Leptospirosis is a bacterial disease; the bacteria are shed in urine of infected animals. The disease is transmitted to animals and humans by contact of abraded skin or mucous membranes with infected urine. Transmission can also occur through bite wounds, venerally, transplacentally and by ingestion of infected tissue. Leptospirosis can be a serious disease in dogs and humans. In humans, flu like symptoms are most common, however multi-organ involvement can occur and deaths are estimated at 5 to 15 % of human cases. It is relatively rare in humans with an estimated 100-200 cases occurring in the United States annually, about half in Hawaii. Like humans the disease in dogs varies from mild illness to multi-organ involvement. Renal failure is the most common serious manifestation in humans and dogs. High antibody titers in dogs have been found in northern California, Oregon, Washington, the upper Midwest, parts of Colorado and Texas, Mid Atlantic coastal regions and the Southeastern US.
Leptospira are motile spirochete bacteria that commonly live in water, soil and infected animals. There are pathogenic and non-pathogenic species. Twenty three pathogenic serovars have been identified. Many domestic animals can be infected including cattle, pigs, horses and dogs. The disease is rare in cats although they may be carriers. Dogs can be infected by contact with infected dogs or wildlife. Known wildlife carriers include rats, raccoons, skunks, squirrels, opossums, deer and sea lions. The study of the relationship of the different serovars are ongoing, will be dynamic and problematic for vaccine development. The focus of this summary will be on dogs in the United States. All pathogenic organisms recognized in the United States are in the species leptospira interrogans and kirchneri. Serovar groups include Icterohaemorrhagiae, Canicola, Pomona, Bratislava, Ballum and Grippotyphosa.
Clinical signs of Leptospirosis vary according to the age and immunity of the dog. Infection in some dogs signs may be mild or go unrecognized. These dogs may shed organisms in their urine presenting the possibility of infecting other dogs and humans. Leptospira can survive in a moist environment for months causing an incidenced increased warm wet weather and flooding. Initially organism will replicate in the blood stream and then spread to other organs. Early signs of infection include a fever (103-104) possibly with shivering and muscle tenderness, lethargy and loss of appetite. Renal disease is the most common presentation. Clinical signs in these dogs may include an increase in thirst and urination, or anuria (no urine production) dehydration, vomiting, diarrhea and abdominal pain. If sufficient renal tissue is spared recovery is possible and these dogs may shed organisms in their urine for some time. Toxins from the organism can cause liver damage, resulting in icterus and bleeding disorders. Acute lung injury can occur resulting in vasculitis and fluid accumulation in the lungs, these dogs will have difficulty breathing. The gastrointestinal tract can become inflamed causing intussuseption and small bowel obstruction. Uveitis (inflammation of vasculature of the eye), meningitis, and abortions are also possible. Complete blood counts, serum chemistries, radiographs or ultrasound may be needed depending on the organs involved. Leptospirosis can be treated with the antibiotic, doxycycline. Supportive therapies including IV fluids, plasma, blood transfusion, and hemodialysis may be required. The earlier the disease is detected and antibiotics are started the better.
Confirming a diagnosis of Leptospirosis can be difficult. The organism can be cultured from blood early in infection and urine later providing a definitive diagnosis. Culturing these organisms is technically difficult, requiring special handling of specimens, special growth media and long culture times. The organism can sometimes be seen in urine. Newer PCR (polymerase chain reaction) assays which detect the nucleic acid of the organism are commercially available. PCR assays can be run on blood and urine. Early infection can be detected with this technique. Serum can be tested for the presence of antibodies (titers) to a panel of five serovars. Vaccine titers or titer from previous infection may be present, confusing the diagnosis. Paired samples taken 7 to 14 days apart showing a four-fold increase in titer are needed to confirm a diagnosis. A single sample with a very high titers is suggestive of but does not confirm infection.
Leptospirosis vaccines are called bacterins , and are made from whole killed organisms. Early vaccines were made from bacteria grown in serum. Proteins from the serum were present in the vaccine and thought to be the cause of vaccination reactions that occurred with these products. Current vaccines are produced in protein free media and /or are washed to remove contaminating proteins. Current 4- way vaccines are effective against Icterohaemorrhagiae, Canicola, Pomona and Grippotyphosa. Current vaccines are thought to be effective for at least 12 months and prevent colonization and shedding. Hunting dogs are considered at risk, however urban dogs with exposure to urban wildlife (raccoons, rats, etc) are also at risk. Initial vaccination requires two doses and annual revaccination is recommended.
Pain or stinging at the injection site has been reported. The most common reaction to vaccination is Type I Hypersensitivity. Symptoms include facial edema, itching, weakness, difficulty breathing and bloody diarrhea. Symptoms may occur up to 8 hours after injection. Your veterinarian can treat these reactions with antihistamines and supportive therapy if needed. Any dog that has allergies or has had previous vaccine reactions is at increased risk. Pretreatment with antihistamines may be helpful to these dogs. Multiple vaccines should not be given at once to these dogs. Risk benefit should be evaluated on an individual basis. Monitoring of titers is not thought to be useful in this case. Immunity to Leptospirosis and the role of cell mediated immunity is not fully understood. Other unknown immunologic factors may contribute to immunity. Therefore it cannot be assumed that a high titer is protective or that a low titer is unprotective.
Decoding the Leptospirosis Puzzle, G E Moore etal. Proceeding North American Veterinary Conference 2011.
2010 ACVIM Small Animal Consensus Statement on Leptospirosis: Diagnosis,Epidemiology, Treatment, and Prevention JE Skyes etal. J VET Med 2011;25:1-13