How did monkeypox spread? What are the observations from genome sequencing?
With cases being reported from across the world, monkeypox has caught everyone’s attention. The present outbreak has a toll of over 220 confirmed cases spread across 19 countries. U.K., Spain, and Portugal are leading the pack with the highest number of confirmed cases but no deaths reported to date.
The present outbreak has been interesting in many ways. While sporadic outbreaks have occurred in Africa and a few outsides of Africa in regions that had recorded travel from areas where outbreaks have occurred, such massive flare-ups spanning multiple countries simultaneously have not happened before. Additionally, many of the affected patients did not travel to regions where the disease is considered prevalent and the initial cases were largely, but not exclusively among young individuals who identify themselves as men who have sex with men (MSM).
What is the monkeypox virus?
Monkeypox is not a new virus. The virus, belonging to the poxvirus family of viruses, was first identified in monkeys way back in 1958, and therefore the name. The first human case was described in 1970 in the Democratic Republic of Congo and many sporadic outbreaks of animal-human, as well as human-to-human transmission, have occurred in Central and West Africa in the past with significant mortality.
After the elimination of smallpox, monkeypox has become one of the dominant poxviruses in humans, with cases increasing over years along with a consequent reduction in the age group affected. Since the transmission occurs only with close contact, the outbreaks have been in many cases self-limiting. Since in the majority of affected people, the incubation period ranges from five to 21 days and is often mild or self-limiting, asymptomatic cases could transmit the disease unknowingly. The outbreaks in Central Africa are thought to have been contributed by close contact with animals in regions adjoining forests. While monkeys are possibly only incidental hosts, the reservoir is not known. It is believed that rodents and non-human primates could be potential reservoirs.
Does the virus mutate?
Monkeypox virus is a DNA virus with a quite large genome of around 2,00,000 nucleotide bases. While being a DNA virus, the rate of mutations in the monkeypox virus is significantly lower (~1-2 mutations per year) compared to RNA viruses like SARS-CoV-2. The low rate of mutation, therefore, limits the wide application of genomic surveillance in providing detailed clues to the networks of transmission for monkeypox, unlike what was possible for SARS-CoV-2.
A number of genome sequences in recent years from Africa and across the world suggest that there are two distinct clades of the virus — the Congo Basin/Central African clade and the West African clade. Each of the clades further has many lineages. The Central African/Congo basin clade is thought to have higher transmission and virulence compared to the West African clade. It is remarkable and noteworthy that the enormous capacity and expertise in sequencing and analysis of genome sequences of viral pathogens built during the COVID-19 pandemic has come in handy for investigating the present outbreaks.
What do the genomes say?
With over a dozen genome sequences of monkeypox now available from across the world due to the current outbreak, it is reassuring that the sequences are quite identical to each other suggesting that only a few introductions resulted in the present spread of cases. Additionally, almost all genomes have come from the West African clade, which has much lesser fatality compared to the Central African one.
This also roughly corroborates with the epidemiological understanding that major congregations in the recent past contributed to the widespread transmission across different countries. While, unlike COVID-19, the slow rate of mutations precludes us from using genomic sequences for fine-tracing of the contact networks, the sequences largely belong to the West African lineage of the virus, which has shown to be associated with lesser virulence. The virus genomes also show very close similarity with those from the recent outbreak in Nigeria during the 2017-2019 period suggesting that the present outbreak is not driven by a particular new variant, but possibly related to unique transmission networks.
Does it have an effective vaccine?
It is reassuring that we know quite a lot more about the virus and its transmission patterns. We also have effective ways of preventing the spread, including a vaccine. Smallpox/vaccinia vaccine provides protection. While the vaccine has been discontinued in 1980 following the eradication of smallpox, emergency stockpiles of the vaccines are maintained by many countries. Younger individuals are unlikely to have received the vaccine and are therefore potentially susceptible to monkeypox which could partly explain its emergence in younger individuals.
Learning from the enormous wealth of knowledge from African countries which have effectively managed the monkeypox outbreaks in the past would go a great way in containing the present outbreak. While we have many effective ways of containing the outbreak, including contact tracing and a vaccine, efforts to bridge the divide in health, knowledge, experience, and infrastructure could contribute to a long-lasting impact in preventing and managing future outbreaks and contribute to an equitable and global public health.
Source: The Hindu