Epidemiological studies on bovine parasitic otitis
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Date
1998
Authors
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Journal ISSN
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Publisher
Sokoine University of Agriculture
Abstract
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.
Description
Thesis
Keywords
Bovine parasitic otitis