Ulcerative balanitis and vulvitis of Dorper sheep in South Africa: a study on its aetiology and clinical features

Abstract

Ovine ulcerative balanitis and vulvitis in sheep of the Dorper breed has been observed in South Africa since 1979. Its aetiology has not been conclusively resolved, and there is some discrepancy in descriptions of its clinical features. In order to identify the pathogenic micro-organism/s that contribute to the occurrence of the disease, the microflora in the genital tracts of both clinically healthy and affected sheep were isolated and compared. Bacteriological examination of materials from affected and unaffected sheep resulted in the isolation of Arcanobacterium pyogenes from 44.2% and 17.2% of them respectively. This difference is statistically significant (P < 0.01). Seventy-four per cent of the isolates originated from severe clinical cases. Mycoplasmas were isolated from 49.3% of 116 clinically normal sheep and 78.2% of 104 affected sheep. There were significant differences in their rates of isolation in clinical groups (P < 0.05). Of all the mycoplasma isolates, Mycoplasma mycoides mycoides large colony variant (MmmLC) was isolated from 61.5% of clinically diseased sheep while 6.0% of the isolates were from apparently healthy animals (P < 0.05). The study threw light on the prevalence of mycoplasmas in the genital tract of apparently healthy sheep and, at the same time the identity of the mycoplasma pathogen associated with ulcerative balanitis and vulvitis was revealed. The findings of this investigation therefore confirmed the involvement of mycoplasma, particularly that of MmmLC large colony, in the disease in Dorper sheep in South Africa, and it was concluded that this microorganism is an important pathogen of balanitis and vulvitis in them. The study furthermore demonstrated a probable synergism between A. pyogenes and MmmLC. Finding these 2 organisms together occurred 53.4 times more frequently in the affected sheep than in the unaffected, which emphasises the probable multifactorial nature of the disease. The association between age and the presence of clinical signs was statistically significant. It was found that young sheep were more likely to have lesions than adult sheep. Clinical observations showed that the typical ulceration appears to be confined to the glans penis and lips of the vulva; no ulceration was observed on the shaft of the penis and prepuce or vaginal vestibule. In uncomplicated cases inflammation of the prepuce and vaginal vestibule is not a regular feature of the disease. Therefore the names ulcerative balanitis and vulvitis most accurately describe the nature of the disease in South Africa.