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Kindred killers: Monkeypox rising in the wake of smallpox eradication

The end of smallpox vaccinations in sub-Saharan Africa three decades ago appears to have opened the door to monkeypox, another deadly disease caused by a related virus.

By Ford Cochran

Humans have lived, and died, with smallpox for thousands of years. Variola major, the more lethal of two viruses responsible for smallpox, claimed at least 300 million human lives during the 20th century alone. Eradication of the dreaded disease outside of laboratories stands as one of the most important achievements of modern medicine.

But according to a new study, the end of smallpox vaccinations in sub-Saharan Africa three decades ago appears to have opened the door to monkeypox, a kindred killer that's appearing with greater frequency among people who live, work, and hunt in the forests where rodents harbor the disease. Given human mobility and the potential evolution of monkeypox to more virulent and transmissible forms, experts worry that such outbreaks have the potential to spread rapidly across the globe.

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I spoke with UCLA epidemiologist Anne Rimoin, the study's lead author, and co-author, Global Virus Forecasting Initiative founder and director, and National Geographic Emerging Explorer Nathan Wolfe about the implications of their findings, published this week by the National Academy of Sciences.

Dr. Rimoin, what are some of the most important things people should understand about your findings on the increased prevalence of monkeypox in the Democratic Republic of Congo?

First, this is the culmination of many years of research by many people, including public health colleagues in the DRC. It's important to state that up front.

I think a couple of things are very interesting about the work. First, the eradication of smallpox from the planet 30 years ago allowed us to stop vaccination. That's the purpose of eradication, right? You get rid of the disease, and then you can focus on other things.

Here's the irony: Our great victory over smallpox allowed this new disease, monkeypox, to flourish. There are always unintended consequences of one health intervention leading to something else. There's a cost and a benefit for any intervention.

Another important thing my study brings into focus is that monkeypox emerged under the rader because disease surveillance wasn't happening. This likely happened steadily over the years, but in a place where there's little health infrastructure. Disease surveillance is one of the last priorities when health care workers are doing all they can just to care for sick patients and provide vaccinations.

Many diseases have emerged in the Congo. Diseases emerge in places that are the poorest of the poor, with no disease surveillance. So here, we had no idea of the magnitude of this as it emerged because no one was watching.

No one had anticipated that other diseases might be held in check by the smallpox vaccine?

Back when they stopped smallpox vaccination, they determined after a few years that monkeypox didn't pose much of a threat. But those studies of transmissibility were done when there were very few people who hadn't been immunized, just kids born between 1980 and 1986.

Since then, there's likely to have been a waning of immunity to pox viruses among those who were immunized, and many people never have been immunized.

What we're seeing today is also an increase far above and beyond anything we'd expect to see just because people are exposed regularly to infected animals. This suggests there's likely to be a lot more secondary transmission--person to person rather than animal to person--than anyone suspected.

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When we evaluate threats, the two most important things to know are how transmissible something is and how virulent it is. How likely is it to spread from person to person? Has the incidence of the disease increased because people have done something to make themselves more susceptible, or is it because the virus has adapted and become more virulent, more capable of spreading, or both?

Before we thought this was a sporadic infection that only happened from time to time in outbreaks. But now we know that in these deep, remote places in the Congo, it's relatively common. That's a big cause for concern. We're sounding a warning.

There's already been at least one outbreak of monkeypox in the United States, correct?

Yes. Back in 2003, we had an outbreak un the U.S. associated with imported rodents that were kept next to American prairie dogs. The prairie dogs became infected, then became what we call amplifying hosts because they were able to maintain the virus in them and then to infect their owners. Dozens of people became sick with monkeypox.

No fatalities occurred in the U.S. outbreak. That could have been related to better nutrition, better health of the population, better health care. But there are two known strains of monkeypox virus. The strain that was introduced here was a West African strain that's known to be milder, whereas the strain in Central Africa where we work is much more virulent with a much greater associated mortality.

The outbreak here in 2003 shows very clearly how easily microbes can cross the globe and become established, not just in human populations. Now that we've eliminated oceans as barriers, there are many opportunities for pathogens to leap from continent to continent, to become quickly amplified in other animals, and to spread rapidly in new places where we've never seen them before.

It's a scenario that's become all too common in recent years. We've seen it with West Nile virus in the United States. We've seen it with SARS (Severe Acute Respiratory Syndrome). This was our concern with avian influenza, a concern with anything that has vectors we can't control. The Andromeda Strain is an extreme fictional example, "popular press," but the concept at base is absolutely right on: We've seen it happen numerous times.

"Monkeypox" is a misnomer, by the way: It was first discovered as a pathogen in monkeys in 1950, but the reservoir for the disease is actually rodents. There are other human populations in constant contact with these animals, and what we're seeing in the Congo is just an example of what could happen anywhere.

Since smallpox vaccine appears to prevent most monkeypox infections, should we start immunizing people against smallpox again?

In terms of vaccination policy, it's always important to balance the risks. There's a cost-benefit to absolutely everything. And our choices depend on what price we're willing to pay. You're always weighing the risks associated with a vaccine with the risks of acquiring a disease. Right now routine vaccination isn't happening with many of the people who are getting monkeypox, and adding another vaccine might divert funds that could be used for other programs and health interventions that might benefit them more.

We really need to understand how transmissible and how virulent monkeypox is and what kind of a threat this is signaling before we can make informed decisions about what to do with vaccinations. If we find that monkeypox is becoming more transmissible, becoming more virulent, we may decide that it's worth the cost of vaccination to stop this virus in its tracks before it has the chance to gain traction and go elsewhere.

Dr. Wolfe, how did you become involved in this research?

Anne and I have a long-term collaboration. We've been working together for ages. The Global Virus Forecasting Initiative exists to catch viral diseases early before they spread, and the DRC is one of our listening posts.

Viruses regularly jump over from animal populations to humans. The situation we have now across the planet is one single connected population. We live in an interconnected world. Viruses which we think are off in distant lands really aren't so distant any more. Natural quarantine is increasingly absent, and little bits of viral chatter--events in which viruses cross from animal into human populations--are more and more likely to have a global effect.

Almost certainly, in this case, where there's smoke, there's fire. This is an ecologically-engaged community. There's a lot of contact with wild animals. People in these regions traditionally hunt local animals: If you're in central Africa, you'll hunt the fauna that's in the forest. What's really changed today is that instead of many many isolated communities, there's sort of a single population the viruses can get into and burn through.

We need to up our game substantially.

Photographs of a child with monkeypox and of Anne Rimoin interviewing a youth with monkeypox in the Democratic Republic of the Congo courtesy Anne Rimoin

Ford Cochran directs Mission Programs online for National Geographic. He has written for National Geographic magazine and NG Books, and edits BlogWild--a digest of Society exploration, research, and events--and the Ocean Now blog. Ford studied English literature at the College of William and Mary and biogeochemistry at Harvard and Yale, with a focus on volcanoes, forests, and long-term controls on atmospheric CO2. He was an assistant professor of geology and environmental science at the University of Kentucky before joining the National Geographic staff.

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