Coinfection with AAV2 and a human adenovirus (HAdV), in particular, appears to leave some children more vulnerable to this acute hepatitis of unknown origin, researchers reported in three studies published online in Nature. Coinfection with Epstein-Barr virus (EBV), herpes, and enterovirus also were found. Adeno-associated viruses are not considered pathogenic on their own and require a “helper” virus for productive infection.
“I am quite confident that we have identified the key viruses involved because we used a comprehensive metagenomic sequencing approach to look for potential infections from any virus or non-viral pathogen,” Charles Chiu, MD, PhD, senior author and professor of laboratory medicine and medicine/infectious diseases at the University of California, San Francisco, said in an interview.
Dr. Chiu and colleagues propose that lockdowns and social isolation during the COVID-19 pandemic left more children susceptible. A major aspect of immunity in childhood is the adaptive immune response – both cell-mediated and humoral – shaped in part by exposure to viruses and other pathogens early in life, Dr. Chiu said.
“Due to COVID-19, a large population of children did not experience this, so it is possible once restrictions were lifted, they were suddenly exposed over a short period of time to multiple viruses that, in a poorly trained immune system, would have increased their risk of developing severe disease,” he said.
This theory has been popular, especially because cases of unexplained acute hepatitis peaked during the height of the COVID-19 pandemic when isolation was common, William F. Balistreri, MD, who was not affiliated with the study, told this news organization. Dr. Balistreri is professor of pediatrics and director emeritus of the Pediatric Liver Care Center at Cincinnati Children’s Hospital Medical Center.
Identifying the culprits
Determining what factors might be involved was the main aim of the etiology study by Dr. Chiu and colleagues published online in Nature.
The journal simultaneously published a genomic study confirming the presence of AAV2 and other suspected viruses and a genomic and laboratory study further corroborating the results.
More than 1,000 children worldwide had been diagnosed with unexplained acute pediatric hepatitis as of August 2022. In the United States, there have been 358 cases, including 22 in which the child required a liver transplant and 13 in which the child died.
This new form of hepatitis, first detected in October 2021, does not fit into existing classifications of types A through E, so some researchers refer to the condition as acute non–A-E hepatitis of unknown etiology.
The investigators started with an important clue based on previous research: the role adenovirus might play. Dr. Chiu and colleagues assessed 27 blood, stool, and other samples from 16 affected children who each previously tested positive for adenoviruses. The researchers included cases of the condition identified up until May 22, 2022. The median age was 3 years, and approximately half were boys.
They compared viruses present in these children with those in 113 controls without the mysterious hepatitis. The control group consisted of 15 children who were hospitalized with a nonhepatitis inflammatory condition, 27 with a noninflammatory condition, 30 with acute hepatitis of known origin, 12 with acute gastroenteritis and an HAdV-positive stool sample, and 11 with acute gastroenteritis and an HAdV-negative stool sample, as well as 18 blood donors. The median age was 7 years.
The researchers assessed samples using multiple technologies, including metagenomic sequencing, tiling multiplex polymerase chain reaction (PCR) amplicon sequencing, metagenomic sequencing with probe capture viral enrichment, and virus-specific PCR. Many of these advanced techniques were not even available 5-10 years ago, Dr. Chiu said.