Sunday, January 27, 2008

Leptospirosis in Dogs

Leptospira is a gram negative spirochete bacteria that is very common in certain parts of the United States. There are over 250 different serovars (subtypes) and it is a zoonotic (meaning that people can contract it) disease. There has been increased prevalence of Leptospira disease since 1983 due to urbanization of rural areas, increasing contact between dogs and wildlife.

Leptospira penetrates through the mucosal membranes—eyes, conjunctiva, mouth, any breaks in the skin. After disseminating in the blood, leptospira tends to target the liver and kidneys but can also go to other organs in the body such as the spleen and central nervous system (CNS).

A reservoir host is an animal that harbors the organism with no clinical signs of disease. The organism is shed in high quantities in the urine. Dogs, rats, pigs, cattle, raccoons, deer, skunks, possums and small rodents (mice) can all serve as reservoir hosts for the different serovars. Man and dog can be an incidental host, in which clinical disease occurs, but the organism is not shed in high quantities.

Leptospira generally targets adult animals one to six years of age, but all ages can be affected. Dogs who are most commonly infected are those who are outdoors with exposure to surface water, dogs over 15 pounds, males, hounds, and hunting, working, or herding breeds. However, all dogs are susceptible. If a house or apartment has a problem with mice or rats, dogs and humans that live there are at risk of exposure.

Environmental risk factors include rural areas; housing developments that encroach on areas previously inhabited only by wildlife, leading to greater exposure of dogs to this organism; and areas with poor drainage or that frequently flood.

Leptospirosis can cause kidney failure, inflammation/toxicity of the liver (hepatitis), inflammation of the blood vessels (vasculitis) causing hemorrhage, inflammation of muscle tissue (myositis and myalgia), inflammation in the eye (uveitis) causing blindness, inflammation in the nervous system (meningitis), abortion in food animals and immune mediated illness with chronic disease.

The most common route of disease transmission is indirect, by contact with stagnant or slow moving water contaminated by urine . Wildlife urinate in a small pond or lake that people and dogs swim in. Leptospira organisms are able to survive for long periods in surface water. Transmission can also occur by direct contact with infected urine; bacteria enter through damaged skin or mucous membranes.

Prevalence of the disease varies markedly and usually correlates with rainfall and warm weather. Incidental host infections can be either sporadic or epidemic. The organism can live for long periods of time in warm water. Freezing will kill it. It is endemic in the wildlife population with infection rates as high as 30-40 percent.

In dogs, the incubation period (time from exposure to signs of clinical disease) varies between 3 and 20 days; therefore, this is the relevant period of exposure that must be considered. The most common signs of disease early on are anorexia, lethargy, vomiting and fever. Also seen are weight loss, increased drinking and urinating (polydipsia/polyuria), diarrhea, abdominal/lumbar pain, icterus/jaundice, stiffness/reluctance to walk (myalgia), enlarged kidneys (renomegaly), small areas of hemorrhage (petechia) or sometimes severe hemorrhage, and low platelet count (thrombocytopenia).

Diagnosis can be made from several different types of diagnostic tests with the most common test involving serology. Treatment involves supportive care and antibiotics. Dogs that recover are carriers of the disease and still shed the organisms when they go home.

Prognosis depends upon how early treatment begins. Diagnosis of this disease can sometimes be difficult if the patient is seen early in the disease before increases in kidney and liver values occur and the symptoms are vague. Even after treatment with antibiotics, liver or kidney disease may still develop. Up to 25% of infected dogs will not survive the initial infection. Thirty-three to 40% of infected dogs will develop chronic renal failure.

Leptospira bratislava and L. icterohemorrhagia were the leading serovars causing disease in the mid 1970’s. Since the mid 1990’s, Leptospira grippotyphosa and L. pomona are the leading infectious causes of acute renal failure in dogs.

Prevention in animals:

Avoid exposure
Isolate suspected cases in the hospital
Quarantine carriers (shedders) in the home or kennel

Owners of infected pets need to wear gloves and masks when cleaning cages and handling bodily fluids/waste. Do not hose down cages of infected animals because it can aerosolize the organism.

Vaccination of dogs for leptospirosis has been a controversial issue for the past several years. Early vaccines protected against strains bratislava and canicola. However, there is no cross protection between the various serovars in vaccines. It was also suspected that older leptospira vaccines caused a large number of vaccines reactions. It has been determined that it was the cellular debris in the vaccine (contaminants) and not the leptospira which caused the reaction.
Fort Dodge’s vaccine, Duramune Max 5-CvK/4L, is a killed vaccine that protects against the four most common serovars: L. grippotyphosa, L. pomona, L. icterohemorrhagia, and L. cannicola. This newer vaccine incorporates state of the art sub-unit technology. This involves separating the surface immunogens from the extraneous cellular debris and reducing the level of contaminants in the vaccine; thereby reducing the potential for adverse reactions while maintaining immunogenicity.

Efficacy studies with the vaccine demonstrated a 90% reduction in clinical signs in the vaccinated animals compared to control animals (those exposed to disease with no prior vaccination). All vaccinated animals were able to clear the infection before it could cause disease. Vaccination with the new Fort Dodge vaccine also prevented clinical shedding by infected dogs.

Numerous safety studies demonstrated less than 1.1% incidence of adverse effects (vaccine reactions) from vaccination. Adverse reactions can include injection site pain and swelling less than 24 hours duration, pruritis (itching) at the injection site immediately, lethargy for one day, increased thirst and anaphylaxis (shock). Banfield Veterinary Hospitals performed their own safety study involving 144, 387 doses of Duramune Max5-CvK/4L to their patients. They estimated less than 0.27% reaction rate over all with 0.01% rate of anaphylaxis. Of those patients that had reactions, small breeds did have a slightly higher reaction rate of 1% compared to 0.25% with large and mixed breed dogs. Interestingly enough, their rabies vaccination (brand not stated) had a slightly higher reaction rate than did the leptospira vaccine. Vaccination with DHPPC (again, brand used not stated) produced the same percentage of reactions as did those vaccinated for leptospira.

Who should be vaccinated? It is recommended that all dogs be vaccinated because of the zoonotic potential of the disease. We strongly recommend that all dogs used for hunting and working, dogs taken camping, dogs living in rural/farm areas, and dogs with access to ponds, lakes, or drainage ditches be vaccinated. Dogs housed where there are problems with rodents, raccoons and wildlife exposure should also be vaccinated.

Vaccines protecting against viral diseases, such as Parvovirus and Distemper virus, are given once every three years after an initial puppy series and a booster vaccination one year later. However, Leptospira is a bacterin, not a virus, and it needs to be given more frequently. Leptospira vaccine initially should be given two times at three weeks apart and then annually. Those dogs that receieved the older leptospira vaccines should still receive the two boosters of the newer vaccine because of the added serovars.

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Article donated by the Claws & Paws Veterinary Hospital. For further information visit

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