An Update on Canine Leptospirosis

What is Leptospirosis?
Leptospirosis, often referred to as “lepto”, is a disease caused by infection with numerous different serovars of bacteria in the genus Leptospira. (Serovars are closely related microorganisms distinguished by a characteristic set of antigens.) It is a zoonotic disease affecting humans and animals that is spread through urine-contaminated water such as stagnant puddles and ponds frequented by infected wildlife. Outbreaks of leptospirosis have been reported after natural disasters such as floods and hurricanes where large amounts of standing water serve as a source of contamination. Even the thaw of snow or heavy rains can wash contaminated animal urine into streams and other bodies of water. In humans, leptospirosis can cause many symptoms such as fever, headache, vomiting, jaundice (yellow skin and eyes), abdominal pain, diarrhea, and rash. Infected dogs can also show a variety of signs, but the most common clinical presentation involves signs secondary to liver and kidney failure such as lethargy, anorexia, vomiting, abdominal pain, and excessive thirst and urination. If caught early, the disease is treatable with antibiotics. However, the prognosis is worse for animals already presenting to the veterinarian with severe organ dysfunction.

Many unanswered questions –
Lepto has historically been considered a disease of rural environments. As the human population grows and urban cities expand, is this still accurate? Are there local hot spots where lepto occurs with more frequency? Which dogs are at greatest risk for infection or severe disease? How can we use this information to best prevent disease in dogs?

With funding from AKC Canine Health Foundation (CHF) Grant 02380-A Estimating Prevalence and Identifying Risk Factors for Canine Leptospirosis in North America, Dr. Jason Stull and his team at The Ohio State University set out to answer these questions regarding leptospirosis in North America. They examined leptospirosis test results (data provided by IDEXX Laboratories, Inc.) in the US from 2009-2016 and in Canada from 2009-2018. They also conducted a case-control study on canine leptospirosis in the Chicago area. Results were recently presented at the 2019 AKC Canine Health Foundation National Parent Club Canine Health Conference and are shared here as the latest epidemiologic data on canine leptospirosis in North America.

Leptospirosis test results in the United States –
Examining over forty thousand test results during an eight-year period in the US, the prevalence of positive test results did vary from year to year, perhaps reflecting variations in a number of dog and environmental factors, such as recent precipitation needed to create the hospitable environment in which lepto can easily spread. Positive test results were more prevalent in the Midwest and Southwest US, as previously reported in a poster presentation by Smith, A, Arruda, AG, Wittum, T, and Stull, J. 2019. Canine Leptospirosis in the United States (2009-20169): Use of PCR Testing to Unravel Complex Spatial, Temporal, Human-and Animal-Level Risk Factors. Positive test results were also more common in the fall season, although this seasonality varied in different regions of the country.

Data analysis revealed the following risk factors for canine leptospirosis:

• Being less than 5 years old
• Being a male
• Living in the Midwest and Southwest United States
• Living in an area with more rainfall and moist conditions
• Fall season

Leptospirosis test results in Canada –
Examining 10,000 test results during a ten-year period in Canada revealed risks similar to those found in the US. One unique finding in Canada is that dogs living in an urban setting were more likely to test positive for lepto than those living in a rural setting.

Case-control study findings –
A case-control study helps determine if a potential pathogen exposure is associated with a disease outcome. Once cases and controls are identified, researchers look back in time to learn which subjects in each group had the exposure. In this study, cases were defined as dogs with clinical signs of leptospirosis and a positive diagnostic test that lived in Chicago, IL for at least four weeks before diagnosis. Controls were defined as dogs without a diagnosis or suspicion of leptospirosis also having lived in Chicago for at least four weeks. Chicago was chosen since the commercial laboratory data described above indicated it as an area with increased prevalence of leptospirosis positive test results and showed a significant outbreak in that region.

Examining the data led to some interesting results:

• More than 25% of lepto cases were fatal.
• Young dogs were more likely to be infected than older dogs and cases did occur in dogs six months of age or younger.
• Small dogs (less than 14 lb) were more likely to be affected than larger dogs (33-60 lb).
• Dogs not vaccinated for lepto were more than 20 times more likely to be affected than dogs that had completed an appropriate lepto vaccination protocol.

The high prevalence of leptospirosis in young dogs and small dogs in this study represents a change from the standard paradigm of lepto being a disease of large-breed dogs living in a rural environment. It indicates a need for further study, increased awareness of this disease among dog owners and veterinarians, and additional prevention efforts.

What does it all mean?
The goal of this research is to identify the geographic areas of greatest risk for canine leptospirosis and to determine key behaviors and practices that can be used to successfully reduce the risk of leptospirosis in dogs. Based on these results, Dr. Stull provides the following recommendations to help prevent canine leptospirosis:

1. Know the risk factors for canine leptospirosis such as dog age, size, sex, geographical location, and season.
2. Reduce your dog’s exposure by avoiding (when practical) slow moving water and puddles – even in an urban environment.
3. Work with your veterinarian to determine the appropriate leptospirosis prevention strategy for your dog. If vaccination is recommended, start when the dog is young and follow recommended protocols as long as your dog is at risk.
4. Stay educated about the latest leptospirosis research through the AKC Canine Health Foundation and your local veterinary resources.

Resources –
The following educational resources are available to help you stay informed about the risks of leptospirosis in dogs:

• AKC Canine Health Foundation Leptospirosis Fact Sheet
• Webinar: The Increasing Threat of Canine Leptospirosis – Keys to Diagnosis, Therapy, & Prevention (original air date April 10, 2018)
• Poster presentations from The Ohio State University on canine leptospirosis research with funding provided by the AKC Canine Health Foundation.

There is more to learn -
The AKC Canine Health Foundation and its donors remain committed to advancing our knowledge of canine leptospirosis and other diseases. “The diversity and depth of AKC Canine Health Foundation-funded research has the capacity to alter the standard of care in veterinary medicine,” states Dr. Stull. The next phase of his leptospirosis research will examine veterinary attitudes and practices regarding this disease to inform and improve communication among dog owners and veterinarians. Together, we can ensure that all dogs live longer, healthier lives. Support CHF-funded research at akcchf.org/donate.

UPDATE: These findings have been published in BMC Veterinary Research. Read the full, peer-reviewed publication at doi.org/10.1186/s12917-019-2148-6.