Sheep Abscesses in a Pastoral Production Area of South Darfur State

Abstract

Field and laboratory investigations were carried out in South Darfur State to determine prevalence and aetiology of sheep abscess. By physical examination of 11461 head of sheep in Nyala district, 139 (1.21%) animals had frank abscesses. At post-mortem at Nyala slaughterhouse, 7589 sheep carcasses were inspected for the presence of abscess and only 241 (3.18%) carcasses had one to three abscesses each; 328 abscesses involved lymph nodes or tissues adjacent to them. In addition, 22 were found in visceral organs and one abscess in scrotal fascia. The general feature of the disease, the distribution of lesions within the carcasses and order of frequency of infection of lymph nodes and visceral organs were recorded. C. pseudotuberculosis, causative agent of caseous lymphadenitis (CLA) was isolated and identified to the species level with 182 samples out of 351 samples examined bacteriologically. 51.85% of sheep abscesses in the production area were due to C. pseudotuberculosis. Moreover, Staph. aureus subsp anaerobius, the causative agent of Morel's disease was isolated and identified to species level with, 95 (27.07%) samples. Other pyogenic bacteria and E. coli as well as cases of mixed infection revealed in 95 (16.81%) samples, whereas 15 (4.27%) samples were bacteriologically negative. C. pseudotuberculosis isolates were tested for toxin production at different incubation conditions. Strain CP13N was found the most oxygenic. Aerobic incubation at 37oC for 48 hrs was found optimal for toxin production by CP13N then it was used in this study as a prototype strain for toxin production. The protein of the crude toxin was found to be 7.6 mg/ml. The minimum reacting dose (MRD) and the minimum lethal dose (MLD) of the crude toxin was 11.875 µg and 23.75 µg, respectively. The minimum haemolytic dose (MHD) was found to be equal to MRD. The immune haemolysis test was developed for diagnosis of CLA with the aim of its application in the field. The test was simple to perform, rapid, specific and sensitive in comparison with tube agglutination and haemolysis inhibition tests. The immune haemolysis inhibition test was found useful in detecting and quantitating the toxigenic strains of C. pseudotuberculosis. The susceptibility of both C. pseudotuberculosis and Staph. aureus subspp. anaerobius strains to some antibiotics was found similar to those reported in literature and no antibiotic resistance was obseved. In conclusion, C. pseudotuberculosis remains to be the main bacterium incriminated in sheep abscesses at South Darfur State and immune haemolysis test was developed with view to be used in the field for the diagnosis of CLA.