What is "filariasis"

Filariasis \Fil`a*ri"a*sis\, n. [NL.]

1. (Zo["o]l., Med.) the presence of filariae within the body of an organism; infection with filariae. It is mostly found in tropical and subtropical regions.

2. (Med.) a disease caused by nematodes in the blood or tissues of the body causing blockage of lymphatic vessels. Death of the adult worms may lead to inflammation and permanent fibrosis; the condition may lead to serious symptoms, such as elephantiasis or blindness. See river blindness

n. A disease common in tropical and subtropical countries resulting from infestation of the lymphatic system with nematode worms transmitted by mosquitoes: characterised by inflammation.

n. a disease caused by nematodes in the blood or tissues of the body causing blockage of lymphatic vessels

Filariasis (or philariasis) is a parasitic disease caused by an infection with roundworms of the Filarioidea type. These are spread by blood-feeding black flies and mosquitoes. This disease belongs to the group of diseases called helminthiases.

Eight known filarial nematodes use humans as their definitive hosts. These are divided into three groups according to the niche within the body they occupy:

• 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 subcutaneous layer of the skin, in the fat layer. 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.

The adult worms, which usually stay in one tissue, release early larval forms known as microfilariae into the host's bloodstream. These circulating microfilariae can be taken up with a blood meal by the arthropod vector; in the vector, they develop into infective larvae that can be transmitted to a new host.

Individuals infected by filarial worms may be described as either "microfilaraemic" or "amicrofilaraemic", depending on whether microfilariae can be found in their peripheral blood. Filariasis is diagnosed in microfilaraemic cases primarily through direct observation of microfilariae in the peripheral blood. Occult filariasis is diagnosed in amicrofilaraemic cases based on clinical observations and, in some cases, by finding a circulating antigen in the blood.