With cases reported in a number of countries, human monkeypox infection is generating global interest and concern as an emerging infectious disease threat even in the midst of the slowly receding COVID-19 pandemic.
What is monkeypox virus?
Monkeypox is a member of a group of closely related viruses in the genus Cordovirus that includes smallpox, cowpox, and camel pox. Monkeypox virus was first discovered in the summer of 1958 as a non-fatal smallpox-like skin disease that affects captive monkeys at a research institute in Denmark.
The name monkeypox is a misnomer because wild African rodents (rats and squirrels) act as a natural reservoir for the virus, while monkeys and other primates are thought to be an occasional host.
When was monkeypox first reported in humans?
The first known case of human monkeypox infection was reported from the Democratic Republic of the Congo in 1970, of a nine-month-old baby with a non-fatal smallpox-like disease.
Since then, sporadic human cases have occurred in many Central and West African countries, and infection has been more common in children and young adults. In countries where monkeypox is endemic (where it is commonly found), recent increases in cases are thought to be associated with climate change, deforestation, war, increased population mobility, and waning herd immunity to smallpox vaccination.
How is monkeypox transmitted?
Transmission occurs through close physical contact with animals or humans, their body fluids, or droplet particles contaminated from respiratory secretions or infected skin lesions, and indirectly via “chimneys” (non-living objects such as bed linen, towels, and hard surfaces that may be loaded with infectious virus particles).
Animal bites and consumption of animal meat are common modes of transmission in endemic areas. Secondary infection occurs among unvaccinated contacts in about 12.3 percent of household contacts and 3.3 percent of others.
When was monkeypox first reported in non-African countries?
The first cluster of human monkeypox infections outside Africa occurred in the United States in 2003. A multistate outbreak of 87 children and young adults has been attributed to close contact with infected prairie dogs obtained as pets from an animal distributor. The final source of infection was found to be imported Gambian rats that transmitted the infection to prairie dogs. There were no human deaths, although three children became severely ill.
Prior to 2022, several travel-related cases were reported in the United Kingdom, Israel, Singapore and the United States among individuals who had visited Nigeria.
What do we know about the global outbreak of monkeypox in non-endemic countries?
On 7 May 2022, UK public health authorities were informed of an imported case of human monkeypox infection in a traveler returning from Nigeria. Since then, more than 550 confirmed human cases of infection have been reported in the UK and 29 other countries. Cases were significantly higher among men who have sex with men, although the virus is not known to be sexually transmitted.
What are the symptoms of monkeypox disease?
Clinical manifestations of human monkeypox infection mimic those of smallpox, but are usually milder. Unlike monkeypox, smallpox is an eradicated disease that has no animal reservoir and does not usually affect lymph nodes.
The incubation period for monkeypox in humans ranges from four to 21 days, followed by a phase of one to five days of fever, chills, sweating, fatigue, and enlarged tender lymph nodes in the neck and groin.
The next stage involves a multi-stage rash that progresses from small skin patches to papules (small bumps on the skin), followed by vesicles (small clear fluid-filled bumps) and then pustules (small pus-filled bumps). They appear prominently on the face, palms and soles of the feet. The blisters disappear by scarring or crusting over the next two to four weeks.
Exposed people may also develop a sore throat, cough, and/or rash on the mucous membranes of the mouth.
How dangerous is monkeypox infection?
The disease is usually mild, although severe illness and death are possible. There are two common genetic variants of monkeypox virus: the Central African variant and the West African variant. Mortality rates of 3.6 percent for the West African variant and 10.6 percent for the Central African variant were reported in endemic areas.
However, no deaths have occurred so far in any of the cases reported outside Africa. All confirmed cases from the 2022 outbreak in 30 non-endemic countries were due to the West Africa variant.
Are there any other general health recommendations for monkeypox?
People with monkeypox should wear surgical masks, and skin lesions should be covered until they have healed. Items of personal use such as towels and sheets should not be shared. Frequently touched surfaces should be disinfected regularly, contaminated clothing should be washed and contact with household and non-family members should be avoided until the disease has resolved.
Healthcare workers should use gloves, gowns, respiratory protection with N95 masks and face shields, and maintain excellent hand hygiene while caring for monkeypox patients. Hospital patients with confirmed or suspected monkeypox should be isolated, taking the necessary precautions for transmission through air, droplets and contact so that they do not become contagious.
Does the smallpox vaccine protect against monkeypox?
Smallpox vaccine — given either before or after exposure to monkeypox — may prevent or reduce the effects of human monkeypox infection. However, rare but serious adverse events have been reported from older generation smallpox vaccines. A new generation of live, non-replicating vaccine is now available and is considered safe for use in the entire population, including those with compromised immune systems.
The US Centers for Disease Control and Prevention’s Immunization Practices Advisory Committee recommends pre-exposure prophylaxis (vaccination before exposure to the virus) with a new generation vaccine for laboratory workers performing monkeypox diagnostic testing, as well as for health care workers treating smallpox vaccine or caring for monkeypox patients. (Its brand name is Jynneos in the United States, Imvamune in Canada and Imvanex in Europe.)
In Canada and other developed countries, people born before 1972 are likely to have been vaccinated against smallpox. Although immunity after vaccination tends to diminish with age, lifelong immunity appears to be the norm after smallpox vaccination in healthy individuals, and its protective efficacy against monkeypox is thought to be as high as 85%.
Is monkeypox the next viral epidemic?
The emergence of infectious diseases such as monkeypox in non-endemic areas has caused a great deal of concern in light of our experience with COVID-19.
Monkeypox was a neglected tropical disease until the current outbreak in the developed world. But the trajectory of these cases, along with the pattern of transmission in Africa, suggest that the virus will not become a pandemic.
The primary replication number (R0), a measure of viral infection, where R0 equals the number of secondary infections transmitted from one case in a non-immunized group, is 0.6 to 1.0 for the Central African variant, and much lower for the West African variant.
In contrast, the R0 for the Omicron variant of SARS-CoV-2 is about 10, and the R0 for measles ranges from 11 to 18. The R0 for the West African variant of monkeypox virus may be too low for human-to-human transmission outside endemic areas.