What is monkeypox and where does it come from?

Monkeypox virus is a relative of another virus you’re probably more familiar with called smallpox, which is in the same family. Monkeypox is a viral zoonotic disease which means it can jump to humans from an animal host – usually rodents but it can also infect non-human primates. Cases of monkeypox are rarely detected outside of Africa where it is primarily found in tropical areas.

The virus can jump to humans through direct contact with body fluids, blood or mucosal lesions of infected animals. The virus was first identified in 1958 and the first human case reported in 1970. Since 2017, Nigeria has had several hundred monkeypox cases. It is very rare that monkeypox makes it to other continents, but when it has, outbreaks have been very contained because most spillover events from animals don’t lead to much, if any, ongoing transmission between people.

If someone has monkeypox, what is the likelihood they will pass it on?

Human-to-human transmission of monkeypox has tended to be quite limited in the past where an infected person would often not transmit the virus to anyone. However, the virus can be transmitted between people from close contact with respiratory droplets, other bodily fluids and skin lesions. The basic reproductive number (the average number of people who contract a virus from an infected individual) is generally estimated to be below 1, meaning that the infection usually always dies out.

How has the virus spread so quickly?

There are currently more than 200 suspected and confirmed cases of monkeypox in almost 20 countries where it is not endemic. The first case was linked to an individual who had recently travelled from Nigeria to the UK. But with more cases cropping up with no obvious contact with infected people suggests that monkeypox virus may be spreading somewhat cryptically from person to person with undetected (or unreported) cases.

This outbreak is unusual in that it has now spread to many people across multiple countries. Possible reasons for this spread include:

1. A change in transmission route that includes sexual transmission.

2. The circumstances of the contact network were favourable allowing the virus to spread widely.

3. The virus has genetically evolved to become more transmissible in humans.

4. The rise in monkeypox incidence is associated with ending smallpox vaccination programmes.

We don’t know yet which of these reasons have played a role and it may be that all four have. It is unclear how large this outbreak will be at this stage.

Which preventions or treatments are available?

The vaccine used to eradicate smallpox is 85 percent effective at preventing monkeypox infection. Most people born after the eradication of smallpox in 1980 haven’t had a smallpox vaccine though. While the clinical presentation of the disease is much like smallpox, it is much less contagious and usually much less severe.

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