Investigations

Previously diagnosis was based on detecting the presence of microfilariae on the blood film

• however this method may not detect infection because of the nocturnal periodicity of the microfilaria. Further there is a possibility of missing microfilaria in the blood smear if they are present in extremely low numbers and thereby introducing an error in diagnosing the active infection (1)

Detection of circulating filarial antigen (CFA)

• more recently tools for diagnosis of Wuchereria bancrofti infections, based on detection of CFA in the patients' blood, have been developed
  • major advantages when compared with the traditional diagnostic techniques searching for microfilariae in night blood specimens, such as a higher sensitivity for infection and the fact that specimens can be collected at any time of the day

Ultrasound

• living adult Wuchereria bancrofti worms can be detected by ultrasound examination of the scrotal area in approximately 80% of men infected with this filarial parasite, the location of the adult worms in the remaining 20% remains unclear
  • using both ultrasound and 'provocative' treatment with diethylcarbamazine (DEC) adult W. bancrofti can be detected in the scrotal area of an estimated 88% of infected men (2)

Lymphangiography may also be performed. This reveals the patency in the main vessels of the lower limbs and may show that the para-aortic vessels are dilated.

Notes:

• if trying to detect presence of microfilariae on blood film then blood is best taken at 1 am. Parasites may also be detectable in a blood sample taken 30 minutes after a dose of DEC

Reference:

1. Lalitha P et al. Quantitative assessment of circulating antigens in human lymphatic filariasis: a field evaluation of monoclonal antibody-based ELISA using blood collected on filter strips. Trop Med Int Health. 1998 Jan;3(1):41-5.
2. Dreyer G et al. Proposed panel of diagnostic criteria, including the use of ultrasound, to refine the concept of 'endemic normals' in lymphatic filariasis. Trop Med Int Health. 1999 Aug;4(8):575-9.