Monkeypox was first reported in 1958 in laboratory monkeys and the first human case was reported in 1970 in a nine-month-old baby in the Democratic Republic of Congo. Nigeria reported its first case of monkeypox in humans in 1970 when one case was detected; there were two human cases of monkeypox in Nigeria in 1978. And after nearly four decades of not reporting any cases, monkeypox (West African clade) made a re-emergence in Nigeria in September 2017. From September 2017 to April 30, 2022, Nigeria has reported 558 cases, of which 231 have been laboratory confirmed. There have been dozens of confirmed cases each year in Nigeria since 2017 — 88 in 2017, 49 in 2018, 47 in 2019, eight in 2020, and 34 in 2021. There have been 15 confirmed cases between January 1 and April 30, 2022.
Based on epidemiological and clinical characteristics of 122 confirmed or probable cases of human monkeypox cases in Nigeria between September 22, 2017 and September 16, 2018, researchers found both primary zoonotic and human-to-human transmission. Two cases of healthcare-associated infection were recorded. Based on genome sequencing, the researchers found multiple introductions of the virus, and a single introduction along with human-to-human transmission in a prison facility. The results were published in the journal The Lancet Infectious Diseases.
Since the outbreak began in Nigeria in 2017 and prior to the latest outbreak in Europe and North America, there have been at least eight instances when monkeypox has been exported to countries outside Africa — the U.K., the U.S., Israel and Singapore. Like all diseases that are endemic only to Africa, the story repeats again. While efforts were made to prevent an outbreak in the non-endemic countries outside Africa, no serious international attempts were made to stop the outbreak in Nigeria nor study the virus characteristics.
According to Stat News, Dr. Chikwe Ihekweazu, the former director general of the Nigeria Centre for Disease Control had sought help to try to decipher what was going on with monkeypox but without success. While in 2003, the U.S. reported the first human case of monkeypox, the virus had only crossed the species barrier from rodents imported from Ghana to one person. Human-to-human transmission outside Africa was first reported in September 2018, when the monkeypox virus spread from a patient to a healthcare worker in the U.K.
Current outbreak
The current outbreak in Europe and North America is the first instance when large-scale human-to-human transmission has been reported outside Africa. The index case was a U.K. resident, who travelled to Nigeria on April 20 and returned on May 3; he was diagnosed with monkeypox on May 6, 2022. It has since spread to 219 people as of May 25 across 20 countries.
The wealthy nations are now waking up to the reality of monkeypox crossing international borders and causing outbreaks in countries where it is not endemic.
“Attention is only paid when certain diseases hit high-income countries — exemplifying our collective failure to properly address ‘epidemic preparedness’ and ‘global health’. It also illustrates the double standard applied to how people’s health is valued between wealthy countries and the rest of the world,” Dr. Emmanuel Nakoune from Institut Pasteur Bangui, Central African Republic and Dr. Piero Olliaro from the Pandemic Sciences Institute, University of Oxford write in the BMJ.
There are no clear answers to how humans are infected as the host animal that behaves as a reservoir for the virus has not been identified in the wild. And how the virus spreads from animals to humans is not known.
Also, how many people, on average, will one infected person spread the virus to is unclear.
“There wasn’t a lot of interest to support that work until now — sadly,” Dr. Ihekweazu told Stat News. “It never really received the interest it needed to answer some of these questions.”
The current outbreak appears to have spread primarily among men who have sex with men. The virus is not transmitted through semen or vaginal fluids but the skin-to-skin contact during sex can result in virus spread.
The draft genome sequences first posted by researchers in Portugal and then Belgium indicate that the virus circulating in Europe and North America belongs to the West African clade, which causes mild infection.
Low mutation rate
Till date over 15 monkeypox genomes have been sequenced. But the monkeypox virus has a lower mutation rate (about two mutations a year) compared to nearly 25 mutations in a year in the case of SARS-CoV-2 virus.
This is because monkeypox is a DNA virus unlike the SARS-CoV-2, which is an RNA virus.
The low mutation rate in DNA viruses is largely due to the differences in mechanisms which create the mutation as also proof-reading mechanisms utilised by the viruses.
“The mutation rates of monkeypox are not well known, but generally other pox viruses have a much lower mutation rate. But almost all outbreaks have been due to spillovers from animals, while sustained human-to-human transmission and sequences from such events are not widely available to accurately estimate the rates,” says Dr. Vinod Scaria, a senior scientist at the Institute of Genomics and Integrative Biology (CSIR-IGIB).
Genome sequencing
Despite the low mutation rate, sequencing more genomes might be prudent particularly from a genetic epidemiology point of view.
According to Dr. Scaria, besides providing insights into emergence, genetic epidemiology helps in understanding evolution through surveillance and fine-trace contact networks.
“The former is still applicable, while even with the loss of resolution, the latter is still useful,” he says.
Though one extra mutation has been found in the sequenced genomes, there is a need for more genome sequences and epidemiological insights to conclusively establish what this mutation indeed means. It is unlikely that the mutation has made the virus more transmissive, despite a large number of cases being reported.
This is because two rave parties in Spain and Belgium have turned out to be super-spreader events, resulting in cases being reported from many countries. It is yet unclear if the virus has acquired the ability of sustained transmission among humans.
“Many of the new cases seem to have come in people who do not have a travel history or known contact with one who has travelled. Still too early to state it is [due to] sustained human-to-human transmission,” Dr. Scaria says.
