Monkeypox: how it is transmitted, what the symptoms are and what to do to avoid being infected

Monkey pox: at least three confirmed cases of Monkeypox in France

Background information

  • There is no specific treatment or vaccine for monkeypox, but prior vaccination against monkeypox is a very effective prevention of monkeypox.
  • The monkeypox virus is primarily transmitted to humans by wild animals, such as rodents and primates.
  • Monkeypox is a rare zoonotic viral disease that occurs primarily in remote areas of central and western Africa near.

tropical rainforests.

The monkeypox virus belongs to the genus Orthopoxvirus of the family Poxviridae.Monkeypox is a rare zoonotic viral disease (i.e., a disease transmitted to humans from animals), with symptoms in humans similar to those seen in smallpox patients in the past, but less severe. After the eradication of smallpox in 1980 and the subsequent cessation of the use of smallpox vaccines, monkeypox became the most pathogenic of the other orthopox viruses to humans. Cases of monkeypox still occur sporadically in parts of Africa, where tropical rainforests are widespread.


Human monkeypox was first identified in 1970 in the Democratic Republic of the Congo (then called Zaire) in a 9-year-old boy in an area where smallpox had been eradicated in 1968. Since then, most cases have been reported in rural areas of the tropical rainforests of the Congo Basin and West Africa, particularly in the Democratic Republic of Congo, where the disease is considered endemic. A major epidemic occurred in the Democratic Republic of Congo in 1996-1997.

In the spring of 2003, confirmed cases of monkeypox were reported in the Midwest region of the United States. This was the first case reported outside the African continent. Most cases were found to be in contact with domesticated grasshopper dogs that had been infected by rodents imported from Africa.

Sporadic cases of monkeypox have been reported in many countries in West and Central Africa, and the number of diagnosed cases has increased with awareness of the disease. Since 1970, human cases of monkeypox have been reported in 10 countries in Africa: the Democratic Republic of Congo, Republic of Congo, Cameroon, Central African Republic, Nigeria, Côte d’Ivoire, Liberia, Sierra Leone, Gabon, and South Sudan. In 2017, Nigeria experienced its last known outbreak, the first in the country in 40 years.


Infection in index cases occurs through direct contact with blood, body fluids, and affected skin or mucous membranes of infected animals. In Africa, human infections have been documented following handling of infected monkeys, Gambian rats, and squirrels, with rodents being the likely reservoir of the virus. A possible risk factor is the consumption of meat from infected animals without proper heat treatment.

Secondary transmission, or person-to-person transmission, occurs through close contact with infected respiratory secretions, skin lesions of an infected person, or objects contaminated with body fluids or materials from diseased lesions.

Transmission is primarily by airborne, prolonged personal contact, which places family members of a person with an acute case at the greatest risk of infection. Transmission can also occur by inoculation or via the placenta (congenital monkeypox). To date, there is no evidence that human-to-human transmission alone is sufficient to sustain monkeypox infection in the human population.

Recent animal studies using a prairie dog and human model of monkeypox have identified two different monophyletic groups of the virus, the Congo Basin and West Africa, with the former being more virulent.

Signs and symptoms

The incubation period (time between infection and onset of symptoms) for monkeypox is usually 6 to 16 days, but can vary from 5 to 21 days.

The invasion period (0-5 days), characterized by fever, severe headache, lymphodenopathy (enlarged lymph nodes), back pain, myalgias (muscle pain), and severe asthenia (weakness) ;
a period of rashes (1 to 3 days after the onset of fever), during which different stages of rashes appear, often first on the face and then spreading to other parts of the body. They appear most often on the face (95% of cases) and on the palms of the hands and feet (75% of cases). The rash goes through several stages, from maculopapules (skin lesions with a flat base) to vesicles (small fluid-filled blisters) and pustules, which form crusts after about ten days. It may take up to three weeks for the crusts to completely disappear.
The number of skin lesions varies from a few to several thousand. They appear on the oral mucosal membranes (70% of cases), the genitals (30%) as well as on the conjunctiva (eyelid) (20%) and the cornea (eyeball).

Signs and symptoms

Some patients develop severe lymphadenopathy (enlarged lymph nodes) before the onset of the rash, which is a distinctive feature of monkeypox compared to other similar diseases.

Monkeypox is usually a self-limiting disease, with symptoms persisting for 14 to 21 days. Severe cases occur most often in children and are related to the degree of exposure to the virus, the patient’s health status and the severity of complications.

Persons living in or near forested areas may have indirect or low-level exposure to infected animals, which may result in subclinical (asymptomatic) infection.

Case fatality varies widely depending on the epidemic, but has been documented to be less than 10%. Most deaths occur in young children. In general, younger age groups may be more susceptible to monkeypox.

Natural carriers of the monkeypox virus

In Africa, monkeypox infection has been found in many animal species, such as striped squirrels, tree squirrels, Gambian rats, striped mice, celevinia and primates. The natural history of the virus remains unclear, and further research is needed to determine the exact reservoir of monkeypox virus and its maintenance mechanism in nature.

In the United States, it is believed that the virus has been transmitted from African animals to some susceptible non-African animal species (such as the meadow dog) as a result of these animals living in common territory.


Reducing the risk of infection in humans
During monkeypox outbreaks, close contact with other patients is the most significant risk factor for infection with monkeypox virus. In the absence of specific treatment and vaccine, the only way to reduce human infections is to raise awareness of risk factors and educate the public about measures that can be taken to limit contact with the virus. Surveillance measures and prompt detection of new cases are essential to control outbreaks.

Public health education should emphasize the following risk factors:

Reducing the risk of animal-to-human transmission. Efforts to prevent transmission in endemic areas should focus firstly on avoiding all contact with rodents and primates and secondly on limiting direct contact with blood and meat, including the need for careful heat treatment of animal products before eating them. Gloves and other appropriate protective clothing should be worn when handling sick animals or their infected tissues and when slaughtering animals.
Reducing the risk of human-to-human transmission. Close physical contact with people infected with monkeypox must be avoided. Gloves and protective equipment should be worn when caring for sick people. Hands should be washed regularly after caring for sick people or after visiting such people. It is advisable to isolate sick people either at home or in a health care facility.

Infection control in health care facilities

Health care workers caring for patients with suspected or confirmed infection with monkeypox virus or handling specimens taken from such patients should take standard infection control precautions.

Health care workers and people in contact with patients with or specimens from monkeypox should contact the national health authorities to consider immunization against smallpox. However, people with compromised immune systems should not be vaccinated against smallpox using older vaccines.

Specimens from humans and animals with suspected monkeypox virus infection should be handled by trained personnel in properly equipped laboratories. When transporting specimens from patients, they should be placed in safe containers and follow the rules for handling infectious materials.

Preventing further spread of monkeypox as a result of animal trafficking

Restricting or prohibiting the movement of small African mammalian animals or monkeys can be effective in containing the spread of the virus out of Africa.

Captive animals should not be vaccinated against smallpox. However, potentially infected animals should be isolated from other animals and quarantined immediately. Any animals that may have had contact with an infected animal should be quarantined and monitored for symptoms of monkeypox for 30 days.

WHO response

WHO assists member states in surveillance, preparedness, and outbreak management in countries affected by monkeypox.

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