Emergence of gyrovirus 3 in commercial broiler chickens with transmissible viral proventriculitis.

Gyrovirus 3 (GyV3) has been identified in faeces from children with acute gastroenteritis. However, whether GyV3 is prevalent in poultry has not been determined to date. To the best of our knowledge, this study is the first to isolate GyV3 from commercial broiler chickens with transmissible viral proventriculitis (TVP) in China. The complete genome of the virus shares 98.4% sequence identity with the FecGy strain that causes acute gastroenteritis in children. Epidemiological investigation from 2013 to 2017 revealed that the infection rate of GyV3 reached 12.5% (42/336) in commercial broiler chickens with TVP, indicating that the infection of GyV3 was ubiquitous in chickens. The emergence of GyV3 in commercial broiler chickens should be highly concerning for public health.

[Cross-species Transmission of Avian Leukosis Virus Subgroup J].

Avian leukosis virus subgroup J (ALV-J) is an avian retrovirus that can induce myelocytomas. A high-frequency mutation in gene envelope endows ALV-J with the potential for cross-species transmission. We wished to ascertain if the ALV-J can spread across species under selection pressure in susceptible and resistant hosts. First, we inoculated (in turn) two susceptible host birds (specific pathogen-free (SPF) chickens and turkeys). Then, we inoculated three resistant hosts (pheasants, quails and ducks) to detect the viral shedding, pathologic changes, and genetic evolution of different isolates. We found that pheasants and quails were infected under the selective pressure that accumulates stepwise in different hosts, and that ducks were not infected. Infection rates for SPF chickens and turkeys were 100% (16/16), whereas those for pheasants and quails were 37.5% (6/16) and 11.1% (3/27). Infected hosts showed immune tolerance, and inflammation and tissue damage could be seen in the liver, spleen, kidneys and cardiovascular system. Non-synonymous mutation and synonymous ratio (NS/S) analyses revealed the NS/S in hypervariable region (hr) 2 of pheasants and quails was 2.5. That finding suggested that mutation of isolates in pheasants and quails was induced by selective pressure from the resistant host, and that the hr2 region is a critical domain in cross-species transmission of ALV-J. Sequencing showed that ALV-J isolates from turkeys, pheasants and quails had moved away from the original virus, and were closer to the ALV-J prototype strain HPRS-103. However, the HPRS-103 strain cannot infect pheasants and quails, so further studies are needed.

Genetic mutations of avian leukosis virus subgroup J strains extended their host range.

The genetic diversity of avian leukosis virus subgroup J (ALV-J) is determined not only by the env gene, but also by its 3' UTR and 3' LTR. They all play important roles in extending the host range and tumour development. In the present study, one ALV-J strain (ZB110604-6) from Black-Bone Silky Fowl (BSF) and three ALV-J strains (ZB110604-3/4/5) from grey partridge (GP), which bore multiple tumours and breed in one house of Farm A, were demonstrated extending their host to GP, while two other ALV-J strains (LC110515-3/4) from BSF of Farm B could not infect the embryo fibroblast of GP. The BSF is a unique species of chicken in China, while the GP is a close relative of the pheasant that previously demonstrated resistance to ALV-J. Histopathology showed that various tumours were induced by ALV-J in the two species. Phylogenetic tree analysis showed that the isolates from Farms A and B, rather than species, belong to two different clusters of ALV-J. Genetic mutations analysis revealed that the isolates obtained from Farm A showed a higher frequency of mutation in the hypervariable region 2 domain than in other variable regions of the gp85 gene. From the nucleotide alignment of the 3' UTR and 3' LTR gene, and the spectrum of tumours observed in this study, we speculate that the deletions or mutations in the redundant transmembrane region, E element and U3 (CAAT boxes, CArG box and Y box) might associate with tumour formation and development. The extension of the host range of ALV-J to the GP suggested that housing different species together provides more opportunities for ALV-J to evolve rapidly.