The mature thread-like spermatozoon of Paragonimus ohirai was shown to be composed of 7 distinct segments which have morphologically different characteristics, following staining with silver nitrate. The first segment (1S) is a needle-shaped structure with a perforatorium. The 2S is composed of two filaments loosely paired; 3S consists of a somewhat coarse thread (vestige of the cytoplasmic projection); 4S is composed of two flagella tightly paired; in 5S, two silver-positive filaments are independently seen as in 2S; 6S has a ‘spiral’ structure composed of two flagella; in 7S, two filaments are seen dissociated from each other. The sperm nucleus exists within the ‘spiral’ structure of 6S and this structure may serve to hold and/or protect the nucleus. The technique presented here is useful for gross morphological observations of the long sperm of flatworms.

The hypothesis that a liver-inhabiting nematode, Capillaria hepatica, can regulate abundance of the house mouse (Mus domesticus) was tested in enclosures, in southeastern Australia. Changes in mouse abundance, and the relationship between mortality and host abundance were compared in three treatment and three control populations. Any effect of C. hepatica on mouse abundance was masked by an unknown regulating factor(s). This factor(s) caused density-dependent mortality in the control and treatment populations and, together with strong seasonal trends in parasite transmission, confounded our test of the ability of C. hepatica to regulate the abundance of house mice. The seasonal trends in transmission have important implications for the potential of this parasite as a biological control agent and for models of the interaction of C. hepatica and mouse populations. Transmission of C. hepatica apparently occurred throughout the 18 month study, further supporting its potential as a biological agent in the control of mouse plagues in this region.

Pseudodiplorchis americanus has an extremely brief opportunity for transmission, restricted to less than 24 h in the year when the host (Scaphiopus couchii) enters water to breed. This strict annual cycle means that invading worms have 1 year to complete reproductive development. Despite this, a large proportion of the parasite suprapopulation is not prepared for transmission at the time of host breeding. The present study correlates detailed soil temperatures for one field site in S.E. Arizona, spanning 3·5 years, with laboratory data on parasite growth and reproductive development at a series of controlled temperatures. Development is totally inhibited at 16°C. Optimal growth and development occurs at 25°C and is slower at both 20°C and a diurnal cycle fluctuating between 20 and 34°C (mean 27°C) (simulating summer temperatures experienced by host and parasite). The effective period for accumulation of infective stages by P. americanus in any one season varies according to the timing of the summer rains in consecutive years. Between 1985 and 1988, the interval between host breedings varied from 11 to 13 months and the period when temperatures were above 20°C varied from 4 to 5·5 months per year. Since the first month post-infection (p.i.) consists of pre-reproductive development, first-year worms have only 3–4·5 months to produce infective larvae. In the shortest seasons, these worms may not be able to complete reproductive preparation in time for the first opportunity for transmission. In different parts of the geographical distribution of S. couchii, different cycles of temperature, rainfall and host breeding occur; varying temperature regimes represent an important abiotic control of P. americanus reproductive biology and transmission.

The white colour of the cyst wall of the metacercaria of Microphallus sp., even in the presence of dihydroxy phenol and phenoloxidase, is due to proteins generated through a possible quinone methide interaction. The quinone methide isomerase converts the phenoloxidase mediated quinone into β-hydroxy catechol. Formation of catechol from quinone by cyst extracts was observed spectrophotometrically and chromatographically. This enzyme is involved in detoxification of excess quinone and β-sclerotization of the cyst wall.

Infective-stage larvae of three different isolates of Toxocara canis were intrinsically ([35S]methionine) labelled in culture, to determine the presence of similarities or differences in the somatic and ES antigens expressed between larvae derived from different hosts and different geographical regions. Two other closely related ascaridids, Toxascaris leonina which infects cats and dogs, and Toxocara vitulorum (Neoascaris vitulorum) which infects cattle, were also compared to T. canis larvae by this method. Overall comparisons were made by 1- and 2-dimensional electrophoresis, while immunological cross-reactivities between the different species were analysed by radio-immunoprecipitation. Our results show that extensive physicochemical characteristics are shared between T. canis isolates, both from different hosts and different geographical locations. A substantial overlap was revealed when T. canis and T. vitulorum antigens were compared, whereas Toxascaris was found to produce a distinct antigen profile: this result was independent of whether methionine- or Iodogen-labelled products were being considered. Antigen recognition by polyclonal antibodies raised to all three species and to the cat ascaridid Toxocara cati, revealed considerable cross-reactivities. The cross-reactions were especially prominent between the Toxocara species, a fact further substantiated when reactivity of T. canis ES-specific monoclonal antibodies were tested against T. leonina and T. vitulorum antigens. The ES antigens of T. leonina were not recognized by the T. canis monoclonals, whereas the majority of these antibodies precipitated antigens of T. vitulorum. One which did not react with T. vitulorum was monoclonal antibody Tcn 2, indicating its species-specific reactivity and therefore its potential for the specific diagnosis of human toxocariasis.

Proteases from infective larval (L3) and adult stages of Nippostrongylus brasiliensis were investigated with a combination of techniques involving gelatin degradation and cleavage of fluorogenic substrates. Analysis of L3 excretory–secretory (ES) products revealed enzymes of Mr 51, 58, 79, ~ 150 and ~ 250 kDa. Inhibition profiles indicate that the major 51 kDa protease is a metallo-enzyme. Significantly, little activity was present in larval somatic extracts, suggesting the synthesis of zymogens or precursor forms prior to secretion. Adult ES contained a distinct enzyme, of 50 kDa, and a number of other proteases were detected in somatic extracts of this stage, ranging from 51 to > 300 kDa. The largest of these adult somatic enzymes is also a putative metallo-protease. While nearly all enzymes from both L3 and adult are heat labile, incubation at 100 °C generated a previously unobserved activity at 20 kDa. Furthermore, a protease of similar size may be found in uninfected rat intestinal tissue, suggesting specific uptake of a host-associated enzyme by the parasite in the form of an inactive, heat-labile complex.

Infectivity of Trichinella pseudospiralis in Chinese hamsters was greater than that of Trichinella spiralis. Concurrent infection with these two species of parasite was accompanied by an increase in infectivity of T. spiralis. The infectivity of T. pseudospiralis, but not that of T. spiralis, was significantly influenced by host age. Regardless of host age, T. pseudospiralis was more infective for the Chinese hamster than was T. spiralis. Early during infection, enteritis (myeloperoxidase activity) in hamsters infected with T. pseudospiralis alone was significantly less than that seen in animals infected with T. spiralis alone or with both species concurrently. Myositis in hamsters infected with T. pseudospiralis alone was significantly less on days 14, 17 and 25 post-infection (p.i.) than that observed in concurrently infected or T. spiralis-infected animals. On days 11 and 14 p.i. inflammation in diaphragm muscle from concurrently infected hamsters was significantly less than that seen in animals infected with T. spiralis alone. Muscle histology supported these chemical data on myositis. Suppression of the host inflammatory response against early muscle-stage larvae of T. pseudospiralis underlies the greater infectivity of this parasite for the Chinese hamster.

An experiment was designed to investigate aspects of the population dynamics of acquired immunity to Heligmosomoides polygyrus in laboratory mice. The influence of host strain (CBA or NIH), rate of exposure (5 or 40 L3/mouse/2 weeks) and diet (3 or 16% protein w/w) on the population dynamics of repeated infection and the response to a standard challenge infection were investigated. The time delay between the end of the period of repeated infection and the subsequent challenge (between 1 and 24 weeks) had no effect on worm recovery. The effects of both exposure and diet were significant and similar whether assessed on the basis of the dynamics of repeated infection or response to challenge: low rates of exposure and low dietary protein were both associated with low levels of acquired immunity. Mouse strain was the most important determinant of worm recovery after challenge, but had no significant effect on the degree to which parasite population growth was constrained by acquired immunity during repeated infection. It is suggested that both CBA and NIH mice raise immune responses which act on parasite survival, but that only NIH mice raise responses operative against larval establishment.

Twelve populations of bats were examined to determine the extent of interspecific associations in determining the species richness of intestinal helminth infracommunities. The pool of helminth species which was available to individual bats ranged from 2 to 21. The ‘summed binomial’ distribution was determined to underlie the host frequency distribution of the number of helminth species per host. Overall covariation in occurrences of species in replicated communities can be detected by testing for the equality of the observed variance of the host frequency distribution to the variance expected when species are allocated to hosts at random. Where statistically significant the covariance was indicative of a majority of positive rather than negative interspecific associations. As the mean number of species per host in a host population increases not only does the number of positive associations increase but so does the proportion of species pairs which exhibit positive associations. Although there is an increase in the proportion of species pairs which exhibit positive associations as the number of species increases, the magnitude of the associations (as indicated by the mean positive or the mean negative pairwise covariances) does not. Therefore, we concluded that positive interactions are more common than negative interactions in determining the species richness of helminth infracommunities of bats. Further, positive associations become even more important as the community becomes more complex. However, the increased importance is derived from the number rather than the strength of the associations.

A genomic library of Meloidogyne incognita Race 1 has been prepared in the bacteriophage λgt10 and screened for specific DNA sequences by hybridization with radio-isotope labelled total genomic DNA from a number of Meloidogyne species. One clone isolated (MR1#15), although not totally species specific, clearly showed preferential hybridization to M. incognita. Following subcloning and sequencing of the 255 bp insert, four stretches of the sequence corresponding to oligonucleotides of approximately equal length (~60 bp) were synthesized and examined for specificity. One of them, MR1#15.2, showed the necessary specificity to be used as a diagnostic tool.

The cercariae of Cryptocotyle lingua have a brief but active life during which they do not feed. In order to maximize the probability of infection they must respond to a variety of host-related stimuli yet conserve their finite energy reserves by minimizing unnecessary muscular activity. In laboratory experiments, simulated shadows representing the passage of a fish host were found to increase population activity levels. Evidence was also found for a relationship between shadow duration and the duration of subsequent bursts of swimming activity. Adaptation to continuous shadowing was recorded, its onset and magnitude being dependent on both the frequency and duration of shadows delivered. As cercariae aged they became less responsive to shadow stimuli, especially those of short duration.

Taenia multiceps coenurus fluid was analysed by fast protein liquid chromatography in order to separate the factors responsible for previously reported modification of immunological activity in macrophages and T-cells. One factor, F7, was found to be mitogenic for murine L3T4+ T-cells, to be macrophage dependent, to require macrophage compatibility at the I region of the H2 complex, to increase the sensitivity of T-cells to regulatory signals from macrophages and to increase the rate of generation of splenic rosette-forming cells (RFC) against sheep red cells. A second factor, F24, was found to alter macrophages so as to render them suppressive, rather than stimulatory, for parasite-activated and Con A-activated lymphocyte transformation, to depress the rate of generation of RFC and to antagonize the mitogenic effect of F7. The combined actions of these two factors are, therefore, sufficient to explain the known immunomodulatory effects of the metacestode.

This investigation reports for the first time the establishment of a trematode life-cycle in the laboratory using in ovo cultivation of the adult stage. Microphallus primas metacercarial cysts were removed from Carcinus maenas crabs and chemically excysted. Using a modification of the technique developed by Fried (1962) the released metacercariae were grown in fertile hen's eggs to ovigerous adult flukes. These were removed from the under surface of the chorio-allantoic membrane of chick embryos 5 days post-infection and the fluke eggs recovered were used to infect laboratory-reared Hydrobia ulvae snails. When challenged against parasite-free crabs the cercariae released from the experimentally infected snails gave rise to metacercarial cysts that were again identified as M. primas.

The behaviour of Heterodera schachtii second-stage juveniles in response to mustard (Sinapis alba) rooxudates was observed and analysed under aseptic conditions in a standardized bioassay. Aggregation of juveniles on an agarose layer occurred within less than 30 min in the area where root exudates had been applied and persisted for several hours. Analysis of time-lapse video recordings showed that the aggregation did not result from a directed orientation of the juvenile towards the root exudate. This was supported by an orientation assay using single juveniles. Aggregated juveniles showed pre-infection exploratory behaviour, including stylet thrusting and head-end bending, while staying at rest for several minutes.

The course of primary infection was studied in BALB and B10 H-2 congenic mouse strains. The duration of infection, as assessed with regular faecal egg counts and worm burdens, was shorter in mice carrying the H-2s, H-2d or H-2q haplotypes when compared to mice with H-2b. Strains with H-2k were intermediate. An experiment was carried out to test the hypothesis proposed by Wassom, Krco & David (1987) predicting that the progeny of I–E+ve mouse strains crossed with I–E-ve strains, would show susceptibility rather than resistance to infection. This hypothesis was not substantiated by our data and we conclude that it does not apply to primary infections with Heligmosomoides polygyrus. It is proposed that the gene products of at least two loci within the H-2 (associated with the H-2b and H-2k haplotypes) are crucial in determining the response phenotype of mice to primary infection with H. polygyrus. One allele, (associated with the H-2b haplotype) may be preferentially affected by parasite-mediated immunosuppression.