Species- and subspecies-specific trypanosome DNA hybridization probes have been employed in the detection and identification of trypanosome infections in Glossina morsitans centralis. Several ways of sample preparation including the use of tsetse organ suspensions, proboscides and dissected midguts, as well as tsetse abdominal content touch-blots were explored. The results of hybridization of radio-isotope-labelled species-specific DNA probes to tsetse samples indicated that it was possible to detect trypanosomes in the organs where parasite development is known to characteristically occur for each subgenus. Duplicate slot-blots of samples prepared from midguts of tsetse infected with 2 strains of T. congolense and from non-infected fly controls show that it is not only possible to detect infection in tsetse but also to identify the strain of parasite present in a sample after hybridization with the DNA probes specific for each strain. The results, obtained after hybridization of sequential abdominal touch-blots from the same fly with the DNA probe specific for one strain of T. congolense, indicated that at least 8 positive signals can be observed after an overnight exposure. Because of their simplicity and potentially low cost, the techniques described here would be appealing for screening large numbers of tsetse samples from the field for the presence of any trypanosome residing in the guts or proboscis of the vector. In addition, the possibility of doing multiple touch-blots from the same fly gives the opportunity of detecting mixed trypanosome infections in the vector.

In the experiments reported here treatment (with a single dose or daily for 4 days) was delayed until 3 days after inoculation. Various combinations of M&B 35769, 2:4-diamino-5-[3(4–4′-chlorophenylphenoxy)propyl-l-oxy]-6-methylpyrimidine HC1, plus sulphadoxine, and of M&B 35769 plus dapsone, were examined and it was concluded that no universally ideal ratio of constituents in a combination is possible because the optimum ratio depends upon the activity of the constituents on their own and therefore varies from strain to strain. Activity was assessed on the 24th day after infection. M&B 35769 was markedly superior to pyrimethamine against all strains when the compounds were given on their own but, although it showed good potentiation with sulphadoxine and dapsone, much of its lead over pyrimethamine was lost in combination. M&B 36821 2–4-diamino-5-[3-(3,4′-dibromobiphenyl-4-oxy)-propyl-l-oxy]-6-methyl pyrimidine HC1, was more active than M&B 35769 against pyrimethamine- and cycloguanil-resistant strains but not against sensitive strains.

Employing a simple method of growing ookinetes of Plasmodium falciparum in culture, 40% of mature gametocytes convert to macrogametes, 4% reach the retort-form ookinete stage and 0·45% become mature ookinetes. A single-step gradient centrifugation method on 12·5% Nycodenz® enriches both gametocytes and ookinetes.

l-Amino acid esters, such as leucine methyl ester (Leu-OMe) can destroy intracellular as well as isolated amastigotes of Leishmania mexicana amazonensis by a mechanism which may involve ester hydrolysis by parasite enzymes. We show here that several other esters prevented the killing of the amastigotes by Leu-OMe. Destruction of Leishmania within macrophages in culture was assessed microscopically and viability of isolated parasites was monitored by reduction of the tetrazolium MTT. The main features of the protective effect were similar for intracellular and for isolated amastigotes. Thus, (i) effective prevention of parasite killing required that the protective ester be present in the medium prior to and during exposure of infected cells or parasites to Leu-OMe; (ii) the same esters protected intracellular and isolated Leishmania against damage by Leu-OMe. Ranks of protective activity, as determined on isolated amastigotes were: Gly-OBz > Tyr-OMe > Ile-OMe > Met-OMe > Val-OMe > Ala-OMe > Gly-OMe > D-Leu-OMe; (iii) several esters were inactive in both systems (Leu-OBz, Trp-OMe and Phe-OMe). Protective activity was associated with leishmanicidal (e.g. Gly-OBz, Tyr-OMe) as well as with non-leishmanicidal (e.g. Ile-OMe, Val-OMe) esters. The results are compatible with the hypothesis that protective esters inhibit the activity of parasite enzyme(s) which hydrolyse Leu-OMe.

Guinea-pigs immunized with equivalent numbers of normal or radiation-attenuated cercariae of Schistosomamansoni are known todevelop close to complete resistance to reinfection at weeks 12 and 4·5 respectively. We here analyse and compare the immune responses induced by the two populations of cercariae. Both radiation-attenuated and normal parasites of S. mansoni elicited an extensive germinal centre response in guinea-pigs by week 4·5 post-immunization. The anti-parasite antibody titre and cytotoxic activity of serum from 4·5-week-vaccinated, or 4·5-week-infected guinea-pigs were approximately equal, but sera from 12-week-infected individuals had high titres of anti-parasite antibody, which promoted significant larvicidal activity in vitro. In all cases, larvicidal activity was mediated by the IgG2 fraction of the immune serum. Lymphocyte transformation tests conducted on splenic lymphocytes from 4–5-week vaccinated guinea-pigs revealed maximal stimulation against cercarial, 2-week and 3-week worm antigens, whereas spleen cells from 4–5-week-infected guinea-pigs were maximally stimulated by cercarial and 6-week worm antigens. The splenic lymphocyte responses of 12-week infected animals were dramatic against antigens prepared from all life-stages of the parasite.

In an attempt to find possible targets for benzimidazole action in muscle-stage larvae of Trichinella spiralis, the effects of mebendazole and thiabendazole were tested in vivo by oral treatment of infested mice and in vitro by including these anthelmintics in an adequate maintenance medium containing decapsulated larvae. The effects of the anthelmintics on succinate dehydrogenase and fumarate reductase activities, measured in the mitochondrial fraction obtained from the in vivo- or in vitro-treated larvae showed that only thiabendazole causes significant inhibition of fumarate reductase activity. On the other hand, measurements of free glucose, glycogen reserves and soluble protein in the treated larvae indicate that in vivo, mebendazole and thiabendazole clearly diminish free glucose levels, although in vitro only mebendazole produces the same diminution. Both the glycogen and protein contents of the larvae remained unchanged after treatment in vivo or in vitro. The importance of these findings with regard to a possible site of action for mebendazole and thiabendazole is discussed.

Protoscoleces of Echinococcus granulosus absorb the l-amino acids proline, methionine, leucine, alanine, serine, phenylalanine, lysine and glutamic acid by a combination of mediated transport and diffusion. All eight amino acids were accumulated against a concentration gradient. Comparison of Kt and Vmax values suggests that a low affinity for a particular compound is compensated for by a relatively larger number of transport sites for that compound. Four systems serve for the transport of the eight substrates studied: 2 for neutral (EgNl, EgN2) and 1 each for acidic (EgA) and basic (EgB) amino acids. All eight amino acids are incorporated into protein to varying degrees and substantial portions of absorbed l-alanine and l-methionine are metabolized into other compounds.

Infection with Hymenolepis microstoma significantly affected the lipid metabolism of young male Balb/C mice. Infection increased the rates of hepatic fatty acid and cholesterol synthesis and cholesterol synthesis by the gut. Decreases were recorded in testicular fatty acid synthesis and in the weights of testes and white epididymal adipose tissue. Plasma glucose decreased rapidly during infection. The observed changes in lipogenesis could not be attributed to changes in food intake or body temperature. The changes are discussed in relation to nutritional interactions between host and parasite and the possible effects on host hormone levels. The presence of newly synthesized fatty acid in H. microstoma is also reported.

Several of the pathophysiological responses made by the beetle Tenebrio molitor, when infected with metacestodes of Hymenolepis diminuta, may be attributed to a parasite-induced reduction in host juvenile hormone titre. It has been suggested that production of this hormone by the corpora allata may be inhibited in parasitized insects. This hypothesis was tested using an in vitro radiochemical assay to compare the biosynthesis of juvenile hormone by single pairs of corpora allata taken from mated 12- and 15-day-old infected and control female insects. The results demonstrate, however, that there was no difference in hormone production associated with metacestode infection. Other possible mechanisms for parasite interference in this host endocrine system are discussed.

Biological characteristics of infectivity, growth rate and fecundity of Hymenolepis diminuta isolated from wild Rattus rattus in Japan were compared with parasites of Texas origin maintained for several generations in this and many other laboratories in laboratory bred Rattus norvegicus. The timing of development and maturation was similar in parasites from both sources, but the mean parasite dry weight was less and the mean egg production lower in Japanese parasites in both single and multiple infections. The differences persisted over 10 weeks in single infections, and were unaffected by rat strain. In all experiments there was much greater variation and heterogeneity in the biological characteristics of the Japanese parasites. It was concluded that the Texas parasites were better adapted to R. norvegicus and in the course of adaptation had become more homogeneous, and that the difference between the parasite strains had a complex genetic basis. Some Japanese parasites of the early isolated generations failed to produce normal eggs, but the proportion of these decreased in later generations. However, selected individual Japanese parasites whose egg production was equal to that of parasites of Texas origin did not produce offspring of larger mean size or higher mean fecundity, and heterogeneity of these characteristics was maintained. In the intermediate host, the mean number of cysticercoids of the Japanese isolate per beetle was higher than that of the Texas strain in Tribolium confusum but lower in Tenebrio molitor. The greater heterogeneity exhibited by Japanese parasites and the genetic basis of the strain difference are discussed with particular reference to geographical isolation, differences in definitive hosts and co-evolution of wild and laboratory host and parasite populations.

Despite the ubiquitous presence of parasites, parasitism has not been considered among the list of regulatory factors in animal populations until recently. A detailed long-term study on the impact of the direct life-cycle nematode Heligmosomoides polygyrus on a breeding population of laboratory mice provides a clear example of the ability of helminths to regulate host abundance. In the absence of the parasite, the mouse population equilibrated at a density of 320 mice/m2 as a result of density-dependent effects on recruitment. When the parasite was added and transmission was maintained at high levels, infected mouse populations equilibrated at densities of < 18 mice/m2. Reduced rates of parasite transmission and elimination of the parasite from the system both resulted in an increase in mouse density. These results have implications for both ecology and parasitology as they demonstrate a potentially important but often ignored component of host populations that may well influence host abundance and community structure.

Morphological and physiological changes that occur during the rehydration of 2nd-stage infective larvae (L2) of Anguina agrostis are described. The first signs of motility, after 2 days of dehydration, were observed 0·5 h after rehydration and 90 % of the nematodes were moving within 15 h. Anabiotic A. agrostis were able to withstand repeated dehydration and rehydration. These procedures caused A. agrostis to accumulate large lipid droplets, which showed most clearly in the tail region. By means of a double labelling technique, it was shown that cuticle permeability of anabiotic L2 of A. agrostis initially increased slightly during rehydration. This was followed by a sharp decrease in permeability between 1 h and 8 h from the start of the experiment. A slower decline in permeability occurred between 8 h and 16 h and little further decrease occurred between 16 h and 24 h. The results are discussed in relation to the possible involvement of the epicuticle.

The epidemiology of Ostertagia ostertagi and other gastrointestinal nematodes in yearling beef cattle was examined in each of 2 successive years. During each year 50 head of newly weaned beef calves were given a single dose of thiabendazole and then placed on experimental pastures. Twenty-four of the animals were designated for monthly slaughter (n = 2) and analysis of worm population characteristics and 25 were designated for blood and faecal collection and for weighing. Parasite-free tracer calves were grazed alongside the yearling cattle each month (n = 2) throughout the 2 years and were also slaughtered for analysis of worm populations. Faecal egg counts, plasma pepsinogen determinations, herbage larval counts, and animal liveweight changes were recorded monthly. Results of this work substantiated previous observations on seasonal changes of populations of the different nematode genera, but greater continuity and definition of patterns was possible in the present work. Ostertagia ostertagi was the predominant nematode present. While minimal numbers of inhibited larvae were observed from autumn into winter, most of the population was adult at this time. Acquisition of inhibition-prone larvae begins in late winter and peak numbers are acquired between March and June. Little transmission of O. ostertagi occurs between June and September. Trichostrongylus axei had a similar seasonal prevalence to O. ostertagi. A major difference in the 2 years was in the pattern of maturation of inhibited larvae. This occurred early, during May 1981, following below average temperatures in May and above average rainfall in May and June. Overt type II disease was not associated with a smaller level of maturation in autumn 1981. In contrast, maturation of large burdens of inhibited larvae did not occur until autumn 1982 following a protracted period of dry and hot weather from spring. Acute type II disease was observed in autumn 1982. Reasons for the differences in maturation pattern, based on worm counts from yearling cattle and tracer calves and association of these with faecal egg counts, herbage larval counts, clinical condition, and liveweight changes are discussed.

Adult males and females of Onchocerca gutturosa were implanted into the peritoneal cavity of mice, and their survival was determined at intervals thereafter by post-mortem examination. Ten of 17 animals receiving males dissected free of bovine host tissues contained live parasites at necropsy up to 4 months later. Female worms digested free from connective tissue by collagenase did not survive well, even though they appeared motile and intact before implantation; only 2 were alive 10 days later in 2 of 16 recipients. When males and females still contained within connective tissue capsules were implanted they survived for up to 2 months, and microfilariae were detected transiently in the skin of 2 recipient mice. The results suggest the feasibility of maintaining adult O. gutturosa in rodents by this means, provided exposure of worms to enzymes used to free them from host tissue is avoided.

Experimental studies on the dynamics of infection of Lymnaea truncatula by the miracidia of Fasciola hepatica show that there is a linear relationship between the net rate of attachment of miracidia to snail epithelium and the density of infective stages. The probability of a snail remaining uninfected after exposure to a single miracidium varies with the size class of the snail. Under the conditions of the experiment (temperature, 15° C; exposure period, 30 min; water volume, 8 ml), the probability was 0·46–0·48, 0·27–0·26 and 0·13–0·19 for snail size classes, 0·5–2·9, 3·0-5·9 and 6·0-8·9 mm respectively.

The cidal properties of some phenolic, halogenated diphenyl, salicylanilide, benzimidazole and diaminophenoxyalkane anthelmintics, against 6-week-old worms of Fasciola hepatica were assessed in vitro. In a conventional fluke culture medium containing RPMI 1640, supplemented with serum with or without rabbit erythrocytes or pink-ghosts, only the halogenated diphenyl and salicylanilide compounds showed activity at concentrations equal to or less than 100 μm. However, when basal, serum and cell-free RPMI 1640 was used, all compounds other than diamphenethide were highly active, their minimum lethal concentrations being some 25–125 times lower under these conditions. The inclusion of rabbit liver microsomes in the basal culture medium resulted in diamphenethide exhibiting cidal activity equivalent to that seen when its free-amine active metabolite was assayed. The possibility that the activity of many of these compounds was masked in vitro because of their serum binding properties is discussed. Recommendations are made that in vitro screens for new fasciolicides should be carried out in serum-free medium and that additional replicates containing mammalian liver microsomes and liver cytosolic extracts be included as means for the metabolic activation of certain otherwise undetectable prodrugs.

The Gyrocotylidea is a group of platyhelminths comprising only a dozen or so species which have been placed in three genera, Oyrocotyle Diesing, 1850, Amphiptyches Grube and Wagener in Wagener, 1852 and Gyrocotyloides Fuhrmann, 1930. All species are highly specific to chimaeroid fish, a small group of present-day holocephalans, and are restricted to the spiral valve intestine of these hosts.