The Gastrointestinal Tract Is an Alternative Route for SARS-CoV-2 Infection in a Nonhuman Primate Model

Abstract

Background and Aims Gastrointestinal (GI) manifestations have been increasingly reported in Coronavirus Disease 2019 (COVID-19) patients. However, the roles of the GI tract in severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection are not fully understood. We investigated how the GI tract is involved in SARS-CoV-2 infection to elucidate the pathogenesis of COVID-19. Methods Our previously established nonhuman primate (NHP) model of COVID-19 was modified in this study to test our hypothesis. Rhesus monkeys were infected with an intragastric or intranasal challenge with SARS-CoV-2. Clinical signs were recorded after infection. Viral genomic RNA was quantified by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Host responses to SARS-CoV-2 infection were evaluated by examining inflammatory cytokines, macrophages, histopathology and mucin barrier integrity. Results Intranasal inoculation with SARS-CoV-2 led to infections and pathological changes not only in respiratory tissues but also in digestive tissues. Expectedly, intragastric inoculation with SARS-CoV-2 resulted in the productive infection of digestive tissues and inflammation in both the lung and digestive tissues. Inflammatory cytokines were induced by both types of inoculation with SARS-CoV-2, consistent with the increased expression of CD68. Immunohistochemistry and alcian blue/periodic acid-Schiff (AB-PAS) staining showed decreased Ki67, increased cleaved caspase 3 and decreased numbers of mucin-containing goblet cells, suggesting that the inflammation induced by these two types of inoculation with SARS-CoV-2 impaired the GI barrier and caused severe infections. Conclusions Both intranasal and intragastric inoculation with SARS-CoV-2 caused pneumonia and GI dysfunction in our rhesus monkey model. Inflammatory cytokines are possible connections for the pathogenesis of SARS-CoV-2 between the respiratory and digestive systems.

Potential intestinal infection and faecal–oral transmission of SARS-CoV-2

“… 93 ), indicating the induced intestinal inflammation by SARS-CoV-2. The expression of CD68, a marker for macrophages, substantially increased in the intestine at the earlier stage (at 1, 4 and 7 dpi) of infection by either intranasal or intragastric challenge, which is consistent with the expression of inflammatory cytokines produced by macrophages such as IL-1, IL-6, IL-12 and TNF 145 . Interestingly, in this study, intragastric inoculation with SARS-CoV-2 led to pneumonia; however, the viral RNAs in the lung were unable to be detected 145 .…”

“…The expression of CD68, a marker for macrophages, substantially increased in the intestine at the earlier stage (at 1, 4 and 7 dpi) of infection by either intranasal or intragastric challenge, which is consistent with the expression of inflammatory cytokines produced by macrophages such as IL-1, IL-6, IL-12 and TNF 145 . Interestingly, in this study, intragastric inoculation with SARS-CoV-2 led to pneumonia; however, the viral RNAs in the lung were unable to be detected 145 . These results led to a hypothesis that activated macrophages in the gastrointestinal tract might induce tissue damage in the digestive tract, and even in the lung, by secreting inflammatory cytokines.…”

“…Notably, both intranasal and intragastric inoculation caused the infiltration of inflammatory cells and loss of mucosal epithelium in gastrointestinal tissues. The immunohistochemistry staining of cleaved caspase 3 was observed in the stomach, jejunum, colon and rectum at 1 dpi in both the intranasal and intragastric groups 145 , highlighting the apoptosis caused by SARS-CoV-2 infection in gastrointestinal epithelial cells. A decreased number of mucin-containing goblet cells, the hallmark of ulcerative colitis 146 , was observed in the small intestine at 4 dpi in the intranasal group and as early as 1 dpi in the intragastric group 145 .…”

“…In another study, Rhesus macaques were infected with an intragastric ( n = 5) or intranasal ( n = 5) challenge with 1 ml of 1 × 10 7 plaque-forming units of SARS-CoV-2 (ref. 145 ). Notably, both intranasal and intragastric inoculation caused the infiltration of inflammatory cells and loss of mucosal epithelium in gastrointestinal tissues.…”

Killed whole genome-reduced bacteria surface-expressed coronavirus fusion peptide vaccines protect against disease in a porcine model

“…They have been used as model systems for many infectious disease vaccine studies (reviewed in (56)). While the syndromes accompanying PEDV infection in pigs largely involve diarrhea, COVID-19 can include significant gastrointestinal (GI) tract symptoms and pathology, with significant GI viral shedding (57, 58).…”