A control programme of opisthorchiasis was carried out for three years in three villages of northeast Thailand in order to compare the effectiveness of two intervention measures. The intervention measures employed were to give praziquantel treatment to all infected people either once (village I) or twice (village II) per year with the integration of regular health education and sanitation improvement. A control village (village III) received no intervention during the study. Sampling of the population in these villages to estimate prevalence, intensity, reinfection and incidence of infection as well as knowledge of opisthorchiasis and number of latrines was performed at 6 monthly intervals throughout the duration of the study. At the initial assessment, there were no significant differences in the prevalence and intensity of infection of villages I and II. Both values were greatly reduced when assessed 6 months after the initiation of treatment, and the decrease in prevalence and intensity of infection did not differ between villages I and II. The control village (village III), during the first 2 years, exhibited slight variation in the prevalence and intensity, and these decreased considerably in the third year of the study. The reinfection rate per 6 months in villages I and II was nearly equal. The incidence rate per 6 months in the two treated villages was lower than that of the control village. Marked improvement in knowledge of opisthorchiasis, behavioural changes of eating raw fish and increased numbers of latrines was evident in all of the villages during this study. The study showed that the effectiveness of annual drug treatment is similar to that of 6 monthly treatments when combined with regular health education and sanitation improvement.

“Piroplasmosis,” or “biliary fever” in horses, has hitherto been regarded as a disease due to a distinctive parasite, Piroplasma equi Laveran. We propose to show that there are two specifically distinct parasites concerned in the production of biliary fever, and that consequently two distinct diseases have hitherto been confused under this name and under the name of piroplasmosis.

Sporulated oocysts or oocyst hulls of Eimeria acervulina given via the crop, and oocyst juice or sporozoites inoculated directly into the in testinal lumen, were tested for their effects on the hypersensitivity of the intestines of immunized and susceptible birds. Only viable sporozoites consistently caused an increase in the permeability of the immunized intestine to macromolecules, shown by the leakage of intravenously injected dye. Repulsion of epithelium and disruption of the villi were seen more often in immunized than in susceptible chickens but there was no correlation with treatment or with dye leakage.

The hypersensitive response of immune intestines challenged with a heterologous organism was approximately half as intense as the response to homologous challenge.

The significance of these findings in relation to immunity to coccidiosis is discussed.

An electron microscopical examination has been made of the fine structure and disposition of pancreatic polypeptide immunoreactive cells associated with the egg-forming apparatus in Diclidophora merlangi. The cell bodies are positioned in the parenchyma surrounding the ootype and taper to axon-like processes that extend to the ootype wall. The terminal regions of these processes branch and anastomose and, in places, the swollen endings or varicosities form synaptic appositions with the muscle fibres in the ootype wall. The cells are characterized by an extensive GER-Golgi system that is involved in the assembly and packaging of dense-cored vesicles. The vesicles accumulate in the axons and terminal varicosities, and their contents were found to be immunoreactive with antisera raised to the C-terminal hexapeptide amide of pancreatic polypeptide. It is concluded that the cells are neurosecretory in appearance and that, functionally, their secretions may serve to regulate ootype motility and thereby help co-ordinate egg production in the worm.

The distribution and abundance of Enterobius vermicularis in a fishing community in South India, as determined by counting worms expelled following mass anthelmintic chemotherapy, was examined in samples of patients stratified by age, sex and family grouping. The results of a worm expulsion study in January 1984 are compared with those of a second expulsion programme in November 1984, following an 11-month period of reinfection. The prevalence of Enterobius infection was consistently high in all age groups of both males and females. A comparison of the overall prevalence and intensity of infection in the January and November surveys revealed significant increases in both the percent infected and the mean number of worms harboured in November relative to the initial level. No significant trends in the intensity of Enterobius according to host age or sex were detected in either survey. The frequency distribution of Enterobius was found to be highly aggregated in the population as a whole and within age groups. At both sampling dates, the most heavily infected 25% of the community harboured over 90% of the total pinworms recovered. There was a significant pattern within most age groups for individuals to re-acquire worm burdens of a similar magnitude to their initial pre-treatment burdens. Heavy infections were found to be associated with household. A selective or targetted approach to treatment of heavily infected individuals or households is likely to be an efficient means of reducing parasite abundance on a community-wide basis. It must be stressed, however, that treatment must be applied at frequent intervals in order to achieve a long-term reduction in pinworm abundance and to avoid the possibility of increasing the intensity of infection, as was observed in this community.

Blastocrithidia triatomae parasitizes vectors of Chagas' disease and is very difficult to cultivate in conventional media. However, co-cultivation with a cell line of its host Triatoma infestans (TI-32; in Schneider's Drosophila medium supplemented with 20% foetal calf serum and 10% tryptose phosphate broth) led to vigorous growth at 24 or 28 °C without an adaptation phase. More than 60 primary cultures were initiated successfully without any failures. Subcultures could be started immediately at weekly intervals. The doubling time was similar in both the primary cultures (41 h) and the 33rd subculture (39 h). The importance of the reduviid cells for B. triatomae became clear after removal of the insect cells, when multiplication of epimastigotes stopped and mainly cysts were formed. Cysts produced in vitro were infective for reduviids. Scanning electron microscopy showed that B. triatomae attached to the host cells, inserted its flagellum into them and destroyed them.

Studies based on the mixed antiglobulin reaction have shown that γ-globulin is adsorbed from normal human sera by the cuticle of parasitic nematodes. Using antiglobulins specific for IgA, IgM and IgG, it was possible to demonstrate uptake to titres of 4, 64 and 128, respectively. Adsorption continued for at least 24 h, and the responsible immunoglobulins could be absorbed from the sera by nematode preparations.

A comparison of normal human sera with sera from cases of ascariasis and visceral larva migrans revealed that there was no significant difference between the titre of anti-cuticular immunoglobulins in normal sera or sera from helmin-thiases. It is suggested that these immunoglobulins adsorbed by the nematode cuticle represent cross-reacting, naturally occurring antibodies.

I am sincerely grateful to Professor R. R. A. Coombs, F.R.S., for his help, advice and encouragement, and to Mr M. J. Eburne for splendid technical assistance.

Parasitic diseases inflict major losses on livestock production throughout the world. Currently, control of the diseases relies largely on prophylactic or therapeutic application of anti-parasitic drugs. In many instances, these measures are only partially effective. Moreover, they must be applied frequently, are therefore costly and time-consuming, and lead to the selection of drug resistance within the parasite populations. Thus, it has been recognized for several decades that effective methods of vaccination against parasitic diseases would have a major impact on livestock production. However, despite considerable efforts over the last 30 years, only a few parasite vaccines are currently in use and all of these involve the administration of live organisms.

Lipid levels of infective larvae of Ancylostoma tubaeforme are reduced and their behavioural activity declines with age. We have measured behavioural activity using the percentage active, rate of activity, and the percentage of larvae able to penetrate a membrane. Neostigmine bromide, a cholinergic drug, increased larval activity in all tests. Larvae, stored at 4 and 10 °C and in hypertonic saline, were inactive but consumed lipid. When returned to isotonic saline at 26 °C, these larvae were no more active than those at 26 °C throughout. We found no evidence that such inactive larvae had entered a state of quiescence. All our results, and those of other workers, have been used to emphasize that larval ageing is related directly to decreased metabolic rates, and not primarily to lipid levels.

CBA/T6 and DBA/2J mice inoculated with Plasmodium berghei ANKA (PbA) develop cerebral involvement 6–8 days post-inoculation, from which the CBA mice almost invariably die and the DBA mice recover. Dexamethasone (DXM; 80 mg/kg) given to inoculated CBA mice twice, on day 3 and again within 48 h, reduced the cerebral symptoms and prevented death from cerebral malaria. Plasma tumour necrosis factor (TNF) levels, which increased at the time of the cerebral symptoms, were also reduced in these DXM-treated mice. Intravenously administered Evans Blue, a dye which binds to albumin, diffused extensively across the blood-brain barrier only during the period of cerebral symptoms, in proportion to the severity of the cerebral symptoms and the disease. In PbA-infected CBA mice, cerebral symptoms and the amount of Evans Blue diffusing into the brain tissue were both reduced by DXM treatment, but only if the steroid was given on day 3 and again within 48 h. Endotoxin injected intravascularly into PbA-infected DBA mice after day 5 resulted in an exaggeration of cerebral symptoms and death between days 6 and 9. Plasma TNF and the amount of Evans Blue in the brain parenchyma increased above normal levels in these mice. Endotoxin injections had only minor effects on the severity of the cerebral symptoms in PbA-infected CBA mice and did not cause the animals to die sooner.

The louse populations of the heads of 93 infested children, 45 boys and 48 girls under 14 years of age from a northern English industrial city have been examined.

The average number of lice per head was 14·8 for all children, 12·7 for boys and 16·8 for girls. The maximum population observed was 142.

The majority of infestations (65%) were light with under 10 lice. Girls were more frequently heavily infested than boys.

Most of the infestations, though light, must have been established at least for some weeks.

A descriptive epidemiological survey was undertaken of the ascarid nematode Toxocara canis in 521 red foxes (vulpes, vulpes) during the period January 1986 to July 1990. Age–prevalence and age–intensity profiles show that worm are significantly higher in cubs than in subadult or adult foxes and higher in subadult than in adult foxes. variations in worm burdens occur, with the highest prevalences and intensities being found during the spring, when are born, and in the summer months. Prevalences and intensities then decrease during the autumn and winter months both subadult and adult foxes, but, during this period, prevalences are significantly higher in male than in female Variations in worm burdens in the fox population are likely to be related to the reproductive cycle of the fox, with proportion of cubs becoming infected in utero. The role of the fox in the transmission of T. canis in the urban environment is discussed.

Survival of the trypanosome (Trypanosoma brucei) population in the mammalian body depends upon paced stimulation of the host's humoral immune response by different antigenic variants and serial sacrifice of the dominant variant (homotype) so that minority variants (heterotypes) can continue the infection and each become a homotype in its turn. New variants are generated by a spontaneous switch in gene expression so that the trypanosome puts on a surface coat of a glycoprotein differing in antigenic specificity from its predecessor. Homotypes appear in a characteristic order for a given trypanosome clone but what determines this order and the pacing of homotype generation so that the trypanosome does not quickly exhaust its repertoire of variable antigens, is not clear. The tendency of some genes to be expressed more frequently than others may reflect the location within the genome and mode of expression of the genes concerned and may influence homotype succession. Differences in the doubling time of different variants or in the rate at which trypanosomes belonging to a particular variant differentiate into non-dividing (vector infective) stumpy forms have also been invoked to explain how a heterotype's growth characteristics may determine when it becomes a homotype. Recent estimations of the frequency of variable antigen switching in trypanosome populations after transmission through the tsetse fly vector, however, suggest a much higher figure (0·97–2·2 × 10−3 switches per cell per generation) than that obtained for syringe-passed infections (10−5–10−7 switches per cell per generation) and it seems probable that most of the variable antigen genes are expressed as minority variable antigen types very early in the infection. Instability of expression is a feature of trypanosome clones derived from infective tsetse salivary gland (metacyclic) trypanosomes and it is suggested that high switching rates in tsetse-transmitted infections may delay the growth of certain variants to homotype status until later in the infection.

1. The rate of penetration of some representative drugs into Ascaris lumbricoides var. suis has been measured.

2. The series of 4-n-alkyl resorcinols shows a typical homologous series effect.

3. l-Nicotine penetrates relatively slowly.

4. Its rate of penetration is greatly influenced by the extent of dissociation of its methyl pyrrolidine basic group.

5. The rate of penetration of nicotine is greatly accelerated in the presence of some surface active substances.

6. Chloroform is the most rapidly penetrating substance studied, and its penetration is not significantly influenced by the presence of proteins, carbohydrates and fats and their products of digestion.

7. An analysis of the experimental results shows that the outermost layer of the cuticle of Ascaris is probably the main barrier to penetration. It behaves as if it were a thin; homogeneous layer of lipoid.

8. The significance of these results in the study of anthelmintics is assessed.

On the whole published data on the host relationships of Ixodes ricinus L. in Britain are rather inadequate, but the following points emerge:

The tick (stages unspecified) has been found on twenty-three mammal, twenty-one bird and one reptile species. These include both wild and domestic animals. There are no records of non-hosts. The host list is incomplete. Its length and variety suggest, however, that the tick will feed on practically any mammal or bird it may meet.

Tick stages found on fifteen mammal, twenty-one bird and one reptile species have been recorded. For a number of reasons (see text) ‘recorded’ absence of any tick stage from an animal is not necessarily reliable. This, together with the incompleteness of the host list, detracts a little from the assertion of several authors, namely, that in general larvae and nymphs occur on both mammals and birds, but adult ticks on mammals only.

No precise host-potentials for any wild species relative to sheep (or other important farm stock) have been published in Britain. But, in one area, Scottish mountain hare, red deer and roe deer have been slaughtered on a large scale because of their alleged importance as hosts. Very inadequate data from two authors seem to suggest that as normally stocked populations (a) grouse are negligible compared with sheep as hosts to female ticks, and (b) mountain hare and red deer may play quite an important part in maintaining female ticks. Suggestion (b) at least should not be taken seriously until comprehensively investigated.

One author shows that an ‘appreciable’ tick population was maintained on a hill grazing by a reduced wild fauna in the absence of sheep.

Another author shows that the tick population of a grazing was considerably reduced by acaricidal treatment of sheep, together with almost complete extermination of a section of the wild fauna. Unfortunately, the two factors cannot be disentangled.

We would like to thank Mr Charles Elton, Director, Bureau of Animal Population, Oxford, and Dr J. MacLeod of the Cooper Technical Bureau, Berkhamsted, for criticism of the MS.; Mr F. Wallace for information on red deer stocking; and Dr V. B. Wigglesworth, F.R.S.,. Director, Agricultural Research Council Unit of Insect Physiology, Cambridge, within whose organization the work was done.

1. A fork-tailed cercaria Cercaria diplostomi phoxini (Faust) has been found to develop in sporocysts in 3·9 % of Lymnaea pereger var. ovata (Drapanaud) in Fron Goch Pool near Aberystwyth.

2. The cercaria is described in detail. The arrangement of spines on the body is characteristic and there is a double row of seventy-two spines on the ventral sucker. The flame cell formula is given.

3. The cercaria is compared with seven closely related types.

4. Infestation experiments show that Cercaria diplostomi phoxini develops into Diplostomulum phoxini in the brain of the minnow.

5. The early stage of infestation of the brain of the minnow is described and compared with an infestation of long standing.

Chick embryos have been infected with sporozoites of Eimeria tenella, but not with E. brunetti, and died from coccidiosis 5 days after infection.

Chick embryos can be protected from death due to coccidiosis by some but not all drugs which give a therapeutic response in chickens. The system is therefore not satisfactory as a screening tool, but may have applications in studies on the nature of drug activity.

As in Parts I and II of this Report (Parasitology, xv, pp. 1–23) the numbers are those given to the original tubes at Cambridge.

Parasites that often grow anaerobically in their hosts have adopted a fermentative strategy relying on the production of partially oxidized end products, including lactate, glycerol, ethanol, succinate and acetate. This review focuses on recent progress in understanding acetate production in protist parasites, such as amoebae, diplomonads, trichomonads, trypanosomatids and in the metazoan parasites helminths, as well as the succinate production pathway(s) present in some of them. We also describe the unconventional organisation of the tricarboxylic acid cycle associated with the fermentative strategy adopted by the procyclic trypanosomes, which may resemble the probable structure of the primordial TCA cycle in prokaryotes.

The larval trematodes described in this paper were obtained from fresh-water molluscs collected from Rostherne Mere and a pond near Ashley, both in Cheshire. Rostherne Mere is a large sheet of water and carries an extensive fauna, vertebrate and invertebrate. The molluscs were collected from various fixed positions in the littoral region, and this method has confirmed previous observations (unpublished) in other stretches of fresh-water on the variation in the distribution and localisation of infected molluscs. How far this may be related to movements of the final host or to physical factors affecting the migration of the molluscs is at present uncertain; further observations are being made in an attempt to elucidate this problem. The molluscs were isolated in the laboratory in 3 × 1 glass specimen tubes, when the infected specimens were easily seen by the swarming of the cercariae, and all observations (including measurements) were made on these living, fully developed cercariae. Infected snails were later crushed in physiologically normal saline in order to obtain living sporocysts or rediae for examination. Measurements are, of necessity, only approximate owing to the slight pressure exerted by the weight of the cover-glass and the great powers of contraction and extension of these larval forms. Neutral red was used as an intra vitam stain; it also inhibits movement. Of the five species described four are new, the fifth, for which a further stage in the life history is described, being little known and not previously recorded for this country.