranes). Membrane filtration of 1 or 2 ml blood is the standard diagnostic procedure!

Molecular diagnosis
PCR followed by RFLP analysis may be used to differentiate filariae of different species in co-endemic areas (e.g. infective larvae in the vector). A recent multiplex PCR method allowed the simultaneous detection of Brugia and Wuchereria in blood and mosquito samples.

Antigen detection

For Wuchereria bancrofti infections, several immunochromatographic rapid diagnostic tests detecting circulating filarial antigens in whole blood are commercially available. There is also an antigen detection available for Brugia infection.

Antibody detection
Many home-made serological tests have been developed for which specificity is the main problem. Extensive cross-reactivity with other filarial infections and strongyloidiasis.
High antibody levels in tropical pulmonary eosinophilia.

 

Diagnostic strategies

  1. To confirm a clinical case
    For individual diagnosis, one can combine blood examination for microfilariae with an antigen detection assay. As a screening test for people returning from endemic countries, serology has some diagnostic value.
     
  2. To screen populations in W. bancrofti endemic areas
    The most convenient method is to detect antigens using a rapid diagnostic test.
     
  3. To evaluate a control programme
    The sensitivity of parasitological diagnosis is too low to detect new infections in an area under control. One might either search for infected mosquitoes using an antigen detection or a PCR method or detect circulating filarial antigens in exposed individuals.
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