After >8,000 infections and >700 deaths worldwide, the pathogenesis of the new infectious disease, severe acute respiratory syndrome (SARS), remains poorly understood. We investigated 18 autopsies of patients who had suspected SARS; 8 cases were confirmed as SARS. We evaluated white blood cells from 22 confirmed SARS patients at various stages of the disease. T lymphocyte counts in 65 confirmed and 35 misdiagnosed SARS cases also were analyzed retrospectively. SARS viral particles and genomic sequence were detected in a large number of circulating lymphocytes, monocytes, and lymphoid tissues, as well as in the epithelial cells of the respiratory tract, the mucosa of the intestine, the epithelium of the renal distal tubules, the neurons of the brain, and macrophages in different organs. SARS virus seemed to be capable of infecting multiple cell types in several organs; immune cells and pulmonary epithelium were identified as the main sites of injury. A comprehensive theory of pathogenesis is proposed for SARS with immune and lung damage as key features.

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In addition to the lungs, the gastrointestinal tract is another target of SARS-CoV infection, as the intestinal epithelial cells and mucosal lymphoid tissue are infected. The findings provide possible explanations for the gastrointestinal symptoms and the presence of virus in the stool of SARS patients.

SignificanceThe geologic record provides evidence of repeated diversification events and mass extinctions, which entailed benchmark changes in biodiversity and ecology. For insights into these events, we explore the fossil record of marine animal communities using a network-based approach to quantifying ecological change over time. The major radiations and mass extinctions of the Phanerozoic Eon resulted in the biggest ecological changes, as they involved the rise and decline of interrelated communities in relative dominance. Our analyses provide support for an ecological severity ranking of mass extinctions and illuminate the long-term consequences of the Ordovician radiation and Devonian mass depletion of biodiversity. Our work highlights the potential for irreversible ecosystem changes with species losses, both previously documented and predicted in the future.