The ultrastructure of the macrogamete and developing oocyst of Eimeria maxima (Weybridge strain) was examined in the intestinal cells of chicks fed 3 different anticoccidial drugs. Amprolium at 125 p.p.m., arprinocid at 35 p.p.m. and dinitolmide at 250 p.p.m. caused considerable morphological abnormality and incomplete development of the wall-forming bodies of Type 2 (WFB II), which did not appear able to participate in oocyst wall formation. The wall-forming bodies of Type 1 (WFB I) were able in each case to participate in oocyst wall formation although amprolium and dinitolmide produced morphological abnormalities in them. In birds medicated with dinitolmide, the outer layer of the oocyst wall was formed initially at opposite poles of the macrogame tes rather than as a uniform layer. Other abnormalities resulting from drug treatment are reported and some evidence that intravacuolar tubules may be formed by the parasite pellicle is presented.

Three strains of Eimeria acervulina and 3 strains of E. mivati were compared. E. acervulina was characterized by the ovoidal shape of its oocysts and their rapid sporulation, small first-generation schizonts containing few merozoites, and its inability to complete development in the chorio-allantois of chicken embryos. E. mivati had more rounded oocysts with a Longer sporulation time, larger first-generation schizonts containing twice as many merozoites and it developed readily in the chorio-allantois. Pre-patent periods were variable but generally shorter with E. acervulina. A strain of E. mivati attenuated by repeated embryo passage showed a reduced pre-patent period.

1. It has been confirmed that Trichomonas foetus fails to survive freezing and thawing in the presence of 10 % glycerol in egg-yolk-citrate diluent. Under the same conditions adequate sperm survival was demonstrated.

2. Trichomonads were particularly sensitive to the toxic effects of glycerol when suspended in egg-yolk citrate.

3. Trichomonads will survive freezing and thawing when suspended in other diluents such as egg-yolk phosphate or milk.

The pyroxene assemblages of four samples of ferrodolerite from the Mesozoic Mount Wellington sill of southern Tasmania are described. The pyroxenes of each sample define an Fe-enrichment trend equivalent to almost half of a Skaergaard-type pyroxene evolution trend. The calcic pyroxenes range from augite to ferroaugite (Ca30–40Mg40–17Fe15–45) and late-stage hedenbergite (Ca45 Mg5Fe50), and the pigeonites from intermediate to ferriferous types (Ca13Mg55–15Fe32–70). XMg numbers (Mg/(Mg + Fe)) of the calcic pyroxenes vary from 0.8 to 0.1, and of the calcium-poor pyroxenes (pigeonites) from 0.62 to 0.17. The chemical variation in the pyroxenes within individual samples is far greater than between the different samples. One sample contains an extremely wide range of pyroxenes which include some of the most ferriferous pigeonites ever recorded (Ca14Mg15 Fe71). Ti and Al contents are also highly varied, Ti:Al ionic ratios ranging from 1:15 to 1:2 with decreasing XMg. The augites have higher Ti and Al contents than pigeonites with corresponding XMg. The hedenbergites have erratic but generally low Ti contents, due to their late precipitation together with ulvospinel. The presence of such highly variable pyroxenes within individual samples and in some cases as single, complex grains makes the recognition of coexisting pyroxene pairs in such dolerites very difficult, but graphical pyroxene thermometers suggest a crystallization temperature range of 1100 to 850 °C.

The range of pyroxene compositions in such dolerites is strongly influenced by the oxygen fugacity (fO2) of the liquid from which they derive. The primary Fe-Ti oxide phase in these Tasmanian dolerites is ulvospinel (now oxidized to ilmenite ‘oxidation-exsolution’ lamellae in titanomagnetite hosts) clearly demonstrating the originally low fO2 of the parental tholeiitic magma of the Mount Wellington sill.

Chicks were treated with cyclophosphamide during the first 3 days of life in order to effect chemical bursectomy. They subsequently showed a reduced capacity for the production of serum agglutinins to Brucella abortus and immunolysins to sporozoites of Eimeria tenella. They also developed a reduced immunity to E. tenella or E. maxima compared with that produced in normal birds. The evidence provided by these experiments for the role of circulating antibodies in immunity to coccidiosis is discussed.

A short list of terms has been compiled which provides for the discussion of variation of coccidia of the genus Eimeria at infrasubspecific levels. Based upon this list, guidelines are given for the designation of strains and lines.

Two strains of Eimeria acervulina were compared. The more recently isolated strain had a higher reproductive potential and produced slightly longer oocysts. Otherwise both strains conformed to the characteristics of the species.

The two strains were not immunologically identical and birds which were solidly immune to one strain would support a degree of infection with the other.

Acknowledgements are due to Mr C. C. Norton for technical assistance and to Dr Helen Hein who provided access to experimental data prior to publication and discussed some aspects of the results. The statistical calculations were carried out by Miss N. Hebert.

Pathogenic effects caused by graded doses of recent isolates of Eimeria acervulina, E. mivati and a new isolate, thought at first to be E. mitis, were compared. Cross-immunity studies were conducted with 3 strains of E. acervulina and 2 strains of E. mivati, together with the new isolate. The results showed marked similarities between E. mivati and the new isolate and clear distinctions between these and E. acervulina. E. mivati produced scattered petechiae but did not form discrete lesions in the intestine comparable to those seen with E. acervulina. Endogenous stages of E. mivati were most numerous in the lower small intestine and proximal caeca. The ratio of villus height to total mucosal thickness in the lower intestine was reduced. Similar changes caused by E. acervulina were seen in the anterior intestine only.

A line of Eimeria maxima acquired resistance to Lerbek (a mixture of clopidol and methyl benzoquate) after serial passage against rising drug levels. Abnormal bisporocystic oocysts which appeared throughout this series were picked out individually and these produced infections in further groups of chicks. Serial passages of selected bisporocystic forms raised their proportion in oocyst yields to about 80% after 10–14 passages, but a few normal oocysts were still present.

1. Methods are described for the isolation and maintenance of a pure strain of Eimeria mitis.

2. The prepatent period of the infection in chicks was 101 hr. The mean dimensions of the oocysts were 15·38 × 13·83μ, and sporulation occurred after 48 hr. at 60° F. (15·5° C.). The production of oocysts following infection with known numbers of oocysts is recorded.

3. When 500,000 or more oocysts of E. mitis were given to chicks aged 6, 17 or 26 days the growth rate of the birds was markedly reduced. Young chicks were most susceptible and a few deaths occurred when 6-day-old chicks received 2·5 million oocysts. E. mitis is unlikely to be of pathological importance under normal conditions of good husbandry practice.

4. Pathological lesions due to this species of Eimeria were not found in sections of intestinal tissues.

5. Developmental stages of this parasite were found throughout the whole of the small intestine.

6. The growth-retarding effects and oocyst production by E. mitis were controlled when 0·2% sodium sulphadimidine was given in the drinking water.

Chicks were given daily inoculations of 1 or 5 oocysts of Eimeria maxima or 5 or 20 oocysts of E. acervulina.

The inoculations ceased after 20 days with E. maxima or 25 days with E. acervulina when oocyst production had stopped. The responses to subsequent heavy challenges showed that with both species the immunity arising from the serial inoculations was stronger and/or more enduring than that produced by single inoculations of comparable numbers of oocysts.

Eimeria mitis and E. acervulina affect different areas of the intestine. Young chicks received E. mitis with or without E. acervulina in doses ranging from 2 to 128 × 104 oocysts. Mixed infections produced significantly more severe effects on growth than single infections of either species. The ratio of villus height to total mucosal thickness was reduced throughout the intestine in birds which received the mixed infection. E. mitis and E. brunetti affect the same area of the intestine. Single infections of E. brunetti in a range of doses from 1.25 to 20 × 103 oocysts produced a similar reduction in growth. When 20 × 103 oocysts of E. mitis were inoculated simultaneously, the effect on growth was not so severe and the oocyst output of both species was reduced. E. brunetti, superimposed 1, 2 or 3 days after an E. mitis infection, produced no greater effect on growth than E. mitis alone. Similarly, infections of E. mitis, superimposed on E. brunetti had no greater effect on growth than the latter species alone. Oocyst output of E. brunetti in superimposed infections was not reduced but peak output was delayed.

The structure and development of microgametocytes of Eimeria maxima from chicks killed during the 6th day of infection were examined using transmission and scanning electron microscopy. Initially, nucleoli disappear and the surface of the microgametocyte invaginates. This is followed by a condensation of the chromatin which then lies at the periphery of the nuclei. Concurrent with this, the flagella are formed and they project into the parasitophorous vacuole and internal invaginations. Eventually, the nuclei become more dense and are seen to protrude from the periphery of the gametocyte. The surface view of mature microgametocytes consists of a large number of closely packed flagella.

Coccidiosis occurs sporadically in lambs at about 6 weeks of age when oocyst output is very high in healthy as well as in diseased lambs. These experiments were designed to throw light on the source of infection and to correlate oocyst output in lambs and ewes with performance in lambs. In two experiments, one indoors on deep litter the other in outdoor paddocks, oocyst output (of different coccidial species), body weight and clinical state of lambs were recorded weekly. Oocyst output in ewes was also recorded, starting 1–4 weeks before lambing. Monensin was included in the concentrates of ewes and/or lambs, up to lambing or before and after lambing. No periparturient rise was detected in the oocyst output of ewes. Monensin drastically reduced oocyst output in animals receiving it. Oocyst output in lambs appeared to be little affected by the output of ewes around the lambing period, but was reduced if the ewes' output was kept low after lambing. Lambs receiving monensin tended to produce drier faeces but their weight gain was not significantly greater than that of controls. Eimeria crandallis was the predominant species in the lambs, followed by E. ovinoidalis and E. ovina.

A series of experiments is described in which two drug-resistant strains of Eimeria maxima were passaged together in untreated chicks. The resultant oocysts were then inoculated into chicks treated with both drugs. When strains resistant to methyl benzoquate and sulphaquinoxaline or clopidol and sulphaquinoxaline were used the resultant infections were not controlled by the double treatment, indicating the acquisition of resistance factors by one strain from the other. When strains resistant to clopidol and methyl benzoquate were used the phenomenon was not observed.

Daily infection with doses of approximately five oocysts of Eimeria tenella produced an infection with an extended patency which ceased by the time the birds had received about 140 oocysts. Total oocyst production was comparable with that in birds given the same number of oocysts in a single dose, but the immunity to subsequent heavy challenge was significantly greater. Continuous exposure to low-level infections may be more comparable to the field situation and the present results suggest how birds can acquire a strong immunity without showing evidence of clinical disease.

The development of strains of Eimeria maxima resistant to buquinolate, methyl benzoquate, clopidol, sulphaquinoxaline and robenidine is described. It was not possible to standardize a schedule of inoculations and drug administration, which would enable the development of resistance to the different drugs to be compared directly. Resistance developed most readily to the quinolones. One robenidine-resistant strain proved to be drug-dependent. Dinitolmide showed unusual effects upon sporogony and three attempts to develop resistance against this activity failed. Chicks previously immunized with the parent strain were completely protected against infection with the drug-resistant strains.

A series of observations on the feeding behaviour of a laboratory strain of Rhipicephalus appendiculatus on rabbits and measurements of the fluid consumption during feeding in vitro have been made.

Male and female ticks less than 5 weeks after moulting were less inclined to attach than older ticks.

Female ticks fed slowly during the early stages of attachment until after approximately 6 days of attachment when engorgement proceeded very rapidly and their body weight increased by approximately thirty times. Male ticks fed steadily until they roughly doubled their weight in approximately 7 days.

By an in vitro feeding technique in which whole blood, serum or plasma was offered in capillary tubes placed over the mouthparts, it was possible to measure the volumes absorbed over a period of 24 h. More serum or plasma was consumed than either defibrinated or heparinized blood. After 4 or 5 days’ attachment on a rabbit, females generally consumed greater volumes than males.

Dr G. H. Freeman, Head of the Statistics Division of the East African Agriculture and Forestry Organization, kindly carried out the statistical analysis of the quantitative data on the in vitro feeding.

Acknowledgements are also due to the technical staff who contributed to this work, especially to Mrs D. Backhurst. Mr K. P. Bailey maintained the colony of R. appendiculatus from which the ticks used in this study were derived.

This work was carried out during the assignment of one of us (L.P.J.) by the Food and Agriculture Organization of the United Nations to the East African Veterinary Research Organization.

A laboratory strain of Eimeria acervulina was found to develop in the caeca when large numbers of excysted sporozoites were injected into that organ. Both schizonts and gametocytes were formed, but parasitization of the caeca was never heavy and did not increase with serial passage. The infection was not increased by the simultaneous injection of betamethasone.