CLOSE RELATIONSHIP BETWEEN EQUINE AND HUMAN MOLLUSCUM CONTAGIOSUM VIRUS DEMONSTRATED BY IN-SITU HYBRIDIZATION

To determine whether the virus responsible for human molluscum contagi osum (MCV) is the causal agent of a similar disease in horses, in situ hybridisations using cloned fragments of human MCV DNA labelled with digoxigenin were carried out on formalin-fixed biopsy sections of lesi ons from two horses with molluscum contagiosum-like skin lesions. In b oth instances there was evidence of specific hybridisation of the labe lled probe to target DNA in the sections under high stringency conditi ons, identified by the development of a deep blue-purple stain in the cytoplasm of cells in the stratum spinosum and stratum granulosum of t he lesions and the absence of non-specific hybridisation in adjacent n on-lesional areas of the epidermis. These results indicate that on the basis of very close homology of their viral DNA sequences, the causat ive virus of equine molluscum contagiosum is either identical with, or very closely related to, its human equivalent.