The plasma of mice infected with pleomorphic Trypanosoma brucei brucei contains a peptidase which has the same electrophoretic mobility on starch gels as a parasite peptidase. An enzyme with this electrophoretic mobility was not detected in the plasma of uninfected mice. The molecular weight of this enzyme in either parasite lysate or plasma from infected mice was approximately 40000 Da when assayed on a size exclusion column using high-performance liquid chromatography. The enzyme can cleave the dipeptides leu-ala, val-leu and pro-leu, but not the dipeptide phe-ala. The enzyme also cleaved the tripeptides tyr-tyr-tyr and leu-gly-gly. Another parasite peptidase which migrates on starch gels to a different position than the above-mentioned peptidase cleaved the dipeptides leu-ala, val-leu and pro-leu but could not cleave the tripeptides tyr-tyr-tyr or leu-gly-gly. Furthermore, incubation of this parasite peptidase with normal mouse plasma at 37 °C resulted in an apparent loss of detectable activity. It is postulated that the plasma of mice modifies either the charge or enzymic activity of this peptidase. We speculate that the parasite peptidase present in the plasma of mice infected with T. brucei could contribute to pathogenesis.

Uric acid is the most important constituent in the urine of insects. Infective metacyclic forms of the stercorarian trypanosomes are produced in the rectum of their insect vector and are thus in contact with uric acid. Using a culture system which permitted the growth of the insect stages of Trypanosoma musculi, we studied the influence of uric acid on the metacyclogenesis of this parasite. When added to the culture, uric acid enhanced the production of metacyclic forms. Furthermore, it rendered these trypanosomes highly infective by the oral route. It is suggested that uric acid may play an important role on the metacyclogenesis of T. musculi.

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.

A population of eels Anguilla anguilla from Lough Derg, R. Shannon, Ireland, harbouring infections of both Acanthocephalus lucii and A. anguillae was studied over three years. Both parasite species had the same intermediate host and eels appeared to be the only definitive host for A. anguillae. Throughout the whole period, A. lucii was the dominant parasite, was over-dispersed throughout the eel population and most frequently occurred as a single species infection. A. anguillae was far less common, its dispersion was close to random at most times and it almost invariably occurred as a mixed species infection. The proportions of the two species remained fairly constant over the period. Despite some indication of site selection in the intestine, the distribution of both species overlapped considerably and there was no evidence of competitive displacement of one species by the other or of resource partitioning in space. The life-histories of both species were similar: they infected eels, bred and were lost from fish at the same time of year and there was no indication of resource partitioning in time. Congeneric species of acanthocephalans can thus co-exist in apparently stable equilibrium in fish as predicted and without any evidence of interactions, but it is still considered that exploitation competition between the species may be occurring in eels.

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.

Teneral male Olossina morsitans centralis, G. austeni, G. palpalis palpalis, G. p. gambiensis, G. fuscipes fuscipes, G. tachinoides and G. brevipalpis were fed on the flanks of Boran calves infected with Trypanosoma vivax stock ILRAD 2241 isolated from a cow in Likoni, Kenya; stock ILRAD 2337 isolated from a cow in Galana, Kenya; stock ILRAD 1392 isolated from a cow in Nigeria; or, stock EATRO 1721 isolated from G. m. submorsitans in Nigeria. The tsetse were fed on the infected hosts for 24 days and were then dissected to determine the infection rates. In G. m. centralis and G. brevipalpis, the mature infection rates of T. vivax from Kenya were 61·1 %, and 75·3% for ILRAD 2241, and 36·2% and 58·2% for ILRAD 2337, respectively. In G. austeni and in the four palpalis group of tsetse, the rates for these two stocks were very low and ranged from 0% in G. p. palpalis to 1·8% in G. austeni for ILRAD 2241 and from 0% in G. f. fuscipes to 5% in G. tachinoides for ILRAD 2337. In contrast, the hypopharyngeal infection rates of T. vivax from Nigeria were quite high in all the 7 tsetse species and sub-species. They ranged from 55·5% in G. austeni to 919% in G. p. gambiensis for ILRAD 1392, and from 71·4% in G. austenei to 97·1 % in G. brevipalpis for EATRO 1721. It is suggested that successful establishment of T. vivax infection in a particular tsetse species could depend on the biochemical characteristics of its attachment sites in the food canal and the efficiency of bloodstream trypomastigotes of a particular T. vivax stock to attach to such sites and undergo complete development to meta-trypanosomes in the hypopharynx of the vector.

Primary infections of Heligmosomoides polygyrus were studied in adult male CD1 mice fed on isoenergetic synthetic diets containing either 2% or 20% protein (casein). A slight reduction in food intake was observed during infection, and this was unaffected by diet. Protein deficiency was also found to have no effect upon worm establishment. Evidence was found, though, to suggest that the worms have a more severe effect upon the host in protein-deficient mice. Hypoalbuminaemia was observed due to diet and also infection, and this was synergistic. There was an increase in non-albumin plasma protein during infection which was not effected by diet. The circulating urea concentration was reduced during protein deficiency, as was the level of essential amino acids, but non-essential amino acid levels were raised. An increase in the levels of urea and essential amino acids was observed at day 4 of infection in mice on the 20% diet, but not on the 2% diet. Splenic atrophy occurred during infection, but the splanomegaly that occurred early during infection was proportionally greater in protein-deficient mice. These results are discussed in terms of the pathophysiology of both protein deficiency and infection, and comparisons are made with human malnutrition syndromes.

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.

The dominant repetitive deoxyribonucleic acid (DNA) sequence in the genome of a clone of Trypanosoma (Nannomonas) simiae has been identified and cloned as a recombinant plasmid. The recombinant plasmid was used in hybridization analyses of DNA samples obtained from various trypanosome species and subspecies. The results indicated that the T. simiae repetitive DNA sequence hybridized with DNA derived only from T. simiae; it did not hybridize with DNA derived from clones or stocks of T. congolense, or from any other trypanosome species examined. A preliminary characterization of the cloned DNA sequence and its use in the identification of T. simiae of similar genotypes are presented.

Studies of patterns of reinfection with four species of intestinal nematodes (Ascaris, hookworm, Trichuris and Enterobius) in 174 individual patients following chemotherapeutic treatment revealed statistical evidence for predisposition to heavy or light infection (relative to the average level in the overall population). Analyses of associations between the abundances of the four species of nematodes within a combined sample of 525 worm burdens showed significant correlations between 5 out of the 6 possible pair-wise comparisons between species. The relevance of these results to the design of control programmes based on chemotherapeutic application is discussed.

The distribution and abundance of Enterobius vermicularis in a fishing community in South India, as determined by counting worms expelled following mass anthelmintic chemotherapy, was examined in samples of patients stratified by age, sex and family grouping. The results of a worm expulsion study in January 1984 are compared with those of a second expulsion programme in November 1984, following an 11-month period of reinfection. The prevalence of Enterobius infection was consistently high in all age groups of both males and females. A comparison of the overall prevalence and intensity of infection in the January and November surveys revealed significant increases in both the percent infected and the mean number of worms harboured in November relative to the initial level. No significant trends in the intensity of Enterobius according to host age or sex were detected in either survey. The frequency distribution of Enterobius was found to be highly aggregated in the population as a whole and within age groups. At both sampling dates, the most heavily infected 25% of the community harboured over 90% of the total pinworms recovered. There was a significant pattern within most age groups for individuals to re-acquire worm burdens of a similar magnitude to their initial pre-treatment burdens. Heavy infections were found to be associated with household. A selective or targetted approach to treatment of heavily infected individuals or households is likely to be an efficient means of reducing parasite abundance on a community-wide basis. It must be stressed, however, that treatment must be applied at frequent intervals in order to achieve a long-term reduction in pinworm abundance and to avoid the possibility of increasing the intensity of infection, as was observed in this community.

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.

The class-specific antibody responses of 3 strains of mice (C57/Bl10, BALB/C and CBA/N) known to vary in their ability to control the microfilaraemia which follows the subcutaneous transplantation of adult female Dipetalonema viteae has been investigated. The 3 mouse strains showed significant variation (a) in total levels of immunoglobulins and (b) in ability to recognize individual radio-isotope-labelled antigens as measured by coprecipitation. Within each mouse strain it was noted that antigens could vary with respect to the nature of the isotype of the antibody response which they elicited. Furthermore, by comparing results obtained from class-specific coprecipitation with surface ELISA it was found that a similar variation between responses to individual epitopes was also likely. No differences were observed in the humoral response of the 3 mouse strains which could explain the known resistance of the C57/B110 strain; reasons for this are discussed.

Chronic primary infections with Heligmosomoides polygyrus (Nematospiroides dubius) are still relatively poorly documented, particularly in relation to the role of host resistance in limiting worm survival. In the present work the duration of infection with H. polygyrus was studied in CFLP mice given doses of infective larvae ranging from 50 to 500 L3. The least heavily infected (50 L3) group ceased egg production earliest (week 36) whereas eggs were still detected in the faeces of mice given 500 larvae in week 42. At autopsy (week 42) mice given 50 larvae had virtually lost their entire worm burden with 5 out of 11 mice still harbouring a single worm each. However, all the mice in the group given 500 larvae were still infected, the highest worm burden being 93. The concentration of serum IgGl and specific antibody was highest in mice given 500 larvae, but sera taken from mice with declining worm burdens 19–38 weeks post-infection did not contain detectable host-protective antibody. During the course of infection in CFLP mice, H, polygyrus sustained irreversible changes in its capacity for subsequent survival. Thus, adult worms transferred to naive mice 2, 7, 14, 30 or 36 weeks post-infection did not live longer than worms of a comparable age in the respective donor group. In contrast, primary infection worms taken from jirds in which expulsion is usually completed by 6 weeks post-infection, re-established in mice and survived considerably longer than in the group of donor jirds. These results were discussed in relation to the possible interactions between parasite senility and immunomodulation, and host resistance in limiting primary infections with H. polygyrus in mice and jirds.

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.

Cyathocotyle bushiensis Khan 1962 is a digenean intestinal parasite of ducks that appears to be involved in seasonal mortality of the definitive host. Temperature dependence of egg hatching and miracidial survival at 25%C were experimentally investigated as part of a study on transmission of the larval stages. Maximum percentage of hatching was obtained at a temperature of 25%C, at which the average hatching time was 21·7 days. The average hatching time decreased linearly from 38·9 days to 9·8 days between 18 and 28%C. Eggs exposed to cold (4%C) prior to incubation at 25%C were significantly less successful in hatching than fresh eggs incubated at the same temperature. Their hatching percentage was much reduced and their average hatching time was increased. Similarly, eggs collected in late autumn (as opposed to summer) and incubated at 23%C had significantly lower hatching success and significantly increased average hatching time. At 25%C, the average life-span of the miracidia was 8·8 h. These results are compared with similar data from other digenean species and their significance is discussed in relation to transmission to the first intermediate host in climatic conditions prevalent in endemic areas.

A mathematical model of the parasitic phase of the life-cycle of Ostertagia ostertagi in calves is described. The model is used in the re-analysis of previously published data from a long-term trickle infection experiment in which groups of calves were infected daily with graded doses of 3rd-stage (L3) larvae. The results of the analysis are consistent with the hypothesis that the observed changes in the intensity of infection in the calves were the result of a decline in the proportional establishment of ingested L3 larvae, and a rise in the death rate of the 5th-stage worms as the duration of exposure to infection increased. The proportion of ingested L3 larvae that become established in the mucosa can be described as an exponential decay function of the duration of the infection. Within the range of trickle intensities investigated, the function appears to vary independently of the level of exposure to infection. In contrast, the rate of mortality of the 5th-stage worms appears to be an increasing linear function of the total cumulative number of 3rd-stage larvae administered.

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.

The nematode Trichinella spiralis is able to modulate the antibody response, as measured by the plaque-forming cell (PFC) technique, to three thymus-dependent (TD) antigens: (1) a heterologous antigen unrelated to the parasite (sheep red blood cells (SRBC)); (2) an antigenic fraction, rich in phosphorylcholine (PC), obtained from T. spiralis (FCpl) and (3) a heterologous antigen unrelated to the parasite, but sharing the PC epitope with the FCpl fraction (PC-KLH). During the life-cycle of the parasite in BCF1 mice, two opposing immunomodulating activities occur: (1) an immuno-potentiating activity in mice infected during the intestinal and larval migratory stages, for all three antigens, and (2) a carrier-specific immunosuppressive response in mice infected and immunized with the FCpl fraction during the muscle phase of the life-cycle. The anti-PC PFC response of these mice is dependent on the infection dose and decreases from day 35 post-infection (p.i.) until at least day 85 p.i.. The factor responsible for the stimulating effect observed during this stage is the presence of migratory larvae in the host. All the foregoing seems to indicate that T. spiralis can use specific suppression mechanisms to aid in its own survival.

Taenia cestodes were obtained from 5 different definitive host species in Kenya and 175 different samples were examined by classical morphological methods and by isoenzyme analysis using isoelectric focusing in agarose. Gels were stained for 17 different enzymes and 3 of these were used in the construction of isoenzyme profiles. The samples fell into 25 zymodemes, and no zymodeme contained more than 1 species of Taenia, indicating that isoenzyme analysis can reliably be used for the identification of species of this genus.