Monkeypox is an infectious disease caused by an orthopoxvirus. Orthopoxviruses are a genus of viruses that include the disease agents that cause human smallpox, cowpox, and camelpox as well as monkeypox. Monkeypox, which was first identified in humans in an outbreak in Africa in 1970, usually produces a less severe illness with fewer fatalities than smallpox. However, its symptoms are similar: fever, pus-filled blisters all over the body, and respiratory problems.
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 the African rain forest. The outbreak that made headlines in the United States in June 2003, however, involved animals purchased as pets from pet stores. In nature, monkeypox has been found in monkeys, chimpanzees, rabbits, prairie dogs, Gambian rats, ground squirrels, and mice. It is not known as of late 2003 whether other wild or domestic animals can contract monkeypox.
Prior to 2003, most monkeypox cases were diagnosed in remote areas of central and west Africa. Between February 1996 and October 1997, however, 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.
The 2003 outbreak in the United States, which was the first confirmed instance of community-acquired monkeypox in North America, came to the attention of the CDC in early June, when a laboratory in Wisconsin identified the monkeypox virus in samples taken from the skin of an infected patient and lymph node tissue from the patient's pet prairie dog. By the end of June, cases of monkeypox in humans had been identified in six Midwestern states (Illinois, Indiana, Kansas, Missouri, Ohio, and Wisconsin). The patients acquired the virus from infected prairie dogs purchased as pets, which in turn were infected through contact with animals imported from Africa that were sold in the same pet stores.
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.
Although the monkeypox virus is related to the smallpox virus, experts do not think (as of late 2003) that it is likely to be cultivated as an agent of bioterrorism. Monkeypox is much less easily transmitted person-to-person than smallpox and has a much lower fatality rate.
Causes and symptoms
The monkeypox virus is transmitted to humans through an infected animal's blood, body sores, or bite; or through handling an infected animal's bedding or cage. Initial symptoms of monkeypox in humans include fever, a bodywide rash (exanthem) of pus-filled blisters, and flu-like muscle aches and fatigue. 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.
The symptoms of monkeypox in pet rabbits, rats, or mice include inflammation of the eyes, a nasal discharge, fever, loss of appetite, a skin rash, and tiredness. Pet monkeys typically develop a rash with pus-filled lesions on the palms of the hands, trunk, and tail. They may also have mouth ulcers.
Since the symptoms of monkeypox resemble other diseases caused by orthopox viruses, definitive diagnosis may require laboratory testing to uncover the virus or evidence (from antibodies in the blood) that it is present. As of 2003, laboratory techniques that can be used to identify the monkeypox virus include electron microscopy, polymerase chain reaction (PCR), immunohistochemistry, and ELISA testing.
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. As of 2003, additional studies report that cidofovir appears to be safe and effective as a treatment for monkeypox in humans. 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.
Monkeypox is one of the diseases that physicians, veterinarians, and public health officials are required by law to report to the CDC.
Although smallpox vaccination offers some protection against monkeypox, experts do not generally recommend getting a smallpox vaccination simply to guard against monkeypox if one has not been exposed to it. However, the CDC recommends as of June 2003 that anyone who has had close contact with humans or animals infected with monkeypox, or has helped to care for them, should be vaccinated against smallpox. The vaccination can be administered as late as 14 days after exposure to the virus. In addition, veterinarians or public health personnel conducting field investigations should be vaccinated before any exposure to monkeypox.
As of late 2003, no cases of monkeypox were identified in cats or dogs belonging to people infected by the June outbreak. The American Veterinary Medicine Association (AVMA) recommends, however, that cats, dogs, or other mammals that have been in contact with an animal known to have monkeypox should be kept in quarantine for 30 days from the date of exposure.
People who have a pet with symptoms of monkeypox should not take it to an animal shelter or release it into the wild. They should isolate it from humans and other animals, and take it to a veterinarian in a closed, chew-proof container with air holes.
On June 11, 2003, the CDC and the Food and Drug Administration (FDA) issued a joint order prohibiting the importation of rats and other rodents from Africa. In addition, the agencies banned the sale and distribution of prairie dogs and six species of African rodents in the United States.
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American Veterinary Medical Association (AVMA). 1931 North Meacham Road, Suite 100, Schaumburg, IL 60173-4360. 〈http://www.avma.org〉.
American Veterinary Medical Association (AVMA). "Foreign Animal Disease Alert: Investigation Uncovers First Outbreak of Monkeypox Infection in the Western Hemisphere," June 23, 2003. 〈http://www.avma.org/pubhlth/monkeypox/default.asp〉.
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Centers for Disease Control and Prevention (CDC). Fact Sheet: Embargoed Animals and Monkeypox Virus. Atlanta, GA: CDC, June 2003.
Antiviral— Refers to a drug that can destroy viruses and help treat illnesses caused by them.
Bioterrorism— The intentional use of diseasecausing microbes or other biologic agents to intimidate or terrorize a civilian population for political or military reasons.
Mutation— A change in an organism's genetic code that causes it to develop new characteristics.
Orthopoxvirus— The genus of viruses that includes monkeypox, smallpox, cowpox, and camelpox.
Symptomatic— Refers to treatment that addresses the symptoms of an illness, but not its underlying cause.
Zoonosis (plural, zoonoses)— Any disease of animals that can be transmitted to humans under natural conditions. Monkeypox is a zoonosis.
Monkeypox is an infectious viral disease that is very similar to smallpox but milder. There is very low prevalence of this disease, with almost all cases occurring in west and central Africa. The first outbreak in the United States occurred in 2003. This disease causes smallpox-like symptoms, including fever, headache, muscle aches, backache, exhaustion, and discomfort in addition to a papular rash over the body. One symptom common in monkeypox but not smallpox is the swelling of the lymph nodes.
Monkeypox is a zoonosis, a disease humans can contract from an infected animal. It is usually contracted via an animal bite, or by coming into contact with the bodily fluids of infected animals. There is no treatment for monkeypox, but fatality rates are low, with most patients recovering in 2–4 weeks. Monkeypox can be prevented by controlling the transmission of the disease from animals to humans. This involves reporting diseased animals, and taking appropriate action to prevent transfer of the virus to humans.
Monkeypox is a rare disease caused by the monkeypox virus. This virus belongs to the orthopoxvirus group of viruses, which also includes smallpox and cowpox. Monkeypox was first discovered in 1958. It was first identified in laboratory monkeys and later in rodents. The first human case of monkeypox was reported in 1970.
Monkeypox is found in many animals including monkeys, mice, rats, rabbits, and squirrels. All mammals are thought to be susceptible to this virus. Humans become infected with monkeypox when they come into direct contact with an infected animal's bodily fluids— either through an animal bite or by touching its lesions. This virus can also be transmitted by airborne droplets from the respiratory tract. Therefore, face to face contact between an infected animal and a human also can spread this virus. Contact with contaminated items, such as bed sheets, can also spread the disease.
Monkeypox is a milder version of smallpox, presenting similar, although less severe, symptoms. Approximately 12 days after infection with the monkeypox virus, a person will develop an illness characterized by fever, headache, muscle aches, backache, exhaustion, and discomfort. Unlike smallpox, monkeypox also causes the lymph nodes to swell. A few days after these initial symptoms, a papular rash (raised bumps on the skin) begins to form. This rash usually develops first on the face before spreading across the body. The bumps develop, crust over, and finally fall off. The infection usually lasts 2–4 weeks. Between 1% and 10% of the people in Africa who contract monkeypox will die of the disease. No monkeypox fatalities have been reported outside of Africa.
Monkeypox was first found in Africa. Most cases of monkeypox occur in central and western Africa, particularly in Zaire, and the countries in which it occurs are characterized by tropical rainforest. There is a low prevalence of the disease. Between 1970 and 1986, only 400 cases worldwide were reported by the World Health Organization.
In 2003, the first ever cases of monkeypox occurred in the United States. Of at least 79 reports of monkeypox, 29 were confirmed as true cases of monkeypox. It is argued that the virus was transmitted to humans by tame prairie dogs that were earlier in contact with infected Gambian rats from Africa. The tame prairie dogs probably contracted the virus from the Gambian rats.
Although the virus is similar to smallpox, which devastated populations prior to its eradication, monkeypox is not as transmissible as smallpox. While smallpox spread rapidly from person to person, only one-third of monkeypox cases arise in this way.
The people most at risk of developing monkeypox are those exposed to infected animals or infected patients. This includes investigators of current monkeypox outbreaks, veterinarians, health care workers, laboratory workers, and friends or family of monkeypox patients.
There is no safe, specific treatment for monkeypox. However, a good health care system, including adequate supportive care for symptoms, as well as good nutrition, aids recovery. The illness normally lasts 2–4 weeks and a person is no longer infectious when the rash lesions are crusted. No fatalities have been reported outside of Africa. However, within rural African regions, where health care is generally poor, monkeypox fatalities may reach 10% of reported cases.
There is no vaccination against monkeypox, although the smallpox vaccination has been found to be effective against monkeypox. However, the CDC does not recommend widespread smallpox vaccination. Instead, use of the vaccine is recommended only for high risk individuals, such as those caring for monkeypox patients, or people who have been in contact with infected animals and are at risk of becoming infected. Vaccination after exposure to the virus has been found to help prevent or reduce the severity of infection. However, vaccination should be avoided in patients with weakened immune systems or patients with life-threatening allergies to the smallpox vaccine and its ingredients, since the smallpox vaccine could be more harmful than the monkeypox virus in these cases.
In order to prevent spread of this disease, infected animals are separated from human populations as soon as possible. These animals are reported to the health department, and appropriate action is taken to keep the animal from transmitting the disease. As contact with fomites (contaminated surfaces such as clothing) and bedding can also result in transmission of the disease, these items must be washed with hot water and detergent to remove the virus.
WORDS TO KNOW
CHAIN OF TRANSMISSION: Chain of transmission refers to the route by which an infection is spread from its source to susceptible host. An example of a chain of transmission is the spread of malaria from an infected animal to humans via mosquitoes.
FOMITE: A fomite is an object or a surface to which an infectious microorganism such as bacteria or viruses can adhere and be transmitted. Transmission is often by touch.
ENDEMIC: Present in a particular area or among a particular group of people.
PAPULAR: A papule is a small, solid bump on the skin; papular means pertaining to or resembling a papule.
ZOONOSES: Zoonoses are diseases of microbiological origin that can be transmitted from animals to people. The causes of the diseases can be bacteria, viruses, parasites, and fungi.
Monkeypox is not a widespread disease. While low mortality outbreaks occur in Africa, few outbreaks have been reported outside of African countries. Prior to 2003, monkeypox had not appeared in the United States and was not considered a threat. Since 2003, there has been one outbreak of monkeypox in the United States and, although the disease was contained, it is now considered a possible threat for United States citizens.
The outbreak in the United States included at least 29 confirmed cases of monkeypox. However, no deaths occurred due to this disease. The effect of this disease on victims in the United States was noticeably milder than its effect on African populations. A better national health care network is thought to have resulted in a more efficient and thus more effective containment of the disease. This health care network includes better nutrition, access to good supportive care, and availability of a vaccine.
IN CONTEXT: REAL-WORLD RISKS
The Centers for Disease Control and Prevention (CDC) states that “past data from Africa suggests that the smallpox vaccine is at least 85% effective in preventing monkeypox.” CDC states that: “for most persons who have been exposed to monkeypox, the risks from monkeypox disease are greater than the risks from the smallpox vaccine.”
“Studies of monkeypox in West Africa—where people live in remote areas and are medically underserved—showed that the disease killed 1%to 10% of people infected. In contrast, most people who get the smallpox vaccine have only expected minor reactions, like mild fever, tiredness, swollen glands, and redness and itching at the place where the vaccine is given. However the smallpox vaccine does have more serious risks too. Based on past experience, it is estimated that between 1 and 2 people out of every 1 million people vaccinated will die as a result of life-threatening reactions to the vaccine.”
Future outbreaks in the United States and in other countries outside of Africa are still possible. However, not only are the chances of transmission throughout a population low, but it is unlikely that a chain of transmission would be sustained within a human community.
There has been some debate within the United States over the potential for monkeypox to be used by terrorists as a biological weapon. However, the efficient containment of this disease during the 2003 outbreak, coupled with the low likelihood that this disease would spread rapidly through the population, significantly reduces its risk as a bioweapon.
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