What is leptospirosis?

Leptospirosis is a spiral shaped bacterium that can infect many different animals, including dogs.  Leptospirosis is a zoonotic disease, meaning it can spread to other animals as well as people.  There are more than 250 serovars of the bacterium, all of which can cause infection.  A serovar is a subspecies of the bacterium.  In the United States, the top species and its associated serovar are as follows:
 
 

Genus and Species	Serovar	Maintenance Host(s)
Leptospira interrogans	canicola	dogs
Leptospira interrogans	icterohaemorrhagiae	rats
Leptospira interrogans	Pomona	pigs, cattle, skunks, opossums
Leptospira interrogans	bratislava	pigs, horses (?)
Leptospira kirschneri	grippotyphosa	raccoons, skunks, opossums

How do dogs get the infection?

Dogs become infected when leptospires enter the body after being deposited on mucous membranes (e.g. gum tissue) or damaged skin (e.g. a cut).  The bacteria are mainly shed in the urine (see below).  The bacteria will then incubate in the body for 3-20 days before starting to circulate in the blood.  During this period, leptospires enter and replicate in many of the body's tissues, including the kidneys, liver, spleen, reproductive tract, nervous system and eyes.

How common is leptospirosis?

Leptospiral serovars prevalent in an area are associated with one or more maintenance host(s).  Maintenance hosts serve as reservoirs of infection.  Maintenance hosts can be wild or domestic animals.  Maintenance hosts shed the bacteria in their urine for months to years after becoming infected.  Indirect or direct contact of contaminated urine from a maintenance host will infect another animal species, called an incidental host.  Incidental hosts can become quite ill.  However, assuming the incidental host survives the infection, it will only shed the bacteria in its urine for a short period of time (days to several weeks). Thus, an incidental host is not a very important reservoir of the bacteria.  For example, a dog infected with serovar grippotyphosa became infected because he/she was exposed to raccoon, skunk, or opossum urine; not urine from another dog.  A dog infected with serovar canicola, however, did get the infection because he/she was exposed to urine from a dog with the disease.  There is no reliable data on the prevalence of canine leptospirosis in different areas of the country.  Prevention is based on decreasing contact between dogs and reservoir hosts as well as vaccinations if needed.  In Colorado, the most commonly reported serovar is grippotyphosa.  Urban and rural dogs can acquire the disease.  The bacteria can live outside the host for many months under the right conditions.  These conditions consist of damp or wet areas protected from sunlight and harsh temperatures.

What are the signs of leptospirosis?

Infections can cause a variety of signs and symptoms and vary from dog to dog.  Signs may include anorexia, fever, vomiting, diarrhea, abdominal discomfort, increased water consumption, increased urination (volume and frequency), bloody urine, jaundice appearance (yellowing of the gums and skin), nose bleeds, joint and/or muscle pain, eye and/or nasal discharge, and coughing.  Most dogs will have only a few of these signs, not all the them.  A significant number of infected dogs will not have recognizable clinical symptoms that warrant a visit to a veterinarian.

How does one diagnose leptospirosis in a dog?

The nonspecific nature of the signs and blood work results makes diagnosing leptospirosis very difficult.  Just because a dog has kidney or liver failure, or coughing, or joint pain, etc., does not mean the dog has leptospirosis.  Many diseases can cause the same clinical signs.  However, leptospirosis should be considered as a possible cause in animals that present with the above mentioned signs, especially if there is possible exposure to one of the maintenance hosts listed above.  Special diagnostic tests are needed to detect Leptospira antibodies in the body and to detect the organism in tissues or body fluids (urine).  Interpreting antibody titers is complicated when it comes to leptospirosis.  In the United States, only antibodies against the serovars canicola, icterohaemorrhagiae, grippotyphosa, Pomona, hardjo, and bratislava are tested for.  A low positive titer can mean infection, or not.  The higher the titer, the more likely the animal has the infection.  Vaccination to leptospirosis can cause low positive results which makes interpretation even more confusing.  Most cases will require rechecking a titer sample 2 weeks after the first titer test in order to check for rising titers.  A rising titer is more indicative of a positive infection.  Culturing the bacteria is not feasible in the majority of cases because most laboratories are not able to perform that test.  Also, the bacteria is not very stable in urine samples.  A culture must be performed in less than 24 hours which also makes this type of test unfeasible.  The other test used to discern infection is the urine PCR test.  The urine must be collected prior to the administration of antibiotics.  The test is fairly sensitive for detecting leptospirosis.  However, it is not 100% accurate and thus again, makes diagnosis difficult.  As of now, the protocol for determining if your dog has leptospirosis is a series of blood titer tests and the urine PCR test.

What is the treatment?

Antibiotics are reasonably effective if they are begun promptly.  However, most of these dogs are so sick that hospitalization and intensive nursing care, including intravenous fluids, is necessary.  Even if dogs do recover from the infection, they may be left with chronic kidney insufficiency.

How can leptospirosis be prevented?

The cornerstone of prevention is through a vaccine.  However, there is much controversy regarding using the vaccine in dogs.  First, the vaccine does not cover for all 250 serovars.  The vaccine only protects against four serovars (canicola, grippotyphosa, icterohaemorrhagiae, and Pomona).  Thus, your dog is not protected from the disease 100%.  Second, there is a higher rate of vaccine reaction with this vaccine versus the distemper or rabies vaccines.  Third, most veterinarians agree that the immunity the vaccine gives does not last a full year.  The general recommendation for giving the vaccine is to give it to dogs that live in high endemic areas, hunting dogs, farm dogs, dogs allowed to roam, dogs living in suburban areas with high wildlife traffic in the yards, and dogs living in urban areas where rodents are a significant problem.  Most of all, avoiding contact with wildlife is paramount.

Leptospirosis in Humans

Humans are susceptible to infection and the route of infection is by direct or indirect exposure to urine from an infected animal.  If your dog is diagnosed with leptospirosis, great care should be taken in handling your dog's body fluids, especially its urine.  Wearing gloves is essential whenever urine and soiled bedding is handled.  Goggles for eye protection may also be needed.  The bacteria are susceptible to disinfectants and contaminated areas can be cleaned.  Sunlight will destroy the bacteria in the yard.  Allow only a small area of the yard to be used by the pet in order to minimize yard contamination.  Using a dilute bleach solution to clean household areas will suffice in destroying the bacteria.  Humans may experience flu like symptoms or become severely ill and die.  Thus, great caution is needed in handling infected dogs.