(from the Texas Veterinarian column by Tammy R. Beckham, DVM, PhD, TVMDL Director)
At TVMDL our diagnosticians routinely test for and confirm leptospirosis in livestock and companion animals. Spirochetes can be found almost anywhere there is moisture or water. The classical history leading to suspicions of leptospirosis might include a dog going for daily swims in a bayou or pond and living the “country” life. But, “urban” leptospirosis has been routinely confirmed of late at TVMDL.
Peri-urban wildlife such as raccoons, opossums, mice and rats may readily shed the organism in their urine, and that allows the spirochetes to persist in the soil or water for extended periods. It is not uncommon for veterinarians to see cases in Austin’s urban areas or in the suburban neighborhoods of Dallas.
Consider the case of a Weimaraner with an upset stomach, thought to be from a jerky treat, which ended up febrile with joint pain, elevated blood urea nitrogen and hyposthenuric proeteinuria, and a titer to Leptospira bratislava that far exceeded the normal ranges. This dog was leash-walked every time it went outside, and no other risk factors, like standing water from a birdbath or raccoons wandering into the yard at night, were mentioned in the dog’s the history.
At TVMDL we run the “gold standard” microscopic agglutination test (MAT) for leptospirosis five days a week, for animals large and small. Our diagnosticians and laboratory technicians are proficient with this complex test, ranking as the most consistent on nationally standardized proficiency exams specifically for the leptospirosis MAT. With this proficiency TVMDL is able to provide veterinarians with quick answers on cases like the Weimaraner mentioned above. The test provides results for up to eight serovars that are pathogenic to large and small animals, including: L. pomona, L. icterohaemorhagiae, L. canicola, L. grippotyphosa, L. bratislava, L. autumnalis, L. hardjo, and L. sejroe. Most veterinarians will simply request Lepto 7 or Lepto 8 panel for small animals when they send in a serum sample, which provides screening for seven or all eight of the serovars mentioned along with titers, if present. The titers register as high as 1:12,800 on our test, as they did with this Weimaraner, and this is the final dilution that we perform despite the possibility that the titer might be much higher. A titer of 1:12,800 is indicative of infection, especially when paired with compatible clinical signs. Even titers of 1:800 are indicative of disease when clinical signs are compatible. When titers register on the high side, there can be a significant amount of cross-reactivity amongst serovars no matter the precision with which the test is run. But, the serovar responsible for infection usually has a titer that persists at a high level.
The only way to assess the persistence of a titer is to look at paired titers, one at two weeks out and another at roughly four weeks out. Another relevant part of running the leptospirosis MAT is consideration of the antibody response in the animal. The infected patient may not develop detectable antibodies for 10-14 days post infection. This is unavoidable, but this diagnostic gap is bridged by another test.
TVMDL also offers a PCR test for leptospirosis that can be run on 2mL of urine. This test can be run stand-alone or as an adjunct to the tried-and-true MAT. Pairing these tests can be useful for a few reasons. Spirochetes can be shed in the urine and are thus detectable on this PCR test before a full antibody response has developed in the patient. The PCR test is also a strong confirmatory test, which matches nicely with the indicators of serovar and titer that the MAT yields. It gives a positive or negative answer, and is only positive when the genetic material of spirochetes is present in the urine. TVMDL’s PCR has been validated against icteroheaemorhagiae, pomona, bratislava, autumnalis, hardjo, and sejroe bacteria. The PCR also helps differentiate a true clinical suspect from an animal that may be showing vaccine titers.
Vaccine titers in a dog can last for several months, and a vaccine can stimulate titers that could be confused with infection titers if taken out of context. Most of the commercially available leptospirosis vaccines for dogs include protection against canicola, grippsotyphosa, icterohaemorrhagiae and pomona. Depending on the type of vaccine used, it will either aid in preventing or provide prevention against leptospirosis. These terms denote different levels of protection, with prevention against eliminating shedding of spirochetes in an exposed, infected animal. Any leptospirosis vaccine should stimulate titers, but vaccine administration will not result in the shedding of spirochetes in the urine.
At TVMDL we field a number of questions regarding the prevalence of leptospirosis, as veterinarians look for assistance in deciding whether to vaccinate certain dogs or to include leptospirosis as a core vaccine in their practice. TVMDL only has data from submissions sent to our lab, resulting in a wide but sometimes patchy picture of the occurrence of clinical leptospirosis in dogs across Texas and elsewhere. However, no one can argue that certain patients may be higher risk based on a quick activity/lifestyle/environment history. There are concerns about vaccine reactions or heavy antigen loads that can come with leptospirosis vaccination.
For questions on leptospirosis diagnostics or to discuss your patient’s clinical presentations with a TVMDL diagnostician, contact TVMDL at 979-845-3414.