Among the new facts discovered in the course of the writer's investigation on the function of the polar filament of the spore of Nosema bombycis (Ohshima, 1927), the following two are considered the most important:

(1) As soon as its filament extrusion is accomplished in the midgut of a silkworm, the spore discharges a viscous fluid through the tube of the filament. This fluid remains hanging in a spherical shape at the extremity of the filament.

(2) Both the polar filament and the viscous fluid are speedily digested by the digestive ferment of the silkworm in a few seconds.

The sequence of appearance of specific lytic activity against more than 20 variable antigen types (VATs) of Trypanosoma vivax in the serum of 27 animals belonging to 5 species has been examined. For each host species there was a characteristic course of infection, with differences in height and duration of parasitaemia and in pathogenicity. The sequence of antigenic variation was similar in all host species, with some VATs consistently eliciting response more rapidly than others. The predominant group, comprising VATs which apparently developed within the first 3 weeks, varied in size according to the total number of trypanosomes in the bloodstream within that period, suggesting there is a spectrum, rather than discrete groupings, in the hierarchy of VAT expression. There was very little evidence for differences in appearance of VATs between host species; the only clear example was one VAT which apparently did not develop in one host species. The sequence of antigenic variation in T. vivax seems to be determined by the parasite rather than the host species.

A total of 121 European eels (Anguilla anguilla) from 2 sampling sites on the River Rhine were investigated in respect of their parasite communities. Special attention was given to the swim bladders, intestines, gills and fins of the fish. Twelve different parasite species were found to live in and on the eels. Data from each sampling site were kept separate. Parasites found in descending order of prevalence were: Anguillicola crassus, Trypanosoma granulosum, Myxobolus sp., Paratenuisentis ambiguus, Pseudodactylogyrus sp., Bothriocephalus claviceps, Myxidium giardi, Pomphorhynchus laevis, Trichodina sp., Raphidascaris acus, Acanthocephalus lucii and Acanthocephalus anguillae. Significantly different prevalences were reported for L3 larvae of A. crassus, adult P. ambiguus, B. claviceps and Myxobolus sp. at the 2 sampling sites. The highest number of parasite species was recorded from the intestine, which contained up to 6 different helminths. The coexistence of the acanthocephalans P. laevis and P. ambiguus, which showed clear patterns of distribution within the intestine of the respective hosts, was reported for the first time. Up to 3 different helminth species were found in the intestine of individual fish. Among those, acanthocephalans were the most prevalent worms with the eel-specific parasite P. ambiguus as the dominant species not only of the intestinal but also of the total component communities. Both infra and component communities exhibited low diversity and were dominated by this single species. The evenness reached only approximately 50% or less and it remained unclear why the helminth communities of the eels from the River Rhine with its huge catchment area exhibit such a low parasite diversity and high dominance.

A natural infestation of bed-bugs which has existed for several years in an animal room has been studied. The bugs feed on the rats kept in cages in the room.

Methods are described by which the bugs were trapped during their periods of normal activity.

Adult bugs appear to feed on an average once every 5 or 6 days when the temperature is in the region of 20–27° C. (68–80·6° F.). Most of the female bugs lay a continuous series of eggs at the rate of nearly three per day.

Female bugs are not usually fertilized more than once a week in this wild population. In laboratory cultures copulation is much more frequent.

In the animal house the bugs were most active between 3 a.m. and 6 a.m. This activity seems to be controlled by some inherent rhythm.

Some marked bugs were released and the proportion of recaptures to others in the total catch was noted. From this a rough estimate of the population was made. It appears that few adults live more than 29 days as they are probably killed by the rats when trying to feed.

Two strains of Eimeria acervulina were compared. The more recently isolated strain had a higher reproductive potential and produced slightly longer oocysts. Otherwise both strains conformed to the characteristics of the species.

The two strains were not immunologically identical and birds which were solidly immune to one strain would support a degree of infection with the other.

Acknowledgements are due to Mr C. C. Norton for technical assistance and to Dr Helen Hein who provided access to experimental data prior to publication and discussed some aspects of the results. The statistical calculations were carried out by Miss N. Hebert.

Chronic infection is a prominent feature of many intestinal nematode infections in man and animals. It is also clear that in such situations host immunity is activated but is unable to induce a protective response. A great deal of work has shown that genetic control of host immunity contributes to the variation in worm burdens often observed in the field. There is increasing appreciation, however, of the capability of infectious agents themselves to modulate the host immune response and potentiate their own survival. Using an immunologically well defined model of intestinal nematode infection in mice (Trichuris muris) we have shown that parasite derived molecules share cross reactive epitopes with the host cytokine interferon-γ using cytokine specific monoclonal antibodies in ELISA, Western blotting and immunoprecipitation assays. Furthermore, the parasite molecules can be shown to bind to the interferon-γ receptor and induce change in lymphoid cells similar to those induced by murine interferon-γ. The functional activity of the molecule in vivo remains to be determined. Previous studies have established that interferon-γ is critical for progression to chronic T. muris infection in mice and, therefore, it raises the distinct possibility that the production of an interferon-γ homologue by the worm may be one mechanism whereby the parasite is able to interfere with the regulation of the host immune response and potentiate its own survival.

This study was performed in order to define Schistosoma mansoni antigens that are able to function as modulator agents in the granulomatous hypersensitivity to parasite eggs in BALB/c and C57BL/6 mice. A fraction of S. mansoni, designated PIII, derived from adult worm antigen preparation (SWAP) was obtained using anion-exchange chromatography on an FPLC system. Immunization of mice with PIII in the presence of Corynebacterium parvum and Al(OH)3 as adjuvant induced an immune response in these animals as determined by ELISA and spleen cell proliferation assays against S. mansoni antigens SEA, SWAP and PIII. In addition, PIII caused a significant degree of protection against a challenge infection in immunized mice as observed by the decrease on worm burden recovered from the portal system. We also showed that PIII profoundly inhibited the vigorous anamnestic granulomatous response to eggs in the liver and lungs. This suppression correlated with a significant decrease in granuloma size. From these results we conclude that the PIII preparation contains antigens that can mediate protective anti-parasite immunity and downregulate granulomatous hypersensitivity to S. mansoni eggs.

The number of Teladorsagia circumcincta 4th-stage larvae in naturally infected lambs from a single farm varied among lambs and among different years. Within each year the distribution of 4th-stage larvae among lambs was similar to that expected from a negative binomial distribution. The ratio of 4th-stage larvae to adult T. circumcincta was low in two years with a low mean intensity of infection but high in two years with a higher mean intensity of infection. The negative binomial distribution is defined by the mean and by k, a parameter that measures dispersion; k was low when mean infection intensity was low but higher when mean infection intensity was high. As k is an inverse index of overdispersion this indicated that the distribution of 4th-stage larvae was more overdispersed at low levels of infection. In a combined analysis, the number of adult T. circumcincta and the plasma IgA activity against 4th-stage larvae were both associated with increased numbers of 4th-stage larvae. There was a statistical interaction between the number of adults and IgA activity that moderated their combined effect.

The nature of the proteins which comprise the in vitro excretory/secretory products (ES) of the fourth-stage larva (L4) and adult Teladorsagia circumcincta are largely undefined, despite the fact that this nematode induces profound changes, in part related to parasite ES, in the cellular architecture of the glands lining the abomasal surface of infected sheep and goats. In this study, the protein components of L4 and adult ES were fractionated using 1D gel electrophoresis and the major protein bands, detected by Coomassie blue staining, excised from the gel and subjected to tryptic digest and subsequent mass spectrometric analysis. The resultant peptide mass fingerprints were used to identify 15 L4 and 13 adult ES proteins. Several proteins, such as globin and some metabolic enzymes, were present in both ES. L4 ES alone contained thioredoxin peroxidase, an enzyme that can detoxify free radicals resulting from host inflammatory responses to the parasite, a cysteine proteinase which may aid penetration of the gastric mucosa and 2 different galectins which may influence cell differentiation and morphogenesis. Adult ES contained a nucleoside diphosphate kinase homologue, an enzyme which has been linked to cellular changes and can affect liquid secretion and goblet cell degranulation.

A comparison was made of the long-term impact of different methods of administration of chemotherapy (oxamniquine, 30 mg/kg in divided doses; or praziquantel, 40 mg/kg) on prevalence and intensity of Schistosoma mansoni infection in four areas in Kangundo Location, Machakos District, Kenya. In Area A, treatment was offered in October 1983 and again in April 1985 to all infected individuals. In Area H, treatment was offered in April 1985 to individuals excreting ≥ 100 eggs per gram (epg) of faeces. In Area H, treatment was offered in April 1985 to all infected school children, within the framework of the primary schools. In the witness area, Area W, treatment was given in April 1985, for ethical reasons, to a small number of individuals excreting ≥ 800 epg. Prevalence and intensities of infection were subsequently monitored at yearly intervals for three complete post-treatment years. In the Area S schools, clinical examination was also carried out at yearly intervals. Treatment of all infected individuals on two occasions (Area A) was the most effective and long-lasting way of reducing prevalence and intensity of infection. In this area, however, some earlier interventions had been carried out and pre-treatment intensities were lower than in the other areas. Treatment only of infected schoolchildren (Area S) also had a marked and prolonged effect, comparable to or better than treatment of individuals with heavy infections (Area H). Treatment of infected schoolchildren also caused a persistent reduction in the prevalence of hepatomegaly, and there was suggestive evidence from intensities of infection in community stool surveys (but not from incidence rates) of an effect on transmission. In all study areas, reinfection was most rapid and most intense among children. These findings are discussed in the light of theoretical considerations and of results from other studies, both on schistosomiasis and on intestinal helminths. We conclude that, in areas of low morbidity such as Kangundo, chemotherapy of schoolchildren only, at intervals of up to 3 years, is a satisfactory way of producing a long-term reduction in both intensity of infection and morbidity.

Sequence comparisons have recently shown that the Schistosoma mansoni protein Sm32 is similar to asparaginyl endo-proteinases, a novel family of cysteine proteinases, of which the legumains rom legumes are the best characterized. By synthesizing and employing fluorogenic peptide substrates for the specific detection of asparaginyl endopeptidases, we have identified this type of activity in extracts of adult S. mansoni. The S. mansoni activity is similar to that of the legumains in its substrate specificity and sensitivity to thiol inhibitors, but differs in its pH and temperature optima for activity. In contrast, unlike the legumains, the schistosome asparaginyl endopeptidase activity is not activated by the reducing agent dithiothreitol. As suggested for legumains, Sm32 may function in the post-translational modification processes that regulate the activity of other molecules.

This study was conducted to quantify the association between meteorological variables and incidence of Plasmodium falciparum in areas with unstable malaria transmission in Ethiopia. We used morbidity data pertaining to microscopically confirmed cases reported from 35 sites throughout Ethiopia over a period of approximately 6–7 years. A model was developed reflecting biological relationships between meteorological and morbidity variables. A model that included rainfall 2 and 3 months earlier, mean minimum temperature of the previous month and P. falciparum case incidence during the previous month was fitted to morbidity data from the various areas. The model produced similar percentages of over-estimation (19·7% of predictions exceeded twice the observed values) and under-estimation (18·6% were less than half the observed values). Inclusion of maximum temperature did not improve the model. The model performed better in areas with relatively high or low incidence (>85% of the total variance explained) than those with moderate incidence (55–85% of the total variance explained). The study indicated that a dynamic immunity mechanism is needed in a prediction model. The potential usefulness and drawbacks of the modelling approach in studying the weather–malaria relationship are discussed, including a need for mechanisms that can adequately handle temporal variations in immunity to malaria.

This paper contains a report on a collection of parasitic protozoa from the blood of some vertebrate animals of Uganda.

Seven new species and a number of parasites recorded for new hosts are described. New observations on some known parasites are also recorded.

An account is given of the life history of the crocodile haemogregarine. It is shown that the schizogony of Hepatozoon pettiti (nomen novum for Haemogregarina pettiti) occurs in the liver of the crocodile, while the sporogony takes place in Glossina palpalis, its intermediate host.

A list of all the blood parasites found, together with their hosts, is given.

Some information on acquired resistance of rabbits against Ixodes ricinus ticks has been obtained by comparing tissue changes and cellular infiltration during 2 successive infestations, with particular emphasis on the cells involved in immediate type hypersensitivity reactions: mast cells, basophils and eosinophils. More degranulated mast cells were observed in tick lesions 2 h after the beginning of re-infestation than in the first infestation and more degranulated basophils were present on the 5th day of re-infestation. Numerous eosinophils infiltrated the dermis, especially on the 5th day of the second infestation.

Female Dermacentor andersoni were induced to feed on defibrinated bovine blood through fixed mouse skin membranes. Their feeding behaviour was recorded electronically, the tick being incorporated into the circuit and acting as a variable resistor during the periods of sucking, salivation and rest. Recordings of the feeding behaviour of these ticks were similar to those of ticks feeding on rabbits. Known concentrations of histamine, serotonin, dopamine, prostaglandin E1 and prostaglandin F2α were added singly or in combination to the feeding medium of ticks attached to the mouse skin membrane. Addition of both histamine and serotonin was followed by a significant reduction in the amplitude or recordings associated with sucking and salivation. The concentration of mediators producing this effect was less than 10 mM, a concentration comparable to that of histamine found locally in the skin of tick-resistant guinea-pigs. Comparisons are made between the effects produced by these mediators in ticks and the effects of serotonin and other amines known to produce modulation of complex behaviour patterns in other invertebrates.

Residents of Daraweesh village in Sudan were monitored for Plasmodium falciparum infection and malaria morbidity in 3 malaria seasons from 1993 to 1996. Malaria parasites were detected microscopically and by polymerase chain reaction (PCR) in a series of cross-sectional surveys. PCR revealed submicroscopical infections during the dry season, particularly among individuals who had recovered from a malaria episode following successful drug treatment. Clinical and subclinical infections were contrasted by assaying for allelic polymorphism at 2 gene loci, MSP-1 and GLURP and 2 hypotheses examined with reference to these data: that clinical malaria is associated with infection with novel parasite genotypes not previously detected in that host, or alternatively, that clinical malaria episodes are associated with an increased number of clones in an infection. We detected more mixed infections among clinical isolates, but people carrying parasites during the dry season were not found to have an increased risk of disease in the following malaria season. There was a clear association of disease with the appearance of novel parasite genotypes.

The phylum Microspora is ancient and diverse and affects a wide range of hosts. There is unusually high use of vertical transmission and this has significant consequences for transmission and pathogenicity. Vertical transmission is associated with low pathogenesis but nevertheless can have significant impact through associated traits such as sex ratio distortion. The majority of microsporidia have mixed transmission cycles and it is not clear whether they are able to modify their phenotype according to environmental circumstances. There is a great need to understand the mechanisms controlling transmission and one of the first challenges for the genomics era is to find genes associated with life cycle stages. Similarly we cannot currently predict the ease with which these parasites might switch between host groups. Phylogenetic analysis suggests that there are strong relationships between Microsporidia and their hosts. However closer typing of parasite isolates, in relation to host range and disease phenotype, is required to assess future environmental risk from these pathogens.

1. Cercaria X (Baylis & Taylor, 1930) and its sporocyst have been redescribed with some additions to the original descriptions.

2. The details of the development of the cercaria into a metacercaria of the diplostomulum type have been obtained and the anatomy of the mature metacercaria is described in detail for the first time. It is proposed to name the metacercaria Diplostomulum X. Development of the cercaria into a metacercaria takes from 40 to 90 days and the metacercariae have been shown to survive for a period of 544 days after the time of infection. This development has been obtained in the lenses of rats, frogs and a wide variety of fish. Development is not completed in any other region of the host's body.

3.The effect of the sporocyst, migration of the cercariae, and the metacercaria on the appropriate host tissues has been considered. All these stages produce extensive changes in the host tissues.

4. Histochemical tests have shown the presence of alkaline phosphatase activity in the cuticle of the sporocyst. The glycogen storage regions of the cercaria are described and it has been demonstrated that the caudal bodies in the tail-stem contain large amounts of glycogen which are utilized during the free-swimming period.

5. Attempts at the completion of the life cycle were unsuccessful.

This study examined whether allelic changes observed when clinical isolates of Giardia intestinalis made in suckling mice were adapted to in vitro growth occurred as a result of gene switching (alternate isoenzymes) or through selection of organisms with different genotypes from mixed infections. Samples were compared electrophoretically at 20 enzyme loci. Marked allelic differences were detected between the uncloned clinical isolates grown in mice and the axenic cultures established from them. Furthermore, the allelic profiles of the uncloned isolates changed during the course of in vivo or in vitro growth. In contrast, all clones produced from each isolate retained identical allelic profiles, regardless of whether they were grown in vivo or in vitro. These findings argue against gene switching as an explanation for the observed allozyme changes and support preferential selection of organisms with specific genotypes by growth conditions. The data indicate the presence of at least 2 and possibly up to 4 distinct genotypes within each clinical isolate. The genetic differences detected between clinical isolates in suckling mice were of similar magnitude to those that separate different axenic isolates of G. intestinalis into cryptic species. Conversely, the genetic differences between the isolates were limited when sampled after establishment in vitro. These findings have significant implications for research on Giardia and other medically important parasites and raise the possibility that culture may exert a similar selective bias on the genotypes isolated from infections with other parasitic protozoa.

Since Professor Kellogg has published a list of Mallophaga, in Wytsman's Genera Insectorum, so recently as 1908, my reasons for preparing the present publication require an explanation. This explanation involves some criticism of Kellogg's list, but my main reasons are concerned rather with the plan of this list than with the few errors and omissions that I indicate.