One Health Resource Center

One Health Resource Center

Issue: April 2017
April 19, 2017
14 min read

One Health approach essential to controlling public health threats

Issue: April 2017
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Rocky Mountain spotted fever can be deadly to both humans and dogs, but diagnosing a dog with the tickborne illness does not guarantee that the owner will be examined for it, even though he or she may have been exposed to the infection through the same environmental risk factors.

Photo by Shatar Munkhduuren

Richard A. Kock, MA, VMB, VMD, MRCVS, professor of wildlife health and emerging diseases at the Royal Veterinary College, stands over a dead saiga in Mongolia, where he said a virus that spread from livestock as a result of human encroachment killed thousands of the endangered antelopes.

“There have been cases where dogs have been sick and the veterinarians knew about it, but because physicians never heard about it, human cases were missed, leading to some fatalities,” Peter Rabinowitz, MD, MPH, associate professor of environmental and occupational health sciences and director of the Center for One Health Research at the University of Washington, told Infectious Disease News. “If there was a mechanism for the vets to talk to the physicians, they could have alerted them to be more aware of Rocky Mountain spotted fever in their patients.”

In this way, Rocky Mountain spotted fever is a classic example of an infectious disease threat that requires a One Health approach. Rabinowitz has used it as an example when talking with clinicians about the need for a collaborative effort between different disciplines.

“When veterinarians see potentially infectious diseases, there’s no way for them to communicate that with local medical providers,” Rabinowitz said. “What they do now is tell the patient to talk to their doctor, and that may not be the most efficient way of communicating an emerging threat. It puts the onus on the patient to go and say, ‘Well, my vet told me to talk to you and I’m not quite sure why.’ It’s like [a game of] telephone, basically.”

According to the CDC, about 75% of newly emerging diseases and 60% of all known human infectious diseases originate in animals, which can serve as sentinels to warn us of illnesses like Middle East respiratory syndrome (MERS), severe acute respiratory syndrome (SARS) and various avian influenzas, steering responses to outbreaks around the world. Addressing human, animal and environmental health systems, and recognizing how they are related, also can help guide antimicrobial stewardship.

All of this falls under the One Health approach, and experts say clinicians can play an important role by becoming more engaged.

“People have said, ‘Well, One Health is great, but it’s sort of a public or global health thing and it’s not going to affect me and my practice.’ We’re saying, ‘No, there’s a role for clinicians in One Health that we’re trying to define and encourage,’ ” Rabinowitz said. “We feel that clinicians need to be aware of it and implement it in their daily practice.”

Infectious Disease News spoke with several experts to better understand the history of One Health, how it can address infectious disease threats and what clinicians can do to be more involved.

New name, old roots

The core concept of the CDC’s One Health approach is that multiple disciplines collaborate at the local, national and international level to improve the health of humans, animals and the environment. This means that physicians, veterinarians, nurses, pharmacists, dentists, epidemiologists and federal health officials all work together on key health issues.

The concept is much older than the name. In the 1800s, German polymath Rudolf Virchow explored links between human and animal health — two areas of medicine that were traditionally kept separate — and coined the term “zoonoses” for the diseases that pass between them, according to the CDC.

Virchow’s dictum about this relationship is widely cited in literature about One Health: “Between animal and human medicine there are no dividing lines — nor should there be. The object is different but the experience obtained constitutes the basis of all medicine.”

Although the idea of One Health dates back to the 19th century, it has gained in importance in recent years, according to Casey Barton Behravesh, DVM, DrPH, DACVPM, director of the One Health Office in the CDC’s National Center for Emerging and Zoonotic Infectious Diseases.

“Because of a number of factors and issues related to the changing interactions between people, animals and the environment, new diseases have emerged and other diseases have re-emerged, making One Health very relevant today,” Barton Behravesh said in an interview.

The One Health paradigm covers a broad range of topics. According to Infectious Disease News Editorial Board member Arnon Shimshony, DVM, associate professor at the Koret School of Veterinary Medicine, Hebrew University of Jerusalem, the most important goal is diagnosing and controlling zoonotic infections. Shimshony is also an animal diseases and zoonoses moderator for ProMED, an internet-based outbreak reporting system that has its own One Health initiative.

Examples of zoonotic disease outbreaks can be found around the world, caused by human contact with birds, insects and any number of other animals, but especially livestock.


“Early recognition of emerging diseases in animals, in particular deciphering their zoonotic potential, is essential for the protection of both animal and man,” Shimshony told Infectious Disease News.

Even household pets can make people sick. Serious infections that spread from dogs and cats to humans include MRSA and toxoplasmosis. Pets may even contribute to the spread of antimicrobial resistance, according to researchers in China, who have suggested in Emerging Infectious Diseases that companion animals like dogs and cats harbor the mcr-1 gene, which confers resistance to the so-called “antibiotic of last resort,” colistin.

Health experts seem to have grown more aware of the symbiotic relationship between humans, animals and the environment, giving the One Health approach broader attention.

“I have traveled to multiple countries around the world over the last year and have heard One Health mentioned in every single country that I’ve been to,” Barton Behravesh said.

Sharing expertise for antimicrobial stewardship

The growing threat of antimicrobial resistance, a key One Health issue, was the focus of a recent high-level meeting at the United Nations General Assembly — just the fourth health-related topic to receive that kind of attention at the U.N.

In a report commissioned by the British government and published last year, Lord Jim O’Neill and colleagues estimated that antimicrobial resistance would result in 10 million deaths annually and a cumulative global cost of $100 trillion by 2050 if left unchecked. As part of a global effort to combat resistance, O’Neill and colleagues called on countries to reduce the use of antimicrobials in agriculture and their dissemination into the environment.

“If you’re looking at antimicrobial resistance and you’re only thinking of the human side, then you’re missing an important part of the story,” Jo Lines, PhD, professor of malaria control and vector biology at the London School of Hygiene & Tropical Medicine, told Infectious Disease News.

In the United States, 70% (by weight) of the antibiotics defined as medically important to humans are sold for use in animals, according to O’Neill and colleagues. In that shadow, the FDA’s ongoing effort to slow the rise of antimicrobial resistance has included guidance for U.S. drug manufacturers to eliminate the use of these antibiotics in livestock.

For example, the FDA has asked pharmaceutical companies to voluntarily change drug labels to remove FDA–approved indications for the use of medically important antibiotics in food-producing animals and to discontinue over-the-counter sales of the drugs. Under the new guidance, these antibiotics cannot be used for production purposes, and their use to treat, control or prevent disease in food animals requires a prescription from a licensed veterinarian.

Peter Rabinowitz

“A large fraction of antibiotics that we use in this country and worldwide are used on animals,” Rabinowitz said. “What we’re trying to do is bring together vets and physicians to share expertise about antibiotic stewardship and find ways to reduce antibiotic use both for humans and animals where there are a lot of antibiotics being used.”

Antimicrobial stewardship interventions are underway around the world. In China, a ban on the use of colistin as an additive in animal feed was expected to go into effect on April 1. The move comes on the heels of the discovery of mcr-1, which was first isolated from a strain of Escherichia coli in pigs in China, but has now been found in animals and humans in several countries, including the U.S., highlighting the need for shared responsibility in antimicrobial stewardship across multiple disciplines.

To this end, Rabinowitz and colleagues have created a database to catalogue drug resistance in not only humans, but also farm and companion animals in their region.

“Improving antibiotic stewardship on the human side is not going to be enough,” he said. “We have to work with veterinary colleagues on a shared stewardship model where we are continually exchanging information about best practices and improving surveillance of emerging antibiotic resistance strains in both humans and animals. ... Antibiotic resistance is a problem that really has called out for a One Health solution, and high-level CDC proposals for antibiotic resistance have talked about a One Health approach to it.”

Shimshony said controlling the use of antibiotics in health care centers and on farms should go hand-in-hand with the improvement of disease-prevention measures.

“This is particularly relevant to farm animals, where the development and use of effective vaccines could save the need to treat infected animals,” he said.

Reliance on livestock

Livestock are instrumental to One Health in other ways. Reliance on animals like cattle, goats, pigs and sheep can be a risk factor for acquiring infectious diseases. In an epidemiological investigation of the health of farmers and their livestock in rural Kenya, for example, researchers found that for every 10 cases of animal sickness or death, the incidence of human disease went up by 31% in the same household, according to a study in PLoS One.

Livestock accounted for up to half of the income in poor households worldwide in a 2012 report to the U.K.’s Department for International Development. The same report found that the top 13 zoonoses cause about 2.4 billion cases of illness and 2.2 million deaths in people worldwide each year.


“Nine of the 13 top-ranked zoonoses were considered to have high impact on livestock, all have a wildlife interface, and all are amenable to agriculture-based interventions,” the authors of the report wrote.

“At least a billion people in the world work closely with animals one way or another as part of their livelihood, so there’s a lot of people out there exposed to a number of livestock diseases,” Rabinowitz said.

Many diseases transmitted from livestock are deadly, but addressing them can be costly. Recently, researchers used mathematical modeling to show that bovine tuberculosis could be eliminated in Morocco — where it accounts for close to 18% of drug-resistant TB in humans — within 32 years if 40% of cattle were tested annually and infected cows were slaughtered. But a preliminary economic assessment showed that the cost of the simulated intervention would be at least $1.56 billion. (Last year, President Barack Obama requested $629 million in CDC funding for zoonotic diseases for fiscal year 2017.)

Northwestern China has dealt with costly outbreaks of rabies among livestock that are caused by bites from stray dogs and wild foxes, according to another study in PLoS Neglected Tropical Diseases. Researchers said the outbreaks can be prevented by vaccines for wild animals and large livestock that are currently unavailable in the country.

According to Barton Behravesh, there is no simple solution to the cost of One Health initiatives, but collaboration between disciplines can make them easier to address.

“What’s important is that by using a One Health approach and working across sectors for the prevention and control of zoonotic disease threats, you can maximize resources,” she said.

Animals as sentinels

Coal miners once carried caged canaries into mines to warn them of the presence of potentially hazardous, but odorless, carbon monoxide gas. In a less deliberate way, animals can serve as sentinels to warn humans of dangerous infections.

Arnon Shimshony

Camels, for example, are likely a major source of MERS infections in humans and can show signs of illness when they are infected. Q fever, a rickettsial disease caused by Coxiella burnetii bacteria that can make humans sick, is identifiable through signs of infection in cattle, goats and sheep, such as abortions.

“That zoonotic disease can spread to people in a variety of ways,” Barton Behravesh said. “People can get infected by breathing in dust that has been contaminated by infected animal feces, urine, milk, and birth products, [and] it can be spread through direct contact with animal body fluids, especially placenta and birth fluids, as well as by contact with newborn animals. It can cause illness in people, and not just an acute illness — there are actually some long-term chronic health issues that can be life-threatening which can be caused by infection with Q fever.”

Influenza viruses originating in birds and pigs are among the world’s biggest infectious disease threats and can cause human pandemics when they mutate and infect people. Therefore, the CDC recently began preparing a new avian influenza A(H7N9) vaccine amid a spike in human cases in China and new evidence that the deadly virus had split into two strains, including one that does not seem to be susceptible to existing vaccines or respond well to antivirals. So far, there has been no sustained human-to-human spread of the new H7N9 strain, although limited transmission has been identified.

Large numbers of infections in the wild do not always signal the same in people. In the Atlanta area, human West Nile virus infections have remained low compared with the rest of the U.S. despite the consistent presence of the virus in the primary vector for the disease, Culex mosquitoes. The reason, according to researchers, is found in the time of year — around the middle of July — when the mosquitoes mysteriously stop feeding on American robins and begin biting cardinals. Compared with robins, who are efficient transmitters of West Nile virus to mosquitoes, cardinals do not carry enough of the virus to infect the feeding insects. This change in feeding habit among Culex mosquitoes helps suppress West Nile transmission between mosquitoes and humans in the late summer months, when virus transmission between birds and mosquitoes is at its highest in urban settings.

Human impact and the environment

Human activity can have a negative effect on disease transmission. In China, for example, land-use patterns and landscape connectivity are expanding the range of the snails that host Schistosoma japonicum parasites, potentially jeopardizing a half-century of progress against schistosomiasis there, according to researchers.

Additionally, the conversion of natural lands to croplands to produce maize in East Africa has set the stage for a significant increase of human infections with plague. Researchers reported in the American Journal of Tropical Medicine and Hygiene that rodent vectors carrying Yersinia pestis favor agricultural lands over the wilderness.

According to Lines, who has spent several decades working on methods to control malaria, the burden of mosquito-borne diseases can be connected to artificial changes in the environment. Lines said ridding Africa of malaria, for instance, is a landscape-epidemiology problem.

“Mosquitoes are, in a way, an expression of the landscape,” he said. “There’s no doubt that rural development is driven primarily by agriculture, and almost all aspects of rural development — from switching crops, deforestation, building roads, irrigation, drainage — deeply affect mosquitoes.”


But the problems are not the same everywhere. In Asia, massive deforestation has helped drive down cases of malaria, according to Lines, and the opposite is true in Africa, where he said deforestation makes the problem of malaria worse. Urbanization drives out malaria, but is favorable to Aedes aegypti and A. albopictus, the vectors of chikungunya, dengue and Zika.

“We can easily predict what the world will be like when it’s paved over,” Lines said. “There will be no more malaria, but there will be a lot of Aedes aegypti-transmitted viruses. There’s a whole queue of them waiting to come.”

Suburban sprawl beyond cities can place humans in contact with the kind of wildlife that can put them at risk for infections, Rabinowitz said. This squeezing together of people and wildlife can increase the incidence of infections like Lyme disease and can also lead to the emergence of other infections.

“We’re learning to be aware of the importance of emerging infections from wildlife,” Rabinowitz said. “If you look at MERS, SARS, Ebola — these are all wildlife pathogens.”

Pick up the phone

According to Richard A. Kock, VMB, VMD, professor of wildlife health and emerging diseases at the Royal Veterinary College, although One Health has received attention, it is still not well-understood.

“Most people, even [veterinarians], don’t really comprehend the subject,” he told Infectious Disease News.

Still, there was a consensus among the experts with whom Infectious Disease News spoke that there is a larger focus on One Health in veterinary schools than in medical schools.

Casey Barton Behravesh

“Veterinarians are trained with One Health in mind. Our patients can’t talk to us,” Barton Behravesh said. “We see a number of zoonotic diseases in our patients, and we are trained to talk to the human owners about those. We have to factor in the animal’s environment. We study many different species of animals that have different habitats and environmental needs. So, thinking about the environmental piece of things is a big part of our training as well. This is why One Health is something that comes naturally to veterinarians.”

One Health programs focus on teaching the approach to medical students. A 1-year program run by Kock and Lines the London School of Hygiene & Tropical Medicine and the Royal Veterinary College even sees “one or two” clinicians enroll each year, Kock said. But medical schools without dedicated One Health programs can take a preliminary step by allowing students to learn about zoonotic diseases during their infectious disease coursework, according to Rabinowitz and Kock.

In addition, Rabinowitz said more CME should be dedicated to zoonotic diseases and how they may affect patients. “We are just dealing more and more with the consequences of zoonotic disease,” he said.

But there are other ways clinicians can become involved in One Health beyond taking a class or CME, such as taking better animal contact histories. In the future, the medical records of pets and owners could be linked so that information is shared by veterinarians and physicians. For now, incorporating a One Health approach into clinical practice could be as simple as picking up the phone.

“Track down a local vet and talk to them about what some of the One Health challenges are in the area,” Barton Behravesh said.

Lines said the inclination to keep different disciplines and skills separate from each another is a “purely human” concept.

“It’s a thing we impose on the world because of the way our brains work,” he said. “It doesn’t reflect any deep reality.” – by Gerard Gallagher

Disclosures: Barton Behravesh, Kock, Lines, Rabinowitz and Shimshony report no relevant financial disclosures.

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