Investigation of sheep-associated malignant catarrhal fever virus infection in ruminants by PCR and competitive inhibition enzyme-linked immunosorbent assay.

Development of control measures for the gammaherpesviral disease of cattle known as sheep-associated malignant catarrhal fever (SA-MCF) has been hampered by a lack of accurate diagnostic tests either for the causative virus or for antibody against that virus. A recently developed competitive-inhibition enzyme-linked immunosorbent assay (CI-ELISA) for the detection of antibody to malignant catarrhal fever (MCF) virus (MCFV) in ruminants based on a monoclonal antibody to a widely conserved epitope of MCFV (H. Li, D. T. Shen, D. P. Knowles, J. R. Gorham, and T. B. Crawford, J. Clin. Microbiol. 32:1674-1679, 1994) and a PCR assay based on previously reported primers (S. I. F. Baxter, I. Pow, A. Bridgen, and H. W. Reid, Arch. Virol. 132:145-159, 1993) were used to detect anti-MCFV antibody and SA-MCFV DNA in sheep and other ruminants. The PCR amplified a specific 238-bp SA-MCFV genomic DNA fragment from peripheral blood lymphocytes of adult sheep and other ruminants with clinical MCF. Of 144 samples from randomly selected healthy adult sheep, 143 (99%) were positive by PCR and 136 (94%) were positive by CI-ELISA. The agreement between the two assays exceeded 95%. Of nine samples collected from cattle and deer with clinical MCF of apparent sheep origin, seven were CI-ELISA positive and all 9 were PCR positive. Among 59 serum samples from presuckling lambs, none contained antibody detectable by CI-ELISA. After suckling, maternal anti-MCFV antibody was detectable for about 10 +/- 3 weeks. Although all colostrum and milk samples from infected ewes were strongly PCR positive, the appearance of detectable SA-MCFV DNA in lambs was correlated generally with antibody patterns, which suggests that the natural infection event in sheep may not occur during the perinatal period but occurs sometime later in life.