Stress can open the door for Histophilus somni bacteria

The disease organism known as Histophilus somni can cause many illnesses in feedlot cattle.

This bacteria has been linked to pneumonia, arthritis, ITEME (infectious thrombo-embolic-meningo-encephalitis), as well as septicemia and heart failure.

Stress can bring on diseases caused by H. somni, which is why the stress of weaning and then commingling and transportation to auction markets or even directly to the feedlots seems to bring it on.

It is primarily a feedlot disease organism, and feedlot veterinarians in their autopsies will open up the heart and check for either scarring or an abscess in or under the papillary muscles that control the heart valves.

If they see this, it is almost a sure thing histophilus-associated disease is involved. The infection directly affects heart valves and the overall functioning of the heart. I have heard heart murmurs on some infected calves.

Using antibiotics to treat infection is too late.

We also see pneumonia cases where it is a mixed infection, often combined with Mannheimia or Pasteurella.

Often, sending away for lab confirmation tells us what bacteria is involved and what antibiotics may work in the future against it.

The key to Histophilus is preventive vaccination and minimizing stress in a calf’s life. Several vaccines are on the market and many in combination with the clostridial vaccines. As a producer, you must realize tetanus vaccines and histophilus vaccines cannot go together. The clostridial vaccines that have histophilus in them never include clostridium tetani. Producers must then make the decision whether tetanus protection is more important to them or histophilus protection. I would venture a guess it should almost always be histophilus and if there is the risk of tetanus as with banding calves you give the additional vaccine ahead of the banding and again at banding. Histophilus should be one of the core vaccines in Western Canada.

There are several of the histophilus vaccines in combination with the clostridials on the market and a couple stand-alone products.

Producers who wean on farm seldom get this disease, probably because of low–stress weaning. In feedlots where it seems like the incidence is much higher the presence of the bacteria is likely high.

All the histophilus vaccines have been around for some time. Because this vaccine can be harder to manufacture, supplies are sometimes limited.

Vaccination ahead of exposure to this organism and following up with the subsequent booster shot is the only way to do a decent job in trying to prevent this disease complex.

Prevention of the brain form of the disease is not on the label: since vaccinations were implemented many years ago the incidence has gone down drastically and I rarely hear about it anymore. Some veterinarians refer to these as brainers, but one must realize that other things such as polio, nervous coccidiosis, lead poisonings or brain abscesses can mimic the clinical signs.

This is a very good reason to have neurological cases autopsied.

We would see the true ITEME in the feedlot as often knuckling, wobbly cattle that would eventually go down and never get up. If tetracycline was used early at the knuckling stage, animals had a reasonable chance for recovery. This is why it is necessary for many feedlots to use pulses of tetracycline or other similar antibiotics under prescription early on in the feeding period. Certain antibiotics are better than others at treatment but once the arthritic or mycocardial form gets established, prognosis is poor. The arthritic form can often be confused with Mycoplasma.

In Western Canada, most cow-calf producers who either wean and feed their own calves or at least keep replacements use a histophilus vaccine at pasture turnout and a booster shot ideally a couple weeks preweaning or at weaning.

Most feedlots have variable rates of incidence of the different forms of the histophilus disease. Vaccination on arrival at the feedlot is often too late because exposure to this organism starts right away. That is why ideally, we must work more with the cow-calf producer to get these cattle vaccinated on the ranch. Most veterinarians would recommend vaccines that include this organism.

If incidents increase, researchers wonder if the organism is evolving and changing but as far as we can tell vaccines are still pretty protective. It may be in the neighborhood of 65 percent seroconversion after one vaccination and closer to 90 percent after two vaccinations, if given appropriately.

This is what we talk about in herd immunity and we still will get some cases with two vaccines because nothing is 100 percent protective. Think about this vaccine and the repercussions it can have at the feedlot next time you are processing.

Because many western calves are shipped east, especially from Manitoba, it is another disease Eastern Canada needs to be concerned about as well.

Roy Lewis works as a technical services veterinarian part time with Merck Animal Health in Alberta.

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