You can be a crack shot and still never bag a trophy if you don't have ammunition.

That pretty well describes the ability of cattle producers to hunt down a type of leptospirosis long thought to be the most common type. Until Pfizer's recent debut of Spirovac®, there were no vaccines with the antigen to guard against hardjo-bovis specifically.

It's not like hardjo-bovis has been hiding out; it's everywhere. In a prevalence study by Texas A&M University's (TAMU) Steve Wikse, samples containing hardjo-bovis equated to a national prevalence rate of 42%, with rates as high as 58% in some southern states.

Carol Bolin, an international leptospirosis expert at Michigan State University, analyzed the samples in the study and explains, “Hardjo-bovis is more prevalent in the U.S. than previously estimated. In fact, this study confirms hardjo-bovis is the most common type of leptospirosis in the U.S.”

Consequently, Wikse, an associate professor of large animal medicine in TAMU's College of Veterinary Medicine, believes, “If you're in the lower two-thirds of the U.S., and concerned about maximizing reproductive efficiency in your herd, I'd recommend you vaccinate for hardjo-bovis because it's likely your herd is already infected or will become infected with the addition of new animals.”

While testing is available, Wikse explains its so costly that vaccinating makes more economic sense. For perspective, testing protocol would include testing 15 head (basis a herd of 100). The blood and urine analysis cost $50/sample. Add in a veterinarian's call charge and you're talking around $1,000. Then, even if testing proves negative, it's likely the herd will become exposed through additional purchases if they aren't vaccinated.

Although hardjo-bovis is more prevalent in the South, Wikse believes even producers in the northern tier of states should discuss with their veterinarians the use of vaccination as a control program.

While that may sound like too general of a recommendation at first glance, add to the prevalence rate mentioned earlier the fact that the test used to identify infection is only 70% sensitive. That means 30% of the animals in the study determined to be negative for hardjo-bovis infection were actually false negatives. Thus, the prevalence rate runs even higher.

“I don't think there's any question about vaccinating for hardjo-bovis in all cattle because of the widespread prevalence of it in beef herds and its proven detrimental effect on fertility. Calves are just too valuable to risk losing,” Wikse says.

A delay here, an abortion there

Hardjo-bovis can cause the whole spectrum of maladies associated with reproductive pathogens, including early embryonic death, abortions, stillbirths, weak calves, delayed estrus and overall reductions in reproductive performance.

What makes it tough to determine hardjo-bovis' exact cost is that, unlike other types of leptospirosis that producers have been able to vaccinate against for years, hardjo-bovis tends to cause sub-clinical symptoms. The other types are often associated with acute clinical signs.

According to researchers, the contrast has to do with the fact that hardjo-bovis produces what's termed a “host-adapted infection” in cattle. That means the maintenance host animal lives with the infection, shows no overt symptoms, but serves as a reservoir to continue shedding the organism.

The infection resides in the kidneys and reproductive tract, whereby the pathogen is shed in both urine and reproductive fluids. An added challenge with hardjo-bovis is it can also infect embryos in utero so that a calf can be born as a maintenance host.

Incidental infections (non-host adapted infections), on the other hand — caused by other common lepto types — can cause acute disease symptoms. But little of the responsible pathogen is shed in the urine, meaning there's little animal-to-animal contamination.

Wikse is the first to point out a high prevalence of a disease organism doesn't necessarily equate to a high level of production loss. But, in the case of hardjo-bovis, he says a growing body of evidence suggests controlling it pays more than the cost of control.

For instance, Wikse points to a study conducted in California dairy heifers. Heifers infected with hardjo-bovis required 3.4 services/conception, compared to 2.1 for uninfected heifers, and they took longer to conceive after first calving — 132 days vs. 95 days for the uninfected heifers. “You can infer you'd see similar results with beef heifers,” Wikse says.

Vaccination and biosecurity

Availability of a vaccine to prevent hardjo-bovis is still new enough that Wikse says there's no industry-standard control program. But he suggests the Cadillac of programs would be vaccinating the whole herd, including bulls, which can pass the infectious agent along in semen as well as urine — the agent enters through small lacerations in the skin, between the toes, etc. Vaccinating mature animals requires treating them with a long-lasting antibiotic first in order to clear up any renal carriers (chronics). With that done, Wikse says you'd vaccinate, booster them in 4-6 weeks, then plan on boostering them every 12 months.

Where it's not possible to treat the entire herd twice within 4-6 weeks, Wikse explains, “An option would be to apply the same program, but only to replacement heifers, so that over a period of years the entire herd, given the annual booster vaccinations, should be protected from infection. If it's a herd already experiencing low levels of reproductive efficiency, I wouldn't recommend this slower option,” Wikse says.

Keep in mind the focus on replacement heifers also has to do with the fact reproductive pathogens impact younger animals more severely than older ones. So the actual damage can be largest in the younger population where the prevalence rate is actually lower.

Moreover, even though producers can identify hardjo-bovis infection by means of collecting blood and urine samples from a portion of the herd, then having diagnostic tests run, Wikse believes the high prevalence rate makes vaccination without testing a wise economic strategy.

Ron Gill, a TAMU Extension beef specialist, says producers must understand the five-way leptospirosis vaccines they've used in the past don't contain the hardjo-bovis antigen.

“To protect against hardjo-bovis, a vaccine must have the hardjo-bovis antigen in it,” Gill says.

More specifically, traditional leptospirosis vaccines have included protection against one type of the organism — hardjo-prajitno — which has never been found in the U.S., while not including an antigen for hardjo-bovis.

So, whether using a monovalent vaccine with the hardjo-bovis antigen, along with a traditional five-way leptospirosis vaccine, or by using a single multivalent vaccine that contains the hardjo-bovis antigen, producers should make sure they're covering all the bases.

“Vaccination for hardjo-bovis is available, and it's highly effective,” Wikse emphasizes. “For a comprehensive leptospirosis control program, producers should use a standard five-way lepto vaccine, plus a vaccine that protects specifically against hardjo-bovis, or a multivalent vaccine that contains it. You need both, since standard five-way lepto vaccines don't have a hardjo-bovis component.”

Given the ease with which hardjo-bovis is transmitted, Wikse points out effective control demands vaccination be accompanied by strategic biosecurity. In addition to the age-old wisdom of knowing some history on the source of new additions and keeping new arrivals separate for observation, Wikse says a growing number of producers are testing new additions for infectious diseases before purchasing or introducing them to the herd. These infectious diseases include bovine leukosis, neosporosis, Johne's disease and persistently infected BVD.

Again, because of the testing costs associated with hardjo-bovis, Wikse repeats his advice to address hardjo-bovis by assuming all new introductions are infected. That means treating them with a long-lasting antibiotic, then vaccinating and boostering them for hardjo-bovis.

Whatever control strategy is chosen, Wikse emphasizes the importance of committing to it over the long haul.

“Diseases are cyclical from year to year. In the case of hardjo-bovis, it may not cause significant reproductive losses every year inside infected herds, but then one year it hits you hard,” he says.

With that in mind, Wikse believes hardjo-bovis control “is part of a ranch management program aimed at enhancing production. If your goal is to have as much protection as possible against disease that can potentially interfere with reproductive efficiency, there is no doubt this kind of protection more than pays for itself over time.

“Now that we have an effective vaccine agains hardjo-bovis, it's time for producers to meet with their veterinarians to discuss how they can use this breakthrough to make their herds more productive and profitable.”