Leptospirosis in Dogs

Filed Under: Dogs, Diseases

Do you have a young dog that is suddenly in renal failure? Is your dog unvaccinated? Has your part of the country been recently subjected to flooding? Maybe Leptospirosis should be on your list of disease differentials.

Leptospirosis is a bacterial infection of mammals that is world-wide in distribution. The disease is caused by a spirochete, which is a tightly-coiled organism that is highly motile with characteristic hooked ends. The infection can produce a severe infection in humans (zoonotic infection) and dogs that may result in multiorgan failure with a high mortality rate (death). Leptospirosis has been classified as an emerging disease due to outbreaks following recreational activities and natural disasters.

There are two species of Leptospira: Leptospira interrogans, which is the species that is pathogenic to humans and a variety of mammals, and Leptospira biflexa, which is saprophytic and nonpathogenic (incapable of causing disease). The species L. interrogans has been subclassified into several serovars based on antigenic similarities and differences. Currently there have been more than 200 serovars identified and 23 pathogenic (capable of causing disease) serogroups. To date, more than 180 different mammalian species have been found harboring Leptospirosis. The four most commonly implemented serovars in canine disease include canicola, icterohemorrhagiae, grippotyphosa, and pomona. Other serovars, especially bratislava, have also been implicated on occasion.

Transmission can occur via direct or indirect contact with infected host urine or other bodily excretion. Only mammals are capable of transmitting the bacteria, although birds and reptiles have also been cultured with leptospira bacteria.

The bacteria are capable of penetrating intact mucous membranes. The kidneys are invaded resulting in acute and possibly fatal renal damage. Leptospira organisms replicate in the renal tubules of the host and are excreted in the urine. Other organs that may become infected include the liver, lungs, pancreas, uterus, and eyes. The incubation period is from 2 to 12 days.

Infection most commonly occurs in late summer because the bacteria need a warm, moist environment in which to survive outside the host. Once excreted from their mammalian host, leptospires can survive in a fairly moist environment for months to years. The optimal conditions for the organisms’ survival is a temperature in the range of 28º to 38ºC in water with a pH range of 6.2 to 8.0. Spirochete survival in water will be inhibited by the presence of sewage contamination or a high acidity or salinity (salt content) to the water. Numerous outbreaks of the disease have been associated with flooding.

Clinical disease in dogs may vary and depend upon the age of the pet, the immunologic status of the animal, and the serovar of the leptospira. With an acute infection, early clinical signs include fever, stiffness, vomiting, dehydration, bright orange urine (bilirubinuria), and pulmonary hemorrhage. In severe cases renal failure and shock may later develop. Subacute infections are characterized by anorexia, depression, and respiratory effects including conjunctivitis and rhinitis. Renal function may show a decline followed by weight loss, vomiting, polydipsia (increase in thirst), and polyuria (increase in urination). Icterus will develop when the liver is affected. Additional signs of liver involvement include ascites (fluid accumulation in the abdomen) and encephalopathy. Meningitis and uveitis are infrequent complications of infection. Typically death occurs due to secondary renal (kidney) failure.

The treatment of choice is immediate doxycycline therapy instead of the once-common protocol of first using penicillin followed by doxycycline. Doxycycline should not be used in pregnant individuals or the very young due to unsightly staining of the teeth secondary to its use. Ceftriaxone and cefotaxime have also been found to be effective in humans. It has been determined that doxycycline will reduce the zoonotic potential of infected urine from the outset of therapy. Early antibiotic therapy will also minimize organ damage. The risk to people becomes minimal within 24 hours of starting doxycycline therapy. Additional precautions should be taken when dealing with infected bodily fluids like wearing gloves and goggles to avoid the splashing of urine onto mucous membranes.

Additional treatment should include aggressive fluid therapy and the balancing of electrolytes.

Reported survival rates are 80% in most studies. Patients presented late in the course of the disease, especially those with impaired renal function and anuria (inability to manufacture urine), are typically responsible for the high mortality rates.

Leptospirosis spirochetes may not be viewed by a regular microscope. Unstained organisms may only be viewed by a darkfield or phase-contrast microscope. With histologic, or tissue, samples the organism may be identified by silver staining methods. Definitive diagnosis is typically based upon serologic detection of anti-Leptospira antibodies. Typically antibodies may be detected in blood samples 5 to 7 days after the onset of symptoms.

Prevention may be difficult, especially when wild animal carriers may roam freely. Dogs should be kept away from standing water such as large puddles or ponds. Even moist, shaded grass could be a source of infection. Flood waters should be avoided.

Bacterins (a similar concept to a vaccine but contains bacterial instead of viral components) are now available from two to four serotypes: canicola, icterohaemorrhagiae, Pomona, and grippotyphosa. Dogs are considered to be the reservoir host for the canicola serovar. Canicola and icterohaemorrhagiae are the most commonly identified serovars found in canine infections. The bacterin appears to be effective for only one year following inoculation. There does not appear to be good cross-immunity between serovars, and therefore, vaccinated dogs may be susceptible to infection with additional serotypes not included in the original vaccination.

The Leptospira vaccine is considered to be a non-core vaccine. This means the decision to use the vaccine should be tailored for each patient based upon their risk of exposure, the safety of the vaccine, and the health of the patient. The German shepherd dog appears more susceptible to infection. Vaccine reactions to the bacterin are not uncommon, especially in smaller and toy breeds of dogs. Dogs are not the definitive host for any of the pathogenic serovars other than canicola. Definitive hosts for the other commonly seen serovars causing disease in the dog include rodents, skunks, raccoons, and deer.

Environmental control shows that the bacteria are sensitive to many types of detergents. A 1:40 bleach solution is adequate for the elimination of the organism. Control of rodents may decrease environmental contamination and therefore decrease the risk of transmission to susceptible hosts.

References:

Barr, Stephen, BVSC, MVS, PhD, DACVIM. “Canine Leptospirosis: What Veterinarians Need to Know”. Insights in Veterinary Medicine. August 2007.

Guerra, Marta. “Zoonosis Update, Leptospirosis.” JAVMA, Vol. 234, No. 4, February 15, 2009. Pp. 472-477.

Kahn, Cynthia, Ed. The Merck Veterinary Manual. 9th Edition. Merial Limited. P. 527-528.

Topics: bacteria, vaccinations

Symptoms: kidney damage, kidney failure

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