Stratospheric ozone depletion threatens to increase exposure to ultraviolet (UV) radiation which is known to be a factor in a number of diseases. There is little doubt that cumulative exposure to UV radiation is important in the aetiology of non-melanoma skin cancers. Evidence is also strong for a link with cutaneous malignant melanoma, although here it appears to be intermittent intense exposure that is most damaging. More controversial is the view that exposure to solar radiation is a significant factor in ocular damage, particularly in the formation of cataracts. Earlier studies pointing to such an effect have been criticized and alternative aetiological hypotheses have been proposed. However, other studies do show an effect of UV exposure on cortical cataract. Concern is also growing that UV may be capable of activating viruses and have immunological effects that might exacerbate infectious disease. Very worrying is the possibility that UV exposure can activate the human immunodeficiency virus which might accelerate the onset of AIDS. Any such health effects that have been observed in human populations are the result of exposure to existing, naturally occurring levels of UV radiation. There is, therefore, great concern about the possible exacerbation of these impacts as a result of increased exposure to UV radiation associated with stratospheric ozone depletion. However, any assessment of the nature and scale of such impacts on human health has to deal with several major problems and these are the focus of this paper. There are uncertainties about recent trends in stratospheric ozone and problems in the prediction of future changes. Following on from this are the difficulties of estimating what effects these changes will have on UV flux at ground level in populated areas. Further problems arise in the prediction of changes in biologically significant doses to humans which might be affected by changes in behaviour as well as by changes in the environment. Finally, the limitations of existing epidemiological knowledge of the effects of UV exposure are a constraint on our ability to predict what the health effects of any changed UV doses might be.

Parasites can influence host population dynamics, community composition and evolution. Prediction of these effects, however, requires an understanding of the influence of ecological context on parasite distributions and the consequences of infection for host fitness. We address these issues with an amphibian – trematode (Digenea: Echinostomatidae) host–parasite system. We initially performed a field survey of trematode infection in first (snail) and second (larval green frog, Rana clamitans) intermediate hosts over 5 years across a landscape of 23 ponds in southeastern Michigan. We then combined this study with a tadpole enclosure experiment in eight ponds. We found echinostomes in all ponds during the survey, although infection levels in both snails and amphibians differed across ponds and years. Echinostome prevalence (proportion of hosts infected) in snails also changed seasonally depending on host species, and abundance (parasites per host) in tadpoles depended on host size and prevalence in snails. The enclosure experiment demonstrated that infection varied at sites within ponds, and tadpole survival was lower in enclosures with higher echinostome abundance. The observed effects enhance our ability to predict when and where host–parasite interactions will occur and the potential fitness consequences of infection, with implications for population and community dynamics, evolution and conservation.

Eosinophils are important immune cells that have been implicated in resistance to gastrointestinal nematode (GIN) infections in both naturally and experimentally infected sheep. Proteins of particular importance appear to be IgA-Fc alpha receptor (FcαRI), C-C chemokine receptor type 3 (CCR3), proteoglycan 3 (PRG3, major basic protein 2) and EPX (eosinophil peroxidase). We used known human nucleotide sequences to search the ruminant genomes, followed by translation to protein and sequence alignments to visualize differences between sequences and species. Where a sequence was retrieved for cow, but not for sheep and goat, this was used additionally as a reference sequence. In this review, we show that eosinophil function varies among host species. Consequently, investigations into the mechanisms of ruminant immune responses to GIN should be conducted using the natural host. Specifically, we address differences in protein sequence and structure for eosinophil proteins.

The World Health Organization suggested that the prevalence of Schistosoma mansoni among 7- to 14-year-olds be used to guide treatment strategies in endemic areas. This study explores how well the prevalence in that age group predicted the overall prevalence in the community in data from stool examinations (Kato–Katz method) from 180000 people in 3 municipalities in Brazil in 1984 and 1985. The median prevalence was higher in 1984, before community treatment was introduced. There was a strong relationship between the prevalence among 7- to 14-year-olds and the overall prevalence in the community. We present sensitivities and positive predictive values for the use of prevalence in the indicator group to select communities for mass treatment as recommended by WHO. For a range of assumptions sensitivity and positive predictive value were never both above 80%. We suggest that the estimates of validity presented in this paper inform future evaluations of strategies for S. mansoni control.

Two new monogenetic trematodes of the sub-order Polyopisthocotylea Odhner were obtained from the gills of marine fishes. The characters of the first (Vallisiopsis contorta) agree with those of the subfamily Vallisiinae Price (family Discocotylidae Price) except in the presence of accessory sclerites in the clamp skeleton. As the mere presence of accessory sclerites does not justify the creation of a new subfamily, I refer this species to the subfamily Vallisiinae the diagnosis of which should, however, include the presence of accessory sclerites as an additional character. The second species described belongs to the subfamily Gastrocotylinae Sproston (family Microcotylidae Taschenberg).

All of the enzymes of proline catabolism were present in Heligmosomoides polygyrus and Panagrellus redivivus and the activities were, in general, similar to those found in rat liver. Both nematodes were also shown to be able to catabolize the branched-chain amino acids leucine, isoleucine and valine, by pathways similar to those found in mammalian liver. There were no significant differences in amino acid catabolism between the animal-parasitic and free-living species of nematode.

In the course of examining some material from small mammals collected in Denmark, the British Isles and the Channel Islands, it has become evident that comparatively little is known of the species of Ixodes involved. A recent paper by Visotzkaya (1951) on the biology of the mouse tick, I. trianguliceps Birula, 1895, is the only one of its kind. Unfortunately, this paper is written in Russian and is comparatively inaccessible.

The application of genome-scale approaches to study Trypanosoma cruzi–host interactions at different stages of the infective process is becoming possible with sequencing and assembly of the T. cruzi genome nearing completion and sequence information available for both human and mouse genomes. Investigators have recently begun to exploit DNA microarray technology to analyze host transcriptional responses to T. cruzi infection and dissect developmental processes in the complex T. cruzi life-cycle. Collectively, information generated from these and future studies will provide valuable insights into the molecular requirements for establishment of T. cruzi infection in the host and highlight the molecular events coinciding with disease progression. While the field is in its infancy, the availability of genomic information and increased accessibility to relatively high-throughput technologies represents a significant advancement toward identification of novel drug targets and vaccine candidates for the treatment and prevention of Chagas' disease.

In 1934 an intensive but unsuccessful search was made for the metacercariae of the Rhodometopa group of cercariae parasitizing Turritella communis Lamarck. Attention was concentrated on the vertebrate and invertebrate fauna of the Rame Mud, as Turritella has a patchy and circumscribed distribution in the Plymouth neighbourhood and is virtually restricted to a few small areas of ground in this region. The high rate of infection suggested that the metacercariae must occur commonly in some species found there, and the behaviour of the cercariae indicated that a fish served as second intermediate host (Rothschild, 1935, p. 169). This has now been proved.

The purpose of this paper is to describe a new tick of the genus Ornithodoros Koch, from South Africa. Specimens were received through the courtesy of Dr Zumpt of the South African Institute of Medical Research, after being collected from the burrow of a striped mouse, Rhabdomys pumilio (Sparrman), near Cathcart, Cape Province, in April 1952. Interest in the ‘burrow haunting’ Ornithodoros of Africa has increased in recent years, because certain of these ticks have been found to transmit spirochaetes of rodents and other small mammals. These spirochaetes may be evolutionary precursors of those that infect man, and cause the well-known sporadic relapsing fever of tropical Africa. Two live Ornithodoros larvae from the burrow were emulsified and inoculated into a white mouse but no spirochaete was isolated (Zumpt, personal communication).

Uptake by the tegument of metacercariae of Bucephalus haimeanus of both particulate material and small molecules in solution is demonstrated by the use of electron-dense tracers and autoradiographic techniques. Ruthenium red (RR) uptake involved pinocystosis and the formation of large, electron-lucent vesicles in the outer cytoplasmic tegument. RR lost its association with these vesicles and became freely dispersed within the cytoplasm as it passed through the outer cytoplasmic tegument, down the cytoplasmic bridges and into the tegumental cell bodies. Ferritin, iodinated insulin and iodinated human serum albumin were also located within the outer cytoplasmic tegument and ferritin collected beneath the inner plasma membrane of the outer cytoplasmic tegument. Horseradish peroxidase was not absorbed by the tegument although it bound strongly to the outer surface of the metacercariae. C-labelled glucose, phenylalanine, tryptophan and tyrosine were all detected in the outer cytoplasmic tegument.

1. Dobell's observations on the production of pure mixed strains of Entamoeba histolytica have been repeated and confirmed.

2. It has been demonstrated that the method devised by Rao did not sterilize the cysts of E. histolytica but merely killed all non-sporing organisms, while the spores of all spore-forming bacteria were unaffected.

Methods are described for the freezing of trichomonads, suspended in a liverinfusion broth, to – 20 °C and – 70 °C, and storage at these temperatures. After 9 months’ storage at – 70 °C, with dimethyl sulphoxide, six strains of T. vaginalis and three strains of T. foetus were alive; three trichomonas strains frozen earlier were also alive after 13 months. Four of the T. vaginalis strains survived equally well for 6 months at – 70 °C, in the presence of either dimethyl sulphoxide or glycerol.

Although trichomonads may be maintained by subculture in a modified Diamond medium, storage at – 70 °C is more economical and less tedious; – 20 °C is not a satisfactory storage temperature for T. vaginalis or T. foetus, even in the presence of dimethyl sulphoxide or glycerol.

The severity of subcutaneous lesions in mice produced by six freshly isolated strains of T. vaginalis, and two out of three stock culture strains of T. foetus, was enhanced by either the addition of agar to the suspending medium or administration of cortisone to the mice. One strain of T. foetus produced lesions only in the presence of agar, cortisone, on the dose schedule used, being ineffective.

After storage at – 70 °C or cultivation in agar medium for 6 months, the virulence of trichomonads of either species was little affected, and lesions in mice were enhanced by agar in a similar degree to that found originally.

For enhancing the severity of subcutaneous lesions in mice the agar method, involving only one injection, is simpler than the repeated administration of cortisone to infected mice; agar was shown to be more effective than cortisone with small infecting doses of one strain of T. vaginalis quantitatively tested.

The subcutaneous injection of mice with trichomonads suspended in a liver-infusion broth containing 0·06% agar regularly produces lesions of the degree of severity required for the evaluation of compounds for therapeutic activity.

We express our gratitude to Mr S. A. Price for constructive criticism and helpful suggestions during the preparation of the manuscript. Dr S. R. M. Bushby kindly provided details of the dimethyl sulphoxide method and apparatus in use in his laboratory for the low-temperature preservation of tumour cells and trichomonads. For supplying the trichomonas strains we are grateful to Dr L. P. Joyner, Miss M. Moore-Tucker and Mr C. S. Ledwich. We thank Mr W. A. Freeman for advice on the composition of the inoculum medium.

Tyrosinase provides an essential activity during egg production in diverse platyhelminths by mediating sclerotization of eggshells. In this study, we investigated the genomic and evolutionary features of tyrosinases in parasitic platyhelminths whose genomic information is available. A pair of paralogous tyrosinases was detected in most trematodes, whereas they were lost in cyclophyllidean cestodes. A pseudophyllidean cestode displaying egg biology similar to that of trematodes possessed an orthologous gene. Interestingly, one of the paralogous tyrosinases appeared to have been multiplied into three copies in Clonorchis sinensis and Opisthorchis viverrini. In addition, a fifth tyrosinase gene that was minimally transcribed through all developmental stages was further detected in these opisthorchiid genomes. Phylogenetic analyses demonstrated that the tyrosinase gene has undergone duplication at least three times in platyhelminths. The additional opisthorchiid gene arose from the first duplication. A paralogous copy generated from these gene duplications, except for the last one, seemed to be lost in the major neodermatans lineages. In C. sinensis, tyrosinase gene expressions were initiated following sexual maturation and the levels were significantly enhanced by the presence of O2 and bile. Taken together, our data suggest that tyrosinase has evolved lineage-specifically across platyhelminths related to its copy number and induction mechanism.

Studies on the biology of Notocotylus attenuatus in the domestic fowl were undertaken with the aim of determining where in the alimentary system the metacercariae excyst and how soon the juvenile worms become established in the caecum of the host. The metacercariae were found to excyst in the lower intestine and juvenile worms were recovered from the caecum after 4 h. Thereafter, as the worms increased in size they changed their position relative to the viii and also moved down the caecum, coming to lie in the blind ending region as the worms approached maturity.

The term “Myiasis” is generally used to indicate the presence of Dipterous larvae in the living body of man or other animals. “ The form of Myiasis most commonly met with in the United Kingdom,” writes Austen (1912), “is that of the alimentary canal, as the result of which living larvae or pupae, greatly to the distress and alarm of the patient, are discharged from the bowel. Cases of Myiasis of the nasal passages and frontal sinuses the external auditory meatus, the subcutaneous tissue, and the urinary passages are apparently of quite exceptional occurrence in the British Islands.” The following pages deal with three hitherto unrecorded cases, two of urethral and one of intestinal Myiasis.