Understanding Monkeypox and How Outbreaks Spread

Understanding Monkeypox and How Outbreaks Spread

Understanding Monkeypox and How Outbreaks Spread

Placeholder while article actions are loading

The global eradication of smallpox more than 40 years ago was one of the greatest achievements in public health history, overcoming a cause of death, blindness and disfigurement that had plagued humanity for at least 3,000 years. But on the other hand, it also led to the end of a global vaccination program that protected against other smallpox viruses. So is monkeypox, which has increasingly blown over from its animal hosts since the 1970s to infect humans in Africa. More recently, monkeypox has led to outbreaks in dozens of countries, mainly in Europe, demonstrating once again how easily an infectious agent surfacing in one country can quickly become an international problem.

Monkeypox is a misnomer due to the fact that it was first discovered in 1958, when outbreaks of a smallpox-like disease occurred in monkeys kept for research. While monkeys are prone 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, which is used in the smallpox vaccine; and cowpox virus. Monkeypox is less contagious than smallpox and the symptoms are milder. About 30% of smallpox patients died, while the monkey pox death rate has recently been around 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 illness usually begins with fever, muscle aches, 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, often starting on the face and then spreading to other parts of the body. The lesions develop into moisture-retaining pustules that form a scab. If a lesion forms on the eye, it can cause blindness. According to the WHO, the illness usually lasts two to four weeks. The person is contagious from the time symptoms begin until the scabs fall off and the sores heal. Mortality is higher in children and young adults, and people whose immune systems are compromised are especially at risk for serious illness.

3. How is it normally transmitted?

Monkeypox usually does not spread easily between people. Contact with the virus from an animal, human or contaminated object is the most important route. The virus enters the body through damaged skin, the respiratory tract or the mucous membranes in the eyes, nose or mouth. Transmission from one person to another occurs through respiratory particles during direct and prolonged face-to-face contact. But it can also happen 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’s unusual this time?

There have been multiple chains of human-to-human transmission, including in sexual networks, in countries where monkeypox is not normally present.

• It does not include recent trips to places in West and Central Africa where the disease is endemic.

• Although anyone can get monkey pox, most cases occur in men. In endemic areas of Africa, this was thought to be related to hunting practices, while in the current outbreak, most people are men who have sex with men, those with multiple sexual partners, or those who have condomless sex.

• Flu-like symptoms have not always preceded the rash, and some patients sought medical attention first for lesions in the genital and perianal area.

• In some cases, the lesions are usually located in these sites, 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 mode of transmission among men who have sex with men.

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

Analysis of the genetic sequence of the virus collected from some patients in Europe indicates that the spread of the strain has a single origin. Belonging to the West African clade, or branch of the evolutionary tree, it is most closely related to viruses found in recent years in cases exported from Nigeria to the UK, Israel and Singapore. Monkeypox virus strains of this group have a mortality rate of 1% to 3.6%. (That compares to 10% for a second clade called Congo Basin, which is on the US government’s list of bioterrorism agents as potentially posing a serious threat.)

5. How fast does it spread?

From just a handful of cases in Europe in early May, more than 1,200 cases, mostly in men, were reported across the region by early June, as well as in the Americas, the Middle East and Australia. Experts told a WHO meeting that monkeypox had been circulating undetected in Europe since at least April. It proves difficult to understand the dynamics of diffusion. A British study found that anonymous sex is a barrier to effective contact tracing, with only 28% of men being able to give the names of recent sexual contacts. This could pose a challenge to efforts to curb transmission ahead of LGBTQ pride celebrations taking place in major cities around the world. Data from outbreaks in Canada, Spain, Portugal and the UK suggest that locations where men have sex with multiple male partners help promote the spread.

6. Where does monkey pox come from?

The reservoir host or main carrier 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 rainforests of West and Central Africa. In 2003, the first outbreak outside of Africa occurred in the US and related to animals imported from Ghana to Texas, which then infect prairie dogs as pets. Dozens of cases were registered in that outbreak.

7. Is monkeypox a pandemic threat?

Outbreaks outside of Africa are uncommon. At least eight exported cases have been reported since 2017, mostly involving international travelers, but have typically not caused any further transfer. Human-to-human transmission raises concerns that the virus may undergo genetic changes to spread more efficiently from person to person. The DNA sequences of viruses collected during recent epidemics harbor a larger constellation of mutations than you might expect given the natural evolution of related viruses, researchers in Portugal said in a report released May 23. However, it is not yet known whether the genetic changes have any clinical significance.

8. How is it treated and prevented?

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

• There are 100 million doses of ACAM2000, which was approved in 2007 for immunization against smallpox. While it can be administered to people exposed to monkeypox when used under an extensive new drug research protocol, it contains a live vaccinia virus that has been linked to some serious potential side effects.

• 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 way to prevent infection is to isolate patients suspected of monkeypox in a negatively pressurized room and ensure that healthcare personnel wear appropriate personal protective equipment.

9. Is there a test for monkey pox?

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

(Updates the degree of dissemination in the first paragraph and section 5.)

More stories like this are available at bloomberg.com