According to Dr. Michael Yabsley, who created a forecast map in 2017 showing Lyme disease infections in dogs across the U.S. at a county level, “Dogs really are the canary in the coal mine for human infection. Our research team has evidence that the relationship between canine disease and human disease is strong.” (1)
Dogs as Indicators of Human Disease
Canines also serve as effective sentinel indicators for human infections because of differences in how dogs and people are diagnosed. Many veterinarians recommend that dogs get tested annually for tick-borne diseases (e.g., the popular IDEXX 4Dx blood test can detect antibodies to Lyme disease bacteria, Anaplasma, Ehrlichia, and heartworms), as well as after a tick bite. (2) This contrasts sharply with people, who are generally only tested if they happen to notice a tick bite or after they have suffered years of increasingly severe symptoms. (Not to mention, many dogs are on tick preventatives year-round to reduce the likelihood of getting bitten in the first place.) As a result of these testing differences, more data is widely available on the prevalence of tick-borne diseases in canines, and research demonstrates how this information can be used to predict the dangers faced by humans.
Canine maps can give the public more information about the spread of ticks and the infections they carry, like Lyme disease, into areas not generally considered endemic. Take the state of Texas, for instance, which is generally not considered high risk for tick-borne diseases. This 2021 study provided evidence that self-reported tick bites from Texas residents overlapped with individuals who had CDC-positive Lyme tests as well as canine-positive Lyme, Anaplasma, and Ehrlichia tests. (3) It also identified county hotspots where the threat of tick-borne illness was high for both dogs and people.
Even in places considered endemic, the risk of contracting Lyme disease or another tick-borne illness can vary greatly depending on the particulars of the region. For example, a 2023 study examined IDEXX 4Dx blood tests from 3,750 dogs living in shelters in 19 states in the Eastern United States. The results found that 8.9% of the canines had Lyme disease bacteria, 2.4% had Anaplasma, and 8% had Ehrlichia. Furthermore, almost 5% of the shelter dogs were suffering from multiple infections. Based on the geographical distribution of these tick-borne infections, researchers will be able to determine better the risks to humans residing in the same areas.
The Value of Canine Mapping for Tick-Borne Infections
It’s not uncommon for patients seeking answers to their mysterious symptoms to hear some variation of: “It can’t be Lyme disease. Lyme doesn’t exist here.” However, canine maps clearly illustrate that Lyme disease and other tick-borne infections have spread across the United States. Studies like this one out of Germany (4) reveal similar patterns in human and canine infections, suggesting that if a dog can get exposed to Lyme and other tick-borne infections, then so can the people living in the same geographical region, even if they are non-pet owners.
For U.S. residents who are wondering about their level of risk, a nonprofit called the Companion Animal Parasite Council (CAPC) has been collecting data and putting together parasite prevalence maps for various vector-borne diseases, including Lyme, Anaplasmosis, and Ehrlichiosis, since 2012. In 2022, for instance, the CAPC reported 424,025 positive cases for canine Lyme disease; essentially, 1 out of every 30 dogs tested positive. (5) The numbers for canine Anaplasmosis and Ehrlichia cases for 2022 were similar, at 425,391 and 295,061 respectively. Compare this to the CDC data, which reports approximately 30,000 human Lyme disease cases per year despite estimating that the true statistics is closer to half a million. (6)
Based on the canine data, it’s clear that tick-borne infections in humans are going underreported and very likely misdiagnosed. Awareness of the prevalence of Lyme disease and other tick-borne illnesses in our canine companions can improve our understanding of how these infections are affecting the human population.
References:
- University of Georgia. “New Lyme disease forecast map targets rising tide of ticks.” ScienceDaily. ScienceDaily, 11 May 2017. <www.sciencedaily.com/releases/2017/05/170511120207.htm>.
- Fatcheric, D.E. “Tick-borne Disease in Dogs: How to Prevent Tick-Borne Diseases,” Whole Dog Journal, 11-Apr-2023. [Online]. Available: https://www.whole-dog-journal.com/health/tick-borne-diseases-in-dogs/. [Accessed: 14-Sep-2023]
- Maxwell, S.P.; McNeely, C.L.; Thomas, K.; Brooks, C. Tick-Borne Surveillance Patterns in Perceived Non-Endemic Geographic Areas: Human Tick Encounters and Disease Outcomes. Healthcare 2021, 9, 771. https://doi.org/10.3390/healthcare9060771.
- Cook, M.J.; Puri, B.K. Estimates for Lyme borreliosis infections based on models using sentinel canine and human seroprevalence data. Infectious Disease Modelling 2020, 5, 871-888. https://doi.org/10.1016/j.idm.2020.10.004.
- The Companion Animal Parasite Council. “Parasite prevalence maps,” 29-Mar-2019. [Online]. Available: https://capcvet.org/maps/#/2022/all-year/lyme-disease/dog/united-states. [Accessed: 14-Sep-2023]
- “Lyme Disease, Data and surveillance,” Centers for Disease Control and Prevention, 29-Aug-2022. [Online]. Available: https://www.cdc.gov/lyme/datasurveillance/index.html. [Accessed: 14-Sep-2023]
