Wild hosts of the virus contaminate neighboring human populations…
As surprising as it may seem, we do not yet know very well what the natural hosts of mpox are. Its original name, monkey-pox (“monkey pox”), could suggest monkeys. Except that it comes only from the fact that it is from these animals that this virus was, for the first time, taken and described in 1958! However, these monkeys had themselves been infected via other species. The latest data tends to show that the natural hosts of mpox are squirrels and other arboreal rodents in the Central African tropical forests. However, formal proof is still lacking: no study has been able to observe the transmission of the same viral strain from an animal to a human.
Protected by the smallpox vaccine
In the 1990s, humans appeared to be an accidental host of the virus. Contamination, of course, is possible via the animal reservoir, but no cases of human-to-human transmission have been reported. At that time, the vast majority of our peers were protected from mpox because, until the 1970s, all newborns were vaccinated against smallpox. Knowing that the two viruses are part of the same family and share 90% of their genome, there is so-called cross immunity: the smallpox vaccine also protects against mpox.
In 1980, smallpox was officially declared eradicated, effectively ending vaccination programs. All people born after 1980 have therefore become sensitive hosts. “The cessation of these vaccination campaigns represents a major factor in the dynamics of mpox epidemics”believes Romulus Breban, who carried out modeling work in 2020 perfectly demonstrating how mpox would pose a growing threat to public health as our immunity against smallpox disappeared.
Thus, we eliminated one disease, smallpox, but others appeared in its wake – fortunately less dangerous. But the end of vaccination is not the only flaw in human defenses: the AIDS epidemic, which considerably weakens the immune system, remains very present in central and western Africa. The virus can therefore penetrate these organisms all the more easily and persist there for a longer period, facilitating transmission but also the occurrence of its mutations. According to studies, between 30 and 50% of cases present co-infection with HIV.
Population movements
Finally, the human host is not just an immune system on two legs: it is a social individual, immersed in an environment of specific interactions. However, here again, the terrain seems favorable to the virus. In Nigeria, for example, the epidemic is growing in the south, where the oil and gas industries are located. There, the men “ have money to spend, which attracts sex workers ”, explains Bolaji OtikeOdibi, Nigerian doctor, in an interview with the magazine Science. These men then return home and help spread the virus widely. In the DRC, “The clade 1b epidemic developed around a mining area experiencing a lot of population movements and political instability. This gives the virus more of a chance to spread.” also underlines Martine Peeters, from the IRD.
The encounter between a more transmissible strain and dense human populations, on the move and having lost any form of immunity against mpox, therefore appears to be a winning combo for the virus. The path towards large-scale diffusion appears inevitable if nothing is done to block the chains of transmission.
SOURCES: ACCORDING TO WHO; ECDC; N. PRECIOUS ET AL. ; ANN. MED. SURG. 2023
