No description available.

A study was made of Nematodirus battus and Trichostrongylus colubriformis infections in New Zealand White rabbits. Experimental studies with N. battus were not continued because of the unsuitability of the parasite in the host. The distribution and development of T. colubriformis in the intestinal environment of N.Z.W. rabbits was studied at various dose levels. The clinical symptoms and pathology of infected animals was studied. The nature of the changes in gut histology and the architecture of villi was established at two sites in the small intestine by examining paraffin sections and studying the surface architecture of villi. The structure of epithelial cells was examined with the electron microscope and the cellular changes were correlated with observations made on enzyme activity using histochemical techniques. The general picture during infection by large doses of T. colubriformis was that of the intestinal malabsorption syndrome. The development of challenge infections given on days 12 and 20 of a primary infection was studied on day 8 post challenge infection. The dose level at which no marked clinical, pathological or immunological changes occurred was used as the dose for the anthelmintic selection study. Rabbits were dosed with a rat strain T. colubriformis and the anthelmintic thiabendazole was used as a selection pressure at 45 mg/body weight against the adult parasite population. After three generations of selection pressure the anthelmintic selected and non-anthelmintic selected povalations were compared in an anthelmintic titration. Following this experiment it was recognised that an anthelmintic resistant population was present. The criterion of resistance was established by studying uterine e-9 counts and the cell development stages in the two populations in anthelmintic treated and untreated rabbits. It was also noted that the response of sheep and rabbit strain T. colubriformis to the anthelmintic was different, the latter was less responsive to the drug. The role of the host in the modification of the parasite phenotype was considered.

This study investigated the epidemiology and taxonomy of Diplostomuni species in the deeper parts of the eye (DPE) of roach Rutilus rutilus (L. ), perch Perca fluviatilis L., ruffe Gymnocephalus cernua (L. ) and gwyniad Coregonus lavaretus (L. ) at Llyn Tegid, North Wales, and in the cranium of catfish Clarias gariepinus (Burchell, 1822) and the vitreous humour of Oreochromis species at Mindu dam and river Ruvu, Tanzania. At Llyn Tegid, two species of Diplostomum metacercariae, large and small forms, coexisted in DPE of perch, ruffe and gwyniad but only one, large forms, occurred in roach. Large forms were distinguished by their large size, oval body tapering at both ends and pseudosuckers at the level of the oral sucker. Small forms were distinguished by their smaller size, oval body with parallel sides and pseudosuckers occurring below the level of the oral sucker. The taxonomy of the two forms was not resolved even after obtaining adults from chickens. Tentatively, small forms keyed close to D. gasterostei Williams, 1966 and large forms to D. volvens Nordmann, 1832. Inadequate identification manuals and remarkable similarity between Diplostonlum species confounded identification. Mean intensity of metacercariae was highest in ruffe and lowest in perch and increased with host size in all hosts. Factors responsible for differences in mean intensity between hosts were discussed. There was no seasonality of occurrence. Recruitment occurred from May - November correlating with water temperatures. Immature metacercariae occurred throughout the period of investigation. Metacercariae were overdispersed in all three hosts. At Mindu and Ruvu two species were present, D. sp. X (1,2) in the cranium of catfish and D. sp. Y in the vitreous humour of Oreochromis sp. D. sp. X (1,2) were distinguished by their elongate body, oval calcareous corpuscles and long hindbody. D. sp. Y were distinguished by a vestigial ventral sucker, glandular Brandes organ, short hindbody and spherical calcareous corpuscles. D. sp. X (1,2) were identified as D. mashonense Beverley - Burton, 1963. Adults cultured in chickens confirmed identification. D. sp. X (1,2) developed to ovigerous adults within 24h. Percent recovery of adults from chickens declined with days p. i. Miracidia developed in eggs in six days. D. sp. Y is considered an undescribed taxon. Prevalence and mean intensity of D. sp. Y in Oreochromis sp. were low and did not fluctuate seasonally. Prevalence of D. mashonense in catfish was similar at Mindu and Ruvu and exhibited no seasonal fluctuations. Mean intensity of D. mashonense in catfish of Mindu fluctuated seasonally, increased with host size and was higher than in catfish from Ruvu. Causes of high intensity and seasonal changes at Mindu were discussed. D. mashonense was overdispersed in catfish at both localities but only data from Mindu fitted the negative binomial model. Small samples and the dynamism of forces creating overdispersion were considered responsible for the situation at Ruvu. Using SEM ciliated-pit and dome-shaped papillae were observed on the surface of metacercariae and adults of D. mashonense . Ciliated-pit papillae occurred only on metacercariae. Dome-shaped papillae, in adults and metacercariae, were aggregated on suckers, excretory and genital atria. Spines were multipointed in adults but single pointed in metacercariae.

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.

No description available.

The isolated and un-managed Soay sheep population of Hirta, St. Kilda, which has been monitored intensively since 1985, is a model system for host-parasite studies. In hosts that died in the 2001/2 population crash, hitherto unknown and unexpected trends in the abundance of the main parasite species with host age were revealed. Specifically, previous studies in this system have failed to identify large <i>Trichostrongylus axei </i>and <i>T. vitrinus </i>burdens in the abomasum and small intestine respectively, which declined with host age, whereas <i>Teladorsagia circumcincta </i>burdens actually increased over the first few host age classes. Also male hosts had significantly higher burdens of <i>Trichostrongylus </i>species than females, with this genus making up a higher proportion of the strongyle-egg producing female adult nematode community in male hosts. These findings raise questions concerning previous interpretations of the main strongyle species contributing to strongyle egg counts. In living hosts sampled in late summer, the inventory of parasite species known to infect the sheep was increased by 40% with the identification of thirteen species of protozoa <i>(Cryptosporidium parvum, Giardia duodenalis </i>and eleven species of <i>Eimeria) </i>most of which have intracellular phases in their life cycles and likely, therefore, to exert contrasting selection on their hosts compared with extracellular helminth parasites. In general, protozoan burdens declined with host age and were higher in males than females; different species’ burdens appeared to lag the host population dynamics to different extents and only <i>C.</i> <i>parvum </i>varied positively with host population density. In living hosts sampled in late summer, simultaneous measures of strongyle, protozoan and ked <i>(Melophagus ovina) </i>intensity for individual hosts each explained independent variation in host body weight. No associations were detected between parasite diversity or intensity and the probability of survival through the 2001/2 population crash, possibly because of low statistical power.

No description available.

No description available.

The objective of this work has been to investigate the frequency of cross-fertilisation between gametes of genetically distinct clones of the human malaria parasite <i>Plasmodium falciparum</i>. Previous genetic experiments involving both rodent malaria parasites <i>in vivo</i> and human malaria parasites <i>in vitro</i> have demonstrated higher than expected numbers of recombinants among the progeny of crosses. It has been suggested that this could be due to a favouring of cross-fertilisation over self-fertilisation in the mosquito phase of the life-cycle. The work has involved examining the genotypes of individual oocysts (derived from individual zygotes) resulting from mixed infection of two clones in mosquitoes. In preliminary work using the mouse malaria parasite <i>P. yoelii nigeriensis</i> attempts were made to examine the chromosomes of single oocysts using pulsed field gradient gel electrophoresis. However there was insufficient DNA in an oocyst to allow chromosomes to be visualised using this technique. The bulk of the work has been concerned with <i>P. falciparum</i>. In the first stage oligonucleotide primers suitable for use in the polymerase chain reaction (PCR) were designed to allow amplification of repetitive regions of two polymorphic antigen genes, denoted MSP1 and MSP2. The two clones of <i>P. falciparum</i> used in the crossing experiments possessed a different allele of each gene. These alleles were found to be recognisable as size differences of the PCR-amplified fragments on agarose gels. Gametocytes of the two clones were grown <i>in vitro</i>. Mixtures of gametocytes of each clone were made and fed to <i>Anopheles stephensi</i> or <i>A. gambiae</i> mosquitoes through membrane feeders. 9 to 10 days later the mosquitoes were dissected and their midguts were examined for the presence of oocysts. Individual oocysts were dissected from the midguts and the DNA extracted from them.

No description available.