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The AKC Canine Health Foundation Infectious Disease Topics

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108 – November/December 2019

By Caroline Coile

I admit to feeling a source of great pride when I attend the AKC Canine Health Foundation National Parent Club Canine Health Conference. When the AKC first announced 24 years ago it was forming the Canine Health Foundation, I recall thinking it was just going to be window dressing. I didn’t even go to the first Parent Club Conference. I could not have been more wrong. And I’m proud to say I’ve attended every one since. One measure of CHF’s impact is the number of CHF funded projects published in peer-reviewed journals: more than 760 and growing! And these have been of such importance that they’ve been cited by other researchers in their publications more than 26,000 times! Partnering with breed clubs, parent clubs, all breed clubs, charitable foundations, the AKC, Nestle Purina, the Orthopedic Foundation for Animals, and others, they’ve invested more than $52 million into research and programs benefitting canine health. The AKC Canine Health Foundation National Parent Club Canine Health Conference is held every two years as a means for researchers, veterinarians and parent club representatives to interact. I covered some of the talks concerning genetic testing and population health last issue. In this issue I’ll cover three talks concerning important topics in infectious disease. Leptospirosis The award for best talk title has to go to Dr. Jason Stull’s “Emergence of Canine Leptospirosis: Coming Soon to a Puddle Near You?” Few vaccines cause more confusion and controversy than the lepto vaccine. Because it’s more likely than other vaccines to cause reactions in puppies, most breeders leave it out of their puppy vaccination regime. But somehow this has morphed into leaving it out of the vaccination schedule altogether. Make no mistake: Leptospirosis is here, its incidence in dogs appears to be increasing, and it is potentially fatal. It is caused by bacteria that infect a wide range of mammals including humans, livestock and companion animals as well as wild animals such as raccoons, mice, opossum, rats and skunks. It’s spread through contact with infected urine, and dogs most often contract it by drinking water from puddles or ponds into which urine has drained, or by having abrasions and wading into such water. They can also contract it by being bitten by, or eating, an infected animal. The bacteria survive for a very, very long time in the environment, even on moist grass. Many dog owners consider lepto to be a concern of rural areas, but it’s also being found in more urban areas. In order to recognize risk factors, Stull and colleagues at the Ohio State University, with funding from an AKC CHF grant “Estimating Prevalence and Identifying Risk Factors for Canine Leptospirosis in North America,” examined more than 40,000 test results from the past eight years from IDEXX laboratories. Overall, about 5% of tests were positive. The Midwest and Southwest U.S. had the most positive cases. Other factors that increased risk were being a male, being under 5 years old, being small, and living in an area with more rainfall. Oddly, in the Canadian dogs (but not U.S. dogs) they tested, urban dogs were more likely than rural dogs to test positive. Dogs under one year of age are 1.5 times more likely to be infected than any other age group. Compared to Sporting breeds, Herding and Terrier breeds are two times as likely to be infected, and Toy breeds are three times as likely to be infected. Looking in depth at just cases from one city (Chicago, which had an increased incidence of lepto), dogs not vaccinated for lepto were more than 25 times more likely to be infected than dogs that were properly vaccinated for lepto. Small dogs (under 14 pounds) were about seven times more likely to be infected than large dogs, and cases were found in dogs less than six months of age. About 30% of infected dogs died. How can you protect your dog? Know your area. Know your risks. Avoid puddles and slow moving water, and areas with high rodent or raccoon populations. Vaccinate. Vaccinate starting at 8 weeks of age, repeat in two weeks, booster annually. The vaccine doesn’t work on every lepto serovar, but it works on most. The vaccine has changed a lot in the past ten years. A 2015 study found 53 dogs per 10,000 vaccinated had reactions to lepto vaccine, compared to 22 dogs per 10,000 to other vaccines. Many years ago I had a very sick dog at the vet school, and the veterinarian said, “Well, I would suspect lepto, but I’m sure she’s vaccinated against it,” to which I meekly replied, “No, she isn’t.” I don’t think I’ve ever felt stupider than when I explained I had not vaccinated her because I was told it was risky. Fortunately it wasn’t lepto, she survived, and I learned my lesson. Bartonella and Hemangiosarcoma As if we didn’t need even more reason to hate ticks and fleas, Edward Breitschwerdt, DVM , DACVIM, has given us even more. Two years ago at the 2017 AKC CHF Parent Club conference Breitschwerdt introduced us to the genus Bartonella, a bacteria spread by ticks and fleas with potentially devastating results. The genus includes more than 20 species, with three of them (B. bacillliforms, B. henselae and B. quintana) known to cause vasoproliferative tumors (highly vascularized tumors) in humans. The most well-known vasoproliferative tumor in dogs is hemangiosarcoma (HSA). HSA affects about 10,000 dogs a year worldwide. Breitschwerdt and colleagues at North Caroline State have demonstrated that at least one subspecies of Bartonella activates a protein that in turn causes the production of vascular endothelial growth factor, which has been found to be higher in dogs with HSA. Dogs with HSA have a high incidence of this Bartonella subspecies compared to dogs without HSA. The high presence of Bartonella in splenic tissue may be because the spleen is responsible for removing blood-borne parasites from circulation. Could Bartonella be associated with HSA? Infections are known to precipitate cancer, and are estimated to be responsible for 25 to 50% of all human cancers. Bartonella can inject proteins in that can influence genes to alter cell proliferation and survival, and stimulates a degree of pro-inflammatory response, all of which can contribute to tumors. There’s evidence that Bartonella does in fact cause vasoproliferative diseases; in fact, the best known case is also a case study in how not to perform research. Daniel Carrion was a young South American MD who believed “Peruvian warts” (Google it) were contagious and were in fact the second, chronic phase of an acute sometimes lethal form of the same illness. So Carrion had his friends inoculate him with blood from a patient with Peruvian warts. He was proven correct on both counts, as he died of the acute phase within weeks. The person who injected him was arrested for murder, but released. At least they renamed the disease in Carrion’s honor. But the important message for dog owners is that these warts are types of vasoproliferative growths, and they turn out to be transmitted by Bartonella carried by sand flies. It’s not just Carrion’s disease. The most well-known Bartonella disease is cat scratch disease. In the early 1990s Bartonella was found to induce endocarditis (an infection of the heart valve) in both humans and dogs. But Bartonella remains difficult to find in a blood culture, because it must “hide” elsewhere in the body at times—-and very likely, according to Breitschwerdt, this hiding place is in the lining of the blood vessels and perhaps the bone marrow. It can be brought out, especially, due to immunosuppressive drugs, and it has been found to have effects on the cardiovascular system, rheumatology and nervous system in humans that can mimic other diseases. And more often than not, these disorders are misdiagnosed and ineffectively treated. Breitschwerdt has CHF funded grants looking for better ways to diagnose Bartonella; the association between Bartonella in dogs with splenic and cardiac HSA in different geographical locations; and the role of Bartonella in the clinical expression of arrythmogenic right ventricular cardiomyopathy in Boxers. For information about testing go to Vector-born Disease and Immune-Mediated Disease Bartonella infection is just one more worry for dog owners concerned about vector-borne diseases. Linda Kidd, DVM, PhD, DACVIMis studying the connection between vector-borne diseases and autoimmune disease. Immune-mediated diseases often present in a seasonal pattern, as do disease vectors. Vector-borne diseases are commonly associated with immune-mediated diseases in the same dog. Many of the clinical signs and laboratory abnormalities caused by vector (mostly tick) born diseases are essentially identical to those of immune-mediated diseases such as hemolytic anemia, thrombocytopenia or immune complex glomerulonephritis. For example Babesia organisms have been found in many dogs with diagnosed immune-mediated hemolytic anemia. It is possible that once Babesia is associated with red blood cells it signals the immune system to attack the cells but for some reason the attack doesn’t stop. Immune-mediated diseases are treated with immunosuppressive drugs, but what if the cause is actually a vector-born infection? Not only will the treatment fail, but the vector-born disease will gain an even stronger foothold. By treating the underlying disease, that disease can be removed, and possibly also remove the trigger for an associated immune-mediated disease. But it’s not always easy to diagnose a tick-born disease. The most common signs are very general ones, such as lethargy, GI upset or decreased appetite. Serology, which screens for antibodies, can miss early stages of infections; PCR tests for the organism itself, but could miss a situation in which there are low numbers circulating at the moment. In addition, the organism seems to circulate intermittently. Using PCR with repeated sampling, Kidd and colleagues found evidence of infection with or exposure to vector borne disease in 24% of southern California dogs who presented for evaluation of clinical signs consistent with immune-mediated or disease. Detection of Ehrlichia and Babesia increased when PCR was performed more than once or on more than one sample. Veterinarians should consider testing using both serology and PCR and in cases where Babesia or Ehrlichia is suspected to repeat the test if the first test is negative. In her latest CHF-funded study, Kidd is comparing retired racing Greyhounds, which usually have a high exposure to ticks, to show-bred Greyhounds, which have a much lower exposure. Overall, both lines of Greyhounds have low blood platelet and white blood cell counts, which is normal for this breed, and many have protein in the urine as well. But these findings can also be caused by vector-borne diseases. By comparing blood values in race-bred and show-bred Greyhounds, Kidd hopes to determine whether these lab results are found with the same frequency in the two populations. The results will help veterinarians decide whether to pursue more aggressive infectious disease testing for Greyhounds. Next time: The gut microbiota! It’s more important than you ever imagined…

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108 – November/December 2019

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