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The origin of the variola virus.

Babkin IV, Babkina IN - Viruses (2015)

Bottom Line: Comparisons of the VARV genome to the genomes of the most closely related orthopoxviruses and the examination of the distribution their natural hosts' ranges suggest that VARV emerged 3000 to 4000 years ago in the east of the African continent.The VARV evolution rate has been estimated to be approximately 2 × 10-6 substitutions/site/year for the central conserved genomic region and 4 × 10-6 substitutions/site/year for the synonymous substitutions in the genome.Presumably, the introduction of camels to Africa and the concurrent changes to the climate were the particular factors that triggered the divergent evolution of a cowpox-like ancestral virus and thereby led to the emergence of VARV.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Molecular Microbiology, Institute of Chemical Biology and Fundamental Medicine, Novosibirsk 630090, Russia. i_babkin@mail.ru.

ABSTRACT
The question of the origin of smallpox, one of the major menaces to humankind, is a constant concern for the scientific community. Smallpox is caused by the agent referred to as the variola virus (VARV), which belongs to the genus Orthopoxvirus. In the last century, smallpox was declared eradicated from the human community; however, the mechanisms responsible for the emergence of new dangerous pathogens have yet to be unraveled. Evolutionary analyses of the molecular biological genomic data of various orthopoxviruses, involving a wide range of epidemiological and historical information about smallpox, have made it possible to date the emergence of VARV. Comparisons of the VARV genome to the genomes of the most closely related orthopoxviruses and the examination of the distribution their natural hosts' ranges suggest that VARV emerged 3000 to 4000 years ago in the east of the African continent. The VARV evolution rate has been estimated to be approximately 2 × 10-6 substitutions/site/year for the central conserved genomic region and 4 × 10-6 substitutions/site/year for the synonymous substitutions in the genome. Presumably, the introduction of camels to Africa and the concurrent changes to the climate were the particular factors that triggered the divergent evolution of a cowpox-like ancestral virus and thereby led to the emergence of VARV.

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World map. The Black circle denotes the putative region of the origin of the camelid (Camelidae) ancestors approximately 45 MYA [60]. The direction of their migration is shown with arrows: 1, migration of the camel ancestors from North America to Asia 2–3 MYA [61]; and 2, introduction of domesticated camels into East Africa approximately 4 TYA [55,56]; hatched oval: the distribution area of naked sole gerbils [53,54]. Legend and figure reproduced from [30].
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viruses-07-01100-f003: World map. The Black circle denotes the putative region of the origin of the camelid (Camelidae) ancestors approximately 45 MYA [60]. The direction of their migration is shown with arrows: 1, migration of the camel ancestors from North America to Asia 2–3 MYA [61]; and 2, introduction of domesticated camels into East Africa approximately 4 TYA [55,56]; hatched oval: the distribution area of naked sole gerbils [53,54]. Legend and figure reproduced from [30].

Mentions: In 2012, Babkin and Babkina [30] proposed a hypothesis about the geographic region of VARV emergence that is based on the assumption that CMLV, TATV, and VARV originated at the same time and in the same geographic area. Indeed, as mentioned above, these three viruses originated from a common ancestral virus. Most probably, this virus was a CPXV-like virus that was able to infect rodents and other mammals. These authors studied the geographic ranges of the hosts of CMLV, TATV, and VARV. It is known that the naked sole gerbil is the only host of TATV [47], this rodent species is distributed from West Africa to Ethiopia, and its distribution range is confined by tropical forests in the south and the Sahara Desert in the north (Figure 3) [53,54]. Domesticated camels were imported for the first time to Africa, specifically, the Horn of Africa, 3500–4500 years ago, further advanced to Egypt in the 6th–7th century BC, and subsequently spread to other regions of the African continent [55,56]. There is evidence that large settlements existed approximately 4000 years ago in the Horn of Africa [57]. This geographic region might be the zone in which the distributions of the CMLV, TATV, and VARV hosts overlapped (Figure 3). Consequently, the putative area in which these three orthopoxvirus species emerged from a common progenitor might be the Horn of Africa. This hypothesis supports the dating of VARV emergence because the camel and naked sole gerbil did not meet in the same area before 4000 years ago. Babkin and Babkina [30] assumed that the evolution of a CPXV-like ancestral virus and its further separation into three highly specialized species were triggered by the introduction of the camel, a new potential host with unique antibodies [58,59], and the need for the virus to adjust to changing conditions.


The origin of the variola virus.

Babkin IV, Babkina IN - Viruses (2015)

World map. The Black circle denotes the putative region of the origin of the camelid (Camelidae) ancestors approximately 45 MYA [60]. The direction of their migration is shown with arrows: 1, migration of the camel ancestors from North America to Asia 2–3 MYA [61]; and 2, introduction of domesticated camels into East Africa approximately 4 TYA [55,56]; hatched oval: the distribution area of naked sole gerbils [53,54]. Legend and figure reproduced from [30].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4379562&req=5

viruses-07-01100-f003: World map. The Black circle denotes the putative region of the origin of the camelid (Camelidae) ancestors approximately 45 MYA [60]. The direction of their migration is shown with arrows: 1, migration of the camel ancestors from North America to Asia 2–3 MYA [61]; and 2, introduction of domesticated camels into East Africa approximately 4 TYA [55,56]; hatched oval: the distribution area of naked sole gerbils [53,54]. Legend and figure reproduced from [30].
Mentions: In 2012, Babkin and Babkina [30] proposed a hypothesis about the geographic region of VARV emergence that is based on the assumption that CMLV, TATV, and VARV originated at the same time and in the same geographic area. Indeed, as mentioned above, these three viruses originated from a common ancestral virus. Most probably, this virus was a CPXV-like virus that was able to infect rodents and other mammals. These authors studied the geographic ranges of the hosts of CMLV, TATV, and VARV. It is known that the naked sole gerbil is the only host of TATV [47], this rodent species is distributed from West Africa to Ethiopia, and its distribution range is confined by tropical forests in the south and the Sahara Desert in the north (Figure 3) [53,54]. Domesticated camels were imported for the first time to Africa, specifically, the Horn of Africa, 3500–4500 years ago, further advanced to Egypt in the 6th–7th century BC, and subsequently spread to other regions of the African continent [55,56]. There is evidence that large settlements existed approximately 4000 years ago in the Horn of Africa [57]. This geographic region might be the zone in which the distributions of the CMLV, TATV, and VARV hosts overlapped (Figure 3). Consequently, the putative area in which these three orthopoxvirus species emerged from a common progenitor might be the Horn of Africa. This hypothesis supports the dating of VARV emergence because the camel and naked sole gerbil did not meet in the same area before 4000 years ago. Babkin and Babkina [30] assumed that the evolution of a CPXV-like ancestral virus and its further separation into three highly specialized species were triggered by the introduction of the camel, a new potential host with unique antibodies [58,59], and the need for the virus to adjust to changing conditions.

Bottom Line: Comparisons of the VARV genome to the genomes of the most closely related orthopoxviruses and the examination of the distribution their natural hosts' ranges suggest that VARV emerged 3000 to 4000 years ago in the east of the African continent.The VARV evolution rate has been estimated to be approximately 2 × 10-6 substitutions/site/year for the central conserved genomic region and 4 × 10-6 substitutions/site/year for the synonymous substitutions in the genome.Presumably, the introduction of camels to Africa and the concurrent changes to the climate were the particular factors that triggered the divergent evolution of a cowpox-like ancestral virus and thereby led to the emergence of VARV.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Molecular Microbiology, Institute of Chemical Biology and Fundamental Medicine, Novosibirsk 630090, Russia. i_babkin@mail.ru.

ABSTRACT
The question of the origin of smallpox, one of the major menaces to humankind, is a constant concern for the scientific community. Smallpox is caused by the agent referred to as the variola virus (VARV), which belongs to the genus Orthopoxvirus. In the last century, smallpox was declared eradicated from the human community; however, the mechanisms responsible for the emergence of new dangerous pathogens have yet to be unraveled. Evolutionary analyses of the molecular biological genomic data of various orthopoxviruses, involving a wide range of epidemiological and historical information about smallpox, have made it possible to date the emergence of VARV. Comparisons of the VARV genome to the genomes of the most closely related orthopoxviruses and the examination of the distribution their natural hosts' ranges suggest that VARV emerged 3000 to 4000 years ago in the east of the African continent. The VARV evolution rate has been estimated to be approximately 2 × 10-6 substitutions/site/year for the central conserved genomic region and 4 × 10-6 substitutions/site/year for the synonymous substitutions in the genome. Presumably, the introduction of camels to Africa and the concurrent changes to the climate were the particular factors that triggered the divergent evolution of a cowpox-like ancestral virus and thereby led to the emergence of VARV.

Show MeSH
Related in: MedlinePlus