Immunodiagnosis of toxoplasmosis in goats

Abstract

A serological survey was carried out on the prevalence of caprine toxoplasmosis in Kerala, by two simple and sensitive serological tests-modified agglutination test (MAT) and carbon immuno assay (CIA). A total of 152 goat sera were collected from the Government Goat Farms, Attappady and Kommeri, Kerala Agricultural University Goat Farm, Mannuthy and from the slaughter houses at Trichur and Ernakulam. The MAT carried out for Toxoplasma gondii antibodies revealed 53.29 per cent as seropositive while CIA revealed 44.07 per cent. A higher prevalence was detected among does than in bucks. A remarkable age-wise prevalence was not observed in this study. Eventhough a higher prevalence was noticed in Malabari breeds, as the number of goats in each breed was too uneven, a breed-wise prevalence could not be ascertained. Area-wise, a higher prevalence was noticed in goats that belonged to Kannur district, both by MAT and CIA. Modified agglutination test was a sensitive and specific test for the serological surveys on caprine toxoplasmosis, while CIA was a cost effective and simple test which could be made use of under our field conditions.

The methods of maintenance and propagation of T. gondii RH strain in mice in the laboratory were standardised and it was found that a dose of 0.30 ml of '+++' infective fluid given intraperitoneally was sufficient for propagation of the strain in mice in the laboratory. White mice experimentally inoculated subcutaneously and intraperitoneally, exhibited similar symptoms like huddling in one corner, anorexia, rough hair coat, respiratory distress and ascites. The intracerebrally inoculated mice showed epileptic symptoms and blindness.

Haemorrhage and congestion of lungs, catarrhal inflammation of stomach and intestine and necrosis of liver were the main gross lesions noticed in the acutely infected mice. Alveolar and interstitial pneumonia coagulative necrosis of liver, destruction of tubular and glomerular epithelium of kidney, necrosis of spleen and destruction of cardiac musculature were the prominent microscopic changes observed.

Infection in mice by bioassay with acid pepsin digested visceral organs of acutely infected mice was successful. This indicated that T. gondii tachyzoites could survive acid pepsin for 75 min, as the tissues utilised for bioassay carried only Toxoplasma tachyzoites. Studies on the sensitivity of T. gondii tachyzoites to heat revealed that they could be killed by incubating at 56°C for 30 min or boiling at 100°C for five minutes. The method of cultivation of T. gondii tachyzoites in duck embryos by the chorioallantoic membrane route was successful resulting in yellowish white pock lesions on CAM, with congestion and haemorrhage on embryos and brain. A successful cryopreservation of T. gondii using tris-glycerol as cryoprotectant for 145 days at -20°C and for 250 days at -56°C was achieved.