The Houghton (H) strain of Eimeria acervulina was attenuated by serial passage through chickens of the first oocysts produced during infection. This selection pressure resulted in a reduction in the pre-patent period of the parasite, shown to be due to the selection of a line predominantly with only 3 instead of 4 generations of schizonts. The precocious line had a reproductive potential much lower than that of the parent strain and it was significantly less pathogenic. Chickens given oocysts of the precocious line were almost completely immune to challenge with the Houghton strain.

Excretory/secretory (ES) products obtained by in vitro culture of infective-stage larvae of Trichinella spiralis and T. pseudospiralis were injected intramuscularly at various intervals into mice. Mini-osmotic pumps containing T. spiralis ES products were also implanted subcutaneously and intraperitoneally into rats. The introduction of ES materials into muscles elicited extensive lesions which included dissolution of myofibres, mobilization of mononuclear and polymorphonuclear leucocytes, angiogenesis, hypertrophy of myonuclei, myotube formation, mitosis, muscle bundles becoming rounded and separated from each other, disappearance of Z, I and A bands of sarcomeres, increase in endoplasmic reticulum and Golgi complexes, decrease in glycogen and relocation of mitochondria. These are considered as degenerative/regenerative changes of muscles to injury. Immunodominant epitopes of specific 45–53 kDa glycoproteins in ES antigens of T. spiralis could not be detected in hypertrophic nuclei of injected muscles by using polyclonal and monoclonal antibodies and immunocytochemical methods. ES products of T. spiralis failed to stimulate unsensitized lymphocytes in the lymphocyte transformation test. Infective-stage larvae of T. spiralis released from muscles were found capable of forming nurse cells after injection subcutaneously into rats. It is postulated that the invasion of muscles by trichinellids elicits two independent events, i.e. a general degenerative/regenerative response of muscles and a specific change in genomic expression of myonuclei. The two events are probably mediated by different effector molecules.

The ability of five staining techniques, originally developed for the rapid identification of Cryptosporidium spp. oocysts in faecal samples, to detect oocysts in water and water-related samples was assessed. All the stains used (modified Ziehl Neelsen, auramine-phenol (Lempert), Wright-Giemsa, safranin-methylene blue and FITC-labelled monoclonal antibody) stained oocysts after storage in water for 2 months at 4 °C (71–89 % of control values). Storage of oocysts below 0 °C greatly reduced the staining ability of auramine-phenol. With the exception of oocysts stored in raw and final waters, the histochemical stains proved less useful in detecting oocysts than the monoclonal antibody. Organisms of similar size and shape took up these stains, causing confusion in interpretation. Cold Ziehl Neelsen and the FITC-labelled monoclonal antibody were best at identifying oocysts from a waterborne outbreak. Screening with a fluorescent antibody, followed by confirmation with cold Ziehl Neelsen, where possible, are the currently recommended procedures for the detection of oocysts in water-related samples.

The diversity in a 925 bp portion of the Plasmodium vivax MSA1 gene in isolates from the Philippines, China, the Solomon Islands and Papua New Guinea was investigated. A total of 74 base pair changes was found in the amplified fragment from 18 isolates. Most of these changes were single or double base pair substitutions. In several regions, these point changes were tightly linked with one set always present or always absent in the different isolates. Seven such blocks were identified. These blocks were present in different combinations in the different isolates indicating that extensive intragenic recombination has occurred.

1. Optimum growth of E. invadens occurred in HSre + S in the presence of Bact. coli, at 24–30° C. The amoebae could not be ‘trained’ to grow above 35° C.

2. The amoebae ingested normal rat erythrocytes, but not those of chick or frog.

3. Mass encystation occurred only under conditions which favoured the growth of the amoebae, but was not dependent on an acceleration in growth rate; in certain strains, an increased production of cysts was correlated with the depletion of starch in the medium.

4. The amoebae were always killed by treatment with N/20-HCl for 1 hr. at room temperature, although usually they did not survive after treatment for only 10 min. At room temperature, the cysts survived treatment with N/10-HC1 for at least 6 days, and with 0·002% HgCl2 for at least 4 hr.

5. The amoebae of E. invadens were adversely affected by aerobic conditions.

6. The amoebae could survive for up to 35 days at 8° C. but for not more than 7 days at 37° C. The cysts survived for at least 14 days at 8° C., for 7, but not 11, days at 24° C., and for less than 7 days at 37° C.

7. It is suggested that, in view of the morphological identity of E. aulastomi, E. invadens, E. moshkovskii and E. histolytica, and the fact that the amoebae of these groups form a series growing at increasingly higher temperatures, these four organisms constitute subspecies rather than full species. The taxonomic status of E. ranarum is still open to question.

(1) Forcipomyia is one of the few genera of the Ceratopogoninae (Chironomidae) whose larvae are not aquatic. They retain, however, the apneustic condition typical of the entire family, and are therefore compelled to live in moist places such as beneath the rotting bark of fallen trees, in the hollow tap roots of dead plants, in wounds and rot holes in trees, in drying horse and cow manure, in decaying fungi, and in the nests of ants. The immature forms are strongly gregarious.

(2) The larvae pass through four stages, each lasting about a week; the successive changes in chaetotaxy at each moult is recorded in the discussion of F. picea. All known European species of this genus hibernate as third or fourth stage larvae. The duration of the pupal stage is about one week; the length of life of the adult has not been determined. There are usually three generations per annum. The adults are known to suck the blood of other insects.

(3) The larvae are eucephalous, more or less cylindrical, 3–6 mm. long, with eleven clearly denned segments (three thoracic and eight abdominal, the eighth divided into two apparent segments). Progression is achieved by means of a retractable, biramous, prothoracic pseudopod, and a ventral hook-studded ridge on the ultimate abdominal segment, with the occasional aid of the mandibles.

(4) The head and body bear numerous lanceolate and simple hairs of great specific importance.

(5) The mouth-parts consist of a fleshy labrum, a pair of small premandibles, a pair of long, slender mandibles working in the sagittal plane on either side of the labrum, a pair of reduced maxillae of fleshy nature with chitinous internal supports, and a simple untoothed labium. Within the head there is a complicated chitinous structure, the hypopharynx; this is figured and described in full detail and its action in comminuting the food is revealed for the first time.

(6) No investigation has hitherto been made of the internal anatomy. The alimentary canal, consisting of buccal cavity, hypopharynx, oesophagus, mid-gut, and hind-gut, is quite simple in structure, without nodules or caecal chambers. It is only slightly longer than the body, a loop occurring in the hind-gut when the larva contracts.

(7) The malpighian tubules are either two or three in number, the latter condition being unique among insects. The third is ventral, passing into the posterior part of the body only.

(8) The salivary glands are a pair of S-shaped bodies closely adhering to the walls of the anterior portion of the mid-gut; they are chiefly composed of large binucleate cells.

(9) The circulatory system consists of a dorsal vessel extending throughout the body and passing between the lobes of the brain above the oesophagus into the head. In the eighth abdominal segment it enlarges slightly to form the heart, with one pair of ostia or valves situated on its posterior extremity.

(10) The nephrocytes are arranged segmentally, four to each abdominal segment and a single mass in the thorax, all attached to the dorsal vessel. The excretory function of these cells was demonstrated by injection of ammonia-carmine into the body cavity.

(11) The nervous system is only very slightly cephalised, there being seven ganglia for the eight abdominal segments and three in the thorax; the normal bilobed brain is situated in the thorax in all larval stages. The sympathetic system is described, and differs somewhat from that of its close relative, Chironomus.

(12) Despite the absence of spiracles there is a well-developed tracheal system in the form of two main trunks with transverse connections, branch tracheae, and subcutaneous plexuses.

(13) The muscular system, oenocytes, fat-body, and gonads have also been studied in detail.

(14) The larval skin is retained upon the last four or five abdominal segments of the pupa.

(15) The characters used for determining the species, in their order of importance, are as follows: Larva: chaetotaxy, prothoracic pseudopod, markings of the head, anal blood-gills. Pupa: cuticular spines, prothoracic horns.

(16) The larvae and pupae of nine species of Forcipomyia are described with particular reference to their specific characters. Descriptions of the adults of two new species, F. radidcola and F. pulchrithorax, by Mr F. W. Edwards, are appended.

(17) Closely related forms are Euforcipomyia and other exotic subgenera not yet named, and the genus Atrichopogon (now including Kempia). Dasyhelea belongs to this group of hairy-winged flies, but its larvae partly resemble those of the bare-winged Ceratopogonines in that they have lost the pro-thoracic pseudopod and macrochaetae, but retain the anal hooks.

The effect of the nematode Toxocara canis on social behaviour and anxiety levels of adult male outbred (LACA) mice was examined following infection with a single dose of 2000 ova. The actual number of larvae recovered from the brain of each individual mouse was determined after behavioural testing. The effect of the parasite on mouse behaviour was analysed by both the initial dose administered (i.e. infected versus control) and the degree of infection in the brain. There was substantial variation in the number of larvae recovered from the brains of the individual mice and the magnitude of behavioural change was associated with the level of infection. Examination of social behaviour for both analyses revealed that the infection reduced levels of aggressive behaviour and increased levels of flight and defensive behaviours. High infection in the brain induced the greatest degree of behavioural change which decreased in mice with lower infections. In contrast the analysis of anxiety levels in mice by initial dose administered revealed no difference between infected and control mice. Mice with low infection in the brain, however, displayed a greater level of risk behaviour by spending more time in the vicinity of a predator odour and in the light area of a light/dark paradigm than control or high infection mice. The results suggest that the behaviour of mice infected with T. canis is influenced by the number of larvae accumulated in the brain. This may have important consequences for the conclusions drawn on the effect of this parasite on murine behaviour.

The localization and distribution of neuropeptides and an indoleamine (serotonin or 5-hydroxytryptamine) in the enteric nervous system (ENS) of the pig roundworm, Ascaris suum, have been determined by the application of an indirect immunofluorescence technique in conjunction with confocal scanning laser microscopy. Whole-mount preparations of pharyngeal, intestinal and rectal regions were screened with antisera to 23 vertebrate peptides, 2 invertebrate peptides and serotonin (= 5-HT). Positive immunoreactivity (IR) was obtained with antisera to pancreatic polypeptide (PP), peptide YY (PYY), FMRFamide, gastrin and serotonin. The only IR observed in the ENS was that evident in the nerve supply to the pharynx and rectal region; no IR was associated with any region of the intestine. The most extensive patterns of IR occurred with antisera to PYY, FMRFamide and serotonin. In the pharyngeal component of the ENS, IR was evident in the lateral and dorsal longitudinal pharyngeal nerves, pharyngeal commissures, nerve plexus, and associated nerve cells and fibres. In contrast, the distribution of IR to the PP and gastrin antisera was more restricted and displayed a lower intensity of immunostaining. The other component of the ENS, the rectal enteric system, only yielded immunostaining to FMRFamide. The possible role of neuropeptides and serotonin in the nutritional biology of nematodes is discussed.

The cellular distribution of a vertically transmitted, feminizing microsporidian was followed in its host Gammarus duebeni. In adult females the parasite was restricted to gonadal tissue, in particular primary and secondary follicle cells. Spores were diplokaryotic with a thin spore wall and a short polar filament, characteristics typical of ‘early’ spores involved in autoinfection. The diplokaryotic life-cycle, absence of spore groupings and of a pansporoblast membrane typify the genus Nosema. However, the unusual globular polaroplast of the spore and restriction of this stage to host ovarian tissue have not previously been described in Nosema. Sporogony occurred only in follicle cells adjacent to developing oocytes and was in synchrony with the process of vitellogenesis. Oocytes were infected after formation of intracellular connections with follicle cells but harboured only vegetative stages of the parasite. Parasites were associated with the perinuclear cytoplasm and, in developing embryos, segregated to daughter cells along the axis of the spindle. In juvenile animals there was no evidence of pathology linked with feminization and the parasite was found at low density in cells under the cuticle. The parasite is highly adapted to transovarial transmission with an efficient mechanism of oocyte infection and no evidence of pathology.

The distribution of Ascaris lumbricoides within a community was examined at an initial mass anthelmintic treatment programme (January 1984) and following an 11-month period of reinfection (November 1984). Similar patterns of the negative binomial parameter k (an inverse measure of parasite aggregation) and the proportion of parasites within the most heavily infected quartile of the community were recorded at the two dates. The pattern of parasite aggregation within individuals, measured by parameter k, appears to be a stable characteristic of this host-parasite relationship. Significant variation in the intensity of infection was observed between households in the community. The number of family members living in the house strongly influenced the mean Ascaris burden and proportion of relatively heavy infections within adults and children. This finding suggests that the density of people in a house positively influences the frequency of exposure to infective stages of Ascaris, which in turn plays a major role in determining which individuals will harbour heavy infections. Positive correlations were recorded between the initial and reinfection burdens of individuals, relative to others in the community. The correlations were strongest in the youngest and oldest age groups and were more frequently significant among age-stratified groups of females, compared to males. A comparative examination of hypothetical treatment strategies suggests that for Ascaris infections in this community, targetting age groups with anthelmintic treatment would probably be more cost-effective in the long term in reducing the abundance of this parasite than selective treatment of individually identified heavy infections.

1. The availability of Nematodirus infection to sheep was followed by grazing successive pairs of worm-free lambs on a contaminated plot. It was shown that lambs did not become infected during the summer following pasture contamination in the spring, but became infected when they were grazed on the plot the following spring.

2. The development and hatching of the eggs and larval stages of N. battus and N. filicollis were followed by the periodical examination of infected faeces set out during May-November. The results showed that development to the infective larval stage occurred during the summer, taking normally about 3 months, but that the larvae then remained dormant within the egg membranes until the following spring.

3. Laboratory studies confirmed the hypothesis that the hatching of the infective larvae was a response to a rise in temperature in the spring, following sensitization by exposure to low temperature during the winter. A rise in temperature to 50° F. was necessary before a high percentage hatch occurred.

4. The epidemiology of Nematodirus infection is discussed in relation to these observations.

Observations that growth of Plasmodium falciparum in vitro is inhibited by high temperatures have led to hypotheses that malaria fever may influence the parasite population dynamics, regulating parasite density and synchronizing parasite growth. In order to investigate the fever hypotheses, we have developed an age-structured coupled Markov chain model that describes the parasite erythrocyte cycle and its interaction with the host fever response. We estimated the model parameters using data collected from laboratory parasite cultures that were exposed to febrile or normal temperature. Using the experimental parameter values, quantitative predictions were made of the effect of fever in determining the parasite population dynamics. It was concluded from the model behaviour that, during the primary infection of a non-immune host, a typical episode of fever can effect density-dependent regulation of the parasite population, maintaining cycles of parasitaemia and promoting synchronous parasite growth.

On the basis of partial amplification of a cloned fragment of kDNA of Leishmania infantum which is specific for this species, we developed a PCR–ELISA technique which avoids the problems associated with classical diagnostic techniques. This technique was tested on 33 L. infantum strains from 19 different zymodemes, which were recognized equally. It was also used on human and canine clinical samples. PCR–ELISA has a higher sensitivity than the other techniques used (IFAT, parasite cultures, optical microscopy of stained samples) and permits detection of a minimum of 0.1 promastigotes or 1 fg of genomic DNA. PCR–ELISA can be used to diagnose human cutaneous leishmaniasis using material obtained by scraping the lesion margin, and human visceral leishmaniasis in HIV(+) individuals and canine leishmaniasis with peripheral blood samples. The presence of L. infantum in dogs with low antibody titres with IFAT technique (20 and 40) was demonstrated indicating that seroprevalence data from epidemiological studies underestimate the true rates of infection.

1. The r.q. of whole Neoaplectana glaseri rose from 0·56 to 1·10 when glucose was added to the medium. The Qo2 was only slightly affected. Respiration of other nematode parasites was largely unaffected by exogenous glucose. Pyruvate had little or no effect.

2. Inorganic phosphate increased when Ascaris lumbricoides muscle brei was incubated. In the presence of fluoride, or when aqueous extracts were used, easily and difficultly hydrolysable phosphate was formed. Phosphatase activity was dominant even in aqueous extracts of A. lumbricoides intestinal tissues and fluoride inhibited Po formation only slightly. Ptot., and PresIdual fell markedly in whole A. lumbricoides which had been incubated anaerobically. Under aerobic conditions Po fell slightly, but the other components rose considerably. Phosphorylative activity of A. lumbricoides ovary was greater than in the muscle. Phosphorus compounds in perienteric fluid did not change during incubation.

3. The breakdown of glycogen and the formation of glucose in aqueous extracts of Ascaridia galli was inhibited by fluoride and phloridzin. Polysaccharide was synthesized in fluoride-poisoned preparations when glucose 1-phosphate was added. Polysaccharide formation in Ascaris lumbricoides fluoridepoisoned muscle preparations was demonstrated without the addition of Cori ester.

4. Fructose 1:6-diphosphate added to aqueous extracts of Ascaridia galli and Nematodirus spp. was rapidly metabolized at pH 6·5. At pH 7·2 the fructose content increased.

5. In aqueous extracts of Nematodirus or Ascaridia brei which had been autolysed for short periods, 55–60% of the glycogen utilized appeared as glucose. Only small amounts of lactate were formed. Aqueous extracts of Nematodirus and Ascaridia brei which had been autolysed for long periods formed glucose in excess of the glycogen disappearing. When perienteric fluid, which contained amylase, was removed from A. galli before autolysis, the amount of glucose formed was very much reduced. It is suggested that the excess glucose was formed from dextrins which were not estimated as glycogen and which were hydrolysed by perienteric fluid amylase during incubation.

Lactate decreased during the incubation of extracts prepared from brei which had been autolysed for long periods.

6. Bicarbonate decreased during the anaerobic incubation of aqueous extracts of Nematodirus spp. and Ascaridia galli which were buffered with CO2-bicarbonate. The decrease in bicarbonate was in excess of the CO2 expelled from the medium by acid formation.

7. The acid-soluble phosphorus compounds of the different tissues of Ascaris lumbricoides were examined. Compounds similar to a.t.p. were found in the intestine, ovary, muscle and possibly also in the perienteric fluid. The acid-unstable phosphorus compounds did not appear to be either creatine- or arginine-phosphate. Compounds similar to Embden ester were found in the ovary and muscle. The occurrence of the phosphate compounds found in the parasite is compared with figures given for other organisms.

8. It is concluded that carbohydrate fermentation as far as lactate in nematode parasites was similar to that found in yeast and mammalian muscle. Energy was transferred by means of high-energy phosphate bonds.

9. Phospholipids, which were found in considerable amounts in the tissues of A. lumbricoides, were estimated as lecithin, sphingomyelin and serine- and ethanolamine-containing phospholipids. The amounts of the phospholipids found in the parasite tissues are compared with figures given for other organisms.

The authors are deeply indebted to Prof. D. Keilin and Dr T. Mann of the Molteno Institute, Cambridge, for their advice and critical reading of the manuscript. Thanks are also due to Dr E. F. Gale and Dr E. Friedemann for advice on analytical procedures.

The history of the ticks (Rhipicephalus appendiculatus) employed for transmission of East Coast fever is detailed in Part I. During the 1st day the ticks generally become attached and are partly held in place by a kind of cement substance (Fig. 1).

Penetration usually occurs at some time during the 2nd day, and the cellular elements of the corium quickly respond. There is a local swelling of the capillary endothelium, an infiltration with polymorphonuclear leucocytes and a slight increase in eosinophiles. More cement substance is produced which hardens about the edges. Some of it enters through the wound and spreads out in the corium along lines of least resistance (Fig. 2).

Later on the eosinophiles increase greatly in number and in turn give place to macrophages which ingest some of the cement substance. Mast cells also become more numerous. The area of reaction extends 2 or 3 mm. from the tip of the proboscis. Marked cytolysis of fibroblasts, of histiocytes and of the swollen endothelial cells occurs. The latter leads to haemorrhage (Figs. 6, 8, 9). The red blood cells and leucocytes are, however, not destroyed. They are sucked up by the tick, the leucocytes first because they accumulate before the haemorrhages take place.

Twenty-five of the sixty-six ticks examined were found to contain parasites in their salivary glands, but no parasites were seen in the sixty-six pieces of skin excised while the ticks were attached. Soon after the parasites enter the blood stream and spread throughout the system the corium of the skin is invaded by them like other parts of the body (Table III).

The medium-sized lymphocytes are the principal cells parasitised; but parasites are also found in lymphoblasts, large and small lymphocytes and occasionally in parenchymatous liver cells. We never saw them in vascular endotheial cells. For this reason we are unable to substantiate the view, which has apparently never been seriously questioned, that they undergo schizogony in this situation. The first agamonts were noted in lymphocytes in gland smears the day the fever first exceeded 103° F. The gamonts appeared about a day later and the intra-erythrocytic forms soon after. Taking the average of a number of cases: (1) The temperature first surpassed 103° F. on the 9·8th day after infestation with ticks. (2) The first Koch bodies within lymphocytes were observed on the 14·8th day, that is to say, 5 days after the fever commenced. (3) The first parasites within the red cells were noted 1·6 days later, on the 16·4th day after infestation.

The cycle which the parasite undergoes in changing from the agamonts to the intra-erythrocytic forms is illustrated in Diagram II (fully described on p. 36).

The alterations in the tissues caused directly or indirectly by the parasitic invasion were studied principally in specimens secured at autopsy from animals killed in extremis. The changes which apparently dominate relate to the lymphatic system. The medium-sized lymphocytes and to a less extent the small and large lymphocytes and lymphoblasts, first in the lymph glands and later in all parts of the body, become infested with Koch bodies which grow in their interior apparently without causing any severe injury. The distribu tion of Koch bodies is recorded in Table III, and their incidence in the lymph glands and in the liver in Tables IV and V. The evidence presented does not support the current conception that the parasites serve as a powerful stimulus to the multiplication of lymphocytes. The enlargement of lymph glands is caused more by oedema than by increase in their number. But there is a marked redistribution of lymphocytes. Their number is reduced in the lymph glands and in the peripheral blood stream and increased in the blood vessels of the liver and some other organs. Perivascular lymphocytic infiltrations are also a notable feature of the reaction in the liver, kidneys, adrenals and several other organs, but they are of rare occurrence in the nervous system. It is uncertain how far they are formed by the emigration of lymphocytes from the blood stream and by the proliferation of lymphocytes previously present perivascularly.

Small haemorrhages constitute a second alteration of importance. They are particularly prone to occur in the epicardium and endocardium, but may be found in almost any part of the body. Evidence is lacking that these haemorrhages play a part in the genesis of the perivasoular lymphocytic infiltrations. The latter are far more widespread and are chiefly observed in locations where haemorrhages are seldom seen.

Oedema is a third type of reaction. It is constantly found in the lymph glands and occasionally in the lungs, especially in the later stages of the disease.

Generally speaking, therefore, the lesions reported in this paper are acute in type. The functional activity of the several organs (except the lymph glands) has not been impaired sufficiently severely or over a time long enough to leave distinct structural changes in the parenchymatous organs; but the specimens examined were not collected from protracted cases of East Coast fever or from animals under suspicion of having undergone repeated attacks of the disease.

It is the parasites in the red blood cells which are capable of continuing the cycle if they are ingested by ticks able to act as vectors. We have recog nised three principal groups: (1) small spherical-ovoid parasites which are the first to make their appearance, (2) tailed parasites, and (3) plunip forms, both of which develop later and become more numerous than the spherical-ovoid parasites. Possible stages of transition are represented in Diagram I (p. 37). Though many parasites undergo differentiation and some probably divide, a variable number degenerate within the erythrocytes.

We question the validity of the genera into which the family Theileriidae are customarily divided on account of the inadequacy of the data on which they are based.

This paper describes patterns of infection with Opisthorchis viverrini within a human community assessed by egg count, parasite-specific antibody levels and worm burden determined by expulsion chemotherapy. All three measurements increased significantly with age, reaching a plateau in young adults. There were no significant sex-associated differences in the prevalence or intensity of infection, antibody levels, or in the frequency of heavy worm burdens. A striking 81·5% of the total Opisthorchis population and 74% of the total egg output were expelled by the most heavily infected 10% of the humans sampled. This extreme over-dispersion, together with recent findings that hepatobiliary disease frequently accompanies heavy infections, argues that the priority for community-based parasite control programmes should be to maximize treatment and health promotion efforts toward heavily infected individuals.

To understand how fisheries affect parasites, we conducted a meta-analysis of studies that contrasted parasite assemblages in fished and unfished areas. Parasite diversity was lower in hosts from fished areas. Larger hosts had a greater abundance of parasites, suggesting that fishing might reduce the abundance of parasites by selectively removing the largest, most heavily parasitized individuals. After controlling for size, the effect of fishing on parasite abundance varied according to whether the host was fished and the parasite's life cycle. Parasites of unfished hosts were more likely to increase in abundance in response to fishing than were parasites of fished hosts, possibly due to compensatory increases in the abundance of unfished hosts. While complex life cycle parasites tended to decline in abundance in response to fishing, directly transmitted parasites tended to increase. Among complex life cycle parasites, those with fished hosts tended to decline in abundance in response to fishing, while those with unfished hosts tended to increase. However, among directly transmitted parasites, responses did not differ between parasites with and without fished hosts. This work suggests that parasite assemblages are likely to change substantially in composition in increasingly fished ecosystems, and that parasite life history and fishing status of the host are important in predicting the response of individual parasite species or groups to fishing.

Following cloning of Leishmania (L.) amazonensis kinetoplast DNA two recombinant clones were identified: one specific for L. (L.) amazonensis and the other specific for L. (L.) amazonensis and closely related isolates. DNA sequences from these clones were compared with those of other kinetoplastids and oligonucleotide primers were designed to be used in the polymerase chain reaction. A pair of these primers has been shown not only to be highly specific for L. mexicana complex isolates but can also be used to distinguish between L. (L.) mexicana and L. (L.) amazonensis isolates. These primers have been tested with water-lysed cultures, crude DNA extracts from human patients, potential host reservoirs, sandfly vectors and with cell pellets after isoenzyme characterization. The results of these tests indicate that the primers can be used specifically in the presence of excess host DNA originating from the majority of South American countries.

Field and laboratory observations on the nature and sequence of the host-finding responses of the hen flea Ceratophyllus gallinae are described. The imago over-winters within the cocoon. Tactile stimuli and a rise in temperature initiate emergence. Emigration from the nest is delayed for a few days by a negatively phototactic response, and begins when this becomes positive. The fleas are negatively geotactic and disperse upwards into the vegetation. Eventually they take up a characteristic posture, oriented towards the light. Jumping is elicited when the light intensity is suddenly reduced, and it is suggested that this enables the fleas to reach their avian host. Those fleas whose jump misses the host fall and form a secondary distribution on the ground. The readiness to jump rises during the first few days after cocoon emergence, then falls again, the rate of fall apparently being partly determined by water loss.

The author is much indebted to the Hon. Miriam Rothschild and Drs E. T. Burtt and M. J. Cotton for valuable advice, and to C. R. Brannigan for a critical discussion of the manuscript. The main part of the research was carried out during tenure of a post-graduate studentship provided by the Department of Scientific and Industrial Research.