Neurological disease in cattle continues to be a diagnostic challenge in the field.
There are a wide variety of causes of nervous diseases in cattle, and many of the symptoms are similar or have subtle clinical differences.
Nervous disease symptoms can be the result of BSE, rabies virus, infectious thromboembolic encephalitis caused by Histophilus somnus, listeriosis, lead toxicity, vitamin A deficiency and polioencephalomalacia (polio) caused by thiamine deficiency or high levels of sulfates in the diet.
It is difficult to diagnose these diseases based only on clinical signs so further tests on the brain and other tissues are often required.
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Several recent scientific publications have looked at some of the forms of neurological disease in cattle that have been a diagnostic dilemma and shed new light on these puzzling diseases.
Dr. Sergio Sanchez and researchers from the University of Saskatchewan’s Western College of Veterinary Medicine and the University of Calgary School of Veterinary Medicine investigated 37 cases of en-cephalitis from Western Canada that were submitted to the diagnostic lab.
All of these cases were from feedlot cattle suffering from nervous disease that did not have a definitive diagnosis other than encephalitis (inflammation of the brain).
Most of these cases occurred in winter, which meant it was highly unlikely that they were caused by a virus that relied on insect transmission, such as West Nile.
The tissues were tested for many of the potential viruses and bacteria that could have caused nervous disease, and most of the cattle tested negative for everything.
One case surprisingly tested positive for rabies virus, which emphasizes the importance of looking for that disease diligently because of the potential for transmission to people.
However, the study demonstrated that even with sophisticated testing, we still have a subset of nervous disease cases in cattle that can’t be explained.
Another research study that was recently published in California in the journal Emerging Infectious Diseases used a similar set of samples from the Veterinary Medical Teaching Hospital at University of California Davis.
They selected 32 cases of bovine encephalitis that had been previously not diagnosed and used a sophisticated mode of testing for viral genetic material known as viral metagenomics on all of the cases.
Once again, many of the cases remained a mystery, and no viruses were found.
However, a new astrovirus was discovered in three of the cases that was associated with the lesions in the brains of these cattle.
Astroviruses have been associated with neurologic disease in mink, but this is the first time it has been linked with nervous disease in cattle.
Further research is necessary, but it would appear that we have yet another potential cause of nervous disease in cattle that may help explain at least some of this subset of unexplainable nervous disease cases.
There seemed to be an increase this past winter in the number of veterinarians who reported nervous disease cases in weaned calves, which we currently diagnose as nervous coccidiosis.
They typically appear in weaned cattle during winter and are often associated with extremely cold weather.
It usually affects only a small percentage of animals, which typically have muscular tremors and will drop to the ground and have convulsions or “seizure-like” activity.
They may appear to recover temporarily but will continue to have episodes of seizures and will eventually be unable to rise. A high proportion of these affected cattle will eventually die.
As the name implies, this disease has been associated with outbreaks of coccidiosis, a parasite that typically causes diarrhea in young cattle.
It has been difficult to explain how the nervous form of this disease occurs, and many veterinarians have suspected that perhaps there is another cause to this form of nervous disease in cattle.
Perhaps new technology such as viral metagenomics can be applied to these nervous coccidiosis cases to determine if other agents are in-volved in these cases.
Viral metagenomics helped discover a new bovine astrovirus that potentially causes nervous disease.
Producers who see cattle in their herds that are exhibiting symptoms of nervous disease such as blindness, staggering, convulsions or nervous tremors should ask their veterinarian to attempt a diagnosis.
The veterinarian may need to submit tissues to the diagnostic lab to confirm a diagnosis.
Some of the conditions, such as rabies and lead toxicity, pose a public health risk, and it is important to rule them out.
