Outbreaks of a rarely seen disease called monkeypox have public health experts on edge. Several countries, including the United States, have recently reported cases of virus infection. No deaths have been reported to date. Although the risk appears to be low for the general public at this time, it is possible that something has changed in the virus or in its relationship with humans, which makes it more transmissible than before.
Countries where cases of monkeypox have been reported
From Thursday afternoonUnited Kingdom, Canada, Spain, Portugal, Italy, Sweden, and the United States has documented cases of monkeypox. The US case involves a Massachusetts resident who recently traveled from Canada, where there have been 13 suspected cases. In the UK, at least seven people are believed to have descended from it, the first reported case believed having contracted it in Nigeria.
Monkeypox was first documented in Africa in the 1970s, and it has been occasionally spotted on the continent since then. But it is a zoonotic disease, which means that infections are usually transmitted from animals to humans (despite their name, rodents are considered the main vector) rather than between people. So these multiple outbreaks in multiple countries, with evidence of local transmission in some, are very different from what we’ve seen before, according to Andrew Pavia, an infectious disease physician at the University of Utah. But there is no clear answer yet as to why this is happening, he adds.
“In the past, human-to-human spread has occurred but has been quite limited. We don’t yet know if it spreads more easily from person to person. That’s a possible explanation, but I don’t I am not yet aware of any evidence supporting this idea,” Pavia told Gizmodo in an email.
What is monkeypox virus?
Monkeypox is caused by its namesake virus, a member of the poxvirus family. It is a close cousin of the smallpox virus, the only human germ to have been completely eradicated to date. Like smallpox, monkeypox infection causes distinct bumpy rashes that usually start on the face and spread throughout the body, along with flu-like symptoms.
It takes one to three weeks after exposure for symptoms to appear, and people are usually sick for about two weeks. Up to 10% of victims can die from it, although documented cases in the UK appear to be caused by a strain of the virus known to be less virulent, with a fatality rate closer to 1%.
There are tools available against monkeypox that we could use if these outbreaks grow into a bigger threat. Smallpox vaccines should remain protective against monkeypox and can be given after exposure to prevent disease, so they can be used as part of a “ring vaccination” strategy to short- circumvent epidemics. There are also approved antivirals that have been shown to be effective against poxvirus infections.
Why is monkeypox spreading now?
It is plausible that the virus has somehow evolved to make it more inherently contagious between people. But some scientists like Jo Walker, an epidemiologist and infectious disease modeler at the Yale School of Public Health, have speculated that this seemingly increased spread may actually be linked to our victory over smallpox decades ago.
Smallpox was declared eradicated in 1980, thanks to the efforts of a global mass vaccination program that created a large network of population immunity. Poxviruses are known to cause cross-immunity with other related viruses (indeed, the weakened virus in the classic smallpox vaccine is not even smallpox). And this buffer of smallpox immunity may also have hindered the spread of monkeypox in humans. Over time, however, our collective protection has diminished over time for various reasons, perhaps allowing monkeypox to finally spread more widely, without needing to change in any major way.
“This ‘waning immunity’ is less due to waning immunity at the individual level, and more to people with immunity dying, and people without immunity being born and then remaining non-immune,” Walker told Gizmodo in a Twitter post.
Walker notes that some researchers have long warned on monkeypox or similar viruses one day filling the niche left by smallpox, and some have argued that this is a major factor in why the germ made a resurgence in Nigeria from 2017, after four decades of zero reported cases.
Another possibility raised by Pavie is that a mysterious animal played an outsized role in seeding these epidemics. In 2003, he points out, the largest but still small known outbreak of monkeypox in the United States (47 cases in total) was retraced fully in contact with infected prairie dogs, an unknown vector at the time.
At the same time, there is evidence of human-to-human transmission in at least some of these cases. In the UK and Spain, the majority of cases have been found in young gay and bisexual men, raising the possibility that these infections were sexually transmitted. Other research has suggested that monkeypox may theoretically survive in the environment as aerosol particles sufficiently intact to be considered airborne.
Getting to the bottom of this monkeypox mystery will require classic medical detective work, Pavia said. Epidemiological investigations will try to determine the type of contact that led to people’s infections and the number of infections that seem to arise from each index case. In the lab, scientists will look for possibly relevant genetic changes in virus samples taken from patients, or test whether these infections behave differently in animal models.
“Given what we know today, there’s no reason to panic or that most people are worried, but it’s the beginning, so that may change,” Pavia said.