NOTE: Leptospirosis is a fatal disease transmitted from wild animals (in the city, that's rats) to dogs, as well as from dog to dog and dog to human through urine. Rats come out at night and urinate in puddles, and dogs just have to walk through these infected puddles for the "spirochete" to make it's way into the dog's bloodstream through micro-lacerations that all dogs have on their paws.

There have been many questions asked by clients about Leptospirosis. Not all veterinarians vaccinate with the same protocol, and some veterinarians don't even recommend the vaccination. At our hospitals, after having experienced two outbreaks on the Upper West Side, we strongly recommend vaccinating your dog against this fatal disease. Despite the outbreaks, many clients still hear that not all veterinarians recommend this vaccination. Below is an article written by various experts in the field of Veterinary Infectious Diseases about this disease.

The most important parts of the article can be summed up thusly:

Over the last few years, leptospirosis has re-emerged as a cause of acute renal failure.
Determining which dogs are at risk is difficult
Virtually all infected dogs in these retrospective studies were unvaccinated.
Data suggests that titers persist for <12 months (often <6 months)
Once excreted in the urine, leptospires can survive in fairly moist environments for months to years.

Authors

Craig A. Datz, DVM, ABVP (Canine & Feline)
VIN Consultant
University of Missouri - Columbia
Columbia, MO

Barrak Pressler, DVM, ACVIM (SAIM)
VIN Consultant
Purdue University
Assistant Professor
West Lafayette, IN

Alice Wolf, DVM, ACVIM (SAIM), ABVP (Feline)
Chief VIN Consultant
Texas A&M University
Adjunct Professor, Small Animal Medicine
Bryan, TX

Mark Rishniw, BVSc, MS, ACVIM (SAIM), ACVIM (Cardiology)
VIN Consultant
Clinical Research Coordinator
VIN
Ithaca, NY

8285688

Introduction

Canine leptospirosis has had a re-emergence over the last few years. How it should be addressed is a controversial topic - should we vaccinate, are they protective, what serovars are involved? Read on...

What is the current thinking on Leptospirosis ?

Leptospirosis has been a concern for veterinarians and dogs for several years. In the past, leptospiral disease in dogs was caused primarily by 2 serovars - L. canicola and L. icterohemorrhagica, with rare cases caused by L. pomona. Vaccination against two of these strains was available, but a small number of adverse vaccine reactions were observed (urticaria, allergic-type responses), especially in smaller breeds. This led many veterinarians to cease administering leptospirosis vaccines.

Over the last few years, leptospirosis has re-emerged as a cause of acute renal failure. However, the serovars associated with these cases have not traditionally been seen in dogs: L. kirschneri ser. grippotyphosa, L. bratislava, L. autumnalis and L. pomona. ^1-3

There appears to be an increased incidence of cases in late summer and fall as well as a positive correlation with high levels of rainfall.^4,5

What is the current thinking on Leptospira vaccination?

What serovars are included in the new vaccines?

Traditional leptospira vaccines (bacterins) have included coverage against L. canicola or L. icterohemorrhagica. The emerging serovars (grippotyphosa, bratislava, pomona, and autumnalis) were not included in these vaccines. Recently, Wyeth-Fort Dodge released new Leptospira vaccines (either as stand-alone, or in combination with the viral vaccines), that contain bacterins against L. canicola, L. icterohemorrhagica, L. grippotyphosa and L. pomona. [Pfizer now also has an approved 4-serovar vaccine]

Vaccination against one Leptospira serovar is not cross-protective against the other serovars. Therefore, dogs vaccinated against L. canicola and L. icterohemorrhagica are still susceptible to infection by L. grippotyphosa or L. pomona. Additionally, vaccinated dogs are susceptible to serovars not contained in even the newer vaccines.

How long is the duration of immunity with Leptospira vaccines?

This is difficult to determine. Some unpublished data suggests that titers persist for <12 months (often <6 months), and that some dogs fail to seroconvert despite vaccination. One year challenge studies have been performed by Fort Dodge for L. canicola and L. icterohemorrhagica, but not the newer strains (or at least data are not available for these studies, if they have been performed). One year challenge studies have also been performed by Pfizer, but data are not readily available for evaluation.

What is the recommended vaccination schedule for dogs?

Dogs should receive at least 2 initial vaccinations with the new bacterin, regardless of previous leptospira vaccination history. Two doses should be administered at least 2 weeks, preferably 3 weeks apart. Some data suggest that dogs require 3 doses of bacterin to develop antibody titers. Yearly vaccination is recommended, although 6-monthly vaccination may be warranted in some cases if the risk of exposure is exceptionally high.

How can I minimize adverse vaccine reactions?

Some dogs given leptospira bacterins develop adverse clinical reactions. Few statistics exist, but some suggest that adverse events occur in less than 1% of vaccinates. The occurrence of these adverse reactions led many practitioners to abandon routine Leptospira vaccination. With re-emergence of leptospirosis, and more vaccinations being administered, the issue of adverse vaccine responses will increase. Anecdotally, small breed dogs and puppies appear to be at the greatest risk for developing adverse vaccine reactions with Leptospira bacterin. Therefore it is best to avoid giving the vaccine to puppies younger than 9 weeks.

Some practitioners advocate pre-treating dogs receiving Leptospira vaccines with antihistamines and glucocorticoids (see message board link). This appears to ameliorate the adverse reactions in most cases. However, given the low incidence of adverse reactions, we do not recommend routine pre-treatment with antihistamines or glucocorticoids. This strategy should be reserved for cases previously demonstrating hypersensitivity reactions, or high-risk cases.

Which dogs are at risk?

Many practitioners are concerned about unnecessary vaccination, and prefer to vaccinate only those dogs considered "at risk". Determining which dogs are at risk is difficult. There are at least 3 studies of risk factors for leptospirosis.^1,6,7 These studies suggested that L. grippotyphosa had previously affected dogs in rural environments (working and herding dogs), but now affects dogs in urban and peri-urban environments. Middle-aged male dogs are at greatest risk. Virtually all infected dogs in these retrospective studies were unvaccinated. However, because the vaccine is relatively new, it is difficult to determine whether the vaccine is truly protective, because there is anecdotal evidence of infection in vaccinated dogs.

There is also evidence that geographic locations have different prevalence of disease.

Thus, it is difficult to determine which dogs should receive Leptospira vaccine in any particular region. If the incidence of leptospirosis in your area is high, vaccination is probably warranted.

What about L. bratislava or L. autumnalis?

Whether these 2 serovars cause disease is still questionable. The Animal Health Diagnostic Laboratory at Cornell University does not routinely measure antibody titers against these 2 serovars, because they claim that "..Given the lack of sufficient clinical evidence to support testing for L. bratislava and L. autumnalis, the AHDL is not recommending routine testing for them..." This is based on the fact that neither serovar has been cultured from any clinical case of leptospirosis. However, serological data suggests that at least L. autumnalis and L. bratislava may cause disease.^2,3 The Cornell AHDL argues that high titers with these serovars are cross-reactive with other serovars - a hypothesis that is supported by the fact that in nearly all cases, patients display seropositivity against multiple serovars.

Regardless of whether these serovars are pathogenic in dogs, treatment of patients with leptospirosis is the same irrespective of serovar.

Do cats get lepto?

No. Cats do not appear to become infected, even when experimentally inoculated.

How do I disinfect contaminated areas or bedding?

Iodine-based or bleach-based disinfectants effectively kill Leptospira. 3-10% (1:30-1:10) bleach solutions are effective as soaks for bedding and for washing kennels. Dessication and sunlight also kill the Leptospira.

How well do leptospira organisms survive in the environment?

Once excreted in the urine, leptospires can survive in fairly moist environments for months to years. For survival of the organisms in water, temperature in the range of 28° to 38°C (82° to 100° F) and pH in the range of 6.2 to 8.0 are optimal. Survival in water is inhibited by contamination with sewage, high acidity, and high salinity. Freezing is detrimental to survival of leptospira (Guerra 2009).

What is the difference between the different diagnostic tests for leptospirosis?

The most commonly used test is serology to identify antibodies directed against various serovars. The microscopic agglutination test (MAT) detects titers ranging from negative to 1:6400 or higher. A single positive titer of 1:800 or greater is supportive of infection or recent exposure. Titers of 1:100 or 1:200 may represent background exposure and are often clinically insignificant. Dogs that have received leptospirosis vaccines in the past 6 months can have positive titers up to 1:400. Each lab should provide its own reference ranges, clinical correlations, and how they are determined.

A more accurate use of the MAT is to perform acute and convalescent samples. A blood sample is drawn on initial presentation or onset of clinical signs and the serum is drawn off and stored in the freezer. One to three weeks later, a second serum sample is collected and then both samples are sent to the diagnostic lab at the same time. A four-fold or greater increase in titer in the convalescent compared with the acute sample indicates recent exposure or infection. Some labs offer ELISA testing, which is more commonly used in humans.

Other diagnostic methods are available but are less commonly used. Urine culture is unrewarding because of the fastidious growth requirements of the organisms. Direct darkfield microscopic examination requires special equipment and both false negative and false positive results are common. Direct fluorescent antibody techniques can be done on urine or tissue samples but are insensitive. The most sensitive test is PCR on urine, blood, CSF, or aqueous humor. However, false negatives and positives are possible and a positive test may indicate a subclinical carrier.

Because of the delay in obtaining results of diagnostic tests, antibiotic treatment should be started immediately in presumptive cases.

How do I interpret Leptospira titers?

In general, there are five rules regarding lepto titers:

1. the highest serovar is considered to be the infective serovar.

2. there is a lot of cross-reactivity between serovars, so positive titers can be seen to multiple serovars (hence, rule #1).

3. differences of less than 4-fold are not significantly different from one another.

4. lepto vaccines can cause positive titers to multiple serovars.

5. titer means antibodies--and thus exposure--and not necessarily disease.

Additionally, as with any infectious serology, changing titers (increasing in acute disease) help determine the accuracy of the diagnosis.

Vaccination titers are generally relatively low (1:100 to 1:400), compared to active infection.

Some studies at Cornell University have shown that Western Blot analysis can discriminate between vaccinal antibodies and antibodies generated in response to natural infection. However, these data are not published.

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REFERENCES

Journal Articles

1. Ward MP, Guptill LE, Prahl A, Wu CC. Serovar-Specific Prevalence and Risk Factors for Leptospirosis Among Dogs: 90 Cases (1997-2002). J Am Vet Med Assoc 2004;224[12]:1958-1963

2. Prescott JF, McEwen B, Taylor J, Woods JP, Abrams-Ogg A, Wilcock B. Resurgence of leptospirosis in dogs in Ontario: recent findings. Can Vet J 2002;43[12]:955-61

3. Boutilier P, Carr A, Schulman RL. Leptospirosis in dogs: a serologic survey and case series 1996 to 2001. Vet Ther. 2003;4(2):178-87.

4. Ward MP. Seasonality of canine leptospirosis in the United States and Canada and its association with rainfall. Prev Vet Med 2002;56[3]:203-13

5. Adin CA, Cowgill LD. Treatment and Outcome of Dogs with Leptospirosis: 36 Cases (1990-1998). J Am Vet Med Assoc 2000;216[3]:371-375

6. Ward MP, Guptill LE, Wu CC. Evaluation Of Environmental Risk Factors For Leptospirosis In Dogs: 36 Cases (1997-2002). J Am Vet Med Assoc 2004;225[1]:72-77

7. Ward MP, Glickman LT, Guptill LE. Prevalence of and Risk Factors for Leptospirosis Among Dogs in the United States and Canada: 677 Cases (1970-1998). J Am Vet Med Assoc 2002;220[1]:53-58

8. Guerra MA. Leptospirosis. JAVMA, 2009;234(4):472-478.

Books and Associate

1. Morgan R. Leptospirosis. VIN Associate Chapter.

Rounds and Other resources

1. Lunn K, Bolin C, Olsen C. Update on Leptospirosis. VIN Rounds June 10, 2001

2. Leptospirosis and Your Pet: A CDC Fact Sheet. VP Client Information Sheets

3. Should We Be Giving Lepto Vaccinations?