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 Wisconsin 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 Wisconsin 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.

This is probably the vaccine about which I get the most questions when it comes to delays. Leptospirosis (aka lepto) is a regionally important and potentially life-threatening infection of dogs (and people) caused by serovars of the Leptospira bacterium. It’s generally considered a non-core vaccine, meaning it’s not needed for all dogs in all areas. However, it’s probably best considered a regionally core vaccine. If leptospirosis occurs where a dog lives or anywhere it to which that dog might travel, I consider this an essential vaccine. This disease is pretty widespread internationally, so that includes a lot of dogs.

Lepto vaccines are killed vaccines, meaning they contain bits of the dead bacterium. Killed vaccines can be effective, but typically require multiple doses given within a specific interval to maximize immunity. For lepto, we typically start with two doses of vaccine 2-4 weeks apart, and then yearly boosters. We need that initial 2-4 week booster to make sure there’s a good immune response (unlike the modified live virus (MLV) core vaccines I mentioned in Part 1). If that 2-4 week booster is missed, we can’t assume there’s much protection or ability to respond to a future single booster shot. Also, yearly booster shots are needed for lepto to maintain immunity, unlike the core vaccines that can often be given every 3 years after the initial series.

Considering all that, if a dog is late for it’s first booster or annual shot, the default is to restart the entire series. The World Small Animal Veterinary Association vaccination guidance gives some leeway for the annual booster, indicating that re-dosing within 15 months (not the labelled 12) is likely okay. Personally, I suspect we can go longer, since the vaccines are good and immune systems usually aren’t dumb. However, the farther we go off-label, the less confidence we have. While many (or maybe most) dogs are probably protected well after a year and will still respond to a single booster, as a veterinarian, I can’t tell an owner with much confidence that that’s the case. So, the default is to go back to the start so we can be sure.

Based on that, when it comes to lepto vaccines, if a dog gets its:

First dose, but is late for the 2-4 week booster

  • Restart the whole series (i.e. 2 doses 2-4 weeks apart, then yearly)

First dose, 2-4 week booster, and then a yearly booster not more than 3 months late

  • Continue with the single annual boosters

First dose, 2-4 week booster, but is more than 3 months late for the yearly booster

  • Restart the whole series (i.e. 2 doses 2-4 weeks apart, then yearly)

What if someone doesn’t want to restart the series (due to cost, logistics, not keen on vaccines, etc.)?

Odds are reasonable the dog will still respond to a single late booster, but confidence in the immunity this will generate drops the later the booster gets. There’s no way to say exactly what the risk is, so not going back to repeat that 2-4 week primary series means the owner has to accept some degree of uncertainly regarding how well protected their pet will be. Additionally, manufacturers tend to stand by their products, but they’re not likely to offer any support if a dog gets lepto when the recommended vaccine schedule isn’t followed. Those are all things that need to be discussed and considered.

I’d prioritize dogs for lepto vaccination in this order:

1a) Starting initial lepto series

1b) 2-4 week booster for dogs that received the first dose

2) Yearly booster for dogs approaching the end of the 3 month extension window

3) Yearly booster for dogs not yet near the 3 month extension window

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

I’ve had a few discussions with people over the past week about geographic variation in disease risk. It’s a great subject because it’s an important and often overlooked issue. Whether it’s animals being imported, animals moving with their owners, animals accompanying owners on vacation or animals being moved between regions within the county, movement between regions can involve picking up or moving diseases at the same time.

From a veterinary standpoint, the challenge is identifying issues that you wouldn’t normally consider, because the disease is rare or non-existent in your practice area. The first step is querying travel history (which is done variably well). The next is figuring out what that means. We don’t have great resources that say “if you go here with your dog, this is what you need to be concerned about.” I get questions about travel risks all the time, and it’s taken a lot of effort to get up to speed with risks in different regions (and I still have a lot of gaps). We’ve published the odd (crude) map to help out, but getting good quality information, ideally based on surveillance data, and assimilating it into a central resource is a more significant challenge than one might think (a goal of ours, for sure, but a slow process given time and money limitations).

Regardless, we’re getting more information all the time and getting that out in the open is important. Dr. Michelle Evason wrote a post on her K9 Lifetime Study blog about the leptospirosis data we’re working on, and I thought that was worth putting up here too. It’s a fairly high level map of a few years of leptospirosis cases in dogs in Canada, based on data from IDEXX Laboratories. There are limitations with any dataset of this kind, so it’s not a perfect representation of this disease. However, it still provides some useful information. Lepto is a nasty disease and also a vaccine-preventable disease. So, understanding where it’s common is important for thinking about it when you have a sick dog (i.e. making a diagnosis) and discussing vaccination programs.

The incidence is adjusted for human population, on the assumption that dog ownership trends are similar across the country. We do that so that we don’t see bias towards big cities. If we just plot the number of cases,  places with a big dog population but low incidence of disease could have more cases than a true high risk area with a lower population, thus hiding the real risk.

This bacterium lives in different wildlife hosts (e.g. raccoons, rodents), is passed in their urine, and survives well in moist, temperate climates. Unsurprisingly, we see lepto concentrated in much of Ontario and east of here, particularly in southern regions, as well as coastal British Columbia. Risks vary within those regions too, and lepto vaccination discussions require some assessment of other risk factors as well (although I consider lepto vaccination a core vaccine in most of the green (and all of the blue) regions on this map).

A Fremont, California dog park was temporarily closed in response to concerns about canine leptospirosis after 4 reports of dogs contracting the disease, potentially associated with exposure at the park. It’s always hard to determine the source of exposure with lepto, but a park is certainly possible. We don’t understand a lot about how and where most dogs get exposed because it’s a somewhat challenging bug to track. Certainly, parks provide great mixing grounds for dogs and wildlife (the latter being the main reservoirs of the bacterium).

What to do with a potentially contaminated park area is a common question (without a good answer). Fremont Parks Supervisor Juan Barajas indicated to NBC Bay Areathat workers have briefly shut down the park and are working on extra sterilizations using diluted bleach on all the surfaces, including the astroturf. This is the first time the infection has been associated with the park and as a part of a new policy, there will be thorough cleanings and sterilizations four times a year.”

I appreciate the sentiment, but doubt this will do much to control disease spread. For one thing, you can’t effectively disinfect the outdoor environment. Bleach gets inactivated readily in the presence of organic debris (e.g. dirt). You can disinfect smooth surfaces and maybe the astroturf, but those aren’t likely the main problem. Leptospira bacteria get into the environment via urine of infected animals, predominantly wildlife. Even if you could sterilize the environment, if infected wildlife are present (which is almost certainly the case), contamination will recur very quickly. Thorough cleaning is never a bad idea, but I don’t expect this to do much to protect against lepto. The most important things that Fremont Parks can do are to spread the word about the potential risk of lepto and encourage dog owners to vaccinate their dogs against this nasty disease.

http://oahn.ca/wp-content/uploads/2016/07/OAHN-Infographic-Lepto-Mgmt-Final-20160704-page-001.jpgAs I’ve mentioned in a previous post, this seems to have been a bad year for leptospirosis in dogs in various areas. In at least a few location in Ontario, we are seeing a very high rate of disease, well beyond what we’ve seen before. I was giving some talks in Buffalo the other day and some people there reported a similar problem. Outbreaks have been identified in other diverse places in North America, including Nova Scotia and Arizona.


It’s always hard to say, and some aspects of this vexing bacterial disease make it a challenge to investigate.

Whenever we’re looking at an apparent increase in disease incidence, a few potential contributing factors come to mind:

More awareness and reporting

  • This can certainly play a role, but I think it’s abundantly clear that there was a true increase in lepto cases this year, at least around here.

New or better tests

  • New tests have become available and our ability to diagnose leptospirosis has improved, but not recently, so this also can’t account for the dramatic increase in cases.

Changes in the reservoirs and sources of the bacterium

  • Leptospira can be carried by various types of wildlife, with rats and raccoons probably posing the biggest risk in this part of Ontario. Changes in the numbers, distribution and lifestyles of reservoir hosts can result in changes in exposure of dogs (and people). Booming populations of these wildlife hosts, movement of them into new areas and other things that increase direct and indirect contact (especially contact with urine from infected animals) could result in increased disease risk.

Changes in Leptospira serovars

  • There are many serovars (types) of Leptospira, and these can have different disease risks, hosts and infectivity. We don’t have a great handle on what’s going on in this respect, and it’s an area I’d love to study more.

Vaccine breakthrough

  • Changes in serovars that are included in vaccines or increases in strains not covered by vaccines could also result in more disease. However, in my experience, lepto is very uncommon in vaccinated dogs. I’m not sure I know of any vaccinated dogs that developed disease in the recent/ongoing situation. So, that’s probably not playing a significant role.

Clearly, we need to figure out more about what’s going on. Hopefully lepto season is at an end here (with cold weather and tonight’s forecast of a blast of snow will help). That’s not necessarily true in warmer areas, and a big question is whether this fall has been an outlier or whether it’s the “new normal.” Only time will tell.

  • From the pet owner’s perspective – because contact with urine from ubiquitous wildlife is almost impossible to preclude if your dog goes outside at all – the biggest thing that can be done is vaccination. It’s safe and effective, and while no vaccine provides a 100% guarantee, it’s a worthwhile investment to protect from a very nasty disease that can be very expensive to treat.
  • For veterinarians, it’s awareness about the disease so that cases can be promptly identified, with treatment provided as early as possible. It’s also important to be aware of potential lepto cases so that proper infection control practices can be used to reduce the risk of zoonotic infection.  The Ontario Animal Health Network (OAHN) has produced a handy infographic for managing lepto patients in-hospital.

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

When Puerto Rico was devastated this fall by Hurricane Maria, I got a few calls from groups thinking about rescuing dogs from the island, and wanting to know what infectious diseases I’d be concerned about. Leptospirosis, a potentially serious bacterial infection that can be transmitted from dogs to people (although that’s fortunately uncommon), was at the top of my list. Unfortunately, that’s turned out to be exactly the case, as several puppies brought north from Puerto Rico by a Vermont rescue developed leptospirosis after arrival.

Importation always carries some inherent disease risks. That’s why we (should) use some common sense practices to reduce the risk. This may include careful selection of animals, pre-screening for certain diseases before exportation, testing on arrival, and infection control practices during for a period after arrival.  These measures are still no guarantee, but they should reduce the risk of the new arrivals carrying, developing or spreading infectious diseases.

There was one additional noteworthy detail from a news article about the puppies in Vermont:

A couple of days later, the puppies were taken to the outdoor patio at Ramunto’s Brick and Brew Pizzeria so that the patrons and customers could interact with them.

  • Not a great idea. Adopted animals need time to adapt to their new environment. They also should be quarantined for a while to see if they have any problems and to reduce the risk of them transmitting anything to other animals or people. Here, their caretakers (well intentioned as they may have been) created more risk by taking newly imported puppies out in public rather than isolating them for a period longer than a couple of days.

More information about leptospirosis is available on the Worms & Germs Resources – Pets page.

Leptospirosis is a potentially nasty bacterial infection that can cause severe kidney disease (among other things) and is acquired from the environment, in cool damp areas that are contaminated with urine from infected reservoir hosts (e.g. rats, raccoons, other wildlife). It can also potentially be transmitted to people through contact with urine from an infected dog.

We’ve called leptospirosis a “re-emerging disease” in dogs in North America for probably 10-15 years. In reality, it’s past the “re-emerging” point and is a well “re-established” disease in many areas. However, it’s been a strange fall for lepto. I’ve gotten more emails and calls about cases in the past few months than ever before, including some places where very high rates of disease are being found. Outbreaks appear to be underway in a few different areas, including a large ongoing problem with lepto in Nova Scotia and what seems to be a fairly high incidence in parts of Ontario. Getting a clear picture is tough because it’s not a reportable disease, and diagnosis can be challenging. Regardless, it’s pretty clear that we’re seeing more cases than normal.

Avoiding lepto exposure is tough, since it can be found in lots of different environments. Staying away from areas densely populated by raccoons and rats isn’t a bad idea, but identifying those is hard, and given the proliferation of raccoons in many urban areas, it’s a challenge.

What can pet owners do?

  • Vaccinate your dog. Vaccination isn’t a guarantee but it will greatly reduce the risk of disease.

What can veterinarians do?

water-ratPublic Health England has launched an investigation following identification of leptospirosis in an animal shelter volunteer. Leptospirosis is caused by the bacterium Leptospira, a bug that can be found in a variety of animal species. It’s shed in urine and loves to survive in cool, moist environments, so people and domestic animals are often exposed in parks and similar outdoor areas.

Information about the animal shelter volunteer’s infection is limited. The person presumably could have been infected at the shelter from direct contact with infected wildlife (e.g. rats), contact with an environment contaminated by infected wildlife, or contact with infected domestic animals (e.g. dogs). However, exposure outside of the shelter is also possible. It may ultimately be difficult to determine the source. Unless the shelter has recently had a dog with confirmed lepto infection and can compare the bacterial types in the person and the dog, or they can detect Leptospira in an animal or the environment after the fact (not easy), a definite link will be hard to confirm.

As reported in the North Hampshire Telegraph, “To ensure the safety and welfare of volunteers and the public, the court order included the following measures which have been carried out: Robust pest control in place; Removal of waste from across the site; Improved welfare provision for the volunteers; Welfare information provided to volunteers by PHE; Public access limited to the front part of the site only.”  All these items are a good idea in terms of infection control at any time.

Outbreaks of leptospirosis in people occur, but almost always from mass exposure to contaminated water sources (e.g. 42% of people in an Eco-Challenge race in Malaysian Borneo). Most likely (and hopefully) this is an unfortunate isolated incident, but surveillance will be underway to make sure more people aren’t infected.

More information about leptospirosis is available on the Worms & Germs Resources – Pets page.

Syringe w needleVaccination discussions can get pretty heated. It’s not as bad with animals as with humans (thanks in part to the discredited (and formerly Dr.) Andrew Wakefield). Yet, there is still a reasonable number of people who are opposed to vaccination of pets, and probably a bigger number who are wary. There are various reasons for this, but a big one is the fear of adverse effects or reactions.

No, vaccines aren’t completely innocuous. Any vaccine can cause an adverse event. It’s rare, but it’s a fact of life that when we try to stimulate the immune system for good reasons, sometimes it doesn’t do what we want. Some vaccines may pose a greater risk of causing problems, and one that frequently gets discussed is leptospirosis vaccines. The concern is based on some reasonable history, since older lepto vaccines did seem to be associated with higher rates of adverse effects (especially among small breed dogs). However, the newer vaccines are both much more effective and seem to pose a much more limited risk of adverse effects. Data now provide more support to this last statement.

A paper in the latest edition of the Journal of the American Veterinary Medical Association (Yao et al 2015) looked at records from 130,557 (yes, over 130 thousand dogs!) that did or did not have a history of lepto vaccination. Retrospective studies using medical records are always a bit dodgy because of the (sometimes poor) quality  of medical record data, but a large and well-designed study helps limit those problems. The authors looked at records from dogs that were vaccinated during their veterinary visit. They then evaluated adverse events that developed within the 5-day period after vaccination. Not all those adverse events would have been caused by vaccination. However, it’s assumed that adverse events not associated with vaccination (e.g. diarrhea caused by some other issue) would be evenly distributed among the groups. It’s likely that this approach underestimates adverse events, but realistically, it probably only missed some mild ones. If the dog developed an adverse event of any consequence, odds are greater that this would be recorded in the medical record.

The results of the study showed:

  • The rate of adverse events in all dogs was 26.3/10,000 (just over 23 dogs out of every 10 thousand had some issues in the five day period after vaccination).
  • The rate in the dogs vaccinated against lepto was 53/10,000. The most common adverse event recorded was “nonspecific vaccine reaction.”
  • The rate in dogs vaccinated against anything else was 22.1/10,000, with “non-specific reaction” again being the main adverse event recorded.
  • Some breeds had higher rates of adverse events. The “winner” was American Eskimo Dogs, with a rate of 110.5/10,000

So, at first glance, this might raise some concern, with a rate of adverse events in lepto-vaccinated dogs that’s double the non-lepto-vaccinated dogs. Even when the analysis controled for other differences between groups, such as unequal distribution of breeds, age and weight, lepto-vaccinated dogs still had adverse events at a rate of 2.13 times that of other dogs.

But, let’s make sure this is put in perspective. This would indicate that vaccination increased the risk by ~26 events/10,000 dogs. So, if you lived long enough to own 400 dogs (or if your dog lived long enough to get 400 lepto vaccinations), you’d eventually get one that developed a complication. Further, most of those were ‘nonspecific’ and presumably mild. There was no significant difference in the incidence of hypersensitivity reactions (which is the more severe and concerning type of vaccine reaction).

The authors’ conclusion is reasonable: “These data suggest that vaccination against leptospirosis should be performed for all dogs at risk of the disease except those that have had hypersensitivity reactions previously.

Lepto vaccination isn’t needed for all dogs, but if you live in an area where lepto is present, vaccination should be considered. It’s a nasty disease, and a quite safe and effective vaccine. Don’t let internet hype lead to an increased risk of disease.

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

Leptospirosis is a bacterial infection that’s been described as a re-emerging problem in dogs in North America. (It’s been described as that for many years now so maybe we should drop the "re-emerging" and just say it’s a problem). The causative agent, Leptospira interogans, is a widespread bug that’s carried by a variety of wildlife species, and it can cause disease in many different animals, including dogs and people.

In dogs, lepto is an important cause of kidney disease in some regions, and infected dogs pose some degree of risk to people who come in contact with their urine. While it used to be mainly associated with rural dogs here in Ontario, it’s increasingly being found in urban dogs because of the proliferation of raccoons (that can shed the bacterium in their urine) in cities.

A recent study from the University of California Davis (Hennebelle et al, Risk factors associated with leptospirosis in dogs from northern California: 2001-2010, Vector Borne and Zoonotic Diseases, 2014) looked at 67 dogs with lepto and 271 non-lepto controls. You can’t extrapolate all the results to other regions, because there are different animal reservoirs and other factors to consider, but the study provides some good information.

Here are the highlights:

  • Vomiting, lethargy, increased white blood cell count and increased kidney values (azotemia) were the most common presenting problems. That’s not surprising but it’s a constant problem. Dogs don’t come in screaming “I have lepto!!!” They often have vague signs and it may be a little while (and a lot of handling) before lepto is considered or diagnosed. That in-between period poses a risk to handlers if good practices to avoid urine contact aren’t used, so practicing good general infection control and keeping lepto under consideration in any of these cases are important to reduce human risks.
  • Dogs with lepto can be pretty sick and treatment can be pretty expensive. On average, affected dogs were hospitalized for 11 days at a cost of $5459 (USD). This doesn’t mean it’s always this expensive. This is a referral hospital that probably sees a caseload that’s sicker than average, but regardless, it’s a serious and often very expensive disease.
  • 13% of affected dogs died. Again, that’s based on a biased caseload, but still shows it’s not to be taken lightly.
  • The main serovar was Pomona. That’s different than we see here in Ontario, where Grippotyphosa (mainly from raccoons) predominates.
  • There were regional differences even in California, with more cases from the central or south coast, Sierra Nevada foothills, San Francisco bay area or north coast compared to the distribution of control dogs.
  • Owners of dogs with lepto were more likely to report that their dog had contact with water or wildlife, or visited a ranch. These are risk factors for lepto that have been found in other studies as well, and make sense biologically.
  • Other risk factors included being 5-10 years of age or over 10 years of age, or being hound breeds.

Lepto’s a big problem in many regions, including around here. That’s why my dog Merlin’s vaccinated against the disease. Lepto vaccines have gotten a bad rap because the older ones were relatively ineffective and associated with increased risk of adverse reactions. However, today’s vaccines protect against the important strains (for most regions) and are quite safe. Discussing the risk of lepto and whether vaccination is indicated is something every dog owner should do with their veterinarian. Knowing regional trends in lepto help make that determination.

Some information about lepto distribution in dogs is available at http://www.wormsandgermsmap.com We don’t have a lot of cases entered yet, so more data would help.  If you are a veterinarian or veterinary technician and would like to know how you can help contribute data, click here.