Molecular Epidemiology of Human Adenovirus from Acute Gastroenteritis Cases in Brazil After the COVID-19 Pandemic Period, 2021-2023

Abstract

Human enteric adenoviruses (HAdV-F40/41) play a crucial role as causative agents of acute gastroenteritis (AGE), particularly affecting children in low-and middle-income countries. This study investigated the prevalence, genetic diversity, and molecular characteristics of HAdV-F40/41 in AGE cases reported in Brazil from 2021 to 2023, a period after the COVID-19 pandemic. A total of 1980 stool samples collected from medically attended AGE patients from nine states were analyzed by TaqMan-based qPCR. Overall, HAdV was detected in 16.6% (n = 328/1980) of cases, with the highest prevalence observed in children under five years of age. The positive HAdV samples were genotyped through partial sequencing of the hexon and/or fiber genes followed by phylogenetic analysis. Enteric HAdVs (HAdV-F40/41) were detected in 3.2% (n = 63/1980) of samples, with HAdV-F41 (44.1%) being the most common genotype. Among the non-enteric types, HAdV-C (29.4%) was the most prevalent, followed by HAdV-B (13.2%), HAdV-A (10.3%), and HAdV-D (2.9%). Phylogenetic analysis of the hexon (HVR1-HVR6) and fiber (Shaft) gene regions identified two major clusters, H-GTC1 and F-GTC2, showing close genetic relationships with global strains. HAdV-F40/41 demonstrated significantly higher viral loads compared to non-enteric HAdVs. These findings highlight the importance of continued surveillance of HAdV-F to better understand its role in AGE cases and support public health strategies, including potential vaccine development.

Keywords: HAdV-F40/41; acute gastroenteritis (AGE); human adenovirus (HAdV); molecular epidemiology.

Figure 1

(A) Monthly distribution of tested acute gastroenteritis samples, HAdV-positive samples, and detection rates in Brazil, 2021–2023. (B) Monthly distribution of surveillance period addition of acute gastroenteritis samples tested. HAdV-positive samples and detection rates in Brazil. (C) Seasonal distribution period addition of HAdV-positive samples for each Brazilian region.

Figure 2

Distribution of viral load of non-enteric and enteric HAdV, noroviruses, and rotaviruses in stool samples, expressed as genome copies per gram (GC/g). Box-and-whisker plots show the first and third quartiles (equivalent to the 5th and 95th percentiles), the median (the horizontal line in the box). **** p ≤ 0.0001.

Figure 3

(A) The total frequency of HAdV types obtained from samples sequenced between 2021 and 2023. HAdV types obtained from co-detection with rotavirus or norovirus are represented by a hatched pattern. (B) Frequency by age group. (C) Distribution of HAdV genotypes identified in samples from Brazil between 2021 and 2023.

Figure 4

Phylogenetic tree based of non-enteric HAdV on the conserved region of the nucleotide (nt) sequences of the hexon gene. Strains isolated in this study (marked with a circle) are shown as country, LVCA internal register number, year of collection, and type (i.e., BRA/LVCA35334/2023/HAdV-C1) and Reference strains were downloaded from GenBank. Maximum likelihood phylogenetic trees were constructed using MEGA X software with bootstrap testing (1000 replicates) applied the on Tamura-Nei (TN93) +G + I. Bootstrap values above 60% are given at branch nodes.

Figure 5

Phylogenetic tree based on the nt sequence of the (A) hypervariable regions (HVR1–HVR6) of the hexon gene and (B) partial shaft region of the fiber gene. HAdV-F40 and -F41. Strains isolated in this study (marked with a circle) are shown as country, LVCA internal register number, year of collection, and type (i.e., BRA/LVCA33516/2023/HAdV-41) and Reference strains were downloaded from GenBank. Maximum likelihood phylogenetic trees were constructed using MEGA X software with bootstrap testing (1000 replicates), applying the HKY model for the hexon hypervariable regions (A) and the HKY + I model for the fiber shaft region (B). Bootstrap values ≥ 60% are shown at branch nodes.