Routine screening for infectious disease-causing pathogens is part of the veterinary day to day. Timely testing in dogs and cats for fecal parasites, heartworm (Dirofilaria immitis), along with canine exposure to tick-borne disease pathogens (i.e. Borrelia burgdorferi, Anaplasma and Ehrlichia spp.) is advised by multiple expert and evidence-based guidelines and groups.1-4 For veterinary teams, detection of fecal parasites or evidence of vector-borne disease (VBD) pathogen exposure is not always isolated to the clinical impact on an individual cat or dog. There may also be environmental, zoonotic, and public health concerns, and with these factors comes a strong need for clear client communication on risks. Recent research has raised awareness on the potential emergence and range expansion of several parasite pathogens of profound One Health significance.5-11 These studies and case reports have implications for pet owners, veterinary and human health professionals, and wildlife researchers. Additionally, fecal surveillance and subsequent parasite detection, along with serologic screening for tick-borne disease, have potential antimicrobial use implications, warranting consideration of antimicrobial (anti-parasite and antibiotic) stewardship. Routine wellness visits for dogs and cats, and veterinary observed increases in screening test positivity in pets,1,7 are reflecting global rising temperatures, climate change, wildlife habitat shifts, and changes in the regional ranges, abundance, and emergence of VBD pathogens and fecal parasites. Results of routine diagnostic screening (fecal and blood sampling) have highlighted the role of veterinarians in One Health, and dogs and cats as sentinels for human infectious disease risk. Let’s look at two routine screening test clinical examples, Frankie (dog) and Reggie (cat): Case 1: Frankie Andrew presents for a wellness appointment with his dog, Frankie, a healthy Westie (female) that gets a lot of exercise, is eating a commercial diet well, and has a physical exam within normal limits. Frankie was dewormed as a puppy. As part of her wellness visit, blood is drawn and sent to a reference laboratory for VBD pathogen (heartworm, tick-borne disease) screening. Frankie’s findings (Seropositive for both Borrelia burgdorferi and Anaplasma spp.) prompt the veterinary team to discuss ticks. When asked, owner Andrew says he pulled a few off the dog (and himself) about a month ago and has been finding ticks in his yard (Calloway County, Mo.). Tick-borne disease pathogens, such as Anaplasma spp. and B. burgdorferi (the agent of Lyme disease), have emerged in previously uncommon regions and remain a significant concern in endemic areas of the U.S. and Canada.1,5 These changes, due to climate shifts impacting the range and abundance of tick vectors, have led to increases in disease risk for dogs and their two-legged companions, aka humans. One example of this is the distribution of Ixodes scapularis ticks, which vector both Anaplasma spp. and B. burgdorferi. Today, I. scapularis distribution is markedly wider (plus further south and west) than in the recent past, and activity of this tick type (and others) is increasingly observed during winter months, such as January and February.5 For many veterinary clinics and pet owners, awareness of Lyme disease and its cause is typically high. However, in new regions, like the southern and west-central U.S., Lyme disease awareness, and the need for tick prevention, particularly during cooler seasons, may be low. It is well established that dogs serve as human disease risk sentinels for Lyme disease, as test seropositivity rises in a region, so too does human Lyme disease incidence.6 Veterinary teams may not be as familiar with Anaplasma spp., and a clinically observed increase in test positivity in canine patients may be cause for concern.1,7 Like B. burgdorferi (Lyme), most dogs that test positive for Anaplasma spp. exposure do not show clinical signs. However, in humans, anaplasmosis has a much higher mortality as compared to Lyme disease and is much less likely to be diagnosed due to decreased awareness among human medical teams.8 For both of Frankie’s test results, a conversation about tick risk, the need for prevention, and the importance of ongoing preventive care for both human and dog are indicated. An algorithm can be helpful as an aid to these conversations and clinical decision-making on Frankie’s next steps. Frankie’s test results highlight One Health and a dog’s role as a sentinel for human disease risk: B. burgdorferi (Lyme) and Anaplasma spp. can cause illness in both dogs and humans and are transmitted by the same tick vector (Ixodes spp.). Frankie’s veterinary screening has alerted Andrew to a shared risk in their environment, and steps can be taken to protect both. By monitoring trends in canine exposure, veterinarians performing the advised screening1-4 proactively identify care needs for the individual dog (e.g. additional testing to detect proteinuria, a CBC to look for changes, and emphasis on the need for parasite prevention products). This day-to-day preventive care enables dogs to serve as sentinels for their human caregivers’ infectious disease risks, plus their families and broader community. Routine wellness visits and diagnostic screenings in pets highlight their role as sentinels for emerging infectious diseases—reflecting broader One Health concerns tied to climate change, shifting wildlife habitats, and the spread of vector-borne and fecal parasites. Case 2: Reggie Lynn presents for a routine wellness visit with her adult cat, Reggie, an indoor/outdoor domestic shorthair (M/N) with no previous health concerns. He is eating a commercial diet, and his physical exam is unremarkable, aside from being overweight (body condition score 7/9). Lynn says she knows Reggie hunts because he sometimes presents her with “gifts.” He receives flea prevention on a seasonal basis and has not traveled outside of Boulder, Colo. As part of Reggie’s wellness visit, a fecal sample is sent to a reference laboratory for routine endoparasite screening. Reggie’s finding of a parasitic co-infection with Toxacara cati, and Echinococcus multilocularis, come as a surprise to his veterinary team. The clinic is promptly contacted by an internal medicine consultant to discuss his results, and advise on next steps for prompt treatment, re-testing, and advisement of outreach to their state public health veterinarian, along with recommendations that Lynn (and any in-contact family members) contact their human health care provider.9,10 Fecal parasites, like T. cati, and E. multilocularis are both zoonotic, and while veterinary teams are well-used to speaking about roundworm (T. cati) risk to pet-owners, awareness of the tiny tapeworm (E. multilocularis), and the concern surrounding infection and the potential outcome of alveolar echinococcosis for humans and dogs, is frequently low, particularly in emerging risk areas of the U.S. and Canada.1,2,8-10 Reggie’s case also illustrates the unique role veterinary teams play through routine screening and testing to accurately and efficiently diagnose common fecal parasites, like roundworm (T. cati), in cats, along with detecting emerging parasites of One Health importance and potentially severe zoonotic risk, like E. multilocularis. In cats, especially those with outdoor access and hunting behaviour, co-infections with multiple parasites occur frequently and some parasites can only be diagnosed with PCR, such as E. multilocularis.9-11 Reggie’s veterinarian team was able to confidently diagnose his multi-parasite infection, target treatment for all parasites, apply actionable antimicrobial stewardship in his case management, identify significant zoonotic concerns, and provide risk counselling for all humans that may have been in contact with E. multilocularis immediately infective eggs, along with work with their relevant public health authority to alert to an emerging infectious disease concern. Reggie’s test result highlights the cat’s role as a sentinel for human disease risk. In One Health, E. multilocularis can cause severe disease in both humans and dogs, and T. cati can cause illness in cats and is a well-established zoonotic concern. Veterinarians performing advised fecal screenings proactively identify care needs for the individual cat (e.g. emphasising the need for and compliance with parasite prevention products), and enable cats (and dogs) to serve as sentinels for their human caregivers’ infectious disease risks—plus their families and broader community. Practicing One Health As veterinary professionals, we have long understood the power of the human-animal bond and how dogs and cats truly are humans’ best friends. These days, a One Health approach is essential in one’s clinic, as infectious diseases that we commonly screen for may well impact our pet patients and beyond. The changing global environment and advances in veterinary diagnostic capabilities have spotlighted disease risks that exist at the intersection of human and animal health, along with the environment (wildlife), in addition to having appropriate clinical antimicrobial use (stewardship) implications. It is frequently up to us to step forward and educate our pet owners, and in some cases, fellow human health care professionals, that due to climate change and other factors, such as travel and pet importation, past conditions surrounding infectious disease-causing pathogen risk may no longer be applicable. Just as those of us in the U.S. and Canada must adapt to seasonal shifts and hotter temperatures, on a human level, we must adapt our clinical practice, grow our awareness, and place value on why we perform screening tests. We must also get comfortable communicating what our cat and dog sentinels are sharing with us to alert them to their own and their human caregivers’ disease risks for the two- and four-legged. Michelle Evason, BSc, DVM, DACVIM (SAIM), has worked in general practice, academia, specialty clinical practice, and in the animal health industry. She serves as global director of Veterinary Clinical Education for Antech Diagnostics, Mars Science & Diagnostics. Michelle has published on numerous infectious diseases, antimicrobial stewardship, nutrition, and pet-owner education-related topics. References Companion Animal Parasite Council (CAPC) Guidelines. Accessed May 2025: https://capcvet.org/guidelines/ Canadian Parasitology Expert Panel (CPEP) Guidelines for the Management of Parasites in dogs and cats, 2019. Accessed May 2025: https://research-groups.usask.ca/cpep/index.php#Protocol Littman MP, et al. ACVIM Small Animal Consensus Update on Lyme Borreliosis in dogs and Cats. J Vet Intern Med. 2018;32(3):887-903. American Heartworm Society (AHS) Guidelines (Canine and Feline). As accessed May 2025: https://www.heartwormsociety.org/veterinary-resources/american-heartworm-society-guidelines Raghavan RK, et al. Unexpected winter questing activity of ticks in the Central Midwestern United States. PLoS One. 2021;11:16(11). Mead PS, et al. Canine Serology as Adjunct to Human Lyme Disease Surveillance. Emerg Infect Dis. 2011;17(9):1710-1712. Sokolchik I, et al. Field Validation of Anaplasma spp. and Ehrlichia spp. Antibody Screening Tests in Dogs. ACVIM Louisville 2025. Dixon DM, et al. Ehrlichiosis and anaplasmosis subcommittee report to the Tick-borne Disease Working Group. Ticks Tick Borne Dis. 2021;12(6). Langs Rund L, et al. Echinococcus multilocularis in a cat: novel report of molecular detection (quantitative polymerase chain reaction) and management in a domestic cat from Canada. Am J Vet Res. 2025; April. Online 1-3. Evason M, et al. Emerging Echinococcus tapeworms: fecal PCR detection of Echinococcus multilocularis in 26 dogs from the United States and Canada (2022–2024). J Am Vet Med. 2024;263 (2):1-5. Evason M, et al. Comparison of Gastrointestinal Parasite Frequency Between Feral and Pet Cats from Houston, Texas. ACVIM Louisville 2025.
