scientists worry virus could infect animals

Monkeypox virus, illustration. Thom Leach | Science Photo Library | Getty Images

In 2003, 47 people across six Midwestern states caught monkeypox from pet prairie dogs that were infected after they were housed with rodents imported from Ghana, Africa. Today's outbreak, which has already infected more than 14,100 people in the U.S. and more than 41,000 across the globe, is spreading mostly through close human contact among gay and bisexual men. But scientists reported the first presumed human-to-pet transmission in a dog in France this month, prompting U.S. and global health officials to step up warnings to ensure the virus doesn't spread to other pets and animals. The recommendation stems from concerns that monkeypox could spill into wildlife or rodent populations as the human outbreak grows, allowing the virus to pass back-and-forth between humans and animals and giving the virus a permanent foothold in countries where it hasn't historically circulated. Prior to the global outbreak this year, monkeypox spread primarily in remote parts of West and Central Africa where people caught the virus after exposure to infected animals. The 2003 outbreak, which was contained, was the first documented case of humans catching the virus outside Africa.

The current global outbreak differs dramatically from past patterns of transmission. Monkeypox is now spreading almost entirely through close physical contact between people in major urban areas in the U.S., European nations and Brazil. But the first presumed case of people infecting an animal in the current outbreak was reported in France this month. A pet dog tested positive for the virus after a couple in Paris fell ill with monkeypox and shared their bed with the animal.

CNBC Health & Science

Read CNBC's latest global health coverage:

WHO officials have said a single incident of a pet catching the virus is not surprising or a cause for major concern, but there is a risk that monkeypox could start circulating in animals if people don't know they can infect other species. If monkeypox becomes established in animal populations outside Africa, the virus would have more opportunities to mutate, which carries the risk of higher transmissibility and severity. Animals could then potentially give the virus to people, increasing the risk of future outbreaks. "What we don't want to see happen is disease moving from one species to the next and then remaining in that species," said Dr. Mike Ryan, director of the WHO's health emergencies program, said during a press conference in Geneva last week. "It's through that process of one animal affecting the next and the next and the next that you see rapid evolution of the virus." The Centers for Disease Control and Prevention has not received any reports of pets infected with monkeypox in the U.S., said Kristen Nordlund, an agency spokesperson. But the virus can spread from people to animals or from animals to people, according to the CDC. "While we are still learning which species of animals can get monkeypox, we should assume any mammal can be infected with monkeypox virus," Nordlund said. "We do not know if reptiles, amphibians, or birds can get monkeypox, but it is unlikely since these animals have not been found to be infected with viruses in the same family as monkeypox." Dr. Rosamund Lewis, the WHO's lead monkeypox expert, said it's important to dispose of potentially contaminated waste properly to avoid the risk of rodents and other animals becoming infected when they rummage through garbage. "While these have been hypothetical risks all along, we believe that they are important enough that people should have information on how to protect their pets, as well as how to manage their waste, so that animals in general are not exposed to the monkeypox virus," Lewis said. Ryan said that while vigilance is important, animals and pets do not represent a risk to people at the current time. "It's important that we don't allow these viruses to establish themselves in other animal populations," Ryan said. "Single exposures or single infections in particular animals is not unexpected."

Rodents in Africa

Although scientists have done some research on monkeypox in Africa, where it's historically circulated, their work was limited due to a lack of funding. So scientists don't know how many different species of animals can carry the virus and transmit it to humans. Scientists have only isolated monkeypox from wild animals a handful of times in Africa over the past 40 years. They included rope squirrels, target rats and giant pouched rats in the Democratic Republic of Congo, as well as two types of monkeys in Cote d'Ivoire. Rodents, not monkeys, are thought to be the host animal population in Africa, though the precise animal reservoir is unknown. Public health officials don't know whether the types of animals in close proximity to people in urban settings in the U.S. -- racoons, mice and rats -- can pick up and transmit the virus. Some types of mice and rats can get monkeypox but not all species are susceptible, according to the CDC. "We know this is a virus that's transmitted from rodents in West Africa," said Dr. Peter Hotez, an infectious disease expert at Baylor College of Medicine in Texas. "Could rats or other rodents in urban environments mean that it gains a foothold there and it also becomes more of a permanent fixture — we don't want that to happen," he said. The CDC recommends that people who have monkeypox avoid contact with animals — pets, livestock, domestic animas and wildlife. If a pet becomes sick within 21 days of contact with someone who has monkeypox, the animal should be evaluated by a veterinarian. Waste contaminated with monkeypox should go into in a lined, dedicated trash can and shouldn't be left outside because wildlife could potentially become exposed the virus, according to CDC.