Viral zoonoses and food of animal origin: caliciviruses and human disease

Atypical Viral Infections in Gastroenterology

Enteric viruses are commonly found obligate parasites in the gastrointestinal (GI) tract. These viruses usually follow a fecal-oral route of transmission and are characterized by their extraordinary stability as well as resistance in high-stress environments. Most of them cause similar symptoms including vomiting, diarrhea, and abdominal pain. In order to come in contract with mucosal surfaces, these viruses need to pass the three main lines of defense: mucus layer, innate immune defenses, and adaptive immune defenses. The following atypical gastrointestinal infections are discussed: SARS-CoV2, hantavirus, herpes simplex virus I, cytomegalovirus, and calicivirus. Dysbiosis represents any modification to the makeup of resident commensal communities from those found in healthy individuals and can cause a patient to become more susceptible to bacterial and viral infections. The interaction between bacteria, viruses, and host physiology is still not completely understood. However, with growing research on viral infections, dysbiosis, and new methods of detection, we are getting closer to understanding the nature of these viruses, their typical and atypical characteristics, long-term effects, and mechanisms of action in different organ systems.

A new generic real-time reverse transcription polymerase chain reaction assay for vesiviruses; vesiviruses were not detected in human samples

Different viruses belonging to the genus Vesivirus infect a broad range of animals, and cause gastroenteritis, vesicular skin lesions, hemorrhagic disease, respiratory diseases and other conditions. A recent report on Vesivirus viremia, as detected by PCR, in samples from patients with hepatitis of unknown etiology in the USA suggested a zoonotic potential for vesiviruses. These results have not been confirmed by another laboratory. In order to do so, a generic PCR assay on the RNA polymerase region was developed, and validated with RNA from 69 different Vesivirus species. Except SMSV serotype-8, all species tested were detected, including the ones that were suggested to be involved in zoonotic transmission in the USA (SMSV serotype-5).

The generic Vesivirus assay was used on RNA extracted from serum samples from patients with hepatitis, stool samples from patients with gastroenteritis, throat-swab specimens of patients with rash illnesses, throat-swab and nose-swabs of patients with acute respiratory diseases, and cell cultures with cytopathologic effect from enterovirus surveillance in which no pathogen was found. None were found positive. In this study a generic Vesivirus assay was developed and it was concluded that vesiviruses are an unlikely cause of common illnesses in humans in the Netherlands.

Inactivation of caliciviruses

The viruses most commonly associated with food- and waterborne outbreaks of gastroenteritis are the noroviruses. The lack of a culture method for noroviruses warrants the use of cultivable model viruses to gain more insight on their transmission routes and inactivation methods. We studied the inactivation of the reported enteric canine calicivirus no. 48 (CaCV) and the respiratory feline calicivirus F9 (FeCV) and correlated inactivation to reduction in PCR units of FeCV, CaCV, and a norovirus. Inactivation of suspended viruses was temperature and time dependent in the range from 0 to 100 degrees C. UV-B radiation from 0 to 150 mJ/cm(2) caused dose-dependent inactivation, with a 3 D (D = 1 log(10)) reduction in infectivity at 34 mJ/cm(2) for both viruses. Inactivation by 70% ethanol was inefficient, with only 3 D reduction after 30 min. Sodium hypochlorite solutions were only effective at >300 ppm. FeCV showed a higher stability at pH <3 and pH >7 than CaCV. For all treatments, detection of viral RNA underestimated the reduction in viral infectivity. Norovirus was never more sensitive than the animal caliciviruses and profoundly more resistant to low and high pH. Overall, both animal viruses showed similar inactivation profiles when exposed to heat or UV-B radiation or when incubated in ethanol or hypochlorite. The low stability of CaCV at low pH suggests that this is not a typical enteric (calici-) virus. The incomplete inactivation by ethanol and the high hypochlorite concentration needed for sufficient virus inactivation point to a concern for decontamination of fomites and surfaces contaminated with noroviruses and virus-safe water.

Inter- and intragenus structural variations in caliciviruses and their functional implications

The family Caliciviridae is divided into four genera and consists of single-stranded RNA viruses with hosts ranging from humans to a wide variety of animals. Human caliciviruses are the major cause of outbreaks of acute nonbacterial gastroenteritis, whereas animal caliciviruses cause various host-dependent illnesses with a documented potential for zoonoses. To investigate inter- and intragenus structural variations and to provide a better understanding of the structural basis of host specificity and strain diversity, we performed structural studies of the recombinant capsid of Grimsby virus, the recombinant capsid of Parkville virus, and San Miguel sea lion virus serotype 4 (SMSV4), which are representative of the genera Norovirus (genogroup 2), Sapovirus, and Vesivirus, respectively. A comparative analysis of these structures was performed with that of the recombinant capsid of Norwalk virus, a prototype member of Norovirus genogroup 1. Although these capsids share a common architectural framework of 90 dimers of the capsid protein arranged on a T=3 icosahedral lattice with a modular domain organization of the subunit consisting of a shell (S) domain and a protrusion (P) domain, they exhibit distinct differences. The distally located P2 subdomain of P shows the most prominent differences both in shape and in size, in accordance with the observed sequence variability. Another major difference is in the relative orientation between the S and P domains, particularly between those of noroviruses and other caliciviruses. Despite being a human pathogen, the Parkville virus capsid shows more structural similarity to SMSV4, an animal calicivirus, suggesting a closer relationship between sapoviruses and animal caliciviruses. These comparative structural studies of caliciviruses provide a functional rationale for the unique modular domain organization of the capsid protein with an embedded flexibility reminiscent of an antibody structure. The highly conserved S domain functions to provide an icosahedral scaffold; the hypervariable P2 subdomain may function as a replaceable module to confer host specificity and strain diversity; and the P1 subdomain, located between S and P2, provides additional fine-tuning to position the P2 subdomain.

Molecular and seroepidemiological evidence of canine calicivirus infections in Japan

Calicivirus infection of dogs was epidemiologically investigated by using canine calicivirus (CaCV) strain 48 as a reference. Similar RNA polymerase gene sequences and neutralizing antibodies against CaCV were detected in 1.7% of clinical specimens and 57% of serum samples, respectively, suggesting a high prevalence of CaCV in dog populations.

Genetic analysis of the RNA polymerase gene of caliciviruses from dogs and cats

Caliciviruses that infect animals including humans cause a specific disease syndrome in their respective hosts. Feline calicivirus (FCV) is a major pathogen of respiratory disease of cats, and human caliciviru is a causative agent of diarrhea. It has been suggested, furthermore, that FCV and newly recognized canine calicivirus (CaCV) may also be possible causes of diarrhea in these animal species. In this study nucleotide sequence of the RNA polymerase gene of two caliciviruses of canine origin, namely CaCV strain No. 48 and FCV-like strain Sapporo/283, and a number of FCV strains of respiratory and enteric origins was examined. The length of sequenced region, from the 5'LKDEL motif through the 3'YGDD motif of the gene, was 555 bp for CaCV No. 48 strain and 552 bp for the other FCV strains including Sapporo/283 strain. In phylogenetic analysis, CaCV No. 48 strain grouped as a distinct branch sharing ancestral roots with San Miguel sea lion virus, and FCVs formed one compact group in which Sapporo/283 strain was included.