Neosporosis:
Sick as a Dog

Researchers have estimated that as much as $24 million may be lost annually
due to the effects of bovine neosporosis in the Texas cow-calf population.

By Kristen Tribe

Who’s the first to get scolded when mud’s tracked across the carpet or a feed sack’s been ripped open? Even if he’s not at fault, it’s usually the dog.

Dogs often become the family scapegoats for the small mishaps in life, but animal health scientists are bringing a more serious charge against them and other canines – playing host to Neospora caninum, a protozoan parasite that can cause disease in cattle, inducing abortion.

N. caninum was only discovered in 1988, so its effects on the beef industry are not completely understood.

"Most of the work, and its been valuable work, has been done in trying to determine the life cycle of this organism and it’s impact on the adult brood cow," explains Dr. Kerry Barling, College of Veterinary Medicine, Texas A&M University. "The work that has been done up to this point has primarily been in dairy cattle and the body of knowledge about this disease in beef cattle is slim."

Researchers believe that N. caninum requires a definitive host, like your dog or a wild canine, and an intermediate host, your cow. Other intermediate hosts can include horses, deer, sheep and goats. The definitive host is responsible for the development of eggs (oocysts) that are infective to the intermediate host.

For example, a dog could eat infected tissues from an aborted fetus or placenta, become infected and then shed the oocysts in its fecal matter. The fecal matter can contaminate the feed or water supply and then cause infection when ingested by your cows, resulting in abortion.

Cows may abort at anywhere from three to eight months of pregnancy, but most neosporosis-induced abortions occur at five to six months. Calves that are carried full term and then delivered don’t always show signs of disease, but it’s estimated that 80 percent of healthy calves born from infected dams are also infected. Neosporosis is not believed to be transmitted venereally, and there have been no known health or reproductive problems in infected bulls.

There is a source of protection, though. Intervet has developed a vaccine for neosporosis that was conditionally licensed by the U.S. Department of Agriculture in December 1998.

"You have to vaccinate the cows that are infected because the vaccine is intended to reduce abortions and protect the fetus," explains Dr. Leszek Choromanski, Intervet’s Neospora vaccine project manager. "It will not cure the cow. The cow will remain infected for life, but the vaccine will interrupt transmission of Neospora to the offspring."

Intervet’s research herd was vaccinated at 35 to 45 days when they were undergoing pregnancy checks and then again in three or four weeks. Each injection was 5cc and was given subcutaneously in the neck.

In August, Choromanski had hopes that USDA would grant the regular license sometime this month or in December. Once the product is fully licensed, Intervet can be more aggressive in its marketing and sales activities and can use its trade name, NeoGuard™.

As a conditionally licensed product, it could only be listed as Neospora caninum vaccine, and Intervet had to get a permit from each state veterinarian to sell the product. In Texas and Oklahoma, there were no restrictions, but in New Mexico, only veterinarians could purchase the product.

In ongoing research, Intervet is conducting a study to determine the prevalence of the Neospora antibody in different regions of the United States.

"So far the highest prevalence in one herd has been in upstate New York, where 69 percent of the cows were infected," Choromanski says. "This year we’re planning on collecting 3,000 samples from the East Coast territory, starting with Maine and going down to Florida. We have a target to collect 9,000 samples from all over the United States and then we will have a picture of Neospora prevalence."

Barling says since the product is conditionally licensed it is safe to give to the cow and it will produce a measurable level of antibodies against Neospora. But he does not recommend a mass vaccination program, unless you know you have a problem with the disease.

"One thing we don’t know yet is the efficacy of the product," he explains. "How well will it prevent abortions? Another situation to consider is if you administer the vaccine to a group of cows and then later start having abortions and one of your diagnostic tools is blood work, the vaccine can confuse the blood test interpretations." If the test turns up positive, you’re left to wonder if it’s the vaccine or actually Neospora showing up.

Diagnosis of neosporosis is only possible by sending a blood sample or an aborted fetus to a diagnostic laboratory for tests. Fetal lesions found on tissues of the central nervous system, heart, skeletal muscle or liver is a positive sign of the disease.

In Texas, you can contact the Texas Veterinary Medical Diagnostic Laboratory in College Station or Amarillo, and in Oklahoma, contact Oklahoma State University’s Animal Disease Diagnostic Laboratory in Stillwater, Okla.

Even if you don’t have an abortion problem, it doesn’t hurt to take preventative measures. If possible, properly dispose of aborted fetuses and placentas and try to keep wild animals away from water or food sources.

Even though a cow can’t transmit the disease to other cows, Barling recommends culling infected animals, but your more valuable cows can be kept as donor cows in embryo transfer programs. Just remember that the embryos can only be transferred into a negative recipient.

The first bovine abortion attributed to N. caninum was in a dairy herd in New Mexico and the findings were published in 1989. But for several years, this was known as the "California disease" because many dairies in the state were suffering abortion storms as a result of Neospora infections, and a lot of the original scientific research was done at the University of California. According to the California Diagnostic Laboratory 1999 Report, Neospora is the leading cause of abortion in California dairy cattle, and it accounts for more abortions than all the other types combined.

Neosporosis can actually be found worldwide, but California has suffered one of the largest economic losses in the United States. It’s been estimated that the California dairy industry loses about $35 million per year due to neosporosis, while Australia’s dairy industry loses $85 million and its beef industry loses $25 million.

Although most of the testing has been on dairy herds, Choromanski has found neosporosis in beef herds in Missouri, Mississippi and Nebraska. Barling first began studying N. caninum as part of his doctoral program and was intrigued because this is a relatively "new" disease.

"I’m primarily tackling it from the feedlot performance side because this is an area of extreme interest and importance to cattle producers and to my knowledge, there’s been very little work done in this area," he says.

Barling used 1,000 calves in the 1998-99 Ranch to Rail program for some of his initial research and 13 percent of these calves tested positive for the N. caninum infection upon arrival. He found those that tested positive gained .11 pounds per day less than negative calves, and they made $17.71 per head less than the negative calves. He also discovered an association with the geographic origin of the positive calves and high numbers of coyotes and foxes in the same area.

In the 1999-00 Ranch to Rail Program, 16.6 percent of 1,200 calves tested positive, which Barling says corresponds with an increase in the coyote and fox population that year. Then in the 2000-01 program 11.5 percent of 700 calves were positive.

In an effort to find out if or why these herds were at a greater risk, Barling sent out a questionnaire to the participating ranchers. The greatest relative risk was for calves from a spring calving season, although Barling doesn’t know why this would be a factor. The second greatest risk comes from ranch raised replacement females. If you’ve got infected cows, they’re probably passing it on to their calves, some of which include the heifers you’re retaining.

The third and fourth highest risks included using a hay ring with round bales and a high stocking density, one cow-calf unit per 5.5 acres or less.

Some factors actually seemed to protect the herd or lessen the chances of a neosporosis outbreak. Although canines carry the protozoan parasite, the use of a cattle working dog actually protected the herd.

Barling hypothesizes that the dog may scare away other wild canines, or a dog may shed oocysts only once in its life, although it’s still unproven, and provide an immunological barrier around the cow herd. Barling says in a recent study, dogs that were experimentally infected and shed oocysts were challenged with a second infectious dose. These dogs did not shed oocysts following the second challenge of infection.

In his latest research project he compared the performance of vaccinated calves vs. non-vaccinated calves, all of which tested negative for neosporosis.

Barling explains, "We just wanted to determine if we gave the vaccine, would it have an impact on performance in a negative calf? Of course, the next logical step, is what would happen if we vaccinated a positive calf? Another obvious question would be if we vaccinated a negative calf and that calf became exposed to the infection, what would happen to that calf’s performance in the feedlot?"

Many questions still remain unanswered. For instance, it’s still unknown how long it takes for a cow to abort once she’s ingested the oocysts. Do dogs really only shed the oocysts once? In the meantime, economic losses have the potential to mount. Texas A&M University researchers have estimated that as much as $24 million may be lost annually due to the effects of bovine neosporosis in the Texas cow-calf population. Barling says when you factor in losses in the feedlot, you might be looking at another $13 million annually.

The potential for such devastating economic loss has jumpstarted even more research, but like any disease, it takes years of study to understand how it will affect the industry and how ranchers can avoid an infection of neosporosis.

The good news is, you don’t have to get rid of your dog.