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I spend a lot of time talking to people about leptospirosis in dogs and the risks to people. From a zoonotic disease standpoint, I spend half my time trying to raise awareness of the potential for transmission of this bacterium from infected dogs to people. I spend the other half trying to talk people off the ledge because ultimately dog-to-human transmission is actually pretty rare.

Dog-to-human transmission of this potentially nasty infection can certainly occur. Exposure to urine from an infected dog is the main route of transmission. I know of multiple cases of zoonotic lepto infection due to exposure to infected dogs, almost all in veterinary technicians.  But transmission from dogs:

  • doesn’t occur very often 
  • seems to be most likely in veterinary personnel (especially technicians/nurses), probably because of greater contact with urine from infected dogs and urine-soaked items/laundry
  • doesn’t likely happen through casual contact

A recent report in CDC’s Morbidity and Mortality Weekly Reports (MMWR) describes a case of leptospirosis in a person linked to an outbreak in dogs (Waranius et al. 2024). Some of the details are pretty vague, unfortunately, but I suspect the factors above also applied in this situation. It’s a good reminder of the potential risks and that the risks to most people are probably limited, and of greatest concern for veterinary personnel.

The report describes a person in Wyoming who was diagnosed with leptospirosis in 2023. It was the first reported human case in the state since 1983, but presumably there have been some sporadic cases that were undiagnosed over the intervening 40 years (since leptospirosis in people is most often mild, many cases may have gone undetected). 

The details provided are disappointingly sparse. The report states that the person had “occupational exposure” to dogs.

  • Knowing whether that was veterinary exposure or some other form of occupational contact (e.g. kennel attendant, groomer) would be really informative. Based on later comments in the report, I assume this person was a veterinarian or veterinary technician.

The person had a range of fairly non-specific signs and symptoms, including fever, nausea, collapse, light-headedness, “brain fog,” headache, shortness of breath and muscle pain. After the onset of disease, but prior to being diagnosed, the patient learned from a colleague about several cases of leptospirosis in local dogs (suggesting the person worked in the veterinary field).  The patient passed on the concern about lepto exposure to multiple healthcare providers. Despite this, and despite having signs that fit with lepto, testing for lepto wasn’t done until 8 days after the person got sick.

  • This shows (not surprisingly) that we still have a long way to go when it comes to implementing a “One Health” approach. Too often, zoonotic diseases are diagnosed late or missed entirely, when a bit of basic questioning and communication could have facilitated a much more rapid and appropriate response. Sometimes the delay results in a fatal outcome. Fortunately, in this case it likely just resulted in the person being sick and uncomfortable for a week longer than necessary.

While the patient didn’t have contact with a dog known to have lepto, the person had had contact with body fluids from some dogs that had died from unknown causes.

  • It’s hard to say if those dogs had lepto or not, but on the same day that this person got sick, a local veterinary clinic diagnosed lepto in 3 dogs. That’s a lot of dogs all at once, even in areas where lepto is pretty common.
  • When Wyoming clinics were asked to voluntarily report lepto cases, 13 cases in dogs were identified between August and October 2023. That means the real number was probably a lot higher, since under-testing and under-reporting are very likely.

There was at least one good outcome from the communications and investigation: more vaccination of dogs.

  • Of clinics that were surveyed after the outbreak, canine lepto vaccination rates went from 5.4% before the outbreak to 33% after.  Vaccination helps protect the dogs and likely helps protect people too, since our canine lepto vaccines are quite good and some are shown to prevent both disease and shedding of the bacterium.
  • Interestingly, rural veterinary clinics recommended the vaccine more frequently than urban clinics. We used to think about lepto as a rural dog disease, from exposure to livestock and wildlife, but over the past couple of decades it’s become very much an urban dog disease, related to exposure to urban wildlife reservoir species like raccoons and rats.

Here are my take-home messages:

  • Leptospirosis is zoonotic. The risk to most people (including dog owners) is likely very low but it’s clearly an occupational risk for veterinary personnel.
  • Good routine infection control practices need to be emphasized to reduce the risks from exposure to infected dogs (known or unknown) in veterinary clinics. 
  • Zoonotic diseases often get overlooked. Even when the concern was raised in this case, there was no action on it for days. This shows the need for better communication and collaboration between human medicine, veterinary medicine and public health.
  • Vaccinate your dog against lepto.

More information about leptospirosis in dogs can be found on the Worms & Germs Resources – Pets page.