Scientists study L. Hardjo vaccines

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Leptospirosis is a contagious disease found in all farm animals, rodents and wildlife. It also is a widespread zoonotic disease that can be transmitted from domestic and wild animals to humans.

In livestock, leptospirosis can cause abortions, stillbirths, reduced milk production and lower fertility, says Richard Zuerner, a former microbiologist with the Agricultural Research Service’s National Animal Disease Center (NADC) in Ames, Iowa.

For cattle producers, the question may be how effective is a vaccine at reducing the shedding and spread of leptospirosis in their herds. To answer this question, NADC scientists continue to develop and evaluate vaccines for potency.

Several years ago, they tested a vaccine and found that it induced some protection against experimental infection with L. borgpetersenii serovar Hardjo, the primary cause of bovine leptospirosis worldwide.

Recently, veterinary researchers and microbiologists in Ames examined the commercial version of the vaccine for its ability to provide short-term and long-term protection against experimental serovar Hardjo infection.

Cattle were vaccinated twice with the commercial vaccine, a standard vaccine, or an adjuvant only (a control vaccine). One year after the second vaccination, animals were challenged with serovar Hardjo.

Another part of the study tested the commercial vaccine’s ability to induce short-term immunity to infection. Animals were immunized twice and challenged 3 months later.

The commercial vaccine appeared to be effective, says David Alt, a veterinary medical officer in NADC’s Infectious Bacterial Diseases Research Unit. It induced greater immunologic responses than the standard vaccine and greater protection against shedding after challenge. However, it did not provide complete protection from shedding.

“One of the big differences between the 3-month versus the 1-year vaccination with the commercial vaccine is that we couldn’t detect any bacteria in either the urine or the kidney at the end of the short-term study,” Zuerner says. “Animals vaccinated and then challenged with the live bacteria were able to clear the bacterial infection of the kidney more efficiently.”

In the yearlong study, only one animal was shown to have bacteria in the kidney, he says.

The immune system of vaccinated animals exhibits a recall response and naturally elicits an appropriate reaction against the bacteria.

“The vaccine triggered immunological memory in NK cells—or natural killer cells—a group of white blood cells that, like gamma delta T cells, are a bridge between the innate and acquired immune system,” Zuerner says. “Results indicate that both NK cells and gamma delta T cells may have a role in limiting or clearing infection.”

Leptospira is a varied group of organisms containing more than 200 serovars that can cause leptospirosis, Alt says. The difficulty is that there’s almost no visible difference within the genus.

“Getting the right vaccine depends on the infecting serovar,” he says. “That’s why it’s important to continue work, despite seeing improvements with the vaccine we evaluated.”

Source: January 2012 Agricultural Research magazine



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