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How Old Is HIV? University of Oxford Researchers Say Hundreds of Millions of Years

JAN 13, 2017 | SARAH ANWAR
University of Oxford researchers’ findings, published in Nature Communications, indicate that viruses from the Retroviridae family, which includes HIV and the human T-cell lymphotropic virus, date back to the Paleozoic Era.
Back in the 1980s in the United States, a new, sexually transmitted retrovirus was found to be the culprit behind a nationwide epidemic: HIV. In addition to the prognosis of infection, the social stigma regarding the lifestyle of many who were diagnosed with HIV caused panic and increased fear of diagnosis. Today, one in eight individuals living with the disease are unaware of their condition. The total estimated prevalence of HIV cases is believed to be 1.2 million in the United States, and 36.7 million worldwide.
HIV is a lentivirus of the Retroviridae family, and scientists have been skeptical as to its origin. According to the Oxford study authors, retroviruses can infect both animals and humans and infections caused by these viruses may even be transferred between species. In addition, these infections can leave behind a viral footprint, known as “genomic fossils.”
To assess the age of retroviruses, the researchers decided to analyze another type of virus whose evolution is more well-known, the foamy virus (FV). These viruses “are characterized by an extremely stable history of co-speciation with their mammalian hosts, at least since the origin of eutherians,” approximately 100 million years ago, and their evolution is, therefore, “described in unprecedented detail.” As such, the researchers gleaned information on 36 foamy-like endogenous retroviruses (FLERVs), identified from the genomes of salamanders, a frog, lobe-finned fish, a shark, and ray-finned fish.
Using this information, the researchers developed a model to measure the time-dependency of the evolution of mammalian FV. The model investigated how the total per-lineage substitutions compared to the evolutionary timescales by backtracking the simian FV’s lineage.
The researchers concluded, “By assuming that viruses infecting modern-day mammals and their ancient vertebrate ancestors share the same [time-dependent rate phenomenon] dynamics, and based on posterior distribution of the Bayesian Pol phylogeny, the glace of mammalian FVs and lobe-finned fish FLERVs was estimated to be ~ 263 (95% HPD = 195–342) [million years old],” while “the age of the entire clade of FVs/FLERVs was estimated to be ~ 455 (95% HPD = 304 – 684)” million years old. Earlier speculations had estimated retroviruses such as HIV to have evolved much more recently than this.
A letter published in Molecular Biology and Evolution discussed a similar study conducted by researchers from the Czech Academy of Science. In this study, researchers analyzed lentivirus genes from exotic Malayan flying lemurs, and estimated that lentivirus “emergence may date as early as 60 [million years ago]." Now, the University of Oxford researchers estimate that these viruses may be hundreds of millions of years old.
Perhaps with a greater understanding of the possible origins of harmful retroviruses, such as HIV, researchers can better design a method to cure infections caused by these viruses. 
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