Evaluation of human adenoviruses 38, 39, 40, and 41 as new serotypes

Four new serotypes of human adenovirus (Ad38-41) have been described in recent literature. We conducted a thorough evaluation of the prototype strains of these types by preparing rabbit and horse antisera to them and performing reciprocal neutralization and hemagglutination-inhibition (HI) tests with all 41 prototype viruses and antisera. Types 38 and 39 are in subgenus D, share hemagglutinins with Ad13 and each other in three-way HI tests, and have been rarely encountered thus far; types 40 and 41 are in subgenus F, are related to each other by serum neutralization and HI tests, and are well-established agents of acute gastroenteritis in infants. All four prototype strains meet the accepted criteria for new serotypes, although special mention is made of the serologic relationship between Ad40 and 41. The horse antisera have stable titers and can serve as international reference reagents for these viruses.