What caused the recent monkeypox outbreaks?
Monkeypox cases have been rising rapidly in non-endemic countries around the world; but what caused the recent outbreaks?
At the beginning of May 2022, countries around the world began to report new monkeypox cases in individuals that had no travel links to areas in which monkeypox is endemic. With little epidemiological information available, researchers began to question the reason for the rapid rise in cases. Now, an article published by researchers from the Royal Veterinary College (London, UK), in collaboration with researchers from around the globe, offers a number of potential explanations for the recent outbreaks.
Monkeypox virus (MPXV) is a zoonotic virus, meaning that it can jump from animal hosts to humans. MPXV has been detected in 10 species, mainly small mammals and non-human primates; however, it has only been isolated from wild animals twice – once from a rope squirrel in the Democratic Republic of Congo in 1986, and once from a sooty mangabey in Côte d’Ivoire in 2012. The article suggests that the lack of information on the diversity and extent of animal reservoir is a limiting factor in understanding the monkeypox virus, and that this could contribute to an increased number of ‘spillover’ events, particularly in areas undergoing urbanization.
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The authors hypothesize that recent outbreaks in non-endemic countries are a result of a rise in cases in west and central Africa, which have spread across continents due to increased travel post-COVID. One suggested reason for the increase in cases in endemic areas is that a rise in rodent populations, in combination with changing land use and increased human density, has led to more interactions between rodents and humans, and potentially more spillover events. This may have been exacerbated by the COVID-19 pandemic, which pushed more people into poverty, forcing them to find alternative food sources, such as hunted and wild animal meat.
Another suggested factor is that the global population with no smallpox immunity from either prior infection or vaccination, has grown significantly since the eradication of the disease in 1980. As the smallpox and monkeypox viruses both belong to the Orthopoxvirus genus, smallpox vaccination is around 85% effective at preventing monkeypox, so a decrease in smallpox immunity will result in a decrease in monkeypox immunity.
Lead author of the study, Najmul Haider (Royal Veterinary College) commented: “More than 50 years have passed since the first case of Monkeypox was recorded but very little research has been undertaken on this neglected tropical pathogen. The epidemic of Monkeypox reminds us of the importance of tackling diseases at their source of origin, through a coordinated One Health approach, or risk the disease spreading and evolving further, with significant consequences.”
