A Review of the Emerging White Chick Hatchery Disease.

White chick hatchery disease is an emerging disease of broiler chicks with which the virus, chicken astrovirus, has been associated. Adult birds typically show no obvious clinical signs of infection, although some broiler breeder flocks have experienced slight egg drops. Substantial decreases in hatching are experienced over a two-week period, with an increase in mid-to-late embryo deaths, chicks too weak to hatch and pale, runted chicks with high mortality. Chicken astrovirus is an enteric virus, and strains are typically transmitted horizontally within flocks via the faecal-oral route; however, dead-in-shell embryos and weak, pale hatchlings indicate vertical transmission of the strains associated with white chick hatchery disease. Hatch levels are typically restored after two weeks when seroconversion of the hens to chicken astrovirus has occurred. Currently, there are no commercial vaccines available for the virus; therefore, the only means of protection is by good levels of biosecurity. This review aims to outline the current understanding regarding white chick hatchery disease in broiler chick flocks suffering from severe early mortality and increased embryo death in countries worldwide.

Astrovirus reverse genetics systems, a story of success.

Astroviruses are one of the main causes of gastroenteritis of medical and veterinary relevance worldwide. Recently, these viruses were associated with neurological disease in mammals, including humans. Reverse genetics systems are the most powerful tool to improve our understanding of the virus replication, and eventually to develop safe vaccine candidates. In the present review, it is summarized the current knowledge on the different strategies used to develop reverse genetics systems for mamastroviruses and avastroviruses, and some of the biological answers that have provided are discussed.

A trivalent vaccine candidate against hepatitis E virus, norovirus, and astrovirus.

Hepatitis E virus (HEV), norovirus (NoV), and astrovirus (AstV) are enterically-transmitted viral pathogens causing epidemic or endemic hepatitis (HEV) and gastroenteritis (NoV and AstV) respectively in humans, leading to significant morbidity and mortality worldwide. While a recombinant subunit vaccine against HEVs is available in China, there is no commercial vaccine or antiviral against NoV or AstV. We report here our development of a trivalent vaccine against the three viral pathogens through our new polymer vaccine technology. All HEV, NoV, and AstV are non-enveloped RNA viruses covered by a protein capsid, featuring surface protruding (P) proteins that are responsible for virus-host interaction. These dimeric P proteins elicit neutralizing antibody and are good targets for subunit vaccine development. The trivalent subunit vaccine was developed by fusion of the dimeric P domains of the three viruses together that formed tetramers. This trivalent vaccine elicited significantly higher antibody responses in mice against all three P domains than those induced by a mixture of the three free P domains (mixed vaccine). Furthermore, the post-immune antisera of the trivalent vaccine showed significantly higher neutralizing titers against HEV infection in cell culture and higher blocking activity against NoV binding to HBGA ligands than those of the post-immune sera of the mixed vaccine. Thus, the trivalent vaccine is a promising vaccine candidate against HEV, NoV, and AstV.

Human astroviruses.

Human astroviruses (HAtVs) are positive-sense single-stranded RNA viruses that were discovered in 1975. Astroviruses infecting other species, particularly mammalian and avian, were identified and classified into the genera Mamastrovirus and Avastrovirus. Through next-generation sequencing, many new astroviruses infecting different species, including humans, have been described, and the Astroviridae family shows a high diversity and zoonotic potential. Three divergent groups of HAstVs are recognized: the classic (MAstV 1), HAstV-MLB (MAstV 6), and HAstV-VA/HMO (MAstV 8 and MAstV 9) groups. Classic HAstVs contain 8 serotypes and account for 2 to 9% of all acute nonbacterial gastroenteritis in children worldwide. Infections are usually self-limiting but can also spread systemically and cause severe infections in immunocompromised patients. The other groups have also been identified in children with gastroenteritis, but extraintestinal pathologies have been suggested for them as well. Classic HAstVs may be grown in cells, allowing the study of their cell cycle, which is similar to that of caliciviruses. The continuous emergence of new astroviruses with a potential zoonotic transmission highlights the need to gain insights on their biology in order to prevent future health threats. This review focuses on the basic virology, pathogenesis, host response, epidemiology, diagnostic assays, and prevention strategies for HAstVs.

Establishment of stably transfected cells constitutively expressing the full-length and truncated antigenic proteins of two genetically distinct mink astroviruses.

Astroviruses are becoming a growing concern in veterinary and public health. To date there are no registered vaccines against astrovirus-induced disease, mostly due to the difficulty to cultivate astroviruses to high titer for vaccine development using conventional techniques. As means to circumvent this drawback, we have developed stably transfected mink fetal cells and BHK21 cells constitutively expressing the full-length and truncated capsid proteins of two distinct genotypes of mink astrovirus. Protein expression in these stably transfected cells was demonstrated by strong signals as evaluated by in-situ PLA and IFA, and confirmed by Western blotting. The recombinant full-length and truncated proteins induced a high level of antibodies in mink, evaluated by ELISA, demonstrating their immunogenicity. In a challenge experiment in mink, a reduction in presentation clinical signs and virus shedding was observed in mink kits born from immunized females. The gene integration and protein expression were sustained through cell passage, showing that the used approach is robust and reliable for expression of functional capsid proteins for vaccine and diagnostic applications.

Chicken astrovirus capsid proteins produced by recombinant baculoviruses: potential use for diagnosis and vaccination.

Chicken astroviruses (CAstVs) have been characterized recently. Due to their relatively poor growth in cell culture, virus-specific antigens are not readily available for the development of diagnostic reagents and vaccines. For this purpose two capsid protein antigens, specified by the 11672 isolate of CAstV, were produced in insect cells following infection with recombinant baculoviruses. The GST-11672 capsid protein, a fusion protein comprising the capsid protein and glutathione-S-transferase (GST) as an N-terminal affinity tag, and the 11672 capsid protein alone were detected by western blotting as proteins of ~100 and 70 kDa, respectively. Immunization with the affinity-purified GST-11672 capsid protein produced a polyclonal rabbit antiserum, which reacted by indirect immunofluorescence with Group B CAstVs but which showed no reactivity with the Group A CAstV isolate, 612. When used as part of an immunoperoxidase-based immunohistochemical procedure, this rabbit antiserum facilitated the detection of CAstV antigen in formalin-fixed, paraffin-embedded kidney tissue at the sites of histopathology characteristic of nephritis. Although further evaluation with sera from commercial chickens is required, a prototype indirect antibody-detecting enzyme-linked immunosorbent assay (ELISA) based on affinity-purified GST-11672 capsid protein as coating antigen demonstrated considerable potential with low ELISA absorbance values being generated with sera from specific pathogen free (SPF) chickens, and high absorbance values being generated with serum samples from experimentally infected chickens. Immunization experiments of SPF chickens showed that, when administered as mixtures with oil adjuvant, crude cell lysates containing the GST-11672 capsid protein or the 11672 capsid protein elicited virus-specific antibody responses that were detectable by indirect immunofluorescence and by virus neutralization assays.

A purified recombinant baculovirus expressed capsid protein of a new astrovirus provides partial protection to runting-stunting syndrome in chickens.

A new viral sequence likely belonging to a virus of the family Astroviridae was determined using the gut content of chickens affected with the runting-stunting syndrome (RSS) in chickens. Since the appropriate virus could not be isolated in cell culture the open reading frame of the viral capsid protein was cloned to generate a recombinant baculovirus. The protein was purified and used as an experimental vaccine in broiler breeders to provide maternal derived antibodies for the protection of the offspring. The presence of specific antibodies was monitored by an ELISA. The offspring of vaccinated breeder hens were partially protected in a RSS challenge model.

Contamination of the hospital environment with gastroenteric viruses: comparison of two pediatric wards over a winter season.

The aims of this study were to examine the extent of gastroenteric virus contamination in a pediatric primary immunodeficiency (PPI) ward and a general pediatric ward over a winter season and to determine whether changes to hospital infection control interventions would have an impact on environmental contamination levels within pediatric units. Environmental swabs were collected weekly from 11 sites in both wards from 15 December 2005 to 3 March 2006 and examined for the presence of norovirus (NoV), astrovirus, and rotavirus (RV) by reverse transcriptase PCR. Viruses were detected in 17% and 19% of swabs from both wards. Virus contamination for NoV and RV decreased from 20% to 6% and 15% to 10% of swabs, respectively, in the PPI ward from the 2004 study by Gallimore et al. (C. I. Gallimore, C. Taylor, A. R. Gennery, A. J. Cant, A. Galloway, M. Iturriza-Gomara, and J. J. Gray, J. Clin. Microbiol. 44:395-399, 2006). Overall, changes to cleaning protocols were deemed to have reduced the level of environmental contamination with gastroenteric viruses, but contamination still occurred due to a breakdown in infection control procedures indicated by contamination in areas frequented by parents but used only occasionally by staff.

Avian astroviruses.

As poultry becomes more important in the world economy, it is increasingly important to fully understand the mechanisms of disease and poor production that affect the industry. To more accurately and reasonably treat these diseases, a more sophisticated understanding of interrelatedness is required. This review focuses on avian astroviruses (AAstVs), in particular the recent advances in our understanding of AAstV molecular biology, and also history, diagnosis, treatment and control. The known AastVs comprise duck astrovirus 1, turkey astrovirus 1 and 2, and avian nephritis virus of chickens. Nucleotide and amino acid identities between the avian and mammalian (human, ovine, bovine) astroviruses is very low (e.g. 20 to 25% and 12 to 15%, respectively) in open reading frame (ORF) 1a. There is also variation among the avian astroviruses, including between the two known types of turkey astrovirus. The ORF 1b sequence contains a number of conserved amino acid motifs; these could be the basis of degnerate oligonucleotide primers. A nomenclature for astroviruses is also proposed, based on: host species-astrovirus-type number/country(state)/reference number/year of isolation. For example, turkey astrovirus 2/North Carolina/034/1999.

Inactivation of an astrovirus associated with poult enteritis mortality syndrome.

Outbreaks of poult enteritis mortality syndrome (PEMS) continue to cause financial losses to the turkey industry. Clinically, PEMS is defined by mortality profiles, diarrhea, flock unevenness, and immunosuppression. PEMS is a very difficult disease to control and prevent. Depopulation of PEMS-affected flocks and thorough cleaning of the contaminated housing have failed to prevent infection (disease) in subsequent flock placements. The relationship of PEMS to other enteric disease complexes of young turkeys is unknown, partly because the causative agent of PEMS remains unknown. Recently, we isolated a unique astrovirus strain from the thymus and intestines of PEMS-infected poults. This strain is molecularly and serologically distinct from the astrovirus that circulated in turkeys in the 1980s. Mammalian astroviruses are very resistant to inactivation. In these studies, we examined the stability of partially purified PEMS-associated astrovirus to inactivation with heat, laboratory disinfectants, and commercial disinfectants used in commercial turkey houses in an embryonated egg model system. Similar to mammalian astroviruses, the PEMS-associated astrovirus is resistant to inactivation by heat, acidification, detergent treatment, and treatment with phenolic, quaternary ammonium, or benzalkonium chloride-based products. Only treatment with formaldehyde, beta-propriolactone, or the peroxymonosulfate-based product Virkon S completely inactivated the astrovirus in the embryo model. These studies provide an alternate means to potentially control at least one virus associated with PEMS through the use of specific disinfectants.