Messenger RNA has been extracted from oocysts of Eimeria maxima. Using the techniques of in vitro translation and SDS–polyacrylamide gel electrophoresis, we have been able to show that major changes in gene transcription occur during sporulation. Following an overall reduction in the abundance of many mRNAs, several genes identified as the result of an increase in the abundance of their transcripts, are highly expressed during the latter stages of sporulation. A study of two genes whose transcription is down-regulated has provided evidence which shows that both single copy and repetitive sequences are regulated during sporulation of the oocyst.

Evidence is presented that Babesia microti may promote its transmission amongst rodents by enhancing the feeding success and survival of its tick vector, Ixodes trianguliceps. Both the mean engorged weight of larval ticks and the percentage moult of larvae to nymphs increased as larvae fed on naive hosts later in the parasitaemic cycle up to a point a few days beyond the loss of a patent infection. This increased feeding success and survival was not dependent on the level of infection by B. microti. Two possible, host-mediated mechanisms for the observed parasite–vector interactions are suggested, the anti-haemostatic effects induced by babesiosis and the interaction of the immunosuppressive effects of Babesia and the development of immunity to ixodid ticks by their vertebrate hosts.

Highly purified mitochondrial fractions have been isolated from the intraerythrocytic stages of two mammalian Plasmodium spp., Plasmodium yoelii of rodents and Plasmodium falciparum of man. Mitochondria of the former parasite are cristate whereas those of the latter are essentially acristate. Isolated mitochondria from both parasite species were heterogeneous with respect to size, shape, density of matrix staining and extent of internal structure. Respiratory assay, by reduction of exogenous cytochrome c, showed NADH, α-glycerophosphate and succinate to be the substrates with the greatest potential for metabolism. Additionally, proline, dihydroorotate and glutamate (P. falciparum only) were oxidized at low rates. A number of NAD+-linked substrates were not utilized. The NADH-dependent reduction of cytochrome c was insensitive to rotenone and antimycin A. Fumarate inhibited the NADH-dependent reduction of cytochrome c and stimulated the oxidation of NADH, suggestive of an NADH–fumarate reductase pathway. Oxidation of either α-glycerophosphate or succinate was fully inhibited by standard mitochondrial electron transport inhibitors, including a number of Complex III inhibitors, although the concentrations required of such inhibitors (notably myxothiazol) were relatively high compared to mammalian mitochondria. Dithionite-reduced minus oxidized difference spectra indicated the presence of cytochromes aa3, b, c and c1 in mitochondria of both parasite species, but at a higher cytochrome to protein ratio in P. yoelii. Freshly isolated mitochondria from either species exhibited only low respiratory control ratios with α-glycerophosphate or succinate as substrates. The apparent absence of a respiratory chain ‘Site I’ in such mitochondria may mean that NADH–fumarate reductase serves to reoxidize mitochondrial NADH.

Up to 200 laboratory reared Anopheles dirus mosquitoes were fed on each of 496 symptomatic Thai men who had patent, naturally acquired Plasmodium vivax gametocytaemia. Mean gametocyte densities were 455/mm3 (range: 0–3281), geometric mean oocyst number was 9 (0–142), mean frequency of infection was 43% (0–100%), and mean sporozoite number in salivary glands was 9525 (0–285 000). There was little relation between gametocyte density and either oocyst number or frequency of mosquito infection. There were, however, statistically strong positive correlations between oocyst numbers and frequency of infection, and between number of oocysts and number of salivary gland sporozoites. The data suggest that each oocyst contributed about 850 sporozoites to a gland infection.

The enzyme-linked immunosorbent assay (ELISA) was used to survey human sera for antibodies to Encephalitozoon cuniculi using spores obtained from in vitro cultures as antigen. Sera were obtained from patients with tropical diseases, neurological and renal disorders, patients who were HIV positive and those who had been tested for HIV but found to be negative. Sera from inhabitants of the village of Jali, The Gambia and from healthy blood donors were also examined. Numerous sera from all groups except the blood donors gave positive ELISA reactions at dilutions of 1:400. On titration, those with titres of 1:400 were reclassified as negative. Antibody titres of 1:800 and above were considered to be indicative of past or present infections with E. cuniculi. Many of these ELISA seropositives were also positive by IFAT or PAP. When examined by Western blotting of SDS–PAGE protein profiles of E. cuniculi spores, sera from many patients who had a tropical association reacted with the characteristic profiles shown by known positive mouse and rabbit sera. Others in the tropical group showed antibody binding to some but not all of the immunodominant polypeptides and yet others were negative in spite of their reactivity in the ELISA, IFAT or PAP test. Less agreement between ELISA and Western blotting results was obtained with the other groups of patients, although reactivity with one or more of the major polypeptide bands was sometimes seen. Serum from one blood donor, examined by ELISA and Western blotting, was positive. Differences in the methods of antigen preparation and of epitopes recognized by individuals may account for different reactivities in the tests. It is concluded that infections of E. cuniculi are common in the tropics and that reactivations of these infections might be a hazard to AIDS patients.

Experiments were conducted in guinea-pigs to elucidate the parameters affecting the development of protective immunity against Schistosoma japonicum induced by a cryopreserved, irradiated schistosomula vaccine such as the number of immunizations, route of injection and the use of adjuvants. Results obtained indicated that the cryopreserved, irradiated schistosomula vaccine was effective by either intradermal or intramuscular injection. One intradermal injection with BCG adjuvant resulted in an average worm reduction of 50·24%, only a little lower than that of a non-cryopreserved, irradiated vaccine, 53·55%, with no statistically significant difference between the two. By intramuscular injection the worm reduction was lower (max. 40%) whether given with or without adjuvants or in 1 or 2 injections.

A new model for the study of granuloma formation in the liver is described. Rats received an injection of 20 000 Schistosoma mansoni eggs in the portal vein and granuloma formation was evaluated at 3, 5 and 7 weeks post-injection. Liver collagen was estimated at the same time and serum procollagen III peptide, a marker of collagenesis, weekly. With this model, wherein the number of S. mansoni eggs and the time of injury are standardized, the effect of high levels of acute phase proteins especially α2-macroglobulin on granuloma formation was studied. It appeared that in rats with high levels of α2-macroglobulin the mean size of granulomas was significantly greater at 3 and 5 weeks compared with controls. In both groups an increase in liver collagen was observed during this period, reaching a peak at 5 weeks in the acute phase group. This model facilitates the study of the effects of S. mansoni eggs on granuloma formation.

Treatment of BALB/c or MF1 mice with cyclosporin A (CsA) around the time of infection with Schistosoma mansoni conferred almost complete protection. The migration kinetics of L-[75Se]selenomethionine-labelled infective cercariae were investigated by compressed tissue autoradiography. Similar levels of skin penetration were achieved by cercariae in control and drug-treated individuals. CsA arrested 87–94% of the worms in the skin and ultimately all of these died in this site. Few worms (7–14%) migrated from the skin to the lungs and none completed migration to the liver. Nevertheless, the autoradiograms revealed a limited degree of lateral cutaneous migration by the worms present in the skins of CsA-treated mice. Results of perfusion recovery experiments carried out during the course of infection reinforced the tracking data.

The results of studies on the schistosomulicidal activity of activated peritoneal and alveolar macrophages (pMø and aMø) from rats immunized with highly irradiated (50 krad.) Schistosoma japonicum cercariae are reported. The authors have examined the activation of these macrophages in terms of spreading, adhesion and ingestion of sheep erythrocytes and pinocytosis of horse-radish peroxidase. Using three criteria, peritoneal macrophages and alveolar macrophages from immunized rats and from rats intraperitoneally injected with BCG were significantly more active than those from normal rats or rats stimulated with 10% proteose-peptone or 1% sodium thioglycolate. A significantly higher percentage of adhesion and ingestion was obtained with the sheep erythrocytes that were co-opsonized by heat-inactivated rat anti-sheep erythrocyte serum and fresh normal rat serum. Schistosomulicidal effects were observed with macrophages from irradiated cercariae-immunized rats in two activation systems: in vitro activation in the presence of macrophage-activating factor (MAF), and in vivo activation by the intraperitoneal challenge with sonicated cercarial antigens.

Infection with Schistosoma haematobium was studied in a rural community of approximately 500 persons in eastern Zimbabwe. The overall prevalence of infection, as determined by urine egg counts, was 40·1%, and of heavy infections (≥ 50 eggs/10 ml urine) was 11·0%. The prevalence of both heavy and all infections was highest in the 8 to 10-year-old age class. During 1987–88 data were obtained from 102 individuals on intensity of reinfection 14 weeks after treatment with praziquantel, the efficacy of treatment having been determined after 4 weeks. The water contact made by these individuals during 2-week periods immediately following treatment was recorded. The relative abundance of patent infected intermediate host snails, Bulinus globosus, was also monitored. An index of exposure was developed which weighted each water contact by its duration, the type of activity, the time of day, and the abundance of infected snails at the site used. The relationships between rates of reinfection, rates of exposure, and age were examined. Although only 13 individuals showed positive rates of reinfection, there were statistically significant and independent effects of both exposure and age on reinfection rate. Quantitative estimates of reinfection rates suggested that individuals aged 12 years or less acquired substantially more infection (measured as egg output) than individuals more than 12 years old.

Subadult and adult specimens of the pond snail Lymnaea stagnalis were infected with the schistosome Trichobilharzia ocellata. Egg production and growth of the snails were monitored over an 8-week period post-infection (p.i.). Snail haemolymph was collected and analysed for the presence of schistosomin, a neuropeptide which antagonizes the action of the snails' female gonadotropic hormones. Snails infected as subadults showed an increase in fecundity during the first 4 weeks p.i. compared with non-infected controls. The possibility is discussed that this increase is caused by an accelerated maturation of the female sex organs due to elevated levels of Dorsal Body Hormone, a female gonadotropic hormone. No difference in fecundity was found between snails infected as adults and control snails during the first 4 weeks p.i. Snails infected as subadults and as adults showed a decrease in fecundity from week 5 p.i. and onwards. This decrease coincided with the appearance of schistosomin in the haemolymph of the snails and with that of differentiating cercariae in the daughter sporocysts. Cercariae are probably involved in the induction of schistosomin release from the snails' CNS into the haemolymph. Snails infected as subadults or as adults grew at approximately the same rate as uninfected snails.

Nine clones were derived from a drug-resistant Trypanosoma congolense stock (IL 2856) and characterized in mice for their sensitivity to isometamidium chloride and diminazene aceturate. All clones were derived from the stock without drug selection and expressed high levels of resistance to isometamidium chloride (50% curative dose [CD50] values ranging from 1·5 to 5·1 mg/kg) and intermediate to high levels of resistance to diminazene aceturate (CD50 values ranging from 5·1 to 21·0 mg/kg). By contrast, the isometamidium chloride and diminazene aceturate CD50 values for a drug-sensitive clone, T. congolense IL 1180, were 0·018 mg/kg and 2·3 mg/kg, respectively. For both drugs, there appeared to be significantly different levels in expression of drug resistance amongst the 9 clones derived from IL 2856. Isoenzyme analysis of 7 enzymes showed that all 9 clones expressed the same electrophoretic variants. Thus, all 9 clones were identical for these phenotypic markers. The clone which expressed the highest level of resistance to isometamidium in mice (IL 3270) was transmitted to Boran cattle via the bite of infected Glossina morsitans centralis. IL 3270 produced an infection rate in tsetse of 5·0%. The resulting infections in cattle were shown to be resistant to intramuscular treatment with 2·0 mg/kg isometamidium chloride and 14·0 mg/kg diminazene aceturate. This contrasts with doses of 0·25 mg/kg isometamidium chloride or 3·5 mg/kg diminazene aceturate which are deemed sufficient to cure fully sensitive infections. Finally, 9 clones (subclones) were derived from IL 3270 and characterized in mice for their sensitivity to isometamidium chloride. Seven of the subclones expressed a significantly lower level of resistance to isometamidium than the parental clone and amongst the subclones there was significant variation in resistance. Thus, expression of a high level of resistance to isometamidium appears to be unstable in the rodent host and at least a component of the genetic determinant(s) for this drug-resistant phenotype is (are) likely to be unstable.

The cercaria of Acanthostomum brauni penetrates the skin of its fish host in response to a combination of two chemical signals from the fish skin surface: free fatty acids and a macro-molecular mucus component. The latter seems to be a protein, as the penetration-stimulating activity of fish skin surface mucus is eliminated by digestion with proteinase, but not by digestion with glycosidases, nor by a removal of glycosaminoglycans. These penetration-stimulating host signals differ from the glycoproteins that stimulate the attachment of A. brauni cercariae to the host and also from the macro-molecular fish host signals which have been found to stimulate the attachment and penetration by Opisthorchis viverrini cercariae.

The relationship of survival and reproduction of Gyrodactylus salaris Malmberg on the Atlantic salmon (Salmo salar) to water temperature (2·5–19·0 °C), was studied on the basis of temporal sequence of births and age at death of individual parasites on isolated salmon, and of infrapopulation growth on isolated and grouped salmon. Mean life-span of the parasite was negatively correlated with water temperature: 33·7 days at 2·5 °C and 4·5 days at 19·0 °C. The average number of offspring per parasite peaked between 6·5 and 13·0 °C, and was approximately 2·4 at these two temperatures. Both the period between the successive births of the offspring (max 4) and the estimated generation time were negatively correlated with temperature. The innate capacity for increase (rm) was positively correlated with temperature: from 0·02 (/parasite/day) at 2·5 °C to 0·22 (/parasite/day) at 19·0 °C. Growth of the infrapopulations was positively correlated with water temperature and was higher on isolated fish than on grouped fish, though less than the potential parasite population growth estimated from rm. In the infrapopulations the mean intensity of parasites continued to increase throughout all the experiments on both isolated fish and on grouped fish.

High molecular weight proteinases of Trichomonas vaginalis (with apparent Mr values 142 and > 220 kDa) and Tritrichomonas mobilensis (Mr 67, 86, 104 and 120 kDa), optimally active at pH 8, were analysed in gelatin-containing polyacrylamide gels. All of these proteinases were resistant to serine-, aspartic- as well as cysteine proteinase inhibitors. Both proteolytic bands in T. vaginalis and two proteinases in T. mobilensis (67 and 104 kDa) were inhibited by EDTA and EGTA suggesting that they belong to the metallo-proteinase class. The 67 kDa proteinase of T. mobilensis was inhibited also by o-phenanthroline. The other two bands of T. mobilensis (86, 120 kDa) were not classified to any proteinase group since they appeared to be resistant to the chelating agents tested in this study.

Monoclonal antibodies raised against antigens present in the excretions/secretions (E/S) of larval Trichinella spiralis, polyclonal antibodies raised against E/S and antisera from rabbits and pigs infected with T. spiralis were used in conjunction with immunocytochemical techniques to detect antigens in sections of muscle from mice that had been infected with T. spiralis for 15 or 30 days. The antibodies recognized epitopes in the stichocytes, on the surface of the cuticle, in the lumen of the oesophagus and in the lumen of the intestine of encysted larvae. Monoclonal antibodies 7C2C5 and 1H7 and the polyclonal antibodies recognized epitopes in the cavity occupied by the larva, in the cytoplasm of the nurse cell, and in the hypertrophic nuclei of the nurse cell, but did not recognize material in the smaller nuclei of the nurse cell, in the cyst wall or in the surrounding muscle. Monoclonals 3B2E6 and 1D11G8B2, which recognized epitopes in the stichocytes and on the surface of the cuticle of the larvae, gave negative results with the cytoplasm and nuclei of the nurse cell. A polyclonal antibody raised against Trichuris suis recognized epitopes in the muscle and hypodermis of encysted T. spiralis but gave negative results with material in the nurse cell and nurse cell nuclei. The possibility that the antigen detected in the cytoplasm and nuclei of the nurse cell is produced by the stichocytes of the nematode and that it is controlling genes of the altered muscle fibre, either directly or indirectly, is discussed.

Many liver-invasive parasites cause extensive liver damage which may result in an impaired ability to catabolize endotoxin. The influence of endogenous endotoxin on the progress of liver-invasive parasitic diseases has been investigated in murine Mesocestoides corti infection. Invasion of liver tissue by tetrathyridia resulted in extensive parenchymal destruction with fibrosis. In association with this, undetoxified endotoxin, in potentially biologically active concentration, was found on peritoneal macrophages, 5 months post-M. corti infection. Host susceptibility was influenced by the Lps gene for responsiveness to lipopolysaccharide (LPS). The parasite burden of LPS-responsive (C3H/HeN) mice was significantly increased in the livers of these mice when compared to LPS-resistant (C3H/HeJ) mice. LPS reduced the ability of normal peritoneal macrophages to kill tetrathyridia, when co-cultured in vitro. LPS also abrogated the ability of recombinant interferon-γ (r.IFN-γ) to enhance macrophage larvicidal activity. These in vitro findings were confirmed in vivo. Daily intraperitoneal administration of LPS, at low concentration, caused a 4-fold increase in parasite burden in the liver, while r.IFN-γ at optimal concentration reduced parasite burden by 57%. Post-infection macrophages have previously been shown to be refractory to cytokine-activation for larval killing. In this report, we conclude that (1) this refractoriness may be due to the presence of undetoxified endotoxin on post-infection macrophages and (2) endotoxin may reduce host resistance by abrogating effector macrophage response to IFN-γ.

This study was designed to test the accessory function of macrophages after activation with products of Taenia multiceps coenuri. Activation was carried out by intraperitoneal injection of mice with coenurus fluid or protoscolex culture supernatant, and function was assessed by adding these macrophages in progressively increasing numbers to macrophage-depleted lymphocyte cultures transforming under the influence of plant mitogens or coenurus-fluid mitogen. In contrast to normal macrophages, which have a progressively enhancing action on the above reactions, parasite-activated macro-phages at similar concentrations were progressively inhibitory. However, low concentrations of the activated macrophages enhanced mitosis as well as, or better than, normal. Lymph node cells from injected mice showed abnormal response to macrophage-derived signals. In particular there was subnormal reaction to macrophages in the presence of coenurus mitogen. These results suggest that T. multiceps coenuri may survive in the host because of their ability to reduce effective interaction between lymphocytes and accessory cells.

In the absence of exogenous divalent cations, the isolated brush-border plasma membrane of Hymenolepis diminuta possesses alkaline phosphatase activity (APA). APA is stimulated in the presence of exogenous Mg2+ and inhibited by low concentrations of Zn2+ or high concentrations of Ca2+, and inhibition of APA by Zn2+ is reversed by both Mg2+ and Ca2+. APA is inhibited by ethylenediamine tetraacetic acid (EDTA), ethyleneglycol-bis-(β-aminoethyl ether) N, N′-tetraacetic acid, and 1, 10-phenanthroline in time- and concentration-dependent fashions, with EDTA being the most effective inhibitor. Following treatment with EDTA, APA is restored by Mg2+ and, to a lesser extent, by Ca2+, but not by Zn2+. Thus, APA represents a Mg2+-dependent enzyme that can be partly activated by Ca2+ but only in the absence of Mg2+.

Natural populations of 3rd-stage Nematodirus battus larvae were present on pastures in North Wales throughout the year; highest numbers were present in late spring, with smaller peaks occurring in autumn. Inter-site variation was observed in the timing and magnitude of these peaks. Hatching on experimental plots occurred 2 months to 2 years following deposition of eggs. Intraspecific and inter-site variation occurred in the timing, and inter-site variation occurred in the magnitude, of the mass hatch on upland and lowland experimental plots. Arrested 4th-stage N. battus were recovered from Welsh Mountain lambs. Percentage arrest and number of arrested worms was greatest during winter and early spring. The prevalence and intensity of N. battus infection in 1-, 2- and 3-year-old Welsh Mountain ewes was low. The plasticity exhibited in the parasite's life-history is discussed in relation to potential changes in the epidemiology of nematodiriasis.