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Title: Observations on the pathogenicity and immunogenic potential of normal and X-irradiated oocysts of Eimeria tenella in the domestic fowl (Gallus domesticus)
Author: Hein, Helen E.
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1964
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Abstract:
The pathogenic effects of the protozoan parasite Eimeria Tenella were studied in the domestic fowl, Callus Domesticus. Observations were then made on the effect of X-irradiation on the pathogenicity and immunogenic potential of the sporulated oocysts of Eimeia tenella. The findings established that severity of an infection can be determined satisfactorily by consideration of the haemoglobin concentration, the clinical signs and the mortality during the acute stage of the disease together with the results of the mean weight gains, the post mortem findings, and total oocyst production of the chickens during the patent phase of the infection. The pathogenicity of the parasite cannot be assessed accurately from consideration of only one aspect of the disease. The disease was reproduced with consistent pathogenicity by administration of a standard dose of sporulated occysts. A definite relationship was suggested between the age of the bird, the number of occysts inoculated and the severity of the disease, although no significant difference in susceptibility to infection was shown which could be directly attributed to the age of the chicken. Marked differences were recorded in the severity of the disease after administration of does ranging from 1.000 to 500.000 oocysts per bird. The administration effects of relatively low levels of infection were reflected in the less satisfactory weight gains and the high total oocyst production during the patent phase of the disease. No significant variation in mortality or haemoglobin concentration was recorded between birds given doses ranging from 32,000 to 500,000 oocysts, the increasing, the lower weight gains and the marked fall in oocyst production. The reproductive potential of the parasite decreased significantly as the dose of oocysts was increased, suggesting correlation with the severity of the caecal lesions at high levels of infection. A significant relationship between the feeding regime before infection and the subsequent pathogenicity of the parasite was demonstrated, the most severe pathogenic effects occurring in birds given free access to food before infection. A significant difference in susceptibility to infection was demonstrated between Broiler and Leghorn Type Hybrid chickens, the severity of the disease being greater in the Leghorn Hybrid chicks. The pathogenic effects of standard dose of oocysts was influenced by the diet of the experimental chickens. The influence of the ration also varied significantly in the Broiler and Leghorn Type Hybrid chickens. Resistance to reinfection was conferred by single dose of sporulated occysts but this method of immunisation was contraindicated by the pathogenic effects of the parasite during vaccination. Observations made on levels of X-irradiation, selected on an arbitrary basis, ranging from 5,000 Roentgens to 80,000 Roentgens demonstrated significant differences between the pathogenicity of normal and irritated oocysts. Exposure to 5,000 Roentgens reduced morbidity and haemorrhage during the acute phase of the disease, attenuation being marked after exposure to 7,500 Roentgens. The findings demonstrated conclusively that sporulated oocysts must be exposed to a minimum dose of 10,000R to avoid deterimental effects during immunisation, the only evidence of infection being shown by the production of a relatively small number of oocysts were recorded, while no indication of infection was indicated after administration of oocysts exposed to levels of x-irradiation ranging from 25,000R to 80,000R. Observations on susceptible chickens reared with vaccinated birds on deep litter suggested that the oocyst production associated with immunisation does not introduce a cycle of continuous reinfection leading to the build up of a heavy challenge infection under intensive management. No significant variation was recorded in the oocyst production after vaccination between chickens given one or two does of vaccine. Significant differences were demonstrated I the effect of certain levels of X- irradiation on the immunogenic potential of the oocysts. The highest level of immunity was conferred by ocysts exposed to 10,000 R.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.776732  DOI: Not available
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