Showing papers in "Parasitology in 1981"

A quick, simple method for purifying Leishmania mexicana amastigotes in large numbers.

Abstract: A rapid method for the bulk isolation of purified Leishmania mexicana mexicana amastigotes from parasite-induced lesions in experimentally infected mice is described. The procedure includes purification steps based on differences in net cell charge, lysis susceptibility and buoyant density between parasite and host cells. Yields of up to 2 x 10(10) untransformed amastigotes with minimal contamination with host cells and cell debris can be obtained. At least 90% of the purified amastigotes are viable as judged by light and electron microscopy, the staining of their lysosomes with acridine orange, their ability to transform to promastigotes and their infectivity to macrophages in vivo and in vitro.

Analysis of antigenic types appearing in first relapse populations of clones of Trypanosoma brucei.

Abstract: Variant antigenic types (VATs) represented in a total of 47 first relapse populations of 6 clones of Trypanosoma brucei LUMP 227 were identified by immunofluorescent staining of living trypanosomes, using antiserum raised against purified surface antigens The relative growth rates of these 6 clones were measured both individually and when grown together in a mixed population, and were found to be different under these two sets of conditions A pattern emerged in the VATs represented in relapses of each clone, with some types being expressed more frequently than others and certain VATs being only very rarely expressed It is suggested that new VATs are expressed according to a statistically definable order of priority which is different for each parent VAT, and that some VATs may be able to change to certain others only after passing through an intermediate VAT The order of priority of appearance of VATs does not appear to correlate with growth rate measured either in individual clones or when clones are grown in a mixed population

Separation of Isospora (Toxoplasma) gondii cysts and cystozoites from mouse brain tissue by continuous density - gradient centrifugation

Abstract: A simple, quick and reproducible method consisting of density-gradient centrifugation of homogenized infected mouse brain tissue on Percoll is described for the isolation and purification of cysts of Isospora (Toxoplasma) gondii. A 100% recovery of cysts, with 74·2% in a single fraction with a specific gravity of 1·056, was obtained by overlaying homogenates of infected mouse brains on a pre-formed Percoll gradient and centrifugation at low g forces. With this procedure recovery was independent of the age of the cysts. Titration of purified cystozoites showed there to be no loss of infectivity.

Immune evasion by Schistosoma mansoni: loss of susceptibility to antibody or complement-dependent eosinophil attack by schistosomula cultured in medium free of macromolecules.

Abstract: Schistosomula of Schistosoma mansoni, recovered either after penetration of cercariae through isolated rat skin or by mechanical transformation of cercariae, become fully resistant after 24-48 h of culture to damage by human blood eosinophils in the presence of human anti-schistosomular sera. Cultured schistosomula are also shown to lose their susceptibility to attack by human eosinophils in the presence of human complement. This resistance is related to the simultaneous reduction of the ability of human anti-schistosomular antibodies and human complement component C3 to bind to the surface of the cultured larvae. The development of insusceptibility to antibody, complement and eosinophil-mediated attack does not require the acquisition by the schistosomula of a protective coat of host or other macromolecules, since it is achieved in chemically defined culture medium free of serum and macromolecules. This supports the hypothesis that schistosomula undergo intrinsic changes which render them insusceptible to immune attack.

Parasites and the fossil record

Abstract: Parasitologists are fond of alluding to the possible antiquity of their chosen group. They may even place the origin in a specific period of geological time and trace its co-evolution, or lack thereof, with the hosts. These speculations usually make only passing comments on the actual fossil record, but a critical examination suggests that this area can throw much light on both the origins and evolution of parasitism. This review is concerned primarily with the fossil record and its immediate implications. It does not appraise parasite evolution in the light of evidence from sources, often of excellent quality, such as comparative anatomy and physiology or ecology. As some parasitologists may not be entirely familiar with the geological column and time scale, Table 1 depicts these and indicates some records of parasitism mentioned here, together with the major events in this history of life.

Isolation and partial characterization of the tegumental outer membrane of adult Schistosoma mansoni

Abstract: Incubation of adult Schistosoma mansoni at 37 °C in chemically defined media caused the shedding of variable amounts of the parasite's tegument. In phosphate-buffered saline, pH 7·4, 37% of 125I-labelled wheat germ agglutinin which was attached to the schistosome surface was released within 5 min. When the released material was collected by centrifugation at 55000 g for 1 h, the pellet was seen to consist of components of the parasite tegument and contained 1% of the parasite protein and 6·2% of the 5′-AMPase activity. By monitoring the release of the gut enzyme, haemoglobinase, it was shown that predominantly tegumental material was released under these conditions. The material released from the parasite was separated by discontinuous sucrose gradient centrifugation into 4 major fractions and it was shown that a material banding at low density was highly enriched in vesicles of parasite outer membrane. Major polypeptides of apparent molecular weights 135000, 110000, 90000, 65000, 47000 and 40000 and glycoproteins of apparent molecular weights 135000, 120000, 65000, 63000 and 30–40000 were identified in this fraction. Comparison of the distribution of 5′-AMPase activity and the contents of each fraction as revealed by ultrastructural examination showed that this enzyme is a good marker for the tegumental outer membrane.

Epidemiology of East Coast fever: some effects of temperature on the development of Theileria parva in the tick vector, Rhipicephalus appendiculatus.

Abstract: The moulting behaviour of nymphal Rhipicephalus appendiculatus from the laboratory colony and 3 field strains from Kenya was greatly influenced by constant temperatures between 18 and 37 °C but was not significantly different for the 4 tick strains. Six batches of R. appendiculatus (Muguga laboratory) nymphs which had engorged on cattle parasitaemic with 4 stocks of Theileria parva (Kiambu 4, Kiambu 5, Muguga and Mbita 4) isolated in Kenya were incubated at constant temperatures between 18 and 37 °C during their pre-moult and post-moult periods. The Theileria infections in the salivary glands of the resultant adult ticks were assessed by staining with Feulgen's stain. Two stocks (Muguga and Kiambu 5) developed their highest infections in ticks incubated at 28 °C while the other two (Kiambu 4 and Mbita 4) developed their highest infections at 23 °C. Constant temperatures of 18, 33 and 37 ° C were detrimental to the development of salivary gland infections. Temperature influenced the rate of development and numbers of the earlier Theileria stages in the ticks. Engorged nymphal ticks incubated for 4 days at 37 °C during their pre-moult period developed lower infections than ticks exposed at 4 °C for 4 days.

Nutritional aspects of Ascaris infection in young protein-deficient pigs

Abstract: Experiments were carried out to investigate the effects of Ascaris suum infection on the growth, food intake, nitrogen and fat utilization and intestinal function of young pigs receiving diets low in protein. An infection procedure was developed which provided relatively uniform and heavy infections in pigs under study. Ascaris -infected pigs showed statistically significant reduction in growth rate and food intake compared to uninfected controls. The reduction in growth rate was observed after the A. suum were mature and eggs were observed in the faeces of pigs. The degree of growth retardation was significantly correlated with worm burden. Infected pigs showed no consistent reduction in nitrogen and total solids digestibility compared to controls but fat digestion was reduced. The infected pigs showed reduced nitrogen retention compared to uninfected controls. Ascaris -infected pigs had heavier intestinal tracts with increased size of the tunica muscularis . Lactase activity in mucosa from infected pigs was significantly lower than in controls, whereas no consistent effect was observed in mucosal sucrase and maltase activity. When Ascaris -infected pigs were given an oral lactose load, blood glucose levels rose less than in control pigs, suggesting that the infection resulted in impaired lactose tolerance.

An improved technique for the cryopreservation of Onchocerca microfilariae

Abstract: Experimental describe the use of ethanediol to store Onchocerca microfilariae in liquid nitrogen. The technique involves a 2-stage incubation of the parasites at 37 degrees C and 0 degrees C in ethanediol, before rapid cooling to -196 degrees C. Viability has been assessed by motility, by migration in a proxy host and by development to the infective stage in the insect vector. A total of 71-79% of the cryopreserved microfilariae was shown to be viable compared to unfrozen controls. The technique is simple, inexpensive and very effective when compared to previous cryopreservation procedures for microfilariae and should be particularly suited for use under field conditions.

Cultivation of infective forms of Trypanosoma congolense from trypanosomes in the proboscis of Glossina morsitans.

Abstract: Two stocks of Trypanosoma congolense were established in culture at 28 degrees C using trypanosomes from the proboscides of infective Glossina morsitans. Successful primary cultures were initiated by placing an infected tsetse proboscis beside a bovine dermal collagen explant in Eagle's minimum essential medium supplemented with foetal calf serum. The trypanosomes multiplied rapidly in the medium and also gradually formed an adherent layer o the plastic surface of the culture vessel. Three primary cultures produced organisms infective for mice from 14, 20 and 35 days after initiation and thereafter continuously until days 76, 76 and 52 when they were discarded. Four attempts to initiate infective cultures using infected tsetse proboscides in medium without dermal explants were unsuccessful. When trypanosomes from primary cultures were placed in culture medium with proboscides from uninfected tsetse flies, the parasites multiplied, formed an adherent layer in the culture flasks and were seen in the proboscides within 24 h. A line of 1 stock was serially sub-passaged in this way 4 times during a period of 215 days. Infectivity titrations in mice indicated that primary and sub-passaged cultures each contained similar numbers of infective organisms. Another line of the same stock was also sub-passaged 4 times in medium alone over a period of 186 days. These sub-cultures again retained infectivity for mice, but titrations showed a decrease in infective organism production in the 4th sub-culture. Primary and sub-passaged cultures all included a variety of morphologically different developmental forms of T. congolense, closely resembling those described in the labrum and hypopharynx of Glossina by previous workers. Short metacyclic-like trypanosomes and organisms with proteinaceous surface coats were present in infective cultures. Cultures were successfully re-established after cryopreservation at -196 degrees C and retained the ability to produce infective organisms.

Hatching mechanisms of nematodes

Abstract: Investigations of nematode hatching have concentrated on the parasitic forms, especially on synchronization between host and parasite life-cycles which, in some species, is so close that the parasite is dependent on the host for the hatching stimulus. Research into nematode hatching reflects the artificial separations created throughout nematology by defining research groups and their activities in terms of the host; consequently, useful comparisons between hatching of plant and animal parasitic nematodes have been few. With the increasing use by geneticists of nematodes as model animals and the interest in them by neuro-physiologists, molecular biologists and others, we hope that such distinctions will be lessened.

Effects of Ostertagia circumcincta infections on plasma gastrin in sheep.

Abstract: Radio-immunoassay of plasma gastrin showed that hypergastrinaemia developed in sheep during experimental infections with Ostertagia circumcincta. Elevations of plasma gastrin occurred within 8 days of the first dose of infective larvae, with the most marked increase being after 11-20 days when adult worms would be expected to be present in the abomasum. Increases of plasma gastrin levels from 69.0 +/- 7.6, 28.7 +/- 5.3, 48.7 +/- 5.9 and 60.6 +/- 9.4 pg/ml before infection to maxima of 650, 230, 900 and 750 pg/ml respectively were recorded in 4 sheep infected for the first time. In 2 others which had been previously infected and then treated with anthelmintic, plasma gastrin rose from 16.0 +/- 4.0 and 377 +/- 87 pg/ml to maxima of 260 and 900 pg/ml at 24 and 29 days after re-infection, respectively. The cause of hypergastrinaemia has not been established. The elevation of abomasal pH which occurs in ostertagiasis may result in increased gastrin levels but is thought not to be the only cause since plasma gastrin increased before the abomasal pH rose and developed in sheep infected for a second time although their abomasal contents remained at pH 4.0 or lower. The presence of the parasite is critical for development of hypergastrinaemia as shown by return of the gastrin level to normal following therapy with an anthelmintic. It was shown that the parasites do not depend on the hypergastrinaemia since O. circumcincta became established in antrectomized sheep in which hypergastrinaemia did not develop.

Infections with blood parasites in the small British rodents Apodemus sylvaticus, Clethrionomys glareolus and Microtus agrestis.

Abstract: Three populations of small wild British rodents were studied by capture–recapture methods over a period of 3 years, a fourth group was studied for 1 year and a fifth was sampled annually for 4 years. Blood smears were taken from 3 species of rodents: the woodmouse A podemus sylvaticus, the bank vole Clethrionomys glareolus (and an island sub-species C.g. skomerensis) and the short-tailed vole Microtus agrestis. The smears were examined microscopically. Four genera of haemoparasites Babesia, Hepatozoon, Trypanosoma and Grahamella were detected. Babesia was absent from C.g. skomerensis, Hepatozoon was rarely found in A. sylvaticus and M. agrestis and Trypanosoma was rare in A. sylvaticus. More males were infected than females but the difference was only statistically significant for the infection with Hepatozoon in adult C.g. skomerensis. Infections with Babesia and Hepatozoon were more prevalent in adult animals and infections with Trypanosoma were more prevalent in younger individuals. Only in C.g. skomerensis was there a significant difference between age classes in the prevalence of infection with Grahamella – there being more adults infected. Concurrent infections were detected, Hepatozoon being the parasite most commonly involved. The prevalence of infections was found to be approximately proportional to the number of animals known to be alive, regardless of the season.

Changes in the food intake and body weight of protein-malnourished rats infected with Nippostrongylus brasiliensis (Nematoda)

Abstract: The daily food intake and related changes in body weight were measured in young rats which were fed on synthetic diets containing 1% (3 experiments), 2% (4 experiments) and 20% (1 experiment) casein respectively. Some rats were infected with Nippostrongylus brasiliensis and allowed to feed ad libitum , some remained uninfected and were allowed to feed ad libitum while others, which were matched by initial weight with rats from the infected group, remained uninfected and were given only the same amount of food as that consumed during the previous 24 h by their infected partners. No significant differences were detected between the rats before the start of the infection. Thereafter, the food intake of the infected undernourished rats was usually found to be significantly lower and the loss of body weight significantly greater than those of the uninfected rats. In infection periods of relatively long duration, the pair-fed uninfected rats did not lose as much weight as their infected partners even though their food intake (1% and 2% casein) was the same. Although the food intake, and consequently the weight, of infected rats fed on the diet containing 20% casein were significantly less than in their uninfected partners, no significant differences were observed between the weights of the infected and pair-fed rats fed on this diet.

Monitoring Theileria parva infection in adult Rhipicephalus appendiculatus ticks

Abstract: A rapid method is described for preparing and staining salivary glands of Rhipicephalus appendiculatus ticks infected with Theileria parva. The technique, involving the use of a modified methyl green pyronin stained minimizes the risk of losing material and allows examination of stained glands within minutes of preparation. The technique was applied in a series of studies in which ticks were either infected with T. parva under different conditions, or maturation of parasites in adult ticks was stimulated by different means. When nymphal ticks were fed on the ears of cattle the subsequent infection rate of the adult ticks showed no correlation with the parasitaemia of the cattle at the time of nymphal engorgement. There was no difference in infection rates between adult ticks in which parasite maturation had been stimulated either by incubation at 37 degree C or by feeding on rabbits. However, parasite maturation took about 1 day longer in incubated ticks than in rabbit-fed ticks. Female ticks were consistently more highly infected than males, both in terms of the percentage of ticks infected and the mean number of infected acini/tick. Ticks were infected with T. parva by injection of nymphs with parasitaemic bovine blood, but the resultant adult infection was lower than that in ticks which had been infected naturally by feeding on cattle.

Antigenic variation in cyclically transmitted Trypanosoma brucei. Variable antigen type composition of the first parasitaemia in mice bitten by trypanosome-infected Glossina morsitans.

Abstract: Tsetse flies were infected with 5 different variable antigen types (VATs) or with a mixture of VATs of the AnTAR 1 serodeme of Trypanosoma brucei . Metacyclic forms from the salivary glands of infected flies were used to initiate infections in mice. Immunofluorescence and trypanolysis reactions employing 24 monospecific antisera were used to analyse the VATs present in the mice following cyclical transmission. Regardless of the VAT used to infect tsetse flies, the first VATs detectable in the bloodstream were those previously identified as metacyclic VATs (M-VATs). These were present until at least 5 days after infection, at which time lytic antibodies against at least 2 of the M-VATs were detectable in the blood of infected mice. In mice immunosuppressed by X-irradiation the M-VATs were detectable in the bloodstream for longer periods, but the percentage of the population labelled with anti-metacyclic sera showed a decrease on day 5 as in non-irradiated animals. The VAT ingested by the tsetse was always detectable early during the first parasitaemia following cyclical transmission and was usually the first VAT detected after the M-VATs. Neutralization of selected M-VATs before infecting mice resulted in elimination of the neutralized M-VAT from the first parasitaemia but had no effect on the expression of other VATs in the early infection.

Trematode–gastropod associations in nine non-lacustrine habitats in the Mwanza region of Tanzania

Abstract: Between August 1978 and July 1979, freshwater gastropods were collected at monthly intervals from 9 different non-lacustrine habitats in the Mwanza region of Tanzania. Of a total of 11708 gastropods representing 14 species, 1748 (14–9%) were infected with trematode sporocysts and/or rediae. Altogether 38 morphologically distinguishable ‘species’ of cercariae were recovered (13 furcocercous, 10 xiphidiocercaria, 6 echin-ostome, 4 cystophorous, 3 gymnocephalous and 2 amphistome species), 22 of which did not conform to previously described African species. The majority (63–8%) of all mature infections were xiphidiocercariae. Biomphalaria pfeifferi, B. sudanica and Ceratophallus natalensis each yielded 11 species of cercariae. Lymnaea natalensis had the highest overall prevalence of infection (36–9%). Cercaria guttera from L. natalensis accounted for 20–4% of all recovered trematode infections and C. blukwa from Biomphalaria accounted for 18–4% of all infections; the high prevalence of these two xiphidiocercariae may alter the transmission patterns of Fasciola gigantica and Schistosoma mansoni, respectively. S. mansoni was recovered from both B. sudanica (22 of 2393 infected) and B. pfeifferi (79 of 1913 infected); S. haematobium (or related species) was recovered from Bulinus (Physopsis) nasutus (50 of 1503 infected) and to a lesser extent from B. (P.) africanus (6 of 186 infected). The findings are discussed in relation to the biological control of trematode diseases in Tanzania.

New defined and semi-defined media for cultivation of the flagellate Trichomonas vaginalis

Abstract: Studies on the nutrition and physiology of Trichomonas vaginalis have been hampered by the lack of a defined synthetic medium in which to grow the organism. New synthetic media free of ill-defined supplements and serum which support good growth of T. vaginalis have been developed in this study. The first successful approach to a defined medium resulted from the modification of the tissue-culture medium CMRL 1066. Essential modifications included (1) lowering the redox potential of the medium by adding high levels of ascorbate and (2) modifying the buffer system. Subsequently, CMRL 1066 was replaced by two new media DL7 and DL8 which have greater flexibility in their formulation and permit improved serum-free growth. Serum was replaced by bovine serum albumin and cholesterol, together with either a glyceryl fatty acid ester or a defined mixture of fatty acids. Preliminary nutritional studies using the new media have indicated a requirement for saturated and unsaturated fatty acids and a sterol.

Acquired immunity against Trypanosoma danilewskyi in goldfish, Carassius auratus.

Abstract: Two groups of goldfish maintained at 20 degrees C were experimentally infected with two different sized inocula of Trypanosoma danilewskyi. One group was inoculated with 380,000 trypanosomes/fish and the other with 3800. Forty and 90% of the fish, respectively, survived. All surviving fish challenged 190 days post-infection were protected from re-infection. The plasma of these fish when inoculated into another group of fish also protected them from infection. Finally, trypanosomes incubated in vitro in immune plasma at 20 degrees C for 2 h were not infective; however, incubations at 5 degrees C or for 1 h were not as effective.

Cellular immune response of Drosophila melanogaster against Asobara tabida

Abstract: The successful cellular immune response of larvae of D. melanogaster against A. tabida is characterized by an increase in the number of blood cells, a premature transformation of spherical plasmatocytes to flattened, disc-shaped lamellocytes, and the lysis of crystal cells. The plasmatocytes and transformed lamellocytes rapidly aggregate around the eggs of the parasite to form a cellular capsule, while the lysing crystal cells release substances causing the melanization of the capsule. The early appearance of large numbers of transformed blood cells in the haemolymph prior to their involvement in capsule formation suggests that transformation is independent of cell contact with the parasite and may be due instead to biochemical stimuli emitted from the parasite and/or by hormonal changes. Quantitative blood cell studies of hosts exhibiting no encapsulation and melanization response indicate that successfully developing parasites are recognized by the immune system but are able sufficiently to block the blood cell transformation and thus prevent capsule formation.

The initial stages of infection of cattle cells with Theileria parva sporozoites in vitro.

Abstract: Large numbers of Theileria parva sporozoites were separated from Rhipicephalus appendiculatus adult ticks by filtration and were then concentrated by centrifugation. The sporozoites were incubated at 37 degrees C with leucocytes from 6 cattle of Bos indicus and B. taurus types. Giemsa-stained smears and living preparations under interference contrast microscopy were used to follow the course of the infection of the leucocytes with sporozoites. Sporozoites were seen to attach rapidly to about 25% of the leucocytes which they penetrated. After penetration by the sporozoites the morphology of the cells changed to show an increase in cytoplasm and an enlargement of the Golgi apparatus, with which the parasite appeared to become associated. The early intracellular or preschizont stages resembled Babesia parasites. From day 3, the parasite showed the typical morphology of the macroschizont of T. parva. Multiple infections were frequent and up to 8 schizonts were observed arranged around the Golgi apparatus. Multiple infected cells did not survive in culture but some of the cells infected with a single parasite divided to produce 2 infected daughter cells and infected lymphoblastoid cell lines were established in all 21 attempts.

The interaction in vitro between bovine immunoglobulin and juvenile Fasciola hepatica.

Abstract: Freshly excysted Fasciola hepatica possess an outer glycocalyx which stimulates an antibody response in cattle infected with F. hepatica metacercariae. Sera from animals receiving either a single or a double infection were examined for levels of IgM, IgG1 and IgG2 specific for the outer glycocalyx of intact live juvenile F. hepatica. High levels of specific IgG1 were found to predominate. Using positive sera in an indirect fluorescent antibody assay, the bovine immunoglobulins labelled the outer glycocalyx in a characteristic reticulated pattern. On incubation at 37 degrees C this pattern rapidly broke up into discrete clumps and progressed until the entire antibody-outer glycocalyx complex was shed. The shedding phenomenon was shown to be continuous and, by using preparations of Fab fragments, was not due to the bivalent binding of the sensitizing antibody.

Parasite utilization of a host community: the distribution and occurrence of metacercarial cysts of Echinoparyphium recurvatum (Digenea: Echinostomatidae) in seven species of mollusc at Harting Pond, Sussex

Abstract: The occurrence, in September 1979, of Echinoparyphium recurvatum metacercarial cysts in a community of molluscan hosts at Harting Pond, West Sussex, was investigated. The parasite exhibited broad host specificity with all 7 species comprising the molluscan community being infected. There were marked differences, however, in the extent to which each host species was utilized and using the mean number of parasites/ individual mollusc as a parameter of infection the mollusc species may be ranked in descending order of utilization as follows: Sphaerium corneum, Lymnaea peregra, Valvata piscinalis, planorbids, Pisidium subtruncatum and Potamopyrgus jenkinsi. Combination of basic infection data with population estimates for each mollusc species in the study area showed that the bivalve P. subtruncatum and the prosobranch V. piscinalis were the most important hosts because they contained approximately 90% of the total number of cysts. In both of these hosts the cyst population was over-dispersed and the degree of over-dispersion increased with host size. The pattern of second intermediate host utilization is discussed in relation to the likely flow of E. recurvatum between the first intermediate host (L. peregra) and wildfowl definitive hosts at Harting.

Schistosoma mansoni : an examination of the reproductive status of females from single sex infections

Abstract: The variation in the development of the reproductive system of female Schistosoma mansoni from single sex infections is described. Vitelline cell development was assessed by staining for phenolic substances and the development of Mehlis' gland and the ovary by electron microscopy. Although there was considerable variation in the development of worms from individual mice harbouring infections of the same age, the mean values indicated that there was a low level of differentiation and turnover of vitelline cells in worms 30–200 days post-infection. The proportion of females which possessed mature vitelline cells showed a general increase with age. The ovary was always in an immature stage but the development of Mehlis' gland showed some variation. The results suggest that the stimulus given by the male to the female is not necessarily to initiate development of the reproductive system but to increase the rate of development of the vitelline gland and to co-ordinate the development of the entire reproductive system.

Genetic control of liability to infection with Nematospiroides dubius in mice: selection of refractory and liable populations of mice.

Abstract: Quackenbush strain and wild Mus musculus were assayed for their liability to primary infection with 100 L3 Nematospiroides dubius using an experimentally derived selection index. Refractory and liable colonies of mice were established over 5 generations. Liability to N. dubius infection was found likely to be controlled by several genes; the heritability (h2) of this trait was estimated at 0–45. Positive linear correlation was found between the number of parasite eggs voided and the number of adult N. dubius recovered, negative correlation between the pre-patent period of infection in days and the number of parasite eggs voided and positive correlation in 2 of 5 generations between live mouse body weight and the number of adult N. dubius recovered. Further, positive correlation was found between the liability of female mice to N. dubius and their progeny litter size number. The genetic mechanisms controlling the liability trait and the possible evolutionary significance of these results are discussed.

Eimeria acervulina and E. mivati: oocysts, life-cycle and ability to develop in the chicken embryo.

Abstract: 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.