All of the enzymes involved in the β-oxidation pathway were identified from juvenile and adult postparasites of the mermithid nematode Romanomermis culicivorax. The postparasites readily took up exogenous [14C-U]palmitate and oxidized it to CO2, indicating that the β-oxidation pathway is functional. The extent to which this pathway is utilized during the natural cycle of the nematode is discussed.

The occurrence, in September 1979, of Echinoparyphium recurvatum metacercarial cysts in a community of molluscan hosts at Harting Pond, West Sussex, was investigated. The parasite exhibited broad host specificity with all 7 species comprising the molluscan community being infected. There were marked differences, however, in the extent to which each host species was utilized and using the mean number of parasites/ individual mollusc as a parameter of infection the mollusc species may be ranked in descending order of utilization as follows: Sphaerium corneum, Lymnaea peregra, Valvata piscinalis, planorbids, Pisidium subtruncatum and Potamopyrgus jenkinsi. Combination of basic infection data with population estimates for each mollusc species in the study area showed that the bivalve P. subtruncatum and the prosobranch V. piscinalis were the most important hosts because they contained approximately 90% of the total number of cysts. In both of these hosts the cyst population was over-dispersed and the degree of over-dispersion increased with host size. The pattern of second intermediate host utilization is discussed in relation to the likely flow of E. recurvatum between the first intermediate host (L. peregra) and wildfowl definitive hosts at Harting.

The activation of the peptidergic neurosecretory system in Diphyllobothrium dendriticum was studied following cultivation of plerocercoids for short times in vitro and in vivo. In the plerocercoid the neurosecretory cells gave a very weak reaction with paraldehyde fuchsin (PAF). After cultivation for 1 h large numbers of neurosecretory cells filled with PAF-positive granules were evident. The significance of the activation of the neurosecretory system during the transfer of the worm from the cold-blooded fish host to the warm-blooded final host is discussed.

The results of control infections from 39 experiments using the ‘exact dose’ technique are analysed and compared with earlier large dose experiments with homogonic S. ratti. A smaller error variance and less added variance between experiments accompany the new method, which therefore provides a more precise experimental system. Using the exact dose technique, it is established that the migratory bahaviour of small numbers of L3 of the homogonic strain in lactating animals is the same as that of large numbers. In previous work the rate of migration of the homogonic strain estimated from conventional large dose experiments (Wilson, Cameron & Scott, 1978b) differed from that deduced from the use of radio-isotope labelled L3 (Wilson, 1979). ‘Exact dose’ data support results with the latter technique. There are significant differences between strains. The heterogonic larvae take longer to migrate in lactating hosts and appear to distribute themselves differently between mother and offspring. The consequences of these findings for theories of pathfinding in hosts are discussed. Experiments are also reported which failed to detect any artifact which might have resulted from ether anaesthesia of rats at injection of larval worms. This observation has implications for other studies in progress in this laboratory.

A method using light and electron microscopes is described which is suitable for the examination of gut penetration by juvenile Fasciola hepatica. It involved the ligation of small sections of the small intestine of rats and the introduction of artificially excysted flukes into these gut loops. By restricting the area of infection in this way it was possible to either recover flukes from the gut lumen or to prepare ultrathin sections for electron microscopy of flukes penetrating the gut wall. In addition, flukes were recovered from the body cavity at various times after preparation of loops in resistant and naive rats. It was found that more flukes reached the body cavity in naive rats than in resistant rats, demonstrating a resistance to infection in the gut loops of sensitized rats.

The temporal distribution of hatching of the embryonated eggs of Transversotrema patialense has been examined under different temperature and illumination regimens. Under a DL 12: 12 regimen at 30°C egg hatching exhibited a circadian rhythm with a period of 24 h. Within a diel time-frame hatching was distributed over the final 9 h of the light period with less than 2% of the eggs hatching during the dark period. This pattern was temperature independent over the range 25 to 30°C and persisted under constant illumination. It is suggested that the timing of hatching is under endogenous control and is functionally related to a circadian rhythm of behaviour of the intermediate host mollusc, Melanoides tuberculata.

Following infection of rats with Fasciola hepatica, an increase in the number of epithelial cells in the common bile duct, labelled with [3H]thymidine, was detected autoradiographically as early as 5 days post-infection (p.i.). This initial mitogenic effect of the infection was limited to that region of the bile duct lying adjacent to the liver, while the region lying next to the duodenum failed to show any increase in labelling until 41 days p.i. Mechanical contact between the parasite and the biliary epithelium did not occur until 41 days p.i. and the initial hyperplasia was evidently not a result of mechanical irritation. The study serves to emphasize the chemical aetiology of the precocious biliary hyperplasia and to more accurately identify its onset.

Observations have been made on the ultrastructure of objects identified as ovarian balls from female Moniliformis after 1, 3, 5, 7 and 9 days in the rat. Similar objects are present in the body cavity of female cystacanths from cockroaches. The ovarian balls from 1-day-old worms are formed of several cells which are enclosed within a surface coat. During development, the ovarian balls increase in size and cell number and the internal organization appears to become more complex. After 9 days of development in the rat, the surface coat of the ovarian balls can no longer be observed and microvilli are present. It also appears that the supporting syncytium has been formed by this time.

The syncytium of the scolex and neck regions of Caryophyllaeus laticeps differs from that of the remainder of the body in a number of ways. The microtriches have short shafts and lamellated spines and the surface cytoplasm is characterized by numerous elongated granules, occasional lipid-like bodies and, in the scolex region, is penetrated by ducts from the frontal glands. The elongated granules arise from the tegumentary neck cells and pass into the syncytium via narrow cell processes possessing extensions of the neck cell microtubule system. The granules have a peripheral sub-structure of regularly spaced electron-lucent areas. Evidence suggests that the granular material becomes more diffuse before extrusion. The spherical, lipid-like bodies also arise from the neck cells, but extrusion from the syncytium was not observed. Homology of the neck cells with the tegumentary cells of the rest of the body is discussed. The frontal glands are restricted to the scolex apex and secrete spherical or sub-spherical, homogeneous granules. The cells, with microtubule-lined ducts, open to the surface via pores which possess an electron-dense ring at which point the microtubule system terminates. Sensory bulbs are also present and will be described in a subsequent communication. The inter-relationships of the gland distribution, scolex morphology and host pathology are discussed.

The resting membrane potential of the acanthocephalan rete system in Macracanthorhynchus hirudinaceus was −35±1·5 mV (n = 20) and was dependent upon the external potassium concentration. The membrane potential reached 0 mV when the external potassium concentration was 160 mM. Spontaneous spike potentials of 45 mV ± 10 were dependent on calcium flux. The membrane potential was depolarized by acetylcholine, potassium-free medium, calcium ions and chloride-free medium but not by changes in the external sodium concentration. Spontaneous potentials were increased in number by acetylcholine and calcium at concentrations above 3 mM, but were decreased in number by chloride- and calcium-free medium. Hence the rete system potentials are very similar to smooth muscle potentials in many respects.

Mice inoculated with 2000 Ascaris suum eggs 7 days before an infection with 2 cysticercoids of Hymenolepis diminuta harboured significantly fewer and/or smaller tapeworms than control mice by day 7 post-infection. When the interval between the infections was increased, the effect on H. diminuta decreased and no effect was found 21 days after the A. suum infection or if the infections were given simultaneously in ńaive or in mice immune to A. suum. Two possible explanations for the rejection and/or stunting of H. diminuta in mice infected 7 days earlier with A. suum are suggested; either a host reaction in the small intestine stimulated by the returning larvae of A. suum after their hepato–pulmonary migration or an indirect effect of decreased food intake of the host caused by this migration. It is concluded that experiments on possible immunodepressive or immunostimulating effects of parasites ought to include studies on living agents and that they should not rely on measurements of immune responses only.

Merozoites of 5 species of Eimeria from the chicken were recovered from this host and inoculated into the allantoic cavity of embryonated chicken eggs. The merozoites developed into sexual stages in the chorio-allantoic membranes, and oocysts of all the species which were tested — E. acervulina, E. brunetti, E. maxima, E. necatrix and E. praecox — were recovered. Many of the oocysts of E. maxima and E. necatrix, and a few of those of E. brunetti, sporulated and were found to be infective for chickens.

Acetylcholinesterase (AChE) activity was measured in Nippostrongylus brasiliensis recovered during the course of a primary infection in normal and in protein-deficient rats. In well-nourished rats the amount of AChE present in N. brasiliensis increased as the infection progressed, concomitant with the development of the humoral response. In malnourished rats, there was a similar and parallel increase in the amount of AChE synthesized by worms between days 7 and 13 of the infection but as the infection progressed enzyme production decreased so that, by day 26 of the infection, the nematodes contained approximately the same amount of AChE as 8-day-old worms. The possible reasons for this change in enzyme production are discussed.

Three strains of Eimeria acervulina and 3 strains of E. mivati were compared. E. acervulina was characterized by the ovoidal shape of its oocysts and their rapid sporulation, small first-generation schizonts containing few merozoites, and its inability to complete development in the chorio-allantois of chicken embryos. E. mivati had more rounded oocysts with a Longer sporulation time, larger first-generation schizonts containing twice as many merozoites and it developed readily in the chorio-allantois. Pre-patent periods were variable but generally shorter with E. acervulina. A strain of E. mivati attenuated by repeated embryo passage showed a reduced pre-patent period.

Experiments were carried out to investigate the effects of Ascaris suum infection on the growth, food intake, nitrogen and fat utilization and intestinal function of young pigs receiving diets low in protein. An infection procedure was developed which provided relatively uniform and heavy infections in pigs under study. Ascaris-infected pigs showed statistically significant reduction in growth rate and food intake compared to uninfected controls. The reduction in growth rate was observed after the A. suum were mature and eggs were observed in the faeces of pigs. The degree of growth retardation was significantly correlated with worm burden. Infected pigs showed no consistent reduction in nitrogen and total solids digestibility compared to controls but fat digestion was reduced. The infected pigs showed reduced nitrogen retention compared to uninfected controls. Ascaris-infected pigs had heavier intestinal tracts with increased size of the tunica muscularis. Lactase activity in mucosa from infected pigs was significantly lower than in controls, whereas no consistent effect was observed in mucosal sucrase and maltase activity. When Ascaris-infected pigs were given an oral lactose load, blood glucose levels rose less than in control pigs, suggesting that the infection resulted in impaired lactose tolerance.

Quackenbush strain and wild Mus musculus were assayed for their liability to primary infection with 100 LaNematospiroides dubius using an experimentally derived selection index. Refractory and liable colonies of mice were established over 5 generations. Liability to N. dubius infection was found likely to be controlled by several genes; the heritability (h2) of this trait was estimated at 0·45. Positive linear correlation was found between the number of parasite eggs voided and the number of adult N. dubius recovered, negative correlation between the pre-patent period of infection in days and the number of parasite eggs voided and positive correlation in 2 of 5 generations between live mouse body weight and the number of adult N. dubius recovered. Further, positive correlation was found between the liability of female mice to N. dubius and their progeny litter size number. The genetic mechanisms controlling the liability trait and the possible evolutionary significance of these results are discussed.

A laboratory strain of Eimeria acervulina and 9 field isolates consisting principally of E. acervulina were tested for sensitivity to amprolium (125 p.p.m.) or dinitolmide (125 p.p.m.) in the food and for effects of the drugs on sporulation of oocysts. Judged by weight gains and lesion scores, medicaments were only partially effective against the 9 field isolates, but were highly effective against the laboratory strain. Oocysts were produced in all the infections but the percentage sporulation of oocysts from field isolates was much higher than sporulation of oocysts of the ‘drug sensitive’ laboratory strain. These results show that coccidia that are resistant to either amprolium or dinitolmide are able to cause lesions in the presence of the drugs and the oocysts that are produced will sporulate normally.

The effect of the anthelmintic Mebendazole on Cysticercus cellulosae maintained in culture medium was studied by transmission electron microscopy. In addition to the well-known morphological changes induced by Mebendazole in other cestode and nematode larvae, it also induced the cytoplasmic appearance of paracrystalline bundles in the secretory cells of the bladder wall. These bundles were formed by groups of large parallel tubules arranged in a hexagonal-like pattern. The tubules, which had an external diameter of about 50 nm and a length that might exceed 5 μm, were surrounded by a matrix and a distance between neighbouring tubules of 80–120 nm centre to centre was estimated. The tubules were stable to colchicine and low temperature. The temporary appearance of bundles is described and some alternative explanations on their origin are advanced.

Treatment of cutaneous leishmaniasis by antimonial compounds when administered by various routes to mice infected with Leishmania major or L. mexicana amazonensis is enhanced, relative to the free drug, by entrapment of these compounds within liposomes. The efficacy of the liposome treatment is dependent on the time and route of administration, and upon the phospholipid composition of the liposomes themselves. Drug-loaded liposomes administered intravenously (i.v.) are more effective at reducing the growth of a cutaneous lesion if they are administered after the nodule has begun to develop, rather than at the time of inoculation of the parasites. In contrast to the i.v. route, liposomes administered subcutaneously (s.c.) at the inoculation site are only effective if given at the time of infection.

Pelodera strongyloides larvae were found in the conjunctival sacs of Apodemus sylvaticus and Clethrionomys glareolus and in hair follicles of A. sylvaticus. Those in the eyes were 3rd-stage larvae while most of those in the dermis were early 4th stages. There was no evidence of pathology and sections of the skin showed that the nematodes were well-tolerated by the mice. Nematodes emerged from the skin of freshly killed mice and moulted once to the adult stage in 1–2 days at 15 °C. The stimulus to resume development appeared to be a reduction in temperature rather than presence of bacterial food or reduction in osmotic pressure. Countless generations ensued on nutrient agar provided the nematodes were periodically sub-cultured onto fresh agar. Nematodes from the eyes died in culture. Dauerlarvae of P. strongyloides were produced in exhausted cultures. They resumed development on fresh agar but not in distilled water. About half could be induced to exsheath by a temperature similar to that of mouse skin. A. sylvaticus probably accumulates nematode larvae in the dermis during its life and the nematodes resume development when the host dies.