The monkeypox virus, which suddenly emerged all over the world last month, could have been spreading "under the radar" for months or even years, according to virologist Marc Van Ranst.
Monkeypox may have been on the rise for much longer, but many of the cases are mild – with researchers calling them "atypically subtle" in some cases – that they can easily be mistaken for sexually transmitted diseases and/or remain undetected.
"The monkeypox virus probably circulated in humans for several months or even longer without being detected," Van Ranst told American TV channel NBC News, adding that his laboratory’s sequencing revealed genetic mutations of the virus that were "limited" and that "none of them are smoking guns."
Het apenpokkenvirus circuleerde waarschijnlijk al meerdere maanden of zelfs langer bij mensen zonder gedetecteerd te worden. pic.twitter.com/NezL67g96q
— Marc Van Ranst (@vanranstmarc) June 6, 2022
"Everybody is interested in more complete genomes (genetic composition of the virus) to get an idea about quite an important question: How long have these viruses been circulating under the radar?" Van Ranst said. "I think nobody believes this jumped out of Africa a couple of weeks ago."
Based on the latest figures from epidemiologist Moritz Kraemer of Oxford University, over 1,000 confirmed cases have been reported worldwide. Last Friday, the Sciensano health institute reported that 17 of those were detected in Belgium.
Weeks, months, years
Normally, the monkeypox virus is mainly found in West and Central African countries, or in people who have travelled through that region, and are transmitted from animal to human. The fact that they are now appearing elsewhere and being transmitted from person to person without any link to this is "unusual" and under investigation.
Undetected transmission could have been going on for "some time," according to Dr Rosamund Lewis of the World Health Organisation (WHO). "We do not know how long that might have been the case. We do not know if it could be weeks, months or maybe a few years."
According to Dr Amesh A. Adalja of the Johns Hopkins Center for Health Security, the virus probably found its way from Africa to a social and sexual network, and then to the rest of the world with the help of events such as the International Fetish Festival in Antwerp in early May.
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"Because the virus is transmitted through close contact, including sex, the lesions are often mistaken for sexually transmitted diseases, resulting in a failure or delay in making the correct diagnosis," he told NBC News. However, due to the attention the virus has received in recent weeks, health authorities are more alert and more cases are found.
According to Van Ranst, the next few days will be crucial. As of 1 June, there were 643 confirmed cases, according to the WHO. If by next week, the cumulative case count follows an exponential curve and hits perhaps 4,000, “then this is not under control,” he said.
But if the figure remains around 1,000 cases, the outbreak is likely only expanding linearly, which "bodes well for global control of the virus," Van Ranst said.