Severe gastroenteritis and foodborne illness caused by Noroviruses (NoVs) during the winter are a worldwide phenomenon. Vulnerable populations including young children and elderly and immunocompromised people often require hospitalization and may die. However, no efficient vaccine for NoVs exists because of their variable genome sequences. This study investigates the infection processes in protein-protein interactions between hosts and NoVs. Protein-protein interactions were collected from related Pfam NoV domains. The related Pfam domains were accumulated incrementally from the protein domain interaction database. To examine the influence of domain intimacy, the 7？NoV domains were grouped by depth. The number of domain-domain interactions increased exponentially as the depth increased. Many protein-protein interactions were relevant; therefore, cloud techniques were used to analyze data because of their computational capacity. The infection relationship between hosts and NoVs should be used in clinical applications and drug design. 1. Introduction Gastroenteritis and foodborne illness epidemics usually occur during the winter. In 1968, an acute gastroenteritis outbreak occurred at an elementary school in Norwalk, OH, USA [1]. Kapikian et al. used immune electron microscopy and an infectious stool filtrate to observe the virus particles and identified them as small round-structured viruses [2]. The nonbacterial pathogen was called the Norwalk virus after the outbreak region and renamed the Norovirus (NoV) at the International Congress of Virology in Paris in 2002. The NoV is the species of the genus of Norwalk-like viruses in the Caliciviridae family. The NoV consists of a positive-sense, single-strand RNA (ssRNA) genome sequence of approximately 7.5？kb with 3 open reading frames (ORFs) [3]. The first open reading frame (ORF1) contains approximately 5？kb of sequences, which may enable 195？kDa polyproteins to support virus duplication. During the duplication phase, polyproteins are divided into at least 6 nonstructural proteins, such as p48, nucleotide triphosphatase (NTPase), p22, Vpg, proteinase, and RNA-dependent RNA polymerase [4–6]. ORF2 is approximately 1.8？kb long, which may transform into 60？kDa major structural protein VP1 with the following functions: self-assembly and capsid formation, receptor recognition, host specificity, strain diversity, and immunogenicity [7]. ORF3 consists of 0.6？kb nucleotides, which may translate into a 20？kDa minor structural protein (VP2), which facilitates the expression and stability of major structural protein
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