The production of excretory-secretory antigens by encysted muscle larvae of Trichinella spiralis has been investigated immuno-histochemically using an antiserum raised by infection in rabbits and purified both before and after conjugation by ion-exchange chromatography. The specificity of the antibody for excretory-secretory products was demonstrated by the pattern of staining of live worms in vitro and the failure of the labelled antibody to stain dead, non-metabolizing worms. Using this labelled antibody, and unlabelled antibody in the immunoperoxidase system, the presence of parasite antigen-bearing cells in close proximity to encysted muscle larvae has been demonstrated. This is believed to be the first demonstration of antigen production by encysted muscle larvae in vivo. The implications of this observation to current concepts of immunity to Trichinella spiralis are discussed.

Test mice have been selectively reared for high (H) or low (L) immune responses to Nematospiroides dubius. After secondary infection with N. dubius, the L mice voided ten times as many eggs in their faeces as the II mice, and at necropsy, 71% versus 20% of the inoculum of N. dubius were recovered as adult worms from the L and II mice respectively. Furthermore, N. dubius were more fecund in the L than in H mice. High or low immune responsiveness was not restricted to N. dubius infection in these mice but was also observed during Toxocara canis infection. The migration of T canis larvae from gut via the liver to skeletal muscle and CNS was inhibited in H versus L mice. Many more larvae were recovered from the livers of II compared with L mice which was indicative of greater immunity in the H mice. The protective immune response in H compared with L mice to both N. dubius and T canis included pronounced cosinophilia and elevated antiparasite antibody titres.

Results are reported of enzyme analyses, following isoelectric focusing (IEF) in polyacrylamide gels, of Plerocercoids of the pseudophyllidean cestodes Ligula intestinalis and Schistocephalus solidus. No polymorphic variants were detectable for the enzymes lactate dehydrogenase (LDH), malate dehydrogenase(MDH), glucose phosphate isomerase (GPI) or phosphoglucomutase (PGM) in 34 individuals of S. solidus. Similarly, no variants were observed in LDH, MDH or GPI of 159 individuals of L. intestinalis collected from four cyprinid fish species from several locations in southern England. In contrast, PGM of L. intestinalis is Polymorphic. The enzyme appears to be controlled by three loci and one of these loci, designated PGM-2, is Polymorphic with three recognizable phenotypes. The polymorphism is not related to the species orgeographical origin of infected fish and it does not reflect strain variation in L. intestinalis. Instead, it is typical of a genetic polymorphism under the control of two co-dominant alleles. Such a balanced polymorphism requires that cross-fertilization must occur, at least transiently, in L. intestinalis. The work indicates that enzymes can be used as markers in future genetic studies with cestodes, and that the combination of IEF and zymogram analysis represents an important method for the detection of cross-fertilization in these worms.

Haemonchus longistipes specimens were collected from experimentally infected Sudanese goats and camels for morphological studies. The specimens from goats were much smaller than those from camels, but their infectivity to camels was not affected by their passage in goats. Goats inhabiting the same areas as camels in the Sudan were found to be naturally infected with H. longistipes, but sheep were not and were resistant to experimental infection.

Gross changes in the size of the secondary lymphoid organs were studied during infection with the nematode parasite Nematospiroides dubius. In the strong responder NIH strain, the wet weight of the mesenteric lymph nodes (MLN) increased rapidly following infection with 400 larvae to peak on day 28 at approximately three times the resting weight. Enlargement of the spleens was also marked but regression to normal size took place when the MLN had achieved maximum size. In contrast in C57BL/10 mice, a slow responder strain, the enlargement of the MLN following infection was relatively slow, and there was no evidence of the regression of the spleen, once maximum enlargement had been achieved.

When adult worms were removed by anthclmintic, the enlarged MLN and spleens returned rapidly to normal size. I lowever, in mice infected with irradiated larvae (25 krad) the MLN stayed enlarged, despite the absence of adult worms but the spleens of these mice returned to normal size fairly rapidly. It was suggested that irradiated worms survive, perhaps as arrested larvae in the intestinal tissue, for a fairly long time, thereby providing a continual stimulus for the MLN.

An established adult infection of Nematospiroides dubius was unaffected by the administration of immune lymphocytes and immune sera whereas an incoming larval infection was expelled. Past experiments have shown that the immune inoculum at least had the ability to recognize adult stages, leading to the hypothesis that adult stages secrete or excrete an immunomodulatory shield around themselves in the gastrointestinal tract. This hypothesis was given further credence by the demonstration that soluble antigens derived from adults abolished the generation of homologous immunity to this parasite. Modulation of immunity was reflected by increased fecundity, increased worm size, and increased survival time in the gut.

The spontaneous expulsion of low-level Echinostoma revolutum infections was markedly impaired in mice harbouring 4-week-old Schistosoma mansoni infections at the time of infection with the echinostome.

Experiments were carried out to define the haematological changes taking place during the first six weeks of a primary infection with Nematospiroides dubius. The general pattern of changes was observed to comprise a rapid increase in circulating leucocytes (4 to 5-fold increase) which consisted of a neutropl a, lymphocytosis, monocytosis and an eosinophilia. However, in strong responder NIH mice leucocyte counts returned to normal more rapidly than in other strains (by day 28). In contrast, in weak responder C57BL/10 mice the leucocyte counts whilst falling significantly relative to day 7 did not return to normal within the experimental period. Mice infected with irradiated larvae did not experience as high a leucocytosis as did mice given an identical number of normal larvae. The peak lymphocytosis, neutrophilia and monocytosis were all lower. The removal of adult worms from infected animals by treatment with pyrantel on days 9,11,13 and 16, also significantly altered the pattern of leucocytosis. The neutrophilia which was evident on day 7 returned rapidly to normal, whereas in mice which had retained their worms a peak neutrophilia was observed on day 14. These haematological changes were discussed and related to the failure of hostprotective immunity to operate effectively during the early stages of a primary infection with N. dubius.

Ivermectin was evaluated against natural and artificial pinworm (Syphacia) infections in mice. Ivermectin given in the diet for 6 days at 0·0005% was 99% effective against both immature and adult worms. A diet level of 0·0004% reduced immature and mature pinworm by 99 and 75%, respectively but 0·0001% was inactive. One oral dose of 2·0mg/kg was 100 and 97% effective against gravid females and immature worms, respectively. A dose of 1·0 mg/kg was 96 and 66% effective against the same parasitic stages. A similar effect was observed against adult male worms where 94 and 86% were removed by one oral dose of ivermectin at 2·0 and 1·0 mg/kg, respectively.

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Attempts were made to manipulate specific responses of baboons to protect them from infection with Schistosoma mansoni. In Experiment 1, cosinophilia was induced in naive baboons with Trichinella spiralis larvae given intravenously before intraperitoneal injection of globulin fractions from S. mansoni-infected baboon sera and subsequent percutancous exposure to S. mansoni cercariac. In Experiment 2, baboons with 8- or 32-week-old primary S. mansoni infections received T spiralis i.v. before an S. mansoni challenge. In experiments 3 to 5 respectively, naive baboons received intramuscularly before challenge: formalin-fixed S. mansoni schistosomula, with Bordetella pertussis as an adjuvant; a preparation of S. mansoni adult worm teguments; and a preparation of NE-immune complexes obtained from S. mansoni-infected rat sera, with Freunds Complete Adjuvant. Minor, but statistically insignificant, protection was obtained in Experiments 2 (32-week infections) and 3, but was far less than that given by intact, irradiated living vaccines. There are signs on the horizon of non-living vaccines protecting rodents against S. mansoni infection and it would be prudent, as with drugs, to test these in primates before proceeding to man. The results of our experiments, though essentially negative, should help the design of any future vaccine trials in primates.

5′-nucleotidases of eight species of digenetic trematodes were studied using five different substrates. All species showed the following preferential order of substrate affinity; AMP>CMP>GMP>TMP>UMP. It was observed that different species occupying similar habitats possessed closely related levels of enzyme activities. The function of 5′-nucleotidases in trematodes is also suggested.

The model of Onchocerca lienalis microfilariae (mff) injected into CBA and T.O. strains of mice has been used to examine immunity to skin-dwelling microfilariae following exposure to a range of species oF nelmmms Mice which had received a primary infection with O. cervicalis mff were significantly resistant to challenge with O. lienalis mfT(58% reduction relative to challenge controls). Immunization with the uterine contents (eggs and mff) of O. lienalis, O. gutturosa or O. volvulus conferred equivalent levels of protection agains challenge with O. lienalis mff (66 to 75%). Similar results were obtained with immunizations in mice that employed either fresh or freeze-killed eggs of O. gutturosa. Significant reductions in the recoveries of O. lienalis mff were also demonstrated following the intraperitoneal implantation of adult male worms of O. gutturosa (30 to 52%), the adults of either sex of Dipetalonema viteae (60%), or after infection witn Trichinella spiralis (27 to 81%). Infections with the trematode, Schistosoma mansoni, had a negligible effect on mff recoveries. It is concluded that partial resistance in mice to Onchocerca mff may be stimulated by factors, yet to be determined, that are neither stage nor species-specific.

The proteins of homogenized adult Opisthorchis viverrini were separated by polyacrylamide gel electro-Phoresis and isoelectric focusing in the presence of detergents. By far the most abundant component(s) had a Mr of 18,000 to 19,000, represented about 47% of the total parasite protein, and did not separate in isotypes.

Infection in mice with Toxocara pteropodis was investigated. In mice fed infective eggs, third-stage larvae hatched out and penetrated the mucosa, predominantly that of the lower intestine. They travelled via the portal vein to the liver, where they remained at least 14 months. They grew in length from 430±15μm, at three days post infection (p.i.), to 600 ± 50 μm, at six to nine weeks p.i., after which time growth ceased. Blood eosinophilia appeared at 28 days p.i., and esosinophil levels continued to rise gradually beyond this time. In female mice the larvae did not migrate from the liver in response to pregnancy or lactation. When infective eggs were inoculated subcutaneously or intra-peritoneally, larvae hatched out and ultimately appeared in the liver in larger numbers than seen with oral infections.