Leptospirosis is an infectious disease that affects domestic dogs and many other mammals, including mice, rats, pigs, horses, opossums, raccoons, skunks, voles and cows. It also can affect people. Commonly referred to as "lepto," this illness is caused by bacteria that are classified as "spirochetes." These organisms are thin, coiled and motile, which means that they can wiggle around and move on their own. They are difficult to detect with conventional diagnostic methods. Although this is uncommon, dogs can die from leptospirosis, without showing any prior symptoms of disease. Some dogs become gravely ill and suffer permanent liver and/or kidney damage. More commonly, infected dogs never show signs of sickness. These animals are considered to be "carriers" of the Leptospira bacteria, and the infection is called "inapparent." Even though they don't become noticeably ill, carrier dogs with inapparent infections still shed the bacteria and are sources of infection for other animals. Leptospira target the kidneys and the liver of dogs – organs that are critical to survival. Although leptospirosis historically has not been a common disease in domestic dogs, it is on the rise, especially in crowded urban environments that are overrun with rats and other rodents.
Causes of Leptospirosis
Leptospirosis is an infectious disease that is caused by a group of spiral-shaped bacteria collectively called Leptospira. These microorganisms, which are classified as "spirochetes," are similar to other bacteria except that they are motile, which means that they can move around by whipping their tail-like membrane, called a "flagella." Many different types of spirochetes exist in nature. Most of them live freely in the environment and do not disturb people or pets. However, two particular types of "spirochetes" have been identified as causing disease in domestic dogs. These are Leptospira, which causes Leptospirosis, and Borrelia, which causes Lyme Disease. Leptospirosis is found all around the world, and is especially prevalent in wet, warm, tropical climates. Dogs living in icy winter conditions are unlikely to develop leptospirosis because the bacteria cannot survive freezing temperatures. The organisms also are killed by heat and prolonged dryness. Where Leptospira survive, and thrive, are in pools of standing water, puddles of urine, raw sewage, muddy patches, marshy areas and damp, neutral or slightly alkaline soil.
Wild and domestic mammals are reservoirs for the bacteria that cause leptospirosis. Carrier animals may or may not show any symptoms of being sick from their infection. Raccoons, skunks, opossums and rats are particularly common carriers. Dogs that come into contact with these animals, or their urine, have an increased chance of contracting leptospirosis. This is true not only in rural environments, but also in densely populated urban areas that are infested with rodents. Leptospira can be transmitted directly across the placenta, infecting unborn puppies. Dogs often become infected when they drink or walk through stagnant water that has been contaminated with the urine of infected animals. Leptospira can enter through a bite wound or other skin surface disruption, and it can also pass through intact skin. Dogs can become infected by eating part of a dead animal that carries the bacteria. The organisms can also be transmitted in semen. Once they penetrate abraded or intact skin or mucous membranes, Leptospira rapidly invade the dog's blood stream and spread to all parts of its body. The organisms eventually settle in the liver and/or kidneys (and sometimes in other organs, such as the spleen, eyes and brain, or in the reproductive and gastrointestinal tracts). For some unknown reason, when they lodge in the liver and kidneys, Leptospira bacteria are sheltered from the dog's immune system and are able to reproduce in large numbers.
Most of the animals that are infected with Leptospira do not become sick. They are called "carriers" of the organism, with an "inapparent" infection. However, when carriers urinate, they shed the bacteria and contaminate the surrounding environment, becoming a source of infection for other animals. They may shed the bacteria in their urine intermittently, or they may shed them for life. Dogs that spend a lot of time in wet, wooded areas frequented by wildlife, and those living in densely populated urban environments that harbor rats and other rodents, have an increased risk of contracting leptospirosis. Dogs that spend most of their time indoors, or in areas that are not likely to be contaminated by the urine of carrier animals, are much less likely to become infected. People can become infected through the same routes as dogs. Leptospirosis is a zoonotic disease.
Prevention of Leptospirosis
The most effective way to prevent leptospirosis is to restrict a dog's access to muddy marshy areas, ponds, irrigated pastures, raw sewage and standing pools of stagnant water. It is important to keep trash well-contained, especially in dense urban areas where rats and other rodents are common. Raccoons, squirrels and other wild animals should not be fed or otherwise encouraged to linger in areas frequented by domestic dogs.
Vaccination against Leptospira is another option for dog owners. Several vaccines are available to provide protection against several of the strains (serovars) of Leptospira. Unfortunately, no current vaccine protects against all of the bacterial subtypes. The conventional vaccine only provides protection against two of the common serovars: L. canicola and L. icterohaemorrhagiae. In 2004, the Ft. Dodge division of Wyeth Pharmaceuticals came out with a multi-strain leptospirosis vaccine produced from Leptospira sub-units, which reportedly provides protection against L. canicola, L. icterohaemorrhagiae, L. pomona and L. grippotyphosa. More recently, in 2010, Intervet/Schering-Plough Animal Health released a four-way canine leptospirosis vaccine that is designed to protect dogs against infection from the same four serovars as the earlier Ft. Dodge vaccine. This newer vaccine is claimed to provide protection from clinical disease and also to prevent colonization of the kidneys by the infective bacteria.
Many veterinarians, as well as the American Animal Hospital Association, consider the leptospirosis vaccines to be "non-core" vaccines for dogs. This means that they do not recommend routinely vaccinating against Leptospira, unless there is a good chance that the dog may be exposed to the infective microorganisms. The reason for this is that the leptospirosis vaccines tend to cause more allergic reactions than other common canine vaccines. These reactions can be as minor as a slight swelling at the injection site. However, they can be more serious, ranging from pain, facial swelling and hives to a potentially fatal anaphylactic reaction. There is no way to predict whether a particular dog will have an adverse reaction to any vaccine. Small breed dogs seem to be predisposed to having bad vaccine reactions. The immunity provided by current leptospirosis vaccines is short lasting; it may only protect the dog for one year, or even less. Most authorities recommend giving a leptospirosis vaccine only to dogs that live in endemic areas, or dogs that have a particular risk of contracting this infection. No vaccine is one-hundred percent effective. However, most vaccines, if administered properly and given at the right time, will tend to make the disease much milder in the vaccinated animal, if it becomes infected by the organism which the vaccine protects against.
Leptospirosis is often seen in companion animals after heavy rains in areas frequented by wildlife. Dogs should not be permitted to drink from standing pools of stagnant water. Owners of infected dogs should be especially careful to avoid contact with their urine or other bodily fluids, until their infection is fully resolved.
Effects of Leptospirosis
Leptospirosis is a bacterial infection that tends to target the kidneys and liver of domestic dogs and, less commonly, cats. Most dogs infected with Leptospira never actually become sick. However, they still carry the bacteria inside their bodies and shed it in their urine and other bodily secretions, which makes them a source of infection for other animals. Dogs that do develop clinical signs of leptospirosis will be sore, stiff and somewhat depressed. They may be reluctant to move. They also may lose their appetite, and lose weight. Basically, they will just feel lousy, and won't have their normal "get-up-and-go."
Symptoms of Leptospirosis
Owners of dogs with leptospirosis usually won't see any signs of sickness. However, occasionally they will have a very ill dog. The observable signs of this infection are highly variable. In rare cases, infected dogs die suddenly, without showing any prior symptoms of illness. Fortunately, this is extremely uncommon. In most cases, dogs infected with Leptospira don't actually become "sick." When they do become sick, their owners may notice one or more of the following clinical signs:
Loss of appetite (inappetence; anorexia)
Shivering; shaking (tremors)
Vomiting (emesis; may contain blood)
Nose bleeds (epistaxis)
Muscle tenderness; soreness; stiffness
Reluctance to rise or move
Difficulty breathing (respiratory distress; dyspnea)
Elevated respiratory rate (tachypnea)
Increased frequency of urination (pollakiuria)
Increased volume of urine output (polyuria)
Increased thirst/water intake (polydipsia)
Bloody vaginal discharge
Blood in the urine (hematuria)
Diarrhea (with or without blood)
Injected (very red) mucous membranes
Dogs at Increased Risk
Middle-aged male dogs tend to become clinically affected by leptospirosis more commonly than other dogs. Large-breed dogs also develop signs of this disease more often than smaller dogs. The association between leptospirosis and large male dogs may be more related to the free-roaming activities of those animals than to their genetic make-up. Leptospirosis is most prevalent in rural areas, where the bacteria are harbored by wildlife. However, pets in urban areas are increasingly at risk due to mutations of the Leptospira bacteria and the preponderance of rats that carry these organisms. Dogs with access to stagnant water or raw sewage, and those that come into contact with rats, raccoons or opossums, have an increased chance of developing leptospirosis. Dogs used for hunting, and those that otherwise frequent wet wooded areas, are at increased risk as well.
Leptospirosis used to be considered a fairly uncommon disease in domestic dogs. It was primarily diagnosed in remote rural areas frequented by wildlife. However, the various strains (serovars) of Leptospira have mutated over time, and the disease is on the rise among pet dogs that live in urban areas because of the proliferation of rats that are attracted to trash and other dirty environments. People can become infected by Leptospira by the same routes that their pets can become infected. Usually, this is by direct contact with urine or other bodily fluids from an infected animal.
Leptospirosis is becoming increasingly common in companion animals, especially in dogs. This disease can be quite challenging to diagnose. Most dogs that are infected with the Leptospira bacteria show no noticeable signs of illness or disease. They are called "carriers" of the organism, and have an "inapparent" infection. Those dogs that do become obviously ill usually have symptoms that are very general and nonspecific, and could easily be attributed to a number of other diseases. In addition, because of the risk of human infection, the diagnostic blood, urine or other samples from dogs suspected of having leptospirosis must be handled very carefully by the veterinarian and laboratory personnel.
The initial assessment of a dog presenting with lethargy, weakness, stiffness, fever of unknown origin and general malaise will include a complete history taken from the owner and a thorough physical examination. Blood and urine samples will probably be taken and submitted to a pathology laboratory for evaluation. The most common blood tests are a complete blood count ("CBC") and a serum biochemistry profile "(chem panel"). The results of those tests hopefully will tell the veterinarian how well the dog's vital organs are functioning, especially its liver and kidneys. They also can give the veterinarian some idea of how the dog's immune system is working. Radiographs (X-rays) and/or ultrasound of the chest (thorax) and belly (abdomen) are also commonly taken to evaluate the size and structure of the kidneys and liver.
The tests described above are routine for almost any dog that is brought to a veterinarian for "just not doing right." However, the gold standard for diagnosing leptospirosis is a microscopic agglutination test (MAT). This test is performed on a simple blood sample, which can easily be drawn by a veterinarian or her technician. The sample will be sent to a laboratory, where it will be evaluated by a pathologist. When a healthy animal comes into contact with Leptospira organisms, its immune system will kick into overdrive and produce antibodies that are specific to those bacteria. Antibodies are the body's warriors against infective organisms. Antibodies against Leptospira target and kill the bacteria. The results of a MAT test will show the level of antibodies, if any, that the dog has produced in response to contact with infective Leptospira organisms. The MAT test will confirm whether a dog has been exposed to those bacteria. If a dog has been vaccinated against Leptospira within the prior 8 to 12 months, it may also have a positive MAT test result.
Many bacterial infections are diagnosed by culturing the bacteria. This basically involves growing the infective organisms in a laboratory setting, so that the best antibiotic can be identified and prescribed for the infected animal. However, it is difficult, and can be dangerous, to culture Leptospira, because these microorganisms are highly infectious to humans. If laboratory personnel come into contact with a blood or urine sample from a dog with leptospirosis, the bacteria can penetrate their skin and ultimately cause severe damage to their kidneys, liver and other organs. Because of this, cultures of Leptospira are rarely attempted in veterinary medicine. The microscopic agglutination test is the safest and best way to diagnose leptospirosis, as long as the person drawing the blood sample takes sensible precautions to avoid contact with the dog's blood. Fluorescent antibody and polymerase chain reaction tests are available to diagnose leptospirosis, but they are not widely used in local veterinary clinics.
Any dog with the sudden onset of signs of kidney or liver dysfunction, or with a sudden fever of unknown origin, should be assessed for leptospirosis. It is important to diagnose and treat this disease as quickly as possible, both for the benefit of the affected animal and also to reduce the risk of its owner or other people becoming infected by the bacteria. This is a zoonotic disease, which means that it can be transmitted from pets to people. Leptospirosis is on the rise in companion animals and is becoming more prevalent in the human population than it has been in the past.
Goals of Treatment
Leptospirosis is becoming more and more prevalent in companion animals, especially in dogs. Fortunately, this bacterial infection is treatable, and it also is curable. The subtypes (called "serovars") of the Leptospira organism are continually mutating, which makes prevention, diagnosis and treatment of this infectious disease increasingly difficult for veterinary professionals. The goals of treating dogs with leptospirosis are to eliminate the organism from the dog's blood stream, promote and maintain a healthy blood supply (especially to the liver and kidneys) and restore normal, productive urine output. If achieved, these goals will not only make the dog healthier, but they will also prevent further disbursement of the bacteria into the environment through urine and other bodily fluids.
Most dogs that have been diagnosed with leptospirosis will be hospitalized for a short period of time, so that they can be given balanced intravenous fluid solutions to correct their dehydration, resolve the symptoms of shock and restore their appropriate electrolyte balance. Oral penicillin antibiotics are usually the first drugs of choice for treating infected dogs. Dogs suffering from acute renal (kidney) failure as a result of leptospirosis will need to have their urine output and blood pressure carefully monitored, to keep track of their kidney function. If the dog has lost blood as a result of gastrointestinal hemorrhage, a blood transfusion may be necessary. Bleach or iodine-based disinfectants should be used to sanitize the kennels and other areas where infected dogs have lived, and especially areas where they have urinated. Strict kennel hygiene is very important to the management of this infectious disease. Owners or caretakers of infected dogs should wear gloves when cleaning the dogs' living quarters or when they otherwise work with the animals. Unfortunately, some dogs that develop leptospirosis end up with chronic liver and/or kidney damage, which may or may not be easily manageable.
Most dogs that develop clinical disease from leptospirosis have a fairly good prognosis, as long as their disease is diagnosed and treated quickly and appropriately. When symptoms come on very suddenly and are quite severe, the prognosis for the dog's recovery is more guarded. Unfortunately, some dogs will develop permanent and irreversible liver or kidney damage. Aggressive, timely therapy is critical, both for the affected animal and for the people that come into contact with it. Remember, leptospirosis is a zoonotic disease, which means that people can become infected if they have direct contact with the Leptospira organisms. This usually happens when a person comes into contact with the urine of an infected animal. The chances of human infection are high when they live with a dog that is showing signs of leptospirosis. People have an equal risk of becoming infected when they live with a dog that is a carrier of Leptospira with an inapparent infection. Those dogs show no signs of illness, but still shed the bacteria in their urine and other bodily secretions and are sources of potential infection for other animals and for people.