|A new test can detect virtually any virus that infects people |
and animals, including the Ebola virus (blue). (Credit:
National Institute of Allergy and Infectious Diseases)
Many thousands of viruses are known to cause illness in people and animals, and making a diagnosis can be an exhaustive exercise, at times requiring a battery of different tests. That's because current tests aren't sensitive enough to detect low levels of viral bugs or are limited to detecting only those viruses suspected of being responsible for a patient's illness.
"With this test, you don't have to know what you're looking for," the researchers said. "It casts a broad net and can efficiently detect viruses that are present at very low levels. We think the test will be especially useful in situations where a diagnosis remains elusive after standard testing or in situations in which the cause of a disease outbreak is unknown."
The research, published in the journal Genome Research, demonstrate that the new test - called ViroCap - can detect viruses not found by standard testing based on genome sequencing. The test could be used to detect outbreaks of deadly viruses such as Ebola, Marburg and severe acute respiratory syndrome (SARS), as well as more routine viruses, including rotavirus and norovirus, both of which cause severe gastrointestinal infections.
The test sequences and detects viruses in patient samples and is just as sensitive as the gold-standard polymerase chain reaction (PCR) assays, which are used widely in clinical laboratories. However, even the most expansive PCR assays can only screen for up to about 20 similar viruses at the same time.
The researchers evaluated the new test in two sets of biological samples. In the first, standard testing that relied on genome sequencing had detected viruses in 10 of 14 patients. But the new test found viruses in the four children that earlier testing had missed. Standard testing failed to detect common, everyday viruses: influenza B, a cause of seasonal flu; parechovirus, a mild gastrointestinal and respiratory virus; herpes virus 1, responsible for cold sores in the mouth; and varicella-zoster virus, which causes chickenpox.
In a second group of children with unexplained fevers, standard testing had detected 11 viruses in the eight children evaluated. But the new test found another seven, including a respiratory virus called human adenovirus B type 3A, which usually is harmless but can cause severe infections in some patients.
In all, the number of viruses detected in the two patient groups jumped to 32 from 21, a 52 percent increase.
"The test is so sensitive that it also detects variant strains of viruses that are closely related genetically," the researchers said. "Slight genetic variations among viruses often can't be distinguished by currently available tests and complicate physicians' ability to detect all variants with one test."
In addition, because the test includes detailed genetic information about various strains of particular viruses, subtypes can be identified easily. For example, the study showed that while standard testing identified a virus as influenza A, which causes seasonal flu, the new test indicated that the virus was a particularly harsh subtype called H3N2.
To develop the test, the researchers targeted unique stretches of DNA or RNA from every known group of viruses that infects humans and animals. In all, the research team included 2 million unique stretches of genetic material from viruses in the test. These stretches of material are used as probes to pluck out viruses in patient samples that are a genetic match. The matched viral material then is analyzed using high-throughput genetic sequencing. As completely novel viruses are discovered, their genetic material could easily be added to the test.
The researchers plan to conduct additional research to validate the accuracy of the test, so it could be several years before it is clinically available.
"It also may be possible to modify the test so that it could be used to detect pathogens other than viruses, including bacteria, fungi and other microbes, as well as genes that would indicate the pathogen is resistant to treatment with antibiotics or other drugs," the researchers said.
In the meantime, the technology can be used by scientists to study viruses in a research setting.
Based on material originally posted by Washington University School of Medicine.