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Thousands of unknown viruses found

11th October 2011

Raw sewage contains thousands of completely unclassified viral specimens, according to a recent joint US-Spanish study.

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The researchers noted that raw sewage was the most diverse collection of viruses ever studied, and that only about 3,000 distinct viruses had ever been identified.

Michael Imperiale of the University of Michigan, said he believed the study on sewage was just the the tip of the iceberg.

He said that, however, in terms of sheer number of viruses, he believed that the ocean would probably contain more viruses by at least a few orders of magnitude.

For the study, the researchers first sampled raw sewage from North America, Europe and Africa.

Using electron microscopes, which can create images of things that are too small for regular microscopes, the researchers were able to confirm the presence of a lot of different viruses inside the samples.

The researchers then purified and concentrated the viruses they found in the waste, resequencing the genome-pieces of all the viruses they found, in order to ensure that DNA and RNA viruses were both represented equally.

As a result, the researchers were able to get 897,647 high-quality base-pair sequences.

The researchers then used a computer programme known as the Basic Local Alignment Search Tool (BLAST) to compare base-pair sequences to known viral specimens.

Using the same method, the researchers were also able to make guesses about the types of viruses they were studying.

About 8,500 of the sequences were related to eukaryotic organisms, which includes human beings, animals, insects, and other moving things.

About 38,000 of the sequences were related to bacteriophages, viruses that infect bacteria.

In terms of known viruses, the researchers found 234 specimens belonging to 26 different families, including human papillomavirus (HPV) and norovirus.

A large number of the known viruses came from plants, which humans evidently ingest when they eat fruits and vegetables.

Imperiale said that some of the unclassified viruses may even be helpful.

He said there was a theory that humans routinely came into contact with viruses that did not cause disease or noticeable symptoms, and that in such a case such viruses may actually benefit people.

 

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