Monkeypox is a viral zoonosis (a virus transmitted to humans by animals) with symptoms similar to those seen in the past in smallpox patients, although clinically it is less severe. With the eradication of smallpox in 1980 and the subsequent cessation of smallpox vaccination, monkeypox has become the most important orthopoxvirus for public health. monkeypox occurs mainly in central and western Africa, often in the vicinity of tropical forests, and has been appearing increasingly in urban areas. animal hosts include a variety of rodents and non-human primates.
Monkeypox virus is an enveloped double-stranded DNA virus that belongs to the genus Orthopoxvirus of the family Poxviridae. There are two distinct genetic clades of monkeypox virus: the Central African (Congo Basin) clade and the West African clade. Historically, the Congo Basin clade has caused more severe disease and was thought to be more transmissible. The geographical divide between the two clades has so far been in Cameroon, the only country where both virus clades have been found.
natural host of monkeypox virus
Several animal species have been identified as susceptible to monkeypox virus. this includes rope squirrels, tree squirrels, Gambian rats, dormice, non-human primates, and other species. Uncertainty remains about the natural history of monkeypox virus, and further studies are needed to identify the exact reservoirs and how the virus is maintained in nature.
human monkeypox was first identified in humans in 1970 in the democratic republic of the congo in a 9-month-old boy in a region where smallpox was eliminated in 1968. since then, most cases have been reported in rural areas and in the tropical forest. regions of the Congo Basin, particularly in the Democratic Republic of the Congo, and increasing human cases have been reported in Central and West Africa. Since 1970, cases of monkeypox in humans have been reported in 11 African countries: Republic of Congo, Democratic Republic of Congo, Gabon, Ivory Coast, Liberia, Nigeria, Republic of Congo, Sierra Leone, and South Sudan. the true burden of monkeypox is unknown. For example, in 1996-1997, an outbreak was reported in the Democratic Republic of the Congo with a lower case fatality rate and a higher than usual attack rate. a concurrent outbreak of varicella (caused by varicella virus, which is not an orthopoxvirus) and monkeypox was found, which could explain real or apparent changes in transmission dynamics in this case. Since 2017, Nigeria has experienced a large outbreak, with more than 500 suspected cases and more than 200 confirmed cases and a case fatality rate of approximately 3%. Cases continue to be reported to this day.
Monkeypox is a disease of global public health importance, affecting not only countries in West and Central Africa, but the rest of the world. In 2003, the first outbreak of monkeypox outside of Africa occurred in the United States of America and was linked to contact with infected pet prairie dogs. These pets had been housed with Gambian rats and dormouse that had been imported into the country from Ghana. this outbreak caused more than 70 cases of monkeypox in the us. uu. Monkeypox has also been reported in travelers from Nigeria to Israel in September 2018, to the United Kingdom in September 2018, December 2019, May 2021, and May 2022, to Singapore in May 2019, and to the United States of America. in July and November 2021. In May 2022, multiple cases of monkeypox were identified in several non-endemic countries. Studies are currently underway to better understand the epidemiology, sources of infection, and patterns of transmission.
Animal-to-human (zoonotic) transmission can occur by direct contact with blood, body fluids, or skin or mucosal lesions of infected animals. In Africa, evidence of monkeypox virus infection has been found in many animals, including rope squirrels, tree squirrels, Gambian rats, dormice, different species of monkeys, and others. The natural reservoir for monkeypox has not yet been identified, although rodents are the most likely. eating undercooked meat and other animal products from infected animals is a possible risk factor. People who live in or near wooded areas may have low-level or indirect exposure to infected animals. person-to-person transmission can result from close contact with respiratory secretions, skin lesions of an infected person, or recently contaminated objects. Transmission via respiratory droplet typically requires prolonged face-to-face contact, putting healthcare workers, household members, and other close contacts of active cases at greater risk. however, the longest documented chain of transmission in a community has increased in recent years from 6 to 9 successive person-to-person infections. this may reflect decreased immunity in all communities due to cessation of smallpox vaccination. transmission can also occur across the placenta from mother to fetus (which can lead to congenital monkeypox) or during close contact during and after birth. Although close physical contact is a well-known risk factor for transmission, it is unclear at this time whether monkeypox can be transmitted specifically through sexual transmission routes. studies are needed to better understand this risk.
signs and symptoms
The incubation period (interval from infection to onset of symptoms) for monkeypox is usually 6 to 13 days, but can range from 5 to 21 days.
The infection can be divided into two periods:
- the period of invasion (lasting between 0-5 days) characterized by fever, severe headache, lymphadenopathy (swollen lymph nodes), back pain, myalgia (muscle pain) and severe of energy). lymphadenopathy is a distinguishing feature of monkeypox compared to other diseases that may initially appear similar (varicella, measles, smallpox)
- The skin rash usually begins 1-3 days after the onset of fever. the rash tends to be more concentrated on the face and extremities than on the trunk. it affects the face (in 95% of cases), and the palms of the hands and soles of the feet (in 75% of cases). The buccal mucosa (in 70% of cases), the genitalia (30%) and the conjunctiva (20%), as well as the cornea, are also affected. the rash progresses sequentially from macules (lesions with a flat base) to papules (firm, slightly raised lesions), vesicles (clear fluid-filled lesions), pustules (yellowish fluid-filled lesions), and crusts that dry and fall off. the number of injuries varies from a few to several thousand. in severe cases, the lesions may coalesce until large sections of skin are shed.
Monkeypox is usually a self-limited disease with symptoms lasting 2 to 4 weeks. severe cases occur more frequently among children and are related to the degree of exposure to the virus, the health status of the patient, and the nature of the complications. underlying immune deficiencies can lead to worse outcomes. Although smallpox vaccination was protective in the past, today people under 40 to 50 years of age (depending on the country) may be more susceptible to monkeypox due to the cessation of smallpox vaccination campaigns throughout the world. world after the eradication of the disease. Complications of monkeypox can include secondary infections, bronchopneumonia, sepsis, encephalitis, and corneal infection with subsequent loss of vision. the extent to which an asymptomatic infection can occur is unknown. Historically, the case fatality rate for monkeypox has ranged from 0% to 11% in the general population and has been higher among young children. in recent times, the fatality rate has been around 3-6%.
The clinical differential diagnosis that should be considered includes other exanthematous diseases, such as chicken pox, measles, bacterial skin infections, scabies, syphilis and drug-associated allergies. lymphadenopathy during the prodromal stage of the disease may be a clinical feature to distinguish monkeypox from chickenpox or smallpox. if monkeypox is suspected, health workers should collect an adequate sample and transport it safely to a laboratory with adequate capacity. confirmation of monkeypox depends on the type and quality of the sample and the type of laboratory test. therefore, samples must be packaged and shipped in accordance with national and international requirements. Polymerase chain reaction (PCR) is the preferred laboratory test due to its accuracy and sensitivity. for this, the optimal diagnostic specimens for monkeypox are skin lesions: the roof or fluid of vesicles and pustules, and dried scabs. when feasible, biopsy is an option. lesion samples should be stored in a dry, sterile tube (no viral transport media) and kept cold. PCR blood tests are generally inconclusive due to the short duration of viremia relative to the time of sample collection after symptoms begin and should not be routinely collected from patients.
As orthopoxviruses are serologically cross-reactive, antigen and antibody detection methods do not provide specific confirmation of monkeypox. therefore, serologic and antigen detection methods are not recommended for diagnosis or case investigation when resources are limited. furthermore, recent or remote vaccination with a vaccinia-based vaccine (eg, anyone vaccinated before smallpox eradication, or vaccinated more recently due to increased risk, such as orthopoxvirus laboratory personnel) could lead to false results positives.
In order to interpret the test results, it is critical that patient information be provided with the specimens, including: a) date of fever onset, b) date of rash onset, c) date of sample collection, d) current status of the individual (rash stage), and e) age.
Clinical care for monkeypox should be fully optimized to alleviate symptoms, manage complications, and prevent long-term sequelae. patients should be offered fluids and food to maintain adequate nutritional status. secondary bacterial infections should be treated as indicated. An antiviral agent known as tecovirimat that was developed for smallpox was authorized by the European Medicines Agency (EMA) for monkeypox in 2022 based on data from animal and human studies. not yet widely available.
If used for patient care, tecovirimat should ideally be controlled in a clinical investigation setting with prospective data collection.
Several observational studies have shown that smallpox vaccination is about 85% effective in preventing monkeypox. therefore, previous smallpox vaccination may result in milder disease. evidence of previous smallpox vaccination can usually be found as a scar on the upper arm. Currently, the original (first generation) smallpox vaccines are no longer available to the general public. some laboratory staff or health care workers may have received a more recent smallpox vaccine to protect them from exposure to orthopoxviruses in the workplace. In 2019, an even newer vaccine based on a modified attenuated vaccinia virus (ankara strain) was approved for the prevention of monkeypox. it is a two-dose vaccine whose availability remains limited. smallpox and monkeypox vaccines are developed in vaccinia virus-based formulations because of the cross-protection they provide for the immune response to orthopoxviruses.
The main prevention strategy for monkeypox is to raise awareness of risk factors and educate people about steps they can take to reduce exposure to the virus. Scientific studies are now underway to assess the feasibility and suitability of vaccination for the prevention and control of monkeypox. some countries have, or are developing, policies to offer vaccines to people who may be at risk, such as laboratory staff, rapid response teams, and health care workers.
reduce the risk of person-to-person transmission
Surveillance and rapid identification of new cases are critical to containing the outbreak. During human outbreaks of monkeypox, close contact with infected persons is the most important risk factor for infection with monkeypox virus. healthcare workers and household members are at higher risk of infection. healthcare workers caring for patients with suspected or confirmed monkeypox virus infection, or handling specimens from them, should implement standard infection control precautions. If possible, individuals previously vaccinated against smallpox should be selected to care for the patient.
Samples taken from people and animals with suspected monkeypox virus infection should be handled by trained personnel working in properly equipped laboratories. Patient samples should be safely prepared for transport with triple packaging in accordance with the WHO Guide for the Transport of Infectious Substances.
The identification in May 2022 of clusters of monkeypox cases in several non-endemic countries with no direct travel links to an endemic area is atypical. Further investigations are underway to determine the possible source of infection and limit further spread. As the source of this outbreak is investigated, it is important to analyze all possible modes of transmission to safeguard public health. You can find more information about this outbreak here.
reduce the risk of zoonotic transmission
Over time, most human infections have resulted from primary animal-to-human transmission. Unprotected contact with wild animals, especially those that are sick or dead, including their meat, blood, and other parts, should be avoided. also, all foods that contain meat or animal parts should be thoroughly cooked before eating.
prevent monkeypox by restricting trade in animals
Some countries have implemented regulations that restrict the importation of rodents and non-human primates. captive animals potentially infected with monkeypox should be isolated from other animals and placed in immediate quarantine. any animal that may have come into contact with an infected animal should be quarantined, handled with standard precautions, and observed for symptoms of monkeypox for 30 days.
how monkeypox is related to smallpox
The clinical presentation of monkeypox resembles that of smallpox, an orthopoxvirus-related infection that has been eradicated. smallpox was more easily transmitted and more often fatal, with around 30% of patients dying. the last case of naturally acquired smallpox occurred in 1977, and in 1980 smallpox was declared eradicated worldwide following a global campaign of vaccination and containment. It has been 40 years or more since all countries stopped routine smallpox vaccination with vaccinia-based vaccines. As vaccination also protected against monkeypox in West and Central Africa, unvaccinated populations are now also more susceptible to monkeypox virus infection.
While smallpox no longer occurs naturally, the global health sector remains vigilant in case it could re-emerge through natural mechanisms, laboratory accidents, or deliberate release. To ensure global preparedness in the event of a smallpox resurgence, newer vaccines, diagnostics, and antiviral agents are being developed. now they may also be useful for the prevention and control of monkeypox.
which supports member states with surveillance, preparedness and response activities for monkeypox outbreaks in affected countries. more information can be found here.