In Europe, the vaccination for leishmaniasis requires a quick blood test to confirm the dog does not have the disease, and then the vaccine is given. Use of a collar or spray to repel ticks, fleas, mosquitoes, and sand flies is recommended as an added precaution. Photo courtesy Claire Williams Importation of dogs from other countries, people traveling or moving overseas with their pets, and climate change are all contributing to more cases being seen of the zoonotic tropical disease leishmaniasis in North America. It is not widespread and is generally found only in certain areas where the climate and environment are hospitable to the sand flies that transmit it, but it is something to be aware of in light of increased mobility and migration of humans and animals, and potential changes in climate that can expand the range of sandfly species that spread it. What is it? Leishmaniasis is a parasitic infection transmitted in North America by the bite of female Phlebotomus sandflies in the genus Lutzomyia, which are restricted to warm tropical areas, predominantly in Central and South America, as well as in the southernmost United States, such as Texas. Sandflies are limited to areas with temperatures above 60 degrees F for at least three months of the year. In Europe, the active season for adult sandflies is April to November, with warmer regions having longer seasons. The disease is named after pathologist and British Army medical officer, William Boog Leishman, who identified certain organisms as trypanosomes in human patients with the disease that was then called kala azar. Natural hosts include dogs and humans.1 Dogs can become infected with leishmania and serve as vectors for the disease when an infected dog is bitten by a sandfly that later bites a human or other animal. Dogs can also spread Leishmania spp. to other dogs via blood transfusions or sexual intercourse. “Dogs are routinely imported from countries endemic for canine leishmaniosis and this is the predominate way infected dogs enter Canada or the United States,” says Katie Clow, DVM, PhD, assistant professor in One Health in the Department of Population Medicine at Ontario Veterinary College, University of Guelph in Ontario, Canada. While dogs infected with leishmania have entered North America, the most “northern” sandfly species—Lutzomyia shannoni—is not yet a confirmed vector of Leishmania spp., Dr. Clow says. “That dramatically drops the risk of transmission.” Currently, in North America, dogs with leishmaniasis pose a low risk of transmission to humans, although it is conceivable in rare cases blood-borne transmission could occur, Clow says. For that reason, she advises veterinarians dealing with leishmaniasis-infected dogs should practice strong infection-control procedures. Dogs at greatest risk are those that have resided in areas with vector-borne transmission of Leishmania spp. More than 90 endemic countries fall into this category, primarily in the Mediterranean basin, Middle East, East Africa, and South and Central America. The World Health Organization (WHO) classified the United States as endemic for leishmaniasis in 2015 and notes with climate change, incidence and geographical distribution of the disease is expected to increase.2 The sandflies that transmit the disease are typically active from dusk to dawn, putting outdoor dogs and those that spend extended periods of time outdoors in rural or peri-urban areas at elevated risk. Also at risk are dogs with little or no access to veterinary care or preventive measures, such as vaccination or collars that repel parasites. “For risk of disease development, dogs that have concurrent medical issues and/or are immunosuppressed appear to be at higher risk,” Clow says. “Age and breed have also been identified as risk factors for disease. There are two age peaks, presenting in young dogs aged two to four, and in dogs older than seven. Boxers, cocker spaniels, rottweilers and German shepherds appear more susceptible to clinical disease, while the Ibizan hound seems to be resistant.” In foxhounds, vertical transmission appears to be a primary way leishmaniasis is spread. In a study conducted over a period of three years,3 researchers found spread of infection in foxhounds and some other dogs occurred by direct dog-to-dog transmission, with possible modes including biting, reuse of needles for injections, blood transfusions, and sexual intercourse. “Dog bites and other abrasions and lacerations occur commonly among working and kenneled foxhounds, which may potentiate exchange of body fluids between hounds,” researchers wrote. “Blood transfusion transmission from infected dogs was documented in a clinical study at the University of Pennsylvania.4 Congenital transmission from infected pregnant foxhounds to their pups was observed by owners and reported during the course of our investigation. Breeding that results in transplacental infection of litters may be the most important mechanism of transmission among foxhounds.” There have been no known cases of hound to human spread of leishmaniasis. However, the University of Pennsylvania study concluded it might be inadvisable to use foxhounds as canine blood donors in North America. Areas of research A primary interest of scientists studying the disease is the expansion of sandflies in the context of climate change. Clow’s lab is working on forecasting that range expansion and has two open studies seeking participants. One is a cross-sectional study that involves completing a simple blood test to screen for infection with Leishmania spp. for any dog imported into Canada from an endemic area within the last three years. The laboratory covers costs for blood collection and testing. Owners are asked to fill out a questionnaire on the known lifestyle and medical history of the dog. “This will give us much-needed baseline data on prevalence of infection,” Clow says. It will also help to identify lifestyle and medical risk factors associated with infection. The other is a case series study, following clinical cases for two years in dogs imported to Canada from regions known or suspected to be endemic for Leishmania spp. The research will contribute to understanding of the nature of the disease and prognosis. Testing costs are covered, and participating veterinarians receive an honorarium. Both studies are funded by the Canine Health Foundation of the American Kennel Club (AKC). Veterinarians interested in learning more or potentially enrolling patients can contact Sydney DeWinter, the PhD candidate leading the project, at sdewinte@uoguelph.ca. At The Ohio State University College of Veterinary Medicine, Christine Petersen, DVM, PhD, is heading up a lab investigating such areas as host-pathogen interaction between the immune system and Leishmania species and identification of reservoirs and prevention of zoonotic diseases. Dr. Petersen is a member of LeishVet, the governing body that determines treatment and control guidelines for global veterinary leishmaniasis. Petersen’s research includes a randomized, controlled, double-blinded field trial to assess effectiveness of a Leishmania vaccine and transmission modeling of leishmaniasis in Brazil.6 Diagnosis and management The parasite cannot be eliminated from the body, and infections in dogs last for life. However, infection does not necessarily translate into clinical disease. While human leishmaniasis takes different forms, the same classifications do not exist in dogs. An infected dog may exhibit no signs or appear severely ill. LeishVet,5 an international nonprofit that studies the disease, has clinical guidelines on leishmaniasis, including a published grading system reflecting the stage, severity, and prognosis of leishmaniasis in dogs. The parasites can infect most tissues in the body, and a spectrum of clinical manifestations ranging from mild to fatal have been documented in dogs with leishmaniasis. Infected and symptomatic dogs may exhibit crusty skin disease characterized by non-itchy, raised reddish bumpy areas near the eyes or on the face, ears, axillary regions, or feet. Other common clinical findings include weight loss, lethargy, fever, generalized enlargement of the lymph nodes, enlarged spleen, vomiting, diarrhea, lameness, bleeding from the nose, increased drinking and urination, and cutaneous and ocular lesions, Clow says. Dogs can also die from renal disease associated with infection. Two blood tests are available for diagnosis. One looks for antibodies to Leishmania spp. (quantitative serology) and the other detects the genetic materials of the parasite in the blood (molecular real-time PCR). Samples of infected tissues, such as skin lesions, can also be analyzed to visualize the parasite or detect its presence in those tissues. “Treatment is challenging and depends on the stage of the disease,” Clow says. “The most important thing to recognize is treatment is not curative, and relapses happen, but for less advanced stages, prognosis for a good quality of life is high. It is recommended any dog that resided in an endemic area be tested as dogs can be infected and subclinical for months to years before disease could develop and prognosis is best when recognized early.” Owners who will be traveling with their dogs to endemic areas should be advised to protect their pets against sand fly bites. “Any dog visiting an area with sand flies should have either spot-on permethrin treatment or deltamethrin-embedded collars for the entire duration of time in that area,” Clow says. “Vaccination does exist. It does not prevent infection but does reduce the likelihood of disease and disease progression. Both can be used in combination.” Kim Campbell Thornton has been writing about dogs, cats, wildlife, and marine life since 1985, and is a recipient of multiple awards for her articles and books from the Cat Writers Association, Dog Writers Association of America, and American Society of Journalists and Authors. References Petersen, C. New Means of Canine Leishmaniasis Transmission in North America: The Possibility of Transmission to Humans Still Unknown. 04 June 2009. Interdisciplinary Perspectives on Infectious Diseases. https://onlinelibrary.wiley.com. Mann, S et al. A Review of Leishmaniasis: Current Knowledge and Future Directions. Curr Trop Med Rep. 2021; 8 (2): 121-132. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7966913/ Duprey, Z et al. Canine Visceral Leishmaniasis, United States and Canada, 2000-2003. Emerg Infect Dis. 2006 Mar; 12(3): 440-446. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3291440/ Owens, S et al. Transmission of Visceral Leishmaniasis Through Blood Transfusions From Infected English Foxhounds to Anemic Dogs. 15 Oct 2001. JAVMA; Volume 219 Issue 8. https://avmajournals.avma.org/view/journals/javma/219/8/javma.2001.219.1076.xml https://www.leishvet.org/ Toepp, A et al. Randomized, Controlled, Double-Blinded Field Trial to Assess Leishmania Vaccine Effectiveness as Immunotherapy for Canine Leishmaniosis. Vaccine, Volume 36, Issue 43, 15 October 2018, Pages 6433-6441. https://www.sciencedirect.com/science/article/abs/pii/S0264410X18312453?dgcid=rss_sd_all
