| Life Cycle | Unique among Nematodes, because they require transmission through skin by a blood-sucking parasite. Larval Development in Man: Female is viviparous, releasing numerous juveniles called Microfilariae. Born in a very immature state, being embryos rather than juveniles. Surrounded by cuticular sheath. Contain rudiments of adult structures. Important structures: Future mouth, nerve ring band, nephridiopore, darkly staining inner mass, 4 large cells, future anus. Microfilariae discharged into lymph vessels enter blood vessels. Circulate with blood and migrate to deeper blood vessels of the thorax. Do not undergo further development till they are sucked by intermediate host (mosquito). In blood of man, microfilariae show day and night periodicity (diurnal rhythm). During the day they are in large, deep seated blood vessels, but at night (when mosquitoes are active) they come to the peripheral cells. Development in Mosquito: In stomach of mosquito, microfilariae lose their sheaths, penetrate the stomach wall and migrate to thoracic muscles or wing musculature. Here, they undergo metamorphosis and grow. Infective juveniles migrate to proboscis. Infection of new human host: When this mosquito pierces proboscis into another human, the infective juveniles enter the human. Through the wound of mosquito bite, they can enter the blood stream. In the new human host, they travel to the lymph glands, where they develop into adult forms. Adults copulate and females deliver microfilariae. |
| Pathogenicity | Elephantiasis: Live in the lymphatic system, where they obstruct the flow of lymph and cause a severe condition known as Elephantiasis. Limbs or other body parts may swell up and enlarge, because lymph cannot get back into the circulatory system, accumulates into organs and causes them to swell. Light infection: filarial fever, mental depression, headache. Lymphatic vessels and lymphatic glands undergo inflammation. Control: Treatment focuses on reduction or elimination of microfilariae from circulation by administering Heterazan and compounds of Antimony or Arsenic. Modern drugs for filariasis are Albendazole, Diethylcarbamazine. |