No significant difference in cercarial production was noted when Biomphalaria glabrata from Brazil were exposed to one or several miracidia of Schistosoma rodhaini from Burundi, even though the dynamics seemed different. The minor differences can be explained by the intramolluscal larval development of this parasite characterized by the production of a high number of daughter sporocysts over a long period.

The callitrichid primates, Callithrix jacchus jacchus (the marmoset) and Saguinus labiatus (the tamarin) were inoculated with infective larvae of Brugia malayi and B. pahangi. Microfilaraemia at low levels developed in 3 out of 4 C. j. jacchus infected with B. malayi and living or dead adult worms found in all 4. Only one of 4 C. j. jacchus became microfilaraemic (mf + ve) when given B. pahangi and adults were found in two. Of 4 S. labiatus given B. pahangi one became very lightly mf + ve and adults were found in 3. It is concluded that these animals are not suitable hosts for chemotherapeutic experiments.

The technique of allozyme electrophoresis was applied to species of Onchocerca from cattle to increase the number of enzyme loci established and therefore provide a genetic basis for a rational species-level taxonomy. Twenty-three enzyme loci were established and provided unequivocal genetic evidence for the taxonomic validity of Onchocerca gibsoni, O. gutturosa and O. lienalis. Furthermore, the diagnostic enzyme markers detected form the basis for identification of life-cycle stages, individuals and species and population structure analyses.

The prevalence and relative density of the monogenean Paradiplozoon homoion, were monitored over one year in populations of roach, Rutilus rutilus, captured in a thermally raised artificial lake located outside a nuclear power station and in a nearby reference locality. Recruitment of P. homoion started earlier in the warmer lake. A temporal shift of the life-cycle was thus observed but there were no differences between the total prevalence or the total relative density of the parasite in the two areas. Since there is no evidence of parasite-induced host mortality, or for the development of protective immunity, the main regulatory process in the heated area are most likely an increased mortality due to reduced thermal tolerance of the adult parasite.

The effect of fatty acids was studied on the developmental direction of Strongyloides ratti first-stage larvae (L1). The proportion of third-stage infective larvae increased markedly when L1 were cultured in faeces with added fatty acids such as palmitic (C16), stearic (C18), oleic (C18:1) and linoleic (C18:2) acids. Unsaturated fatty acids were more effective than saturated ones. Moreover, the proportion of infective larvae increased with quantity of linoleic acid but the triacylglycerols of any fatty acid had no effect. These results suggest that these free fatty acids cause physiological changes that determine the developmental course of L1 of S. ratti in nature.

Development of exact doses (<100) of Strongyloides venezuelensis third-stage larvae in adult Wistar rats was insignificant (mean proportion of 0·076 of the dose at day 8, n = 16) compared with a homogonic strain of S. ratti (0·538, n = 6; 0·726, n = 6) and heterogonic S. ratti (0·681, n = 6). Newly-weaned Wistars allowed development of a mean proportion of S. venezuelensis of 0·298 (n = 4) compared with 0·013 (n = 4) of the same sample of larvae in adult hosts. Experiments with 75Se-labelled larvae established that S. venezuelensis effectively failed to migrate from skin to intestine in adult animals, while mean proportions of 0·141 (n = 5) and 0·138 (n = 4) of the label was found in the intestines of newly-weaned rats 72 h after skin application. Labelled larvae of homogonic S. ratti migrated equally well in both age groups of host (0·350 and 0·358 in 12- and 3-week-olds respectively). Adult S. venezuelensis transferred surgically to the intestines of previously uninfected full-grown Wistars survived over a 21-day period to the same extent as either strain of S. ratti. Resistance of Wistar rats to S. venezuelensis therefore appears to affect the migratory stage preferentially. S. venezuelensis developed better in mature PVG inbred rats (mean = 0·301, n = 20). Studies of S. ratti showed that infections of both strains initiated by exact (<100) doses in Wistar rats had decayed to insignificance between days 26 and 32. The rate of loss of adults of the heterogonic strain was significantly greater than that for the homogonic. The egg content of worms declined as infection progressed and rats were idiosyncratic in their influence on parasite reproduction from the earliest time of sampling (8 d). It was established that ‘autoinfection’ was an unlikely feature of the biology of homogonic S. ratti following the surgical transfer of 450 first-stage larvae to the intestines of 8 adult Wistar rats. No evidence of infection appeared in the guts of these animals 8 days post-transfer. The significance of these results in terms of the biology of Strongyloides spp. naturally occurring in the rat is discussed.

Artificially prepared cow pats containing Ostertagia ostertagi eggs were deposited on two comparable grazing plots at weekly intervals during June and July 1987. Before deposition the cow pats, on the one plot, were inoculated with 0·250 g mycelial fragments per kg of faeces of the predacious fungus Arthrobotrys oligospora. On the other control plot comparable numbers of non-inoculated cow pats were placed at the same time. Subsequently, in July, two equal groups of calves were turned out one on each plot to graze for two months after which they were necropsied. The number of infective O. ostertagi larvae in inoculated cow pats was reduced by 42% and herbage larval infectivity around them by 50–71% as compared with the corresponding parameters in control pats and surrounding herbage. After a grazing period of two months the calves on the plot with inoculated cow pats had acquired worm burdens that were on average 37% lower than those of calves on the control plot. The lower degree of parasitism in these calves was also reflected in lower egg counts, lower serum pepsinogen levels and higher body weight.

Five experimental grass paddocks were sequentially contaminated with fresh bovine faeces containing known numbers of eggs of predominantly Haemonchus and Cooperia spp. during the 1984/85 dry season (November to March). Faecal, herbage and soil samples were examined at regular intervals between November and June in order to determine the rate of development and mortality of infective larvae (L3) in faeces, the pattern of herbage infestation with L3 and the role of faeces and soil as reservoirs of L3 during the dry season and early rains. L3 first appeared in faeces approximately 4 days post contamination (PC) and peak counts were obtained 28, 14, 7 and 14 days PC in the paddocks contaminated in December, January, February and March, respectively. The counts initially declined linearly at the rate of approximately 7535 L3/week and 10 947 L3/week in P2 and P4 respectively, due primarily to mortality but later there was an accelerated fall in the counts as the surviving L3 moved out of the faecal pads onto herbage. The overall trend of faecal larval populations in each paddock was therefore distinctly curvilinear. Although large numbers of L3 were present inside dry faecal pads in most paddocks throughout the dry season, none migrated on to herbage at that time of the year. Translation of L3 to herbage was very rapid and occurred simultaneously in all the paddocks 24 hours following the first heavy rainfall in late March. Consequently peak herbage infestations in all paddocks were coincident and occurred a few days after commencement of larval migration. The closer to the end of the dry season the contaminations were carried out, the larger were the subsequent early rains rise and the peak herbage infestation and the longer this infestation survived on herbage. No L3 were recovered from soil throughout the study, which suggests that faecal pads were the sole reservoir of L3 during the dry season and hence the source of the early rains herbage infestation.

The surface structure of adult Haplorchis pumilio from experimentally infected hamsters was studied in detail using scanning electron microscopy. Almost the entire surface of the worm was covered with scale-like spines regularly arranged in transverse rows. Most spines were pectinate. The size of the spines and the number of the teeth in each individual were largest in the spines around the middle region of the worm. The area surrounding the excretory pore was free of spines displaying a slightly wrinkled appearance. Many ciliated papillae were present on the anterior two-thirds of the body. The papillae on the oral sucker were more abundant than those elsewhere. The body papillae were distributed in a bilaterally symmetrical arrangement, appearing in groups, pairs or singly between the spines.

The distribution of zinc in representative groups of parasitic helminths was determined by the use of the atomic absorption spectrophotometer. The results of these analyses have shown that growing flukes (smaller forms) with active oogenesis and spermatogenesis contained more zinc than old (large) or very old adults with an empty uterus and large lobulated testes. In cestodes, the neck region and immature proglottids showed more zinc concentration than mature and gravid proglottids and fully grown cyst walls. Similarly, the youngest endogenous daughter cysts of Echinococcus granulosus contained more zinc in their walls than those of larger/older forms. Zinc was concentrated more in nematode eggs than in adult females.

Metacercariae of Plagiorchis species 1 were observed to hatch by an active mechanism in a medium free of enzymes. A hatching opening in the bilayered cyst wall was formed by the combined action of caecal fluid extruded by the activated larva through the mouth opening and an internal pressure due to the tendency of the cyst wall to contract on hatching, resulting in an explosive expulsion of part of the metacercarial body. The cyst wall was apparently pierced at any place where the larva delivered its caecal fluid. After excystation the hatching medium contained high phosphatase and proteinase activities and was able to dissolve the inner walls of empty cyst envelopes. The phosphatase activity assayed on 4-methylumbelliferyl phosphate was optimal at pH 3–5. The proteolytic activity was demonstrable on photographic film, Azocoll, and synthetic chromogenic and fluorogenic peptides. A preference for peptides was found which are also susceptible to plasmin. The proteolytic activity was optimal at pH 3–9 and 40–45°C and, when assayed on Suc-Ala-Phe-Lys-MCA, was only due to thiol proteinase(s) according to inhibitor studies. It is suggested that the proteinase(s) represent the hatching enzyme(s) of the metacercaria, because (a) only proteolytic activity was detectable in the pH range optimal for excystment, (b) the inner cyst wall is stabilized by proteins, and (c) the inner wall is dissolved by other proteinases such as trypsin. Enzyme histochemical investigations of metacercariae showed that, in the caeca, acid phosphatase was present mainly before hatching and non-specific esterase developed after hatching. Proteolytic activity was not localized with the methods used although it was suggested that it derived from the caecal fluid. A possible relationship of the thiol proteinase(s) detected in the hatching medium to haemoglobin-digesting proteinases from the gut of schistosomes is discussed.