Microbiology Laboratory


Written by MicroDok

AIM: To detect and identify the microfilariae of Onchocercia volvulus in skin snips as an aid in the diagnosis of Onchocerciasis.

Technique: There are two techniques to performing this test, viz: the slide technique and the test tube technique, but only the slide technique shall be expanded here as it is the most common and widely method of detecting microfilariae of Onchocercia volvulus.

MATERIAL/APPARATUS: Skin snip, microscope, glass slide, cover slip, normal saline, bulb pipette, scalpel blade, 70% ethanol, cotton wool.


  1. Clean the skin with 70% of ethanol using a cotton wool and allow to dry.
  2. Make a short quick stroke or cut at the skin where the specimen is to be collected using a scalpel blade.
  3. Cut of the piece of skin with a different scalpel blade, and place the skin snip obtained on a glass slide already containing 2 drops of normal saline.
  4. Cover the glass slide with a cover slip.
  5. Examine the slide under the microscope using ×10 and ×40 objective lens.

NOTE: A bloodless skin snip should be collected so as not to contaminate the specimen.


The presence of any microfilariae is reported, and when not found it is reported as absent. A nodule present on the skin area where the skin snip is collected is also reported.

Onchocerciasis is a major health and socioeconomic problem, especially in endemic areas in Africa. It is caused by Onchocercia volvulus, and its clinical features are the formation of nodules, inflammatory dermatitis which is usually accompanied by intense irritation & raised papules on the skin, and inflammatory reactions in the eye leading to blindness. Onchocerciasis is also thought to be a risk factor for epilepsy.

Blindness is one of the most serious complications of Onchocerciasis, and it occurs when microfilariae of O. volvulus in the skin of the face migrate into the eye. There is redness and irritation of the eye. Progressive changes caused by inflammatory reactions around damaged and dead microfilariae can cause sclerosis keratitis which can lead to blindness. O. volvulus microfilariae can also be found in urine, blood, and in most body fluids. These specimens especially blood can also be obtained from affected patients for microbiological examination. Snip means a cut with scissors or blade using short quick strokes.

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