Stephanie Seifert felt a wave of terror when she heard about the first dog known to catch monkeypox from a human. “I have dogs. So I was like, ‘Well, that’s terrible,'” she says.
But Seifert, a viral ecologist at Washington State University in Pullman who studies how viruses jump between species, also understood the potential significance of the matter. In the months since the wave of worldwide monkeypox cases, which began in May, she and her colleagues have been waiting for reports of animals getting the virus from humans. The first case of human-to-dog transmission was reported in August. The Italian Greyhound in France had slept in the same bed with a couple who had symptoms; The dog’s viral DNA matched that of one of the owners. That same month, Brazil’s Ministry of Health announced the case of a puppy who contracted the virus from a person.
The problem isn’t the strange case of human-to-dog transmission, says Malachy Okeke, a virologist at the American University of Nigeria in Yola. Sick pets can be isolated at home. Scientists are more concerned about a scenario where the monkeypox virus establishes itself in wild animals, such as rodents, outside its usual range in West and Central Africa. Such animal reservoirs could then transmit the virus to humans. “Then we’re in trouble,” Okeke says. Controlling the spread in wildlife populations would be extremely difficult, he explains, making the virus “impossible to eliminate.”
Monkeypox is known to infect more than 50 species of mammals, according to data collected by researchers at the University of Liverpool, UK. But scientists don’t know the exact reservoir of the virus — the animal or animals that continuously carry and spread the virus without getting sick. Evidence to date indicates that rodents and other small mammals in Africa – including Gambian possums, tree squirrels, rope weekhorns and target rats – are responsible for the virus circulating in the wild there. Outbreaks of monkeypox in humans have been popping up in parts of Africa for decades.
In recent months, many more people have been infected than in previous outbreaks, increasing the chance of the virus interacting with animals. World Health Organization data shows that the number of weekly reported cases peaked at nearly 7,500 in August; more than 3,400 new cases were confirmed last week.
If the virus were to establish itself in a rodent population outside Africa, it could pose problems, according to a pilot study published on Sept. 11.1. The model, which mimics the spread of monkeypox, predicts an outbreak in a hypothetical metropolitan area. When the model took into account the existence of a mouse reservoir, it predicted that animal transfer would cause many earlier peaks and multiple waves.
When human-to-animal and animal-to-human spread is factored into the transmission process, things get much more complicated, says disease modeler Huaiping Zhu, director of the Canadian Center for Disease Modeling at York University in Toronto, and the study’s leader. . author. Without understanding how animals change transmission dynamics, scientists will struggle to control the spread of the virus and prevent future outbreaks, he says.
Part of the reason scientists don’t know the reservoir of the virus is a lack of active, long-term surveillance of monkeypox in the wild, Okeke says. But there is also the lack of interest. “Because this virus is endemic in the so-called poor countries, people didn’t take it seriously,” he adds. “I’m ashamed to say this, but that’s the reality.”
With little data from the field to indicate how animals might influence the course of the current outbreak, some scientists are taking other approaches. For example, if officials can predict which species are more susceptible to infection than others, they’ll know where to increase surveillance, says University of Liverpool virologist Marcus Blagrove.
Blagrove and his colleagues collected vast amounts of data, including the genetic structure of monkeypox and 62 other poxviruses, and characteristics of nearly 1,500 mammals, including their diet, habitat and daily activities. They then trained machine learning algorithms to analyze the information and locate potential monkeypox hosts.
Their results, posted to bioRxiv’s preprint server on August 15 and not peer-reviewed2, suggest that two to four times more animal species are susceptible to infection with the virus than is currently known, mainly rodents and primates. “There are many potential hosts around the world,” says Blagrove, including in Africa, as well as regions such as Europe, China and North America.
Whether these creatures can become reservoirs and shed the virus is difficult to predict. Scientists are missing important data, such as information about the immune responses of the potential hosts and direct evidence that the virus passes from those animals to another species, which would suggest that the host is a reservoir, Seifert says.
The best way to prevent the monkeypox virus from spreading to more animals and potentially creating a reservoir outside of Africa, Seifert adds, is to stop the spread between humans. And the best way to do that is to increase the distribution of vaccines. “That’s how we reduce the chances of these rare events happening, by protecting people,” she says.