Herpes Viruses Originated From Africa, The Continent Where Most Infectious Diseases Are ‘Born’
Source: Thailand Medical News Jan 13, 2020 4 years, 11 months, 1 week, 3 days, 9 hours, 7 minutes ago
A new research conducted by an Italian research team from the IRCCS Medea in collaboration with the University of Milan have shown that the origins of two extremely common pathogens in human populations today,
herpes simplex virus type 1 and type 2 are from
Africa. The study findings have just been published in the advanced online edition of Molecular Biology and Evolution.
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As most individuals may have experienced, literally on the skin, the common
herpes simplex virus type 1 is a primary cause of orofacial lesions. The less prevalent form,
herpes simplex virus type 2, is usually responsible for genital herpes. Both viruses can also cause very serious diseases, including non-epidemic encephalitis and neonatal
herpes infection. In the latter case, the virus is generally transmitted by the mother during delivery and the consequences can be extremely serious for the infant.
In order to understand the origins of the virus, the research team has shown that the evolutionary history of these two viruses is different and more complex than previously thought.
Lead researcher Dr Diego Forni explained to
Thailand Medical News, "We analyzed the diversity of the two viruses in relation to their geographical origin and what we noticed are that viruses deriving from distinct continents were not particularly different, an observation that is not consistent with the hypothesis of an ancient migration. Our data, however, clearly indicated that the two viruses originated in
Africa. We therefore thought it was necessary to estimate when the viral strains circulating today among human populations left the
African continent."
Similar to other other viruses belonging to the
Herpesviridae family (e.g., viruses that cause chickenpox and mononucleosis),
herpes simplex viruses type 1 and 2 are very similar to viruses that infect
African great apes. In many cases these viruses have evolved together with their hosts and have infected our species since it originated in Africa. To date,
Africa remains the continent where
herpes simplex viruses type 1 and 2 are most prevalent. This gave rise to the hypothesis that the viral strains that infect us today left
Africa in very ancient times. It was thought this coincided during the major "Out of
Africa" migratory event that, around 60,000 years ago, led humans to populate all other continents.
Dr Manuela Sironi, coauthor of the study added, "Recently, thanks to the study of viruses found in archaeological remains, the scientific community has a better knowledge of the speed at which viral species evolve. Thus, we can use rather precise methods that allow the dating of viral origin and dispersal. By applying these methods, we estimated that the circulating strains of
herpes simplex virus type 1 migrated from
Africa about 5000 years ago. The exit from
Africa of
herpes simplex virus type 2 was even more recent and probably occ
urred in the eighteenth century."
The
herpes simplex virus type 2 result draws a link between epidemiological data and a major historical event ie the height of the transatlantic slave trade. In this century, millions of people were deported from
Africa to the Americas. Most likely, this heinous forced human migration also led to the initial spread of
herpes simplex virus type 2 in the Americas. In fact, the prevalence of the virus is higher in this continent than elsewhere and it is second only to
Africa.
The
herpes simplex virus type 2 is probably not the only pathogen to have been introduced to the American continent as a result of the slave trade. Previous studies have shown that the same happened for yellow fever virus and for a parasitic worm (Schsitosoma mansoni). For ecological reasons these pathogens remained confined to tropical or subtropical areas.
Herpes simplex virus type 2, instead, found no barriers to today's planetary spread.
Reference: Recent out-of-Africa migration of human herpes simplex viruses
Diego Forni, Chiara Pontremoli, Mario Clerici, Uberto Pozzoli, Rachele Cagliani, Manuela Sironi, Molecular Biology and Evolution, msaa001, https://doi.org/10.1093/molbev/msaa001
