Certain African squirrels and primates carry a virus that causes monkeypox in humans. This virus is related to the smallpox virus, but it usually produces a less severe illness with fewer fatalities. However, symptoms are similar: fever, pus-filled blisters all over the body, and respiratory problems.
Most monkeypox cases have been diagnosed in remote areas of central and west Africa. Contact with infected animals is unusual because they are isolated in forests, away from humans. However, between February 1996 and October 1997, there were 511 suspected cases of monkeypox in the Democratic Republic of the Congo (DRC, formerly Zaire). This outbreak, the largest ever, raised fears that the virus had mutated and become more infectious.
In late 1997, the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) announced that this relatively large outbreak was likely due to human behavior, rather than virus mutation. During the outbreak, the DRC was embroiled in civil war. Food shortages increased reliance on hunting and raised chances that people would come into contact with infected animals.
Monkeypox is less severe than smallpox and can sometimes be confused with chickenpox. It seems partly preventable with smallpox vaccination, but vaccination programs were discontinued in the late 1970s. (Barring samples stored in laboratories, smallpox has been eradicated.) People under the age of 16—those born after smallpox vaccination ended—seem the most susceptible to monkeypox. During the 1996-97 outbreak, approximately 85% of the cases were in this age group.
This outbreak also seemed to indicate high person-to-person transmission. Initial reports claimed as many as 78% of suspected cases were transmitted person to person rather than animal to person. However, according to WHO and the CDC, further study revealed that about 8% of cases were transmitted this way.
Causes and symptoms
The monkeypox virus is transmitted to humans through an infected animal's blood or by its bite. Initial symptoms are a fever and a bodywide rash of pus-filled blisters. These symptoms can be accompanied by diarrhea, swollen lymph nodes, a sore throat, and mouth sores. In some cases, a victim may experience trouble breathing. Symptoms are at their worst for 3-7 days, after which the fever lessens and blisters begin to form crusts.
Since the symptoms resemble other pox diseases, definitive diagnosis may require laboratory testing to uncover the virus or evidence that it is present.
Like most viruses, monkeypox cannot be resolved with medication. The only treatment option is symptomatic—that is, patients are made as comfortable as possible. In March 1998, the U.S. Army Medical Research Institute for Infectious Diseases reported that an antiviral drug called cidofovir may combat monkeypox infection. The drug has worked successfully in primates, but further research is needed to determine its effectiveness in humans.
Children are more likely to contract the disease and have the highest death rate. Monkeypox is not as lethal as smallpox, but the death rate among young children may reach 2-10%. In some cases, hospitalization is required. Recovery is good among survivors, although some scarring may result from the blisters.
Although smallpox vaccination may protect against monkeypox, experts do not generally recommend getting a smallpox vaccine simply to guard against monkeypox. This vaccine carries risks, including severe, potentially fatal complications. For most people, the risk posed by the smallpox vaccine far outweighs the odds that they might come in contact with the monkeypox virus.
Fenner, Frank. "Human Monkeypox, a Newly Discovered Virus Disease." In Emerging Viruses, ed. Stephen S. Morse. Oxford University Press, 1993.
Cohen, Jon. "Is an Old Virus Up to New Tricks?" Science 277 (18 July 1997): 312.
World Health Organization. 7 June 1998 <http://www.who.int/home-page/index.en.shtml>.