Expression of acquired immunity to gastrointestinal parasites usually breaks down during the periparturient period, which is characterised by an increased worm burden and nematode egg excretion. It is believed that this breakdown of immunity may have a nutritional basis, and that by reducing nutrient scarcity the lactating animal will be able to reduce her worm burden. Therefore, the aim of this thesis was to carry out four experiments to investigate the potential use of metabolisable protein as an alternative way to control gastrointestinal parasitism in periparturient animals. A lactating rat model was used to address this issue as lactating rats exhibit a breakdown of immunity to the gastrointestinal nematode Nippostrongylus brasiliensis. The first experiment (chapter two) aimed to verify that a reduction in worm burden is indeed related to changes in nutrient supply and not associated with changes in the gut environment. This was achieved by manipulating nutrient (litter) demand whilst nutrient supply was maintained constant. The results showed that the periparturient breakdown of immunity to N. brasiliensis (measured by a reduced worm burden) was sensitive to changes in nutrient demand and that these effects were independent of changes in the gut environment. The second experiment (Chapter Three) tested the effect of increased protein supply or reduced protein demand on the resistance to parasites in lactating rats whilst energy intake was kept constant. Under these conditions effects of protein supply could not be confounded with effects of any nutrient or energy intake. The results supported the view that under a restricted feeding regime, breakdown of immunity to N. brasiliensis (measured by a reduced number of eggs in the colon content) was sensitive to changes in protein scarcity. Following on from this, the next experiment (Chapter Four) assessed the effects of a gradual increase in protein supply on resistance and immune responses to N. brasiliensis in lactating rats. It was shown that as protein contents of the diets progressively increased, the number of worms and eggs present in the colon decreased. Although we found that differences in protein supply affected parasite burden, we found no affects of protein supply on local immune responses. This may have been due to the single sampling point used. Therefore, the objective of the last experiment (Chapter Five) was to assess temporal effects of increased protein supply on resistance and immune responses to N. brasiliensis. In agreement with previous experiments, the results showed that an increase in protein at times of protein scarcity improved resistance to N. brasiliensis, illustrated by a lower number of nematode eggs in the colon. The results also showed that local immune responses such as immunoglobulin levels (IgA, IgE & IgG2a), RMCP II levels and goblet cell counts were affected by differences in protein supply at various time points post secondary infection. The potential application of using a lactating rat as a suitable model to fully understand the underlying immunological basis of relaxation in immunity during the periparturient period and its sensitivity to nutrient scarcity is considered in the General Discussion (Chapter Six).

Interactions between two digenean parasites, Diplostomum spathaceum and Schistosoma mansoni , and their respective intermediate snail hosts, Lymnaea stagnalis and Biomphalaria glabrata , were investigated. D.spathaceum infections in juvenile L.stagnalis became patent 9 to 10 weeks post-infection and inhibited initiation of host oviposition. Adult L.stagnalis resisted infection with D.spathaceum . Both juvenile and adult B.glabrata were susceptible to S.mansoni and the infections become patent 5 weeks after infection. B.glabrata infected as juveniles failed to begin egg-laying whilst those infected as adults showed a dramatic reduction of oviposition 4 weeks post-infection, i.e before the onset of patency. Infection with D.spathaceum , but not S.mansoni , resulted in the appearance of three polypeptides (68.3, 40.8 &'38 34.5 kDa) in snail serum. The additional peptides were not directly related to failure of snail reproduction and are probably of parasite origin. Reproductive failure of infected snails was linked to the later stages of cercarial development by a method developed to manipulate infections using the anthelmintic, praziquantel. D.spathaceum and S.mansoni infections were suppressed in their snail hosts following oral treatment with praziquantel. Praziquantel was selective for cercariae and inhibited cercarial shedding of both digenean species for approximately 5 to 6 weeks before recovery. In mature B.glabrata , harbouring 7 week-old infections of S.mansoni , suppression of cercarial shedding was accompanied by temporary recovery of reproduction. Snail fecundity was halted once more 2 weeks prior to resumption of cercarial shedding. Reproductive recovery depended upon the state of infection and maturity of the host at infection. Failure of D.spathaceum to infect adult L.stagnalis was attributed to the more developed and therefore more competent internal defence system of adult snails. Infection of juvenile, immunologically immature, L.stagnalis with D.spathaceum resulted in several changes in the snail immune system and infection seemed to prevent normal development of several facets of snail immunity.

No description available.

Mortality in eiders (Somateria mollissima) on the Ythan estuary, Aberdeenshire, and elsewhere, has been claimed to be associated with the spiny-headed worm, Profilicollis botulus. Eiders acquire the disease by eating crabs (Carcinus maenas) infected with the cystacanth stage of the parasite. A detailed quantitative study was undertaken to elucidate some of the factors which control the abundance of the parasite in its intermediate and definitive hosts. During 1979-81 the P. botulus burdens in eiders and crabs were regularly monitored. Eiders were either taken alive off the estuary, or off the nest, and sacrificed, or found dead on the shore line. Crabs were caught in traps at two sites on the estuary. Female P. botulus in eiders were assigned to one of five categories according to the state of development of the eggs contained within their pseudocoelom. To estimate the size range and numbers of crabs eaten by eiders, crab chelipeds, or parts of chelipeds, were recovered from eider faeces collected monthly from roost sites. Regression equations relating certain cheliped dimensions to crab carapace width were used to estimate the size range eaten. The numbers of chelipeds per unit weight of faeces, equivalent to the quantity excreted per eider per day, was used to estimate the numbers of crabs eaten. Daily P. botulus infection rates in eiders were calculated by combining the quantitative data on crab intake by eiders with the cystacanth burdens in the crabs. Captive eiders, reared from eggs, were used to determine the age, days post-infection, of the five categories of female parasites. These development times were combined with the burdens found in the eiders sampled from the estuary to produce a static life-table of the mortality of female P. botulus. From this, estimates of the parasite's establishment rate, mortality rate and lifespan were obtained.

No description available.

The ability of Leiophron uniformis (Gahan) to parasitize 4 Lygus spp. was determined. While L. uniformis readily attacked Lygus hesperus (Knight), L. lineolaris (Palisot de Beauvois), L. elisus Van Duzee, and L. desertinus Knight, only 6.7% of the L. lineolaris attacked were parasitized compared to 84-87% parasitization of the other species. Two factors were found to cause the low rate of parasitism of L. lineolaris. L. uniformis oviposited in (accepted) few of the L. lineolaris nymphs attacked and most eggs found were encapsulated by the host. Nymphs less than 48-hr old were readily parasitized because they were accepted by the wasps and the hosts encapsulated few of the parasitoid eggs. As nymphal age increased, parasitism dropped rapidly as the acceptance of the host decreased and the host's encapsulation ability increased. Different strains of L. lineolaris were found to differ greatly in their susceptibility to parasitism, their ability to encapsulate, and their acceptance by the parasitoids. A host strain from Arizona was very resistant to parasitism, whereas a strain from Delaware (NJLBR) that had been in culture for 7 years was easily parasitized. The NJLBR strain had no encapsulating ability and it was readily accepted by L. uniformis. A recently established host strain from Delaware (DELBR) encapsulated 23-27% of the parasitoid eggs while an Arizona strain (FILBR) encapsulated 66-76% of the eggs. The DELBR nymphs were accepted in 42-43% of the attacks while the FILBR nymphs were accepted in only 5-14% of the attacks. Delaware and California parasitoid strains did not differ in their acceptance of L. lineolaris or in their ability to resist encapsulation. Rearing L. uniformis for only 1 generation on L. lineolaris did not precondition the wasps to accept that species as a host in preference to L. hesperus. L. uniformis, which had been reared on L. lineolaris for 5 or more generations, did accept that host 2.5 times as often as wasps reared on L. hesperus. The parasitoids did not known any increase in resistance to encapsulation even after they had been reared on L. lineolaris for 11 generations.

No description available.

No description available.

No description available.

No description available.