| Viral enteritis/enteropathy, also known as runting stunting syndrome (RSS), is an enteric disease of chickens that has had a major economic impact on producers worldwide over the last several years. RSS is characterized in commercial broilers by unevenly sized of chickens, reduced growth rates, reduced body weights at processing, and losses in feed conversion. Clinically, chickens present with pasted vents, watery droppings, undigested feed passage, pale and thin-walled intestines, yellow and gaseous ceca, and sometimes atrophied spleens and bursae. Chicken astrovirus (CAstV) and avian orthoreovirus (ARV) can induce RSS in experimentally infected chickens. Additionally, co-infection with these two viruses results in exacerbation of RSS. One chicken astrovirus (CAstV-HB), three ARVs (ARV-MM, ARV-11P, and ARV-GF), and two fowl adenoviruses (FAdV-PTS and FAdV-XonL) were isolated from commercial chickens with RSS. All six viruses were plaque-purified twice prior to their characterization in vivo, which included pathogenesis evaluations. In vitro characterization included genome sequencing and antigenic comparisons. CAstV, ARVs, and FAdVs induced RSS in susceptible broiler chickens when inoculated via the oral/intratracheal route. The gross lesions were similar to those seen in field settings and included pale, thin-walled, flattened, and constricted intestines; yellow-gaseous ceca; and unabsorbed yolk sacs. Microscopic lesions included villous atrophy and crypt hyperplasia in the intestines and duodenum, different forms of carditis with ARV infection, and hepatitis and pancreatitis with FAdV infections. ARVs and FAdVs also caused lymphoid depletion in bursae and to a lesser extent in thymi. Body weight reductions were occasionally apparent in individual chickens, but the average body weight differences were not usually statistically significant. Genomes of CAstV, ARVs, and FAdVs were sequenced using Illumina high-throughput technology. CAstV-HB was highly similar (91%) to CAstV-GA2011, which was also isolated from commercial chickens with RSS. Polyclonal antiserum made against CAstV-HB neutralized two other CAstVs suggesting that all three of these viruses were of the same serotype. FAdV-PTS and FAdV-XonL are 100% identical at the nucleotide level, and their antisera cross neutralized completely showing that these two adenoviruses are identical although they were isolated from different farms. The genomic and antigenic diversity of ARVs studied here is much broader, although some cross-neutralization with polyclonal antisera did exist among some of the isolates. Antigenicity did not correlate with sequence differences for any particular gene, suggesting that ARV antigenicity is complex and likely determined by multiple gene products. Viral co-infections were evaluated by inoculating chickens at one or three days of age with different combinations of ARV-GF and FAdV-PTS. Inoculation of ARV-GF and ARV-PTS together at one day of age resulted in more severe RSS than inoculation of either virus alone or inoculation of this virus combination at three days of age. Finally, the impact of RSS on the response to infectious bronchitis vaccine virus was evaluated. Commercial chickens and experimental chickens with induced RSS frequently exhibit signs and lesions consistent with chronic reactions to IBV vaccination. The reactions have caused losses at processing over the last few years. In experiments reported here, IB vaccine virus persisted in the tracheas of chickens exposed to ARV-GF and FAdV-PTS through five weeks of age. The effect on IBV persistence was greater with these viruses than with IBDV. Antibody titers were numerically lower in chickens with experimentally induced RSS at five weeks of age, but the decrease was not as great as that seen in IBDV-infected chickens. This suggests that although antibody responses were affected by RSS, the effect on cellular immune responses may be more important for clearance of IBV. The results obtained here show that FAdVs in addition to CAstV and ARVs are etiological components of viral enteritis/enteropathy. Co-infections with these viruses exacerbate the disease and can have an effect on other diseases such as IBV. Our results also suggest that a potential RSS vaccine should include at least one CAstV, one FAdV, and several ARVs to achieve a broad coverage against RSS. |
