Leptospirosis in Dogs: Part 1
Last week, reasder "dogpeople" commented, "I wonder if you could talk about another zoonotic disease… leptospirosis." Happy to oblige.
Leptospirosis is the name of the disease caused by infection with bacteria from the genus Leptospira. We know of several species of Leptospira; the most important one for dogs is L. interrogans. Unfortunately the bacteria’s genealogy doesn’t end there. Over 200 serovars (distinct variations) of L. interrogans have been identified, and the best vaccine we have available today only protects against four of the most common ones — canicola, icterohaemorrhagiae, grippotyphosa, and pomona.
While we’re on the topic of vaccination, lepto vaccines can certainly be helpful, but they have some drawbacks in addition to containing only a limited number of serovars. Immunity doesn’t always last a full 12 months, and protection against even the serovars that are included isn’t complete. Historically, lepto vaccines were also responsible for more than their fair share of adverse vaccine reactions, but with improved manufacturing techniques the newer vaccines are much safer. I don’t mean to discourage owners from vaccinating when their dogs are at risk for contracting leptospirosis, just realize that vaccinated dogs are at a lower but not negligible risk in comparison to unvaccinated dogs.
Dogs typically develop lepto after having contact with the urine of an infected animal or when they wade/swim in contaminated bodies of water, usually those that are stagnant or slowly moving. This explains why dogs living in the suburbs and rural areas are at highest risk. City dwellers should not tune out, however. Rat urine can also be a significant source of exposure. Your local veterinarian is in the best position to provide information about how common lepto infections are in your area and whether or not vaccination is in your dog’s best interests.
The lepto bacteria enter a dog’s bloodstream through small wounds in the skin, extremely wet skin, or through the mucous membranes. Lepto can also be transmitted via bite wounds, through sexual contact, across the placenta, or if a dog eats infected tissues (from infected animals). Once in the body, the bacteria travel through the blood vessels (damaging them as they go) and typically take up residence in the kidneys and sometimes the liver. Other organs (e.g., the brain and eye) can also be affected although this is relatively uncommon. Lepto bacteria secrete toxins and incite a lot of inflammation, which can result in severe tissue and organ damage wherever they end up.
The clinical signs associated with leptospirosis vary depending on the serovar involved, the severity of the infection, and where it is predominantly located. Some animals die so quickly that few symptoms are noted, but most of the time, a dog will first develop a fever and then about a week later evidence of kidney and/or liver failure dominates the clinical picture. Lethargy, poor appetite, muscle and joint pain, vomiting, increased thirst, the production of abnormally large or small amounts of urine, yellow mucous membranes, and bleeding or bruising are common. Routine blood work and a urinalysis can often diagnose kidney and liver failure, but specific tests are needed to identify leptospirosis as the underlying cause.
Dr. Jennifer Coates