Salmonella in chickens.

Abstract

Abstract There are over 2000 Salmonella bacterial species, many of which have very wide host-species ranges. Infection with Salmonella in chickens generally progresses through three distinct phases: first, invasion via the gastrointestinal tract; second, establishment of a systemic infection in internal organs; and third, one of three distinct outcomes in the final phase. In the final phase, Salmonella infections in chickens may be completely resolved by effective immune mechanisms, or may cause acute and severe pathology, even death, or may result in an asymptomatic and chronic carrier state. Carrier birds can shed bacteria into eggs and into the environment, causing vertical and horizontal transfer of bacteria, and may serve as a source of microbial contamination of poultry meat and eggs. Thus, in addition to negatively impacting chicken health, Salmonella contamination of poultry products represents a threat to human health. With strong consumer preferences and, in some countries, legislation limiting the use of antimicrobial drugs in poultry production, enhancing genetic resistance to Salmonella is an attractive component of a comprehensive programme to control disease in poultry. The chicken's response to Salmonella is complex, with many cellular components, including early-responding macrophages and heterophils, and utilizes innate immune mechanisms, Th1 cytokine production and protective cellular and humoral immune responses. There is strong evidence for genetic control of many facets of host response to Salmonella infection. As reviewed in this chapter, distinct lines of chickens have been characterized with different responses to Salmonella, several specific genes have been demonstrated to have structural or expression variation associated with salmonellosis or Salmonella carrier state, quantitative trait loci (QTL) for Salmonella response have been identified by genomic scans and transcriptional analyses have elucidated key genes and pathways that are altered in response to infection with Salmonella. Therefore, although there is much remaining to be discovered, a foundation of knowledge already exists about the genetic control of resistance to Salmonella in chickens that will enable the use of genetic approaches to enhance bird health and reduce microbial contamination of poultry products.