Leptospirosis In Your Dog
How Dogs Catch It, How Vets Try To Cure It, How We Can Prevent It
Ron Hines DVM PhD
What Causes Leptospirosis?
Leptospirosis is a disease found in temperate climates throughout the world. It is caused by a bacteria – a peculiar, very thin, corkscrew-shaped organism with a hooked-shaped “tail” (they really have no front or rear). Each has undulating motility organs that remind me of Dracula’s cape. ( read here ) The group are called spirochaetes . Most species of spirochaetes live their lives free in the environment causing no illnesses. But a few species have evolved to cause particularly nasty diseases. Those undesirable ones include the eight varieties of leptospira that cause leptospirosis, as well as their close relatives, the spirochaetes responsible for Lyme disease , relapsing fever and syphilis. (read here) None of them, other than syphilis, are particularly choosy about whom they infect.
Traditionally, the threat of leptospirosis was associated with areas of heavy rainfall, high humidity, a temperate or tropical climate, flooding and lack of basic sanitation. (read here) Rats were traditionally thought to be the main transmitter. Apparently healthy rats can carry the organism in their kidneys and spread it through their contaminated urine. But that may no longer be the case. Expand the map at the top of this page to see where most cases in dogs occur in the USA. Late summer and fall see the most cases. The leptospirosis organism usually enters the body from contaminated water or soil through the mouth, nose, eyes or even broken skin . Hawaii at one time led the Nation in reported cases. It is also the state with the highest average rainfall. The CDC now reports that ~ 50% of the leptospirosis cases in humans now occur in Puerto Rico
You Mentioned Varieties. Is There More Than One Type Of Leptospirosis Organism?
Yes, there are many. They are called serotypes or serovars.
Serovars differ in the structure of certain of their surface constituents (lipopolysaccharides). These surface compounds contain both carbohydrate and fatty components. Since these compounds are the ones that your dog’s immune system must recognize and respond to by producing “exact fit” antibodies, immunity to one subtype/serovar may not provide strong immunity to other serovars. There have been over 300 different leptospirosis serovars reported. (read here) The ones that most commonly infect dogs are Leptospira icterohaemorrhagiae, L. canicola and L. kirschneri/grippotyphosa. Other serovars are occasionally responsible for infections in dogs. The prevalence of all of them vary from place to place and time to time.
Both Zoetis’ Vanguard® L4 and Boehringer Ingelheim ’s Recombitek® 4, current leptospirosis-containing vaccines contain killed portions of the L. canicola, L. grippotyphosa, L. icterohaemorrhagiae and L. pomona organisms – the serovars they feel your dog is most likely to be exposed to. But when your dog becomes infected, our current diagnostic test, the MAT test (aka modified Faine’s antibody test) has limited ability to accurately determine which of the leptospira serovar(s) is causing your dog’s infection. Read more about MATs tests farther along.
How Would My Dog Catch Leptospirosis ? How long After Exposure Might My Dog Become ill?
Most of the infected wild animals and most of the domestic livestock that spread leptospirosis do not appear ill. In those carrier animals, leptospira have taken up residence and found shelter from the animal’s immune system in its kidneys. Residing there for long periods, they are shed in high numbers in the animal’s urine. Chronically infected animals can shed leptospira intermittently or continuously. In infected dogs, it takes about 2 weeks before leptospira begin to appear in their urine. Often leptospira are only shed in the dog’s urine for a few days; but in some cases leptospira are said to have persisted in their urine for more than two years. ( read here ) . I suppose that one could never be certain that the dog was not reinfected with a different serovar.
The incubation period for leptospirosis – the time from exposure to illness – can be only a few days or as long as two weeks. In experimental studies, the average incubation period was about a week. ( read here ) But as I previously mentioned many dogs that become infected or exposed never become visibly ill. ( read here & here )
Today most dogs in the developed (prosperous) world that catch leptospirosis, catch it from wildlife reservoirs, not other infected dogs. The species of animals most responsible for spreading the disease vary from place to place, time to time and even season of the year. In areas of poverty where rats are prevalent, rodents are thought to be the prime transmitter. In prosperous areas where urban wildlife like raccoons are abundant, suspicion falls on them. (read here & here )
It is probably not that cute and endearing raccoons are any better carriers of leptospirosis than a number of other critters. Its just that they are the most clever and fearless about invading human and dog-occupied space in their search for food.
Nothing interested your dog more than sniffing the scent of exotic urine. By the time your dog sniffs a urine-contaminated location, the raccoon or other leptospirosis vector is long gone (has departed). Leaving food out for stray cats presents the same under appreciated threat. ( read here , here & here ) The second way leptospirosis travels is when that urine gets washed into bogs, streams and impoundments that your dog frequents. Drainage pipes and culverts are a choice location for raccoon latrines.
I cannot tell you which is most likely – although floods and heavy rainfall are often associated with leptospirosis outbreaks. Dogs and cats that spend their days indoors are considerably less likely to encounter leptospirosis than those that spent much of their time off-leash and out of doors.
What Are Some Signs I Might See If My Dog Became ill With Leptospirosis?
I mentioned earlier that many dogs show very few signs of illness when infected with leptospirosis and succeed in ridding their bodies of these organisms on their own. There is really no advantage for a disease organism to kill its host or make it seriously ill. But there is really no way of knowing which dog will react violently to a leptospira infection and which will not. Perhaps it is the damaging ability (virulence) of the particular leptospirosis serovar your dog was exposed to. Perhaps the genetic abilities of your dog’s immune system factors in. Perhaps the size of the dose of leptospira organisms it encountered is another factor. Perhaps all three. Veterinarians really don’t know.
It is the fever, muscle pain, depressed mood and lack of appetite associated with leptospirosis that motivate dog owners to bring their pet to their veterinarian. Vomiting and diarrhea ares also common. The pet’s midsection (abdomen) might be tender to the touch. As the disease progresses, some of these dogs show a yellowish hue to their gums and the whites of their eyes – evidence of jaundice. The dog’s liver is a common target of leptospira. Some of the dogs so affects are left with chronic liver problems. (read here) Abnormal blood liver tests confirm liver involvement. But occasionally that jaundice is the result of a slowdown in blood clotting and/or destruction of red blood cells by the leptospirosis toxins. (read here) Occasionally the lungs are the primary target of leptospira. That can be due to the bleeding tendency I just mentioned. Those dog have shortness of breath (dyspnea). They might cough up blood or have nose bleeds, an increased tendency to bruising or the presence of blood in their stools or urine. Read about those problems here. Leptospira move freely through the bloodstream. When the dog’s kidneys are a prime site of damage, their kidneys sometimes fail. Read about that here.
What Tests Will My Veterinarian Use To Diagnose Lepto In My Dog?
Like many infectious disease your veterinarian encounters, the initial blood analysis reports are rarely definitive for a single disease organism. Your dog’s total white blood cell count (WBC) will often be elevated. It is quite common for the dog’s thrombocyte count , the cells involved in blood clotting, to be low and for its neutrophil count to be high. Because of the bleeding often associated with leptospirosis, you dog might be anemic as well. Since the pet’s kidneys are often a destination for leptospira, tests might detect a decrease in kidney function ( elevated BUN and creatinine ). Liver tests (ALT, GGT & bilirubin ) are commonly abnormal as well. Alkaline phosphatase (AP) – an enzyme released by many injured tissues, is often elevated. Your pet’s urine analysis (urinalysis) often confirms of kidney infection as well (pus cells, casts and protein).
The symptoms that I mentioned earlier, along with a history of your dog being exposed to places were leptospirosis lurks, and these blood results might lead your veterinarian to suspect that your dog had contracted leptospirosis. If that is the case, your vet might order one or more of three specific leptospirosis tests: the MAP test, a PCR test, or a leptospirosis IgM test. All these tests have their limitations – but they are the best we veterinarians currently have to offer. ( read here )
MAT Test Modified Leptospirosis Agglutination Test
This test looked for antibodies in your pet’s blood directed against leptospira – evidence the organism is or had been present. Weakly positive tests can be quite hard to interpret. Also, the test can be negative early in the disease – before the pet has had time to produce the antibodies this test looks for. Some positive tests have been from previous leptospirosis vaccinations the dog received. It usually takes 10-14 days for a current leptospirosis infection to produce MAT-positive results (an elevated antibody titer ) – although some dogs develop a positive titres earlier.
Generally, the only way to be certain that a positive titre is related to a current infection is to measure it early and again later during the illness and find that the titre has increased substantially. It is usually the first test your veterinarian runs because it is readily available at central labs and relatively inexpensive as test costs go. It is not an easy test for laboratory staff to run. First, as I mentioned, the results can be quite hard to interpret (there is quite a bit of subjectivity). Live cultures of various leptospirosis serovars must be maintained at the laboratory – always a threat to the employees. Different laboratories have been known to interpret test results differently for the same dog. Antibodies to one serovar frequently cross-react with others. So using the MAT test, one can never be certain which of the many leptospira strain or strains your dog is reacting to. That is really irrelevant when it comes to saving your pet’s life. Treatment for all strains of leptospirosis organisms is the same. But it does confound research veterinarians and pharmaceutical companies when it comes to deciding which strains (serovars) to add to their vaccines.
The PCR Test ….Leptospirosis Polymerase Chain Reaction Test
PCR tests amplify (“clone”) telltale leptospira DNA components, making them appear in quantities that can be identified as to their origin. This test is likely to pick up the presence of leptospirosis before a MAT test does. Test results are not influenced by prior leptospirosis-containing vaccinations. The PCR test is best performed before a dog begins antibiotic therapy and before the dog might naturally clear (eliminate) the leptospira from its body. Both of of those situations can yield a false-negative PCR result leading your veterinarian astray as to the nature of your pet’s illness. During the first ten days after infection, blood samples are the specimens of choice. After that, urine might be a better choice. Some veterinarians send in samples of both. The test rarely misses the leptospirosis organisms when they are present in moderate or high numbers in the samples, but the PCR test also has limited ability in determining which serovar of lepto we are dealing with. The PCR test also can not tell the difference between a recovered dog that is still chronically infected with leptospirosis and simply shedding leptospira in its urine or a recently infected dog that is ill with the disease.
In Office Tests
Two companies, Idexx Laboratories and Zoetis, market in-office leptospirosis tests that veterinarians can perform on the spot. These tests rely on detecting an early antibody type (IgM) that the dog’s immune system produces when it first encounter the leptospirosis organism. Later on, and in vaccinated dogs, the antibodies are mostly IgG). The development of these tests has been a great help in getting leptospirosis-infected dog into therapy quickly – before the results of central lab MAT and PCR tests have time to arrive. Not all commonly dispensed antibiotics are equally effective in destroying leptospira organisms. The best are one of the penicillin derivatives (ampicillin, amoxicillin, etc.), a cephalosporin, or doxycycline.
The Idexx test is their SNAP®Lepto ; the Zoetis test is their Witness®Lepto. I can not tell you if one is superior to the other. Zoetis funded a study that found their product better than Idexx’s. But I have very little faith in company-funded articles. It doesn’t matter if it’s a car, shaving cream or a veterinary laboratory test; whoever funded the research always finds their product superior to the competition.
Other Diagnostic Methods
Pathologists and veterinary microbiologists can sometimes identify individual leptospira when blood and tissues samples are examined using dark field microscopy. A variety of other methods have been reported as well (eg RSAT, CF, LFA), but none to my knowledge are readily available to practicing veterinarians like myself.
Laboratories and research centers can also attempt to grow the leptospirosis organisms from tissue samples submitted to them. Leptospira can be quite difficult and expensive to grow. Other irrelevant bacteria that might also be in the sample frequently crowd out the leptospira. So growing (culturing) leptospira organisms is generally reserved for scientific experimentation aimed at providing new knowledge about the disease.
Is There A Danger I Could Catch Leptospirosis From My Dog?
It is theoretically possible but quite unlikely. Using common sense, sanitation products and practice good hygiene is usually all that is required to stay safe. ( read here )
Here are some other things that minimize the transfer of infectious diseases of all kinds. They apply to an active case of leptospirosis in your dog as well:
Have only one, healthy, family member care for the dog. It should not be a child. Confine your pet to an easily sanitized area of your home. Prevent exposure of your other pets. Wear protective gloves when cleaning up after your dog. Take your dog out on a leash frequently to urinate and defecate. Only allow the pet to urinate and relieve itself on 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 a common disinfectant. Alcohol-based sanitizers, povone iodine and Lysol all kill leptospira rapidly. So does bleach, heat and drying. Should you feel ill, always inform your physician about your pet’s illness. If you are a worrier and want to be more certain your dog does not remain a leptospirosis carrier, have a PCR test or two performed on its urine after its recovery.
How Will My Veterinarian Treat Leptospirosis In My Pet?
Every veterinarian who diagnoses a case of leptospirosis in a dog will place that dog on antibiotics. I mentioned the best ones earlier. When vomission and/or diarrhea is a symptom in your dog, oral doxycycline might not be the best choice. That is because it causes some dogs to vomit. When nausea, stomach or intestinal inflammation are present, antibiotics are best given by injection rather than orally. No studies I know of have found that antibiotics are effective in preventing the development of carrier dogs but I would probably keep the patient on antibiotics past the time of early recovery and perhaps give alternating medications.
Very sick dogs require intense supportive care to get them through the early stages of leptospirosis. Dogs that vomit or show intestinal involvement generally get medications to calm their stomachs (eg metoclopramide , maropitant/Cerenia® ) and meds to decrease stomach acidity (eg ranitidine/Zantac® or omeprazole/Prilosec® ). Diarrhea needs attending to as well. Many also need intravenous fluids to combat the dehydration vomiting, diarrhea and inappetence produce. If their tummies are sensitive or they show other evidence of pain, they benefit might from pain-control medications (eg buprenorphine). Those with respiratory distress benefit from oxygen and some from theophylline. Dogs that are not willing eat need to receive their essential nutrients in other ways.
Some dogs whose kidneys have swollen and fail due to an acute leptospirosis infection might still have the ability to recover if hemodialysis takes over the work of their kidneys for a while. When hemodialysis is attempted, it is rarely suggested for more than a few weeks. If a dog’s kidneys have not begun to recover by then, hemodialysis is unlikely to be helpful. Your veterinarian would have to refer you to one of the very limited number of centers where such procedures might be attempted.
If My Dog Recovered From Leptospirosis, Can It Catch The Disease Again?
Yes, that is possible; although veterinarians have no easy way to confirm that it happens. Since it is very uncommon for dogs to develop leptospirosis twice, we have very little data to go on. What we do know that dogs and humans remain immune to the specific strain of leptospira that infected them for as long as protective antibodies linger in their bodies. Perhaps even longer if immunological memory is factored in. We also know that sometimes that antibody immunity cross-protects against different leptospirosis serovars/strains and sometimes it does not.
How Can I Help Prevent My Dog From Being Exposed To Leptospirosis?
I believe that in the United States, the most successful ways to limit your dog’s exposure to leptospirosis is to limit its exposure to contaminated water and to limit its exposure to the urine of infected wildlife, rats and feral cats and livestock. The prime attractor of all potential leptospirosis carriers is available food – food placed intentionally for those animals or food left outside for your dogs and cats. Without those food sources (as well as unsecured garbage) there would not be an urban reservoir of leptospirosis and other similar diseases. Kind hearted people mean well. But intentionally upsetting the balance of Nature does animals and people no service. Keep your cats only indoors to prevent their exposure to the rodents that are a prime carrier of leptospirosis throughout the world. Rodents and small mammals are their natural prey.
Leptospira organisms generally enter the body through the mouth or a skin abrasion. Some have associated leptospirosis exposure with feeding leptospirosis-contaminated raw meat to dogs. But that is highly unlikely to happen when it is American supermarket meat is consumed. ( read here ) Leptospirosis organisms are very dependent on water, mud or damp clay soils to survive. That is because they do not possess a waterproof membrane or spores to protect them from drying. Leptospira die quickly on dry surfaces – even if those surfaces were contaminated with urine from infected animals. Temperatures at or above 131 F (42 C) kill leptospira quickly. All common household disinfectants (bleaches, alcohol based products, vinegar, lemon juice etc.) kill the organisms. Porous items need to be completely submersed in these solutions. Standing water can be disinfected using swimming pool chlorine tablets (but realize that those products are toxic to all aquatic life). Common industrial chemicals are so toxic to leptospira that obviously polluted effluent water is not as much a leptospirosis threat to your pet as are destination lakes and streams with water that appears pristine. The United States Army once experimented with giving their soldiers in Panama doxycycline in an attempt to prevent them from contracting leptospirosis. ( read here ) I do not know if that approach holds promise.
Your other option is to have your pet vaccinated against leptospirosis. The American Animal Hospital Association (AAHA) considers leptospirosis vaccine a “non-core” vaccine for dogs. That is, they do not recommend that dogs receive the vaccine unless there is a good chance they will be exposed to leptospirosis. The main reason for that is that veterinarians see more vaccination reactions following the administration of vaccines containing leptospirosis than other vaccine they administer. These reactions range from the minor inconvenience of pain at injection site, to facial swelling and hives, to fatal anaphylactic reactions. Which pet will experience them cannot be predicted. However I believe that the one-size-dose-fits-all philosophy accounts for most of the leptospirosis reactions that veterinarians see. Read about that here .
Only you can decide if your pet’s risk of catching leptospirosis justifies the risk of yearly leptospirosis antigen-containing vaccinations. In making that decision you need to ask yourself if your dog frequents areas that are likely to harbor the disease. Ask your public health department how many confirmed cases of leptospirosis have occurred in your community in the last few years. Places that I suggest you avoid include doggy parks. You also need to consider if your dog, or its siblings, or its parents have had previous vaccination reactions to a leptospirosis-containing vaccine or even a vaccine that did not contain leptospirosis antigen.
Currently available canine leptospirosis-containing vaccines not always prevent infection. But they are said to make the disease much milder when a leptospirosis infection does occur. How long immunity might persists after vaccination has not been well established.