Submitted to: Veterinary Record
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/5/1996
Publication Date: N/A
Citation: Interpretive Summary: Malignant catarrhal fever (MCF) is traditionally considered as a disease with a short clinical course and high death rate. Owing to the limitations of the diagnostic assays in laboratories in the past, it was difficult to study the clinical phenomenon of sheep-associated MCF, particularly when the cattle recovered from an MCF-like clinical disease. Recently-developed diagnostic assays, called competitive- inhibition ELISA and PCR, were used to confirm chronic and recovered sheep-associated MCF cases in cattle. 11 cattle that survived MCF for up to two-and-a-half years were identified by detection of the viral DNA (genomic materials)in blood by PCR. The study detailed the lesions of these survival cattle and compared with the acute cases, which adds new information for MCF histopathology. The viral DNA was consistently detected by PCR in all 11 chronic and recovered sheep- associated MCF cattle and the antibody to MCF virus was detected by CI-ELISA in 8 out of the 11 cattle. These observations indicate that recovery and chronic disease are a significant part of the clinical spectrum of MCF and that such cases occur with some frequency. The affected cattle remain persistently infected with the virus.
Technical Abstract: Malignant catarrhal fever (MCF) is traditionally regarded as a disease with a short clinical course, low morbidity and high case fatality rate. Owing to the limitations of the assays used in laboratory diagnosis, it was difficult to characterize the clinical spectrum of sheep-associated MCF, particularly when the cattle recovered from an MCF-like clinical syndrome. Over a period of three years, 11 cattle that survived MCF for up to two-and-a-half years were identified on four premises. A clinical diagnosis of MCF was confirmed by detection of ovine herpesvirus 2 DNA in peripheral blood leukocytes using polymerase chain reaction (PCR) assay that detects a specific 238 base-pair fragment of viral genomic DNA. Of the 11 cattle examined, six recovered clinically with the exception of bilateral corneal oedema with stromal keratitis (four animals) and unilateral perforating keratitis (one animal). The 10 animals available for post mortem examination had disseminated sub-acute to chronic arteriopathy. Recovery was associated with the resolution of the acute lymphoid panarteritis that characterizes the acute phase of MCF, and with development of generalized chronic obliterative arteriosclerosis. Bilateral leucomata were due in part to the focal destruction of corneal endothelium secondary to acute endothelialitis. Formalin- fixed tissues and/or unfixed lymphoid cells from all 11 cattle were positive for sheep-associated MCF by PCR. These observations indicate that recovery and chronic disease are a significant part of the clinical spectrum of MCF and that such cases occur with some frequency in the area studied. The affected cattle remain persistently infected.