We can’t seem to get a break from infectious diseases. The Covid-19 pandemic continues, and a third of Americans live in areas where the spread of the virus is currently so high that they should consider wearing masks indoors once again. Avian influenza H5N1 has hit a number of domestic poultry populations throughout the U.S., leading to almost 38 million birds killed to reduce its spread. And now close to 100 suspected human cases of monkeypox have been identified in at least 10 countries — Italy, Spain, Portugal, England, the United States, Canada, Australia, Germany, Belgium and Sweden — leading some to worry that the outbreak could be heralding a second pandemic.
There’s an animal virus spreading in the human population, appearing in multiple countries practically overnight.
Certainly, some of the news reports sound worryingly similar to what we heard in early 2020. There’s an animal virus spreading in the human population, appearing in multiple countries practically overnight. There’s a gap in our knowledge about how the virus jumped species, from the animal reservoir to the first infected human. We’re trying to piece together how it moved from person to person, contact to contact and continent to continent.
But monkeypox isn’t SARS-CoV-2. We have many decades of understanding of the virus, and most critically, we have existing vaccines and treatments that we can use to help curb the outbreak. That means we’re not starting from square one.
But a bit of background on monkeypox may be helpful, since even the name is a bit misleading. Monkeypox is a poxvirus, in the same family as the now-eradicated human scourge of smallpox. But like other animal poxviruses, when monkeypox infects a human, it tends to be milder than smallpox and is more difficult to spread person to person. It was first recognized in humans in 1970. Because its symptoms were very similar to smallpox, distinguishing between the two viral diseases became critical, and scientists began ramping up studies of monkeypox.
Like smallpox and SARS-CoV-2, monkeypox is a respiratory virus that can be spread though coughing, sneezing and potentially just breathing. The virus has been found throughout central and into parts of western Africa. Nigeria has been a hot spot for human cases in the last five years, with some evidence of human-to-human spread. There are two separate types of monkeypox viruses: those from west and central Africa, with the former thought to cause less serious illness in humans. The current cases seem to be from the milder West African “clade” (type).
The name comes from infections in nonhuman primate species, who get a blistery rash that looks similar to human infections. Because these animals can be severely infected, they are probably not the "reservoir" or host — reservoir species spread the pathogen but typically are not acutely harmed by it. A more probable host includes several species of African rodents, which could carry and spread the virus without clear symptoms.
Undetected monkeypox infection in some of these rodents is what led to a U.S. monkeypox outbreak in 2003, the first such epidemic outside Africa. In spring 2003, not too far removed from the attacks of 9/11 and the subsequent anthrax attacks that left a lingering specter of biowarfare, cases of a smallpox-like rash were reported to physicians and then local public health authorities in the Midwest. By July, 71 cases had been identified in six states (Wisconsin, Indiana, Illinois, Missouri, Kansas and Ohio). After interviewing the patients (and/or their parents, as several of those infected were children), it was determined that the common exposure was recently purchased pet prairie dogs.
Investigators found those prairie dogs housed alongside exotic rodents imported from Ghana, in West Africa. Some of those rodents — including Gambian giant rats, dormice and rope squirrels — tested positive. Thus the African rodents apparently spread the virus to the prairie dogs, and from there it was transmitted to the human caretakers.
After interviewing the patients, it was determined that the common exposure was recently purchased pet prairie dogs.
Currently, the monkeypox cases documented in various countries have not been epidemiologically linked — that is, the cases identified to date do not have an obvious common exposure (for example, that they spent time at the same airport while traveling the globe, attended the same concert or have a clear chain of transmission). But public health authorities are still gathering information on all the places the cases may have been, exposures they may have in common and who else was in contact during their incubation period.
This process should now be familiar from our years of Covid response. Contact tracing is a critical way to slow the spread of a poxvirus, because contacts can be vaccinated even after an exposure. (You can vaccinate for Covid after exposure, but it doesn’t seem to work as well because the incubation period is much shorter than it is for a virus like monkeypox.)
More good news: Although monkeypox and smallpox viruses are distinct, they are similar enough that the human smallpox vaccine (which uses a third poxvirus, called vaccinia) protects against infection from both. Individuals who have been exposed to a person spreading monkeypox can be vaccinated after this exposure, and subsequently those who they’ve had contact with, in a process known as “ring vaccination.” This creates “rings” of immunity around each case, limiting the potential spread of the virus.
In the U.S., we stopped routinely vaccinating for smallpox in 1972, due to the risk of side effects that outweighed the risk of the virus. (America had not suffered a smallpox epidemic since 1949.) The vaccine is still used in the military and by scientists conducting work with poxviruses. And we do maintain a stockpile of smallpox vaccine, so ring vaccination or, if needed, community-wide vaccination campaigns can be quickly implemented in the event of an exposure.
In addition to a solid vaccination strategy to control monkeypox spread, we also have some antiviral drugs that can help treat those who are already infected. Immune globulin can also be used against monkeypox, though its effectiveness is uncertain.
The current outbreaks are concerning, primarily because we rarely see extended chains of human-to-human spread of monkeypox. There are a lot of unknowns. Has the virus evolved, such that it more easily spreads between people, more like its smallpox cousin? Has the reduction of population-level immunity to poxviruses allowed for the emergence of monkeypox?
This is the first time in recent human history that such a large percentage of the population has lacked immunity to these viruses. For centuries, humans obtained immunity to smallpox via infection, inoculation or vaccination. Community vaccination ceased with the eradication of the virus in 1980, and there have been concerns that the cessation of routine smallpox vaccination may have enabled the emergence of monkeypox.
That bottom line is that it is unlikely the current outbreak heralds that emergence, but we should be vigilant, prepared, rapid and nimble in our response. The past two years have shown us that anything is possible.