Baermann Examination

This technique is used to recover live nematode larvae from fresh (or sometimes frozen) faeces or, on occasion, organs, tissues or vegetation. It will detect larvae of Dictyocaulus viviparus, D. filaria, D. arnfieldi, Muellerius capillaris, Filaroids osleri, Crenosoma vulpis, and Aelurostrongylus abstrusus as well as those of other nematode species.

If fresh (or previously frozen- some species of larvae are able to survive freezing) faeces are immersed in water for some time, live nematode larvae will migrate from the fecal material into the surrounding water, from which they can be recovered and identified.

250 ml beaker

12cm x 12cm square of window screen

Cheesecloth

Vacuum pump, pipette or syringe

Centrifuge Test tubes

Compound or Dissecting microscope

1. Fill a 250 ml breaker almost to the top with tepid water.
2. Create a small “envelope” by folding a square (~12cm x 12cm) of window screen in half.
3. Line the envelope with a single layer of cheesecloth then place faeces (5-10g) in the envelope
    and staple closed the open edges.
4. Submerge the fecal sample in the beaker maintaining the sample near the water surface.
5. Leave set up for at least 6 hours (preferably 18-24 hours).
6. Remove envelope and discard.
7. Being careful to disturb the sediment as little as possible, decant, using gentle vacuum suction,
    pipette or syringe, all but ~50ml of the beaker contents.
8. Centrifuge sediment in test tube for approximately 10 minutes at approximately 1500 rpm.
9. Examine the sediment for the presence of larvae.

Traditionally, the funnels were used to hold the water and faeces; more recently, these have been replaced by beakers, which increases larval recovery. As with flotations, the Baermann technique can be quantified.

Forrester SG and Lankester MW (1997) Journal of Wildlife Diseases 33: 511-516.

Factors including initial water temperature, room temperature, lighting, time period before examination, and species of nematode present, may all influence the success of larval recovery. In addition, sometimes when only small numbers of larvae are present, they may not be detected using this technique, producing a false negative test result. Problems may also arise if the faeces used are not fresh, leading to contamination by larvae hatched from eggs in the faeces or from free-living nematodes.