A Study of Cross-Protection between Eimeria maxima Immunovariants

Authors: Jenkins, Mark; Obrien, Celia; Parker, Carolyn; Tucker, Matthew

Submitted to: Pathogens
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2024
Publication Date: 1/9/2024
Citation: Jenkins, M.C., Obrien, C.N., Parker, C.C., Tucker, M.S. 2024. A Study of Cross-Protection between Eimeria maxima Immunovariants. Pathogens. 13(1). Article e13010066. https://doi.org/10.3390/pathogens13010066.
DOI: https://doi.org/10.3390/pathogens13010066

Interpretive Summary: Coccidiosis is a parasitic disease of poultry causing an estimated $ 14 billion yearly loss to worldwide chicken producers due to poorer weight gain, lower feed efficiencies in broilers and egg layers infected with the causative agent Eimeria. The disease has been controlled for years by medication of feed with drugs that inhibit replication of the parasite. However, drug resistance in Eimeria and consumer pressure to reduce antibiotics in poultry has led to the use of live vaccines to control the disease. Vaccination is effective because by ingesting live Eimeria oocysts in the vaccine, chicks develop immunity to subsequent Eimeria infection. In this study, Eimeria maxima, one of the most important species of Eimeria infecting chickens, was isolated from poultry litter 1.5 months after the chicks had received a coccidiosis vaccine. The new strain, named EmaxAPU3, was tested for its ability to induce resistance against infection with E. maxima lab strains (EmaxAPU1 and EmaxAPU2) that had been isolated from drug-using and vaccine-using poultry farms. Interestingly, EmaxAPU3 could protect chickens against only EmaxAPU1, but not against EmaxAPU2. The reverse was also seen with immunization of chicks with Emax1 protecting against Emax3, but giving chicks EmaxAPU2 did not protect them against Emax APU1 nor EmaxAPU3. This information is important to poultry companies and manufacturers of coccidiosis vaccines because it provides evidence for immunovariation in Eimeria. The ability of E. maxima to evade immunity by displaying components on its surface that are different from those possessed by E. maxima in vaccines suggests that vaccines to control this disease may need multiple types of E. maxima to protect chickens during their lifespan.

Technical Abstract: For reasons unknown, Eimeria maxima is unique among Eimeria species infecting chickens in the immunovariability it displays among isolates from different geographical areas. Eimeria maxima oocysts (named EmaxAPU3) were isolated late in grow-out (6 weeks) from litter in a commercial broiler operation that was using Eimeria vaccination as the coccidiosis control program. Cross-protection studies (n = 4) were conducted in immunologically naïve chickens between EmaxAPU3 and two E. maxima lab strains (EmaxAPU1, EmaxAPU2) by immunizing with one E. maxima strain and challenging with either the homologous or heterologous E. maxima. As measured by oocyst output, immunization with EmaxAPU1 protected against homologous challenge (EmaxAPU1) and against heterologous challenge with EmaxAPU3, but not against EmaxAPU2. Similarly, immunization with EmaxAPU3 protected against homologous challenge (EmaxAPU3) and against heterologous challenge with EmaxAPU1, but not against EmaxAPU2. Immunization of chickens with EmaxAPU2 elicited a protective response against homologous challenge (EmaxAPU2), but not against EmaxAPU1 nor EmaxAPU3. The most plausible explanation for the appearance of this immunovariant late in grow-out is that E. maxima APU3 escaped immunity directed to E. maxima antigenic types in the commercial vaccine.