Читать книгу Principles of Virology, Volume 2 - Jane Flint, S. Jane Flint - Страница 85

If you have ever received a blood transfusion, along with the red blood cells, leukocytes, plasma, and other components, you also were likely infused with a collection of viruses. A recent study of the blood virome of more than 8,000 healthy individuals revealed a total of 19 different DNA viruses in 42% of the subjects.

Viral DNA sequences were identified among the genome sequences of 8,240 individuals that were determined from blood. Of the 1 petabyte (1 million gigabytes) of sequence data that were generated, ∼5% did not correspond to human DNA. Within this fraction, sequences of 94 different viruses were identified. Nineteen of these were human viruses. The method is not expected to reveal RNA viruses except retroviruses that are integrated as DNA copies in the host chromosomes.

The most common human viruses identified were herpesviruses, including cytomegalo virus, EpsteinBarr virus, herpes simplex virus, and human herpes viruses 7 and 8, found in 14 to 20% of individuals. Anelloviruses, small viruses with a circular genome, were found in 9% of the samples. Other viruses found in less than 1% of the samples included papillomaviruses, parvoviruses, polyomavirus, adenovirus, human immunodeficiency virus type 1, and human Tcell lymphotropic virus (the latter two integrated into host DNA).

The other 75 viruses are likely contaminants from laboratory reagents or the environment. These include sequences from nonhuman retroviruses, four different giant DNA viruses, and a virus of bees, all found in fewer than 10 samples. These findings illustrate the challenge in distinguishing bona fide human viruses from contaminants.

Identifying viruses in blood is an important objective for ensuring the safety of the blood supply. Donor blood is currently screened for human immunodeficiency virus types 1 and 2, human T-cell lymphotropic virus-1 and -2, hepatitis C virus, hepatitis B virus, West Nile virus, and Zika virus. These viruses are pathogenic for humans and can be transmitted via the blood. Some viruses, such as anelloviruses and pegiviruses, are in most donated blood, yet their pathogenic potential is unknown. It is not feasible to reject donor blood that contains any type of viral nucleic acid—if we did, we would not have a blood supply.

Continuing studies of the blood virome are needed to define which viruses should be tested for in donated blood. The human papillomavirus (17 people), Merkel cell polyomavirus (49 people), human herpesvirus type 8 (3 people), and adenovirus (9 people) detected in this study could be transmitted in the blood, and their presence should be monitored in future studies.

It is important to emphasize that this work describes only viral DNA sequences, and not infectious virus particles. The blood supply is screened by nucleic acid tests, but it is crucial to determine if infectious virus particles are also present . If viral DNA is present in blood but particles are never found, then it might not be necessary to reject blood based on the presence of certain sequences.

 Moustafa A, Xie C, Kirkness E, Biggs W, Wong E, Turpaz Y, Bloom K, Delwart E, Nelson KE, Venter JC, Telenti A. 2017. The blood DNA virome in 8,000 humans. PLoS Pathog 13:e1006292.