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Diagnosing Leptospirosis in Dogs

Source: PetWave, Updated on July 16, 2015

Initial Evaluation

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.

Diagnostic Procedures

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.

Special Notes

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.

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