A 30-year first shows power of successful vaccine development

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A vaccine is being hailed for its key role in delivering a breeding season in Kentucky’s Bluegrass region without one confirmed leptospirosis abortion in horses.

That hasn’t been seen for at least 30 years.

No cases were found in data compiled by the University of Kentucky Veterinary Diagnostic Laboratory for the 2019-2020 reproductive season.

The milestone wasn’t a happy accident, said Dr Craig Carter, director and professor of epidemiology at the laboratory. It was a result of work by many people at the university and within the equine industry, the outcome of which was a licensed leptospirosis vaccination introduced in 2015 by Zoetis.

While assessing the loss to other states is impossible, the laboratory estimates that the disease cost Kentucky’s Bluegrass Region a total of $US102 million in losses from 1993 to 2012, with an average loss of $US3m to $US5m a year.

Leptospirosis is a bacterial infection that can lead to abortion, chronic uveitis – also known as moon blindness – or kidney failure in horses. It is a zoonotic disease, which means it can also infect humans, as well as pets and other livestock.

It is a disease found worldwide, especially in developing countries. The bacterium thrives in wet climates, so horses exposed to standing water, flooding, wetlands, streams or ponds have a greater likelihood of coming into contact with and being infected by it.

In the midst of all the Covid-19 chaos and stress, Carter said he was thrilled with the great news presented to him by Dr Jackie Smith, an epidemiologist with the lab, that it had no confirmed cases of equine leptospiral abortion for the 2019-2020 reproductive season.

The drive to develop a vaccine started in Kentucky with a national epidemiological study, funded by the Kentucky Thoroughbred Association/Kentucky Thoroughbred Owners and Breeders.

That study, which took place between July 2010 and April 2011, looked at the sero-prevalance (level of exposure to a pathogen in a population, as measured in blood serum) of leptospirosis among horses in the United States and Ontario, Canada.

Researchers studied the residual sera from Equine Infectious Anemia submissions at 30 diagnostic laboratories.

The study of 1495 horses showed evidence that there was leptospirosis exposure and infection across 29 states in the US, as well as in Ontario, Canada, and that this exposure could lead to abortion in mares, clinical disease in horses and foals and could present a risk of zoonotic disease in farm workers and equine veterinarians.

Subsequently, in 2014, the drug company Zoetis conducted a national study evaluating serum from more than 5000 healthy horses nationwide. The study showed that 75% of healthy horses in 18 states have been exposed to one or more types of leptospires.

This, in turn, led to a commitment by Zoetis to create a licensed vaccine against leptospirosis for the horse, which was introduced in 2015. It is the first and only equine vaccine to help prevent leptospirosis caused by L. pomona.

“Equine leptospirosis is a costly, devastating and underdiagnosed disease that can affect the entire equine industry,” Dr Jaci Boggs, a senior equine technical services veterinarian at Zoetis, told the Equine Science Review.

“It is exciting to see the power of research and the positive impact this vaccine has had in Kentucky’s Bluegrass Region this past season with zero confirmed equine leptospirosis abortions.”

According to Dr Carter, there were many people involved in the research leading to the vaccine. Some of the key individuals included:

  • Bill Bernard, DVM, Dipl. ACVIM, then an equine medicine specialist with Rood & Riddle Equine Hospital;
  • Boggs, DVM, MS, DACVIM, who led the effort to develop, license and market the vaccine;
  • Stuart Brown, DVM, then with Hagyard Equine Medical Institute;
  • Carter, DVM, PhD, Dipl., ACVPM, FNAP, who in addition to the research work also served on the Zoetis leptospirosis vaccine committee;
  • Noah Cohen, VMD, PhD, Texas A&M University College of Veterinary Medicine;
  • Nancy Cox, PhD and dean of UK’s College of Agriculture, Food and Environment;
  • Erdal Erol, DVM, PhD, head of microbiology at the UKVDL;
  • Gloria Gellin, MPH, PhD student under Carter;
  • Deborah Maples, DVM, head of diagnostic services at the UK VDL;
  • Tom Riddle, DVM, Rood & Riddle Equine Hospital;
  • Jackie Smith, PhD, epidemiology section head at the UK VDL;
  • Meg Steinman, MPH, MT (ASCP), head of serology at the UK VDL;
  • David Switzer; then with KTA/KTOB, now retired.

Reporting: Holly Wiemers

Article courtesy University of Kentucky College of Agriculture, Food and Environment.

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