May 21, 2020

Evidence for gastrointestinal infection of SARS-CoV-2, and ACE2 gene expression differences between children and adults

By Denise Baez

NEW YORK -- Mary 21, 2020 -- In today’s DG Alert, we cover transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via fecal-oral route, and differences in angiotensin-converting enzyme 2 (ACE2) gene expression between children and adults.

A study published in Gastroenterology provides new evidence that transmission of SARS-CoV-2 via fecal-oral route is possible.

“Receptor-mediated viral entry into a host cell is the first step of viral infection,” wrote Fei Xiao, the Fifth Affiliated Hospital, Zhuhai, China, and colleagues. “Our immunofluorescence data showed that ACE2 protein, which has been proven to be a cell receptor for SARS-CoV-2, is abundantly expressed in the glandular cells of gastric, duodenal, and rectal epithelia, supporting the entry of SARS-CoV-2 into the host cells.”

For the study, the researchers examined the viral RNA in feces from 73 patients (age range, 10 months to 78 years) with SARS-CoV-2 infection during their hospitalisations. The viral RNA and viral nucleocapsid protein were examined in the oesophageal, gastric, duodenal, and rectal tissues from 1 of the patients by endoscopy. Histologic staining as well as viral receptor ACE2 and viral nucleocapsid staining were performed. The images of fluorescent staining were obtained by using laser scanning confocal microscopy.

ACE2 stained positive mainly in the cytoplasm of gastrointestinal epithelial cells, and was abundantly distributed in the cilia of the glandular epithelia. Staining of viral nucleocapsid protein was visualised in the cytoplasm of gastric, duodenal, and rectum glandular epithelial cells, but not in oesophageal epithelium. 

The mucous epithelium of oesophagus, stomach, duodenum, and rectum showed no significant damage with histological staining.

The duration of positive stool results ranged from 1 to 12 days, and 23.29% continued to have positive results in stool after showing negative results in respiratory samples. According to current guidance (in China), the decision to discontinue transmission-based precautions for hospitalised patients with SARS-CoV-2 is based on negative results by real-time reverse transcriptase-polymerase chain reaction (rRT-PCR) from at least 2 sequential respiratory tract specimens collected ≥24 hours apart.

“However, in more than 20% of patients with SARS-CoV-2, we observed that the test result for viral RNA remained positive in feces, even after test results for viral RNA in the respiratory tract converted to negative, indicating that the viral gastrointestinal infection and potential fecal-oral transmission can last even after viral clearance in the respiratory tract,” the authors wrote. “Therefore, we strongly recommend that rRT-PCR testing for SARS-CoV-2 from feces should be performed routinely in patients with SARS-CoV-2 and that transmission-based precautions for hospitalised patients with SARS-CoV-2 should continue if feces test results are positive by rRT-PCR testing.”

In another study, published in JAMA, researchers found that ACE2 gene expression in the nasal epithelium is age-dependent, with lower expression found in children compared with adults. 

A retrospective examination of nasal epithelium from individuals aged 4 to 60 years (49.8% had asthma), found that ACE2 gene expression was lowest (mean log2 counts per million, 2.40; 95% CI, 2.07-2.72) in the younger children (n = 45) and increased with age, with mean log2 counts per million of 2.77 for older children (n = 185), 3.02 for young adults (n = 46), and 3.09 for adults (n = 29).

Linear regression with ACE2 gene expression as the dependent variable and age group as the independent variable showed that compared with younger children, ACE2 gene expression was significantly higher in older children (P = 0.01), young adults (P < 0.001), and adults (P = 0.001). As the distributions of sex and asthma varied among the age groups, a linear regression model adjusted for sex and asthma was built, which also showed significant adjusted associations (P ≤ 0.05) between ACE2 expression and age group.

“The results from this study show age-dependent expression of ACE2 in nasal epithelium, the first point of contact for SARS-CoV-2 and the human body,” wrote Supinda Bunyavanich, MD, Icahn School of Medicine at Mount Sinai, New York, New York, and colleagues. “Lower ACE2 expression in children relative to adults may help explain why COVID-19 is less prevalent in children.”

The authors noted that a previously published study of bronchoalveolar lavage fluid from 92 patients with acute respiratory distress syndrome showed no association between ACE2 protein activity and age; however, that study did not examine epithelial gene expression, and ACE2 protein may be variably shed into bronchoalveolar lavage fluid.

“Furthermore, the lung and nasal environments are distinct, with known differences in gene expression,” the authors wrote. “This study provides novel results on ACE2 gene expression in nasal epithelium and its relationship with age.”

SOURCE: Gastroenterology and JAMA