30
sugars and terpines replace water by inert dehydration (Poinar and Hess 1985).
During these processes, arthropod tissues are often partially cleared, thus revealing
associated microorganisms.
The oldest amber with abundant identifiable insects is 120–130 million year old
Lebanese amber (Poinar and Milki 2001). The oldest evidence of vertebrate pathogens occurs in 100 million year-old Myanmar amber. In this amber is evidence of
cytoplasmic and nuclear polyhedrosis viruses as well as pathogenic spirochetes,
rickettsia, actinomycetes and protozoa in bloodsucking arthropods and indirect evidence of polydnaviruses. In Cenozoic amber are examples of virus-like tumors and
a range of pathogenic bacteria. In both Myanmar and Dominican amber is evidence
of symbiotic and parasitic protozoa, often inside their arthropod vectors. Based on
these findings, it is clear that invertebrate and vertebrate viruses as well as a range
of pathogenic bacteria and protozoa were well established by the mid-Cretaceous.
By the mid-Cenozoic, these infective agents had spread to various host groups,
many of which remain infected today. Ages of the various amber deposits with
samples discussed below are 15–45 million years ago for Dominican (IturraldeVinent and MacPhee 1996; Cepek in Schlee 1990); 22.5–26 million years ago for
Mexican (Berggren and van Couvering 1974); 45–55 million years ago for Baltic
(Wolfe et al. 2016); 76.5–79.5 million years ago for Canadian (Eberth and Hamblin
1993) and 97–110 million years ago for Myanmar (Burmese) (Cruickhank and Ko
2003; Shi et al. 2012).
2.2 Virus Fossils
Viruses are quite ancient and based on molecular studies, may date back to the
origin of life on earth (Foreteer 2006). And since virus particles are so small, fossil
evidence of them is quite rare. Presently, most studies on viral evolution are based
on “molecular fossils” that explores endogenous retroviruses (EVRs) that have
become established in their host’s genome. If these viruses were the result of a single infection event, then phylogenetic screening of related hosts can be used to
predict when such infections occurred, thus providing putative dates when the virus
was incorporated into the host genome. Using these genomic methods, retrovirus
infections have been traced back millions of years (Katzouakis 2014; Lee et al.
2013; Suh 2021).
Other branches of paleovirology involve searching for ancient remains that show
physical signs or symptoms of ancient viruses such as in amber fossils. In the present work, fossil evidence of viruses is discussed under “direct evidence” and “indirect evidence.” Direct evidence is when polyhedra (inclusion bodies) or virions are
recovered in well-preserved fossils. Historic evidence of viruses in humans is usually based on genetic evidence in Pleistocene samples. If the specimens are well
preserved, then the viruses can be identified from their remains by genomic techniques, which is how most ancient viruses infecting humans have been found
(Duggan et al. 2016), thus providing information on widespread epidemics that
occurred during historic times, such as discovering evidence of smallpox in Africa
at 3700 bc (Schatmayr 2014).
G. Poinar
sugars and terpines replace water by inert dehydration (Poinar and Hess 1985).
During these processes, arthropod tissues are often partially cleared, thus revealing
associated microorganisms.
The oldest amber with abundant identifiable insects is 120–130 million year old
Lebanese amber (Poinar and Milki 2001). The oldest evidence of vertebrate pathogens occurs in 100 million year-old Myanmar amber. In this amber is evidence of
cytoplasmic and nuclear polyhedrosis viruses as well as pathogenic spirochetes,
rickettsia, actinomycetes and protozoa in bloodsucking arthropods and indirect evidence of polydnaviruses. In Cenozoic amber are examples of virus-like tumors and
a range of pathogenic bacteria. In both Myanmar and Dominican amber is evidence
of symbiotic and parasitic protozoa, often inside their arthropod vectors. Based on
these findings, it is clear that invertebrate and vertebrate viruses as well as a range
of pathogenic bacteria and protozoa were well established by the mid-Cretaceous.
By the mid-Cenozoic, these infective agents had spread to various host groups,
many of which remain infected today. Ages of the various amber deposits with
samples discussed below are 15–45 million years ago for Dominican (IturraldeVinent and MacPhee 1996; Cepek in Schlee 1990); 22.5–26 million years ago for
Mexican (Berggren and van Couvering 1974); 45–55 million years ago for Baltic
(Wolfe et al. 2016); 76.5–79.5 million years ago for Canadian (Eberth and Hamblin
1993) and 97–110 million years ago for Myanmar (Burmese) (Cruickhank and Ko
2003; Shi et al. 2012).
2.2 Virus Fossils
Viruses are quite ancient and based on molecular studies, may date back to the
origin of life on earth (Foreteer 2006). And since virus particles are so small, fossil
evidence of them is quite rare. Presently, most studies on viral evolution are based
on “molecular fossils” that explores endogenous retroviruses (EVRs) that have
become established in their host’s genome. If these viruses were the result of a single infection event, then phylogenetic screening of related hosts can be used to
predict when such infections occurred, thus providing putative dates when the virus
was incorporated into the host genome. Using these genomic methods, retrovirus
infections have been traced back millions of years (Katzouakis 2014; Lee et al.
2013; Suh 2021).
Other branches of paleovirology involve searching for ancient remains that show
physical signs or symptoms of ancient viruses such as in amber fossils. In the present work, fossil evidence of viruses is discussed under “direct evidence” and “indirect evidence.” Direct evidence is when polyhedra (inclusion bodies) or virions are
recovered in well-preserved fossils. Historic evidence of viruses in humans is usually based on genetic evidence in Pleistocene samples. If the specimens are well
preserved, then the viruses can be identified from their remains by genomic techniques, which is how most ancient viruses infecting humans have been found
(Duggan et al. 2016), thus providing information on widespread epidemics that
occurred during historic times, such as discovering evidence of smallpox in Africa
at 3700 bc (Schatmayr 2014).
G. Poinar