Official publication of The American Animal Hospital Association
Note: This article was originally published on January 1, 2023 and has been updated to include some more recent information
In an age where infectious diseases such as Amans), New World Screwworm (NWS) is once again spreading in the U.S., and where significant environmental changes are linked more often to human activity, the concept of One Health has become increasingly important. According to the American Veterinary Medical Association (AVMA), One Health indicates that “humans, animals, and the world we live in are inextricably linked.
Protecting the links between these groups and support their collective health requires the collaboration of many different disciplines, including veterinary professionals, human healthcare professionals, and others. To some, it may seem like common sense that humans would work to improve animal and environmental health for our own benefit, and indeed it is (at least in theory). Some of the ways in which this can be done, however, may not be so intuitive. And the central role of all members of the veterinary team in the success of One Health initiatives cannot be overstated.
A brief history of One Health programs
The veterinary industry has been integral in advancing the visibility of One Health programs worldwide.
In 2007, AVMA President Roger Mahr, DVM, established the One Health Initiative Task Force (OHITF). Ron Davis, MD, then president of the American Medical Association (AMA), oversaw approval of a resolution to “engage in a dialogue with the American Veterinary Medical Association to discuss strategies for enhancing collaboration between human and veterinary medical professions in medical education, clinical care, public health, and biomedical research.”
The American Public Health Association (APHA) then sent a liaison to join with those from the other two associations in the OHITF. The AVMA and multiple individual veterinarians continued to have an active role in the One Health Commission as it grew.
Check out the 2025 AAHA One Health Guidelines
The 2025 AAHA One Health Guidelines: Navigating cross-disciplinary partnerships provide expert insights and detailed roadmaps to help veterinary professionals work seamlessly with other healthcare professionals within a One Health System. Read up on common scenarios, case studies, and more
One Health stories
Examples abound of how human, animal, and environmental health affect each other. Here are a few instances of particular interest to the veterinary community.
Rabies
Sometimes, decisions made to treat animals can have significant implications for human health. Take, for instance, the public health crisis in India surrounding cattle, vultures, dogs, and humans.
Cattle are raised in India for milk, for pulling carts and farm equipment, and for producing fertilizer, and generally not slaughtered due to cultural and religious beliefs. Thus, cattle are allowed to die naturally and then left for vultures to scavenge after they die.
In the late 1990s, there was a significant die-off in the number of vultures, which left many cow carcasses rotting in fields. Feral dogs seized the opportunity to scavenge this food
The problem with this change was that these dogs were, by and large, not vaccinated for rabies. The subsequent rise in feral dogs was associated with over 39 million dog bites to humans and an estimated 48,000 rabies deaths in humans in the region.
After an exhaustive investigation, the cause of the vulture die-off was determined to be diclofenac poisoning from consuming carcasses of cattle that had been treated with this anti-inflammatory drug. Diclofenac was banned in cattle in India in 2006 as a result.
Even in countries like the U.S. where feral dog numbers are lower and rabies vaccine rates are higher, humans still die from rabies every year. And a general fear and distrust of medical guidance and scientific information has contributed to vaccine hesitancy that has extended, in some cases, to vaccination against rabies in pets, which has the potential to increase the number of preventable human exposures and deaths.
FIP
Human disease can also affect animal health and treatment. One such example is the current treatment climate for cats suffering from feline infectious peritonitis (FIP).
Once considered a uniformly fatal disease in cats, FIP saw a new treatment option begin to gain traction between 2016 and 2019. Named after its manufacturer Gilead Sciences, GS-441524 is an antiviral drug that works by preventing the formation of viral proteins. In experiments, this drug was found to be incredibly successful in curing cats diagnosed with FIP who would have otherwise died.
Just when it seemed like the path might have been paved for approval of GS-441524 for treatment of FIP in cats, the COVID-19 pandemic hit. Because FIP and COVID-19 were both caused by (different) coronaviruses, it was found that both could be treated with similar drugs.
In fact, one of the drugs found to be most successful in treating COVID-19 in humans, remdesivir, is rapidly converted to GS-441524 in the body.
Because of fears that production of GS-441524 for cats would hinder the production of remdesivir needed for critically ill humans during the pandemic, Gilead Sciences chose not to pursue approval of their drug for use in animals. Given the large need for the drug in cats, a newts in the United States and many other countries—began to circulate.
Because of the legal implications of administering an unapproved drug, veterinarians were largely unable to obtain, dispense, or prescribe this drug formulation. As a result, desperate cat owners, breeders, rescuers, and others developed their own network of distribution involving Facebook pages, unmarked give daily subcutaneous injections at home.
This story began to change in 2024, when the first compounded version of GS-44124 became available in the U.S. Now multiple compounded formulations exist, which has removed many of the barriers veterinarians faced with regard to prescribing the drug to their patients who need it most.
Global warming and pet food
Animal and human health also contribute to and are affected by environmental changes around the world. The raising of food animals for meat (for both humans and animals) contributes to deforestation and increased production of carbon dioxide and methane, both of which contribute to global warming. It is estimated that meat production to produce pet food alone creates about 64 million tons of carbon dioxide per year.
Although eliminating meat in cat and dog diets is not likely to be a feasible solution at this time, there are studies looking at the use of lab-grown meat and insects as more environmentally friendly options for protein
Leptospirosis
A JAVMA article identified factors that increase leptospirosis risk among humans and animals. These factors include increased flooding due to more frequent and severe weather events, increased human travel and human encroachment on animal environments, and under recognition of leptospirosis as a concern in both humans and animals because of its nonspecific clinical signs and a presumption that it is limited to tropical climates.
Human medical practitioners, for example, may mistake leptospirosis signs as evidence of COVID-19. Veterinarians in certain parts of the country (and world) may also assume that the risk of leptospirosis in their region is too low for their patients to recommend vaccination.
However, leptospirosis cases have recently been identified in both humans and animals in areas of the southwestern United States, where the climate is semiarid as opposed to tropical, and in urban settings including Boston. This highlights the need for human and veterinary health professionals to share information on disease trends and to continue to learn how environmental changes can affect the health of their respective patients.
Sidebar: canine vaccine guidelines with lepto as core
The AAHA 2022 Canine Vaccination Guidelines were updated in 2024 to reflect a change in status of the leptospirosis vaccine from non-core to core. This is following consensus statements from the American College of Veterinary Internal Medicine (ACVIM) and the World Small Animal Veterinary Association (WSAVA), and the recommendation of AAHA’s vaccine guidelines task force.
Avian influenza
While aars, it was only in 2024 when the virus was first noted to have spread from sick wild birds to nearby dairy cattle and then to cats present on dairy farms.
As of 2025, at least 70 cases of H5N1 influenza have been reported in humans, with most of them linked to direct exposure to dairy herds, poultry operations, or other animal contact.
Because of the wide variety of species affected and influenza viruses’ ability to mutate rapidly, preventing the spread of disease requires strict biosecurity measures, careful surveillance, and education of pet owners and the general public about the risks associated consuming raw dairy, beef, or poultry, and the risks of feeding these products to pets.
New World Screwworm (NWS)
After having been previously eradicated from the U.S., NWS has now been reported in animals in Texas and New Mexico, with cases reported in both cattle and dogs.
This parasite is considered to be more aggressive than other fly species whose larvae infest animal wounds because the larvae feed on living tissue and can invade very small wounds including scratches, insect bites, the umbilicus of newborn animals, and the wounds created by placing an ear tag in livestock species. Additionally, the parasite is known to cause rapidly progressing and painful lesions in the animals they infest.
While there is no threat to food safety and the risk to humans and animals is still considered to be low, NWS still poses an economic threat to livestock industries and has disrupted or complicated the movement of animals between the U.S. and Mexico.
In response to the presence of NWS in the U.S., Mexico has banned the import of most livestock species from the U.S. along with zoological species, many types of birds, and ferrets. Additionally, pet dogs and pet birds require additional documentation that they have been inspected and been found to be free of NWS and any wounds that could become infected with the parasite.
And the threat to humans still exists, especially among individuals who sleep or spend a lot of time outside, those who have open wounds or sores including incisions from recent surgery, and those with medical conditions such as skin disease or cancer that cause delayed skin healing.
The previous eradication of NWS from the U.S. and much of Central America relied on the coordinated release of sterile NWS flies at the southern tip of Panama (called the Darien Gap) that successfully prevented the flies from reproducing.
NWS flies and cases of human and animal myiasis with the parasite began reappearing north of the Darien Gap in 2023, however. While not all the reasons for this resurgence are well understood, experts have suggested a few possible causes: a decrease in sterile fly production during the COVID-19 pandemic, the illegal movement of cattle across the southern border of Panama, and limited surveillance across parts of Central America.
One Health in veterinary practice
Maria N. Donnelly, DVM, MSPH, has worked in both private practice and with the Florida Epidemic Intelligence Service Program (FL-EIS). She was drawn to a career in public health after growing up overseas in developing countries, and as she puts it, she “saw firsthand the impact of clean drinking water and a safe food supply make to people’s lives.”
Donnelly encourages all veterinary professionals to “become a part of organized veterinary medicine to stay informed with policy changes affecting One Health.” Apart from organized veterinary medicine, there are many ways that all members of the veterinary team can help improve and protect the health of animals, humans, and the environment.
Veterinary team members
Client service representatives, veterinary technicians, and veterinary assistants often have the first contact with an animal owner, whether over the phone, in person, or through a text or email. They are often the ones who experience the greatest emotions from a client: their fear or anxiety, their excitement and gratitude, or their anger. While clients wait to be called into an exam room or explain over the phone why they must change their appointment, team members may learn details of a client’s life, health, and challenges they are facing. They may be able to share some of this information with the rest of the team, when appropriate, to help personalize the care given to their animal.
Types of relevant information include their pet’s role as an assistance dog (service, therapy, or emotional support animal) and physical challenges of the owner that might interfere with their ability to follow through on treatment and lifestyle recommendations for their pets.
Physical challenges might include mobility concerns, trouble lifting, handling, or medicating their pet, or even trouble reading a medication label or opening a child-proof lid. If the client volunteers that they or someone in their home are pregnant, immunosuppressed, or managing any number of different health conditions, this information may affect the types of recommendations, cautions, and even referrals for outside assistance that the team makes for this client.
Other helpful information can include financial constraints that can affect their ability to consent to recommended treatment, and even preconceived notions or misconceptions about their animal’s health and care. The veterinary team may be able to help resolve some of these obstacles if they know about them.
Apart from picking up on and relaying important information at the beginning of the appointment, team members will often be the last ones to see the client when they leave. They can help to repeat and reinforce recommendations made by the veterinarian, ensure that the client feels comfortable carrying out the treatment at home, and receive any feedback or last-minute questions from the owner. In some cases, the client will feel comfortable expressing thoughts and emotions to a team member that they did not feel comfortable sharing with the veterinarian.
Veterinarians
As a veterinarian currently working in small animal private practice, Donnelly points out how she and her colleagues use their public health knowledge every day, and that it is “one of the most important aspects of our job.” This is evident in discussions of zoonotic transmission of intestinal parasites and prevention of dog bites in children.
Indeed, veterinarians recommend and prescribe treatment to protect human and environmental health in addition to improving the health of their patients. This can include vaccination for important zoonotic diseases, educating cat owners on the environmental effects of outdoor cats, and being responsible stewards of antibiotics to prevent resistance. Veterinarians can also highlight the power of the human-animal bond, for the benefit of both humans and animals.
Donnelly points to the US Centers for Disease Control and Prevention (CDC) slogan, “Healthy Pets, Healthy People,” as a great reminder of the connectedness between human and animal health. Veterinarians are uniquely qualified to understand the health risks of zoonotic diseases for both animals and humans. Although they cannot provide medical advice to their human clients, veterinarians can convince their clients of the importance of preventing zoonotic transmission and advise them when to seek appropriate medical treatment for themselves.
Apart from private practice, veterinarians work as pathologists, epidemiologists, researchers, and in a variety of government roles. In these capacities, they study trends in infectious diseases, protect our food supply, pioneer new treatments that can benefit both human and animal health, and ensure the safe transport of animals while reducing the risk of infectious disease transfer.
When asked about the most exciting advances in One Health recently, Donnelly pointed to the “increase in awareness of One Health as evidenced by more academic institutions with public health programs, increased education through the AVMA, and US and international government programs and policies focused on One Health.” This increased awareness shines a light on veterinary medicine and the important work that we do.
As we continue to work together with our fellow professionals, we can make a big difference in the lives of animals and humans, and in the health of the planet we call home. Perhaps more than anything else, this is a reason to keep learning, sharing, and innovating despite all the challenges we face in our profession.
Photo credit: FotoSpeedy/iStock via Getty Images
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