Filariasis is a parasitic disease caused by an infection with roundworms of the Filarioidea type. These are spread by blood-feeding insects such as black flies and mosquitoes. They belong to the group of diseases called helminthiases. These parasites exist in the wild in subtropical parts of southern Asia, Africa, the South Pacific, and parts of South America. One does not acquire them in temperate areas like Europe or the United States.Eight known filarial worms have humans as a definitive host. These are divided into three groups according to the part of the body they affect:

Lymphatic filariasis is caused by the worms Wuchereria bancrofti, Brugia malayi, and Brugia timori. These worms occupy the lymphatic system, including the lymph nodes; in chronic cases, these worms lead to the syndrome of elephantiasis. Subcutaneous filariasis is caused by Loa loa (the eye worm), Mansonella streptocerca, and Onchocerca volvulus. These worms occupy the layer just under the skin. L. loa causes Loa loa filariasis, while O. volvulus causes river blindness. Serous cavity filariasis is caused by the worms Mansonella perstans and Mansonella ozzardi, which occupy the serous cavity of the abdomen. Dirofilaria immitis, the dog heartworm, rarely infects humans.The adult worms, which usually stay in one tissue, release early larval forms known as microfilariae into the persons blood. These circulating microfilariae can be taken up during a blood meal by an insect vector; in the vector, they develop into infective larvae that can be spread to another person.
For these worms, diagnosis relies upon skin snips and can be carried out at any time. Concentration methods
Various concentration methods are applied: membrane filter, Knotts concentration method, and sedimentation technique.Polymerase chain reaction (PCR) and antigenic assays, which detect circulating filarial antigens, are also available for making the diagnosis. The latter are particularly useful in amicrofilaraemic cases. Spot tests for antigen are far more sensitive, and allow the test to be done anytime, rather in the late hours. Lymph node aspirate and chylous fluid may also yield microfilariae. Medical imaging, such as CT or MRI, may reveal "filarial dance sign" in the chylous fluid; X-ray tests can show calcified adult worms in lymphatics. The DEC provocation test is performed to obtain satisfying numbers of parasites in daytime samples. Xenodiagnosis is now obsolete, and eosinophilia is a nonspecific primary sign. Treatment
The recommended treatment for people outside the United States is albendazole combined with ivermectin. A combination of diethylcarbamazine and albendazole is also effective. Side effects of the drugs include nausea, vomiting, and headaches. All of these treatments are microfilaricides; they have no effect on the adult worms. While the drugs are critical for treatment of the individual, proper hygiene is also required. There is good evidence that albendazole alone; or addition of albendazole to diethylcarbamazine or ivermectin, makes minimal difference in clearing microfilaria or adult worms from blood circulation.