Overview
Coccidiosis remains a major disease and economic challenge for the global poultry industry, with an estimated global annual cost for the industry of ~$10 billion (Blake et al., 2020).
Coccidiosis in chickens is caused by host-specific Eimeria species that display tissue trophism and cause haemorrhagic (E. brunetti, E. necatrix, and E. tenella) or malabsorptive (E. acervulina, E. maxima, E. mitis, E. praecox) disease (Blake and Tomley, 2014). Chickens become infected through ingestion of sporulated oocysts (resilient, thick-walled structure containing 4 sporocysts, each with 2 sporozoites), which are ubiquitous, particularly in areas of intensive production. Numerous studies have indicated complex relationships between lesion score severity, immunity and bird growth, and this makes understanding differences in how birds ‘manage’ Eimeria infection (e.g. resilient, resistant and/or tolerant) very pertinent (Boulton et al., 2018).
Although humoral immunity plays some role in protection from coccidiosis, cell-mediated immunity is regarded as most important (Shivaramaiah et al., 2014). The early response to Eimeria infection in immunised chickens includes migration of heterophils (and lymphocytes), causing initial leukopenia, and, subsequently, a primary role for cytotoxic T-cells as Eimeria spp. are intercellular parasites. Proinflammatory, increased IFN-Ƴ:IL-10 ratio or neutralising intestinal IL-10 seems to provide some benefit for Eimeria infected chickens (Broom and Kogut, 2019).
Good husbandry and the prophylactic use of anticoccidial drugs and/or live parasite vaccination have been the primary control measures employed to date (Chapman, 2018). Resistance to anticoccidial drugs is widespread, while the availability of these drugs has become restricted due to legislation and consumer pressure on chicken production. Vaccination challenges include exposure to relevant Eimeria spp., appropriate oocyst cycling to induce adequate immunity without causing (sub)clinical disease, and cost (particularly live attenuated vaccines) (Blake and Tomley, 2014). Therefore, there is great interest in alternatives, such as next generation vaccines based on parasite genes and antigens that induce effective, less risky protection, or feed (or water) additives with coccidiosis control potential (Broom, 2020).
References
Blake et al., 2020. Re-calculating the cost of coccidiosis in chickens. veterinaryresearch.biomedcentral.com/articles/10.1186/s13567-020-00837-2
Blake and Tomley, 2014. Securing poultry production from the ever-present Eimeria challenge. doi.org/10.1016/j.pt.2013.10.003
Boulton et al., 2016. Phenotypic and genetic variation in the response of chickens to Eimeria tenella induced coccidiosis. gsejournal.biomedcentral.com/articles/10.1186/s12711-018-0433-7
Broom, 2020. Evidence-based consideration of dietary 'alternatives' to anticoccidial drugs to help control poultry coccidial infections. www.preprints.org/manuscript/202012.0039/v1
Broom and Kogut, 2019. Deciphering desirable immune responses from disease models with resistant and susceptible chickens. doi.org/10.3382/ps/pey535
Chapman, 2018. Applied strategies for the control of coccidiosis in poultry. www.cabdirect.org/cabdirect/abstract/20183254614
Shivaramaiah et al., 2014. Coccidiosis: Recent advancements in the immunobiology of Eimeria species, preventive measures, and the importance of vaccination as a control tool against these apicomplexan parasites. doi.org/10.2147/VMRR.S57839
Coccidiosis remains a major disease and economic challenge for the global poultry industry, with an estimated global annual cost for the industry of ~$10 billion (Blake et al., 2020).
Coccidiosis in chickens is caused by host-specific Eimeria species that display tissue trophism and cause haemorrhagic (E. brunetti, E. necatrix, and E. tenella) or malabsorptive (E. acervulina, E. maxima, E. mitis, E. praecox) disease (Blake and Tomley, 2014). Chickens become infected through ingestion of sporulated oocysts (resilient, thick-walled structure containing 4 sporocysts, each with 2 sporozoites), which are ubiquitous, particularly in areas of intensive production. Numerous studies have indicated complex relationships between lesion score severity, immunity and bird growth, and this makes understanding differences in how birds ‘manage’ Eimeria infection (e.g. resilient, resistant and/or tolerant) very pertinent (Boulton et al., 2018).
Although humoral immunity plays some role in protection from coccidiosis, cell-mediated immunity is regarded as most important (Shivaramaiah et al., 2014). The early response to Eimeria infection in immunised chickens includes migration of heterophils (and lymphocytes), causing initial leukopenia, and, subsequently, a primary role for cytotoxic T-cells as Eimeria spp. are intercellular parasites. Proinflammatory, increased IFN-Ƴ:IL-10 ratio or neutralising intestinal IL-10 seems to provide some benefit for Eimeria infected chickens (Broom and Kogut, 2019).
Good husbandry and the prophylactic use of anticoccidial drugs and/or live parasite vaccination have been the primary control measures employed to date (Chapman, 2018). Resistance to anticoccidial drugs is widespread, while the availability of these drugs has become restricted due to legislation and consumer pressure on chicken production. Vaccination challenges include exposure to relevant Eimeria spp., appropriate oocyst cycling to induce adequate immunity without causing (sub)clinical disease, and cost (particularly live attenuated vaccines) (Blake and Tomley, 2014). Therefore, there is great interest in alternatives, such as next generation vaccines based on parasite genes and antigens that induce effective, less risky protection, or feed (or water) additives with coccidiosis control potential (Broom, 2020).
References
Blake et al., 2020. Re-calculating the cost of coccidiosis in chickens. veterinaryresearch.biomedcentral.com/articles/10.1186/s13567-020-00837-2
Blake and Tomley, 2014. Securing poultry production from the ever-present Eimeria challenge. doi.org/10.1016/j.pt.2013.10.003
Boulton et al., 2016. Phenotypic and genetic variation in the response of chickens to Eimeria tenella induced coccidiosis. gsejournal.biomedcentral.com/articles/10.1186/s12711-018-0433-7
Broom, 2020. Evidence-based consideration of dietary 'alternatives' to anticoccidial drugs to help control poultry coccidial infections. www.preprints.org/manuscript/202012.0039/v1
Broom and Kogut, 2019. Deciphering desirable immune responses from disease models with resistant and susceptible chickens. doi.org/10.3382/ps/pey535
Chapman, 2018. Applied strategies for the control of coccidiosis in poultry. www.cabdirect.org/cabdirect/abstract/20183254614
Shivaramaiah et al., 2014. Coccidiosis: Recent advancements in the immunobiology of Eimeria species, preventive measures, and the importance of vaccination as a control tool against these apicomplexan parasites. doi.org/10.2147/VMRR.S57839