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Showing papers in "Parasitology in 1971"


Journal ArticleDOI
TL;DR: From the overdispersed frequency distributions exemplified by the Negative Binomial distribution a specially truncated form is derived and shown to fit the data of Hynes & Nicholas (1963) and these form the basis of a definition of parasitism.
Abstract: The frequency distribution of parasites among hosts is used as the basis of the quantitative assessment of the nature of parasitism. The host–parasite system is regarded as an ecological relationship between populations of two different species of organisms. From the overdispersed frequency distributions exemplified by the Negative Binomial distribution a specially truncated form is derived and shown to fit the data of Hynes & Nicholas (1963). The theoretical consequences are discussed and these form the basis of a definition of parasitism. I am indebted to Professor H. B. N. Hynes who so readily understood my general aims and freely provided detailed information about his work. I also have great pleasure in thanking Professor John H. Whitlock, not only for the original computing facilities which he so generously provided, but also for his many other kindnesses. I am also very grateful to Dr Charles Henderson Jun. for his work on the original computer program and to Dr Mark Westwood for his ingenuity and labours in producing a new approach to the computations.

638 citations


Journal ArticleDOI

269 citations


Journal ArticleDOI
TL;DR: All three species of parasites found in sticklebacks from Priddy had overdispersed distributions, similar in shape to host–parasite distributions described by other authors, and the shape and parameters of the original distribution have been investigated.
Abstract: All three species of parasites found in sticklebacks from Priddy had overdispersed distributions, similar in shape to host–parasite distributions described by other authors.The distributions of both Echinorhynchus clavula and Diplostomum gasterostei were fitted closely by the negative binomial. The values of k were similar for both species, being always less than unity; the Diplostomum distributions were more overdispersed and therefore had higher values of p.The Schistocephalus distributions were mostly described by the log normal, but the high percentage infection and relatively low overdispersion meant that the fit was often not close. There was also some truncation at the upper end.The relationship between the parameters of the negative binomial (p and k) and the shape and parameters of the original distribution have been investigated, both theoretically and with respect to the distributions of the stickleback parasites.In general p varied as the overdispersion and k as the percentage infection.The advantages of an overdispersed distribution to the host and parasite populations are discussed and related to the life cycles of the parasites.I am most grateful to Dr H. D. Crofton for his help and encouragement during this study, and to the staff of the Computer Unit, University of Bristol for their assistance with programming problems. This work was supported by a Science Research Council research studentship and a NATO studentship.

151 citations


Journal ArticleDOI
TL;DR: It is indicated that for the successful artificial feeding of tsetse, it is essential to circulate the blood and regulate the temperature of the medium and the feeding surface to approximately 36 °C.
Abstract: An apparatus for the artificial feeding of tsetse has been described. Fresh defibrinated blood at 36 °C is circulated with a peristaltic pump through feeding capsules. The efficiency of the method has been compared with that of the Cockings' method and with the live host feeding. The flies exposed to feeding on this apparatus showed significantly higher feeding frequency than those allowed to feed on the Cockings' apparatus. Compared with the live host feeding, the feeding frequency for circulating blood method was slightly lower but the difference was not significant. Once the fly is induced to feed, it would in most cases complete engorgement unless disturbed. The rate of crop emptying in flies fed by the Cockings' method was abnormally slower as compared to those fed on the circulating blood. The present study indicates that for the successful artificial feeding of tsetse, it is essential to circulate the blood and regulate the temperature of the medium and the feeding surface to approximately 36 °C.I wish to thank Mr S. B. Kutuza for technical help, and the Director of E.A.T.R.O. for permission to publish this work.

102 citations


Journal ArticleDOI
TL;DR: In general the infections increased in summer and autumn and decreased in winter and spring, although in Schistocephalus the differences in the level of infection between the two years were greater than between seasons.
Abstract: A population of three-spined sticklebacks, Gasterosteus aculealus, from a pond in Somerset was sampled about every three weeks for 19 months, a total of 1863 fish being collected. Three species of parasites were found in the fish: Schistocephalus solidus, Diplostomum gasterostei and Echinorhynchus clavula.Seasonal changes in the incidence and intensity of the three parasitic infections are described. In general the infections increased in summer and autumn and decreased in winter and spring, although in Schistocephalus the differences in the level of infection between the two years were greater than between seasons.The largest increases in the Schistocephalus and Echinorhynchus infections occurred in August and September and in the Diplostomum infection in May and June. These increases could be related to the feeding activity of the sticklebacks and to the abundance and level of infection of the Cyclops, Asellus and Limnaea pereger populations.Reduction in the sizes of the infections was by predation and death of heavily infected fish in the case of Schistocephalus and Diplostomum and mainly by death of individual worms in Echinorhynchus.These mechanisms are shown to be adapted to the life cycles of the parasites.I am most grateful to Dr H. D. Crofton for his help and encouragement during this investigation and to Dr R. A. Avery for useful discussions and advice. This work was supported by a Science Research Council research studentship and a NATO studentship.

86 citations



Journal ArticleDOI
TL;DR: A population of Gasterosteus aculeatus from Priddy pool in Somerset was infected with three species of parasites: Schistocephalus solidus, Diplostomum gasterostei and Echinorhynchus clavula, which suggested that the old fish are becoming senile and are therefore less able to support large parasite burdens.
Abstract: A population of Gasterosteus aculeatus from Priddy pool in Somerset was infected with three species of parasites: Schistocephalus solidus, Diplostomum gasterostei and Echinorhynchus clavula. The variations in the incidence and intensity of the infections with the sex, age and size of the sticklebacks are described.The infections with the three parasites were very similar in male and female sticklebacks. The weights of Schistocephalus were greater in the females, however;the mean weight of the plerocercoids was larger suggesting that they grew more rapidly in female fish.The Schistocephalus infection increased in small fish, under 1 year of age, but in older larger ones the infection decreased. These changes can be related both to the feeding habits of the fish and to the weight relationships of host and parasite.It was found that the weight of Schistocephalus did not greatly exceed that of the fish, and also that the combined weight of fish plus Schistocephalus was rarely greater than 3 g. Therefore the proportional weight of Schistocephalus, or parasite index, was lower in sticklebacks heavier than about 1·5 g.The Diplostomum and Echinorhynchus infections both increased with age and size of fish, but the largest sticklebacks were not the most heavily infected. These increases can be related to the feeding habits of the fish in the case of Echinorhynchus and to accumulation with time in the case of Diplostomum.In all three species the largest and oldest fish were not the most heavily infected.It is suggested that the old fish are becoming senile and are therefore less able to support large parasite burdens.I am very grateful to Dr H. D. Crofton for his constant advice and encouragement during this study, and to Dr R. A. Avery for useful discussions. This work was supported by a Science Research Council research studentship and by a NATO studentship.

76 citations


Journal ArticleDOI
TL;DR: It was concluded that under the levels of inoculation employed during the study there were no significant effects of A. galli infections on blood protein values as well as p.c.v. and Hb.
Abstract: The pathogenicity and pathology of Ascaridia galli infections of poultry were studied using repeated doses of varying numbers of eggs No significant effect due to infection was seen on pcv and Hb values of infected chickens Haemo concentration occurred parallel with sporadic diarrhoea, which follows high levels of repeated dosing This phenomenon complicated the interpretation of blood protein values A/G ratios were, however, worked out and analysed No significant differences were noticed between the groups and it was concluded that under the levels of inoculation employed during the study there were no significant effects of A galli infections on blood protein values as well as pcv and Hbvalues of infected chickensSymptomatic developments, macroscopic lesions and pathological changes of intestinal tissues due to infection were followed up in detail They were most severe in chickens on the least nutritive diet and sustaining the highest levels of repeated doses Pathogenicity of larval and adult parasites was described The presence of large numbers of adult parasites was associated with intestinal obstruction in host This was seen mostly in chickens on low nutrition and sustaining either low or high levels of repeated inoculation, and very rarely also in chickens under high plane of nutrition but sustaining repeated inoculation of small numbers of eggs Cellular infiltration as a result of infection was found to be extremely rareIt was present as fibroblasts and only in association with dead larvaeThe author is indebted to the Department of Technical Cooperation, under whose Fellowship the study was carried out; the Department of Zoology, Edinburgh University, for facilities provided; the Ministry of Agriculture, Fisheries and Food; Lasswode Poultry Research Laboratories, for the free supply of chickens used here; Dr J A Campbell of Edinburgh University for his keen interest, encouragement and advice throughout this work; and finally to G Obiwelozor for reproducing the photographs from the original manuscript

65 citations


Journal ArticleDOI
TL;DR: The transmissibility of thetrypanosomes was assessed on the bases of the infection rates in tsetse flies used to transmit the strains and the periods required for the development of the trypanosome in the flies and bovine hosts.
Abstract: Two strains of T. congolense and two strains of T. vivax, resistant to normal therapeutic doses of trypanocidal drugs, were transmitted by G. morsitans and G. tachinoides through series of cattle in the absence of drugs to assess the transmissibility of the trypanosomes by tsetse flies and the stability of drug resistance in the organisms during cyclical development. The characteristics of both strains of T. vivax and one strain of T. congolense were typical of the species, but the infectivity of the second strain of T. congolense for laboratory animals was abnormally low. The transmissibility of the trypanosomes was assessed on the bases of the infection rates in tsetse flies used to transmit the strains and the periods required for the development of the trypanosomes in the flies and bovine hosts. The transmissibilities of both strains of T. vivax and the first strain of T. congolense were normal by comparison with data obtained by cyclically transmitting non-resistant trypanosomes of the same species, but the period required for the development of the second strain of T. congolense in tsetse flies was abnormally long. There was no loss of drug resistance in any of the strains examined in the experiments. A strain of T. congolense retained resistance to diminazene aceturate at a dose rate of 7-0 mg/kg, homidium chloride at 2-0 mg/kg, quinapyramine sulphate at 4-4 mg/kg and isometamidium chloride at 0-5 mg/kg during a series of eight transmissions by tsetse flies in a period of 376 days.

64 citations




Journal ArticleDOI
TL;DR: Acetylcholinesterase activity, measured per unit wet weight, is relatively low in the eggs and infective larvae of N. brasiliensis but increases rapidly during the parasitic phase, especially in the late 3rd- and early 4th-larval stages.
Abstract: Acetylcholinesterase activity, measured per unit wet weight, is relatively low in the eggs and infective larvae of N. brasiliensis. It increases rapidly during the parasitic phase, especially in the late 3rd- and early 4th-larval stages. Activity in normal adults is extremely high (× 15 egg activity) and this is doubled again in immune-damaged adults. Possible functions of N. brasiliensis acetylcholinesterase are discussed.It is a pleasure to acknowledge the technical assistance of Miss Anne Cronin and Miss Beryl Crooks.


Journal ArticleDOI
TL;DR: There is a close correlation between the concentrations of pyrimethamine and trimethoprim required to inhibit the dihydrofolate reductase in a cell-free system and the growth of the parasite in vitro.
Abstract: A dihydrofolate reductase has been isolated from free-parasite preparations of the primate malarial parasite, Plasmodium knowlesi. Its properties are similar to those reported for the enzyme from the rodent malarial parasite, P. berghei, even though the base compositions of the DNA of these two species are quite different. The Kms for substrate and cofactor are 3 × 10−6M and 1 × 10−6M respectively and the molecular weight is ˜ 200000. Concentrations of pyrimethamine and trimethoprim as low as 1 × 10−9M and 3 × 10−8M respectively are sufficient to cause 50% inhibition of enzyme activity. The sensitivity to inhibition by pyrimethamine and trimethoprim of growth of cultures of P. knowlesi has also been investigated. Preliminary experiments showed that it was only the schizont stage that was susceptible to the action of the drugs and that in their presence, normal nuclear divisions and segmentation did not occur and subsequently, no reinvasion of fresh red cells took place. The minimum concentrations of drug required to produce these effects were 10−9M for pyrimethamine and 10−7M for trimethoprim. Thus, there is a close correlation between the concentrations of pyrimethamine and trimethoprim required to inhibit the dihydrofolate reductase in a cell-free system and the growth of the parasite in vitro. Pyrimethamine (10−9M) did not, however, affect the incorporation of radioactive precursors into DNA, RNA or protein of schizont stage parasites until after morphological damage could be seen and reinvasion was complete in control cultures. The time courses of incorporation of [14C]algal protein hydrolysate into protein in the presence (10−9M) or absence of pyrimethamine are the same as those described recently with immune serum. The possibility is thus raised as to whether pyrimethamine and immune serum act in the same way.One of us (P.I.T.) received financial assistance from the World Health Organization. We thank Dr F. Hawking for many helpful discussions, Miss Jane Dunnett and Mr T. Scott-Finnigan for technical assistance and Dr O. D. Standen for samples of pyrimethamine and trimethoprim.



Journal ArticleDOI
TL;DR: The population dynamics of Ascaridia galli infections of poultry was studied under repeated doses of 10, 100 and 1000 eggs and it was postulated that the ‘tissue phase’ phenomenon is not an obligatory part of the normal life-cycle of the parasite but represents a reaction to factors of resistance inherent in chickens and controlled by a complex dynamic interplay of dose size and the chickens.
Abstract: The population dynamics of Ascaridia galli infections of poultry was studied under repeated doses of 10, 100 and 1000 eggs. Daily doses were continued for 6 weeks only. At low dose rates patency is noted by the fifth week. At higher dose rates there is an accumulation of larvae whose development has been arrested at a precise developmental stage, i.e. the third larval stage. Sporadic development of some of these larvae to adults occurs later. Arguments are produced to show that this inhibition of larval development is a resistance and not a density-dependent phenomenon. The epidemiological significance of this inhibition is discussed. This resistance phenomenon is shown to occur in single infection experiments where 1000 eggs were used. This gives rise to the development of a worm population of two facies. The whole finding is suggested to be related in some way to the phenomenon of ‘tissue phase’, which is accepted as a normal life-cycle behaviour of this parasite. A brief review of previous work on this is given and it is postulated that the ‘tissue phase’ phenomenon is not an obligatory part of the normal life-cycle of the parasite but represents a reaction to factors of resistance inherent in chickens and controlled to a large extent by a complex dynamic interplay of dose size and the chickens.I wish to thank the Department of Technical Co-operation and the Federal Government of Nigeria for financing this project, Dr Boulton of the Poultry Research Centre, Edinburgh, for advice on nutrition, and the Department of Zoology, especially Dr J. A. Campbell, University of Edinburgh, for facilities and advice on the work. I am greatly indebted to the Ministry of Agriculture, Fisheries and Food, Poultry Research Laboratories, Lasswade, for the free supply of chickens used in this work.

Journal ArticleDOI
TL;DR: It is suggested that the kinetics of low-level repeated infections of Nippostrongylus brasiliensis in the laboratory rat more closely approximate those found under natural conditions than do those of a ‘classical’ laboratory infection.
Abstract: The kinetics of low-level repeated infections of Nippostrongylus brasiliensis in the laboratory rat were studied. The administration of five infective larvae each weekday to the rats produced an infection which was cumulative over 16 weeks and which did not produce an acute host immune response. The repeated administration of 50 larvae/weekday produced a primary immune response after 14 days. This caused partial worm expulsion and the suppression of egg output but the resistance of these rats to reinfection was not as pronounced as that seen in classical laboratory infections where heavier but less frequent larval exposures are used. The secondary worms that established in these rats did not elicit an acute host immune response even when the worm burden was as high as 756 worms. It is suggested that the kinetics of this type of infection more closely approximate those found under natural conditions than do those of a ‘classical’ laboratory infection. We wish to thank Misses G. Merchant, L. Cleaver and J. Cobb for able technical assistance, and Dr B. M. Ogilvie (National Institute for Medical Research, Mill Hill, London) for her helpful comments and discussions.


Journal ArticleDOI
TL;DR: Differences in the arrangement of the midgut tissues in adult and larval T. molitor were detected and shown to account for the failure of hexacanths to complete migration in the larvae.
Abstract: The hatching of Hymenolepis diminuta eggs and penetration of the emergent hexacanths in adult and larval Tenebrio molitor beetles had been described. Hatching was shown to be a two-stage process involving rupture of the eggshell by the insect's mandibles and digestion of the remaining egg-layers in the midgut lumen. Penetration of hatched embryos was examined by histological methods that demonstrated the rate of migration and the route taken by hexacanths entering the haemocoel of adult beetles. Differences in the arrangement of the midgut tissues in adult and larval T. molitor were detected and shown to account for the failure of hexacanths to complete migration in the larvae. The role of the embryonic hooks and penetration gland secretions during hatching and penetration has also been discussed.I should like to thank Professor T. R. E. Southwood for providing generous research facilities, Dr June Mahon for her advice and encouragement, and in particular, Dr W. Mordue for his continuous interest and many useful criticisms. This work was conducted during the tenure of a Science Research Council Studentship at Imperial College of Science and Technology, London, S.W. 7.


Journal ArticleDOI
TL;DR: Demodex carolliae, a parasite of the bat Carollia perspicillata, is described for all stages of its life cycle in this article, and the sequences and adaptive features of this life cycle are detailed.
Abstract: Demodex carolliae, a parasite of the bat Carollia perspicillata, is described for all stages of its life cycle. The sequences and adaptive features of this life cycle are detailed. Some information is presented on the population structure and the pathogenicity of this species.This research was supported in part by Grant W83–1 to Dr F. Lukoschus from the Netherlands Foundation for the Advancement of Tropical Research (WOTRO).


Journal ArticleDOI
TL;DR: The speed of the response to the parasite indicates that circulating antibodies produced in response to C. laticeps cannot be involved in the rejection, and the factors responsible for the death of the parasites became effective within this period.
Abstract: Farm-reared Leuciscus idus were experimentally infected with the intestinal tapeworm Caryophyllaeus laticeps, and maintained at different temperatures. At 12 °C and lower temperatures there was an initial loss of parasites after infection, but the survivors persisted for up to 1 month. At 18 °C only temporary survival of the parasite was possible, and worms were killed and rejected after 3 days. Experimental transplants to fresh hosts after 2 days indicated that the factors responsible for the death of the parasites became effective within this period.Neither inhibition of peristalsis nor host starvation affected the parasite's survival. The speed of the response to the parasite indicates that circulating antibodies produced in response to C. laticeps and directed specifically against it cannot be involved in the rejection. Other possible mechanisms of rejection are discussed, together with the significance of the results to the interpretation of data based on field observations.I should like to thank Mr J. Harris for allowing me to refer to some of his unpublished data and for helpful discussions.

Journal ArticleDOI
TL;DR: The fine structure of the macrogametocyte,macrogamete and the early stages in the formation of the oocyst wall of Eimeria acervulina have been described and compared with other species of EIMeria.
Abstract: The fine structure of the macrogametocyte, macrogamete and the early stages in the formation of the oocyst wall of Eimeria acervulina have been described and compared with other species of Eimeria. It has been shown that type II wall-forming bodies are formed in cisternae of the granular endoplasmic reticulum in association with Golgi complexes. The developing oocyst has been shown to be enclosed by three membranes: the outermost is the original membrane of the merozoite and macrogametocyte; the second membrane appears when the wall-forming bodies are appearing in the cytoplasm of the macrogametocyte and the innermost membrane appears after fertilization. The wall-forming bodies discharge their contents between the innermost membrane and the middle membrane.We wish to thank Mr P. L. Long for much valuable discussion, Mrs B. Fisher for technical assistance and Mr B. Carter for assistance with the photography.



Journal ArticleDOI
TL;DR: A drug-resistant strain of T. vivax was transmitted through a series of four duikers and a gazelle by G. rufifrons and G. tachinoides, and infection rates in tsetse flies fed at early stages of infection on the antelope were similar to those found in flies fed on cattle infected with the drug- resistant strain.
Abstract: A drug-resistant strain of T. vivax was transmitted through a series of four duikers (S. grimmia) and a gazelle (G. rufifrons) by G. palpalis and G. tachinoides. The cyclical transmission of the strain in cattle, started in earlier work, was continued for control purposes. Infections with the drug-resistant strain in the antelope were of the same type as those produced by field strains of T. vivax in the same host species, and infection rates in tsetse flies fed at early stages of infection on the antelope were similar to those found in flies fed on cattle infected with the drug-resistant strain. The strain retained resistance to diminazene aceturate at a dose rate of 7-0 mg/kg and quinapyramine sulphate at 5'0 mg/kg in the absence of the drugs for 7 months in tsetse flies and antelope, and for a total period of 29 months in tsetse flies and cattle.We wish to thank Dr A. A. Amodu, Director of the Nigerian Institute for Trypanosomiasis Research, for permission to publish this paper.

Journal ArticleDOI
TL;DR: It has been concluded that worms without eggs are newly matured individuals and that seasonal variations in fecundity reflect similar fluctuations in the age distribution of the adult populations.
Abstract: A large proportion of Strongylus vulgaris, S. edentatus and Trichonema nassatum collected from the gut lumen of slaughtered horses during the winter did not contain eggs. The proportion of Trichonema catinatum without eggs declined to a low level during the winter and rose to relatively high levels during the summer, It has been concluded that worms without eggs are newly matured individuals and that seasonal variations in fecundity reflect similar fluctuations in the age distribution of the adult populations. These fluctuations are related to seasonal differences in the numbers of infective larvae ingested and to the length of parasitic development.Most Strongylus vulgaris, S. edentatus and Trichonema nassatum reach the adult stage during the winter and it has been suggested that an increase in worm numbers during this period is responsible for a rise in the faecal egg counts of horses in the spring. The observations on T. catinatum indicate that the level is maintained by the arrival of new individuals during the summer.I wish to thank Dr H. D. Crofton for his constant advice and encouragement during this work and Professor H. E. Hinton, F.R.S., for the provision of laboratory facilities. I am indebted to Mr L. J. Potter for allowing me to collect the parasites from his slaughterhouse at Bishop Sutton, near Bristol. This work was carried out during a research studentship funded by the Horse Race Betting Levy Board.

Journal ArticleDOI
R. Keller1
TL;DR: It was concluded that mast cells and their constituents were not an essential factor in the second step of worm elimination and the bulk of the parasites are expelled at a time when histamme and mast cell levels are low.
Abstract: This paper describes experiments to determine whether intestinal tissue mast cells and/or intestinal histamine are involved in the second, expulsive step of worm elimination. In neonatal rats, intestinal tissue contains only very little histamine and mature mast cells are encountered only sporadically. From birth to the adult age, there was a gradual rise in both intestinal mast cells and histamine. During Nippostrongylus brasiliensis infection in the adult rat, the concentration of histamine in the small intestine was clearly lower than in uninfected controls.Especially low histamine values were found to occur on days 6–12 of a primary infection in the region where the main worm burden was located. Similarly, the number of tissue mast cells present in the epithelium of the jejunum was decreased in the same region and during the same period of time. From the observation that the bulk of the parasites are expelled at a time when histamme and mast cell levels are low, it was concluded that mast cells and their constituents were not an essential factor in the second step of worm elimination This work was supported by the Schweizerische Nationalfonds zur Forderung der wissenschaftlichen Forschung (Grant 5200.3). The skilful technical assistance of Miss I. Beeger, Miss R. Keist and Miss M. Iseli is gratefully acknowledged. I thank Mr H. Berchtold, Biostatistisches Zentrum der Universitat Zurich, for the statistical evaluation of the data.