Thursday, March 1, 2001

Johne’s Disease

The field of communication is on the threshold of an electronic explosion that is putting a large amount of information into our learning library.
 For many years, I have written articles for veterinary and lay journals and magazines; however, due to today's mode of communication through computers and Internet, this will be my first Internet newsletter.
A quarterly newsletter will allow me to align with the seasons (Summer, Fall, Winter, Spring). Special updates will be written as needed.
Everyone has different needs and/or concerns. I do not have all the answers but will possibly know someone that can help find the answer; therefore, please e-mail me at with your questions, needs and/or concerns.
Current diseases of concern for my clients and me are:
     Johne's Disease and
Johne's Disease
Johne's disease was identified more than a century ago, yet remains a common and sometimes costly infectious disease of dairy cattle that has been documented in beef herds throughout the U.S.
The Beef 97 Study, a recent project by the USDA's National Animal Health Monitoring System (NAHMS), showed that 92.2 percent of beef producers were either unaware of Johne's disease or recognized the name but knew little else about it.
Johne's disease typically starts as an infection in calves, though clinical signs do not generally appear until cattle are 2 to 5 years of age. The infection is difficult to detect in its early stages and there is no cure once an animal becomes infected.
While this is a complex disease that we do not completely understand, basic information is available about the bacteria that causes the disease, how it is transmitted and how to control it.
Johne's disease results from infection with bacteria called Mycobacterium paratuberculosis. This organism grows very slowly, causes a gradually worsening disease condition, and is highly resistant to the infected animal's immune defenses. Infected animals may therefore harbor the organism for years before they test positive or develop disease signs.
The bacteria primarily infect the intestine, leading to prolonged diarrhea, poor digestion, and excessive weight loss. These bacteria are typically shed, in varying numbers, in an infected animal's feces. Once outside the animal, the bacteria no longer multiply, however they are quite hardy, living for months in water, feed, and manure. Susceptible, non-infected animals may pick up the bacteria through fecal contaminated feed or water. These newly exposed animals may develop disease and spread it within the herd.
Calves less than 6 months old are most vulnerable to infection. Under intensive housing conditions with a high level of exposure of young cattle to the organism, clinical Johne's disease can become common in cattle from one to three years of age.
Contrary to earlier notions that fecal contamination of feed and water was the sole means of transmission, infection of calves before they are born is possible. Fetal infection can occur in 20 to 40 percent of calves from infected cows showing clinical signs and about 10 percent of calves from infected cows not showing clinical signs.
DiagnosticsBoth fecal culture and blood serum antibody tests are available to producers to determine the disease status of a herd or an animal. Both tests fail to detect early infections because blood antibody development and detectable fecal shedding do not usually occur until late in the course of the infection. However, informed use of tests along with a history of clinical signs of disease in the herd can provide information to assist disease management in the individual cow and the herd.
Principles of Johne's disease control include:
     Reducing exposure and infection of replacement cattle
     Identifying and removing the most highly infected cattle, and
     Preventing introduction of infection by screening sources of replacements.
Johne's disease control programs require a long-term commitment to prevention and must be adapted to individual herds.
Additional sources of information include
     Your local veterinarian
     USDA:APHIS Info Sheet August 1999(referenced for this newsletter)
     Johne's Information Center on the World Wide Web at http://www.aphis.usda/vs/ceah
     (For Johne's disease information, see the Center for Animal Health Monitoring then the Dairy Cattle or Beef Cow-calf pages.

Mycoplasma Bovis
Mycoplasma infections seem to be the "buzz" word or concern in my practice at this time.
Dr. Ricardo Rosenbush of Iowa State University presented a paper to the Academy of Veterinary Consultants " Should Mycoplasma Bovis Be A Concern in Feedlots" and I will be using his presentation as one of the references.
This infection, caused by Mycoplasma bovis, can have a variety of clinical signs. Pneumonia and arthritis are important clinical signs for feedyards, but we shouldn't necessarily assume that you have to have both pneumonia and arthritis to have a M. bovis infection. Many times we see pneumonia as the only presentation. In one disease outbreak at Agri Research Center, there were 21 deads from respiratory clinical signs only with Mycoplasma being isolated from 12 of the 21 head.
 Outside of feedyards, mastitis is also an important disease caused by M. bovis and calves from these dairy herds may end up fed in feedyards.
Skin abscesses according to Dr. Rosenbush may also be seen.
Middle ear infections (Droopy Ear Syndrome) tend to be a significant problem in lighter calves after a high morbidity/pull rate has occurred.
What seems to be the most significant cause of concern is the lack-of response to antibiotic therapy. Different types of antibiotic therapy programs have been used with striking unresponsiveness. At necropsy multiple abscesses are noticed which tend to be distributed at the cranial aspect of the lung. (See figures 1,2, 3)
1.Mycoplasma abscesses     
2.Pasteurella fibrinous pleuritis
3. Haemophilus fibrin
Also at necropsy, the joint capsule would be thickened but otherwise be unremarkable; however, the synovial sheaths and the areas above the joint are enlarged with both excess fluid and the presence of abscesses similar to those seen in the lung. The joint fluid is usually clear whereas with Haemophilus arthritis the joint fluid is purulent.
DiagnosticsWhen dealing with pneumonia and arthritis, the best diagnostic method is a lung-tissue submission.
As of today, in the United States it's not possible to use serology to control M. bovis outbreaks in feedyards because of all the false positives without the actual disease being present.
VaccinationThere is no licensed vaccine in the United States; however, there is activity in autogenous bacterins with sporadic to questionable results.