‘Significant’ monkeypox transmission occurs before symptoms appear, study suggests

‘Significant’ monkeypox transmission occurs before symptoms appear, study suggests

Author: Jennifer Rigby

LONDON (Reuters) – Monkeypox can spread before symptoms appear, British researchers said on Wednesday, providing the first evidence that the virus can be transmitted in this way.

Monkeypox was previously thought to be transmitted almost entirely by people who were already ill, although pre-symptomatic transmission has not been ruled out, and some routine screenings have detected asymptomatic cases.

Monkeypox, a relatively mild viral disease that is endemic to several countries in West and Central Africa, exploded around the world earlier this year, with outbreaks in dozens of countries where it had never appeared before.

Since then, there have been nearly 78,000 confirmed cases and 36 deaths, according to the US Centers for Disease Control and Prevention. Although the number of cases has peaked in many countries, this week the World Health Organization said the epidemic remains a global health threat.

The virus is known to spread through close contact and causes symptoms including fever, body aches and often painful, pus-filled skin lesions.

To learn more about how monkeypox was transmitted in Britain, a team from Britain’s Health Safety Agency used routine surveillance and contact tracing data for 2,746 people in the country who tested positive between May and August.

Their average age was 38, and 95% of patients reported being gay, bisexual, or men who have sex with men.

Related video: 2 Chicago residents die in October after being diagnosed with monkeypox

The researchers analyzed the “series interval” — the time from the onset of symptoms in the first case to the onset in a related case — as well as the incubation period, typically the time from exposure to the virus to the onset of symptoms.

Using two statistical models, they found that the mean serial interval was shorter than the mean incubation period. This indicated that “significant” transmission had occurred before the onset or detection of symptoms, the researchers wrote in a paper published in the British Medical Journal.

Four days was the longest period before symptoms began to detect transmission, and the team said up to 53% of transmission could have occurred before symptoms began.

The study raises questions about the fight against monkeypox around the world, including whether requiring people to isolate themselves when symptoms appear is enough to stop the spread of the virus.

Many wealthier countries have vaccinated high-risk populations to contain the epidemic, but vaccines are limited and unavailable in Africa.

Independent experts say the results could have important implications for global infection control, if supported by other studies.

“These are urgent questions that need answers,” said Boghuma Kabisen Titanji, assistant professor of medicine at Emory University in Atlanta.

Other scientists said the work was robust but needed clinical data before it could be labeled definitive or applied globally.

“It’s an important piece of the transmission puzzle,” said Jake Dunning, a senior fellow at Oxford University’s Institute of Pandemic Sciences, “but I personally want to see it put together with the other pieces.”

(Reporting by Jennifer Rigby; Editing by Bill Berkrot)

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