Monkeypox: An emerging menace!
Here’s something I wasn’t worried about before today: apparently there have been outbreaks of monkeypox over the past decade, and they are potentially spreading in number and range. This is via a review article in the February issue of Trends in Microbiology (note you must be on campus to download this link). So far outbreaks have been relatively limited to the Democratic Republic of the Congo (DRC), however epidemiologists are examining whether cessation of smallpox vaccination in the 1970’s, and current loss of protection to smallpox in populations might be leading the emergence of monkeypox infections in humans.
This discussion rekindles the ongoing debate as to whether stocks of variola (smallpox) virus should be destroyed. Arguments can be put forward supporting either stance; many view the potential risk of bioterrorism outweighing any possible medical benefit, whereas I argued in the above linked essay that we cannot predict future research needs that might be facilitated by having variola virus in the laboratory. This position seems to be borne out if the link between monkeypox and smallpox is valid.
The epidemiology of infection by smallpox and monkeypox are not the same. Although both viruses are related members of the orthovirus family, smallpox is exclusively a pathogen of Homo sapiens, a fact that greatly facilitated the eradication effort during the mid-20th century. Viable smallpox virus is no longer found anywhere in the wild, and currently exists only in freezers in the United States and Russia. Monkeypox on the other hand is a zoonotic disease, mainly found in non-human primate populations, and in the past has only very occasionally jumped the species barrier to infect humans. Unlike smallpox, monkeypox historically has had a very low mortality rate, and traditionally has not posed a significant health risk.
Current epidemiologic analysis suggests that the rate of infection has jumped approximately 10-fold in regions where the disease has been considered endemic. Furthermore, the highest rates of infection are found in individuals younger than 15 years of age, with increasing trends in the 15 to 30 year old cohort, all groups that were never vaccinated against smallpox or were too young to have ever had smallpox. This phenomenon argues for the possibility that smallpox offered protection against other orthovirus infections, which are now emergent in populations that have no protection against smallpox.
An interesting conundrum comes out from this scenario however; monkeypox has a broader distribution than just the Congo Basin, and increasing infection rates appear to be limited to that specific geographic region at present. Research into the pathogenesis of specific virus isolates, and mechanisms as to how the virus modulates the immune system may shed light into these geographical differences, and on the infection process of orthovirus infection and recovery. The review article concludes with the consideration that not only environmental and social concerns (climate change, human habitat modification, sociologic factors), but also the expansion of potential ecological niches in human hosts via changes in vaccination programs is altering host-pathogen balances, and may lead to further outbreaks of other infections.