With lambing season at its peak, the risk of Malignant Catarrhal Fever (MCF) in cattle is also heightened. To mitigate the threat of transmission, the Texas A&M Veterinary Medical Diagnostic Laboratory, TVMDL, recommends separating cattle from sheep and looking to diagnostics to assist in detection.
What is MCF?
MCF is a viral disease caused by a group of gammaherpesviruses. This disease predominantly impacts cattle, deer, bison and other ruminants, often resulting in severe outcomes.
“We often see various tissues affected because the underlying lesion is centered on blood vessels, so the disease usually presents as a multisystemic infection,” said assistant agency director for pathology Gabriel Gomez, DVM, PhD, DACVP.“MCF is almost always fatal in these susceptible species once symptoms appear.”
Infected cattle and other susceptible species develop high fevers, nasal and ocular discharge, swollen lymph nodes and oral ulcers. The eyes of affected animals may also appear cloudy and opaque. This symptom is commonly known as ‘cloudy eye.’ Furthermore, animals with MCF may also develop neurological symptoms, such as incoordination or even aggression. MCF is maintained in nature in reservoir species such as sheep, goats, wildebeest and other wild ruminants. These reservoir species are usually asymptomatic carriers, and show no signs of infection.
Transmission
Sheep are the primary transmitters of one of the main viruses associated with MCF, ovine herpesvirus 2. They usually carry the virus without showing symptoms and easily spread it to susceptible species through respiratory droplets or direct contact. Juvenile sheep, typically between 6 and 9 months of age, are often the most contagious.
“Housing arrangements are critical,” Gomez said. “Keeping sheep and cattle or bison separated as much as possible can help reduce risk.”
Testing for MCF
For testing, TVMDL encourages the collection of lymphoid tissue and affected organs (e.g. liver, spleen, kidneys and lungs) from a deceased animal suspected of being infected with MCF.
“In live animals, blood samples and nasal or ocular swabs can be helpful, though we don’t always get as clear a result as we would with postmortem tissues,” Gomez said.
“When in doubt, just give us a call to get clarification on what samples to submit or just submit the whole animal for necropsy.”
TVMDL determines infection of MCF by examining affected tissues for evidence of the virus.
Histopathology is widely recognized as the standard diagnostic approach for MCF. By thorough examination of tissues under a microscope technicians can observe if there is heavy presence of immature lymphocytes and inflammation of blood vessels. These conditions are strong indicators of the disease.
TVMDL also offers PCR testing, which can detect viral DNA of gammaherpesviruses. Interpretation of diagnostic results when detecting MCF depends heavily on clinical context. Detecting the virus in reservoir species and non-clinical animals, like sheep, does not necessarily imply they will develop disease.
Biosecurity as the bottom line
Preventing the spread of MCF begins with biosecurity measures. Sheep and susceptible animals like cattle, cervids and bison should be kept in separate enclosures from reservoir species to minimize the risk of transmission. Studies have shown nasal shedding to be the predominant mode of transmission in sheep. Infected adolescent sheep between 6-9 months of age shed more virus into the environment through their nasal secretions. Biosecurity, coupled with diagnostic testing, is useful in mitigating the threat of MCF within herds.
For more information about Malignant Catarrhal Fever and testing at TVMDL, visit tvmdl.tamu.edu or call the College Station lab at 1.888.646.5623.
