By Ethan Covey
A human case of leptospirosis was reported in Wyoming during August 2023, the first in the state since 1983. The case was linked to occupational exposure to an active canine leptospirosis outbreak (MMWR Morb Mortal Wkly Rep 2024;73[27]:602-606).
“Although most individuals exposed to leptospirosis recover with no or only mild symptoms, the disease can cause severe illness in both people and dogs,” said Brittney Waranius, DVM, an Epidemic Intelligence Service officer with the CDC. “Early treatment can reduce illness severity and duration in both dogs and people, so it’s important to identify individuals at higher risk as early as possible.”
The case patient initially reported body aches, fever, nausea and sweating, and was treated in both an area emergency department and by their primary care provider. Their condition worsened and symptoms progressed to include calf pain, shortness of breath, cough, headache, conjunctival hyperemia, lower extremity edema, lightheadedness and “brain fog.”
Despite symptoms consistent with leptospirosis, and reported exposure to dogs, it was not until day 8 of illness that the person was tested for leptospirosis. Upon initiation of oral doxycycline, the patient recovered. On the same day as the individual’s illness onset, an increase in cases of leptospirosis among dogs was reported to the Wyoming office of the State Animal Health Official by a local veterinarian.
“Although leptospirosis is most common in tropical or temperate climate regions, we know that the bacteria is present in wildlife and peri-domestic species (like rodents) in many countries worldwide,” Dr. Waranius said. “Given the right environmental conditions or increased exposure to animals that may be carrying the disease, we can see the disease pop up even in areas where cases are less common.”
Investigators hypothesized that an unusually wet summer may have contributed to the bacteria being able to survive in the environment.
“Many of the canine cases in this outbreak may have been exposed in the general environment, which then allowed for dog-to-dog spread in a kennel environment,” Dr. Waranius said. “Given that Wyoming has relatively dry climate and the disease is rare, we found that the leptospirosis vaccine was not routinely given to dogs in the city that experienced this outbreak. We believe that the low vaccination rate in dogs, combined with occupational exposure to animals, likely contributed to the spread of leptospirosis to our human case.”
Although leptospirosis in humans is rare and asymptomatic or mild in most cases, Dr. Waranius recommended that clinicians should consider the disease when evaluating patients with clinically compatible illness, and inquire about occupation as well as exposure to risk factors like animals, standing water and mud—even in historically low-risk areas.
“Because of the potential for dogs to spread the illness to both other dogs and people, all dogs should be vaccinated, even if they live in a geographic location where leptospirosis is less common,” she said.
The case also highlights the importance of a One Health approach when responding to zoonotic disease events.
“Although canine leptospirosis is not a reportable disease in Wyoming, the investigation into this outbreak began when a local veterinarian alerted public health authorities that they were seeing a significant increase in canine leptospirosis cases at their clinic, which facilitated rapid intervention by both human and animal-focused public health authorities,” Dr. Waranius said. “Collaboration by public health authorities focused on human, animal, and environmental health can aid in controlling outbreaks and preventing spillover of diseases, like leptospirosis, that can spread from animals to people.”
