PS for Filaria in Dehradun

What is a PS for Filaria?

Lymphatic filariasis is caused by thread-like parasitic worms transmitted by mosquitoes, and the adult worms live in the lymphatic vessels where, over years, they cause obstruction, recurrent inflammation and eventually the gross limb or genital swelling known as elephantiasis. The blood smear looks for microfilariae, the larval stage that the adults release into the bloodstream. The defining feature of this test is timing, and it is unlike almost any other blood test. In most parts of India the parasite shows nocturnal periodicity: microfilariae appear in peripheral blood mainly between about 10 at night and 2 in the morning, matching the biting habits of the mosquito that transmits them, and are largely absent during the day. A daytime sample can therefore be negative in someone with a substantial infection, and this is the commonest reason filariasis is missed. Sensitivity is also limited in early or low-density infection, and in the late stage where lymphatic damage is established the adult worms may have died and no microfilariae remain, so a negative smear cannot exclude the diagnosis in someone with chronic swelling.

Why take this test?

A filaria smear is advised for recurrent episodes of fever with painful, tender swelling and red streaking along a limb, which is the classic acute presentation, and for progressive swelling of a leg, arm, breast or scrotum. It is indicated for a hydrocele or lymph node swelling in an endemic area, and for unexplained persistent eosinophilia, where filarial infection is one of the causes worth excluding. It is used in screening in endemic districts and in evaluating people who have lived in or travelled from such areas. The single most important practical point is to give the sample at night, ideally between 10 pm and midnight, unless your doctor has specified otherwise, since a convenient morning sample is likely to be falsely negative. Antigen tests and ultrasound of the lymphatics are available where smears are negative but suspicion remains, so discuss those with your doctor rather than accepting a single negative result.

• Recurrent fever with painful, tender limb swelling and red streaking
• Progressive swelling of a leg, arm, breast or scrotum
• Hydrocele or lymph node swelling in an endemic area
• Unexplained persistent eosinophilia
• Living in or travelling from a filariasis-endemic district
• Sample timed at night, when microfilariae circulate

FAQs: PS for Filaria in Dehradun