Why American outbreak of monkeypox wasn’t fatal

Why American outbreak of monkeypox wasn’t fatal
Press release from Saint Louis University Health Sciences Center
July 15, 2005

ST. LOUIS, July 15 — An outbreak of 72 cases of monkeypox in the United States during the summer of 2003 didn’t produce a single fatality, even though the disease usually kills 10 percent of those infected.

Why did none of the patients die? New research from Saint Louis University Health Sciences Center and several partner institutions may provide an answer.

In this month’s issue of Virology, researcher and senior author Mark Buller, Ph.D., from Saint Louis University Health Sciences Center and colleagues conclude that some strains of monkeypox are more virulent than others, depending on where in Africa the virus came from.

Monkeypox background from the CDC What is monkeypox? Monkeypox is a rare viral disease that occurs mostly in central and western Africa. It is called “monkeypox” because it was first found in 1958 in laboratory monkeys. Blood tests of animals in Africa later found that other types of animals probably had monkeypox. Scientists also recovered the virus that causes monkeypox from an African squirrel. These types of squirrels might be the common host for the disease. Rats, mice, and rabbits can get monkeypox, too. Monkeypox was reported in humans for the first time in 1970. Is there monkeypox in the United States? In early June 2003, monkeypox was reported among several people in the United States. Most of these people got sick after having contact with pet prairie dogs that were sick with monkeypox. This is the first time that there has been an outbreak of monkeypox in the United States. What causes monkeypox? The disease is caused by Monkeypox virus. It belongs to a group of viruses that includes the smallpox virus (variola), the virus used in the smallpox vaccine (vaccinia), and the cowpox virus. What are the signs and symptoms of monkeypox? In humans, the signs and symptoms of monkeypox are like those of smallpox, but usually they are milder. Another difference is that monkeypox causes the lymph nodes to swell. About 12 days after people are infected with the virus, they will get a fever, headache, muscle aches, and backache; their lymph nodes will swell; and they will feel tired. One to 3 days (or longer) after the fever starts, they will get a rash. This rash develops into raised bumps filled with fluid and often starts on the face and spreads, but it can start on other parts of the body too. The bumps go through several stages before they get crusty, scab over, and fall off. The illness usually lasts for 2 to 4 weeks. Can you die from monkeypox? In Africa, monkeypox has killed between 1 percent and 10 percent of people who get it. However, this risk would probably be lower in the United States, where nutrition and access to medical care are better. How do you catch monkeypox? People can get monkeypox from an animal with monkeypox if they are bitten or if they touch the animal’s blood, body fluids, or its rash. The disease also can spread from person to person through large respiratory droplets during long periods of face-to-face contact or by touching body fluids of a sick person or objects such as bedding or clothing contaminated with the virus. How do you treat monkeypox? There is no specific treatment for monkeypox. In Africa, people who got the smallpox vaccine in the past had a lower risk of monkeypox. CDC has sent out guidelines explaining when smallpox vaccine should be used to protect against monkeypox. For example, people taking care of someone infected with monkeypox should think about getting vaccinated. Contact your state or local health department for more information.

“We have at least two biological strains of monkeypox virus — one on the west coast of Africa, and the other in the Congo basin,” Buller said. “The 2003 outbreak in the United States was from West Africa. If it had come from Congo, we might have had a bigger problem on our hands and very well might have seen patient deaths.”

Researchers from the University of Victoria, Washington University School of Medicine, U.S. Army Research Institute of Infectious Diseases, the University of Alabama, East Carolina University and the Centers for Disease Control and Prevention are co-authors of the research.

Buller said that recent studies suggest the incidence of monkeypox is increasing due to encroachment of human into habitats of animal reservoirs. Monkeypox is classified as a “zoonosis,” which means that it is a disease of animals that can be transmitted to humans under natural conditions. The first cases of monkeypox reported in humans involved contact between humans and animals in Africa.

The first outbreak of monkeypox in the Western hemisphere occurred in the U.S. Midwest from April to June of 2003. The virus entered the U.S. in a shipment of African rodents from Ghana in West Africa destined for the pet trade. At a pet distribution center, prairie dogs became infected and were responsible for 72 confirmed or suspected cases of human monkeypox.

“Unlike African outbreaks, the U.S. outbreak resulted in no fatalities and there was no documented human-to-human transmission,” Buller said.

Monkeypox is part of a family of viruses that cause human smallpox, cowpox, and camelpox as well as monkeypox. Monkeypox usually produces a less severe illness with fewer fatalities than smallpox. But its symptoms are similar: fever, pus-filled blisters all over the body, and respiratory problems.

“Our finding may explain the lack of case-fatalities in the 2003 monkeypox outbreak in the United States, which was caused by a West African virus,” Buller said.

The research was funded in part by grants from the Defense Advanced Research Projects Agency, the National Institute of Allergy and Infectious Diseases and the National Institutes of Health to The Midwest Regional Center of Excellence for Biodefense and Emerging Infectious Diseases Research.

Established in 1836, Saint Louis University School of Medicine has the distinction of awarding the first M.D. degree west of the Mississippi River. Saint Louis University School of Medicine is a pioneer in geriatric medicine, organ transplantation, chronic disease prevention, cardiovascular disease, neurosciences and vaccine research, among others. The School of Medicine trains physicians and biomedical scientists, conducts medical research, and provides health services on a local, national and international level.

Press release from Saint Louis University Health Sciences Center