Avian colibacillosis: still many black holes

Abstract

Avian pathogenic Escherichia coli (APEC) strains cause severe respiratory and systemic diseases, threatening food security and avian welfare worldwide. Intensification of poultry production and the quick expansion of free-range production systems will increase the incidence of colibacillosis through greater exposure of birds to pathogens and stress. Therapy is mainly based on antibiotherapy and current vaccines have poor efficacy. Serotyping remains the most frequently used diagnostic method, only allowing the identification of a limited number of APEC strains. Several studies have demonstrated that the most common virulence factors studied in APEC are all rarely present in the same isolate, showing that APEC strains constitute a heterogeneous group. Different isolates may harbor different associations of virulence factors, each one able to induce colibacillosis. Despite its economical relevance, pathogenesis of colibacillosis is poorly understood. Our knowledge on the host response to APEC is based on very descriptive studies, mostly restricted to bacteriological and histopathological analysis of infected organs such as lungs. Furthermore, only a small number of APEC isolates have been used in experimental studies. In the present review, we discuss current knowledge on APEC diversity and virulence, including host response to infection and the associated inflammatory response with a focus on pulmonary colibacillosis.

Studies on avian pathogenic Escherichia coli in commercial broiler chicken in South East Queensland

“…The severity of colibacillosis in chickens depends on the pathogenicity of the APEC, the chicken's immune status and the presence of predisposing risk factors, such as poor chicken welfare, immunosuppression and co-infections that can increase host susceptibility (Dho-Moulin and Fairbrother, 1999;Ewers et al, 2004;Guabiraba and Schouler, 2015;Nolan et al, 2013;Vandekerchove et al, 2004a). A number of overseas studies identified vectors humans (farm worker and visitors), wild birds and rodents, source and type of treatment(s) applied to the drinking water and unfavourable housing conditions as major risk factors associated with avian colibacillosis (Kemmett et al, 2013;Nolan et al, 2013;Vandekerchove et al, 2004a).…”

“…Escherichia coli that is capable of causing localised or systemic extraintestinal infections in chickens, turkeys, geese, ducks and other species of birds is known as APEC (Circella et al, 2012;Guabiraba and Schouler, 2015;Nolan et al, 2013). APEC can cause infections in all age groups of birds (Guabiraba and Schouler, 2015;Nolan et al, 2013), acting as a primary (Vandekerchove et al, 2004b) or secondary pathogen (Guabiraba and Schouler, 2015;Kabir, 2010;Kaper et al, 2004;Nolan et al, 2013).…”

“…APEC can cause infections in all age groups of birds (Guabiraba and Schouler, 2015;Nolan et al, 2013), acting as a primary (Vandekerchove et al, 2004b) or secondary pathogen (Guabiraba and Schouler, 2015;Kabir, 2010;Kaper et al, 2004;Nolan et al, 2013). Although APEC is present in the intestinal microbiota, the main route of entry into birds is through the respiratory system via inhalation of APEC contaminated aerosols.…”

“…The production of extracellular polysaccharide capsules are considered to be one of the E. coli serum resistance mechanisms that can lead to bacteraemia (Guabiraba and Schouler, 2015;Miajlovic and Smith, 2014). The somatic O-antigens and capsular K-antigens act as a barrier to the host defence mechanisms and were described in the 1960s and 1980s, respectively (Boerlin and White, 2013;Perry et al, 2014).…”

“…Variation in serum resistance mechanisms among APEC could be due to the presence of different types, as well as, combinations of capsules (Mainil, 2013). Overall, the wide variation in the presence of certain serum resistance VGs and the prevalence of these VGs could be reflected in the different clinical symptoms and pathological changes seen with avian colibacillosis (Guabiraba and Schouler, 2015;Mellata et al, 2003).…”