For the first time the development of the alimentary tract of Levinseniella brachysoma metacercaria (Trematoda: Microphallidae) obtained experimentally from Gammarus oceanicus has been described. The foregut primordium in 16-day-old metacercariae is represented by a syncytial cylindrical cord, resulting from the fusion of embryonic cells. Non-fused parts of the plasma membranes of adjacent cells are revealed as gap cavities within the cord. Later (30th day post infection) the lumen of the foregut is formed as a result of both partial vacuolization of the cytoplasm and by a broadening of the gap cavities, resulting from a thinning of the cytoplasmic spaces between them. Besides the usual organelles, the foregut of the mature metacercaria (42nd day p.i.) contains dense secretory granules in the apical cytoplasm region and numerous microtubules in basal areas. The cellular gastrodermis is formed later than the foregut syncytium (on day 30 p.i.); its large cells contain well-developed Golgi complexes, RER and mitochondria. A noteable inclusion of the gastrodermal cells of mature metacercariae are spherical granules of moderate electron density measuring up to 3 μm in diameter. On the basis of an analysis of the ultrastructural data the possible functioning of the metacercarial alimentary tract is discussed.

The life-cycle of Tremiorchis ranarum Mehra and Negi, 1926 (Trematoda: Plagiorchiidae) infecting Rana tigrina and R. cyanophlyctis is elucidated. Life-cycle stages, from egg to egg-producing adults, were successfully established in the laboratory. Life-cycle took more than two months for completion. Cercariae were found in the snail, Pila virens collected from paddy fields at Chelembra in the Malappuram district of Kerala during the monsoon months. Cercariae are of the xiphidiocercous type. Metacercariae occurred beneath the skin and in head, tail and body musculature of tadpoles of R. tigrina and R. cyanophlyctis. Adult frogs are refractory to cercarial infection. Frogs became infected when they fed on tadpoles containing metacercariae. Successive stages in the development to adult from the metacercariae were followed. Chronological synchronization in the reproductive activity of the host and the parasite is briefly discussed.

In order to determine the prevalence of intestinal parasites among labourers from Thailand in Taiwan, the stool samples from 1364 Thai labourers were examined by the formalin-ether concentration method and 18·0% were found to be infected with one or more parasites. The infection rates of hookworm, Opisthorchis viverrini, Strongyloides stercoralis, Enterobius vermicularis, Ascaris lumbricoides, Hymenolepis nana, Capillaria philippinensis, Schistosoma japonicum, Echinostoma sp., Entamoeba coli, Giardia lamblia, and Entamoeba histolytica, were 7·6%, 7·0%, 3·2%, 0·5%, 0·3%, 0·1%, 0·1%, 0·l%,0·l%, 0·4%, 0·2%, and 0·1% respectively. The prevalence was highest among the 21–25 age group (24·8%). Among the 245 infected persons, 91% were infected with one parasite, 8% with two parasites and 1% with three parasites. The finding that parasitic infections are prevalent among Thai labourers demonstrates the need for control measures in foreign labourers in Taiwan and further studies to determine the susceptibility of O. viverrini to the snail hosts of Clonorchis sinensis.

Conjunctivitis due to the trematode Philophthalmus in a 13-year-old Israeli girl is described. A single worm, probably a mature Philophthalmus palpebrarum, was detected on the palpebral conjunctiva of the upper eyelid of the right eye. Removal of the worm resulted in rapid abatement of the ocular symptoms. This is the first documentation of human philophthalmosis in Israel.

Distribution of some elements during development of endogenous daughter (hydatid) cysts of Echinococcus granulosus of buffalo origin was determined by atomic absorption spectrophotometry. These analyses showed that the distribution of copper and cobalt was highest in the smallest cysts. These elements gradually decreased in the cysts as they enlarged. The distribution of zinc, iron and manganese was very high in the smallest cysts in comparison to copper and cobalt, but these three elements decreased greatly in larger cysts. Iron and manganese were the only two elements found in very high concentrations in “thin-walled” cysts. Like all other elements both calcium and magnesium decreased as the cysts increased in size. In the thin-walled cysts magnesium increased by four times initially and this was followed by a two-fold “influx” of calcium in the “white-spots” in the above cysts. The significance of these findings is discussed in relation to earlier works.

The results of a 5 year study of helminth parasites of Mus spretus, are reported. Six nematode and 5 cestode species were identified but no helminth showed 100% prevalence in M. spretus, the most commonly encountered nematode and cestode species being Syphacia obvelata (46·6%) and Taenia taeniaeformis (22·4%). Among the more unusual helminth species identified was Eucoleus bacillatus, a capillariid nematode inhabiting the stomach musculature. This species was identified in 3 of the 5 years of the study. The results are discussed in the broader context of previous studies and the epidemiology of rodent helminth infections in general.

The transmission of bovine Onchocerca spp. in Britain was investigated by studying the Ceratopogonidae and Simuliidae which attacked bait cattle between April and October at two sites in North Wales, where either Onchocerca lienalis and O. gutturosa (Cynwyd), or O. lienalis alone (Pentrefoelas) occurred. Based on the relative abundance of each species, their seasonal variation in abundance and preferential feeding sites on cattle, the presence of Onchocerca sp. infective larvae and the development of patent infections in bait cattle, vectors were identified as Simulium ornatum s.1. at Pentrefoelas and S. reptans at Cynwyd (0·5% and 1·5% of parous flies infective, respectively). There was no significant difference between the lengths of the infective larvae from vectors at either site (Pentrefoelas: mean = 543·5 μm, SD = 29·45; Cynwyd: mean = 550·86 μm, SD = 35·26; p > 0·1), which were consistent with descriptions of O. lienalis. The identity of a vector for O. gutturosa was not determined and the role of certain candidates is discussed. In this respect, the absence of Culicoides nubeculosus was notable. Transmission of Onchocerca sp. was limited to a short period of about 8 weeks, by a combination of vector abundance and parasite uptake from dermal skin layers, and a mean daily temperature requirement of 15°C or more for complete parasite development in the vector. The effect of this temperature restriction in relation to the geographical distribution of the two species is discussed.

Laboratory experiments were performed to investigate the ability of isolates from the predacious fungus species Arthrobotrys conoides (one isolate) and A. robusta (four isolates) to trap and kill infective Haemonchus placei larvae. Three groups for each isolate were formed: group 1, fungi and infective larvae; group 2, fungi; group 3, infective larvae. There were statistically significant differences (P<0.05) between the antagonistic effects of three isolates of A. robusta, but there was no such difference between the isolate of A. conoides and isolates of A. robusta. This result indicates that there can be a variation in the predatory capacity of different isolates within a single fungus species. After 20 days of assay, there was greater recuperation of infective H. placei larvae in group 3 compared to group 1.

Rabbits were experimentally infected with two levels (5000 and 17000) infective larvae of Nematodirus spathiger. Histological (villus length, mucosa to serosa ratio, crypt surface) and biochemical (protein content, alkaline phosphatase and leucine aminopeptidase activities) measurements relating to the small intestinal mucosa were examined along the entire length of the organ. In the proximal intestine, the presence of worms was associated with villus abrasion, increased crypt surface and decreased alkaline phosphatase and leucine aminopeptidase activities. Conversely, beyond the main Site of infection in the distal small intestine, some signs of hypertrophied villi and crypts were noted without any changes in enzyme activities. These distal variations were similar to those previously described in experimental Trichostrongylus colubriformis infections of rabbits. These results tend to confirm the use of the rabbit as an experimental model to study Nematodirus infection. They also suggest that the distal adaptive process in the nematode-parasitized small intestine could occur independently of the worm species.

Second-stage larvae of Toxocara canis were maintained in vitro for one year. Susceptibility of the larvae to drugs was evaluated by means of minimal larvicidal concentration (MLC) and larval bursting percentage. MLCs of citral and decanoic acid were almost constant throughout all stages of incubation. However, bursting percentage markedly varied within the first 20 weeks of incubation. Therefore, while larvae are available for use in the MLC assay at any stage of incubation, those beyond the first 20 weeks after incubation should be used for the bursting assay to obtain reproducible results.

The relationships between the number of infective larvae (L3s) to which animals were exposed and the establishment of A. ceylanicum and N. americanus in hamsters were examined. There was no evidence of density-dependent constraints on the establishment of A. ceylanicum in the range 10–1000 larvae, but an experiment in which the range was extended to 1500 L3s gave a significant negative correlation between the magnitude of the infecting dose and percentage establishment. Even so the percentage reduction was relatively small, approximating to 0·89% per 100 larvae administered, and in practice density-dependent constraints on establishment are unlikely to affect experiments with this species in which much lower doses (<250 L3) are generally employed. The range of doses for N. americanus L3s was smaller (10–400). Of the four experiments reported, two gave a significant reduction of establishment with increasing dose and two did not. When the data was split into low doses (<100 L3s) and high doses (>100 L3s), falling establishment with increasing dose was only detected in the lower dose range. There was no difference in the establishment when doses of 100 L3s were compared with 250 or 400 L3s. On balance, it was concluded that density-dependent constraints on establishment of N. americanus in hamsters were not marked and would have little significant effect on experiments utilizing fewer than 200 L3s (approximately 7·6% reduction between 10 and 200 L3s). These results are discussed in relation to host regulation of hookworm burdens.

All 23 6–8-week old outbred female ICR mice, each fed 100 metacercarial cysts of Echinostoma caproni, were infected on days 2, 4, 6, and 8 postinfection (PI) with a mean of 45 worms/host. To examine worm distribution in the mouse, the small intestine was divided into five equal sections (segments 1–5 beginning with the pylorus). Worms were found mainly in segments 3 and 4 and were never found in segment 1. Mean body area of worms fixed in 10% neutral buffered formalin (NBF), hot alcohol-formalin-acetic acid (AFA) and aceto-carmine increased slowly until day 4 and then rapidly until day 8 PI. There was a significant difference in the mean body area of worms fixed in hot AFA, NBF, and aceto-carmine on all days except 4 and 6. Distinction of the ovary and ootype was apparent by day 6 and uterine cooling was observed by day 8 PI. Only 2 of 50 worms showed eggs in the uterus on day 8 PI.

Immunological memory generated by infection with S. ratti was studied separately in the migratory and intestinal phases in mice. Protection against reinfection in the migratory phase was 96–98% at 2 weeks but significantly decreased to 60% at 12 weeks after the primary infection. However, protection in the intestinal phase was 96% even 12 weeks after the primary infection. Recall of immunity against the intestinal phase persists for longer than that against the migratory phase in mice.

The usefulness of hatched but non-activated oncospheres as a candidate vaccine was evaluated using a Taenia taeniaeformis/rat system, since preparation of these oncospheres in vitro is known to be very simple. The findings were: (1) rats vaccinated with non-viable oncospheres became completely resistant to challenge infection; (2) intra-venous injection was the most effective to induce complete resistance; (3) a single oncosphere was sufficient to induce complete resistance in infected rats, whereas approximately 50 and 500 non-viable oncospheres were required to evoke strong and complete resistance, respectively, in vaccinated rats. The usefulness of non-viable oncospheres without adjuvant is discussed.