Likely Cause of Mysterious Hepatitis Outbreak Identified

Investigators found that simultaneous infection with adeno-associated virus type 2 (AAV2) and certain other viruses is associated with the outbreak of mysterious pediatric hepatitis cases worldwide.

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 report in three studies published online in Nature. Co-infection 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 School of Medicine, told Medscape Medical News.

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, 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 Balistreri, MD, who was not affiliated with the study, told Medscape Medical News. Balistreri is a professor of pediatrics and director emeritus of the Pediatric Liver Care Center at Cincinnati Children’s Hospital Medical Center in Ohio.

Identifying the Culprits

Determining what factors might be involved was the main aim of the etiology study by Chiu and colleagues published online March 30 in Nature.

The journal also 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 1000 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. 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.

They 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, Chiu said.

Key Findings

Blood samples were available for 14 of the 16 children with acute hepatitis of unknown origin. Among this study group, AAV2 was found in 13 (93%). No other adeno-associated viruses were found. HAdV was detected in all 14 children: HAdV-41 in 11 children and HAdV-40, HAdV-2, and an untypeable strain in one child each. This finding was not intuitive because HAdVs are not commonly associated with hepatitis, according to the study.

AAV2 was much less common in the control group. For example, it was found in none of the children with hepatitis of known origin and in only four children (3.5%) with acute gastroenteritis and HAdV-positive stool. Of note, neither AAV2 nor HAdV-41 was detected among the 30 pediatric controls with acute hepatitis of defined etiology nor 42 of the hospitalized children without hepatitis, the researchers write.

In the search for other viruses in the study group, metagenomic sequencing detected EBV, also known as human herpesvirus (HHV)–4, in two children, cytomegalovirus (CMV) in one child, and HAdV type C in one child.

Analysis of whole blood revealed enterovirus A71 in one patient. HAdV type C also was detected in one child on the basis of a nasopharyngeal swab, and picobirnavirus was found in a stool sample from another patient.

Researchers conducted virus-specific PCR tests on both patient groups to identify additional viruses that may be associated with the unexplained acute hepatitis. EBV/ HHV-4 was detected in 11 children (79%) in the study group vs in one child (0.88%) in the control group. HHV-6 was detected in seven children (50%) in the study group, compared with one case in the control group. CMV was not detected in any of the children in the study group versus vs children (1.8%) in the control group.

“Although we found significant differences in the relative proportions of EBV and HHV-6 in cases compared to controls, we do not believe that these viruses are the primary cause of acute severe hepatitis,” the researchers write. The viral load of the two herpes viruses were very low, so the positive results could represent integrated proviral DNA rather than bona fide low-level herpesvirus. In addition, herpes virus can be reactivated by an inflammatory condition.

“Nevertheless, it is striking that among the 16 cases (in the study group), dual, triple, or quadruple infections with AAV2, adenovirus, and one or both herpesviruses were detected in whole blood from at least 12 cases (75%),” the researchers write.

Management of Suspected Hepatitis

The study’s key messages for parents and healthcare providers “are awareness and reassurance,” Balistreri told Medscape Medical News.

Vigilance also is warranted if a child develops prodromal symptoms including respiratory and/or gastrointestinal signs such as nausea, vomiting, diarrhea, and abdomen pain, he said. If jaundice or scleral icterus is noted, then hepatitis should be suspected.

Some patients needed hospitalization and quickly recover. In very rare instances, the inflammation may progress to liver failure and transplantation, Balistreri said.

“Reassurance is based on the good news that most children with acute hepatitis get better. If a case arises, it is good practice to keep the child well hydrated, offer a normal diet, and avoid medications that may be cleared by the liver,” Balistreri added.

“Of course, COVID-19 vaccination is strongly suggested,” he added.

Some existing treatments could help against unexplained acute hepatitis, Chiu said. “The findings suggest that antiviral therapy might be effective in these cases.”

Cidofovir can be effective against adenovirus, according to a report in The Lancet . Similarly, ganciclovir or valganciclovir may have activity against EBV/HHV-4 or HHV-6, Chiu said. “However, antiviral therapy is not available for AAV2.”

The three studies published in Nature “offer compelling evidence, from disparate centers, of a linkage of outbreak cases to infection by AAV2,” Balistreri said. The studies also suggest that liver injury was related to abnormal immune responses. This is an important clinical distinction, indicating a potential therapeutic approach to future cases — immunosuppression rather that anti-adenoviral agents, he said.

“We await further studies of this important concept,” Balistreri said.

Many unanswered questions remain about the condition’s etiology, he added. Is there a synergy or shared susceptibility related to SARS-CoV-2? Is the COVID-19 virus helping to trigger these infections, or does it increase the risk once infected? Also, are other epigenetic factors or viruses involved?

Moving Forward

The next steps in the research could go beyond identifying presence of these different viruses and determining which one(s) are contributing the most to the acute pediatric hepatitis, Chiu said.

The researchers also would like to test early results from the United Kingdom that identified a potential association of acute severe hepatitis with the presence of human leukocyte antigen genotype DRB1*04:01, he added.

They also might investigate other unintended potential clinical consequences of the COVID-19 pandemic, including long COVID and resurgence of infections from other viruses, such as respiratory syncytial virus, influenza, and enterovirus D68.

The study was supported by the Centers for Disease Control and Prevention, the National Institutes of Health, the Department of Homeland Security, and other grants. Chiu is a founder of Delve Bio and on the scientific advisory board for Delve Bio, Mammoth Biosciences, BiomeSense, and Poppy Health. Balistreri had no relevant disclosures.

Nature. Published online March 30, 2023. Full text 1; Full text 2; Full text 3

Damian McNamara is a staff journalist based in Miami. He covers a wide range of medical specialties, including infectious diseases, gastroenterology and critical care. Follow Damian on Twitter: @MedReporter.

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