# Advances and Future Perspective on Detection Technology of Human Norovirus
## 1 Introduction  
Norovirus (NoV) is a single-stranded sense nonenveloped RNA virus, which belongs to the Caliciviidae family. It is classified into 10 genogroups (GI-GX) and further divided into 48 confirmed capsid genotypes on the basis of the amino acid sequences of the major capsid protein (VP1). Amongst the genogroups, GI, GI, GIV, GVIII and GX can infect humans, and they are commonly referred to as human noroviruses (HuNoVs) [1]. HuNoVs are recognised as the main food-borne pathogen causing acute gastroenteritis in humans worldwide. The proportion of food-borne infections caused by HuNoV in the world is 18% each year [2]. Statistics show that the global annual direct economic loss caused by HuNoVs is USD 4.2 billion, and the socioeconomic loss is USD 60.3 billion (of which, infants and children under 5 years old cost USD 39.8 billion) [3]. HuNoVs have become a leading factor in nonbacterial gastroenteritis [4, 5, 6].  
The genome of HuNoV is divided into three open reading frames (ORFs) (Figure 1) [7]. ORF1 encodes six nonstructural proteins [8, 9]. ORF2 and ORF3 encode the major capsid protein (VP1) and minor capsid protein (VP2), respectively. The VP1 is composed of a conserved S domain and a P domain [10]. The P domain is further divided into the P1 subdomain and a highly variable P2 subdomain. It has multiple neutralising epitopes, and it can bind to the known viral ligand, namely, histo-blood group antigens (HBGAs) [11]. The VP2 is located inside the capsid [12]. Therefore, VP1 or partial sequences of ORF1 are usually selected as the target sites for HuNoV detection.  
HuNoV is highly infectious. It is usually transmitted through faecal-oral routes, aerosols, contaminated water and food, or direct human-to-human contact [13, 14]. Various fresh foods such as berries, leafy vegetables and shellfish are carriers of HuNoVs [15, 16, 17]. However, HuNoVs detection in food and environmental samples are difficult due to the complicated matrix of backgrounds. Moreover, the high stability of virions against normal disinfection methods in these samples cause numerous food-borne HuNoV infections [18, 19, 20, 21].  
Another obstacle to developing efficient detection methods is the lack of mature HuNoV culture modes in vitro and in small animal models. [PERSON] et al. reported the successful replication of HuNoV in human B cells. However, only HuNoV GII.4 can be replicated in this system [22; 23]. [PERSON] et al. successfully developed a culture system using human intestinal enteroids. However, the HuNoV titres in this culture system are limited [24; 25]. Animal models have also been explored. [PERSON] et al. reported HuNoV replication in zebrafish larvae. However, the highest virus titre has reached only \(10^{7}\) PFU/mL [26]. Therefore, the inability to collect sufficient HuNoV makes studying various detection methods and developing antiviral strategies difficult.  
At present, the control for HuNoV outbreaks primarily depends on the detection technology for achieving early detection, control and prevention. The most important goals for the development of HuNoV detection methods are high safety, good sensitivity, strong specificity, quickness and simplicity. With continuous research on the biological mechanism of HuNoVs, progress has been made in the detection of HuNoVs. According to different detection principles, HuNoV detection technologies can be divided into morphological methods based on HuNoV particles, immunological methods based on antigen-antibody reactions, molecular detection methods based on nucleic acids and biosensor methods which have developed in recent years. This article summarises the development of major detection technologies for HuNoVs.