The occurrence, in September 1979, of Echinoparyphium recurvatum metacercarial cysts in a community of molluscan hosts at Harting Pond, West Sussex, was investigated. The parasite exhibited broad host specificity with all 7 species comprising the molluscan community being infected. There were marked differences, however, in the extent to which each host species was utilized and using the mean number of parasites/ individual mollusc as a parameter of infection the mollusc species may be ranked in descending order of utilization as follows: Sphaerium corneum, Lymnaea peregra, Valvata piscinalis, planorbids, Pisidium subtruncatum and Potamopyrgus jenkinsi. Combination of basic infection data with population estimates for each mollusc species in the study area showed that the bivalve P. subtruncatum and the prosobranch V. piscinalis were the most important hosts because they contained approximately 90% of the total number of cysts. In both of these hosts the cyst population was over-dispersed and the degree of over-dispersion increased with host size. The pattern of second intermediate host utilization is discussed in relation to the likely flow of E. recurvatum between the first intermediate host (L. peregra) and wildfowl definitive hosts at Harting.

The temporal distribution of hatching of the embryonated eggs of Transversotrema patialense has been examined under different temperature and illumination regimens. Under a DL 12: 12 regimen at 30°C egg hatching exhibited a circadian rhythm with a period of 24 h. Within a diel time-frame hatching was distributed over the final 9 h of the light period with less than 2% of the eggs hatching during the dark period. This pattern was temperature independent over the range 25 to 30°C and persisted under constant illumination. It is suggested that the timing of hatching is under endogenous control and is functionally related to a circadian rhythm of behaviour of the intermediate host mollusc, Melanoides tuberculata.

Observations have been made on the ultrastructure of objects identified as ovarian balls from female Moniliformis after 1, 3, 5, 7 and 9 days in the rat. Similar objects are present in the body cavity of female cystacanths from cockroaches. The ovarian balls from 1-day-old worms are formed of several cells which are enclosed within a surface coat. During development, the ovarian balls increase in size and cell number and the internal organization appears to become more complex. After 9 days of development in the rat, the surface coat of the ovarian balls can no longer be observed and microvilli are present. It also appears that the supporting syncytium has been formed by this time.

The resting membrane potential of the acanthocephalan rete system in Macracanthorhynchus hirudinaceus was −35±1·5 mV (n = 20) and was dependent upon the external potassium concentration. The membrane potential reached 0 mV when the external potassium concentration was 160 mM. Spontaneous spike potentials of 45 mV ± 10 were dependent on calcium flux. The membrane potential was depolarized by acetylcholine, potassium-free medium, calcium ions and chloride-free medium but not by changes in the external sodium concentration. Spontaneous potentials were increased in number by acetylcholine and calcium at concentrations above 3 mM, but were decreased in number by chloride- and calcium-free medium. Hence the rete system potentials are very similar to smooth muscle potentials in many respects.

Acetylcholinesterase (AChE) activity was measured in Nippostrongylus brasiliensis recovered during the course of a primary infection in normal and in protein-deficient rats. In well-nourished rats the amount of AChE present in N. brasiliensis increased as the infection progressed, concomitant with the development of the humoral response. In malnourished rats, there was a similar and parallel increase in the amount of AChE synthesized by worms between days 7 and 13 of the infection but as the infection progressed enzyme production decreased so that, by day 26 of the infection, the nematodes contained approximately the same amount of AChE as 8-day-old worms. The possible reasons for this change in enzyme production are discussed.

Quackenbush strain and wild Mus musculus were assayed for their liability to primary infection with 100 LaNematospiroides dubius using an experimentally derived selection index. Refractory and liable colonies of mice were established over 5 generations. Liability to N. dubius infection was found likely to be controlled by several genes; the heritability (h2) of this trait was estimated at 0·45. Positive linear correlation was found between the number of parasite eggs voided and the number of adult N. dubius recovered, negative correlation between the pre-patent period of infection in days and the number of parasite eggs voided and positive correlation in 2 of 5 generations between live mouse body weight and the number of adult N. dubius recovered. Further, positive correlation was found between the liability of female mice to N. dubius and their progeny litter size number. The genetic mechanisms controlling the liability trait and the possible evolutionary significance of these results are discussed.

Pelodera strongyloides larvae were found in the conjunctival sacs of Apodemus sylvaticus and Clethrionomys glareolus and in hair follicles of A. sylvaticus. Those in the eyes were 3rd-stage larvae while most of those in the dermis were early 4th stages. There was no evidence of pathology and sections of the skin showed that the nematodes were well-tolerated by the mice. Nematodes emerged from the skin of freshly killed mice and moulted once to the adult stage in 1–2 days at 15 °C. The stimulus to resume development appeared to be a reduction in temperature rather than presence of bacterial food or reduction in osmotic pressure. Countless generations ensued on nutrient agar provided the nematodes were periodically sub-cultured onto fresh agar. Nematodes from the eyes died in culture. Dauerlarvae of P. strongyloides were produced in exhausted cultures. They resumed development on fresh agar but not in distilled water. About half could be induced to exsheath by a temperature similar to that of mouse skin. A. sylvaticus probably accumulates nematode larvae in the dermis during its life and the nematodes resume development when the host dies.

Hymenolepis citelli caused a marked mortality in Tribolium confusum during the first 14 days of infection. The mortality was higher when the beetles were starved for 6 days immediately prior to infection (73–93%) than when they were starved for 1 day (51%). Regardless of the starvation time, the majority of beetle deaths occurred between days 8 and 11 post-infection (p.i.) and the precise survival time for individuals tended to vary inversely with the number of parasites they contained. With few exceptions beetles that survived until day 15 p.i., when the experiments were terminated, contained 14 or fewer cysticercoids, whereas those that died on or before day 14 p.i. contained 20 or more parasites. Mortality was equally high in both sexes but the mean survival time was significantly shorter for female beetles (8·8 days) than for males (9·6 days). Also, parasite development rate varied with the sex of the host. When parasite populations recovered from beetles that died on the same day were compared, the degree of development attained by those from males was significantly higher than in the populations grown in female hosts. The line of H. citelli used in these experiments has been maintained in the laboratory for the past 5 years. The results obtained with the current generation of this line were compared with those obtained with it 2 years earlier (approximately 16 generations ago). Mortality was lower with the current generation (67%) than with the earlier generation (93%). However, with the latter generation, the mean parasite population size in beetles that survived to day 15 p.i. was significantly higher (14·1 cysticercoids/beetle) than in those infected with the recent generation (7·3–7·9) cysticercoids/beetle). These findings suggest that relatively high selection pressures have been applied by T. confusum to H. citelli, thereby reducing the number of parasite lines with high infectivity and consequently improving host survivorship. The host also responded to artificial, directed selection for reduced cysticercoid number (heritability estimates of 0·30 ± 0·12 and 0·26 ± 0·12) and increased survival (heritability estimates of 0·28 ± 0·12 and 0·15 ± 0·083). The realized heritability was 0·37 for cysticercoid number and 0·17 for increased survival.

The prevalence of Taenia saginata (Cestoda) among 146 predominantly Pokot tribesmen in western Kenya was studied in an attempt to assess the reliability of detecting infections by faecal examinations. Firstly, a single faecal sample was microscopically examined after being processed by a standard ether sedimentation technique. Secondly, all subjects were treated with niclosamide and a purgative and the tapeworms were recovered. In this way the efficiency of diagnosing infections by faecal examinations was estimated. T. saginata eggs were found in the faeces of 68% of the men who were eventually found to be infected. Information was collected by interview from all subjects about whether they were or ever had been infected with tapeworms and about the form of treatment previously sought or taken. Eleven out of 25 men were apparently unaware of their tapeworm infections while no evidence of infection was found among 10 of the 24 reportedly infected men. A change in the pattern of treatment for tapeworms was reported which may have resulted in a recent decline in the prevalence of infection.

A simple, quick and reproducible method consisting of density-gradient centrifugation of homogenized infected mouse brain tissue on Percoll is described for the isolation and purification of cysts of Isospora (Toxoplasma) gondii. A 100% recovery of cysts, with 74·2% in a single fraction with a specific gravity of 1·056, was obtained by overlaying homogenates of infected mouse brains on a pre-formed Percoll gradient and centrifugation at low g forces. With this procedure recovery was independent of the age of the cysts. Titration of purified cystozoites showed there to be no loss of infectivity.

Large inocula of dividing form-enriched Trypanosoma musculi parasites, harvested from the peritoneal cavity of infected CBA mice, were given intravenously to mice at various times during the infection. Mice infected for 10 or 15 days (including T cell-deprived, infected mice) eliminated dividing parasites from the blood within a few min, whereas those at earlier stages (1 or 5 days) were less efficient. The initial control of T. musculi parasitaemia thus appears to be due to a trypanocidal mechanism rather than reproduction-inhibiting factor (ablastin).

Trypomastigotes of Trypanosoma dionisii, a stercorarian trypanosome from bats, are effectively killed by neutrophils from human peripheral blood but are less sensitive to the cytotoxic action of human monocytes. The mechanism of killing appears to involve peroxidase and hydrogen peroxide. Trypomastigotes are as effective as epimastigotes in inducing the formation of hydrogen peroxide by effector cells. They are, however, less sensitive than epimastigotes to the cytotoxic effect of peroxidase and hydrogen peroxide. They are therefore susceptible to the high concentrations of peroxidase found in the phagosome of the neutrophil, but resist the lower levels encountered in monocytes.

Studies on the nutrition and physiology of Trichomonas vaginalis have been hampered by the lack of a defined synthetic medium in which to grow the organism. New synthetic media free of ill-defined supplements and serum which support good growth of T. vaginalis have been developed in this study. The first successful approach to a defined medium resulted from the modification of the tissue-culture medium CMRL 1066. Essential modifications included (1) lowering the redox potential of the medium by adding high levels of ascorbate and (2) modifying the buffer system. Subsequently, CMRL 1066 was replaced by two new media DL7 and DL8 which have greater flexibility in their formulation and permit improved serum-free growth. Serum was replaced by bovine serum albumin and cholesterol, together with either a glyceryl fatty acid ester or a defined mixture of fatty acids. Preliminary nutritional studies using the new media have indicated a requirement for saturated and unsaturated fatty acids and a sterol.

Experiments describe the use of ethanediol to store Onchocerca microfilariae in liquid nitrogen. The technique involves a 2-stage incubation of the parasites at 37 °C and 0 °C in ethanediol, before rapid cooling to − 196 °C. Viability has been assessed by motility, by migration in a proxy host and by development to the infective stage in the insect vector. A total of 71–79% of the cryopreserved microfilariae was shown to be viable compared to unfrozen controls. The technique is simple, inexpensive and very effective when compared to previous cryopreservation procedures for microfilariae and should be particularly suited for use under field conditions.

The development of T cell reactivity toward schistosomula during murine Schistosoma mansoni infection has been studied using an adaptation of the in vitro lymphocyte proliferation assay in which the response is elicited by exposure to living schistosomula. The reactivity measured in this system was shown to be a T lymphocyte function and to require the presence of adherent cells. This assay may therefore provide a new method for analysis of basic interactions between host cells and schistosomula. Lymph node cell responses were observed in two phases, the first of which appeared during the second week after infection, reflecting the immunogenicity of schistosome larval forms. A later, more pronounced response appeared during the chronic stage of infection, where sensitization appeared to be stimulated primarily by ongoing exposure to adult worms, rather than eggs. Lung-stage and skin-stage larvae elicited a similar degree of thymidine uptake by cells from chronically infected mice. Intact skin-stage larvae and particulate fractions provoked greater proliferation than soluble larval constituents, indicating that the lymphocyte response is directed in large part toward determinants which remain associated with the schistosomula during culture. However, the presence of major histocompatibility complex products on the membrane of lung-stage schistosomula did not influence the presentation of larval antigens to sensitized lymphocytes. The implications of these findings in immunity to schistosomiasis are discussed.

Incubation of adult Schistosoma mansoni at 37 °C in chemically defined media caused the shedding of variable amounts of the parasite's tegument. In phosphate-buffered saline, pH 7·4, 37% of 125I-labelled wheat germ agglutinin which was attached to the schistosome surface was released within 5 min. When the released material was collected by centrifugation at 55000 g for 1 h, the pellet was seen to consist of components of the parasite tegument and contained 1% of the parasite protein and 6·2% of the 5′-AMPase activity. By monitoring the release of the gut enzyme, haemoglobinase, it was shown that predominantly tegumental material was released under these conditions. The material released from the parasite was separated by discontinuous sucrose gradient centrifugation into 4 major fractions and it was shown that a material banding at low density was highly enriched in vesicles of parasite outer membrane. Major polypeptides of apparent molecular weights 135000, 110000, 90000, 65000, 47000 and 40000 and glycoproteins of apparent molecular weights 135000, 120000, 65000, 63000 and 30–40000 were identified in this fraction. Comparison of the distribution of 5′-AMPase activity and the contents of each fraction as revealed by ultrastructural examination showed that this enzyme is a good marker for the tegumental outer membrane.

Three populations of small wild British rodents were studied by capture–recapture methods over a period of 3 years, a fourth group was studied for 1 year and a fifth was sampled annually for 4 years. Blood smears were taken from 3 species of rodents: the woodmouse A podemus sylvaticus, the bank vole Clethrionomys glareolus (and an island sub-species C.g. skomerensis) and the short-tailed vole Microtus agrestis. The smears were examined microscopically. Four genera of haemoparasites Babesia, Hepatozoon, Trypanosoma and Grahamella were detected. Babesia was absent from C.g. skomerensis, Hepatozoon was rarely found in A. sylvaticus and M. agrestis and Trypanosoma was rare in A. sylvaticus. More males were infected than females but the difference was only statistically significant for the infection with Hepatozoon in adult C.g. skomerensis. Infections with Babesia and Hepatozoon were more prevalent in adult animals and infections with Trypanosoma were more prevalent in younger individuals. Only in C.g. skomerensis was there a significant difference between age classes in the prevalence of infection with Grahamella – there being more adults infected. Concurrent infections were detected, Hepatozoon being the parasite most commonly involved. The prevalence of infections was found to be approximately proportional to the number of animals known to be alive, regardless of the season.

Large numbers of Theileria parva sporozoites were separated from Rhipicephalus appendiculatus adult ticks by filtration and were then concentrated by centrifugation. The sporozoites were incubated at 37 °C with leucocytes from 6 cattle of Bos indicus and B. taurus types. Giemsastained smears and living preparations under interference contrast microscopy were used to follow the course of the infection of the leucocytes with sporozoites. Sporozoites were seen to attach rapidly to about 25% the leucocytes which they penetrated. After penetration by the sporozoites the morphology of the cells changed to show an increase in cytoplasm and an enlargement of the Golgi apparatus, with which the parasite appeared to become associated. The early intracellular or preschizont stages resembled Babesia parasites. From day 3, the parasite showed the typical morphology of the macroschizont of T. parva. Multiple infections were frequent and up to 8 schizonts were observed arranged around the Golgi apparatus. Multiply infected cells did not survive in culture but some of the cells infected with a single parasite divided to produce 2 infected daughter cells and infected lymphoblastoid cell lines were established in all 21 attempts.

The moulting behaviour of nymphal Rhipicephalus appendiculatus from the laboratory colony and 3 field strains from Kenya was greatly influenced by constant temperatures between 18 and 37 °C but was not significantly different for the 4 tick strains. Six batches of R. appendiculatus (Muguga laboratory) nymphs which had engorged on cattle parasitaemic with 4 stocks of Theileria parva (Kiambu 4, Kiambu 5, Muguga and Mbita 4) isolated in Kenya were incubated at constant temperatures between 18 and 37 °C during their pre-moult and post-moult periods. The Theileria infections in the salivary glands of the resultant adult ticks were assessed by staining with Feulgen's stain. Two stocks (Muguga and Kiambu 5) developed their highest infections in ticks incubated at 28 °C while the other two (Kiambu 4 and Mbita 4) developed their highest infections at 23 °C. Constant temperatures of 18, 33 and 37 ° C were detrimental to the development of salivary gland infections. Temperature influenced the rate of development and numbers of the earlier Theileria stages in the ticks. Engorged nymphal ticks incubated for 4 days at 37 °C during their pre-moult period developed lower infections than ticks exposed at 4 °C for 4 days.

Guinea pigs acquired resistance to the feeding of immature Amblyomma americanum ticks after a single infestation. The initial larval and nymphal feedings resulted in cumulative mortalities of 27·2 and 28·9%, respectively. The second and third larval infestations yielded cumulative mortalities of 50·5 and 52·4%, compared to 18·9 and 24·4% cumulative mortality from controls. Second and third nymphal feedings resulted in 75·7 and 73·4%, and ticks from controls exhibited 36·6 and 34·7% cumulative mortality. The development of host resistance adversely affected tick feeding and resulted in abnormally coloured ticks and a protracted moulting period with a marked decrease in moulting ability. Histological examination of tick feeding sites on guinea pigs challenged twice revealed greater cavity and lesion sizes in hosts fed upon by nymphs than larvae. The primary cell type within these feeding sites were basophils at 12 h post-attachment, but by 72 h post-attachment eosinophils were dominant. The upper epidermal layer adjacent to both larval and nymphal feeding ticks had accumulations of basophils with a few eosinophils. Lymphocytes may have been involved in the resistance response because local lymph nodes in resistant hosts were much larger than in uninfested and singly infested hosts. Some of these nodes had secondary germinal centres.