Comedian Rodney Dangerfield’s tag line, “I don’t get no respect,” could apply to some of the pathogens out there. They might not be household words, but they can cause economic losses in beef herds.
Some of these diseases have been around at significant levels for a long time but were, perhaps, under-diagnosed. Some others might be gaining in prevalence because of changes in production practices. As the beef industry evolves and producers change management practices, they can influence disease patterns, says University of Missouri veterinarian Bob Larson. When producers make changes in grazing systems, weaning practices, calving seasons or other methods, they need to be aware of potential health implications. Their changes, Dr. Larson says, might reduce the incidence of some diseases, but potentially open the door to new ones.
One pathogen that has been attracting attention lately is Hardjo-bovis, a form of Leptospirosis technically known as Leptospira serovar Hardjo-bovis. Earlier this year, a large-scale study confirmed widespread prevalence of Hardjo-bovis in U.S. beef herds. The study, led by Texas A&M University veterinarian Steve Wilkse, involved coordination with field investigators around the country. The researchers randomly selected 12 herds from each of six geographic regions for testing and found the Hardjo-bovis pathogen in 48 percent of the samples. Highest prevalence was in Mississippi with 58 percent of the sample herds testing positive. Veterinarian Carole Bolin, at Michigan State University’s diagnostic laboratory, analyzed the samples collected in the study. “Hardjo-bovis is more prevalent in the United States than previously estimated,” she says. “In fact, this study confirms that Hardjo-bovis is the most common type of Leptospirosis in the United States.”
Dr. Larson, one of the cooperating researchers in the prevalence study, says Hardjo-bovis has been a challenging pathogen for veterinarians and producers for several reasons. Although it is a relatively common diagnosis implicated in late-term abortions, the disease appears sporadically, rather than in large outbreaks. Just a few cases in a herd, how-ever, are enough to cause significant economic losses. The disease can be difficult to diagnose, and risk-assessment in individual herds can be challenging, Dr. Larson says. Results of the prevalence study, he adds, indicate that the risk is not limited to any particular part of the country or climatic conditions.
Unlike other types of Leptospirosis, Hardjo-bovis is a maintenance-host infection, meaning that untreated host animals can harbor the bacteria in their kidneys or reproductive tracts for years.
Often the first signs turn up in the form of reproductive problems — too many open females, calving seasons strung out longer than usual, and weak or premature calves. Veterinarians can test herds by sending urine and blood samples to a diagnostic laboratory, with the urine sample used to determine whether the animal has Leptospirosis, and the blood sample allowing diagnosis of the specific pathogen involved.
Standard Lepto-5 vaccines do not cover the Hardjo-bovis serovar. The “Hardjo” antigen in standard five-way vaccines is not derived from Hardjo-bovis, but Hardjo-prajitno, a different pathogen with a similar name. Spirovac, a new vaccine from Pfizer Animal Health, contains inactivated whole-cell cultures of Hardjo-bovis and is the first vaccine marketed for the prevention of the disease.
The new vaccine looks promising as a tool for preventing the disease in at-risk herds, Dr. Larson says. He recommends that producers work closely with their veterinarians to determine the risk of Hardjo-bovis in their herds and vaccinate accordingly. He also reminds producers that Spirovac only protects against the Hardjo-bovis strain of Leptospirosis. Producers still need to use the conventional five-way Lepto vaccines to protect against other important strains.
In some cases, veterinarians can use antibiotic therapy to successfully clear carrier animals of Hardjo-bovis, Dr. Larson says. Whether the treatment is needed or will be cost-effective depends on the risk level within the individual herd and should be under the direction of a veterinarian, Dr. Larson notes.
Johne’s disease generally has low prevalence in beef herds, but it can be of economic importance, Dr. Larson says, especially for seedstock producers. The pathogen involved, Mycobacterium paratuberculosis, resists detection and control because of its slow development. Cattle typically become infected as calves but do not show any clinical signs until they are several years old.
Eventually, the bacteria attacks the intestine, causing diarrhea, poor digestion and excessive weight loss. But an animal can begin shedding the bacteria, infecting a pasture and other cattle in the herd, well before it shows any signs of the disease. Once the disease finds its way into a herd, it is difficult to eliminate. There is no known cure, and culling animals that show signs of disease typically just scratches the surface with more cases turning up later.
Veterinarian David Smith, an epidemiology specialist at the University of Nebraska says some scientists believe Johne’s disease could have human-health and food-safety implications. Although the cause is not yet proven, scientists increasingly have linked the M. paratuberculosis bacteria with a human illness known as Crohn’s disease.
Dr. Smith says the first time many producers hear about this disease is after several of their cows abort their calves. Neosporosis, he adds, probably is one of the leading causes of abortions, which can occur anytime during pregnancy but especially during the mid-trimester. Neospora caninum, the pathogen involved in Neosporosis, typically enters herds either by producers introducing infected cows, or from dogs or wild canines. Producers need to work with their veterinarians and state diagnostic laboratories to determine the cause of any aborted calves, Dr. Smith says. The best current control measures are to protect feed and water from exposure to
canines, combined with not keeping daughters of infected cows. There is no effective treatment for the disease.
Anaplasmosis is caused by Anaplasma marginale, a pathogen that invades the red blood cells. This insect-borne disease is most prominent in southern states but can be economically important across the country.
Primary disease signs include anemia, jaundice and fever. Outbreaks are most typical during summer, but the disease can remain at sub-clinical levels only to be triggered by stress later, such as during processing or shipping. Healthy carrier animals can serve as reservoirs from which insects and ticks spread the disease. Control of insects and ticks is an important part of a prevention program, with timely antibiotic treatment for clinically ill or carrier animals.
This disease tends to emerge in sporadic outbreaks, primarily during the summer in the Southwest, as it did this year in Texas, New Mexico and Colorado. The typical signs of infection include blister-like lesions in the mouth and on the dental pad, tongue, lips, nostrils, hooves and teats, and drooling and frothing at the mouth. The painful mouth lesions prevent cattle from eating or drinking, leading to severe weight loss.
Vesicular stomatitis is itself an economically damaging disease in infected herds, but because of its sporadic nature, it does not cause widespread losses. It is, however, a reportable disease because its signs are so similar to foot-and-mouth disease. The only way to differentiate these diseases is through laboratory tests. To protect the U.S. livestock economy, Dr. Larson stresses that rapid quarantine will be critical if a case of FMD ever turns up in the country. For that reason, he says, it is important that producers report and obtain diagnosis for “look-alike” diseases.
Although not an infectious disease, lead poisoning is surprisingly common, particularly in calves soon after turnout in the spring, Dr. Smith says. It is common enough, he says, that at Nebraska’s diagnostics laboratory, lead poisoning is one of the first things diagnosticians look for in cases of calf deaths in the spring. The typical cause is old batteries left to corrode in pastures or farm fields. Curious young calves lick the batteries, potentially consuming toxic levels of lead.
Dr. Larson stresses that although some of the lesser-known, exotic-sounding diseases deserve attention, the more typical, mundane ones have not gone away.
“Health problems such as scours, respiratory disease, pinkeye and footrot make up most of the day-to-day challenges for producers and veterinarians.”