Filaria

Specimen:

5 mL fresh blood in EDTA tube; delivered immediately to the laboratory.

For suspected Bancroftian and Brugian filiariasis, blood must be collected when the patient is febrile, usually after midnight unless the patient is from the South Pacific.

For suspected loiasis daytime collection of blood is required.

The pathologist should be consulted prior to collection.

Method:

Direct microscopy of fresh blood or blood filtered through a polycarbonate filter (3-5 mm) followed by lysis of red cells.

Application:

Investigation of recurrent (particularly nocturnal) fever in a patient from an endemic area for Bancroftian or Brugian filiariasis; investigation of possible loiasis in a patient who has lived in or visited an endemic area.

Interpretation:

The presence of microfilariae in blood provides a definitive diagnosis.

In obstructive disease, circulating microfilariae are absent and the diagnosis must be made on clinical criteria.

The presence of eosinophilia and positive filaria antibodies supports the diagnosis.

See Filaria Ab.

The diagnosis of loiasis is established by finding microfilariae in the blood.

Failure to find microfilariae does not rule out the diagnosis, which is usually made on clinical grounds.

Reference:

Grove DI. In: Mandell GR et al eds. Principles and Practice of Infectious Diseases. 2005 6th ed. Churchill Livingstone.

Bain BJ. Blood Cells. 2002 3rd ed. Blackwell.