Imagine you go out to check some heifers and find one animal has died suddenly.
All of the animals looked great yesterday and there have been no recent illnesses or treatments. They have all been on a good vaccination program and seemed to be doing fine.
We might suspect bloat or lightning, but there is no evidence that either of those problems were the cause of death.
A post-mortem is performed, and the only major lesions seen are signs of pneumonia in the lungs.
You might start to question your sanity. Nobody looked sick yesterday and now one is dead of pneumonia?
Maybe the veterinary pathologist is imagining things? Perhaps you weren’t paying attention over the last day or so and missed identifying a sick animal?
However, a few days go by and another heifer dies, and then another. In each of the deaths, the animals did not appear sick and then were suddenly dead the next day. The only lesions that can be seen on the subsequent post mortems are indicative of a fairly severe pneumonia.
I was recently involved in an outbreak very similar to this description.
The cause of the pneumonia was a bacteria known as Bibersteinia trehalosi. It has been known as a disease-causing agent in sheep for many years and has been associated with pneumonia and septicemia in four- to 10-month-old lambs. Bibersteinia trehalosi has also been associated with large-scale outbreaks and mortalities in wild populations of big horn sheep.
This bacteria is closely related to a common bacteria of cattle known as Mannheimia hemolytica, which is one of the most common bacterial agents associated with bovine respiratory disease in feedlot cattle.
The bacteria are so closely related that in the past, laboratory diagnosticians may not have been able to distinguish between them. However, more modern laboratory methods provide a means for identifying this new pathogen.
Early reports of this bacteria being associated with cattle respiratory disease cases came from Europe. It is now considered part of the respiratory disease complex of cattle on that continent.
Several case reports have been published since 2012 that have also identified this bacteria in North American cattle in a variety of settings and outbreak situations. Like most of the respiratory bacteria of cattle, the organism can also be isolated from nasal passages of healthy individuals.
Although not a lot has been published on this bacteria, the outbreaks that have been described are often similar in nature to the one I described at the start of this column. The cattle affected are not necessarily under any stressors such as transportation and weaning that we see with the more common form of bovine respiratory disease. Outbreaks have been observed in mature pregnant beef cows on pasture, mid-lactation dairy cows and in backgrounded cattle more than a month after arrival.
One of the hallmark signs of these outbreaks is animals that die very quickly, often without being observed ill by the livestock manager. It is estimated that death can occur as early as 12 hours after clinical signs begin, making it very difficult to select and treat affected individuals.
In most cases, the post mortem findings show a severe pneumonia affecting at least 50 percent of the lungs, and in some cases there is evidence of septicemia, which is a more widespread blood-borne infection.
Several of the outbreaks described have mortality levels as high as 10 to 15 percent. There has not been a lot of evidence to date that would suggest viruses or other bacteria are involved in these outbreaks, but only a few studies have been published in North America.
We don’t have a good understanding of why this bacteria, which can be in the nasal passages of healthy cattle and sheep, can suddenly become a deadly infection.
It’s been suggested that vaccines for Mannheimia hemolytica may provide cross-protection against Bibersteinia trehalosi. No concrete evidence has been provided that would make this a certainty, but using these vaccines may be one option if your veterinarian feels your herd is at risk.
In this outbreak, we were dealing only with a small group of cattle and so we used antimicrobial therapy in the remaining animals to limit the spread of the disease.
This was my first experience with this emerging disease, and I can see why it would be a very frustrating one for managers of any cattle operation. Cattle that looked completely healthy one day were suddenly found dead the next day, and we actually thought we might be dealing with blackleg or some other disease that causes sudden death.
It was hard to believe that a bacteria causing pneumonia could affect the animals so quickly. This experience also reinforced the importance of doing a post-mortem and using the diagnostic lab. Without the use of the bacteriology lab, we might still be wondering what was causing the sudden death of these animals.