Exposure History

As with most parasites, it is important to first establish a history of exposure to the vector. Visiting an endemic area will often not result in high levels of microfilariae unless the visit was for a long duration of time. Establishing residency in an endemic area, however, is important because it likely translates to an increased exposure to the vector and filaria (Reference 23).

Filariasis Diagnosis through Antigen Detection

ICT Test (Image 10)

Testing for filarial antigens is a good diagnostic tool because it is very sensitive and very specific. If a patient has very low levels of microfilariae that may not be detected by microfilariae tests, antigen detection will most likely detect any presence of the disease. The test is also specific, as it tests for specific antigens for lymphatic filariasis and allows for the differentiation between microfilarial diseases. The most useful antigen detection test is the antigen card test known as the ICT. Not only is this test highly specific and highly sensitive, but it also quick (ready in 10 minutes), mobile and cheap. In addition, this test can be administered during the day or night, unlike other tests that require blood samples to be taken when microfilariae is at high levels in the blood (Reference 24).

However, the antigen detection test cannot differentiate between active and inactive microfilariae. Antigens can still be present in the blood if any trace of dead microfilaria remains in the circulation. Hence, a positive ICT test result may not mean the patient has active, living microfilaria (Reference 24).

X Ray Detection

The use of radiographs and ultrasonographs can be useful in diagnosing lymphatic filariasis. As the worms in the circulation or tissue die, their remains become calcified and can be detected by X ray. Ultrasonography can be used to detect the characteristic "filarial dance sign" or FDS of adult filariae (Reference 25).

Microfilarial Detection

Blood Film Test (Image 11)

Of course, a patient cannot be sure whether or not they have microfilariae in their blood unless they exhibit microfilariae in their blood. This makes microfilarial detection a highly reliable method that served as the diagnostic goal for many years, and still serves that role in many regions. Microfilarial detection can be done by a skin biopsy in which a small piece of tissue is taken from the body and studied for microfilarial manifestation. This is effective if microfilariae resides in the tissue. However, in lymphatic filariasis, the microfilariae are concentrated mainly in the circulation, so a blood test is generally more effective. Once microfilariae are detected, their morphology can be studied to determine the species (Reference 23).