Astrovirus-induced "white chicks" condition - field observation, virus detection and preliminary characterization.

Chicken astrovirus (CAstV) was recently indicated as the factor of the "white chicks" condition associated not only with increased embryo/chick mortality but also with weakness and white plumage of hatched chicks. In February 2014, organ samples (livers and kidneys) from dead-in-shell embryos, as well as 1-day-old whitish and normal chicks, were delivered from one hatchery in Poland for disease diagnosis. The samples originated from the same 30-week-old breeder flock in which the only observed abnormal signs were 4-5% decrease in the number of hatched chickens and the presence (about 1%) of weaker chicks with characteristic whitish plumage among normal ones. CAstV was detected in submitted samples and was then isolated in 10-day-old embryonated specific pathogen free (SPF) chicken eggs. We also reproduced an infection model for the "white chicks" condition in SPF layer chickens using the isolated PL/G059/2014 strain as the infectious agent. Results of experimental reproduction of the "white chicks" condition were somewhat more serious than field observation. The administration of the CAstV material into the yolk sac of 8-day-old SPF chicken eggs caused delay and prolongation of hatching, as well as death of embryos/chicks, and also a change of plumage pigmentation. Only two chicks of a total of 10 inoculated SPF eggs survived and were observed for 2 months. A gradual elimination of the CAstV genome was noted in this period. Moreover, a few contact-naive SPF chicks, which had been placed in the same cage, were infected with CAstV. Molecular characterization of detected CAstV was performed by nucleotide sequencing of the full ORF2 region encoding the capsid precursor protein gene. Phylogenetic studies showed that the PL/G059/2014 isolate clustered in the subgroup Aiii of CAstV. In the light of the new classification rules, the Polish PL/G059/2014 CAstV isolate could be assigned to a new species of the Avastrovirus genus.

Subclinical circulation of avian hepatitis E virus within a multiple-age rearing and broiler breeder farm indicates persistence and vertical transmission of the virus.

In a prospective longitudinal study, a broiler breeder flock and its progeny were monitored for the presence of avian hepatitis E virus (HEV) RNA and antibodies. The flock was part of a multiple-age farm where the presence of avian HEV with clinical signs (increased mortality and decreased egg production) was demonstrated in several previous production cycles. Samples were taken twice at the rearing site and several times at the production site from broiler breeders including cockerels and day-old chicks. The samples were investigated by conventional and real-time reverse transcriptase-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and histological methods. At all time points, samples from the hens were positive for avian HEV RNA. The birds did not show any clinical signs, even though histopathological lesions of non-specific aetiology in the liver and spleen could be demonstrated. A significant increase in the number of positive birds and viral load was seen in week 45, in accordance with an increase in antibody titres. In comparison, cockerels investigated in week 62 tested negative by RT-PCR and ELISA. Avian HEV RNA was also detected in day-old chicks hatched from eggs laid in week 25, indicating vertical transmission. All partial helicase and capsid sequences retrieved within this study clustered together and were identical to previous sequences obtained from the same multiple-age farm. In conclusion, avian HEV persisted on the farm over years and circulated between the rearing and the production sites without causing any clinical signs although high viral loads in the adult hens were observed.