Animal filariasis is an important helminthic infection caused by large number of parasites. In bovines, it is caused by setaria, stephanofilaria, parafilaria and onchocerca parasites. Of these, setariasis is more common resulting in economic losses to the buffaloes.
Etiology: The adult worms of setaria parasites are present in peritoneal cavity of buffaloes and cows and are nonpathogenic but its larval stages are circulating in blood and damage the tissues. Prevalence of microfilariasis is dependent on the ecological conditions of a particular region. The spread of disease occurs through biting flies and mosquitoes particularly Aedes species.
Pathogenesis: The adult male and female worms are present in the peritoneal cavity and lay larvae. These larvae reach the circulation and migrate to different tissues like liver, kidney, spleen and lymphoid organs. During migratory phase, larvae may lodge in abnormal sites and develop into mature stage. They may be lodged in liver, small intestine, eyes, pericardium, lungs and kidneys and damage these sites. Few larvae may reach in the brain causing cerebral nematodiasis which is common in sheep.
Clinical signs: There is slight rise in body temperature and animals show reduced feed intake, continuous weight loss and weakness. They become debilitated, lean and thin and have rough and dry skin coat. There is watery discharge from nostrils and conjunctivae are congested and had mucopurulent discharge. Lactating animals reveal continuous reduction in milk yield, and in late lactation stage, milk is completely absent. There is swelling of dependent parts of body and joints of legs. Affected animals have higher heart and respiration rates while rumen motility is reduced. In few cases, circling, head pressing against fixed objects and other nervous symptoms may also be observed.
Diagnosis: The disease is diagnosed by clinical symptoms and can be confirmed by blood examination for the presence of larvae in the circulation. As the number of larvae is variable in circulation, it is not always possible to get them in direct blood smear examination. So, the plasma and buffy coat are examined which can reveal if larvae are present in low numbers. For it, blood is filled in ESR tube and kept for 1 h after which cells are removed and plasma and buffy coat are spread on a slide and examined under microscope. For quick diagnosis, a capillary is filled by blood and centrifuged for about 2 min in capillary centrifuge. It is broken and plasma and buffy coat are spread over slide and examined for the presence of microfilariae.
Ha ematological examination reveals significant eleva tion in erythrocyte sedimentation rate, low haemoglobin and packed-cell volume and high lymphocyte and eosinophil counts. Various liver specific enzymes and urea nitrogen and creatinine are also elevated in affected animals. The disease can also be confirmed by complement fixation, indirect fluorescent antibody, ELISA and blast transformation tests.
Treatment: The treatment should be aimed to remove adults as well as larvae. For the removal of adults, broad-spectrum anthelmintics like mebendazole, levamisole or tetramisole may be used. For the treatment of larvae, diethyl carbamazine citrate (10-
25 mg/kg body weight for 10-15 days), lithium antimony thiomalate (120 mg total dose intramuscularly on alternate days for 10-12 days) or combination of both alternately for 10-15 days may be used. Ivermectin is effective against larvae as well as adults and can be given @ 200µg/ kg body weight subcutaneously. The drug may be repeated on third day. In severe cases, it requires 3 treatments. Supportive treatment in the form of iron and vitamin B complex and liver tonics helps in early recovery. Mosquitoes and flies population should be checked in the environment for the control of disease.
Other filarial worms like parafilaria causes haemorrhagic nodules or cutaneous bleeding, stephanofilaria is responsible for hump sore, ear sore, and dermatitis. Onchocerca causes subcutaneous nodules and dermatitis. For the treatment of stephanofilariasis, antimosan, neguvon or tartar emetic may be given while parafilariasis can be treated with antimosan and sodium or potassium antimony tartrate.