By: Makayla Ross
Image courtesy of NIAID; CC-BY.
The Current Situation
Over 900 confirmed cases of monkeypox have now been reported in 28 countries where the virus is not considered endemic, with even more suspected cases of this disease currently under investigation (1,2,10). The United Kingdom (UK), where the first cases were reported this year outside of central and western Africa, has recorded 302 cases of the disease as of 6 June (3). Prior to this multi-country outbreak, cases of monkeypox have primarily been restricted to endemic countries in central and western Africa, with only a few sporadic cases occurring on other continents that have been directly linked to international travel or imported animals (4). The most recent instance of imported infection with monkeypox occurred in a person who returned to the UK on 4 May after traveling to Nigeria. UK health officials initiated prompt isolation of the case as well as contact tracing and were successful in ensuring the imported case did not spread any further. (5) However, on 13 May, two additional cases of monkeypox were confirmed in the UK that did not have any connection to the initial imported case nor any history of travel to an endemic country, leading officials to believe these infections were acquired locally in the UK. On 16 May, four more cases were confirmed in the UK among people who self-identified as gay, bi-sexual or other men who have sex with men. (6,7) Since then, multiple other countries have reported findings consistent with the idea that cases are occurring through community transmission and not as a result of travel to an endemic country. For example, Australia’s first case was in a man who had recently returned from travelling to the UK, and the United States’ first case occurred in a man who had recently returned from Canada; these cases do not have any connection to a country endemic for monkeypox, which is what makes this particular outbreak so unique. (1,4)
Public health experts have noted that this multi-country outbreak seems to be exploiting a previously underrecognized mode of transmission between people, demonstrating an unprecedented and therefore quite unusual scenario. Health officials predict that we will likely see more cases emerge worldwide in the coming days. While it is important to remain aware of monkeypox signs and symptoms, officials would like to remind people that the risk of transmission for the general public still remains low. (2)
Background on Monkeypox
The monkeypox virus is a member of the Poxviridae family and Orthopoxvirus genus, a classification which also includes the viruses that cause smallpox and cowpox. Human infections typically occur when a person comes in contact with an infected animal, human or object infected or contaminated by the virus. Animal-to-human transmission occurs through contact with or consumption of an infected animal, while human-to-human transmission is thought to occur primarily through direct contact with bodily fluids or infectious skin lesions or through indirect contact with contaminated materials, such as clothing or bedding. Transmission through large respiratory droplets can also occur occasionally but requires prolonged face-to-face contact, making it less common. The animal reservoir for monkeypox remains unknown but is suspected to be rodents or non-human primates, as contact with animals is a known risk factor for infection.
The incubation period for monkeypox ranges from 5-21 days and symptoms can last for 2-4 weeks, during which time a person remains infectious to anyone they have direct physical contact with, a key factor in managing an outbreak of this disease. For this reason, many countries involved in the current outbreak have already initiated a 21-day period of isolation for monkeypox cases. (7) Clinically, monkeypox is considered a milder version of smallpox, with initial symptoms that include fever, headache, muscle aches and exhaustion that soon progress into a rash on the face that then spreads to other parts of the body. The major difference between monkeypox and smallpox is that monkeypox causes the lymph nodes to swell while smallpox does not. The case fatality rate depends on the clade of monkeypox virus but can range from 1-10%. Currently, the clade circulating within the non-endemic countries seems to be the West African clade of monkeypox, which has a case fatality rate of less than 1%. A vaccine against monkeypox does exist (and the smallpox vaccine can also provide some protection) but it is not widely available. (4,5,8)
Brief History of Monkeypox Outbreaks
The first human case of monkeypox occurred in the 1970s in the Democratic Republic of Congo (DRC) during the time of the smallpox eradication campaign. Since then, human cases have been relatively rare and outbreaks have been restricted to the African continent, with the few cases occurring outside of Africa linked to international travel or imported animals. (4) Prior to the current outbreak, the UK had only reported seven total cases, and the US had recorded only two, all of which were linked to travel to Nigeria. In the past few years, four countries in Africa have reported outbreaks of Monkeypox: Cameroon, Central African Republic, DRC, and Nigeria. Since 2017, Nigeria has consistently reported cases of monkeypox, for a total of 558 suspected cases to date. (5,9) In addition, the DRC is currently in the midst of one of the largest monkeypox outbreaks, with over 1,200 cases and 58 deaths reported so far this year and likely many more left undiagnosed, according to the WHO. Furthermore, the strain of monkeypox that has been circulating in Nigeria and the DRC this year is known to be a more virulent (and therefore more dangerous) strain than the one currently spreading through multiple non-endemic countries. (8,9)
Stay Up to Date on the Current Outbreak
This is a rapidly developing outbreak, with confirmed and suspected case counts changing daily. The HealthMap and Global.health teams, along with collaborators in the scientific community have created an open-source resource of verified case-level data on the monkeypox outbreak. Verified sources include government reports and news media reporting of health official statements. As verified information and official statements are published, we document secondary sources and update the metadata in the dataset. We do not enter unverified cases, and have multiple curators review each case. Access this resource to stay up to date on the monkeypox outbreak here: https://docs.google.com/spreadsheets/d/1CEBhao3rMe-qtCbAgJTn5ZKQMRFWeAeaiXFpBY3gbHE/edit#gid=0 A visualization of the monkeypox tracker is available here: https://monkeypox.healthmap.org/.