- While vaccination against smallpox is very effective in preventing monkeypox, there is no specific treatment or vaccine.
- Monkeypox virus is mainly transmitted to humans by various wild animals such as rodents and primates, but there is limited secondary human-to-human transmission.
- Monkeypox is a rare viral zoonotic disease that occurs mainly in remote areas of Central and West Africa near tropical rainforests.
Monkeypox is a species of orthopoxvirus in the Poxviridae family.
Monkeypox is a rare viral zoonotic disease (virus transmitted from animals to humans) with symptoms similar to those observed in the past in smallpox patients, but with less clinical severity. With the eradication of smallpox in 1980 and the subsequent cessation of vaccination against smallpox, monkeypox became the most serious orthopox virus. There are still sporadic cases of monkeypox in the tropical rainforests of central and western Africa.
Human monkeypox was first identified in 1970 in a 9-year-old boy in the Democratic Republic of Congo (formerly Zaire), where smallpox was eliminated in 1968. Since then, most of the reported cases have been in the Congo Basin and the rainforest regions of West Africa, particularly the Democratic Republic of Congo, where it is considered endemic. In 1996-1997, a large outbreak occurred in the Democratic Republic of Congo.
In the spring of 2003, monkeypox cases were confirmed in the United States. This is the first reported case of monkeypox outside the African continent, with most patients reported to have had close contact with imported pet prairie dogs infected with African rodents.
Sporadic cases of monkeypox have been reported in West and Central African countries. With increased awareness, more countries have detected and notified cases. Since 1970, 10 African countries (Democratic Republic of Congo, Republic of Congo, Cameroon, Central African Republic, Nigeria, Côte d’Ivoire, Liberia, Sierra Leone, Gabon and South Sudan) have reported cases of monkeypox in humans. In 2017, Nigeria experienced the largest outbreak on record. The last confirmed case of monkeypox in the country was about 40 years ago.
Index cases acquired infection through direct contact with blood, body fluids, skin or mucosal lesions of infected animals. Human infection has been documented in Africa by handling infected monkeys, Gambian giant rats or squirrels. Rodents are the main hosts for viruses. Eating improperly cooked meat from infected animals is a possible risk factor.
Secondary or person-to-person transmission results from close contact with infected respiratory secretions, skin lesions of an infected person, or items recently contaminated with body fluids or diseased material of a patient. Transmission is primarily through prolonged face-to-face contact with respiratory droplets, so family members of active cases are at greater risk of infection. Transmission can also occur through vaccination or the placenta (congenital monkeypox). To date, there is no evidence that human-to-human transmission alone allows monkeypox to persist in humans.
In a recent prairie dog-human monkeypox animal model study, two different virus strains, the Congo Basin strain and the West African strain, were identified, and the Congo Basin strain was more virulent.
Symptoms and Signs
The incubation period (the time interval between infection and onset of symptoms) for monkeypox is usually 6 to 16 days, but can range from 5 to 21 days.
Infection can be divided into two stages:
- Onset period (0-5 days): fever, severe headache, lymphadenopathy (swollen lymph nodes), back pain, myalgia (muscle pain), severe fatigue (lack of energy);
- Rash phase (within 1-3 days after the onset of fever): The rash occurs in different stages, often starting on the face and then spreading to other parts of the body. The most common rashes are on the face (95% of cases), palms and soles (75%). The rash varies from maculopapular (lesions with a flat bottom) to vesicles (fluid-filled vesicles), pustules, and scabs in about 10 days, and the scabs take about three weeks to completely disappear.
The number of lesions varies from a few to several thousand and affects the oral mucosa (70% of cases), genitalia (30%), conjunctiva (eyelid) (20%) and cornea (eyeball).
Some patients develop severe lymphadenopathy (swollen lymph nodes) before the rash, which can help identify monkeypox because other similar diseases do not have this feature.
Monkeypox is usually a self-limiting disease, with symptoms lasting 14 to 21 days. Severe cases are more common in children and are related to the degree of exposure to the virus, the patient’s health status, and the severity of complications.
People living in or near forested areas may have indirect or low-level exposure to infected animals that can lead to subclinical (asymptomatic) infections.
Mortality rates in monkeypox epidemics vary widely, with less than 10% of recorded cases, mainly in young children. In general, younger age groups seem to be more prone to monkeypox.
Clinical differential diagnoses that must be considered include other rash disorders such as smallpox (although eradicated), chickenpox, measles, bacterial skin infections, scabies, syphilis, and drug allergies. The presence of lymphadenopathy early in the disease may be a clinical feature that distinguishes monkeypox from smallpox.
Monkeypox can only be diagnosed by a laboratory. The virus needs to be determined by a number of different detection methods in specialized laboratories. If monkeypox is suspected, medical personnel should collect appropriate samples (see below) and transport them safely to a laboratory with appropriate capabilities.
The best samples for diagnostic testing are swabs of vesicles or pox scab lesions in dry sterile tubes (virus-free storage tools) and should be kept cool. Blood and serum samples can be used, but the diagnosis may not usually be confirmed due to the short duration of viremia and the timing of sample collection. To assist in the interpretation of test results, it is critical to provide patient information along with the sample. Patient information included: (a) approximate date of fever, (b) date of onset of rash, (c) date of specimen collection, (d) current status of patient (rash stage), (e) age.
Treatment and Vaccines
There is no specific drug or vaccine for monkeypox, but outbreaks can be controlled. Although vaccination against smallpox has been shown in the past to protect against monkeypox with an 85% efficacy rate, the smallpox vaccine is no longer available to the general public after the global eradication of smallpox. Previous vaccination against smallpox may reduce monkeypox symptoms.
Natural host of monkeypox virus
In Africa, monkeypox is found in a variety of animals: rope squirrels, squirrels, giant gambian rats, striped mice, dormouse, and primates. Questions remain about the natural history of the virus, and further research is needed to determine the exact host of monkeypox virus and the survival of the virus in nature.
In the United States, the virus is thought to have spread from African animals to other susceptible animals (such as prairie dogs) with which it was housed.
Reduce the risk of infection in the population
During a monkeypox outbreak, close contact with other patients is the most important risk factor for monkeypox virus transmission. In the absence of specific treatments and vaccines, the only way to reduce infection in the population is to raise awareness of risk factors and educate people about the steps needed to reduce exposure to the virus. Surveillance and rapid identification of new cases are critical to containing outbreaks.
Public health education should focus on the following:
- Reduce the risk of animal-to-human transmission. In areas where monkeypox virus is endemic, prevention of transmission should first focus on avoiding any contact with rodents and primates, and secondly should limit direct contact with the blood and meat of animals, which must be thoroughly cooked before eating. Gloves and other appropriate protective clothing should be worn when handling sick animals or infected tissues and during slaughter.
- Reduce the risk of human-to-human transmission. Avoid close physical contact with people infected with monkeypox and avoid working with contaminated materials. Gloves and protective gear should be worn when caring for a sick person. Wash hands as prescribed after caring for or visiting a sick person. It is recommended that the patient be isolated at home or in a medical facility.
Implement infection control in health care settings
Health care workers should practice standard precautions for infection control when caring for patients with suspected or confirmed monkeypox virus infection or handling patient specimens.
Smallpox vaccination should be considered for health-care workers and those who treat or come into contact with monkeypox patients or patient specimens, but should not be given to people with compromised immune systems.
Collection of human and animal samples suspected of being infected with monkeypox virus should be performed by trained personnel and handled in a properly equipped laboratory. Shipping patient samples should ensure safe packaging and follow infectious material handling guidelines.
Preventing the spread of monkeypox through the animal trade
Restricting or banning the movement of small African mammals and monkeys could effectively reduce the spread of the virus outside Africa.
Smallpox vaccination should not be given to captive animals. Infected animals should be isolated from other animals and quarantined immediately. Any animals that may have come into contact with infected animals should be quarantined and treated according to standard precautions and observed for monkeypox symptoms for 30 days.
WHO supports Member States in monkeypox surveillance and preparedness and supports outbreak response in affected countries.