Enteric viruses of poultry are common and pervasive. They are potentially as diverse as enteric bacteria and are responsible for production diseases resulting in substantial financial losses. Many of these viruses have RNA genomes that continually evolve, leading to multiple circulating strains of varying pathogenicity. They can be difficult to diagnose due to confounding issues, such as their presence in healthy birds, variable pathogenicity, age-related resistance, coinfection with other pathogens, and lack of convenient diagnostic tests. They are associated with complex syndromes, such as malabsorption syndrome Malabsorption Syndrome in Poultry Malabsorption syndrome is characterized by stunted growth and lack of pigmentation in growing chickens. A viral cause is suspected but has not been confirmed. There are no confirmatory tests... read more of broiler chickens and poult enteritis mortality syndrome, but also of diseases outside the enteric system, such as tenosynovitis Viral Arthritis read more caused by avian orthoreovirus. Recent metagenomics studies are beginning to shed light on the causes of some complex production diseases, and some of the more prominent virus families are described in this chapter, including astroviruses Astrovirus Infections in Poultry Avian astroviruses are common in several species of poultry and typically cause enteritis and growth retardation in young birds. Diagnosis is generally made by PCR; serologic tests are available... read more , coronaviruses Coronaviral Enteritis of Turkeys Coronaviral enteritis is an acute, highly contagious disease of turkeys characterized by depression, anorexia, diarrhea, and decreased weight gain. The causative agent is turkey coronavirus... read more , parvoviruses Chicken Parvovirus and Turkey Parvovirus Infections Chicken and turkey parvovirus infections occur worldwide and primarily affect growing birds. The primary signs are related to production and include poor weight gain, poor feed conversion, and... read more , picornaviruses Picornavirus Infections in Poultry Picornaviruses are found in a variety of bird species. Some cause significant diseases, including enteritis and malabsorption syndrome. Diarrhea, stunted growth, and increased mortality in young... read more and rotaviruses Rotavirus Infections of Poultry Avian rotavirus (AvRV) infections range from subclinical to acute with enteritis and diarrhea. Globally, AvRV is detected in chickens, turkeys, ducks, guinea fowl, pheasants, partridges, pigeons... read more .