What to Know About Monkeypox and the Potential for an Outbreak in the U.S.

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Updated May 23, 2022

With monkeypox cases on the rise in the United Kingdom and appearing in the U.S., epidemiologist and professor at George Mason University Amira Roess discusses monkeypox and the U.S.

The first patient in the United States was recently diagnosed with monkeypox, raising questions and concerns about the rare disease. The Centers for Disease Control and Prevention is tracking clusters of monkeypox in countries that rarely report outbreaks, including United Kingdom, Spain, Portugal.

Epidemiologist and professor at George Mason University Dr. Amira Roess specializes in infectious diseases, especially reducing the transmission of diseases that originate through animal-human contact, including monkeypox, which she first worked on while serving as an Epidemic Intelligence Service officer at the CDC in 2008. She shares the most essential information about monkeypox and is available for further comment.

What is monkeypox?

Monkeypox is a rare disease that is caused by infection with monkeypox virus that causes a person to be ill for 2 to 4 weeks. Monkeypox is a member of the Orthopoxvirus genus. Smallpox is a member of that same genus.

How contagious is monkeypox and how does it spread?

Monkeypox is contagious. It is spread through contact with bodily fluids that contain the virus, which includes respiratory droplets and fluid from monkeypox lesions or sores. Shared items that have been contaminated with fluid or sores can also spread the virus.

The incubation period (time from infection to symptoms) for monkeypox is usually 7−14 days, but can range from 5−21 days. The infected person can spread the virus before symptoms appear.

There is a lot of work being done right now to understand how widespread the current outbreak is and some speculation about the main route of transmission in many of the cases who belong to overlapping social and sexual networks.

What are monkeypox symptoms?

Monkeypox symptoms may appear similar to those of smallpox, a well-known cause of global outbreaks. Smallpox has since been eradicated due to a global vaccination effort that used vaccines to eradicate it. Monkeypox causes less severe disease and is less contagious than smallpox; however, we know a lot less about monkeypox than other viruses.

Initial symptoms usually include fever, headache, muscle aches, swollen lymph nodes, chills, and exhaustion. One to three days after a fever, infected persons often develop a rash and lesions or sores. Symptoms typically last 2-4 weeks.

How can you tell the difference between monkeypox, a cold, and COVID-19?

Monkeypox symptoms typically include swollen lymph nodes, a rash, and lesions or sores that a cold, the flu, nor COVID-19 have.

In the U.S., should we be worried about a monkeypox outbreak?

Most Americans do not currently have to be concerned about monkeypox. Those who have traveled to places that have current monkeypox outbreaks should pay attention to any symptoms that they may develop upon return. The CDC and local health departments are prioritizing investigations of monkeypox and are doing what they can do identify suspected cases and stop transmission.

What should someone do to protect against monkeypox?

People should avoid contact with infected people or animals, as well as material, such as bedding, that has been in contact with any monkeypox-infected person or animal. Continue to practice good hygiene, such as washing your hands with soap and water or using alcohol-based hand sanitizer. Many of the same practices that prevent COVID-19 can prevent the spread of monkeypox. Common household disinfectants can kill the monkeypox virus on surfaces.

How common is monkeypox around the world?

Monkeypox outbreaks have historically occurred in central and west African countries, but is still relatively rare compared to other viruses. There are two strains of monkeypox. Unfortunately, we are seeing an increase in cases and this may be due in part to the increasing encroachment of people into wildlife habitats where monkeypox reservoirs are thought to be. 

Outbreaks typically start with a spillover event—a human picks up the virus from an animal reservoir, often a rodent. These events have been increasingly noted in part due to increased contact with wildlife and in part due to urbanization and globalization. Once the spillover event occurs then the infected individual can transmit monkeypox to their contacts. Historically, we didn’t see large monkeypox outbreaks because the infected individuals just didn’t have close contact with many people outside of their household or their local municipality. What we are seeing now, and what we saw with the Ebola outbreak, is that the increase in urbanization and globalization means that it takes days for viruses to emerge and move with their human host from one side of the globe to another. This is why we need to prioritize global surveillance and cooperation.

In 2003, there was an introduction of monkeypox into the U.S. through the importation of wildlife from west Africa. Several Americans became infected, but luckily the more mild form of the virus was introduced in that outbreak,  and it seems that the current global outbreak is also caused by the “weaker” strain of the virus.

In theory, the smallpox vaccine can protect individuals against monkeypox. In practice, a very limited number of individuals have received a smallpox vaccine and so more and more of our population is susceptible to Orthopoxviruses such as monkeypox.

How is monkeypox related to smallpox?

Monkeypox is related to smallpox and the two share symptoms. However, smallpox, which is now eradicated, caused more severe disease and is a well-known cause of global outbreaks. Smallpox was eradicated due to a massive global effort led by the World Health Organization that relied on a highly-effective, affordable vaccine shared with the world and a robust quarantine strategy.

Read Dr. Roess' other tip sheets for more information on monkeypox:


Dr. Amira Roess specializes in infectious diseases, especially reducing the transmission of diseases that spread between animals and humans, including coronaviruses like MERS-CoV and SAR-CoV-2, the latter of which causes COVID-19. She worked on monkeypox and other viruses when she served as an Epidemic Intelligence Service Officer at the CDC’s Poxvirus and Rabies Branch.

She is a professor of Global Health and Epidemiology at George Mason University's College of Health and Human Services, Department of Global and Community Health. Her expertise includes infectious diseases epidemiology, multi-disciplinary and multi-species field research and evaluating interventions to reduce the transmission and impact of infectious diseases. 

Dr. Roess holds a PhD in global disease epidemiology and control from Johns Hopkins University. Her current studies are in the US, Bangladesh, Egypt, and Ethiopia. Prior to joining academia, Dr. Roess served as the Science Director for the Pew Commission on Industrial Food Animal Production at Johns Hopkins, and was an Epidemic Intelligence Service (EIS) officer at the CDC. She has served as consultant for the United States Agency for International Development, the World Bank, and Westat Inc. She has a master degree from the UMDNJ/ Rutgers University School of Public Health.

For more information, contact Michelle Thompson at 703-993-3485 or mthomp7@gmu.edu.

About Mason
George Mason University, Virginia’s largest public research university, enrolls 39,000 students from 130 countries and all 50 states. Located near Washington, D.C., Mason has grown rapidly over the last half-century and is recognized for its innovation and entrepreneurship, remarkable diversity, and commitment to accessibility. In 2022, Mason celebrates 50 years as an independent institution. Learn more at http://www.gmu.edu.

About the College of Health and Human Services
The College of Health and Human Services prepares students to become leaders and to shape the public's health through academic excellence, research of consequence, community outreach, and interprofessional clinical practice. The College enrolls more than 1,900 undergraduate and 1,300 graduate students in its nationally-recognized offerings, including 6 undergraduate degrees, 13 graduate degrees, and 6 certificate programs. The college is transitioning to a college of public health in the near future. For more information, visit https://chhs.gmu.edu/.