Norwalk virus: How infectious is it?

Abstract

Noroviruses are major agents of viral gastroenteritis worldwide. The infectivity of Norwalk virus, the prototype norovirus, has been studied in susceptible human volunteers. A new variant of the hit theory model of microbial infection was developed to estimate the variation in Norwalk virus infectivity, as well as the degree of virus aggregation, consistent with independent (electron microscopic) observations. Explicit modeling of viral aggregation allows us to express virus infectivity per single infectious unit (particle). Comparison of a primary and a secondary inoculum showed that passage through a human host does not change Norwalk virus infectivity. We estimate the average probability of infection for a single Norwalk virus particle to be close to 0.5, exceeding that reported for any other virus studied to date. Infected subjects had a dose-dependent probability of becoming ill, ranging from 0.1 (at a dose of 10(3) NV genomes) to 0.7 (at 10(8) virus genomes). A norovirus dose response model is important for understanding its transmission and essential for development of a quantitative risk model. Norwalk virus is a valuable model system to study virulence because genetic factors are known for both complete and partial protection; the latter can be quantitatively described as heterogeneity in dose response models.

Diverse norovirus genotypes identified in sewage-polluted river water in South Africa

“…NoVs are characterized by high environmental stability and a very low infectious dose [6]. Accordingly, NoVs are frequently implicated in foodborne and waterborne gastroenteritis outbreaks [7].…”

Design of Post-Treatment Unit for Compost from a Composting Toilet with Microbial Risk Assessment

“…• Highly infested person of viral infection excretes a maximum of 10 11 viral copies/g in faeces from highly infected person [1,7,8] was used for the risk assessment taking account of the highest risk. Assuming this concentration, the initial concentration was estimated at 6.72 × 10 8 viral copies/g-dry compost.…”

“…For norovirus, the dose response data set of Teunis et al [1] was used in place of the β-Poisson equation [13].…”

“…Because, noroviruses are a major cause of human gastroenteritis, and they are frequently associated with food, water contamination [1] and accidental ingestion. On the other hand, Ascaris infections are very common in developing countries.…”

Comparative Virucidal Efficacy of Seven Disinfectants Against Murine Norovirus and Feline Calicivirus, Surrogates of Human Norovirus

“…More recently, the 50% human infectious dose was estimated to lie between 18 and 1000 viral particles or between 1320 and 2800 genome equivalents for the HuNoV prototype Norwalk strain (Teunis et al 2008;Glass et al 2009;). This infectious dose could vary depending on both the involved strain and the experimental methodology.…”