Subscribe
The World Health Organization (WHO) declared the monkeypox outbreak in Africa a public health emergency of international concern for the second time in two years. However, the outlook this year looks different.
Scientists have documented clusters of transmission linked to heterosexual intimate or sexual contact, which was not a common observation during the 2022 multi-country outbreak. These infections, according to a paper in the journal JAMA, can be attributed to the clade 1b of the monkeypox virus. It has since been detected in four countries Burundi, Kenya, Rwanda and Uganda that have not reported cases of mpox before. Sweden, too, reported one case of clade Ib.
Clade1b is a new offshoot of clade I virus. According to WHO, it was first reported in the Democratic Republic of the Congo in 2023 and has been spreading through sex and other types of close contact. Studies are underway to understand the properties of this new strain.
“Some public health officials are referring to clade Ib as having pandemic potential, a judgment that is being echoed in media reports. Although information is still limited, clade Ib is transmitting differently and may yet change further as cases proliferate,” reads the JAMA paper.
The monkeypox virus was classified into clades I and II. Clades are a group of organisms consisting of a shared ancestor and its descendants. Clade I is endemic to Central Africa while clade II was earlier known as the West African clade and is further divided into subclades: Clade IIa and Clade IIb. Clade IIb drove the 2022 multicounty outbreak.
Clade I is estimated to cause more severe disease and higher mortality than clades IIa and IIb. Clade I is associated with a mortality of up to 10 per cent, whereas clade IIa has a mortality of less than 1 per cent.
Some reports suggest that the case fatality risk of clade Ib can be as high as 5 per cent in adults and 10 per cent in children. There are also reports of pregnancy loss.
“Given these demographic patterns, it seems likely that new modes of transmission such as household contact, and heterosexual contact for clade Ib are significant contributors to spread, necessitating a very different approach to assessing and reducing risk compared with the 2022 epidemic,” the JAMA paper read.
Monkeypox virus was first discovered in 1958 during an outbreak in an animal facility in Copenhagen, Denmark. The first human case was detected in a nine-month-old boy in the Democratic Republic of the Congo in 1970.
Historically, mpox has been a zoonotic disease with little human-to-human transmission and until 2022 was largely limited to regions of Africa, reads a 2023 study published in the journal PNAS. Researchers are unsure of what caused the unexpected spread in 2022. They suspected behavioural and environmental factors could be at play. It is also possible that the virus is adapting to a new host.
Clade IIb infections were first reported in Nigeria. Since 2017, this clade has caused infections in the United Kingdom, Israel, Singapore, the United States, France, Germany, Portugal, Italy, Portugal, Australia and India.
The clade IIb virus has been further classified into A.1, A.1.1, A.2, A.2.1, A.2.2, A.3 and B.1 lineages. While most countries have reported monkeypox cases associated with Clade IIb–B.1 lineage, isolates in India were primarily Clade IIb–A.2 and Clade IIb–A.2.1, according to a 2024 study published in the journal Infectious Medicine.
Another 2023 study noted the changing nature of the monkeypox virus. Studies have reported that the median age of patients was 37 years, and skin-to-skin contact during sex was the dominant mechanism of transmission of mpox in Spain.
The virus is increasingly displaying a trend toward adults, and the disease’s spread also shifted to unusual sexual transmission routes.
Monkeypox virus is a DNA virus and shows slow rates of evolution compared to RNA viruses like HIV. However, scientists highlighted that the virus is undergoing microevolution to adapt to human hosts. A 2022 study in the journal Frontiers in Microbiology suggested that the viruses appear to have micro-evolved from 2017-8 to 2022, gradually accumulating mutations in key proteins to seed a multi-country outbreak in 2022.
Further, researchers also suspected that the virus could be amassing mutations due to interactions between the host and the virus. It remains to be seen whether these mutations are bystanders or have roles in causing the disease.
During the first six months of 2024, 1,854 confirmed cases have been reported in the WHO African Region, according to WHO. Of these confirmed cases in the WHO African region in 2024, 95 per cent can be traced to the Democratic Republic of the Congo.
It has already seen more than 15,000 clinically compatible cases and over 500 deaths, already exceeding the number of cases observed in the DRC in 2023.