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History of One Health

Oreta M. Samples

Department of Veterinary Science and Public Health, Fort Valley State University, Fort Valley, GA, 31030, USA

The concept of One Health is not a new idea in the annals of modern medicine. Originally introduced by William Osler and Rudolf Virchow, it was reintroduced by Calvin Schwabe in 1984 (Schwabe 1984). Within the text "Veterinary Medicine and Human Health," he observed that an interdependence between human and veterinary medicine would encourage collaboration among the various disciplines leading to improved health outcomes in humans and animals and a renewal of healthy environments (King 2008).

According to Rudolf Virchow, "between animal and human medicine, there are no dividing lines ." (King 2008). This statement is attributed to the 19th Century German physician who is also credited with coining the term "zoonoses," providing an endorsement for what would become known as "One Health." The theory was further enhanced by Dr. Rudolf Osler, a student of Virchow. Recognizing that pathology could serve as the cornerstone of all veterinary medical disciplines, he applied the science of autopsy investigations to teach both human and veterinary pathology during his tenure at Montreal Veterinary College as a faculty member (Saunders 1987).

Currently, the idea of One Health is built on the foundation that the health of humans is dependent upon two things: animal health and the health of the environment (Atlas, 2014). Essentially, this leads to a concern for all "living things" as related to specific factors. The first factor that affects living organisms of every kind is the microbiological influence that a vast array of microbes has on both healthy animals and the progression of disease. This is most important, as infectious microbes often are at the heart of zoonotic disease spread. The second factor is that of the physical environments on which all living things depend for survival and the overall "health" of the environments in their ability to sustain life. Finally, the overall interactions that occur between animals and humans may be of a positive or negative nature with similar consequences. When combined, one can see how these factors come together both to support and influence the health of living things while advocating for the support of healthy environments in which to exist (Riegelman 2018).

One may ask: "Why is One Health important now?" In the 21st Century, when global inhabitants are faced with challenges such as the COVID-19 pandemic and global warming, there is a need for immediate protection of the environment to not only prevent the spread of disease, but also safeguard against shrinking ecosystems that are home to species in danger of losing their home environments to such things as rising temperature. The protection of environments and the resident species is all important if the planet is to survive and thrive. Encroachment by mankind on natural habitats continues to force interactions between species that are not "naturally" supposed to happen. Negative interactions occur when mammalian species such as raccoons and opossums are forced to live near humans due to "urban sprawl" efforts. Though naturally adept at foraging for food and living in forested areas, these animals wreak havoc and cause destructive damage when forced to forage for food from garbage cans or shelter in the attics and crawl spaces of human dwellings. This "cohabitation" leads to the possible spread of diseases and parasitic infections because of urine and fecal contamination of areas utilized by humans and companion animals (e.g., pets).

1.1 Purpose of One Health Initiative

The One Health initiative is driven by the three aforementioned factors; however, it serves to address several outcomes that are ever-changing. The achievement of optimal health outcomes for all living beings when faced with health challenges because of interspecies interactions may be among the most important. While some diseases, such as rabies, may simply be avoided by lack of interaction with certain environments or animals, others may be more insidious in the mode of transmission. Such is the case of Escherichia coli being spread to fruit or vegetable crops due to crop irrigation with wastewater containing coliform bacteria. There is also the challenge of one's perception of healthy practices, which may differ from country to country. This is especially true of countries dealing in the import of foodstuffs from other countries.

Another outcome is to recognize the results of connections that may occur between people, animals, and the environment within which all come together. This is most easily demonstrated when pets are not regularly treated with flea and tick preventative. As a result, the pet, while outside, encounters a tick such as the "black-legged tick" (Ixodes scapularis), which attaches itself to the pet's fur. When the animal comes inside the house and settles on the couch, the tick falls off. Later, it attaches itself to feed on the human sitting on the couch. Unbeknownst to humans until they find the engorged insects (sometimes hours or days later), they may have been infected with Anaplasma phagocytophilum, a bacterium that causes the disease anaplasmosis. They may in fact not realize that they have this disease even when symptoms appear, as the signs are often described as "flu-like" and may go undiagnosed. The correct diagnoses may be arrived at when the three factors of human-animal interactions in a supportive environment for the tick Ixodes scapularis are exploited (Center for Disease Control and Prevention 2023a, 2023b).

A third outcome that has become quite important is the need for and ability to identify opportunities that pinpoint novel occurrences of zoonotic diseases through shared/encroachment on environments (see Figure 1.1). An example of this would be the spread of Baylisascaris procyonis, a nematode found in raccoons that is commonly transmitted to the environment through fecal excrement. Eggs within the excrement may be accidentally ingested by humans, then hatch into larvae, which then may migrate to various tissues, resulting in visceral larval migrans (VLM), ocular larval migrans (OLM), or most severely, neural larval migrans (NLM), which may lead to severe eosinophilic meningoencephalitis (Center for Disease Control and Prevention 2023c). Children who happen upon shared raccoon "latrines" often found on woodpiles, crawl spaces, or in wooded areas may accidentally contaminate hands and ingest eggs when subsequently handling food without proper pre-meal hand sanitation.

Figure 1.1 Field identified with warning to hikers regarding presence of ticks which may cause disease to humans.

Source: Schlegelfotos/Shutterstock.

1.2 Common Issues Addressed by One Health

One Health as a global initiative addresses a variety of zoonotic diseases that plague humans worldwide, as well as antimicrobial resistance. Among the diseases addressed are emerging and reemerging zoonotic diseases, endemic diseases, neglected tropical diseases, and vector-borne diseases.

1.2.1 Zoonotic Disease Types

There are many zoonotic diseases that have been documented throughout history. The prevalence of such diseases is often based on specific environmental conditions being conducive to the causative organisms. Secondary to these conditions are the humans or animals that may be affected and whether they are in a state of susceptibility. Oftentimes, emerging diseases first are detected in an animal species, with some of the most notable diseases being West Nile virus, AIDS, and hantavirus.

Emerging diseases are by definition, diseases or infections that are newly seen in a population, also referred to as an "outbreak." While all diseases originate from something, these diseases generally leave these questions initially unanswered. By contrast, a reemerging disease is one which has been regarded as a major health issue at some point in history. Reemergence may occur due to lack of precautions that may have stopped its initial progression, such as vaccines, sanitation efforts, or vector control. Examples of reemerging diseases include tuberculosis, measles, and malaria (John Hopkins University 2024; NIAID 2024).

Endemic zoonotic diseases pose a special threat as they cause constant and regular outbreaks within susceptible populations. Such diseases include rabies, cysticercosis, and leptospirosis. Endemic diseases provide a special challenge, as while many have either preventative vaccines or strategies to limit widespread infection, they may also be capable of infecting various animal populations which cannot realistically be treated to prevent spread to humans. An example is rabies, which can be spread to warm-blooded mammalian species. While companion animals and farm animals can be regularly vaccinated against this viral disease on a yearly or every three-year schedule, wildlife species cannot be realistically vaccinated on a regular basis. Since many wildlife species encroach on areas inhabited by companion/farm animals and humans, they present an ever-present danger.

Neglected tropical diseases are diseases that are known to be problematic in...