Experimental ovine fasciolosis: a comparative study of clinicopathological features in two breeds of sheep

Abstract

Twel ve Red Masai Sheep and twelve Dorper sheep aged between six and nine months were acquired from a fluke free area. Animals of each breed were divided into two groups of six animals each. six of the animals in each breed were experimentally infected with 400 viable metacercariae of Fasciola gigantlca each, with the aim of comparing the susceptibility of the two breeds to the parasite. The other six sheep of each breed acted as uninfected controls. The animals were monitored regularly for any evidence of clinical disease and their body weights measured. Blood samples were also taken from each sheep at weekly intervals and used to determine the packed cell volume, haemoglobin concentration, red blood cell counts, erythrocyte indices, total and differential leucocyte counts, and serum levels of total proteins, albumin, bilirubin, and gamma glutamate transferase and for plasma fibrinogen levels. In addition faecal samples were screened on a weekly basis for fluke egg counts. Postmortem was conducted at the ninth ~nd eighteenth weeks of the experiment or on death of the animals to study the pathology and recover and count the flukes. Red blood cell counts and packed cell volumes generally dropped faster an the infected Dorper sheep than in the infected Red Masai sheep starting from the tenth week to the end of the experiment (P< 0.05) The absolute eosinophil counts rose to a much higher level in the infected Dorper sheep than in the infected Red Masai sheep (P < 0.05). 1 Bilirubin and GGT were elevated to significantly higher levels in the infected Dorper sheep than in the infected Red Masai sheep (P < 0.05), while fibrinogen was elevated much earlier in the infected Red Masai sheep than in the infected Dorper sheep. The Dorper sheep shed significantly more fluke eggs than the Red Masai sheep and the mean fluke counts after recovery from the livers ~ere 23.5 for the Red Masai and 41.77 for the Dorper sheep. The gross pathological findings in all the animals included excessiv~ amounts of blood tinted fluid in the body cavities and severely damaged livers. The lesions in the livers were generally more numerous in the Dorper sheep than in the Red Masai sheep. Microscopically, foci of haemorrhages, .hepatocyte degeneration, leucocytic infiltrations, and proliferation of the small bile ducts were evident. In addition, the animals sacrificed at 18 weeks post-infection revealed adhesions of the liver to the viscera and toughening of the livers, which were difficult to cut with a knife. Histologically, these livers were fibrotic and this was more marked in the Dorper sheep than in the Red Masai sheep. On the basis of these clinicopathological criteria and fluke egg counts, Dorper sheep were found to be more susceptible to experimental F. gigantica infection than Red Masai sheep.