Factors which may be important in the large-scale extraction of coccidial oocysts from faeces have been investigated with Eimeria tenella. Age of bird, inoculum, feeding status at the time of inoculation, period of collection, feeding status during collection, collection medium, homogenization and sieving, flotation, washing, sporulation and further purification have all been considered. The aim has been to establish a method to produce the maximum number of oocysts of a required degree of purity and viability, with the expenditure of the minimum amount of physical effort, time, animals and chemicals. In our method, groups of chickens 3–4 weeks of age are inoculated with 5000 oocysts of E. tenella and food is supplied ad lib. Over the period 5–8 days after inoculation, faeces are collected in trays containing 2% (w/v) potassium dichromate solution, while food intake is restricted. The faecal material is homogenized, passed once through 40 and 100 mesh sieves, centrifuged and the oocysts recovered from the sediment by 3 flotations in saturated salt solution. Following washing, oocysts are sporulated by forced aeration at 30°C and may be further purified by hypochlorite treatment, or passage in 5% Tween 80 solution through a glass bead column followed by sucrose density gradient centri-fugation. Routine passages along these lines over a 5 year period have given a recovery of 46% of the oocysts excreted by over 7000 birds.

Sporozoites of 3 species of Eimeria were introduced into the caecum of young chickens. E. praecox and E. maxima failed to develop in this site, but light infections of E. acervulina were detected. Infection of the small intestine with all 3 species occurred when sporozoites were introduced via the caecum.

Infections were produced when mucosal scrapings of small intestine from birds, inoculated via the caecum 1–4 h previously, were inoculated orally to susceptible chickens. Experiments with 51Cr-labelled sporozoites of E. praecox introduced in the caecum, confirmed that small numbers of sporozoites are capable of migrating from the lower to the upper intestine. Sporozoites were not transferred with liver tissue from birds given sporozoites via the caecum but were transferred with the liver of chickens given sporozoites intraperitoneally.

Almost 100% of 7- to 10-day-old Hymenolepis diminuta became established when surgically transplanted from donor mice into the duodenum of naive recipient mice. Transplanted tapeworms survived 8–12 days, by which time they had survived much longer in total than they would have done in the donor. Mice previously immunized by a primary infection rejected transplants within 4 days. Sub-lethal irradiation (550 rad) delayed rejection by immune mice but such mice still rejected worms much more quickly than did naive mice.

Surgery was shown to delay by 2–3 days the rejection of worms by naive mice, and the importance of circumventing surgery by administering the worms per os is emphasized.

Prospects for reconstituting irradiated immune mice are considered vis-à-vis work with nematodes, and the differences which, on present knowledge, appear to exist between nematode and cestode rejection are briefly discussed.

Vulvar phenotypes and the rate of development of eggs over a range of temperatures were used to compare Haemonchus contortus populations in New York State and Ohio. These parameters indicated that the westernmost boundary of the subspecies Haemonchus contortus cayugensis is the Chautauqua valley in New York. The Haemonchus ecotype in Ohio had a vulvar phenotype formula similar to that described for the subspecies Haemonchus contortus contortus. The relationship between slope and intercept of the regression of rate of egg hatch on temperature was different for morphs within ecotypes as well as between the New York and Ohio ecotypes. Linguiform-A appeared to be the cold-adapted morph in both ecotypes. Smooth was the warm-adapted morph in New York with linguiform-B filling that niche in Ohio.

A particulate polysaccharide was isolated by differential centrifugation and alkali extraction from homogenates of the cestode Moniezia expansa. The polysaccharide had the structure of a glycogen. Its chemical properties, infra-red spectrum and optical rotation showed that it consisted of α-1, 4- and α-1, 6-linked glucopyranose units. Examination of the complex with iodine and the precipitate with concanavalin-A showed that the structure was highly branched. Oxidation with periodate and hydrolysis with α- and β-amylase were used to measure mean chain lengths. For the particulate preparation the average chain length was 12·9 glucose units and the exterior and interior chain lengths were 9·0 and 2·9 units respectively. The particulate preparation had a very high sedimentation constant (s20, w = 910) with a smaller component at about s20, w = 600, but the alkali extracted material had an s20, w = 61 similar to that shown by alkali degradation of the particulate preparation. The morphology of the particulate material was similar to that of rat liver glycoge, α, β- and possible γ-particles being identified by electron microscopy. The α-particles were relatively stable under acidic conditions remaining intact down to pH 2·5. At pH 1·7 the α-particles dissociated into their constituent β-particles with a consequent decrease in the opalescence of the solution. The nitrogen content of 0·9% was high for a glycogen.

Unsporulated oocysts were recovered from the allantoic cavity of 5 chicken embryos inoculated with a single sporozoite of Eimeria tenella; some of these oocysts sporulated. Both macrogametes and microgametes are required for the formation of viable oocysts. The results conclusively demonstrate the bisexual nature of the sporozoite, suggest that sexual differentiation is influenced by environmental factors, and show that true clones of Eimeria can be established from individual sporozoites.

Larvae of Hymenolepis diminuta develop in the haemocoele of the beetles Tribolium and Tenebrio, and of the locust Schistocerca gregaria, without being encapsulated by haemocytes. The mechanism of this evasion of the haemocytic defence reaction has been examined using various techniques. Larvae grown in culture and injected into S. gregaria have few or no haemocytes adherent even after 8 h, although latex beads injected at the same time have been thickly encapsulated. This, and results of transplanting cysticercoids and host tissue between different insect species, suggests that the surface of the larvae may bear an inherent similarity to the surface of host tissues and thus escape recognition as ‘not-self’ by the host’s haemocytes.

Experiments were carried out to investigate the effect of variations in humidity and osmotic pressure upon the development and hatching of the eggs of Nematodirus battus. It was found that no development or hatching took place unless there was free water available, though humidity effects could enhance the subsequent response of the eggs in water. Larvae were found to be very resistant to prolonged exposure to low humidity. The concentration of the hatching medium showed little effect upon development of eggs, though the rate of larval emergence was reduced as the concentration of the culture medium increased. The relevance of this information is discussed in the context of other requirements of the egg stages during their hatching phase and how this may affect the behaviour of this nematode under field conditions.

The initial process in the hatching mechanism of Ascaris eggs is the sudden onset of permeability in the previously impermeable ascaroside membrane. During this change the ascaroside membrane remains intact and no chemical changes can be detected. Using the molecular probe 1-anilino-8-naphthalene sulphonic acid no conformational changes were detected in the ascaroside membrane during the induction of permeability. It is suggested that either the permeability change is due to a very localized chemical or conformational change, not detectable by conventional analytical techniques, or the change is due to mechanical damage of the ascaroside membrane, brought about by the activity of the infective larva.

Samples of largemouth bass were collected from Par Pond located on the Energy Research and Development Administration's Savannah River Plant in Aiken, South Carolina, from June 1972 to May 1973 inclusive. The sampling stations reflected water temperatures which were both normal and greater than 10°C above normal for the area. The acanthocephalan Neoechinorhynchus cylindratus was the dominant species found in the bass sampled. Incidences of infection for this parasite were generally greater than 95% regardless of location. A pronounced seasonal cycling pattern in the intensity of infection was noted in both thermal regions. Significant differences, however, in the mean density of N. cylindratus per host in fish taken from the heated area as compared with unheated areas were noted.

Turnover in the acanthocephalan population was measured by following the percentage of individuals less than 2 mm long. Fall proved to be the most intense parasite recruitment season, followed by maturation of the parasite and subsequent loss from the fish host.

The principal factors responsible for the seasonal incidence and intensity patterns are considered to be changes in the fish feeding behaviour and annual temperature regimes.

Growth and behaviour of Boophilus microplus larvae on British breed cattle, with different resistance levels to the tick, were studied to elucidate the nature of resistance. On highly resistant animals, larval growth rate was slower for the first 3 days, but by day 4 they had attained the normal weight and the majority were subsequently able to moult.

Using phosphorus-32 labelled larvae, it was found that attachment times were shorter and more time was spent wandering on highly resistant animals during the first 16 h. On the second day, attachments had stabilized, but more detachments were still made from highly resistant animals. This was considered to impose an additional stress as the cattle skin environment can rapidly desiccate larvae. However, the larvae were able to compensate by uptake of fluid from the host.

Loss by repulsion of live larvae from the host or drowning in serous exudate were also not considered of major importance. The nature of rejection is discussed in a further paper.

The distribution of larvae after 24 h suggests that their early behaviour largely determines the areas favoured by adults. Movement to, and accumulation in, favoured areas is discussed.

The life-cycle of canine Isospora bigemina was studied in dogs, cattle, cats and mice. Under experimental conditions dogs served as both definitive and intermediate hosts. Unsporulated oocysts (11 × 12 μm) were shed in the faeces and sporulated outside the host within 12 h at 30–37 °C and 36 to 48 h at 23 °C. Sporulated oocysts measured 12 × 13 μm and contained 2 sporocysts which in turn contained 4 sporozoites. Sporocysts averaged 6 × 9 μm and sporozoites averaged 2 × 6 μm. Although no stages were found microscopically in tissues or in faeces of 23 dogs orally inoculated with sporulated oocysts, the oocysts were infectious because 5 of 14 dogs that ingested tissues of dogs fed oocysts, shed oocysts. Prepatent periods were 7 to 15 days; patency was 1–3 days. No dogs became ill. In the naturally infected dog and one experimentally infected dog, schizonts were found in epithelial cells, distal to the host cell nucleus at the tips of villi throughout the small intestine. Schizonts were 5–7 μm and contained 3–12 merozoites. In the naturally infected dog, gametes were found in the same location. Male gametocytes were 6–8 μm and contained 6–12 microgametes, and female gametes were 7–8 μm.

Sporulated I. bigemina oocysts from a naturally infected dog were not infectious to cattle, cats or mice. Structurally identical oocysts were shed by 2 dogs after ingesting hearts and diaphragm from naturally infected cattle; these oocysts were also not infectious to cattle. Although dogs acted as both intermediate and definitive hosts under experimentation, this is not likely to occur in nature. A canine-bovine-canine cycle would appear to be the natural mode of infection but I. bigemina was not infectious to cattle under experimental conditions.

Records are presented of 11 species of parasitic helminths recovered from 37 American avocets. Birds were collected in Kansas and Colorado from April 1973 to August 1974. Parasites found included 3 trematodes, 2 nematodes, 1 acanthocephalan and 5 cestodes, 4 of which are new species. Hymenolepis cervotestis sp.n. (Hymenolepididae) is described from the small intestine of 7 avocets. It exhibits extreme protandry with the testes appearing before external segmentation is evident. Sobolevicanthus coloradensis sp.n. (Hymenolepididae) is described from the small intestine of 4 avocets. This species is found to have its scolex embedded in the intest-tinal mucosa of its host. Diorchis recurvirostrae sp.n. (Hymenolepididae) is described from specimens recovered from the small intestine of 5 avocets. Diplophallus coili sp.n. (Acoleidae) is described from the small intestine of all 37 avocets. The family Diploposthidae is suppressed and the family Acoleidae is emended to include the 4 genera previously placed in Diploposthidae. A key to the genera of Acoleidae is presented.

Subcutaneous injection of nursing mothers from day 16 to day 20 post partum with infective larvae of Strongyloides ratti or Nippostrongylus brasiliensis does not result in the development of worms in the litters if 1 h is allowed between injection and resumed nursing, and suckling is terminated 24 h later. Thus the low numbers of N. brasiliensis (1% of the dose) which develop in litters after 24 h, 4 day or 5 days suckling when mothers are injected and returned to their young immediately, represent skin invasion and not milk-borne infection.

Taking precautions consistent with the foregoing, S. ratti equivalent to 28%, 45%, 45% and 48% of the dose were shown to be transmitted in the milk to suckling rats of 4 mothers injected with 4000 L 3 on day 18 post partum and 72 h before weaning. One mother of the same batch failed to transmit worms (1% of the dose in the litter) and the take in all 5 mothers was insignificant (max. = 3% of the dose versus an average of 21% in controls).

Large numbers of S. ratti were subsequently found in the intestines of mothers whose litters were weaned immediately after (21%) or 6 h after (16%) injection, whereas very few (less than 1%) developed in mothers deprived of their offspring 24 h after injection. Dynamic, rather than static, determinants of larval routes inside the host present the only logical basis for an explanation of these facts.

The taxonomic status of the haemoproteid parasites hitherto described from the avian genus Passer is reviewed. It is concluded that 1 species only is valid Haemoproteus passeris Kruse (1890), all other species being designated as synonyms. From material obtained from Passer domesticus a re-description is given of H. passeris which has been shown to exhibit a wide range of morphological forms. The reasons for this are discussed. Schizogonic stages are described for the first time for this species, and evidence is presented which suggests that H. passeris does not belong to the sub-genus Parahaemoproteus. Schizogonic stages previously considered to be from Passer spp. probably originated from birds of another genus and family. H. passeris appears to be restricted to the avian genus Passer in which it has a world-wide distribution.