What’s behind the rise in monkeypox cases? Here’s what scientists know so far

A handful of monkeypox cases have now been reported or are suspected in Britain, Portugal, Spain and the United States.

The outbreaks are alarming because the viral disease, which is spread through close contact and was first discovered in monkeys, occurs mainly in West and Central Africa, and only very occasionally spreads elsewhere.

Here’s what scientists know so far.

“Very unusual”

Monkeypox is a virus that causes fever symptoms as well as a distinctive bumpy rash. It is generally mild, although there are two main strains: the Congolese strain, which is more severe – with up to 10% mortality – and the West African strain, which has a mortality rate in around 1% of case. The UK cases have been reported as the West African strain.

“Historically, very few crates have been exported. This has only happened eight times in the past before this year,” said Jimmy Whitworth, professor of international public health at the London School of Hygiene and Tropical Medicine, who said it was “very unusual”.

Portugal has recorded five confirmed cases and Spain is testing 23 potential cases. Neither country has previously reported cases.

The United States also reported a case.


The virus is spread by close contact, both by animals and, less frequently, between humans. It was first found in monkeys in 1958, hence its name, although rodents are now considered the main likely animal host.

The transmission this time baffles experts, as a number of cases in the UK – nine as of May 18 – have no known link to each other. Only the first case reported on May 6 had recently traveled to Nigeria.

As such, experts have warned of wider transmission if cases go unreported.

The UK Health Security Agency’s alert also highlighted that recent cases have mainly been among men who identify as gay, bisexual or men who have sex with men, and advised these groups to be aware .

Scientists are currently performing genomic sequencing to see if the viruses are related, the World Health Organization (WHO) said this week.

Why now?

One possible scenario behind the rise in cases is increased travel as COVID-19 restrictions are lifted.

“My working theory would be that there are a lot of them in West and Central Africa, travel has resumed, and that’s why we’re seeing more cases,” Whitworth said.

Monkeypox puts virologists on alert because it belongs to the smallpox family, even though it causes less serious illnesses.

Smallpox was eradicated by vaccination in 1980, and the vaccine has since been phased out. But it also protects against monkeypox, and so stopping vaccination campaigns has led to an increase in monkeypox cases in areas where the disease is endemic, according to Anne Rimoin, professor of epidemiology at UCLA in California.

She said an urgent investigation into the new cases was important because “they could suggest a new way of spread or a change in the virus, but all of that remains to be determined.”

Experts urged people not to panic.

“It’s not going to cause a nationwide outbreak like COVID has, but it’s a serious outbreak of a serious disease — and we need to take it seriously,” Whitworth said.

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