The main objective of this study was to investigate the effect of concurrent parasitic and viral diseases on the immune response by analyzing how the concurrent infections influence on each other in the period from vaccination till slaughter. This was done using the antibody response towards ND vaccine virus in chickens with and without endoparasites as an indicator for changes in the humoral response and changes in differential and total counts of the white blood cells as an indicator for changes in the cellular immune response.
Poultry production is a growing and economically important industry and therefore the interest in improving the production results through improved health of the poultry is great. Investigations have shown that concurrent infections in free range chickens is very common (Pandey, 1992) and since Newcastle Disease and endoparasites are two very common infections in free range poultry these would be obvious to investigate in a concurrent perspective. Furthermore, lack of efficiency of vaccines against ND has been reported (Spradbrow, 1988) and previous investigations have indicated that infection with endoparasites can reduce the immune response towards ND vaccines (Bhopale et al., 1998; Hørning et al., in press). The present experiment has given some indications about the immune mechanisms in concurrent infections in chickens but with the methods used no conclusions can be drawn regarding the involvement of Th1/Th2 responses. We conclude that there is a significant reduction in NDV specific antibody production post vaccination in individuals with endoparasites compared to anthelmintic treated birds and that the level of endoparasite infection is also important.
The results shows that individuals with concurrent infections has a significantly lower number of lymphocytes than the control birds and that the birds infected only with virus show a significantly higher number of lymphocytes than the birds infected with parasites alone or with concurrent infections. The granulocyte number was significantly higher in the birds with concurrent infections than in the control birds and further more the birds infected with virus alone had a significantly lower granulocyte number than the individuals infected with parasites alone and the birds with dual infections. Furthermore, females had a significant lower lymphocyte count than the males and in the highly infected groups there was a trend that females had a higher granulocyte count compared to the males in the same group. The vaccinated birds were having a significantly higher monocyte count compared to the non-vaccinated but no significant connection was found between number of monocytes and parasite infection or concurrent infections. The total WBC count did not have any significant connection neither in concurrent infections nor in single infections. The anthelmintic treated chickens had a higher weight gain ratio than the non-treated chickens. Heavy infection level (level 2) of endoparasites has an effect on the weight gain and even a mild infection level (level 1) apparently has a depressing influence on the end weight. The end weight among birds with different parasite infection levels showed to be significant.
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