For a long time, experts believed that monkeypox would stay in Africa. The World Health Organization declared Sunday that the zoonotic virus was a moderate strain after it appeared in 23 countries.

The director of the WHO's Pandemic and Epidemic Diseases Department said that it was an unusual situation. It's out of the box now.

An electron microscope image showing both oval-shaped and round monkeypox virions.
A 2003 electron microscope image shows mature, oval-shaped monkeypox virions and spherical immature virions obtained from a sample of human skin associated with a prairie dog outbreak. (Cynthia S. Goldsmith, Russell Regner/CDC via AP)

The sudden increase in cases in Europe, where the U.K. and Spain have so far recorded 300, is prompting health authorities to issue alerts, warning sexually active populations, particularly those who engage in high-risk activities, to be on the lookout for symptoms. The U.K. has told people with monkeypox to not have intimate relations, not to leave their homes for a month, and not to have any contact with pets.

The officials in the U.K., which on Tuesday confirmed 179 cases, and Spain, where the health ministry on Monday announced 120 cases, believe that a vaccine for the related virus given within four days of exposure can be used.

Click image for more graphics from the World Health Organization.
Click image for more graphics from the World Health Organization.

The former director of crisis management at the WHO told Yahoo News that the disease will probably not affect large swath of the population. The eradication of smallpox in 1980 is an encouraging sign. The good news is that most of the people who werevaccinated against smallpox may be less likely to contract monkeypox if they are older than 45.

The recent outbreak of monkeypox in Europe, which is shooting higher than most African countries where the disease is endemic, shows that human-to-human transmission is possible, and that human sexual contact is now what is spreading the disease.

Two of the events that helped spread monkeypox across Europe took place in Spain, according to Spanish health officials. The gay sauna in Madrid was closed after it was linked to at least 20 infections. The Canary Islands, a Spanish territory off Africa, hosted a 10-day Gay Pride event in early May that 80,000 people attended and resulted in cases in other European countries.

Francesco Vaia, director of Spallanzani Infectious Disease Hospital, talks to reporters at the end of a press conference, in Rome on May 20. Vaia said that three cases of monkeypox have been confirmed and isolated at the Spallanzani hospital in two patients who traveled to the Canary islands and one to Vienna. (Andrew Medichini/AP)

It's not a gay disease, it could have happened at a business conference or a political rally, according to Dr. Roger Paredes, chief of the Infectious Diseases Department at Barcelona. It is being transmitted through close skin contact and is just as likely to be passed on to heterosexuals as it is to other people.

It is possible to transmit the disease through close physical contact, such as talking closely for a long period and even dancing, as well as through clothing and bedding.

Health experts believe that monkeypox may have been spreading for months or even years, previously going unrecognized and only now presenting itself in large enough numbers to warrant global alert.

Lopez-Acu said that some practitioners were confused at the beginning, thinking that it could be a case of a different disease.

The fear of stigmatizing those who show symptoms makes the issue more difficult.

The arms and torso of a patient with lesions due to monkeypox in Democratic Republic of the Congo in 1997. (AP)

According to Dr.Rosamund Lewis, the WHO's leading monkeypox expert, some people who have it may show up in the nether regions.

The recommended one-month quark period is hard to maintain.

The world has an opportunity to stop this outbreak if people with monkeypox identify themselves to medical professionals and commit to self-isolation.

Even though monkeypox is not an official sexually transmitted infections, some experts, including Lopez-Acu, believe it could make its way onto the list if it isn't stopped soon. He shrugs off the whole debate of whether it is an STD or not.

The hands of a monkeypox patient who displayed the characteristic rash during its recuperative stage in 1997. (AP)

David Heymann, a professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine, is not surprised that monkeypox is being transmitted through sex. He was sent to Africa by the Centers for Disease Control and Prevention in the 70s to investigate monkeypox, a disease that was mostly seen in children. Three years ago, he chaired a seminar at the London think tank Chatham House that looked at the rapid increase in monkeypox rates in Africa, which was attributed in part to more frequent global travel.

He told Yahoo News that there was a hypothesis that people with monkeypox could transmit the disease if they were close to each other.

Even though monkeypox has been seen in humans for over 40 years, there are still a number of unknowns. There is a risk of transmission to pets, but our main concern is if pets are exposed to other animals and get sick. He said that the safety of public swimming pools is uncertain and that people with monkeypox should stay isolated.

A computer screen shows positive test results for monkeypox, at the Hospital Ramon y Cajal in Madrid. (Carlos Lujan/Europa Press via Getty Images)

According to Heymann, health officials are relieved that the West African strain of monkeypox is not the more serious Central African strain, which is the one most likely to be shown in photographs accompanying reports. According to the WHO, that strain may prove fatal for 10 percent of people who acquire it. Heymann attributes that strain's absence in Europe to the fact that people who get it are less likely to travel.

Paredes said that monkeypox is not going to be a super-spreader disease that everyone can get everywhere. It depends on how well we do in the upcoming weeks.

Lopez-Acuña suggests that the measures put in place to combat COVID may benefit those who want to minimize the risk of monkeypox. Staying clear of crowds and wearing masks are some of the things that are included. Despite a renewed sense of freedom in Spain, where indoor COVID mask mandates were lifted only in late April, he noted that 4,000 Spaniards died from COVID in the past two months.