The course of infection with a local strain of Schistosoma mansoni was investigated in Kenyan baboons (Papio anubis). A single exposure to 5000 cercariae per baboon (cpb) killed five 4–8 kg baboons; a sixth survived the full 30-week post-exposure period, with suppressed egg production after week 11. Lower doses were not lethal. A single exposure to 1000 cpb gave satisfactory adult worm recoveries, high and steady faecal egg excretion, and a high tissue egg recovery, predominantly from the large intestine. A similar but less consistent picture was obtained with a single exposure to 200 cpb. Baboons receiving 5 monthly exposures of 200 cpb (1000 cpb total) showed some evidence of the development of protective immunity. Three animals showed patterns resembling those for 200 and 1000 cpb. The other 3 had suppressed egg production (faecal and tissue) indicating, perhaps, some immunological process. They also had an abnormally high percentage of eggs in the liver.

A relatively simple, standardized hatching test was devised, tested and used to estimate the Schistosoma mansoni hatching rate for 88 St Lucian subjects selected by age, sex and intensity of infection.

The hatching rate was dependent on the intensity of infection and rose proportionately with it. The rate also decreased with increasing age of the subject. Sex alone had no direct effect but there was a suggestion of an interaction between sex and age.

These results suggest that several hatching tests are necessary, before and after treatment in schistosomicidal drug trials, to permit valid conclusions to be drawn. The hatching data are used in conjunction with survey results to calculate the contamination potential of different age groups in a population. School children (5–14 years old) are about twice as important as young adults (15–29 years old) who, nevertheless, contribute over a quarter of the total contamination potential. However, whereas school children are fairly accessible for mass chemotherapy control programmes, young adults often are not and, furthermore, involve problems associated with the treatment of women of child-bearing age.

The development of resistance by the Houghton strain (H) of E. tenella to robenidine has been studied, in the laboratory, by serially passaging the strain in chickens fed increasing concentrations of drug. Resistance to robenidine developed more readily in experiments using larger numbers of birds with higher numbers of oocysts in the inoculum. Both these factors increased the parasite population and increased the chance of selecting parasites resistant to the drug. E. tenella (H) was made resistant to 264 ppm robenidine and showed no cross-resistance to other anticoccidial agents. Resistance arose in a series of ‘steps’ as the concentration of drug was increased. E. tenella (H) was continuously passaged at concentrations ranging from 2 to 33 ppm of robenidine. After 16 passages, lines passaged at 2, 4 and 8 ppm were not resistant to 33 ppm robenidine, suggesting that the degree of resistance developed was dependent upon the drug selection pressure.

Infections in the chicken embryo have been used to study the development of drug resistance in an embryo adapted strain of E. tenella. Resistance was developed to decoquinate, clopidol and robenidine by serially passaging this strain, but evidence for the development of resistance to amprolium was inconclusive. Resistance to decoquinate developed more readily than to the other drugs. Attempts to increase resistance to clopidol, robenidine and amprolium by increasing the sporozoite inoculum and by the use of a mutagenic agent were unsuccesful. No cross-resistance was found between the 4 drugs.

Drug resistant lines of the Houghton strain (H) of E. tenella, made resistant to the 4 anticoccidial drugs by passage in chickens, were found to be resistant when evaluated using chicken embryo infections. Lines made resistant to decoquinate were not controlled by any concentration of this drug, suggesting that resistance, once developed, was absolute and not dependent on drug concentration. Lines made resistant to robenidine, clopidol and amprolium, however, were controlled by higher drug concentrations suggesting that in this case resistance was dependent on drug concentration.

The anticoccidial action of 6 drugs was studied by treating cell cultures with drug for 24 h after inoculation of the cultures with sporozoites of Eimeria tenella. A monitoring technique was used to confirm that the drug was being removed. Only monensin was shown to be coccidiocidal. Amprolium, lasalocid, methyl benzoquate, nicarbazin and robenidine were coccidiostatic at their minimum effective doses. Misleading coccidiocidal effects were observed when higher concentrations of methyl benzoquate, nicarbazin or robenidene were used.

Features of the anticoccidial activity of nicarbazin, amprolium, zoalene, sulphadimidine, diaveridine, Darvisul, spiramycin, chloramphenicol and Oxytetracycline have been re-investigated both in vivo and in cell culture using Eimeria tenella. Of the drugs studied, only spiramycin was appreciably coccidiocidal, although nicarbazin and amprolium showed possibly slower coccidiocidal activity. In order to show activity against a particular stage in the life-cycle, higher concentrations of drug than those usually recommended for field usage had in most cases to be used. Under these conditions, parasites were usually inhibited as multinucleate 1st generation schizonts. With delayed medication, effects against 2nd generation parasites were in most cases found, and in many cases, although the parasites never matured to give viable merozoites, the large degenerating forms produced were able to cause extensive tissue destruction and haemorrhage. Methodology in this type of study is discussed in relation to more active and more recent anticoccidials, and some further experiments with robenidine reported.

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.

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.

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.

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.

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.

Echinococcus granulosus cysts were cultured in vitro from the oncosphere, and cyst morphogenesis is described. Cysts grew to a mean diameter of 16 mm in 120 days, with a maximum of 20 mm. An amorphous layer was apparent around the larvae during early post-oncospheral re-organization. Organisms became vesicular at 6 days and laminations appeared in the amorphous layer at 10 days. Confluence of proliferating cells to form the syncytium of the germinal membrane was observed.