Development of a Protective Index to Rank Effectiveness of Multiple Treatments Within an Experiment: Application to a Cross-Protection Study of Several Strains of Eimeria maxima and a Live Vaccine

Epidemiological investigation and drug resistance of Eimeria species in Korean chicken farms

Background

Coccidiosis is a poultry disease that occurs worldwide and is caused by Eimeria species. The infection is associated with reduced feed efficiency, body weight gain, and egg production. This study aimed to investigate the current status of coccidiosis and anticoccidial resistance to anticoccidial drugs used as part of control strategies for this disease in Korean chicken farms.

Results

An overall prevalence of 75% (291/388) was found. Positive farms contained several Eimeria species (mean = 4.2). Of the positive samples, E. acervulina (98.6%), E. maxima (84.8%), and E. tenella (82.8%) were the most prevalent species. Compared with cage-fed chickens, broilers and native chickens reared in free-range management were more at risk of acquiring an Eimeria infection. Sensitivities to six anticoccidial drugs (clopidol, diclazuril, maduramycin, monensin, salinomycin, and toltrazuril) were tested using nine field samples. Compared with untreated healthy control chickens, the body weight gains of infected chickens and treated/infected chickens were significantly reduced in all groups. Fecal oocyst shedding was significantly reduced in four clopidol-treated/infected groups, three diclazuril-treated/infected groups, two toltrazuril-treated/infected groups, one monensin-treated/infected group, and one salinomycin-treated/infected group, compared with the respective untreated/infected control groups. Intestinal lesion scores were also reduced in three clopidol-treated/infected groups, one monensin-treated/infected group, and one toltrazuril-treated/infected group. However, an overall assessment using the anticoccidial index, percent optimum anticoccidial activity, relative oocyst production, and reduced lesion score index found that all field samples had strong resistance to all tested anticoccidial drugs.

Conclusion

The results of this large-scale epidemiological investigation and anticoccidial sensitivity testing showed a high prevalence of coccidiosis and the presence of severe drug resistant Eimeria species in the field. These findings will be useful for optimizing the control of coccidiosis in the poultry industry.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03369-3.

Does selection for growth rate in broilers affect their resistance and tolerance to Eimeria maxima?

Chickens exhibit varied responses to infection with Eimeria parasites. We hypothesise that broilers selected for increased growth rate will show lower resistance and tolerance to a coccidian challenge. 288 chickens of fast (F) or slow (S) growing lines were inoculated with 0 (control), 2500 (low-dose), or 7000 (high-dose) sporulated E. maxima oocysts at 13 days of age in two consecutive rounds. Gain and Intake were measured daily and their values relative to BW at the point of infection were calculated over the pre-patent (days 1-4 post-infection), acute (d5-8 pi), and recovery (d9-12 pi) phases of infection to assess the impact of infection. Levels of plasma carotenoids, vitamins E and A, long bone mineralisation, caecal microbiota diversity indices, and histological measurements were assessed at the acute (d6 pi) and recovery stage (d13 pi). In addition, we measured the levels of nitric oxide metabolites and the number of parasite genome copies in the jejunumat d6pi. In absolute terms F birds grew 1.42 times faster than S birds when not infected. Infection significantly reduced relative daily gain and intake (P < 0.001), with the effects being most pronounced during the acute phase (P < 0.001). Levels of all metabolites were significantly decreased, apart from NO which increased (P < 0.001) in response to infection on d6pi, and were accompanied by changes in histomorphometric features and the presence of E. maxima genome copies in infected birds, which persisted to d13pi. Furthermore, infection reduced tibia and femur mineralisation, which also persisted to d13pi. Reductions in measured variables were mostly independent of dose size, as was the level of parasite replication. The impact of infection was similar for S and F-line birds for all measured parameters, and there were no significant interactions between line x dose size on any of these parameters. In conclusion, our results suggest that line differences in productive performance do not influence host responses to coccidiosis when offered nutrient adequate diets.

The effect of infection with mixed Eimeria species on hematology and immune responses following Newcastle disease and infectious bursal disease booster vaccination in broilers

BACKGROUND

Coccidiosis is an important parasitic disease of chickens, causing high mortality and morbidity. This morbidity is believed to be correlated with altered population dynamics of blood cells and immunocompromisation.

OBJECTIVES

This study investigated the effects of mixed Eimeria species (viz., tenella, maxima, acervulina and necatrix) infection on hematology and immune responses following Newcastle disease (ND) and infectious bursal disease (IBD) booster vaccination in broilers.

ANIMALS AND METHODS

One-day-old broiler chicks (Hubbard; n = 200) were divided into two equal groups A and B. On day 16, group A was infected orally with Eimeria species (7 × 10(4) sporulated oocysts), whereas group B served as control. Both groups were analyzed for hematological parameters on post-infection days 6-8. Sera from both groups were analyzed for antibody titers against ND and IBD vaccines. On day 8 post-infection, lymphoid organs were also examined.

RESULTS

Significantly lower (P < 0.05) levels of plasma proteins, globular volume, hemoglobin concentration, packed cell volume, total erythrocytes, mean corpuscular volume and mean corpuscular hemoglobin concentration were found in infected chickens compared with non-infected control chickens. In addition, the infected group exhibited significantly increased (P < 0.05) numbers of different leukocytes. Infected chickens also showed significantly lower antibody titers against ND and IBD with decreased relative organ weights of all lymphoid organs except spleen.

CONCLUSION AND RECOMMENDATIONS

Mixed species of Eimeria adversely affected the hematology and immune efficiency of broilers. Thus, inexpensive immune potentiators and hemotonics along with appropriate anti-coccidial medications are suggested to avoid the complications and subsequent economic losses.

Guidelines for evaluating the efficacy and safety of live anticoccidial vaccines, and obtaining approval for their use in chickens and turkeys

These guidelines are intended to aid those engaged in poultry research in the design, implementation and interpretation of laboratory, floor-pen and field studies for the assessment of the efficacy and safety of live anticoccidial vaccines for immunization of chickens and turkeys against Eimeria species. In addition to efficacy and safety requirements, manufacture, quality control and licensing considerations are discussed. The guidelines do not address subunit vaccines comprising non-viable material, but many of the principles described will be relevant to such vaccines if they are developed in the future. Guidelines are available in some countries for avian vaccines of bacterial or viral origin but specific standards for anticoccidial vaccines in poultry have not, as far as we know, been produced. Information is provided on general requirements of registration authorities (based upon regulations applicable in the European Union and the USA) for obtaining marketing authorizations for vaccines. These guidelines may assist poultry specialists in providing specific information for administrators involved in the decision-making process leading to registration of new vaccines, and are intended to facilitate the worldwide adoption of consistent, standard procedures.

Cross protection studies with Eimeria maxima strains

The purpose of this study was to determine whether differences in fecundity of Eimeria maxima isolates were related to their abilities to elicit cross-protective immunity. Immunizations were initiated by low-dose gavages of sporulated oocysts to day-old broiler chicks under conditions that allowed parasite recycling, and chickens were challenged with homologous and heterologous strains. Immunization efficacies were measured using a protective index calculated from weight gain, gross lesion score, plasma carotenoid, and NO2- + NO3- data. A 4x4 cross- immunization study of four E. maxima strains (designated A-D) showed that strain A, which displayed the lower fecundity, provided no cross-protection against the other three strains. Following several maintenance passages, the fecundity of strain A was increased to that of strain C, and infection with strain A oocysts was able to provide cross-immune protection against challenge with strain C. This study indicates that parasite fecundity is important in providing good immune stimulation, and should be carefully monitored when characterization of the unique immune potentials of Eimeria strains is undertaken.