Companion pet parents are likely to be confused as to whether their dogs should be vaccinated against leptospirosis. We think several issues add to the confusion in helping them to make informed decisions.
Foundation
What is leptospirosis?
Leptospirosis is caused by infection with the Leptospira bacteria. It is a zoonotic disease – meaning it can spread between species, including humans.
Leptospira Bacteria
Each Leptospira bacterium is called a serovar, which is a distinct variation within a species of bacteria. They are then grouped into serogroups. So, a serogroup could have one or more serovars.
Leptospirosis Infections
The general incubation time – before clinical disease is apparent – is between 2 and 14 days.
Most commonly, dogs acquire the disease by closely sniffing or walking through urine-contaminated water, soil, or food. Active infections in dogs can vary from mild to severe. Severe cases could cause acute liver or kidney failure, severe anemia, or even death.
Cats are considered to be relatively disease resistant, but they can still shed the bacteria.
Testing for Leptospirosis
Several tests are available to diagnose an active clinical case of leptospirosis. The two primary tests used jointly are the microscopic agglutination test (MAT) and DNA-PCR.
DNA-PCR detects the presence of Leptospira DNA in blood or urine early in the course of disease. It does not measure vaccinated immunity.
The MAT is an antibody test. It will indicate if an animal has mounted antibodies against a serogroup. Interpretation of MAT needs to account for vaccinated immunity, which will affect the titer level.
Leptospirosis Vaccines
Canine vaccines are available for leptospirosis but only cover four clinically significant serovars out of the seven (possibly ten): L. canicola, L. icterohaemorrhagiae, L. grippotyphosa, and L. pomona in the United States. In Europe, the serovars in the vaccines are against L. icterohaemorrhagiae, L. canicola, L. grippotyphosa, and L. australis.
Currently, the leptospirosis vaccine is considered ‘non-core’ and its recommended use is based on patient and caregiver environment and lifestyle.
The vaccines are considered >80% effective. Some studies have shown that the currently available bacterins elicit serogroup‐specific immunity.
The guideline for canine administration is an initial two doses at 2-4 weeks apart and then a booster given once annually. If the annual booster lapses, the dog will need to start the protocol again from the beginning.
A horse vaccine is available against L. pomona.
No vaccines against leptospirosis exist specifically for cats.
Reportable Disease?
As of 2024, leptospirosis is a nationally reportable disease in humans according to the Centers for Disease Control and Prevention (CDC).
The United States Department of Agriculture (USDA) regulates nationally reportable diseases in animals. Leptospirosis is not on the 2024 list.
States can also determine if leptospirosis in animals is reportable or not. However, a county or city may require leptospirosis reporting in animals when a state does not.
Additional factors come into play:
- What animals?
- When does the disease have to be reported?
- What qualifies as a leptospirosis case?
For example, the Commonwealth of Massachusetts requires reporting of all animal leptospirosis cases within 72 hours.
The State of Michigan requires reporting of canine leptospirosis infections within seven days.
New York State requires notification of leptospirosis in equine animals within one month. New York City overrides that and requires all animals (including dogs) to be reported within 24 hours of laboratory diagnosis.
…And so on…We would recommend you search “reportable animal diseases” for your state, city and county.
Frustration: Public Reporting of Results
Los Angeles County
In 2021, Los Angeles County experienced an outbreak of leptospirosis in dogs. According to the county, the majority of dogs had attended dog daycare or were kenneled, and were unvaccinated. The county also indicated that the serovar was “more than likely” L. canicola without providing the data to support that claim.
A confirmed case definition in Los Angeles County is:
- 4-fold change in antibody titer to at least one serovar (samples drawn 2-4 weeks apart) in a dog that did not receive a Leptospira vaccine in 6 months before testing (MAT), or
- PCR positive urine or blood sample, or
- Silver stain or immunostaining positive histology, or
- Positive silver or immunostaining of urine sediment positive, or
- Isolation of Leptospira organisms by culture of urine or tissue
This is too dependent on whether or not the dogs were given the vaccine. The established vaccination guideline is to administer two doses 2-4 weeks apart and then booster once annually. If greater than 12 months lapse, initial two doses should be re-administered.
Secondly, please notice that it is “or, or, or, or”. Granted, it may be difficult to catch a PCR sample due to the transient nature of Leptospira, but the consensus is that both PCR and MAT testing should be completed. Indeed, a 4-fold change 2-4 weeks apart gives the infection too much time to develop into severe clinical disease.
Chicago
In Illinois, Chicago, and Cook County, leptospirosis in dogs is not a reportable disease. Amanda Smith of Ohio State University conducted a study titled, Descriptive and Spatio-Temporal Analyses of 45 Canine Leptospirosis Cases in Chicago, 2015-2018. She and her team contacted 40 Chicago veterinary clinics. It appears that two clinics responded.
According to their results:
- Vaccination: Five cases (11%) had received a leptospirosis vaccine, but none were fully immunized (4 additional cases had no referring clinic and vaccination status was unknown).
- Testing: Most frequently based on PCR (n=30, 67%), followed by MAT (n=13, 29%), PCR and MAT (n=1, 2%), and in-clinic antibody test (n=1, 2%).
Why weren’t the dogs fully immunized? We plan to discuss this topic soon.
Secondly, only one dog had both PCR and MAT?!
New York City
The New York City Department of Health and Mental Hygiene (NYCDHMH) releases a surveillance summary about dogs every five years. We find its 2022 report more thoughtful and well-rounded.
- “The average of 24 canine cases per year in 2017-2021 increased from an average of 17 cases in 2012-2016. This may be a true increase, or possibly attributable to an increase in the use of PCR as a diagnostic tool. PCR reports increased from 15 during 2012-2016 to 59 from 2017-2021. Although fewer MAT tests were received since 2017, the number and proportion of dogs with rodent-associated serovars was similar in both time periods. The percent of hospitalized and fatal canine cases in 2017-2021 was also similar to the previous 5-year period (2012-2016).”
- “During 2017-2021, 143 reports were received from the laboratory (n=118, 83%) or veterinarian (n=30, 21%), including 5 reported from both (4%). A total of 121 dogs met the case definition (61 confirmed, 60 probable). Among the remaining 22 reports, 1 investigation was incomplete and 21 were not classified as a case due to recent leptospirosis vaccination, incompatible symptoms, or residence outside NYC.”
Thoughts: Are they excluding cases with recent leptospirosis vaccinations because only MAT was used as the diagnostic tool without PCR?
As the Updated ACVIM (American College of Veterinary Internal Medicine) Consensus Statement on Leptospirosis in Dogs states, “Nevertheless, published data is limited regarding the incidence of naturally occurring leptospirosis (clinical or asymptomatic shedding) in such (vaccinated) dogs. This situation may partly relate to the difficulty in definitively diagnosing leptospirosis in fully vaccinated dogs.”
In essence, we do not know if the dogs were vaccinated properly, if MAT testing hampered the results, actual infections in dogs that were properly vaccinated to improve the vaccines or add serovars, or the effectiveness of the vaccines.
- “Leptospira serovars can help identify the animal reservoir host(s) responsible for infection; however, cross-reactivity is common on the microscopic agglutination test (MAT), which is specific to the serogroup and not the serovar. Of the 94 cases that acquired their infections in NYC, only 53 (56%) had MAT performed. For most of these, the serovars with the highest titer or change in titers was icterohaemorrhagiae and/or L. bratislava (n=37, 70%), both of which are associated with rats; 25 of the dogs (68%) were in areas where rats were observed. Thirteen cases (25%) had the highest titer or change in titers to L. grippotyphosa, which is associated with raccoons, opossums, and skunks; 8 dogs (62%) were in areas with those animals.
Thoughts: This is truly helpful as it allows companion pet parents to make an informed decision about the vaccine. Both L. icterohaemorrhagiae and L. grippotyphosa serovars are “covered” by the vaccine.
While contested by anecdotal incidents, a laboratory experiment determined that L. bratislava usually does not cause clinically significant disease in dogs.
- “Based on our findings, leptospirosis appears to be uncommon in NYC dogs.”
- “Although infected dogs pose a risk to people through contact with the dog’s urine, such direct transmission has been infrequently documented in the literature and, based on the past 16 years of surveillance data, infected dogs have not been identified as a source of human infection in NYC.”
Vaccination Confusion
For years, the ‘non-core’ leptospirosis vaccine for dogs has been combined with ‘core’ vaccines against distemper, adenovirus-2 (provides cross-protection against adenovirus-1, which causes infectious canine hepatitis), parvovirus, and ‘non-core’ parainfluenza. After the initial puppy shots, veterinarians would usually give this combo-vaccine every year.
It should be noted that vaccine manufacturers continue to provide this combination.
Nowadays, there is a concerted effort by major veterinary associations like the World Small Animal Veterinary Association (WSAVA) and American Animal Hospital Association (AAHA) to start separating vaccines based on length of vaccinated immunity, core vs. non-core (lifestyle; environment), and to reduce adverse events.
The ACVIM appears to indicate that leptospirosis vaccines should be added to the ‘core’ vaccination guidelines without saying it directly, which causes more confusion.
The 2022 AAHA guidelines indicate that the Leptospira vaccines are ‘non-core’.
The 2024 WSAVA Vaccination Guidelines are now calling vaccinations against leptospirosis ‘core’ based on environment whereas previously the association deemed it as ‘non-core’ based on environment and lifestyle. The association states, “In countries or regions where canine leptospirosis is endemic, where implicated serogroups are known and where suitable vaccines are available, vaccination of all dogs against leptospirosis is highly recommended and the vaccines should be considered core in those places.” Plus, starting the vaccination at 8 weeks of age.
The ACVIM and AAHA both do not recommend the Leptospira vaccines before 12 weeks of age. Hemopet prefers that they be separated from other vaccinations and that the youngest age to start it is 14 weeks. More on this later.
Granted, the shifting status between ‘core’ and ‘non-core’ should be expected based on the disease. However, questions remain such as when to start the vaccine.
Here’s another example of vaccination confusion. After the initial puppy shots and a booster at one year of age, AAHA indicated in 2022 to give distemper, adenovirus-2, parvovirus, with or without parainfluenza vaccine every three years. AAHA is essentially recategorizing parainfluenza from a ‘core’ vaccine to a lifestyle vaccine and pairing it with the Bordetella, which we prefer as well.
WSAVA now stipulates the parainfluenza vaccine is ‘non-core’, but says that revaccination at 6 months of age should be considered against distemper, adenovirus-2 and parvovirus followed by boosters every three years.
Hemopet recommends titer testing every three years to determine if a booster vaccination is necessary against these core viruses.
It is the right call to lengthen the interval between distemper, adenovirus-2 and parvovirus shots. Even though vaccinated immunity can last anywhere from five to seven years.
The “plus or minus” of parainfluenza adds confusion. It is generally accepted that parainfluenza virus infection is rarely diagnosed as a clinical entity. Additionally, parainfluenza vaccinated immunity is relatively short-lived just like leptospirosis.
Thus, a number of issues are at play here: ACVIM, AAHA, WSAVA, and vaccine manufacturers are not working together to provide the information concisely and coherently, and the industry continues to make vaccines that contradict the expert guidelines.
Adverse Events
Currently, the occurrence of adverse reactions associated with the leptospirosis vaccine is often dismissed or ignored. AAHA noted, “Based on available information, adverse reactions to leptospiral vaccines seem to be rare, with < 53 adverse events per 10,000 doses.” However, this brief statement did not provide the complete context.
According to the 2015 study by Yao et al. the organization referenced, “The Incident Reports/10,000 dogs for owner-reported postvaccination Adverse Events was 26.3/10,000, whereas that for dogs that received a Leptospira vaccine alone or with other vaccines was 53.0/10,000.”
The updated ACVIM statement points to the study produced by Moore et al. in 2023, which asserts, “While vaccine safety concerns are often expressed anecdotally about leptospirosis vaccines, crude AE rates in this study were not greater for it than for DA2PP (distemper, adenovirus-2, parvovirus, parainfluenza) or rabies vaccines.”
Yes; according to their statistics, this is a true statement.
However, Moore’s study removed the key qualifier, bacterin. Indeed, Dr. Ronald Schultz has said, “In addition, of all the bacterin vaccines, leptospirosis causes the most adverse reactions.”
The popular bacterin (bacterial) vaccines for dogs are Bordetella, Lyme, and Leptospirosis. DA2PP and rabies are vaccines against viruses, not bacteria.
So, according to Moore’s statistics regarding bacterin vaccines specifically, Bordetella had the lowest number of reported AEs per doses administered, followed by Lyme, and leptospirosis had the greatest. Thus, it proves Dr. Schultz’s comment to be correct.
Our View
We have demonstrated a lack of unified and universal data to support this call for leptospirosis vaccination because mandatory reporting varies by region, research into properly vaccinated dogs that develop disease does not exist, uniform testing for infection is not applied based on public reports, the vaccination confusion, and uncertainty about adverse events to the leptospirosis vaccine.
The NYCDHMH puts it simply, “Based on our findings, leptospirosis appears to be uncommon in NYC dogs.”
We do not recommend the Leptospira vaccines for general use. However, the ultimate decision here lies with companion pet parents and their veterinarians based on a companion dog’s lifestyle or environment. The established vaccination guideline should be followed. Again, that guideline is two doses 2-4 weeks apart and then booster once annually. If the annual booster lapses, the dog will need to start the protocol again from the beginning. We also prefer that Leptospira vaccines be separated from other vaccinations and that the youngest age to start it is 14 weeks.