Malignant catarrhal fever

Abstract

Malignant catarrhal fever is briefly reviewed and recent findings are described. Initially the disease was observed as a disease of cattle in Europe where, although no cause could be identified, circumstantial evidence implicated sheep as a source of infection and it was thus designated 'sheep-associated' malignant catarrhal fever. Subsequently the disease was observed in Africa where it became evident that a herpesvirus which normally infects wildebeest was the cause. It is now apparent that deer are highly susceptible to both forms of the disease, the sheep-associated form being a serious problem in farmed deer. The wide spectrum of clinical and pathological changes that occur in affected deer are described. A major constraint to studies of sheep-associated malignant catarrhal fever has been the absence of an experimental laboratory system. However, from affected deer it has been possible to transmit the disease to rabbits and thus has allowed detailed pathogenesis studies to be made which are summarised in this paper. It is suggested that the agent of sheep-associated malignant catarrhal fever is a virus and that when a particular subpopulation of T-lymphocytes is infected a profound immunological perturbation results; the lesions of malignant catarrhal fever being explained by a benign T-lymphocyte hyperplasia accompanied by a deregulation of cytotoxic natural killer lymphocytes that gives rise to tissue necrosis.

The Pathology of Malignant Catarrhal Fever, With an Emphasis on Ovine Herpesvirus 2

“…[12][13][14][15]45,118,119 Past reports of the isolation of OvHV-2 represent inadvertent contamination of cell cultures with AlHV-1. 122,130 Successful isolation of MCFVs from affected or latently affected animals is achieved by cellular cocultivation, since the virus is strictly cell associated. 109 Leukocytes from peripheral blood and lymphoreticular tissues are the most common source of samples for attempted isolation.…”

“…They consist predominantly of T lymphocytes, with smaller numbers of B lymphocytes, monocytes-macrophages, and neutrophils. 122 Outbreaks involve direct or indirect exposure to sheep. Atypically large outbreaks have occurred when lamb and cattle feedlots were adjacent to each other.…”

“…The latter may induce lesions through nonspecific cytotoxicity. 122 Interestingly, suppression of lymphoid hyperplasia did not prevent fatal MCF in rabbits. 14 There is little indication that B lymphocytes play a significant role in preventing or exacerbating disease, notwithstanding their presence in lesions.…”

“…35,36 This review focuses on OvHV-2 from the standpoint of diagnostic pathologists. Recently published reviews address other aspects of MCF such as its occurrence in domesticated species in Europe and North America, 52,112 as well as in freeranging and captive wildlife; 44 its lesions in domesticated and wildlife species; 11 prospects for effective vaccines; 75 diagnostic assays; 22,59,116,144 and molecular virology and pathogenesis. 126 One aspect of the disease we would like to review but cannot is the impact of OvHV-2 on producers in developing countries.…”

Infection with Ovine Herpesvirus 2 in Norwegian Herds with a History of Previous Outbreaks of Malignant Catarrhal Fever

“…In addition, although the case fatality rate is very high in affected animals, many develop inapparent infections during an outbreak. 18 Alcelaphine herpesvirus 1 and OvHV-2 are endemic and widespread in their natural host species, but other ruminant species (especially when in captivity) may be susceptible to infection and develop disease. In sheep populations globally, OvHV-2 is known to infect and lead to the development of latency in most adults.…”