An enzyme analysis of diploid and triploid Paragonimus westermani was conducted using starch gel electrophoresis. In total, 16 enzymes, probably encoded by 18 loci, were studied for 3 populations of the diploid form sampled from 2 localities, and 4 populations of the triploid form from 4 localities. Comparison of the enzymes of the triploid and the diploid digeneans showed 5 different patterns; diaphorase (EC 1.6.2.2), glutamic-oxaloacetic transaminase (EC 2.6.1.1), hexokinase (EC 2.7.1.1), leucylglycylglycine aminopeptidase (EC 3.4.1.3), and phosphoglucomutase (EC 2.7.5.1). On the basis of the numbers of bands and their patterns, all individuals of the triploid are probably heterozygous at each of these 5 loci and homozygous at the remaining 13 loci. The occurrence of fixed heterozygotes found in triploid populations cannot be easily explained by only a single mutation. It is suggested that the variability may have been introduced by hybridization with a different sub-species or a closely related species and may, thus, have been maintained since the time of the origin of triploids.

Cercarial transmission of Schistosoma mansoni and S. mattheei was monitored in two small rivers near Durban, South Africa. The seasonal patterns recorded corresponded to those already documented for these parasites. Tn the case of S. mansoni, however, this was interrupted at the height of the transmission season. The reason for this was believed to be very low oxygen concentrations in the snail habitat due to unusually extensive growth of the plant Ludwigia stolonifera over the water. The failure of the spring rains, which would normally have flushed the system is seen as contributing to this phenomenon. Infection rates in the snail intermediate hosts were low ( > 10%). A preponderance of male worms of both schistosome species was noted.

A total of 65 enzymes in the 8 European pathotypes of the potato cyst nematodes Globodera pallida and G. rostochiensis were examined by isoelectric focusing (IEF) for possible polymorphic variants which may aid rapid pathotype recognition. Quantitative variation was seen with glucose oxidase (EC 1.1.3.4), with high levels of this enzyme present in G. rostochiensis Ro3. Mannose phosphate isomerase (EC 5.3.1.8) also varied between the pathotypes with G. rostochiensis Ro4 and Ro5 differing from the other pathotypes in the relative absorbance of some bands. Phosphoglucomutase was examined on a narrow-range pH gel and additional differences to those described previously were detected.

Antigenic proteins on the surfaces of different developmental stages of Schistosoma mansoni were radio-iodinated by the lodogen-catalysed method and identified by immunoprecipitation with a panel of antisera. The sera comprised specific immune serum from mice harbouring a chronic schistosome infection or vaccinated with γ-irradiated cercariae; serum from rabbits immunized with adult schistosome tegumental outer membranes or a partially purified Mr32K glycoprotein from adult worm membranes; and a monoclonal antibody recognizing an Mr20 K antigen on the surface of schistosomula. The Mr38–32 K glycoproteins were the major antigens identified in surface-labelled cercariae and their probable association with the glycocalyx is discussed. Schistosomula transformed from cercariae either mechanically or by penetration of host skin in vitro, expressed a similar pattern of surface antigens to that identified for cercariae, but low molecular weight antigens of Mr20, 17 and 15 K were also detected. The Mr38–32 K glycoproteins, although present on newly transformed schistoso mula, were progressively replaced with time, by a single dominant glycoprotein (Mr 32 K) expressing identical epitopes to those on the Mr 38–32 K complex. Moreover, the data confirm that the Mr 32 K glycoprotein persists on the tegument after in vivo maturation and is conserved, together with Mr 20 and 15 K antigens, through to the adult stage. New antigens (Mr 97 and 25 K) were also detected during in vivo maturation and were present in late-stage schistosomes recovered from infected hosts. In addition, the enzyme alkaline phosphatase is expressed on the surfaces of 3-week-old liver worms as a dominant antigen (Mr 65 K); this feature may be related to nutritional and/or physiological processes in the tegument of this metabolically active stage of development.

Curie-point pyrolysis gas-liquid chromatography (PGLC) was used to detect gross chemical differences between the 8 European pathotypes of the potato cyst nematodes Globodera rostochiensis and G. pallida. No qualitative differences were seen with either flame ionization or flame photometric detection systems, although quantitative differences between pathotypes were detected. Cluster analysis of these differences failed to group the pathotypes into species, but separation of some economically important pathotypes was achieved. The potential of PGLC for nematode identification is discussed.

The gross- and histopathology of natural and experimental Schistosoma curassoni infections in sheep were studied. The data obtained showed that S. curassoni infection in sheep causes only slight clinico-pathological manifestations with preferential involvement of the liver, the lower intestine and the urinary bladder. A variable spectrum of host reaction to the eggs within an individual animal was observed, reflecting the duration of presence of eggs in the organs. In the liver, egg granulomas were most numerous in the perilobular regions, while in the intestine, lesions were most pronounced in the mucosa of the rectum. The presence of eggs in 10% of the urinary bladders examined indicated some bladder involvement.

An ultrastructural study has been performed on radiation-attenuated parasites fixed in situ during their extended stay in the lungs. At day 7 post-infection all parasites were located within blood vessels. In contrast to normally migrating parasites, at days 13 and 21 post-infection the majority of radiation-attenuated parasites were lying free within alveoli. As far as could be seen, radiation-attenuated parasites had undergone the normal develop mental changes associated with the lung stage of migration. These included elongation of the body and loss of mid-body spines and the fibrous layer beneath the tegument. No ultrastructural evidence was found to suggest why schistosomula failed to migrate further and instead burst into alveoli. No parasites observed on day 7 post-infection were associated with a host inflammatory reaction. At day 13, inflammation was noticeable but could have been a response as much to pulmonary tissue damage as to the presence of parasites. At day 21 post-infection some parasites were internally disrupted but were not associated with host inflammatory reactions and had intact tegumental surfaces – all facts consistent with death by autophagy. One parasite was observed at day 21 with an adherent neutrophil infiltrate and extensive tegumental damage. The relevance of persisting lung-stage parasites to the induction of resistance to challenge is discussed.

The development of the male reproductive system in Gyrodactylus gasterostei has been followed using parasites of known age maintained on isolated hosts. The penis develops shortly after the parasite has given birth for the first time (at an age of 24–30 h at 13°C) and the first active spermatozoa appear after 40–50 h. Spermatogenesis occurs more rapidly in G. gasterostei than in any other parasitic flatworm (including those from warm-blooded hosts) in which it has been measured, and the onset of male maturity is further hastened by a reduction in the number of pre-spermatogenic germ cell divisions. Spermatogonia have a diploid chromosome complement of 12, and spermatocytes undergo meiosis to produce haploid spermatozoa. No evidence of aneuploidy in spermatozoa was obtained. Although the development of haploid spermatozoa suggests that sexual reproduction can occur, production of embryos by isolated flukes which lack a mature male system indicates that other means of reproduction may also be employed.

Mice of the inbred P strain fail to develop significant resistance to challenge Schistosoma mansoni infection at 6 weeks after either low-grade primary infection or vaccination with attenuated homologous parasites, in contrast to other strains such as C57B1/6, and thus provide a model for comparison of potential immune resistance mechanisms in low versus high responder animals. In this study, the antigen-specific cellular responses found to correlate with resistance in these strains were delayed cutaneous hypersensitivity, production of macrophage activating lymphokine and macrophage larvicidal activity, all of which were greater in infected or vaccinated C57B1/6 mice than in similarly immunized but non-resistant P mice. Humoral responses correlating with resistance were IgM reactivity to schistosomula surface antigens in both infected and vaccinated animals, as well as both IgM and IgG reactivity to soluble schistosome antigens in infected mice. Immune responses that showed no relationship with resistance included IgG reactivity to larval surface antigens and immediate hypersensitivity to soluble worm antigens. In infected mice, neither granuloma size nor extent of hepatic fibrosis correlated positively with resistance to challenge infection. Thus, similarities exist between patterns of resistance and immune response at this early time after immunization with either viable or attenuated parasites. These observations suggest that common immune effector mechanisms could be involved, with activated macrophages playing a central role in resistance.

The hamster cheek pouch has been used to investigate the skin migration of schistosomula at the ultrastructural level. Parasites have been observed up to 72 h post-infection. Despite rapidly reaching the epidermal basement membrane schistosomula remain in an epidermal location for at least 40 h post-infection, by which time the acetabular glands and their ducts have been lost and the transformation from cercaria to schistosomulum completed. Entry into the dermis and exit from the skin via the blood vessels is therefore by mechanical means or by lytic secretions emanating from a source other than the acetabular glands. The head gland which persists in the dermal schistosomula is a probable source of such secretions. The observations suggest that the apical area and musculature of the head capsule are important in gaining access to the lumen of blood vessels.

Heterogeneity in susceptibility of guppies (Poecilia reticulata) to infection with Gyrodactylus bullatarudis was examined by comparing the establishment, reproduction and survival of the parasite on 4 inbred strains of the fish host following low and high levels of exposure to infection. The 4 strains fell into 2 broad categories of innately ‘resistant’ and ‘susceptible’ fish on the basis of strain differences in (a) the rates of growth and decay of the parasite populations, (b) the proportional occurrence of susceptible and resistant fish within each strain, (c) the average duration of primary infection, and (d) the duration of resistance to reinfection following recovery from a primary exposure. The results suggest genetic control of resistance/susceptibility traits and experiments with hybrids tentatively suggest dominance of resistance over susceptibility. The potential of the guppy – Gyrodactylus laboratory system for the investigation of the role of genetic factors in the study of host–parasite interactions is discussed.

Digenean flukes can be broadly classified into three basic groups according to their location within the host: (1) the lumen of the alimentary canal or associated organ, (2) body cavity or tissue and (3) external surfaces. We selected three species of Proterometra that represent these basic groups and tested their capacities for cutaneous transport of glucose. Facilitated diffusion is the type of transport system in the tegument of P. edneyi, which lives in the gut of its host. An activetransport system is present in P. dickermani, the tissue-dwelling species. No cutaneous system for transporting glucose is present in the ectoparasitic P. macrostoma. The known capacities for tegumental sugar transport in other digeneans are correlated with similar habitats. Such associations involving unrelated as well as closely related species suggest that the niche biology of digeneans involves evolutionary specializations of the tegument for absorbing sugar.

A number of published studies of competition between parasite species are examined and compared. It is suggested that two general levels of interaction are discernible: these correspond to the two levels of competition recognized by workers studying free-living animals and plants: ‘exploitation’ and ‘interference’ competition. The former may be defined as the joint utilization of a host species by two or more parasite species, while the latter occurs when antagonistic mechanisms are utilized by one species either to reduce the survival or fecundity of a second species or to displace it from a preferred site of attachment. Data illustrating both levels of interaction are collated from a survey of the published literature and these suggest that interference competition invariably operates asymmetrically. The data are also used to estimate a number of population parameters which are important in determining the impact of competition at the population level. Theoretical models of host-parasite associations for both classes of competition are used to examine the expected patterns of population dynamics that will be exhibited by simple two-species communities of parasites that utilize the same host population. The analysis suggests that the most important factor allowing competing species of parasites to coexist is the statistical distribution of the parasites within the host population. A joint stable equilibrium should be possible if both species are aggregated in their distribution. The size of the parasite burdens at equilibrium is then determined by other life-history parameters such as pathogenicity, rates of resource utilization and antagonistic ability. Comparison of these theoretical expectations with a variety of sets of empirical data forms the basis for a discussion about the importance of competition in natural parasite populations. The models are used to assess quantitatively the potential for using competing parasite species as biological control agents for pathogens of economic or medical importance. The most important criterion for identifying a successful control agent is an ability to infect a high proportion of the host population. If such a parasite species also exhibits an intermediate level of pathology or an efficient ability to utilize shared common resources, antagonistic interactions between the parasite species contribute only secondarily to the success of the control. Competition in parasites is compared with competition in free-living animals and plants. The comparison suggests further experimental tests which may help to assess the importance of competition in determining the structure of more complex parasite-host communities.

The immune status of a group of sheep naturally infected with hydatid cysts was investigated. Low specific anti-hydatid antibody (Sab) titres and negative results in intradermal and leucocyte migration tests occurred in hosts with high hydatid antigen-stimulated lymphocyte transformation(LT). Total(non-specific) IgG was elevated in infected sheep and was positively correlated with LT. Circulating hydatid antigen (cAg) was detectable in some infected sheep, but not in all of those with low Sab. Relationships between eAg, Sab and immune complex levels suggest that most eAg is present in immune complexes.

In laboratory studies with 3 species of Calliphora more than half were shown to ingest eggs of Taenia hydatigena from the surface of clog faeces with a maximum of over 5000 eggs in 1 fly. Most eggs were voided within 48 h and between 38 and 48% of these eggs had lost their embryophores. In field studies carried out in the South Island of New Zealand, traps baited with dog faeces captured the following blowfly species in decreasing order of abundance: Hybopygia varia, Calliphora quadrimaculata, C. hortona and C. stygia. Peak numbers were trapped in January, February and March. Almost 25% of wild flies, caught after feeding for up to 3 mm on dog faeces naturally contaminated with taeniid eggs, had eggs in their intestine. When administered to lambs all 4 species of fly transferred infection. Lambs grazed in winter on plots near kennels that had housed dogs with patent infections of T. hydatigena acquired higher worm burdens than those grazed further away. The burdens were greater downwind of the prevailing wind. After removal of the dogs, blowflies caught in the vicinity contained taeniid eggs but the contents of pitfall traps did not. Blowflies, and to a much lesser degree the insects and dust caught on sticky traps during the presence of the dogs, transferred infection when administered to naive lambs.

Media are described which stimulate the eggs of Notocotylus attenuatus to hatch in vitro. Hatching involves opening of the operculum and emergence of the opercular cord to form a tube measuring approximately 75 μm in length along which the sporocyst passes. The sporocyst is then released from the end of the tube. It is suggested that in vivo the opercular cord serves to inject the sporocyst through the snail host's gut wall into the haemocoel.

The hydrolytic, reductive and oxidative enzyme systems involved in the phase I biotrans formation of xenobiotic compounds have been investigated in Hymenolepis diminuta. Adult H. diminuta are able to carry out a range of hydrolytic and reductive reactions, but in common with other helminths oxidative detoxification reactions were absent (oxidative demethylation, aniline hydroxylation, nitrobenzene hydroxylation, biphenyl hydroxylation). These oxidative reactions were readily demonstrated in rat liver. Extracts of H. diminuta hydrolysed nitrophenylphosphates and inorganic pyrophosphate, but not arylsulphates, nor could epoxide hydratase activity be detected. N-Deacetylase activity was present. However, O-deacetylase activity could not be demonstrated, although butyrate and palmitate, but not benzoate, esters were hydrolysed. H. diminuta was capable of hydrolysing a range of a-and β-glycosides, but not β-glucuronides. Extracts of H. diminuta reduced azo-compounds, aldehydes and disulphides, but ketones and aromatic nitro-compounds were not reduced. The phase I detoxification systems of H. diminuta differ considerably from those of its rat host; the results also suggest that, within the cestodes, there may be considerable species variation in detoxification reactions.

During the course of a primary infection of Nippostrongylus brasiliensis in protein-malnourished rats, plasma concentrations of corticosterone were found to decrease from 0.89±0.03 at the start of the infection to 0.28±0.08μmol/l, 9 days post-infection (p.i.). Similarly, adreno-corticotrophic hormone levels were also observed to fall from 62.09±12.06 to 20.54±1.81 by 5 days p.i. and to 35.12±16.61 nmol/l by 9 days p.i. However, no significant changes were seen in the dry weight of the adrenal glands other than those expected in relation to changes in body weight. Concentrations of both plasma tri-iodothyronine and thyroxine were also severely depleted over the same period from 5.33±0.34 to 1.09±0.42 and 104.43±10.4 to 34.12±8.95 nmol/l respectively. This was considered not to be due to any change in the capacity of the plasma to bind these hormones. Results for insulin were highly variable, but overall were lower from protein-malnourished rats than results documented for well-nourished rats and a reduction from 18.07±3.17 to 6.08±2.18μunits/ml, 9 days p.i. was observed. The results are discussed in relation to the role of these hormones in protein metabolism in a protein-malnourished animal.

The effect of the protostrongylid nematode, Elaphostrongylus rangiferi, on the fecundity and survival of an intermediate snail host, Arianta arbustorum, was studied. Over an experimental period of 12 weeks, infected snails had a significantly lower egg production than uninfected control snails. No significant difference in survival was found between infected and uninfected adult snails. Infected juvenile snails showed a consistent decrease in survival with increasing mean density of parasites. A linear relationship was found between snail instantaneous death rate over a 28–day interval and the mean number of parasites/snail. When calculated for 4–day intervals, the instantaneous death rate was highest between 8 and 12 days post–infection. It is concluded that the most pathogenic phase of this parasite is during the first moult.

The pattern of daily food intake of well-nourished rats infected with Nippostrongylus brasiliensis included 2 distinct phases when food intake was much less than that of uninfected controls (days 0–4 and days 6–10 p.1.). These phases were separated by a period (days 4–6) of still reduced but relatively constant food intake. From day 10 p.i. food intake increased so that between days 12 and 17 infected rats ate more than uninfected controls. In each of the phases of reduced food intake there was a threshold dose above which food intake was further decreased as dose increased. In contrast to the obvious relationship between food intake and dose, food intake could not easily be related to the size of the adult Nipposirongylus population, as judged by egg and worm counts. The relationship appears to be complicated by host variability in susceptibility to infection and to the pathological effects of infection. Effects of N. brasiliensis on the daily pattern of food intake can be explained with respect to stages in the development of the parasite and host responses directed against the adult worms.