Malignant catarrhal fever (MCF) is a rare, under-explored lethal viral infection of cattle with gammaherpesvirus aetiological agents. Most often, the disease occurs on farms where cattle and sheep are kept together. However, other trigger mechanisms and environmental factors contribute. This study investigates the causation of MCF. An outbreak of MCF occurred in June - August 2017 in Kharchev village in Irkutsk Oblast, Russia. In this paper, we provide epidemiological (sanitary status of pastures, watering places, and premises) and weather data during the outbreak, and descriptions of the clinical signs and post-mortem changes in cattle. The virus was detected and isolated from pathological material samples and identified by molecular methods. Extreme weather conditions, mixed-herd cattle and sheep farming, and unsatisfactory feed quality contributed to the outbreak. A virus related to herpesvirus OvHV2 was isolated and typed (MCF/Irkutsk/2017). Phylogenetic analysis showed its close genetic relationship to isolates from cattle and sheep in Germany, USA, and the Netherlands. Sporadic outbreaks of MCF caused by biotic and abiotic factors together are typical for the Russian Federation, and the Irkutsk outbreak epitomised this. Temperature anomalies caused pasture depletion, resulting in feed and water deficiency for grazing animals and dehydration and acidosis. Heat stress in animals ultimately led to the occurrence of MCF in the herd.

Concentrations of serum and vitreous humor constituents at time of death, and concentrations of vitreous humor constituents at time of death and at 7 postmortem intervals were compared in 70 domestic, female New Zealand White rabbits (Oryctolagus cuniculus). Urea nitrogen concentration was significantly (P = 0.0094) different, but was linearly correlated in serum and vitreous humor at time of death and at the 4- and 8-hour postmortem intervals. Concentrations of gamma-glutamyltransferase were not significantly different in serum and vitreous humor at time of death, nor were concentrations significantly different in vitreous humor at time of death and at the 4-hour postmortem interval. The vitreous humor concentrations of glucose, triglycerides, sodium, potassium, cholesterol, total protein, albumin, lactate dehydrogenase, creatine kinase, aspartate transaminase, bilirubin, cortisol, and IgG were neither similar to nor predictive of serum constituents. Vitreous humor can be used as a source for estimates of serum urea nitrogen and gamma-glutamyltransferase up to 8 and 4 hours after death, respectively.