Chicken astrovirus (CAstV)
Chicken astrovirus (CAstV) is a recently emerged virus and the most recently identified member of the avian astroviruses in chickens. Similar to other astroviruses, CAstV is a small, round, nonenveloped virus typically <35 nm in diameter with a positive sensed, single-stranded RNA genome.
Astroviruses primarily cause enteric infections and infect many animal species including humans, where they are a leading cause of infant diarrhea. CAstV is one of two astrovirus species that infect chickens and are both associated with growth problems, enteritis and kidney lesions in young birds. The second astrovirus that occurs in chickens is the avian nephritis virus (ANV).
CAstV is an enteric pathogen and infections often occur very early, either transmitted horizontally by the fecal–oral route, or some CAstV strains can also be vertically transmitted from naive in-lay parent birds, and chicks may hatch shedding high levels of CastV. CAstV is more resistant to disinfection and cleaning than other viruses as it is non-enveloped. CAstV infections usually occur within the first days or week of life, and, and the earlier they are contracted, especially vertical infections, may result in a worse outcome, although this will depend on the particular CAstV strain, since, as is typical of viruses with RNA genomes, they vary widely in pathogenicity.
Also the viral load (dose) at the time of infection and the presence of maternal antibodies against CAstV will impact on the development of disease. Other important factors include the presence of other enteric pathogens such as ANV, which is frequently detected in co-infections with CAstV, and also avian orthoreoviruses and fowl adenoviruses, to name some of the more ubiquitous enteric viruses often found in co-infections with CAstV. In addition a flock may be infected with more than one strain of CAstV concurrently.
CAstV and other enteric viruses are so common and widespread in commercial broiler flocks. Recently CAstV has become associated with hatchery diseases, most noticeably “White Chicks”, reports of which have come from various Scandanavian countries, North America, Poland and Brazil, but also with the “clubbed down” problem.
Currently there are no medicines to treat RSS, CAstV-associated kidney disease or White Chicks disease nor are there any vaccines to prevent transmission of CAstV to broiler chicks. Hygiene and biosecurity are the only ways in which CAstV infection risk can be minimized.