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Onchocerciasis Diagnosis
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Onchocerciasis
Diagnosis

Diagnostic methods

Parasitological diagnosis

The classical way to diagnose onchocerciasis is by taking skin snips (six or more) and detecting microfilariae. However, the sensitivity is restricted in light infections (e.g. in drug- or vector-controlled areas).

Molecular diagnosis

Molecular methods have been described to demonstrate strain differences (e.g. between forest and savannah). In addition, infective larvae from related species can be differentiated from O. volvulus.
Detecting DNA in skin snips may improve sensitivity but needs biopsies.

Antigen detection

A new antigen detection dipstick method has been described which showed high sensitivity when urine samples were tested. Specificity also seems to be excellent.

Antibody detection
Many attempts have been undertaken to improve specificity of serological methods by using recombinant antigens. However, a decrease in sensitivity has often been observed. In a rapid format card test, IgG4 antibodies have been detected using the Ov16 recombinant antigen.

 

Diagnostic strategies 

  1. To diagnose an individual case
    In returning travellers with limited exposure, definite diagnosis is difficult to achieve. One might combine clinical findings, skin snips and the demonstration of specific serum antibodies.
     
  2. To assess a control programme
    Detecting microfilariae in skin snips is not adequate for the assessment of a control programme due to the low sensitivity of this method and the length of the pre-patent period. There have been many attempts to develop immunological methods for early diagnosis. However, they were either unsuccessful or have not been fully validated so far.

 

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