Malignant Catarrhal Fever

Gerald Hauer, DVM
Bison Production Specialist
Alberta Agriculture, Food and Rural Development
Bison Centre of Excellence, Leduc, Alberta.
Phone: (780) 986-4100

Reprinted from The Tracker, August/September 1998

Summary

Malignant catarrhal fever (MCF) is a viral disease of ruminants.  Sheep are resistant to the disease but can act as carriers, spreading the virus to other more susceptible species.  In the last few years there have an increasing number of bison that have died from the disease.  It is a large problem for some herds of bison in our province.

Malignant Catarrhal Fever

Some of you may have heard of a disease that has appeared in bison recently and wondered what it was.  Malignant catarrhal fever (MCF) has been diagnosed in a bison herd in Alberta and it has a few people concerned.  This article will briefly describe the disease and discuss what you, as a farmer, can do to prevent this disease from affecting your herd.

What is it?  Malignant catarrhal fever is a viral disease of ruminants and is seen worldwide.  It is not a new disease and has been seen sporadically in Alberta over the years.  Worldwide, two forms of the disease have been recognized.  The wildebeast associated MCF is caused by a virus and affects cattle and deer in Africa.  It isn’t a concern in Canada except in zoos so we will limit our discussion to the other form of the disease.  The sheep associated MCF affects cattle, bison, and deer species in North America, New Zealand, and other parts of the world.  The agent that causes it has not been identified yet, but it is assumed that it is also a virus.   MCF occurs in ruminants that are closely associated with sheep or goats.  Both sheep and goats appear to be resistant to the virus and remain healthy even when infected but they can shed the virus and are an important source of infection for other species.   White-tailed deer are very susceptible to the virus and die very quickly.  Bison and elk are moderately susceptible with some natural resistance to the disease.

How is the disease spread?  Right now we don’t know.  It appears to spread from sheep and goats to the other species but does not spread readily between individuals within these other species.  It can be transmitted to bison, elk, and deer when sheep are:

• pastured  on the same or nearby pastures
• run through a common handling facility
• kept in pastures that drain into neighboring pens
• transported in the same vehicle.

There seems to be an increased chance of infection during spring and fall because weather conditions are cool and allow the virus to survive for longer periods of time.

What does the disease look like?  The virus affects the animals by attacking the lymph nodes and the walls of the blood vessels throughout the entire body, therefore many organs are affected and the appearance of the disease can be quite variable.  Death can occur in a few hours or it may take a few weeks.  Typically the affected animal is lethargic, has a fever, cloudy eyes, diarrhea, sores in its mouth, enlarged lymph nodes and discharge from the eyes, mouth, and nose.  Be careful if you are trying to interpret these clinical signs as there are some other more common and sometimes less severe diseases that share some of these symptoms such as pinkeye, IBR, and BVD.   If some of these symptoms are seen in your animal, veterinary advice should be sought to make a diagnosis.

How do I treat the disease?  Unfortunately there is no reliable treatment.   The agent causing the disease is a virus, therefore antibiotics are ineffective and there are no available antiviral drugs at this time to treat the disease.  Once the animal is sick with MCF it usually dies.  There are a few animals that survive but they are often poor doers and do not thrive.  Prevention is the key!

How do I prevent the disease?  There is no vaccine available for this disease.  The best means of prevention is to keep your bison, elk and deer away from sheep and goats to stop the transmission. 

Do not:

• pasture them together or near each other
• keep your animals in pens where water drains from a sheep or goat pen
• work them in the same facilities
• use the same vehicles to transport them

That is the easy part.  The difficult question is what to do if your neighbor has sheep and keeps them close to your animals.  That will require some creative problem solving that you and your neighbor will have to work out. 

A couple of blood tests are available that can identify exposed, infected and carrier animals.  They are the PCR assay and an ELISA test and are effective at determining if an animal or a herd has the potential to infect your bison , elk, or deer. 

After reading this, you might be alarmed and think that every ruminant that sees or smells a sheep is going to die from MCF but that isn’t the case.  There are very few sheep in western Canada so avoiding  contact is usually not a problem.  Also, not every animal that comes in contact with the virus will get sick.  In nine years of veterinary practice I have only seen one case of the disease.  It was in a dairy steer that was pastured in a small pen adjacent to a small flock of sheep.  The intent of this article is not to alarm you, but to inform you and make you aware of a potential problem that exists in your industry.