Blastocrithidia familiaris were found to be parasitic in the midgut, ileum and rectum of Lygaeus pandurus. The host—parasite relationship is described. Attachment of parasites in the midgut and ileum occurs by interdigitation of expanded flagella over and between the microvilli. No attachment to microvilli was observed where extracellular membranes form well-organized layers which lie parallel to the gut wall and completely separate the microvilli border from the lumen. The extracellular membranes originate from delamination of the outer unit membrane of microvilli which consists of a double plasma membrane. The function of the extracellular membrane layers and their possible role as a peritrophic membrane in preventing parasite attachment is discussed in relation to previous studies on midgut cells in Hemiptera with a similar apical coat on midgut microvilli. In the rectum, parasites attach to the cuticle of the gland cells and not to the rest of the rectal wall. Attachment to the cuticle occurs by the formation of hemidesmosomes. A comparison of the relationship of B. familiaris and its host to previous ultrastructural studies of associations between kinetoplastid flagellates and their respective hosts is discussed.

We examined a host system (Peromyscus maniculatus) in which a single autosomal gene controls susceptibility or resistance to infection by the cestode parasite Hymenolepis citelli. Parasite deaths of both primary and secondary (challenge) infections were examined, using a probabilistic model, to see if deaths were random and uncorrelated within each genotype. Within susceptible hosts, post-patent survival of primary worms was not random and heterogeneity was due to among-host effects rather than parasite-age effects, suggesting a second genetic or immunological process. Secondary infections in susceptible hosts appear to be lost randomly, independent of primary infection age or burden. The loss rate is similar to that for primary worms. The lack of correlation or alteration in (susceptible) host response to primary and secondary infections suggests that the latter are eliminated by a process that differs from that acting on primary worms. In resistant hosts, parasite survival rates suggest that the immunological process elicited by the primary infection also acts to eliminate the secondary infection more rapidly. Suggestions are made for improving experimental methods when dealing with mixed genotype populations. Experiments should permit direct estimation of genotype frequency and of parasite death rates within each genotype. This separation of host type is particularly important when studying correlation of successive worm burdens since any host or treatment mixture (genotype, age, sex, size or infection dose) may induce correlations that could be mistakenly interpreted.

Professor Gwendolen Rees, or Gwen as she prefers to be known, was educated at the Intermediate School for Girls, Aberdare, between 1918 and 1924. Aberdare, a valley community in South Wales was, in the nineteenth century, world-famous as a centre for the Welsh iron and coal industry. Unlike its neighbouring town, Merthyr, however, it was not totally dominated by industry and it is especially renowned for its spacious and beautiful park near the town centre. During Gwen's early life, Aberdare was one of the largest and most influential centres of literary culture in Wales, and a place where education was of prime importance in the community. As far back as 1867, Aberdare men and women had claimed that ‘what we think today, Wales will think tomorrow’. Could these be the reasons why Aberdare has produced so many distinguished academics? None, however, has achieved greater distinction than Gwendolen Rees who, in 1971, became the first woman academic in Wales to be elected a Fellow of the Royal Society. Since she has often been affectionately referred to as ‘one in a million’ by her former students, the metaphor assumed literal significance in 1971, when the female population of Wales was 1446000. Because of a phenomenal life-long dedication to her chosen career as university teacher, researcher and administrator, together with a genuine lack of desire for personal acclaim, there may have been many people who had never heard of her until 1971.

Oocysts of fowl coccidia, suspended in a 12% aqueous solution of alginic acid, were dropped into 5% calcium chloride solution to form beads. Following ingestion by chicks, excystation of sporozoites was not affected. Oocyst viability was best when beads were air-dried to 33% of their original weight and stored in airtight containers at 4°C. Infectivity was fully maintained for 8 weeks. Trickle infection, using beads administered orally to 2- or 3-week-old chickens, or mixed daily in food of chicks from 1-day-old, established a high level of immunity. This method of oocyst administration offers some practical advantages for the conduct of immunity and chemotherapy experiments.

This study describes experiments which demonstrate the presence of a parasite-induced or derived factor in the haemocoel of Onchocerca lienalis-infected simuliids. Haemolymph, when transferred from previously infected donor flies to previously untreated recipient flies, using fine glass needles, confers protection against a subsequent challenge to the recipients. In three trials using Simulium ornatum sl. or S. linealum, significant levels of protection in ‘immunized’ compared to ‘challenge control’ groups were achieved (84% and 81% with S. ornatum sl. and 85% with S. lineaturm). This is despite the fact that the worm burdens of the infected donor groups in the three trials were very different (means of 33·1 and 3·4 larvae/fly with S. ornatum sl. and 1·6 larvae/fly with S. linealum). The use of sham-operated and bentonite-inoculated control groups demonstrate that this effect is not merely a non-specific reaction to trauma, but is probably parasitic in its derivation. The use of double infections separated by 4 days shows that the donor flies have themselves probably acquired resistance to O. lienalis. Frequency distributions of O. lienalis burdens in individual flies show that there is a shift froni a normal to a skew distribution when comparing ‘challenge control’ flies with ‘immunized’. This possible acquired resistance could have important implications in the transmission of forest and savanna human onchocerciasis by the Simulium damnosum complex.

Computer-aided reconstruction from serial sections has been used to analyse the 3-dimensional structure of entire amastigotes of Leishmania mexicana mexicana and to determine the number, arrangement and volume of each organelle. In two reconstructions, the lysosome-like ‘megasomes’ were the most numerous organelle, there being 34 in one amastigote, and they comprised as much as 15% of the total cell volume. In contrast, as few as 9 glycosomes were present, accounting for less than 1% of the cell volume. The unitary nature of the mitochondrion was confirmed and its complex basket-like structure was revealed. The spatial arrangement of the cell organelles is here displayed in stereo-pairs.

We have compared the surface radio-iodinated proteins of uninfected and Plasmodium falciparum-infected erythrocytes from natural infections of human patients. Cryopreserved infected blood from Gambian children with falciparum malaria was thawed, cultured to the middle trophozoite stage, and surface radio-iodinated. Trophozoite-infected cells were enriched about 10-fold on a Percoll gradient newly designed to separate cells based on their differential permeability to sorbitol. Infected blood was radio-iodinated and erythrocyes from the fraction enriched in parasitized cells and uninfected erythrocytes from the same sample obtained from the gradient and compared by SDS–PAGE and autoradiography. In each sample, parasitized erythrocytes contained one or more polypeptides of very high molecular weight (Mr 250000–300000) that were not found on uninfected erythrocytes from the same patient. These proteins were isolate-specific in size and number, suggesting that natural isolates contain a variable number of different P. falciparum phenotypes for this surface protein. In addition, these radio-iodinated surface proteins could not be extracted from the host cell membrane by the non-ionic detergent Triton X-100, but were extracted by SDS. The properties of these proteins suggest they are the equivalent for natural infections of the strain-dependent antigen previously described (Leech, Barnwell, Miller & Howard, 1984) on the surface of P. falciparum-infected Aotus erythrocytes. In addition, we observed a second parasite-dependent modification of labelled proteins on infected erythrocytes with the appearance of a new band of Mr 30000. There were also variations in the pattern of radio-isotope labelled proteins on uninfected erythrocytes from different patients.

Eimerian oocysts were found in 98% of 422 faeces samples from goats in SE England. It was found that 74% of the samples contained thousands or tens of thousands of oocysts/g. Kids less than 1 year old had higher oocyst counts than yearling or adult goats. Nine species of Eimeria were identified, and 65% of the samples contained 3–5 species. The most prevalent species were E. arloingi (94%), E. hirci (69%), E. christenseni (64%) and E. caprina (55%). E. ninakohlyakimovae (48%), E. alijevi (42%) and E. apsheronica (23%) were common, and E. joichijevi (8%) and E. caprovina (4%) were comparatively rare. Developmental stages of E. caprina destroyed the crypt epithelium in the mucosa of the large intestine, causing severe haemorrhagic enteritis similar to that produced by E. ninakohlyakimovae. The literature on Eimeria species in sheep and goats is reviewed and, on the grounds of priority, E. bakuensis is the correct name for E. ovina in sheep.

The effects of parasitization by Hyposoter exiguae on the nutritional physiology of Trichoplusia ni were influenced by the dietary sucrose level. The results confirmed that host nutrition plays a significant role in the manifestation of parasitic infection during the insect parasite-host association. Increased dietary sucrose level resulted in an increase in haemolymph trehalose concentration in both control and parasitized insects, but the increase was greater in the latter group. However, when the sucrose level was increased without energetic compensation and the dietary casein level was maintained constant, the haemolymph trehalose concentration was affected very little in unparasitized individuals but was markedly elevated in parasitized hosts. This result suggests that the de novo synthesis of carbohydrate in parasitized T. ni may not be regulated by dietary sugar intake.

The nuclear DNAs of 71 trypanosome stocks from different African countries, representative of the three Trypanosoma brucei subspecies, and one T. evansi stock, have been analysed by the combined use of restriction endonuclease digestion, gel electrophoresis and molecular hybridization with both trypanosome surface-antigen-specific and undefined genomic DNA probes. In contrast with T. brucei brucei and T. brucei rhodesiense stocks, all the T. b. gambiense stocks are characterized by a conserved, specific DNA band pattern, regardless of the probe. This allows T. b. gambiense to be non-ambiguously identified. On the contrary, T. b. brucei and T. b. rhodesiense, which could not be discriminated by the same criteria, both yield highly variable DNA band patterns. Our data confirm that domestic animals like pig, dog and sheep constitute a potential reservoir for T. b. gambiense. Using a numerical analysis of the DNA hybridization patterns we have measured the degree of similarity between the 72 trypanosome stocks. This investigation shows that all T. b. gambiense stocks are included in the same homogeneous population, while the stocks from the two other subspecies seem to be distributed in several heterogeneous groups, some of these showing correlation with the geographical origin of the trypanosomes. It is concluded that (i) T. b. gambiense stands out as a real subspecies that has undergone a distinct evolution relative to the ‘non-gambiense’ group, (ii) the alleged T. b. rhodesiense subspecies does not fit with any of the groups evidenced by our cladistic analysis and hence does not appear as a distinct subspecies and (iii) ‘non-gambiense’ trypanosomes are probably evolving much more rapidly than T. b. gambiense. Different aspects of trypanosome relationships and evolution are discussed.

The effects of malaria infection on RBC sialic acids and sialoglycoproteins were studied with asexual blood-stage infections of Plasmodium knowlesi in rhesus monkeys. Glycoprotein radio-isotope labelling methods were used to compare the sialoglycoproteins of normal RBC and P. knowlesi schizont-infected RBC (SI-RBC). Tritiation of glycoproteins from SI-RBC with the standard sialidase + galactose oxidase/NaB3H4 method or standard periodate/NaB3H4 method was significantly decreased when compared to normal RBC. However, tritium uptake into glycoproteins was normal when SI-RBC were treated with 5-fold higher concentrations of both enzymes in the first labelling method, or with a 5-fold increase in the molar ratio of periodate to sialic acid in the second method. The mobility of tritiated host cell glycoproteins on SDS–polyacrylamide gels was identical for SI-RBC and normal RBC. New bands, possibly glycoproteins, of 230, 160, 90, 52, and 30 kDa were detected after labelling SI-RBC by the modified periodate/NaB3H4 method. Sialic acid analysis of normal rhesus monkey RBC (62μg/1010 RBC) revealed that 46% of the total sialic acid was N-glycolylneuraminic acid, 33% was N-acetyl-9-O-acetylneuraminic acid, and the remainder N-acetylneuraminic acid. SI-RBC collected either directly from infected monkeys or after in vitro culture of ring-infected RBC in horse serum, had increased total sialic acid (126 or 115μg/1010 RBC, respectively). The sialic acid content of infected RBC must increase during parasite development since RBC infected with ring-stage P. knowlesi had the same content as normal RBC. There was no significant difference in the ratio of the three sialic acids of SI-RBC and normal RBC. In contrast, the uninfected RBC from infected blood of different monkeys showed marked variation in sialic acid composition and generally had a lower sialic acid content than normal RBC.

In merozoites of Plasmodium knowlesi, rhoptries have a dense substructure of fine (2·5 nm diameter) granules and short rods. These are not altered by lipid extraction, and stain with ethanolic phosphotungstate indicating a proteinaceous composition. Various types of fixation also show multilamellar whorls with a periodicity of 5–7 rim in the tips of rhoptries or extruded at the merozoite apex. In merozoites fixed during invasions of red cells, membrane continuity typically occurs between the rim of the rhoptry canal and the red cell membrane, but where this contact has apparently been lost, extensive membranous whorls and blebs are often found at the apex of the parasite. Similar structures occur at the spices of merozoites within late-stage schizonts. It is suggested that the same mechanism which generates these lamellae forms the parasitophorous vacuole by inserting membranous elements formed by the parasite into the red cell membrane, so causing its invagination. A similar mechanism may be responsible for the release of merozoites from the late-stage schizont.

The organizers of this symposium felt that it could be helpful if the first paper provided a general introduction to the concepts and techniques associated with this rapidly developing area of biology. It is widely but wrongly believed to be a complex and difficult subject. The details of some of the manipulations are sometimes extremely complex, but the general principles are not. Of those responsible for this paper, Andrew Simpson and Tina Walker are active workers in the field, but Roland Terry is not. Following the principle embodied in an old Arabic proverb (Fig. 1), roughly translated as ‘What one fool can understand, another can’, Roland Terry presented the paper.

Electrophoresis of extracts of schizonts of Plasmodium knowlesi in non-dissociating polyacrylamide gels, separates several bands of acid endopeptidase activity. A polyclonal antiserum, produced by immunization with purified merozoites, failed to distinguish between different bands of the parasite enzyme, indicating that they are serologically related. Apart from the loss of one minor peak, extraction in Triton X-100 did not reduce the enzyme's electrophoretic heterogeneity. The antiserum did not react with red cell acid proteases.

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.

Three species of filarial worms, Wuchereria bancrofti, Brugia malayi and Brugia timori, are the causative agents of lymphatic filariasis in man, defined by the characteristic tropism of adult worms of each species for the afferent lymphatics. Reproductive activity leads to the release of large numbers of microfilariae, which circulate in the vascular system, and upon ingestion by an appropriate mosquito vector, develop through to infective third-stage larvae (L3) within 10–14 days. After a subsequent bloodmeal, the infective larvae enter the definitive host via the wound and mature to the adult stage over several months, involving two moults, during which the entire nematode exoskeleton (cuticle) is replaced.

Schizont-infected red blood cells (SI-RBC) from Plasmodium berghei-infected mice contain between 2 and 10 times as much sialic acid as uninfected RBC from the same blood (99–550 μg/1010 RBC versus 33–65 μg/1010 RBC). Total RBC samples from infected animals containing up to 63% ring- and trophozoite-infected cells had identical sialic acid contents to purified RBC samples (of < 3% parasitaemia) from the same blood (52–64 μg/1010 RBC). We conclude that RBC containing immature parasites have the same sialic acid content as uninfected RBC from infected blood and that total cellular sialic acid increases during maturation to the schizont stage. Uninfected RBC from infected blood had 25–50% as much sialic acid as normal mouse RBC (33–65 μg/1010 RBC versus 126 μg/1010 RBC). There were no qualitative changes in RBC sialic acids, all RBC samples having 60–70% N-acetyl neuraminic acid, 30–40% N-acetyl-9-O-acetylneuraminic acid and 5–10% N-gly colylneuraminic acid. The quantitative changes we observed during infection must reflect changes in murine sialoglycoconjugates, as we have shown elsewhere that Plasmodia do not synthesize or contain sialic acids. Since the sialic acid composition of mouse serum glycoconjugates is quite different to that of the RBC fractions studied here, the quantitative data suggest that part of the sialic acids of the uninfected RBC has been transferred to SI-RBC. With higher molar ratios of periodate to substrate than generally used, we were able to radio-isotopically label normal murine sialoglycoproteins on SI-RBC and purified uninfected RBC from infected blood by the periodate/NaB3H4 method. Several new proteins were then tritiated with SI-RBC but these proteins may be intracellular and could even lack sialie acid.