By Jill Pease
History is rife with examples of disease outbreaks caused by animals infecting humans: avian influenza, Lyme disease and the plague, to name a few. But it turns out that animals may have as much to fear from people. A new University of Florida study turns up some fascinating examples of humans sickening animals.
“With increased interactions between people and animals we’re seeing a lot more emerging and re-emerging zoonotic diseases that are a public health concern,” said Amber Barnes, one of the study authors and a doctoral student in the department of environmental and global health at the UF College of Public Health and Health Professions. “It makes sense that if these pathogens have a human-animal component and could be transmitted one way, surely they can be transmitted the other way.”
UF investigators searched thousands of scientific papers and discovered 56 journal articles with documented cases of reverse zoonosis, or people infecting animals, in the past 30 years. It is believed to be the first systematic literature review of its kind. The findings were published Feb. 28 in the journal PLOS ONE.
The concern with reverse zoonosis is not just that we may be making our pets sick or causing damage to wildlife populations, Barnes said. Spreading disease to animals poses a threat to human health as well.
“When we infect animals, they can in turn transmit disease back to other humans,” she said. “Once pathogens move into another species they can mutate and become more harmful.”
The UF researchers, which also included Ali Messenger, Ph.D., a 2013 graduate of the UF doctoral program in environmental and global health and an instructor at Florida Gateway College, and Gregory C. Gray, M.D., M.P.H., chair of the department of environmental and global health and a member of UF’s Emerging Pathogens Institute, found published reports of humans infecting animals in every continent except Antarctica. In 50 percent of the cases, wildlife was affected, 43 percent involved livestock and nearly a quarter of cases involved companion animals. The most common pathogens were bacteria, followed by viruses, parasites and fungi.
Among the journal articles, the UF team noted several examples of people in the United States and Canada infecting their pets with the bacterium methicillin-resistant Staphylococcus aureus, or MRSA, and farmers in many countries transmitting the H1N1 influenza virus to livestock.
The UF researchers also found surprising instances of humans spreading disease to animals when there appeared to be little close contact between species. The African painted dog, an endangered canine found in sub-Saharan Africa, has been infected with human strains of a parasite that causes diarrheal illness. Scientists believe the pathogen was spread by tourists and locals defecating in and around national parks. In Tanzania, a colony of wild chimpanzees experienced a fatal outbreak of measles, which was probably transmitted by researchers or visitors at a national park where the primates live.
“We have very specific ecosystems that are fine-tuned for the flora and fauna within,” Barnes said. “As humans continue to encroach on these habitats we’re introducing and re-introducing different agents into these environments. This can have a long-term devastating impact on these animals.”
The UF study calls attention to the importance of a One Health approach to environmental, human and animal health, Barnes said. One Health brings together experts in public health, veterinary medicine and environmental health to solve difficult health problems.
“We’re all sharing this one place on the map and if we protect ourselves and we protect our animals and the environment, then inevitably it will lead to better overall health,” she said.