The present study followed a Plasmodium falciparum population through its life-cycle at the level of individual hosts and vectors. The aim was to determine to what extent genotypes of the parasite that were found in the host were transmitted to the vector. Mosquitoes were collected that had fed on people sleeping under mosquito nets with holes. Genes determining 2 highly polymorphic merozoite surface proteins, MSP-1 and MSP-2, were used to characterize the parasite by PCR at different stages of the life-cycle. The parasite genotypes found in the host were compared to the genotypes of the oocyst stages after transmission to the mosquitoes. The results show that there was no significant correlation in the rate of oocyst-positive mosquitoes and the presence of parasites in the blood samples. For MSP-1, most of the parasites characterized in the human blood by PCR fragment size were also found afterwards in the oocyst-stage (22 of 29; MSP-2: 17 of 36). This study indicates that there is no selective transmission of distinct genotypes to the vector. In addition, the frequencies of the allelic families of both genes are similar in the blood samples and in the oocysts for the whole population.

Different stocks and stabilates within a stock of Theileriaparva were analysed for genotypic differences and for their effect on the expression of host cell surface antigens following infection of BoT8+ T lymphocyte clones. The parasites were characterized in vitro by hybridization of T. parva- specific DNA probes to Southern blots of endonuclease-digested DNA from the infected T cell clones. Phenotypic changes in the host lymphoblastoid cells before and after infection were examined using lineage-specific monoclonal antibodies which reacted with the differentiation antigens BoT2, BoT4, Bo6, BoT8 and a null cell marker on bovine T cells. Expression of Class I and Class II major histocompatibility complex (MHC) antigens on the cell populations was also assessed. Results of this study indicate that genotypically different parasites exist among and within T. parva stabilates and that the expression of Bo6, BoT8 and the null cell marker was differentially altered by infection with parasites from different stocks or from different stabilates of the same stock. Expression of Class II antigens was significantly increased after infection. Moreover, clones that were derived from the same cell line but had genotypically distinct T. parva parasites, also showed differences in expression of Bo6 and BoT8 and the null cell marker.

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.

The study of regulatory peptides has its origins in the classical work of Bayliss & Starling (1902). Their pioneering work on the presence of a factor in intestinal extracts which, when injected into the bloodstream of experimental animals, elicited pancreatic secretion, led to the genesis of the concept of the hormone, i.e. a chemical messenger which is released from one part of the body in response to a stimulus to travel in the bloodstream to a distant target tissue where it would elicit a physiological response appropriate to the original stimulus. In keeping with accepted scientific tradition, this concept had its critics. Pavlov, who had been studying secretory stimulation from a different perspective, concluded from his work on salivation in dogs, that this was mediated via neural pathways. With hindsight, and the benefits of knowledge obtained from nearly a century of scientific research, we now know that these pioneers were in actual fact studying different aspects of the same process and that both theories were complementary. In fact, it is becoming increasingly difficult to ascribe secretory control to either circulating or neuronal factors as both appear to be intimately involved in regulation.

We examined the patterns of parasite melanization in Gammarus insensibilis using data on microphallids from Pomorie Lagoon (Black Sea) in the light of 3 predictions associated with host survival: (i) hosts invest more in defence in an environment where the likelihood for infection is higher; (ii) multiple immune challenges exhaust host reserves and result in decreased melanization rates in older hosts; (iii) host immune response is directed against the cerebral metacercariae of Microphallus papillorobustus that alter amphipod behaviour and are most detrimental to the host. G. insensibilis was capable of melanizing the metacercariae of all four species of trematodes found to be hosted by the amphipods. The frequency of melanization and mean abundance of melanized metacercariae were substantially higher than those observed in the same amphipod-gammarid system on the French Mediterranean coast. However, the rate of melanization was low and showed a significant decrease with amphipod size. Although the 4 species were differentially melanized, the host response was largely directed against Microphallus hoffmanni and M. subdolum. We suggest that (i) the lower melanization efficiency with age is due to the mode of infection, probably leading to loss of haemolymph and monopolization of the defence resources for wound healing and (ii) in the French system, host response focuses on the most prevalent and abundant species.

Fed adult Argas (Persicargas) arboreus produce a fecundity-reducing pheromone which affects all or most females in crowded conditions. Unfed adults and unfed and fed nymphs do not produce this pheromone. The effect of this pheromone is probably additive, increasing with additional crowding of adults. Mechanical disturbance is excluded as the cause of fecundity reduction. Fed females separated by a perforated barrier from crowded adults also exhibit very low fecundity. Adult excretory materials used 31 days post-feeding do not contain the fecundity-reducing pheromone. Preliminary experiments suggest that this pheromone is spatially limited in action, does not affect gonadotropic hormone synthesis and/or release, and does not induce oviposition deterrence behaviour. This may be considered to be a primer pheromone, causing alteration in normal vitellogenin synthesis and/or uptake and deposition in oocytes. The source and chemical nature of this pheromone should be investigated.

The introduction, establishment and subsequent history of a population of the eye-fluke Tylodelphys podicipina in perch in a small lake was studied over a period of 2 years. The introduction was a natural, chance colonization, and within 2 years of its first appearance the parasite was infecting 100% of the 0 + perch. Its dispersion within the perch population was initially random and fitted a Poisson model, but subsequently it became over-dispersed. Infection of fish took place only in or about June and only young of the year fish were susceptible. Fish were infected on one occasion only, shortly after birth, and there was no subsequent re-infection or mortality within the eye. The parasites lived for at least 2 years and there was no evidence of parasite-induced host mortality. Infection levels are thus an indication of the recruitment level in the year in which the fish were born. T. podicipina therefore differs from all other species of eye-flukes, which accumulate in fish throughout their life, but this infection strategy facilitates transmission of the parasites to their definitive host. Lower infection levels in older fish here and in other localities are considered to be due to the parasite being a recent introduction to the British fauna, and to its still being in the expansion phase of colonization in all localities.

Rats harbouring 35-day-old primary infections of Moniliformis moniliformis and Hymenolepis diminuta were inoculated with equal doses of Nippostrongylus brasiliensis and were autopsied 10 days later. Significant reductions were found in the dry weight of Moniliformis and Hymenolepis and in the numbers of Nippostrongylus recovered compared with single infections. Similarly, in infections with two parasites, the numbers of Nippostrongylus were reduced when concurrent with Moniliformis and the dry weights of Moniliformis and Hymenolepis decreased in the presence of each other. A comparison of the concurrent infections themselves revealed that Moniliformis weighed significantly less in the presence of Hymenolepis than in the three parasite infections. Parasite interactions and their possible mechanism are discussed and comparisons are made with the relevant single infection for each parasite.

Cyclosporin A (CsA), administered in 5 daily subcutaneous doses of 50 mg/kg to MF1 mice immediately following infection with Hymenolepis diminuta enhanced parasite growth relative to controls. Drug administered at 24 h intervals for 10 days, and thereafter every 48 h to MF1 and CBA/Ca mice infected with H. diminuta, increased worm survival and growth, delayed host-mediated expulsion of the parasite and enabled some worms to develop to patency. Worm survival and weight both increased in a dose-dependent manner following daily CsA treatment of infected CBA/Ca and BALB/c mice (0–150 mg/kg CsA/day). Delay in parasite elimination was accompanied by increased frequency of worm-attachment in the anterior small intestine (MF1 mice given 5 daily doses of CsA [0–150 mg/kg] following infection); posteriad migration of worms was restricted in a dose-dependent manner. The data presented contrast markedly with the action of the same drug on H. microstoma in mice. Thus CsA treatment acts in opposing ways on two closely related parasites in the same host; this possibly reflects the mechanistic antagonism between immunosuppression and anthelmintic activity. This paper reports the first use of a specific T cell-suppressive drug on H. diminuta in the mouse, implicating the role of T cells in protective immunity to this parasite.

The ability of various mammals to transmit Dracunculus medinensis has been investigated. The most suitable definitive host for laboratory transmission was the rhesus monkey (Macaca mulatta) and, in 11 out of 14 of these animals female worms emerged 321 to 371 days after first infection. The parasite has now been maintained in monkeys for four laboratory cycles. Five of 11 dogs and 17 of 30 cats had developing parasites in their tissues when autopsied, but no worms emerged from two dogs left for over a year and only a single worm from one of nine cats. Monkeys showed a seemingly haphazard pattern of susceptibility to infection and reinfection, although none of the 17 animals exposed was completely refractory. Cyclops vernalis americanus (Marsh) was an easily maintained and efficient intermediate host; a 90% infection rate with an average of two infective larvae per Cyclops was obtained.

This work was supported by a grant from the Tropical Medicine Research Board through the Ministry of Overseas Development. Thanks are due to Mrs Vivian Duckett for technical assistance.

A single specimen 141 long, 3 broad. Genital pore in centre of proglottis margin, vaginal pore posterior to cirrus sac. Testes approximately 100, in a broad band posterior to female glands and extending laterally to excretory vessels: between ovaries testes extend more anteriorly and are in six transverse rows. Cirrus sac 0·31–0·56 x 0·04–0·06 long, extending just past excretory vessels, containing a small vesicula seminalis. Ovaries practically touching the respective excretory vessels. Vitelline gland rather aporal and posterior to ovary. Gravid segments absent.

Acetylcholinesterase (ACHE) is present in the muscle and on the tegument of schistosomes. Molecular forms of schistosome AChE were examined because particular AChEs are found in tissues of distinct function elsewhere. The dimeric globular form (G2) is the only form evident in adult Schistosoma haematobium: 32 % of the muscle AChE is hydrophilic and 61 % is membrane associated. A substantial amount of this enzyme is phosphatidylinositol (PI) anchored since it could be released by PI-specific phospholipase C from both muscle and tegumental membranes.

The kinetics of uracil, thymine, 5-bromouracil, hypoxanthine, guanine and adenine uptake by Hymenolepis diminuta were studied using shortterm (2 min) incubations. The effects of other purines and pyrimidines on the uptake of these compounds was determined. The data suggest that the purine-pyrimidine transport system of H. diminuta contains at least three distinct transport loci and that two of these loci contain multiple substrate binding sites. The three loci are characterized as follows: (1) A thymine-uracil locus which is responsible for the absorption of thymine and uracil via allosteric mechanisms and, therefore, apparently contains two binding sites for these pyrimidines. Adenine and hypoxanthine are non-productively bound to this locus; purine and 6-methyluracil are also bound to this locus, but it is unknown if binding is productive. (2) A locus which transports hypoxanthine (denoted as hypoxanthine locus no. 1), guanine, and adenine. The latter purine is apparently transported by an allosteric mechanism and, therefore, this locus apparently contains two adenine binding sites. Uracil and 5-bromouracil also bind to this locus, however, the nature of binding is uncertain. (3) A second hypoxanthine locus (hypoxanthine locus no. 2) can also be demonstrated which nonproductively binds adenine. Purine is also bound to this locus, but it is unknown if this binding is productive.

Specimens of nematodes from the stomach, oesophagus and trachea of the cat, previously reported and described by Led et al. (1968), were found to resemble L. major more closely than other species in the genus. In the shape of the interlabia and the number of pits on the surface of the eggs, they conformed to this species. Accordingly they were identified as L. major although they differed from L. major in the width of the lips in relation to the postlabial collar and their more slender appearance, especially in the tail region. This is the third report of L. major and extends the host range and geographical distribution of this species.

Several of the pathophysiological responses made by the beetle Tenebrio molitor, when infected with metacestodes of Hymenolepis diminuta, may be attributed to a parasite-induced reduction in host juvenile hormone titre. It has been suggested that production of this hormone by the corpora allata may be inhibited in parasitized insects. This hypothesis was tested using an in vitro radiochemical assay to compare the biosynthesis of juvenile hormone by single pairs of corpora allata taken from mated 12- and 15-day-old infected and control female insects. The results demonstrate, however, that there was no difference in hormone production associated with metacestode infection. Other possible mechanisms for parasite interference in this host endocrine system are discussed.

An account is given of the incidence and intensity of infection of the gulls Larus argentatus Pont., L. fuscus L., and L. marinus L. with Cestoda on the coast of Wales. Eleven species of cestodes were found in the three species of gulls, nine in L. argentatus, eight in L. fuscus and six in L. marinus. Nine new host records and two new British records are listed.

The presence of the cestode parasites did not appear to be harmful to the birds.

Ecological and systematic notes are given on each of the cestode species. The basic cestode fauna of L. argentatus, L. fuscus and L. marinus on the coast of Wales comprised three species, namely Tetrabothrius cylindraceus (Rud.), T. erostris (voennberg) and Anomotaenia micracantha (Krabbe).

The factors influencing the intensity and incidence of infection are considered and it is concluded that infection is determined mainly by the food and feeding habits of the host. It is shown that the number of cestodes per bird may be represented by a negative binomial distribution. There is some evidence to suggest that high intensities of infection were associated with high incidences. Three main stages in the development of the helminth-fauna of gulls are described and are related to the age and activity of the bird.

It is a pleasure to record our personal thanks to those to whom we are indebted, namely the Nature Conservancy and the West Wales Naturalists' Trust for permission to work on Skomer Island, to Mr D. R. Saunders, Warden of Skomer Island, for help in the collection of some of the Great Black-backed Gulls, to Mr P. Hope Jones who collected the gulls from Malltraeth, and to Professor J. G. Baer, Departement de Zoologie, Université de Neuchâtel, Professor W. E. Kershaw, Department of Parasitology and Entomology, University of Liverpool, and Mr Stephen Prudhoe, British Museum (Natural History), for the loan of specimens, and to Mr M. D. B. Burt, Department of Natural History, University of St Andrews, for identifying the specimens of Paricterotaenia paradoxa.

The participation of one of us (M. P. H.) in this work was made possible through the generous assistance of a D.S.I.R. research studentship, which is gratefully acknowledged.

The oocysts of Plasmodium falciparum that form on the midgut wall of anopheline vectors represent the meiotic products of the sexual cycle of the parasite and are useful for genetic analyses. Recognizing the limitations of current markers for the analysis of genetic variation, we describe a protocol for the DNA isolation and PCR amplification of microsatellite loci from individual oocysts. We present a simple method for the storage and isolation of individual Plasmodium oocysts from wild-caught mosquitoes and demonstrate that it is possible to extract sufficient oocyst DNA for approximately 50 amplifications. Genotyping was successful for 10 microsatellite loci and, using Genescan technology, we found extensive microsatellite polymorphism in an analysis of a dozen oocysts from each of 2 Anopheles gambiae female specimens collected within 6 months at the same location in northern Tanzania. All of the loci exhibited at least 2 alleles, with a maximum of 5. Homozygous and heterozygous oocysts could easily be discerned, but most of the oocysts were homozygous. The procedure has great potential for shedding light on genetic mechanisms operating during meiosis in mosquito vectors and the influence this may have on the genetic structure of natural populations of P. falciparum.

Mice which have recovered from infections with P. atheruri are immune to challenge with the homologous parasite and are also strongly resistant to challenge with P. v. chabaudi and, to a lesser extent, B. rodhaini, B. microti and P. b. yoelii. There is little protection against P. v. vinckei and none against P. b. berghei. In the reciprocal experiments, the greatest degree of protection against P. atheruri occurs after P. v. chahaudi infections but over two-thirds of mice are protected by B. rodhaini or B. microti, half by P. v. vinckei or P. b. berghei but hardly any by P. b. yoelii. The considerable degree of cross-protection which exists between P. atheruri and P. chabaudi can be correlated with some antigenic similarities between these parasites but these are not greater than those of parasites which do not protect against one another.

Developing and adult Schistosoma mansoni and S. haematobium intact worms do not bind specific antibodies, likely because of structural and biochemical modifications of the outer lipid bilayer. We have estimated the amount of cholesterol in the apical membrane of adult schistosomes via extraction with the membrane-impermeable, cholesterol-binding drug, methyl-β-cyclodextrin (MBCD), followed by filipin staining of the worms, and evaluation of the amount of cholesterol released in the medium by a commercially available, enzymatic colorimetric assay. Positive correlations between amount of released cholesterol, MBCD concentration, and worm number and age provided evidence for the sensitivity and validity of the newly developed method. Treatment with 40 mm MBCD for 2 h at 37°C led to total loss of cholesterol from the worm outer membrane, as assessed by filipin staining, and the released cholesterol values were used to estimate the amount of cholesterol per worm and per an approximate surface area unit. Additionally, total depletion of outer membrane cholesterol was associated with exposure of surface membrane antigens to specific antibody binding in 50% and 70% of S. haematobium and S. mansoni worms, respectively. These findings together suggest that cholesterol is an essential, but not the sole, factor in sequestration of surface membrane antigens in schistosomes.

The first experiments upon the transmission of T. lewisi by fleas were carried out by Rabinowitsch and Kempner (1899) who observed that three fresh rats placed with others harbouring trypanosomes in their blood subsequently (after 11–15 days) became infected. Fleas (species?) were found on these rats. They next teazed the bodies of fleas taken from infected rats and inoculated them into fresh rats with the result that in five out of nine experiments the fresh rats became infected with T. lewisi. In one experiment they removed 20 fleas from infected rats and placed them on a clean animal with the result that the latter became infected after 2–3 weeks. They regarded this one experiment as conclusively proving that T. lewisi is transmitted by rat fleas.