Epidemiological studies on bovine parasitic otitis

Thesis

Experimental infection with Rhabditis bovis, Pseudomonas aeruginosa and Actinomyces pyogenes was carried out on fifty-three male weaner calves. The calves were inoculated into their ears with seven different combinations of suspensions of Rh. bovis, P. aeruginosa and A. pyogenes, the eighth group (control) was inoculated with phosphate buffered saline (PBS). Twenty-five calves (47.2%) developed mild to severe clinical manifestations in-groups inoculated with the nematode and the bacteria. Calves inoculated with the bacteria alone and the control did not develop clinical manifestations. There was significant difference (P<0.05) in responses between groups one, two, three and four which were inoculated with bacteria and nematode and those inoculated with bacteria alone and the control group. The responses were not significantly different (P>0.05) between groups five, six, and seven which were inoculated with bacteria alone and the control group. Histopathological studies revealed polymorphonuclear cell infiltration, thickening and desquamation of the epithelium of the aural canal. In this study, Rh. bovis was shown to be a primary pathogen although histologically there was no evidence of the involvement of the nematode. Bacteria exacerbated the clinical effects only in the presence of the nematode. Studies on the roles of dips and spray races in the transmission of the nematode Rh. bovis were carried out by subjecting 20 healthy cattle to dipping, 20 to spraying using Steladone®, and 20 to a topical application with Ectopor® SA 020 (Ciba - Geigy Limited Switzerland) as controls. No animal in all three groups contracted the disease. The dip wash and mud from the footbath and in the collecting pens were examined for the presence of nematodes. Nematodes were isolated from manure from night pens in only one farm and one dip and none from the footbath and collecting pens. Dip tanks were established as temporary reservoir of the nematode only during dipping and nematodes were introduced mainly through ears of infected animals. The prevalence of P. aeruginosa and A. pyogenes in the ears of clinically healthy cattle and those clinically affected with bovine parasitic otitis was established by bacteriological examination of 652 samples from diseased animals and 410 from non­ diseased animals. Prevalence rates of 1.5% in diseased ears and 5.1% in non-diseased ears for P. aeruginosa and 4.9% and 2.5% in diseased and non-diseased ears for A. pyogenes respectively were determined. From this study, it has been found that severe clinical disease of bovine parasitic otitis is significantly associated with A pyogenes (OR=1.27) while P. aeruginosa has a “sparing” effect (OR=0.27) Further studies on the role of flies on the transmission of bovine parasitic otitis are required.

Swedish Agency for Research and Co-operation in the developing countries (SAREC) in collaboration with Sokoine University of Agriculture (SUA)