Leptospirosis is a disease that many dog owners are familiar with by name, as it is commonly included in their pet’s vaccine schedule and reminders. However, as a veterinarian I find that most pet parents are unfamiliar with what leptospirosis is or how it is spread. Here we will overview some basic information about leptospirosis so that we can understand the purpose and benefit of vaccination.
What is Leptospirosis?
Leptospirosis is the disease caused by spirochete bacteria of the genus Leptospira. There are at least 16 species of bacteria classified as Leptospira, with each species including potentially over one hundred serovars, or subgroups. This is significant because these different serovars of Leptospira bacteria have different antigens (surface proteins), so vaccines may need to be tailored to recognize these different antigens in order to be effective. In practical terms, the vaccine your pet may be receiving for protection against leptospirosis may include protection against several serovars, but will never be completely protective against all strains of leptospirosis. Dogs appear to be affected more commonly by the following serovars: grippotyphosa, braislava, canicola, icterohaemorrhagiae, and pomona.
How is Leptospirosis spread?
Leptospira bacteria thrive in warm, moist environments, commonly stagnant or slow moving water. They can survive for months in wet conditions without a host, and peak incidence of leptospirosis in dogs occurs between July and November, often after periods of rainfall or flooding. Leptospira bacteria are shed in the urine of infected animals, thus it tends to end up accumulating in still water from runoff. Animals become infected when the bacteria enters broken skin. Bite wounds, reproductive secretions, or consumption of infected tissue (eating an infected animal), and contact of broken skin with contaminated water all can transmit infection.
Who is affected by Leptospirosis?
It is common for veterinarians to recommend vaccination against leptospirosis based on lifestyle and exposure risks. In the past, it was often not recommended unless the pet was very active outdoors (e.g. roaming or working outdoor dogs, especially if swimming in natural bodies of water). Today this is not the case; Disease incidence appears to be increasing in suburban and urban environments due to spread by rodent and urban wildlife populations, and vaccination may now be recommended to all dogs – even the little Yorkshire terrier walking down the city street.
Leptospirosis is more prevalent in warm, tropical environments throughout the world. In the United States, dogs are affected in Hawaii, West coast states, the upper Midwest, the Northeast, and mid-Atlantic coastal regions.
Many different species of animals (e.g. dog, mouse, rat, raccoon, cow, pig, horses and humans) can be infected by leptospira bacteria, with certain serovars affecting different species of animals. Younger animals seem to be more severely affected than older animals, and there may be a genetic predisposition for infection in German Shepherd dogs.
Of note, leptospirosis is considered a zoonotic disease, as humans can contract the infection from contact with contaminated animal urine. Veterinarians, animal caretakers, sewer workers, and farmers may be at increased risk due to exposure.
How do Leptospira bacteria cause disease?
Once the bacteria enter the bloodstream, it spreads quickly and begins to replicate in the kidneys. This causes inflammation in the kidneys and can potentially cause acute renal failure. Some serovars of leptospire can cause other organ failure, most commonly the liver. The leptospires produce a toxin which can cause liver damage and acute or chronic hepatitis. Lung tissue can also be injured by the toxin, secondary to vasculitis (fluid leaking from blood vessels).
What are the signs of leptospirosis?
Leptospirosis can be marked by fever, joint pain, loss of appetite, nausea and lethargy. Excessive drinking and urination may be secondary to kidney damage, typically starting about a week after the fever. Jaundice and bleeding disorders may be caused secondary to liver damage, resulting in bruises, hemorrhaging, epistaxis (bleeding from the nose), bloody stool or vomit.
How is leptospirosis diagnosed?
Basic blood chemistry can be performed to support a clinical suspicion of leptospirosis before more advanced testing is ordered by the veterinarian. Increased kidney and liver enzymes will often be noted. Blood tests to detect antibodies against Leptospira can be performed. An initial titer of 1:800 or greater supports a positive diagnosis, a second antibody titer must be performed between 2 and 4 weeks later. If the second titer shows a four-fold increase, the diagnosis of leptospirosis is confirmed. Unfortunately, vaccination may affect test results since vaccines cause antibody production. If a dog was vaccinated within the past 3 months, testing may be difficult to interpret due to their high antibody level. If antibodies are detected against a leptospire serovar for which there is no vaccine, it must be a positive test result and the individual has leptospirosis. There is also a PCR test (polymerase chain reaction test), which detects Leptospire bacterial DNA, enabling the lab to detect even small amounts of bacteria present. The PCR test is an excellent choice for a diagnostic test, especially if there has been recent vaccination in an individual.
Urine testing can also be performed, but because the bacteria may be shed only intermittently, detecting the infection may be inconsistent. The bacteria can be seen using darkfield microscopy, which uses a dark background to highlight the paler leptospire organisms. Unfortunately, darkfield microscopy is not readily available to most animal hospitals and the typical urine culture tends not to be very successful.
Kidney biopsy may be also performed, but this is obviously a much more invasive procedure.
How is leptospirosis treated?
Patients with leptospirosis are treated with antibiotics, commonly penicillin and a tetracycline (such as doxycycline). They also need supportive care for their fever and other signs (e.g. blood transfusions if bleeding disorders occur, anti-emetics if vomiting), and require intravenous fluids to maintain good blood flow to the injured kidneys. With aggressive and appropriate treatment, 80 – 90% recovery rate in dogs is reported.
It is also very important to clean the patient’s environment and anywhere the contaminated urine may have touched. An iodine-based cleaner should be used anywhere the urine may have contacted, and gloves should be worn by anyone touching the patient and cleaning up after them.
Conclusions: Should I vaccinate my dog against leptospirosis?
Leptospirosis is a very serious disease and may be on the rise. Infected individuals may quickly develop signs of illness and have extensive organ damage in a short time. The vaccines available are against the species Leptospira interrogans, including only the serovars canicola, grippotyphosa, pomona and icterohaemorragiae (some vaccines have all four serovars, others only have two of the four available). Though there are other serovars that can cause infection, these are the more common serovars causing disease in dogs. Due to the use of the vaccine for many years, it is difficult to determine incidence of the disease in environment, but reported cases of leptospirosis caused by these four serovars have decreased (as opposed to those serovars for which no vaccine exist). The vaccines are associated with allergic reactions in some patients, causing signs like hives, facial swelling, and rarely life-threatening anaphylaxis. If a patient has a history of significant vaccine reaction, it may be recommended to avoid this particular vaccination. Otherwise, for most dogs it is a useful, relatively safe vaccine due to the seriousness of the disease and the potential zoonotic risk to human family members. As always, the pros and cons of vaccination should be discussed with your veterinarian about your specific pet, as every individual case may be unique.
Morgan, R., DVM, DACVIM, DACVO and Rothrock, K., DVM. Leptospirosis, from VIN libraries. January 2012
Brooks, W. Leptospirosis: Client Education, from VIN libraries. August 2011