Canine Leptospirosis

Summertime’s warm weather means that dogs get to spend more time playing outside. A great majority of dogs love to swim at the cottage and explore the different smells the environment has to offer. Summertime also means that local wildlife, such as raccoons and skunks, are out and about looking for food and raising their families. Unfortunately, as harmless as most of these critters are, they often carry many infectious organisms transmissible to other animals and humans. One of these organisms has recently re-emerged in the companion animal world, an agent that causes the disease known as Leptospirosis.

The bacterium Leptospira comes in an assorted variety (known as “serovars”). Each serovar is host-adapted, meaning it preferentially infects a selected mammalian species and uses it as its carrier species.

For example, the host species for the serovar “grippotyphosa” are raccoons and skunks. When an animal belonging to the host species is infected, the disease is usually mild and may go unnoticed. The animal can live its lifetime unaffected symptomatically by this bacterium, but at the same time can be continuously shedding the organism. If the same serovar, shed from the host animal, goes on to infect an animal that is not a host species, such as a dog, the severity of disease produced can range from undetectable to severe. There are several serovars that are known to cause disease in dogs, and these are most commonly found in raccoons, skunks, voles, mice, cattle, and pigs.

Leptospirosis was an important disease affecting domestic animals in the 1970’s. Thanks to an increased awareness and a rigorous vaccination protocol, the incidence of disease has decreased over the years. However, dogs can become severely ill with the new serovars that have recently emerged, prompting some concern in the veterinary community.

The bacterium survives best in warm, moist weather, and as a result, Leptospirosis is most commonly diagnosed in the spring and autumn. The organism is shed in the urine of infected animals and can survive in the environment, under ideal conditions, for up to six weeks. Dogs may become infected by contact with contaminated water bowls, puddles and streams, wet grass, soil, or food. Infection requires only ingestion of the bacterium or contact with mucous membranes such as the gums or nose. It has been reported that the incidence of infection is highest in large-breed dogs, such as Retrievers, Shepherds, mixed breeds, and working dogs. This, however, is likely related to the amount of time the dog spends outdoors, since larger breeds tend to enjoy activities such as swimming a little more than smaller breeds. Infection can occur in both suburban and rural areas, with a higher incidence reported in suburban locations.

The majority of Leptospirosis infections in dogs are subclinical, meaning no obvious symptoms of illness are present. These infections go unnoticed and the dog may exhibit no more than some “flu” symptoms for one or two days. More serious infections, however, are not uncommon and aggressive treatment is necessary. Animals may not show signs of disease for several weeks after infection with the bacterium. The organism causes damage to the blood vessels, especially in the kidney and liver. When serious, kidney failure and severe liver disease can occur. The dog may show non-specific signs of disease, such as vomiting, dehydration, fever, loss of appetite, or sudden collapse. The mucous membranes may develop a yellow tinge (indicating liver disease) and the dog’s water intake may suddenly increase (and subsequently urination). Permanent organ failure and even death can result if the disease goes untreated. In general, the earlier the disease is diagnosed and treatment started, the better the prognosis for preserving organ function.

Diagnosis of the infection is not always easy and can require several consecutive blood tests for confirmation. Your veterinarian will check for blood abnormalities and signs of organ dysfunction, paying particular attention to the liver and kidneys. A specific screen for antibodies against the Leptospira serovars will also be done, which appear in the blood seven to ten days after infection and continue to rise for a little while afterwards. While waiting for the test results, your veterinarian may begin treatment after making a presumptive diagnosis based or your dog’s history and symptoms.

As Leptospirosis can result in kidney failure and severe liver disease, immediate and aggressive treatment with intravenous fluids and a long course of antibiotics is required. A lengthy stay in the hospital may be necessary until the dog is stable enough to maintain adequate hydration on its own. The antibiotics used are quite effective if a dog is treated early on in the infection, with a good chance of recovery if no organ damage has occurred.

Finally, it should be noted that Leptospirosis is zoonotic, meaning that it can be transmitted to humans. This can occur through contamination of the environment or via an infected dog shedding the organism. It is considered rare, however, for a human to acquire the disease from an infected dog, and is usually related to occupational hazard (such as veterinarians and wildlife rehabilitators). In humans, most cases are mild and some may even go unnoticed. Rarely, an infected person may experience severe disease with symptoms such as sudden fever and chills, severe headache, vomiting, muscle pains, and/or abdominal pain. If left untreated, meningitis, kidney failure, and liver disease can develop, much like in dogs. Sanitation is likely the most effective way to prevent transmission from an infected dog to human, with protective clothing, frequent hand washing, and disinfection of possibly contaminated surfaces.

Since climate change results in warmer temperatures and infection with Leptospira can be so devastating, vaccination of dogs at risk is highly recommended. There is now a widely used vaccine for the most important Leptospira serovars, and its efficacy has been reported to be quite good. The vaccine provides one year of protection, and dogs are boostered annually along with their other vaccines. Rodent and wildlife control in the area is also important to keep the risk of infection low. It is difficult and not practical to keep a dog from swimming, but it is recommended that standing water be removed and that the dog’s water and food bowl not be left outside. With all the preventative measures in place, you can be sure that your dog’s risk of infection will be low and that you are doing the best you can to prevent Leptospirosis.

By Beverly Wong – Pets.ca writer