Standard biopsy sites:
(1) left shoulder
(2) right shoulder
(3) left hip
(4) right hip
(5) left calf
(6) right calf
The biopsy does not need to be very deep. A deep biopsy with blood may give a false positive from non-tissue microfilaria.
A site showing the sowda reaction has a very low number of organisms and thus would be a poor choice for making the primary.
Handling:
(1) Weigh the biopsy in milligrams.
(2) Place the biopsy in a small amount of either saline or tissue culture medium at 37°C.
(3) Within 15 minutes microfilaria will start to emerge into the fluid where they can be counted. Most will have emerged within 3 hours.
The microfilarial load is expressed as microfilaria per mg tissue.
microfilaria per mg tissue (mf per mg) =
= (number of microfilaria count) / (weight of the biopsy in milligrams)
Interpretation:
• The diagnosis can be made by a skilled observer with only 1 microfilaria.
• A heavily infected person may have up to 600 mf per mg.
• Skin snips may be performed several months after starting therapy to determine the therapeutic response.
Ways to increase sensitivity:
(1) incubate the biopsy in the medium for 24 hours
(2) digest the biopsy with collagenase
(3) perform PCR on an homogenate
(4) increase the number of biopsies taken
Differential diagnosis: The microfilaria of Mansonella streptocerca may also be found in skin biopsies.
