A key question for norovirus researchers is determining when a dominant variant, called genotype II.4 (or GII.4), first emerged, notes Dr. Green. "This genotype has been associated with the majority of global outbreaks of acute norovirus gastroenteritis since the mid-1990s," says Dr. Green. "The GII.4 genotype was first described around 1987, but no one knew for sure whether that genotype emerged then or if it existed earlier."
To answer the question, Dr. Bok customized a new techniquereal-time reverse transcriptase-polymerase chain reaction (RT-PCR)and applied it to stool samples originally collected from infants and young children hospitalized at the Children's National Medical Center in Washington, D.C., between 1974 and 1991. Samples were taken from infants and children with gastroenteritis and from others (controls) who did not have gastroenteritis. Essentially, Dr. Bok crafted genetic hooks capable of fishing out matching genetic sequences of any norovirus present in the samples. Fifty out of 5,424 samples tested contained norovirus. The most commonly seen genotype was GII.3 (48 percent), but the second most common genotype was GII.4 (16 percent). Some GII.4-containing specimens dated back to 1974, allowing the researchers to conclude that this now-dominant genotype had been circulating for years before its more recent identification as the cause of severe global outbreaks of norovirus disease.
Next, using a strategy developed by NIAID scientist Stanislav Sosnovtsev, Ph.D., the researchers determined the complete genetic sequences of five older GII.4 viruses and compared th
|Contact: Anne A. Oplinger|
NIH/National Institute of Allergy and Infectious Diseases