Studies on rhabditis species associated with bovine parasitic otitis

Abstract

A field study was carried out to determine the prevalence of Bovine parasitic otitis in the semi arid (hot dry) and the high potential (cold humid) areas of Kenya. A prevalence ranging from 27.3% to 78.3% was recorded in the semi arid areas of Kajiado and of between 5% and 13.6% in the high potential areas of Makuyu (Hurang~a) where the disease also occurred ina less severe form. There was a significant difference in the prevalence (P < 0.001) and severity of the disease between the two agro-ecological regions. However~ the observations in the semi arid areas were comparable to what have been reporteq_ from the hot and humid (coastal) areas where the disease is known to be more prevalent. Rhabditis (Rh) boyis alone was found to be associated with the infection in the semi arid while Rh . bovis and Rh. blumi in separate or mixed infection were identified from the high potential areas. Where it occurred alone 7 Rh. blumi was found to be associated with mild and chronic cases. Rb. bovis was not isolated from any of the dips used by infected cattle while Rh. blumi was recovered from one dip. The nematodes survived in dip samples from the understrength dips for an average of 3 days for Rh bovis and more than 3 weeks for Rh. blumi •. In freshly prepared correct strength acaricide solutions, both species were killed within 10 minutes by Amitraz a diamide (Triatix-Coopers) and in less than 2 hours by Chlorfenvinphos (Supona, Shell and Supadip, Wellcome). In Delnav (DeLnav DFF-Wellcome) and in water Rh. bovis survived for only 3 days whereas Rh. blumi survi ved for 28 days. Delnav and understrength Chlorfenvinphos dips are good reservoirs of Rh. blumi but can act as source of infection for both species during cattle dipping. In an experimental study to determine the pathogenicity of the two Rhabditis species, three of the four cattle infected with Rh. bovis developed a bilateral moderate, severe, or very severe otitis externa within 5 to 17 days (10) after infection. and histological changes were The clinical, pathological similar to what have been reported on field cases of the disease. No animal infected with Rh. blumi developed clinical otitis, but all of them showed a unilateral or bilateral increase in soft cerumine secretion from which worms were recovered. The reaction receded soon after the worms disappeared from the canal. One ear in which the reaction persisted for 76 days had a hyperaemic mucosa. This together with two others, showed a partly disrupted and necrotic epidermis and inflamed dermis on histological examination. The changes however, appeared to be a result of the pyogenic bacteria found in the ears rather than from worms. These results support the field study and other reported studies that Rh. blumi is a less pathogenic free living species whose occurrence in the ear may be a chance contamination.