Leptospirosis is a contagious disease caused by Leptospira bacteria. It's transmitted naturally from infected domestic animals and wildlife to humans through urine-contaminated water, food or soil. The disease can cause a severe infection in humans.
In livestock such as cattle, leptospirosis can cause abortions, stillbirths, lower fertility and reduced milk production, says Richard Zuerner, a retired microbiologist who worked at the Agricultural Research Service. It can also result in uveitis, a potential cause of blindness in horses.
Scientists are constantly looking for effective vaccines that reduce the spread of leptospirosis in cattle. They recently evaluated a commercial vaccine for its ability to provide short- and long-term protection against experimental infection with L. borgpetersenii serovar Hardjo, the main cause of bovine leptospirosis.
In the study, cattle were vaccinated twice with the commercial vaccine, a standard vaccine, or a control vaccine. Animals were challenged with serovar Hardjo a year after the second vaccination. To test the vaccine's ability to induce short-term immunity to infection, cattle were challenged three months after a second vaccination.
"The commercial vaccine induced greater immunologic responses than the standard vaccine and greater protection against shedding after challenge," says David Alt, a veterinary medical officer for the National Animal Disease Center. "However, it did not provide complete protection from shedding."
With the commercial vaccine, scientists were not able to detect any bacteria in either the urine or the kidney at the end of the short-term study. Cattle vaccinated and then challenged with the live bacteria cleared the bacterial infection of the kidney more efficiently, Zuerner says. Results of the year-long study indicated that only one animal had bacteria in the kidney.
To determine the effects of leptospirosis and evaluate potential vaccines, scientists need a reliable model. Scientists used a hamster model to evaluate two closely related L. borgpetersenii serovar Hardjo strains. Hamsters were challenged with a strain that produced an acute, potentially lethal infection and another strain that produced a chronic infection.
Results of the chronic strain experiment revealed large numbers of bacteria in the kidney of hamsters. The infection closely mimicked the type of infection observed in cattle.