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The host- parasite relationship of a hybrid strain of domestic rabbit, Or ctola,gus cuniculus, and the ruminant nematode Trichostronrylus colubriformis was studied. The main techniques used to follow the infections were faecal egg counts, live weight gains, worm counts at autopsy, haematology and serum biochemistry. The newly -weaned rabbit was found to be a moderately good host for the nematode. Most animals developed patent infections and worm egg production was of varying size and duration. The sex of the host appeared to have little influence on the numbers of worms establishing or on the subsequent course of the infections. Adaptation of the parasite to the rabbit by successive passage through 16 senerations indicated that total egg production by the worms increased over the first three generations, dropped in the fourth, rose up to the seventh and then stabilised. Further evidence for such adaptation was provided by an experiment in which it was shown that the total egg production by a fifth generation rabbit -adapted strain of the worm was significantly greater than that of a sheep strain. Doses as high as 15,000 infective larvae of either strain of the worm did not appear to be very pathogenic in the rabbit and acute disease was produced on only three occasions. The most consistent clinical sign was anorexia. Most animals showed only transient clinical signs of disease or none at all and a true chronic trichostrongyliasis as described in sheep and goats was never seen. An age -related resistance was observed in rabbits aged 13 weeks and older and this was manifested mainly by a reduction in the numbers of worms reaching the adult stage. Most newly- weaned rabbits eventually developed acquired resistance to a primary infection and expelled their worm burdens apparently in a self -cure reaction. _bout this time a transient eosinophilia often accompanied by a basophilia occurred in the peripheral blood. After this the rabbits were resistant to a challenge infection which they ejected within 12 days. A similar blood response was seen during the first 11 days of this infection. However a minority cf rabbits failed to self -cure after their primary infections and these rabbits were not then resistant to a challenge infection. No blood response was observed in these or in worm -free controls. during a primary infection. Experience of primary infections, chemically abreviated after 12 days by thiabendazole did not appear to give the rabbits the ability to resist a challenge infection but the results were inconclusive because of interference by age resistance. No variation from the normal was observed in the serum proteins of rabbits infected with the nematode. The current theories relating to the function of the eosinophil and basophil leucocytes of mammals are discussed and possible roles for these cells in the mechanism of the self -cure reaction to T.colubriformis in the rabbit are suggested. It is pointed out that the rabbit -T.colubriformis host- parasite relationship affords a useful system for studying the phenomenon of self-cure. It is also noted that the pathogenicity and immunology of T.colubriformis infections in the rabbit are different to those in the guinea pig.

A study has been made of the serological responses occurring in domestic animals as a result of natural infestation with helminth parasites. The helminth infestations studied were those of Fasclola hepatica. Cysticereus bovls. Ascaris lumhrlcoides, Dlctyocaulua vlviparus and Trichlnella spiralis, F.HEPATLCA. The serological response, as indicated by the precipitin test, in F.hepatlca infestation was most marked when the immature parasites were in their migratory phase. Thereafter the precipitin antibody level became lower Specific complement fixation antibodies were demonstrated in the sera of only one infested animal. This was indicative that the complement fixation technique was unsuitable for the demonstration of antibodies in P,hepatica infestation. Alcoholic extracts of the parasite were found to give varying degrees of r.on specific complement fixation with sheep sera, irrespective of F.hepatica infestation. The miracidia of F.hepatlca were observed to suffer a lethal effect when placed in sheep serum. Complement was necessary for the reaction. Hypersensitivity, demonstrable by an JLOD Intradermal test, was evident in a large percentage of animals infested with F.hepatica. In some cases this hypersensitivity was passively transferable, "by means of serum, to a non sensitive animal. Local skin desensitisation could "be produced to a marked degree hut generalised skin desensitisation was less obvious when large quantities of antigenic material were administered. G.BOVIS. Precipitin antibodies were demonstrated in the sera of animals which showed multiple eysticerci in the musculature. When only a few (1 or 2) eysticerci were present a serological response was frequently absent. Polysaccharide solutions of the parent parasite, T. saglnata produced precipitin reactions with the sera of animals infested with P.hepatica only. This was thought to be due to an isoagglutinin like producing antigen present in both T.saginata and hepatlca. Animals infested with F.hepatica produced hypersensitive skin reactions to extracts of C.bovls. A common allergen In the two parasites was thought to be responsible. A.LUMBRIOOIDEA. Precipitin antibodies were demonstrated in the sera of pigs. These were found to bear no relationship to the presence of mature A.lumbricoides In the intestine. They did, however, show a relationship to the degree of chronic focal interstitial hepatitis. Hypersensitivity to extracts of A.lumbricoldes was evident in the majority of swine. This was similar to the precipitin reaction, in that it was related to the degree of chronic focal interstitial hepatitis but not to the presence of intestinal forms of A.lumbrlcolfles. D.VIVLNARUS. The majority of cattle examined showed skin hypersensitivity to D.vivlparue extracts. This hypersensitivity was most evident in the age group 2-j? to 3-j years. The hypersensitivity demonstrated occurred in the absence of parasites. Intestinal helminths did not influence the hypersensitive state. Hypersensitivity was demonstrated in sheep undergoing a sub-clinical infestation with 13.filaria Infestations with other lung worms produced a hypersensitive state which could be demonstrated by D.filaria extracts. This was indicative of a group reaction. T,SPIRALIS. Hypersensitivity to extracts of T.spiralis was demonstrated in only 5# 4$ of swine. Only 0.91 of swine showed marked reactions. Since these occurred in animals possessing marked hypersensitivity to A.lumbrlcoidea it was concluded that a strong hypt rsensitivity to A,lmribrlcoltl.es could sensitise pigs to extracts of T.spiralis. Infestations with T.trlchiura did not produce hypersensitivity to T.spiralis extracts. The use of animals at an abattoir afforded the opportunity to correlate the serological findings with post mortem evidence of infestation. Since the lack of helminth eggs in the faeces does not necessarily indicate absence of helminth infestation the post mortem examinations carried out gave a more complete picture of the parasitic burden. As a result it was found that light infestations or pathological evidence of helminth infestation could be correlated with the serological findings (vide P.hepatica. C.bovls and A.lumbrlcoldes). If faeces examination had been the sole criterion of evidence of infestation no correlation between serological findings and infestation would have been evident and false conclusions may have been drawn.

This study was financed by the Ministry of Overseas Development, and was carried out in two parts. The first part involved a year of preliminary work in the Department of Zoology, at the University of Edinburgh, and covered the first exploratory enquiries into standards of development and survival under laboratory conditions. The second part was conducted while the writer served a 30-month tour of duty at the East African Veterinary Research Organisation, Muguga, Kenya, and during this time the initial tre x of the studies was followed up while making a concurrent examination of development and survival under near - natural conditions at two contrasting outside sites of typical East African character. The studies carried out on the engorgement of Rhipicephalus appendiculatus on rabbits, cattle and various other hosts revealed no evidence of host specificity. In only two aspects were variation in feeding performance directly attributable to factors within the tick. First, a lack of vigour, produced by delaying application to the host for prolonged periods after emergence, resulted in a decline in the proportion of successful engorgements yielded by a given number of ticks applied. Second, the completion of engorgement by adult females was shown to be completely dependant upon mating. An initial impression that a greater degree of infestation resulted in a shortening of the engorgement period was not substantiated, and it was concluded that this impression arose from a pre-attachment elimination of the slower-to-attach proportion of the ticks applied. The character of individual host response appeared to be one of the principal factors in the variation in tick feeding performance. It was established that successive applications of R. appendiculatus to rabbits produced a prolongation of the engorgement period; a decline in the number of successful engorgements and in the degree of repletion; and an increasing severity in host reaction. The rate of development was shown to be determined by temperature and that, provided that the ticks survived, the level of humidity had no influence on this aspect. There was no evidence of any diapause mechanism in any stage of R. appendiculatus. No development of any sort was recorded at 9?C or below, and sustained temperatures of 4?C were lethal to engorged instars. Observations at the two outside sites showed that only one life cycle could be completed each year at Muguga, whereas the rate of development at Kedong would permit two life cycles to completed each year in conditions of high humidity. Survival was shown to be governed by water relations. In the unfed instar, this was a straightforward relationship with saturation deficiency, so that the effects of low humidity were more rapidly lethal at higher temperatures. Thus, at 20% RH, all unfed instars survived for roughly twice as long at 18 ?C as they did at 25 ?C. There was some indication that, in proportion to their size, unfed adults were more adapted to dry conditions than immature instars. Eggs were very sensitive to aridity, and no hatching was observed in egg batches which had been exposed to 40% RH for periods longer than 14 days - at any temperature. Unfed ticks were shown to regain moisture from the atmosphere. Though low humidities were lethal to engorged instars, the relationship with saturation deficiency was by no means as clearly defined as with unfed instars. Observations at the two outside sites emphasised the important influence that the physiognomy of grass cover has upon the survival of ticks. It was apparent that the life cycle of R. appendiculatus could be completed at Muguga no ratter at what season of the year it was commenced. At Kedong, on the other hand, it was apparent that the survival of a R. appendiculatus population would depend upon whether or not conditions were moist enough to allow the hatching of wet-season eggs. A comparison between the survival of ticks free on the herbage at Kedong and the survival of ticks confined in containers within the same grass cover indicated the crucial influence which transpirational microclimates may have on the survival of the species in such marginal areas. This indication was to some extent reinforced by results obtained with an environmental model constructed for studies in the laboratory. The findings of the study are discussed in relation to observations made during previous field experience. An example is given of a R. appendiculatlis population increasing under a system of improved grassland management because the timing of grazing rotations coincided favourably with the development rate of the species. Some aspects of traditional grass- burning regimes are discussed in conjunction with associated vegetational successions. Although not in fact used for the purpose for which it was devised, a successful and useful system of labelling ticks with the radio-isotope Cerium-144 is described in an appendix to the study.

1. A review of the protozoa reported from animal-parasitic helminths is first made. 2. A detailed, description is given of the morphology of the microsporidian found in Moniezias in this country. 3. This parasite has been shown to be identical with Nosema helminthorum Moniez, 1887, Plistonhora helminthophthora Labbe, 1899, and Nosema bischoffi Weiser, 1951. The valid name for this organism therefore is Nosema helminthorum Moniez , 1887. 4. A 'pre- metachromatic granule' appearing in the sporont stages, and the metachromatic bodies of the mature spores have been studied from the point of view of their chemical nature. 5. The spore wall of this parasite has been proved to consist of chitin. 6. The mode of emergence of the sporoplasm has been shown to occur in a manner hitherto unobserved in microsporidia. 7. N. helminthorum has been shown to infect Hymenolepisnana of mice and rats, under experimental conditions. In three tapeworms, this microsporidian undergoes a similar development to that in the Moniezias, but the spores assume a smaller size. 8. A Taenia aaginata of man was also infected with this organism but only early division stages were obtained. 9. Two oribatid mites Xebillus tegeocranus and Ceratoppia bipilis were fed on the spores of N. helminthorum, and the cells of the midguts of these mites became infected. The spores appearing in the mites were smaller than those in the mice worms. 10. The significance of the experinmental infections has been discussed, and the life-cycle of N. helminthorum has been described from them. 11. The host distribution and the geographical distribution of N. helminthorum and its host-parasite relationships have been considered. This parasite is shown to be non-pathogeneic and the question of its host-restriction has been discussed. 12,. A paraneoxenous association between Giardia ovis and Nematodirus fillicollis of sheep has been discussed. 13. Finally a description is given of a new genus of schizolregarine and a new species of microsporidian, from the fat body of the flour beetle Tribolium castaneum. The oöcysts of the schizogregarine were used in some of the experimental infections of Hymenolepis nana.

Studies have been carried out on protozoan parasites of freshwater fish from the Amazon region of Brazil, and the British Isles. Special emphasis has been given to aspects of the taxonomy and life - history of species of the order Myxosporida. In section 1, full descriptions are given of Myxosporida from Brazilian and British fish. The Brazilian species include three of the genus Myxobolus from piranha (Serrasalmus sp, and S. rhombeus) and tambaqui (Colossoma bidens), and Agarella gracilis from lungfish (Lepidosiren paradoxa). In British fish, Myxobolus species are described from roach (Rutilus rutilus), gudgeon (Gobio gobio) and dace (Leuciscus leuciscus); Myxidium species are described from roach, gudgeon and salmon (Salmo salar). The similarity of the genera Myxobolus and Myxosoma is noted, and the difficulty of distinguishing them is pointed out. From the result of histochemical tests for glycogen In spores of selected species, it is proposed that the two genera should be synonymised as Myxobolus. Accounts are given of attempts to establish infections of Myxidium in Myxidium - free roach and salmon. The negative results of these experiments suggests that myxosporidan spores may need to undergo some form of further development outside the host before becoming infective to a new host. Check - lists are given of species of Myxobolus, Myxidium and, recently described Myxosoma species. In section 2, other protozoa, including two species of Microsporida, one coccidian species, and Rhabdospora thelohani are described and discussed.

Between August, 1960 and December, 1963, more than five hundred and seventy-six birds representing twelve orders, thirty families and seventy-nine species were examined for helminth parasites in the County of Pembrokeshire. The overall infection was 61.4% and only twelve species were uninfected. The material recovered consisted of eighteen species of trematodes, forty-three species of cestodes and seventeen species of nematodes. Two new species are described, Choanotaenia larimarina Elce, 1962 and Gymnophallus numenii sp. nov. There are thirty-seven new host records for western Europe. Three species are new to Europe and five species are new to Britain. Forty-four new host records for Britain are recorded and thirty-two species are recorded for the first time in Wales. The incidence of helminths is related to the host's diet and the ecological background. A survey was made of the helminths in domestic birds in Pembrokeshire, both by faecal examination and by post-mortem. The most common parasites were the nematodes Haterakis gallinarum (Schrank, 1788) - 73.9%, Capillaria obsignata Madsen, 1945- 45.05%, and Asacaridia galli (Schrank) 1788) - 35.1%. The results are compared with recent surveys by other workers and differences are due to this work being based on field tests and not the more usual laboratory postmor toms. Infective eggs of the above species were fed to selected wild birds, principally rooks (Corvus frugilegus L. ) and jackdaws (Corvus nomedula L. ), which were maintained on a normal and on a Vitamin A deficient diet. Wild birds do not act as hosts to poultry helminths and their significance as disseminators is limited to infected droppings. Dissemination of eggs on feathers and claws is difficult to estimate. The life cycle of Capillaria resecta (Dujardin, 1843) was attempted to assess Madsen' s suggested synonymy with c. anatis (Schrank, 1790). Circumstantial evidence indicates that the species are not synonymous.

This thesis consists of four parts, and is based on a survey of the helminth parasites of Hertfordshire birds. Part I. (Section 1), deals with four species of trematodes found in Hertfordshire birds, Lyperosomum longicauda Rudolphi, 1809, Lutztrema monenteron Price & McIntosh, 1935, Dicrocoelioides petiolatum Railliet, 1900 and Brachylaemus fuscatus (Rudolphi, 1819) var. nicolli (Witenberg, 1925). 14 now host records and 1 new record for this country are confirmed. Part I. (Section 2), A new trematode, Reesella doviensis gen, ct sp. nov., from the Oystercatcher is described. (Reprint from J. Helminth. , 30, 81-86. ) Part II deals with sixteen species of cestodes recovered from Hertfordshire birds. Descriptions are given of Choanotaenia unicoronata Fuhrmann, 1908, Dilepis undula Schrank, 1788, Anomotaenia constricta Molin, 1858, A. borealis. Krabbe, 1869, Paricterotaenia parina Dujardin, 1845, Anonchotaenia globata von Linstow, 1879, Hymenolepis serpentulus Rudolphi, 1810, H. stylosa Rudolphi, 1809, H. amphitricha Rudolphi, 1819, H. farciminosa. Goez, 1782, H. fringillarum Rudolphi, 1809, Aploparaksis dujardinii Krabbe, 1869, and Raillietina (Skrjabinia) bonini Megnin, 1899. Three new forms are also described, Anomotaenia verulamii n. sp. from the mistlethrush, Paricterotaenia albani n. sp. from the starling and P. mariae n. sp. from the robin. A total of 13 new host records and 22 new records for this country are confirmed. Part III, (Section 1). deals with seven species of nematodes found in Hertfordshire birds. Descriptions are given of Porrocaecum ensicaudatum Zeder, 1800, Syngamus trachea Montagu 1811, S. merulae Baylis, 1926, Capillaria ovopunctata von Linstow, 1873, C. resecta Dujardin, 1845, C. colubae Rudolphi, 1819, and C. exilis Dujardin, 1845. One new host record and two new records for this country were confirmed. Part III. (Section 2), Descriptions are given of nine further species of Capillaria recovered from birds in Great Britain. They are Capillaria anatis Schrank, 1790, C. contorta Creplin, 1839, C. logicollis. Mehlis, 1831, C. nyrocinarum Madsen, 1945, C. obsignata Madsen, 1945, C. retusa Railliet, 1895, C. spinulosa von Linstow 1803, C. tenuissima Rudolphi, 1803, and C. triloba von Linstow, 1875; Four new host records and ten new records for this country were confirmed, Part IV. The results of a survey of the helminth parasites of Hertfordshire birds are tabulated. A total of 571 birds representing 22 species were examined. Of the birds examined 396 (69.3%) were found to be infected with helminths. During the survey 28 new host records and 25 new records for this country were confirmed. A total of 32 new host records and 35 new records for Great Britain are recorded in this thesis.

The respiratory pigments and the amino acid composition of planorbid snails which act as intermediate hosts for human schistosomes were compared with those of insusceptible snail species. The absorption spectra of haemoglobins from different snail species were similar to one another and closely related to those of mammalian haemoglobins. The occasional appearance of additional absorption bands suggested that substances other than the pigment protein appear infrequently in snail blood. Electrophoresis showed that, in general, the respiratory pigment was the only protein present in the blood. The mobility of haemoglobin and haemocyanin pigments was not affected by change in pH, and the rates of movement of haemoglobins from twelve different snail species were the same. Other proteins occurred occasionally in the blood of most species examined, and these additional fractions seemed to form a common pattern in four species. The factors determining their appearance were investigated. No qualitative differences were observed in the amino acid content of haemoglobins from different snails, but quantitative differences were demonstrated. The free amino acids of snail blood were in low concentration but were qualitatively similar in three snail species, which also contained similar bound and free amino acids in the digestive glands and ovotestes. Australorbis glabratus, however, differed from Planorbarius corneus and Lymnaea stagnalis since free methionine was found in its anterior tissues. The methionine was not present in glabratus snails infected with Schistosoma mansoni, and they contained lower concentrations of free amino acids than uninfected snails. It was shown that methionine was one of the seventeen amino acids identified in the protein of S. mansoni cercariae.

The present investigation has been devoted to parasitic protozoa of freshwater fish of Great Britain, Europe and India.

The thesis reports on investigations during 1967-69 of endoparasitism in Simulium ornatum Mg., with particular reference to the larval stage, from the English rivers Lea (hertfordshire) and Tilling Bourne (Surrey). Methods included record of visual evidence of infections, dissections and smears of fresh material, and histological examinations of all material by light, and, by arrangement with Dr R. G. Bird of the E. M. Laboratory, L. S. H. & T. M., by electron microscopy, in the case of certain microsporidia. In preliminary observations no parasites were observed in either pupal and adult stages of Simulium ornatum; the study is concerned with larval parasites, of which several kinds were found. The Order Microsporidia of the protozoan Class Cnidosporidia was well represented by 3 genera, Thelohania, Plistophora and Nosema of the Family Nosematidae. Pseudocysts from two forms of Thelohania, and one form of Plistophora, examined by electron microscopy, revealed the fine structure of sporogonic stages of the sporont and, of the spore of Thelohania and, less intensively, of Plistophora. Microsporidian spore size has been accepted by several investigators, with some controversy from others, as a major criterion for specific classification. In this connexion, spore measurements carried out for Thelohania infections, from S. ornatum were, by statistical and graphical analysis, recognisable as composing four separate forms (A-D), with a minor form also, form E on the basis of spore shape. All Thelohania infections of larvae from the River Tilling Bourne are of form A, having the smallest spore dimensions. The other four forms, "B", "C", "D" and "E", occurred in Simulium larval populations of the River Lea. In the case of Plistophora another criterion in classification, in addition to spore dimensions, was notable, viz. the number of spores produced by the sporont. Two forms of Plistophora were thus distinguished. Nosema infections were of one kind only. All these forms, found in the simulium ornatum larvae, are new records for microsporidia in the British Isles and, on taxonomical features different from those of other microsporidian parasites described from simuliidae from elsewhere. Histological examination also revealed a light infection of a microsporidia-like organism in the Gut epithelial cells of Simulium ornatum larvae from the Tilling Bourne only. Fungal infections were also common. The pathogenic fungi, Coelomycidium sp. of the Order Chytridiales, occurred [missing page] larvae revealed 3 distinct larvae generations of Simulium ornatum per year, and the occurrence and abundance of the several parasites was noted in respect to these different larval populations. Laboratory culture of "clean" material was desirable for the transmission experiments undertaken for Thelohania, and for Coelomycidium. To obtain such a culture, it was necessary to affect both copulation of Simulium ornatum adults and to induce females to blood-feed. Repeated attempts at artificial insemination proved unsuccessful; blood-feeding was successful with only a low percentage of adult females. Failing to establish a "clean" culture resort was made to the use of apparently uninfected wild-caught larvae for experiments on the transmission of infections, but without success in inducing hatching of Thelohania spores or propagation of Coelomycidium ingested by Simulium larvae. It remains still obscure whether or not, in nature, the Thelohania infections are transmitted transovarially through infected adults emergent from infected larvae; and the mode of transmission of Coelomycidium is also not determined. While the pathogenic parasites found must have controlled larva densities in the two streams, much remains to be studied and understood about their biology, transmission and cultivation before their application in biological control could be envisaged.