The need-to-know latest on canine leptospirosis vaccinations

Recently updated (2024) American Animal Hospital Association (AAHA) vaccine guidelines for leptospirosis now designate this zoonotic disease as a core canine vaccine.¹ Due to the contagious nature of this disease and its higher-than-previously understood prevalence, as well as its often indistinct clinical presentation, modifications have been implemented in vaccine recommendations. Leptospirosis impacts humans, wildlife, and companion animals, with environmental contamination a valid threat, elevating its risk profile due to the human-animal-urban-wildlife interface. How can we address vaccine hesitancy in the face of these new guidelines and effectively inform clients about the One Health risks and needed protection associated with this disease?

Leptospirosis: A key One Health disease

Leptospirosis provides a great One Health example of a disease that can wreak havoc on numerous species, including humans. The disease is global and endemic in numerous regions, including in the United States. While some regions are at a higher risk than others, understanding the disease, clinical signs, risk factors, bloodwork dyscrasias, and recognizing when to test will help with disease identification. Further, the importance of instituting lepto vaccination as a core practice, if it is not already standard fare, should become clearer.

Leptospirosis, a zoonotic gram-negative, obligate aerobic spirochete, is a true One Health concern. The incidence estimates for global cases of leptospirosis in people are over one million cases and 60,000 deaths annually. This demonstrates its significance as one of the most common One Health infectious risks globally.^2–6

Lepto hosts and concerns

Though most clinical cases are recognized in dogs, swine, cattle, and horses, all mammals are susceptible to infection with Leptosira serovars. Classified globally as a re-emerging infectious disease, incidence rates have not slowed.^7–9Estimates from 2015 remain unchanged and are likely underreported.³ Disease prevalence varies with seasonality in temperate climates and is more consistent in tropical regions. An increased incidence can be seen after rainfall. Human infection occurs most commonly due to occupational exposures. However, human cases may also arise in individuals with higher exposure risks based on activities. These include hunting, gardening, hiking, outdoor cleaning and yardwork, and recreational water activities from swimming in natural bodies of water, to kayaking, and more. Because humans shed for a short period of time, human-to-human transmission is rare.¹⁰

Note, humans are incidental, not maintenance hosts. Depending on the serovar causing infection (which is much more difficult to determine than we would hope), an animal may be a maintenance or an incidental host. Over 250 serovars have been identified, with seven key serovars identified with known maintenance hosts.¹¹  See below for known maintenance hosts and related serovars. (From the Merck Veterinary Manual.)

When lepto should be on your differential list

When evaluating patients, common clinical signs of leptospirosis can be vague. A thorough history, including exposure risks, recent activities, travel history, vaccination status, and more, plays a crucial role in determining if your patient could have leptospirosis, even before you get and evaluate your bloodwork results.