Understanding monkeypox and how outbreaks spread

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The global eradication of smallpox more than 40 years ago was one of the greatest achievements in public health history, eliminating a cause of death, blindness and disfigurement that had plagued mankind for at least 3,000 years. On the flip side, however, it also led to the end of a global vaccination program that provided protection from other smallpox viruses. These include monkeypox, which has spread from its animal hosts to humans in Africa since the 1970s. Monkeypox is now a serious, evolving threat, having sparked outbreaks in dozens of countries, mostly in Europe, this year, showing once again how easily an infectious agent found in one country can quickly become an international problem can.

Monkeypox is a misnomer given that it was first discovered at the Statens Serum Institut in Copenhagen in 1958 when outbreaks of a smallpox-like disease occurred in monkeys kept for research. While monkeys are susceptible to it, just like humans, they are not the source. The virus belongs to the genus Orthopoxvirus, which also includes variola virus, the causative agent of smallpox; the vaccinia virus used in the smallpox vaccine; and cowpox virus. Monkeypox is less contagious than smallpox and symptoms are milder. About 30% of smallpox patients died, while the recent mortality rate from monkeypox is about 3% to 6%, according to the World Health Organization.

2. What does monkeypox do?

After an incubation period of usually one to two weeks, the disease typically begins with fever, muscle pain, fatigue and other flu-like symptoms. Unlike smallpox, monkeypox also causes swelling of the lymph nodes. Within a few days of the onset of the fever, patients develop a rash that often begins on the face and then spreads to other parts of the body. The lesions grow into fluid-containing pustules that form a scab. If a lesion forms on the eye, it can lead to blindness. According to the WHO, the disease usually lasts two to four weeks. The person is contagious from the time symptoms begin until the scab falls off and the sores heal. Mortality is higher in children and young adults, while people with compromised immune systems are particularly at risk of developing serious illness.

3. How is it usually transmitted?

Monkeypox does not usually spread easily between people. Contact with the virus from an animal, human or contaminated object is the main route. The virus enters the body through broken skin, the respiratory tract or the mucous membranes in the eyes, nose or mouth. Transmission from one person to another is believed to occur through airway particles with direct and prolonged face-to-face contact. However, it can also occur through contact with bodily fluids or lesion material, or indirectly through contact with contaminated clothing or bedding. Common household disinfectants can kill it.

4. What is unusual this time?

In countries where monkeypox does not normally occur, there have been multiple human-to-human transmission chains, including through sexual networks.

• Cases are not related to recent travel to locations in West and Central Africa where the disease is endemic.

• Although anyone can get monkeypox, most cases occur in men. In endemic areas of Africa, this has been thought to be related to hunting practices, while in the current outbreak, most individuals are men who have sex with men, people with multiple sexual partners, or people who practice bareback sex.

• Flu-like symptoms did not always precede the rash, and some patients initially sought medical attention for genital and perianal lesions.

• In some cases, the lesions are primarily in these areas, making them difficult to distinguish from syphilis, herpes simplex virus, shingles, and other more common infections, according to the US Centers for Disease Control and Prevention.

• Close skin-to-skin contact during sex is the primary route of transmission between men who have sex with men.

• Sperm from four patients in Italy, collected around the time their symptoms appeared, was positive for monkeypox DNA in three of the cases. It is not yet known whether the liquid alone can transmit the infection.

5. Has the monkeypox virus mutated?

Analysis of the genetic sequence of the virus, collected from patients in Europe, suggests the current outbreak in non-endemic countries is being caused by a strain that likely differs from the monkeypox virus that infected 2018, according to a June 24 study -19 triggered an outbreak in Nigeria in naturopathy. The authors, from Portugal’s National Institute of Health in Lisbon, identified around 50 genetic changes or differences compared to the original strain, including several mutations that made the virus more easily transmissible. That’s about 6 to 12 times more than scientists would expect based on the observed evolution of orthopoxviruses, they said. “Current data points for a scenario with more than one introduction from a single origin, with superspreader events (eg, saunas for sexual encounters) and foreign travel likely triggering the rapid global spread,” the authors said. The cultivar belongs to the West African clade or branch of the evolutionary tree. Previous research found it to be most closely related to viruses found in cases exported from Nigeria to the UK, Israel and Singapore in recent years. Monkeypoxvirus strains in this group typically have a case fatality rate of less than 1%. (This compares to 10% for a second clade called the Congo Basin, which is listed as a potentially serious threat on the US government’s list of bioterrorism agents.)

6. How fast is it spreading?

From just a handful of cases in Europe in early May, by the end of June more than 4,100 cases, mostly in men, had been reported across the region, as well as in the Americas, the Middle East, Asia and Australia. One death was reported in an immunocompromised person. Experts at a WHO meeting said monkeypox had been circulating undetected in Europe since at least April. Preliminary research estimates that among cases identifying as men who have sex with men, the virus has a reproductive number greater than 1, meaning more than one new infection is estimated to have resulted from a single case. Overall, the number of reproductions is estimated at 0.8. Understanding propagation dynamics is proving difficult. A UK study found that anonymous sex has proven to be a barrier to effective contact tracing, with only 28% of men able to provide the names of recent sexual contacts. This could challenge efforts to curb transmission ahead of LGBTQ Pride celebrations in major cities around the world. Data from outbreaks in Canada, Spain, Portugal and the United Kingdom suggest locations where men have sex with multiple male partners contribute to the spread.

7. Where does monkeypox come from?

The reservoir host or primary vector of monkeypox disease has not yet been identified, although rodents are suspected to play a role in transmission. It was first diagnosed in humans in 1970 in the Democratic Republic of the Congo in a 9-year-old boy. Since then, most human cases have occurred in rainforest areas of West and Central Africa. In 2003, the first outbreak outside of Africa occurred in the United States and was linked to animals imported into Texas from Ghana, which then infected pet prairie dogs. Dozens of cases have been recorded in this outbreak.

8. Is monkeypox a pandemic threat?

A meeting of the World Health Organization’s Emergency Committee on June 23 determined that the event does not currently constitute a public health emergency of international concern. The committee recognized “the emergency nature of the event and that controlling the further spread of the outbreak will require intensive response efforts” and recommended reviewing the situation after a few weeks, once more information becomes available. A modeling by researchers at non-profit research institute RTI International predicts that if public health measures are not taken to contain ongoing outbreaks, the introduction of three cases in a non-endemic country could cause 18 secondary cases, 30 could cause 118 secondary cases cause , and 300 cases could cause 402 secondary cases. The findings, published June 23 in the Lancet Microbe journal, are consistent with WHO’s assessment that the overall public health risk at a global level is currently “moderate,” the authors said. “Observed outbreaks in non-endemic countries should be contained fairly quickly, especially if appropriate mitigation measures are taken,” they said.

9. How is it treated and prevented?

The disease is usually mild and most patients recover within a few weeks; Treatment is primarily aimed at relieving symptoms. Smallpox vaccine, antivirals, and vaccinia immunoglobulin can be used to control a monkeypox outbreak, according to the CDC. Vaccination against smallpox can be given both before and after exposure and is 85% effective in preventing monkeypox, according to the UK Health Security Agency, which offers the Imvanex smallpox vaccine to close contacts of a person who has been diagnosed with monkeypox. It lists cidofovir and tecovirimate as antiviral drugs that can be used to control outbreaks. Tecovirimat was approved by the European Medical Association for monkeypox in 2022 based on data from animal and human studies, but is not yet widely available, according to the WHO. Newer vaccines based on non-replicating versions of the vaccinia virus have been developed, one of which has been approved for the prevention of monkeypox. Limited supplies of two adult vaccines are available in the US, JAMA magazine reported in late May:

• There are 100 million doses of ACAM2000 approved in 2007 for immunization against smallpox. Although it can be given to people exposed to monkeypox when used as part of a new expanded-access trial protocol, it contains a live vaccinia virus that is associated with some serious potential side effects.

• There are 1,000 doses of JYNNEOS, a live, non-replicating vaccinia virus vaccine manufactured by Bavarian Nordic A/S and approved by the US Food and Drug Administration in 2019 for the prevention of smallpox and monkeypox.

The main method of preventing infection is to isolate patients suspected of having monkeypox in a negative pressure room and ensure healthcare workers wear appropriate personal protective equipment.

10. Is there a test for monkeypox?

Yes. Monkeypox is diagnosed using polymerase chain reaction (PCR) testing to detect viral DNA in samples taken from the crusts or swabs of a patient’s lesions. In the US, these are available from the state health departments and the CDC.

(Adds Section 5 on research into genetic sequences; updates Section 6 on how quickly it is spreading and Pandemic Threat Assessment in Section 8.)

For more stories like this, visit bloomberg.com

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