Biochemical and immunological studies on some helminth diseases of domestic animals

The work carried out in this thesis was concerned primarily with immunological studies on Fasciola hepatica infections using the rabbit as an experimental animal, and Dictyocaulus viviparus infections in the bovine. Experiments on the anaemia associated F. hepatica infections in the rabbit are also reported. The thesis is divided into four sections and the main results are summarised as follows: Section I Immunity studies on Fasciola hepatica. 1. Prior immunization of rabbits with the proteins of Fasciola hepatica resulted in a retardation in development of the parasites without a significant reduction in the numbers which developed from a challenge with 50 cercariae. The F. hepatica proteins were highly immunogenic as they elicited a marked antibody response in the sera of the immunized rabbits. 2. Prior immunization of rabbits with a polysaccharide fraction of F. hepatica resulted in one experiment in a significant reduction in the numbers of flukes but in a second experiment only in a retardation of development of the flukes. In both experiments the rabbits were challenged with 50 cercariae. Section II Studies on the anaemia produced in rabbits by Fasciola hepatica infections 3. A measurement of the amount of blood lost by fluke-infected rabbits was made using 32P-labelled red cells and 151I-labelled plasma albumin. The amount of blood present in the flukes was calculated by a comparison of their radioactivity with that of the circulating blood at the time of autopsy. The calculated blood loss per day was consistent with the observed degree of anaemia. 4. The simultaneous use of 32P-labelled red cells and 151I-labelled plasma albumin suggested that the flukes preferentially absorbed and/or retained 32P (labelled red cells) relative to 151I (labelled plasma albumin). 5. A preliminary experiment on the use of 51Cr-labelled red cells in estimating blood loss gave a higher value for blood loss per fluke than either 32P-labelled red cells or 151I-labelled plasma albumin. Section III Studies on Dictyocaulus viviparus infection in the bovine. 6. A study was made of the serological response and the degree of immunity in' calves resulting from primary and subsequent infections with the bovine lung-worm, Dictyocaulus viviparus. During the primary infection the level of complement fixing antibodies in the serum rose slowly and reached a peak after the bulk of the infection had been thrown off. At the second and third infection a typical secondary response was observed. Administration of the primary infection as a series of divided doses did not materially alter the serological response. The resulting immunity of both single and divided primary infections was very good. 7. Passive immunization of calves with serum from 'hyperimmune' donor animals resulted in a high degree of immunity when the calves were challenged with 4000 normal infective D. viviparus larvae. 8. Prior immunization of calves with whole worm antigens of D. viviparus did not produce a significant reduction in the numbers of worms which developed from a challenge infection with normal infective larvae. Section IV Studies on Dictyocaulus viviparus infection in the bovine. 9. Prior immunization of calves with D. viviparus larvae treated with a suitable dose of x-rays resulted in a very high degree of immunity. An immunization dose of 4000 larvae treated with 40,000r enabled calves to withstand a challenge of 4000 normal larvae. 10. Prior immunization of calves with 1000 D. viviparus larvae irradiated with 40,000r resulted in an acceptable degree of immunity without any marked clinical reaction during immunization. 11. The potential value of the irradiation method both in immunization against worm diseases and as an experimental tool in the study of helminth immunity is discussed, 12. An extension of this work has led to the first field vaccine against a parasitic worm