Why Does Leptospira Persist In The Kidneys Of Carrier Animals?

Pashu Sandesh,04 September 2017

Parvinder Kaur Lubana

Each species of wildlife has serovars (strains) of leptospira that live in relative harmony with it. We call these their “primary reservoirs hosts”. 

Early in infection, these, leptospira are found throughout the carrier animal’s body. This includes their liver, spleen, kidneys, eyes and genital tract. As the animal produces antibodies, these spirochetes are cleared from most organs. However, within the kidneys, of carrier species (vectors), these leptospira are hidden from the animal's antibodies and continue to live in the microscopic tubes that carry urine out to the bladder (the proximal renal tubules). There, they are protected by a poorly understood membrane-bound protein mechanism.

These leptospira and their host animals have learned to live together in harmony. However, when these leptospira find their way into a new animal - such as your dog - the harmonious relationship does not occur. 

What Happens When Dog Catches Leptospirosis? 

Not all dogs that are exposed to leptospirosis become visibly ill. In a 2007 Michigan study, 25% of the unvaccinated healthy adult dogs examined in had antibody to leptospirosis which indicates that they had been previously exposed to leptospirosis without their owners noticing a problem. 
But we do not know if these pet's long-term health remained unaffected. Chronic kidney inflammation (Chronic Interstitial Nephritis, CIN or chronic kidney damage) is a leading cause of kidney failure and death in dogs. You can read about chronic kidney damage here. Although there are many causes, this form of kidney damage can be one outcome of leptospirosis.

When leptospirosis does cause sudden disease in dogs, it tends to be most severe in unvaccinated dogs that are younger than 6 months old. These are the pets most likely to suffer life-threatening liver and kidney damage. In these cases, L. grippotyphosa is often responsible. It takes about 4-12 days after exposure for the pet to feel ill.

In dogs of any age that become ill, the leptospira spread rapidly through the pet’s blood stream, usually causing high fevers, depression and joint pain. Leptospira produces powerful toxins that can attack the liver and kidneys, leading to failure of these organs. Strains of lepto vary in their intensity and in the portions of the body they attack most severely. Some varieties primarily cause liver damage, while others concentrate in the kidneys. In other pets, blood fails to clot normally - leading to bleeding.

What Are The Signs Of leptospirosis in Dog?

There are typical symptoms that veterinarians associate with leptospirosis. But because no two cases proceed exactly alike, not all of the typical signs are likely to be present in any one pet. The most common signs are fever and depression. These pets are cold, shivery, and stiff.

They may carry their tummies tucked up do to pain. Some drool and vomit and most loose their appetite. Fever causes many dogs to drink excessively. Later in the disease, a few pets will develop eye inflammations (uveitis), nervous system abnormalities or pass red-tinged urine. As the disease progresses, the pet may become dehydrated due to the fever, vomiting and disinterest are drinking. A drop to subnormal body temperature is a very grave sign. A few dogs, particularly juveniles, will die suddenly before many of these signs occur.

When the liver has been damaged, the pet’s skin may take on a yellowish tinge (=jaundiced = icteric) and show all the symptoms of hepatitis. When the kidneys have been severely damaged, the pet may show the signs of uremia. These organ changes can be temporary or permanent.

How Would Veterinarian Diagnose Leptospirosis In Dog?

The symptoms that I discussed above, along with a history of your dog being exposed to places were leptospirosis lurks, might make your vet suspect this disease. Leptospirosis sometimes occurs in outbreaks, and your veterinarian may be aware that it is presently occurring in your community. If your veterinarian zeros in on leptospirosis on the first examination, you are very fortunate. Because symptoms vary so much between pets and because most veterinarians only see a few cases from time to time, it is common to miss the diagnosis on the first examination. 

To make the diagnosis – or rule it out – your veterinarian will order blood tests (CBC and blood chemistry). One of the typical signs found in blood tests as leptospirosis progresses is an elevation in the number of white blood cells (WBC) in the pet’s blood. The cells that tend to go up in leptospirosis are the neutrophils. However, very early in infection, white blood cell numbers can be lower than normal. There are often other chemical abnormalities that suggest leptospirosis – changes in Liver enzymes, blood-clotting cells (thrombocytes) and kidney health values (BUN and creatinine). Evidence of damage to the pet’s kidneys would also be reflected in abnormal urine analysis results. 

There are a very large number of diseases of dogs that can give test results identical to that seen in cases of leptospirosis. These include ehrlichiosis, babesiosis, autoimmune disease, infectious canine hepatitis, canine herpes virus, canine brucellosis and certain poisonings. Because of this, your veterinarian may place your pet on antibiotics while another test is run. This is the leptospirosis PCR test. This test is extremely sensitive in finding the presence of leptospira in your pet’s body and the results can be obtained rapidly. Both urine and blood from your pet are submitted. After the first ten days of infection, antibodies against leptospirosis can be detected in your pet’s blood if it has encountered leptospira. However, antibody detections are not as valuable as a positive PCR test in dealing with leptospirosis. The antibody test can be positive in pets due to previous vaccinations or a prior exposure to lepto that has nothing to do with your pet’s current health problem. Occasionally the diagnosis can be made by seeing leptospira microscopically in the pet’s urine.

Is There A Danger I Could Catch It? 

Yes, if the organism gets into your body, you can also become ill. You could experience any of the same symptoms I have described in your pet. The most common ways people contract leptospirosis is from primary or secondary exposure to an infected dog or rat urine. However, a 2010 study found that you are very unlikely to be exposed if you take proper sanitary measures. 

Because urine is the most common spreader of leptospirosis, it is very important that you take hygienic steps not to expose yourself to your pet’s urine. Because recovered pets can shed lepto in their urine for months, you need to continue to observe strict hygiene even after your pet has recovered. 

Here are some things you should do to minimize your risk: Have only one, healthy, family member care for the dog. Confine your pet to an easily-sanitized area of your house. Prevent exposure of other pets. Wear protective latex gloves whenever cleaning up after your dog. Take your dog out on a leash frequently to urinate. Only allow the pet to urinate on the dry concrete surface that can be easily sanitized with bleach. When you are potentially exposed to any secretions or waste from your pet, disinfect your hands liberally with an iodine-based disinfectant. Doing these things will considerably lower your risk but not eliminate it entirely. Should you feel ill, you need to inform your physician about your ill pet.

Treatment of leptospirosis in dogs.

The treatment of leptospirosis is much easier than the diagnosis. Fortunately, many common antibiotics will kill leptospira. Antibiotic resistance is not a problem in leptospirosis so ordinary penicillin, tetracycline, and erythromycin all work well. Doxycycline is probably the best since it seems most effective in preventing dogs from becoming silent carriers of the disease organism in their kidneys after recovery.

Sick pets require intense supportive care to get them through the early severe stage of the disease. Dogs with stomach involvement need anti-emetic medications to lessen vomiting. Dogs that vomit need intravenous fluids to stem dehydration and correct blood acid/base balance. Rigorous fluid therapy also helps flush out the pet’s kidneys and, hopefully, protect them from permanent damage. When the pet’s kidneys have shut down and toxins are accumulating in its blood, hemodialysis has even been used. 

Many pets make a full recovery. A few go on to suffer chronic renal failure or develop chronic active hepatitis – neither of which is curable. 

If Dog Recovered From Leptospirosis, Can He Catch Lepto Again?

Yes, it could. But since it is very uncommon for dogs to develop leptospirosis twice, we have little data to go on. We know from experimental data that your dog will remain immune to the specific strain of leptospira that infected it for as long as protective antibodies linger in its body. How long, differs from dog to dog. But it will remain susceptible to other strains of leptospirosis when they are present in its environment. Vaccines that are now in use protect against multiple strains of leptospira. If your dog’ life style continues to expose it to sources of leptospirosis, it should continue to receive this vaccination periodically. 

How Can we Prevent Pets from Catching Leptospirosis?

Limiting your pet’s access to contaminated water is the best way to avoid leptospirosis. But there is another potentially larger problem. Feeding pets and wild critters outside your home attracts rodents and possible wildlife-carriers and should be avoided. Sanitation is important in reducing rat populations around the home. Few realize that feeding urban pests, such as raccoons, or maintaining feeding stations for feral cats also increases the risk that your pet (and you and particularly young children) will be exposed to leptospirosis and other serious diseases.