We describe a novel procedure for the immunofluorescent investigation of Plasmodium falciparum. This has allowed us to visualize clearly microtubular structures and their changing conformation through the erythrocytic cell-cycle, to the stage of cytodifferentiation leading to merozoite release. The images of spindle development we observed, together with an analysis of nuclear body numbers in large numbers of parasites, indicate that there is an apparent asynchrony in chromosomal multiplication within a single parasite. Using antibodies specific for post-translational modification of α- tubulin, we also demonstrate that the C-terminal tyrosine-containing epitope of P. falciparum α-tubulin I is similar to that of other organisms. Lysine-40 in the same molecule, a target for highly specific in vivo acetylation in some organisms, is unmodified in the blood stages we examined here. After in vitro acetylation of this residue, however, the epitope to which it contributes was recognized by antibody, showing that the conformation of this part of the molecule is also conserved, despite a lack of primary sequence homology immediately downstream of the target lysine residue.

Giardia lamblia localize and multiply in the small intestine and may cause acute or chronic diarrhoea with malabsorption of fat, protein and other nutrients. Abnormal pancreatic function has been documented in giardiasis and trophozoites directly inhibit pancreatic lipase activity in vitro. The aim of this study was to examine the effect of Giardia trophozoites on pancreatic trypsin, chymotrypsin and amylase activity in vitro. Axenically cultured Giardia trophozoites (Portland-1 stock) were incubated with a range of concentrations of trypsin, chymotrypsin and amylase and enzyme activity assayed over time. Tryptic activity was decreased after incubation with Giardia trophozoites. This reduction was time dependent and linear over the incubation period of 2 h. At a trypsin concentration of 18 BAEE units/ml, there was a 35.5±4% reduction in enzyme activity after 2 h compared to controls. The total amount of activity lost was proportional to the initial trypsin concentration up to 185 BAEE units/ml. At this initial concentration, the activity was reduced by 46.5±3 units/ml after 2 h. Above this concentration, little further loss of enzyme activity was seen. To investigate the nature and specificity of this effect, similar experiments were conducted using killed trophozoites and with a related protozoan. Trichomonas vaginalis. No loss of enzyme activity was evident. Media previously incubated for 2 h with trophozoites did not diminish tryptic activity. Trophozoites had no effect on chymotrypsin or amylase activities over the range of concentrations tested. Giardia trophozoites directly diminish pancreatic tryptic activity in vitro, by an active process which appears specific and not mediated via a secretory product. This mechanism may enhance parasite survival in the small intestine by allowing trophozoites to escape destruction by luminal proteases and may also contribute to malabsorption.

A Neospora sp. was isolated from the brains of two aborted bovine foetuses and grown continuously in vitro in bovine cell cultures. A comparison of the antigenic reactivity of in vitro cultivated tachyzoites with polyclonal antisera to Neospora caninum, Hammondia hammondi or Toxoplasma gondii revealed that the bovine protozoal isolates were similar to N. caninum and antigenically distinct from T. gondii. Tachyzoites of both bovine isolates had similar ultrastructural features, including an apical polar ring, conoid, electron-dense rhoptries and micronemes. The orientation of the micronemes, presence of micropores and a large number of electron-dense granules in the posterior portion of the bovine isolate tachyzoites differed from previous descriptions of N. caninum in vivo. Tachyzoites of the bovine isolates were ultrastructurally more similar to in vitro cultivated N. caninum tachyzoites than to tachyzoites of T. gondii or H. hammondi. The antigenic and ultrastructural similarities between N. caninum and the protozoal parasites isolated from aborted bovine foetuses in this study support the proposition that these parasites belong to the genus Neospora.

Two mathematical models are developed that investigate the transmission dynamics of Theileria parva by the ixodid tickRhipicephalus appendiculatus to cattle in endemically stable areas. A method of estimating the rate of infection to cattle ofT. parva at the endemically stable state is given. Empirical estimates of ail the parameters in the model are available. The degree to which animals that have recovered from theileriosis (the ‘carrier’ state) are able to transmit the infection to tick nymphs or larvae is a crucial determinant of the dynamics of infection in a herd. Two control methods influencing the transmission of infection are considered – infection and treatment immunization and the reduction in tick feeding by acaricide application. The impact of each method on the transmission of infection is evaluated. Future developments and the data required to predict the dynamics of T. parva infections in cattle and ticks are discussed.

The effect of experimental non-host snail (NHS) communities on the infection of Lymnaea truncatula with Paramphistomum daubneyi and Fasciola hepatica miracidia was studied. The results obtained indicated that NHS had variable effects on basic population parameters of host infection. Specifically, NHS were able to produce aggregation of sporocyst number/snail in the experimental host populations. Proposed hypotheses for decoy effect mechanisms failed to explain completely the experimental results. A new mechanism is suggested, based on a distance response of miracidia to snail chemo-attractants, to explain effects of NHS on miracidial host finding behaviour. It is assumed that miracidia have evolved the ability to discriminate among individual snail chemical attractants in a community already at a distance. This attribute of miracidial behaviour allows NHS to induce variations in the effectiveness of individual host localization by miracidia. The resulting aggregation of successful infections/host is assumed to be the specific component of snail decoy effect at the community level. It was also established that NHS affected trematode reproduction in the host inducing a compensatory increase in the intramolluscan population. Intraspecific competition among developmental stages is suggested to be the mechanism of this compensatory reaction.

Teneral Glossina morsitans centralis were fed on the flanks of African buffalo, N'Dama or Boran cattle infected with Trypanosoma vivax IL 2337. The infected tsetse were maintained on goats and on day 25 after the infected feed, the surviving tsetse were dissected to determine the infection rates. The mean mature infection rates (% ± S.E.) in the tsetse fed on buffalo, N'Dama and Boran cattle were 34·3 ± 9·9, 33·7 ± 13·4 and 58·9 ± 7·1, respectively. Logistic regression analysis indicated that infection rates in the labrum and hypopharynx of the tsetse were significantly lower when fed on the infected buffalo or N'Dama than Boran cattle. Similarly, the risk of infection was significantly lower in male than female tsetse. When teneral G. m. centralis, G. pallidipes, G. p. gambiensis, G. brevipalpis and G. longipennis were fed simultaneously on either the buffalo cow, the N'Dama bull or the Boran steer infected with T. vivax IL 2337, the mature infection rates were higher in the two morsitans group than the two fusca group tsetse, whilst G. p. gambiensis was relatively refractory to the infection, irrespective of the host species on which they fed. Logistic regression analysis indicated that the infection rates in the labrum and hypopharynx were significantly different amongst the five tsetse species for each of the three infected host animals. Nevertheless, the trypanotolerant African buffalo and N'Dama cattle may serve as reservoirs of T. vivax infection as can trypanosusceptible Boran cattle.

A control programme of opisthorchiasis was carried out for three years in three villages of northeast Thailand in order to compare the effectiveness of two intervention measures. The intervention measures employed were to give praziquantel treatment to all infected people either once (village I) or twice (village II) per year with the integration of regular health education and sanitation improvement. A control village (village III) received no intervention during the study. Sampling of the population in these villages to estimate prevalence, intensity, reinfection and incidence of infection as well as knowledge of opisthorchiasis and number of latrines was performed at 6 monthly intervals throughout the duration of the study. At the initial assessment, there were no significant differences in the prevalence and intensity of infection of villages I and II. Both values were greatly reduced when assessed 6 months after the initiation of treatment, and the decrease in prevalence and intensity of infection did not differ between villages I and II. The control village (village III), during the first 2 years, exhibited slight variation in the prevalence and intensity, and these decreased considerably in the third year of the study. The reinfection rate per 6 months in villages I and II was nearly equal. The incidence rate per 6 months in the two treated villages was lower than that of the control village. Marked improvement in knowledge of opisthorchiasis, behavioural changes of eating raw fish and increased numbers of latrines was evident in all of the villages during this study. The study showed that the effectiveness of annual drug treatment is similar to that of 6 monthly treatments when combined with regular health education and sanitation improvement.

Previous studies from this laboratory have suggested the presence of antibody-binding molecules on the surface of Taenia crassiceps metacestodes. We now report the purification of a T. crassiceps Fcγ -binding protein which has an equivalent molecular size (96 kDa), is antigenically similar and exhibits significant amino acid sequence homology to schistosome paramyosin. The similarities in molecular weight of the T. crassiceps protein, Schistosoma mansoni paramyosin and antigen B of T. solium, the close amino acid sequence homologies between the T. crassiceps protein and S. mansoni paramyosin and between S. mansoni paramyosin and antigen B of T. solium, and the antigenic similarity of the T. crassiceps protein with paramyosin indicates that this family of platyhelminth proteins are closely related. The known characteristics of T. solium antigen B (collagen binding affinity; disruption of complement function) and the Fcγ -binding activity of the T. crassiceps molecule suggests that this class of proteins may be multifunctional, fulfilling not only a structural role but also as components interacting with the host immune system to increase parasite survival.

The infectivity and distribution of Echinostoma trivolvis were studied in male, conventional and congenitally athymic nude mice, each infected with 30 metacercarial cysts. In conventional mice, worm recoveries at 6 and 8 days post-exposure were58·3 and 54·0%, respectively. Worm recovery declined to 44·0% by day 10, to 4·3% by day 13, and 0% by day 17. In athymic mice, worm recoveries at 6 and 8 days post-exposure were 61·7 and 36·3%, respectively. Worm recovery declined to 27·7% by day 10, to 0·7% by day 13, and 0% by day 17. The distribution of worms demonstrated a posteriad migration over time in both groups. Kinetic changes in the number of goblet and mucosal mast cells in the upper ileum of mice infected with E. trivolvis were examined. In conventional mice, the number of goblet cells increased rapidly to reach a peak at day 13 and then declined gradually. The number of goblet cells in athymic mice also increased to reach a peak at day 13, and then declined rapidly. However, the number of goblet cells in athymic mice was always less than that inconventional mice. The mast cell number in infected conventional mice increased rapidly to reach a peak at day 17 and then declined. There was no increase in the mast cell number of infected athymic mice throughout the experiment. Whereas common pathological changes occurred in the intestines of both mice groups infected with echinostomes some ultrastructural differences were observed in the gut epithelial cells of conventional versus athymic mice.

The localization and distribution of neuropeptides in the central nervous system of the pig roundworm, Ascaris suum, have been determined by an indirect immunofluorescence technique in conjunction with confocal microscopy. Antisera to 25 vertebrate peptides and two invertebrate peptides were used to screen the worm for immunoreactivity (IR). Immuno-staining was obtained with antisera to pancreatic polypeptide (PP), peptide YY (PYY), neuropeptide Y (NPY), gastrin, cholecystokinin (CCK), substance P (SP), atrial natriuretic peptide (ANP), salmon gonadotropin-releasing hormone (SGnRH), mammalian gonadotropin-releasing hormone (MGnRH), chromogranin A (CGA) and FMRFamide. The most extensive patterns of IR occurred with antisera to PYY, FMRFamide and gastrin. IR was evident in nerve cells and fibres in the ganglia associated with the anterior nerve ring and in the main nerve cords and their commissures; IR to FMRFamide also occurred in the posterior nerve ring. Immunostaining for the other peptides was confined to the nerve cords, with the number of immunoreactive nerve fibres varying from peptide to peptide.

When incubated in vitro for 24 h, oncospheres of Hymenolepis diminuta absorb and metabolize radioactive glucose. Between 0 and 12 h post-activation, oncospheres absorb glucose, but glucose is neither metabolized into other carbohydrates nor incorporated into the ethanol-precipitable fraction (which would contain glycogen). Between 12 and 24 h post-activation glucose is incorporated into a number of higher molecular weight carbohydrates that are demonstrable in ethanol extracts of the larvae, as well as the incubation media. Furthermore, measurable amounts of radioactivity are incorporated into the ethanol-precipitable carbohydrate fraction of oncospheres. To determine if these temporal changes in carbohydrate metabolism occurred spontaneously following activation, oncospheres were pre-incubated for 12 h (0–12 h post-activation) in the absence or presence of glucose, and then transferred to media containing radioactive glucose for an additional 12 h (12–24 h post-activation). In these latter experiments, glucose absorption and metabolism between 12 and 24 h post-activation were virtually identical to glucose metabolism in oncospheres that were incubated in radioactive glucose for 0–12 h immediately following activation. Thus, these data do not support the hypothesis that the temporal shift in carbohydrate metabolism occurs spontaneously.

The intestines of 170 long-finned pilot whales, Globicephala melas, caught off the Faroe Islands (N.E. Atlantic) were examined for helminth parasites. Eight species were detected but only 4 occurred in at least 10% of the sample. No core or recurrent group of species were identified and no correlations between abundances of species were significant. Diversity values were far below those reported for other endotherms. Colonization by helminths was random, whales not being readily colonized. These features point to largely unpredictable, isolationist infracommunities, there being little potential for inter-specific interactions. Older hosts tended to harbour more diverse infracommunities, offering more opportunities for such interactions. Two hypotheses, which might also apply to other cetaceans, are proposed to account for the depauperate helminth communities of the pilot whale: (i) some ancestral helminth species failed to adapt their cycles to the marine habitat and (ii) the hosts' isolation from land prohibited new infections with helminths of mammals.