Cultured adult chick kidney (CK) cells inoculated with sporozoites of Eimeria tenella showed progressive alterations in their morphological and adhesive characteristics. Scanning electron microscopy (SEM) showed that during a 3-day period following the inoculation of parasites there was a gradual loss of contact between the cells. Initially, the cells remained connected by long cytoplasmic bridges but with the breakdown of these, the cells began to round up, losing complete contact with each other and remaining attached to the substratum by means of retraction fibres. By 3 days many cells had completely detached. The factors inducing these alterations were transmissable via the medium as the alterations were mimicked by non-parasitized cells in co-culture with parasitized cells. Studies with the reflection interference microscope (RIM) showed that the changes were accompanied by an increase in the cell-substrate separation distance and the loss of focal contacts. These changes were not effected by substances transmissable via the medium. Parasitized cells showed enhanced agglutination with Concanavalin A (Con A) which could be eliminated by pre-fixation. The possibility that changes to the host cell indicate a rearrangement of cytoskeletal apparatus is discussed.

The pattern of DNA synthesis in chicken kidney (CK) cells parasitized by Eimeria tenella was altered; a 2-fold increase in the uptake of [3H]-thymidine occurred in these cells compared with that shown by the controls. This difference was significantly different at 16 h post-inoculation (p.i.) and reached a peak at 20 h p.i. Non-parasitized cells in co-culture with parasitized cells showed a level of incorporation intermediate between that of the parasitized and non-parasitized mono- cultures. It was shown that this stimulation was due to a factor released into the medium by the parasite or the parasitized cell. A possible course of events leading to induced and prolonged DNA synthesis by the host cell and the significance of this change in the life-cycle of the parasite is discussed.

The ultrastructure of immature exo-erythrocytic forms of Plasmodium berghei in rat hepatocytes was studied at stages between 25 and 51 h of development. A new method was successfully applied to localize the parasites in a small portion of the liver by temporary ligature of blood vessels to the majority of the liver, and from the spleen and the pancreas. Nuclear profiles appeared to be part of a highly lobed nuclear reticulum. Peripheral vesiculation and vacuolization of the cytoplasm was increasingly prominent and ushered in the formation of pseudocytomeres. Spacing between host- and parasite-derived membranes could first be observed after 43 h of development. In general, organellar development was found to follow closely that described for plasmodial oocysts.

A strain of the cattle piroplasm Babesia divergens isolated from a fatal human infection was propagated in the Mongolian gerbil through 150 semi-continuous intraperitoneal passages. The infection was normally fatal; death, accompanied by profuse haemoglobinuria and debilitation, occurred as early as 44 h after intraperitoneal inoculation of heavily parasitized blood with precipitous drops in red blood cell and platelet counts. The average maximum parasitaemia achieved increased on continuous passage reaching 80% by the 150th stage. Twenty-four hours after infection erythrophagocytosis and splenic congestion were apparent by light and electron-microscopical examination and by 48 h hepatic necrosis, renal tubular damage with haemoglobin cast accumulation and ischaemic necrosis of ileal mucosa had developed. Gerbils were highly susceptible to small numbers of parasites when the inoculum was either fresh parasitized blood in high dilution or erythrocytes concentrated from animals showing minimal parasitaemia. Animals inoculated with parasites preserved in dimethyl sulphoxide at low temperatures usually developed fatal infections. However, occasionally animals suffered at most a low grade parasitaemia subsequent to recovery with parasite elimination. These animals were immune to further challenge, and no chronic infections developed. A. field strain of B. divergens isolated locally from a case of bovine redwater behaved similarly to the human strain on continuous passage in gerbils.

Histochemical and thin-layer chromatographic (t.l.c.) analyses were made on neutral lipids in the free (unencysted) metacercariae of Amblosoma suwaense (Brachylaimidae). As determined by t.l.c. the major neutral lipid fractions in metacercariae removed directly from Campeloma decisum snails were free sterols and sterol esters. Metacercariae incubated for 1 h at 37±1° C in sterile Locke's solution released mainly sterol esters and a lesser amount of free sterols into the medium. As determined by Oil Red O (ORO) staining, metacercariae accumulated neutral lipid in the intestinal caeca during incubation and the excretory system was ORO negative. Behavioural studies showed that metacereariae paired and aggregated in vitro and were attracted to lipophilic but not to hydrophilic worm products. Following t.l.c. preparative analysis it was demonstrated that metacercariae were attracted to sterol ester worm products but not to free sterol products.

The ultrastructure of the pseudohaptoral squamodiscs of the monogenean Diplectanum aequans is described. The most prominent feature of the squamodisc is the presence of epidermally-embedded spines which are covered by the outer epidermal membrane. These spines, which are ‘hollow’, are composed of a moderately electron-dense material with denser fibrils embedded within it. The squamodisc epidermis is similar in appearance to the haptor epidermis, with the exception of the epidermis ‘inside’ the spines. Here the epidermis contains free ribosomes and stacks of alternating electron-lucent/electron-dense, membrane-bound sacs. The arrangement of the musculature of the spines is described. The free, prehensile, edges of the squamodiscs contain numerous radially orientated nerves, some of which are assumed to be mechano-receptors.

Cholinesterase activity has been demonstrated histochemically in the nervous system, tegumental and sub-tegumental musculature of the haptor and in the pharyngeal bulb of the oncomiracidium of Pricea multae. The presence of cholinesterase in the nervous system is attributed to neurotransmission and its presence in the tegumental and sub-tegumental musculature of the haptor and pharyngeal bulb is discussed. The nervous system of the oncomiracidium with respect to cholinesterase activity is described and is compared with the nervous system of the oncomiracidium of Protopolystoma xenopodis.

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.

Clun Forest sheep, aged between 3 and 18 months and worm-free from birth, were given a single dose of 25000 infective larvae of the nematode Haemonchus contortus. The host animals were killed between 4 and 100 days after infection and the nematode populations were examined to determine size and composition. The relation between worm body length, dry weight and age was studied and growth curves were constructed. Variations in the sex ratio for infections of different ages were noted. No evidence was found for a relation between rate of growth and population density. The rate of expulsion was determined and its variability discussed.

Details are given of a method for the separation of the eggs of the nematode Nematodirus battus from sheep faeces. Faecal pellets obtained from worm-free lambs experimentally infected with N. battus were homogenized and passed through a graded series of metal sieves. The material retained in a 53, µm aperture sieve was transferred to a cylindrical column and the eggs were cleaned and separated from other suspended material by controlled differential flotation using tap water. A model experiment indicated that, within limits, the principle held for any size of tower. The density distribution for eggs at the morula stage of development was determined. Suggested flow rates for a specified tower are given.

The effect of temperature on the behaviour of the infective larvae of Trichostrongylus colubriformis has been investigated. Larvae acclimatized at 3°C or 20°C respond to sudden or gradual increases in temperature by coiling. Increased temperature may indicate a risk of exposure to desiccation and elicits a behavioural response which optimizes survival. Larvae are straight when inactive; coiling is an active response to specific stimuli. Larval activity is initiated by exogenous stimuli. Mechanical disturbance is a major stimulus, the response being affected by changes in temperature. Larvae acclimatized at 3°C or 20°C show a peak of activity at temperatures between 15 and 25°C.

The influence of genes in the major histocompatibility complex (MHC) of the guinea pig on the susceptibility to infection with the parasitic nematode Trichostrongylus colubriformis was investigated. Back-cross analysis of 2 lines of guinea pigs suggests that genes that map in or near the I region of the guinea pig MHC influence susceptibility to infection by the parasite. However, other genes, possibily not linked to the guinea pig MHC, may also be required for the full expression of susceptibility.

Corynosoma spp. (Acanthocephala) infection in ringed seals (Pusa hispida) is compared in spring and in autumn in the Bothnian Bay, northern Baltic Sea. The material consists of more than 13400 specimens: 7590 from the intestines of 13 seals captured in April and May 1978 and 5850 from 29 seals captured in October and November.

Corynosoma strumosum infection had approximately the same intensity in spring and autumn (mean 76 and 66 individuals/infected seal, maxmum 313 and 324 individuals, respectively). C. semerme specimens, on the other hand, were 37 times more numerous in spring than in autumn (504 compared with 136/infected seal, maximum 1700 and 1230 individuals, respectively). The ratio of C. strumosum to C. semerme was 1:6·3 in spring and 1:2·0 in autumn, as calculated from the total material. Corynosoma infection was more recent on average in spring than in autumn, as judged both from the proportion of males and immature females and from the distribution of C. semerme in the intestine. The feeding habits of the ringed seals and the rate of development of Corynosoma infection are discussed.

The histology of the reproductive system of male Moniliformis dubius has been studied by a variety of microscopical techniques. The system includes 2 testes from each of which arises a vas efferens. Products from the testis enter the vas efferens through openings present in the wall of the vas efferens. The testes are contained in a ligament sac and each testis is enveloped separately by an outgrowth of the ligament sac wall. There are 8 unicellular cement glands. The cement substance contains spherical electron-dense droplets presumed to be lipids. Saefftigen's pouch appears to be a hydraulic mechanism to regulate the turgidity of the wall of the bursal cap to effect successful copulation with female worms. The muscles attaching the genital sheath and bursa to the body wall are likely to be concerned with bursal eversion and inversion. Stimuli receptors connected to the genital nervous system are located in the penis and bursa.

Biozzi mice of Selections 1 and 3, each exhibiting either high- or low- antibody responses to a wide range of antigens, were exposed to primary, secondary and tertiary infections of the nematode, Nematospiroides dubius. The course of these infections was followed by monitoring egg output and by examination of the worm burdens on the 14th day after each exposure to the parasite. When exposed to a primary infection, high and low responders were equally susceptible to the parasite, and the egg production of the infections was similar in all groups. However, when the mice were exposed to a 2nd infection of N. dubius, marked differences in the susceptibility of the hosts were seen. The high-responder mice of both Selections 1 and 3 were significantly more resistant to infection, far less adult worms being found in these. Resistance to a 3rd and final infection of the parasite was amplified appreciably in all groups but, again, the high-responder mice were significantly more resistant than the low responders. These results imply that host antibodies play an essential role in immunity to this parasite and that resistance cannot be attributed solely to non-specific macrophage activity or cell-mediated immune reactions, since the latter are equivalent in high and low lines and the macrophages of the Ab/L line of Selection 1 are hyperactive.

The spontaneous free-swimming behaviour of the cercaria of Transversotrema patialense was recorded using a high-speed micro-cinematographic technique. The sequential change in configuration of the cercaria was analysed quantitatively and the angular relationships of the cercarial components determined with respect to the trajectory of the organism. The cercaria swims tail-first while the tail stem oscillates through an arc of 100–120° with a frequency of 30 Hz at 24°C. The body region oscillates, almost exactly out of phase, through an arc of 180°C at the same frequency. The two furcae execute alternate effective and recovery strokes so that two symmetrical effective strokes are performed during each propulsive cycle. The Reynolds number of the swimming cercaria was approximately 2. The relative importance of viscous and inertial forces in cercarial propulsion is discussed.

The transfer of infective larval stages of helminths via the mammary glands is probably more common than generally recognized. Recent investigations of both natural and experimental infections of various animals have shown that the transmammary transmission of some helminths is a major avenue of infection. Other studies indicate that there are at least 13 helminth parasites which may be transmitted as prenatal infections and at least 17 transmitted via the mammary glands. The majority of these are nematodes. However, in one case the tetrathyridia of the cestode Mesocestoides was observed. In this report the life-cycle and transmission of 2 species of diplostomatid trematodes in the genus Pharyngostomoides is described. The raccoon, Procyon lotor, is the only definitive host; a planorbid snail, Menetus dilatatus, and a branchiobdellid annelid, Cambarincola osceola, a commensal on crayfishes, are intermediate hosts. Records for a period of 11 years are now available for the maternal transmission and longevity of this trematode. During this time one infected female raccoon was maintained in the laboratory on a diet of commercial dog food, sweet potatoes and corn. She produced 25 offspring, most of which were infected with Pharyngostomoides, through the 6th litter. There was a declining number of worms in each litter, ranging from nearly 2000 in one of the 1st litter, to none in the 7th litter. After nearly 12 years she continues to pass a few trematode ova. Rather than assume she has retained the same adult worms for 12 years, it is reasonable to conclude that mesocercariae move through her body and eventually mature in the intestine. Because the mesocercariae have a predilection for the lactating mammary gland, it seems likely that a hormonal influence is present. The transmammary transmission of larvae is a viable alternative in the life-cycles of a number of helminths, and in some instances it is probably the major route of infection.

R. R. Young and A. C. Trajstman wish to point out that in their article which appeared in Parasitology 80, 42531, the figure 50 %, on the fifth line of the Summary, should have read 90%.