Showing papers in "Advances in Parasitology in 1967"

Toxoplasma and Toxoplasmosis

Abstract: Publisher Summary This chapter focuses on the literature appearing during 1963–66 in the context of toxoplasmosis. The chapter outlines the advances in the electron microscopy of Toxoplasma and discusses the mechanisms of transmission, summarizing the serological work carried out in this regard. It also summarizes and comments on new epidemiological data and presents observations on the association of Toxoplasma with various disease conditions, papers concerned with anti-Toxoplasma drugs, and a few papers on physiology, tissue culture and toxin production of Toxoplasma. The usefulness of pyrimethamine and sulfa drugs in the treatment of toxoplasmosis has been generally accepted and well demonstrated. One disadvantage of pyrimethamine is teratogenesis. In addition, hematological side effects are frequently seen and must be monitored.

The biology of the acanthocephala.

Abstract: Publisher Summary This chapter discusses the biology of the acanthocephala. The morphology, functional anatomy, histology, cytology, ultrastructure development, biochemistry, host-parasite relationships, epidemiology, and medical and veterinary helminthology of acanthocephala are briefly discussed. A combination of experimental physiology and histology has given a clearer understanding of how the uterine bell apparatus and proboscis work in comparison to work based on earlier purely histological studies. The movement of the acanthor is also elucidated. The fine structure of acanthocephalan spermatozoa is given. The relationship between acanthocephala and cestoda can now be better understood as a result of advances in knowledge of biochemistry and fine structure. Other comparisons between these two groups are made in relation to intermediary metabolism and finally there is a phylogenetic explanation of peculiarities of acanthocephalan embryonic and larval development.

Dynamics of parasitic equilibrium in cotton rat filariasis.

Abstract: Publisher Summary The chapter focuses on the dynamics of parasitic equilibrium in cotton rat filariasis. From investigations of primary infections and superinfections of the filarial worm, L. carinii, in cotton rats, several mechanisms appear to come into play to maintain in a cotton rat community microfilaraemias consistent with efficient transmission to reinfection varying from time to time within a wide range of possibilities. Cotton rats exposed from their first infection onwards to intensively continuous reinfections are affected rather differently. Judging from the relatively light pleural infections, and seldom peritoneal infections, found in animals with histories of this kind, a particularly high proportion of infective larvae die off in the early migratory or developmental phase. The variability of the equilibrium that a cotton rat is capable of maintaining with its filarial parasite, both as an adult worm infection and as a microfilaraemia, and particularly the sensitivity of the microfilaraemia to changes in incident transmission, together with the capacity of the vector for efficient transmission whether feeding on low or high microfilarial infections, are adaptations of this parasitic system well suited to perpetuate an overall incidence of infection in the cotton rat community, in the transmissible form of the microfilaraemia, sufficing to ensure continuing transmission of the parasite despite such fluctuations as may occur seasonally, or for other reasons, in host–vector contact in the natural environment. A few comparisons with other experimental filarial models and some wider implications from this synthesis of cotton rat filariasis are briefly considered in the chapter.

Evolutionary Trends in Mammalian Trypanosomes

Abstract: Publisher Summary This chapter discusses the multiformity of variation and the heterogeneity among mammalian trypanosomes, which have furnished abundant material for deductions regarding the evolution of these haemo-flagellates. Evidence of some of the phases of the evolutionary process is provided by certain “relict” species, while indications of incipient speciation are found among infrasubspecific strains or demes exhibiting minor biological divergence. The gradual transition from one morphological and biological type of trypanosomes to another, as well as the progressive complication of the life cycles and mode of transmission of these parasites, supply clues to their phylogenetic relations. These, in their turn, serve as a basis for the natural classification of the mammalian trypanosomes.

Experimental Studies on Entamoeba with Reference to Speciation

Abstract: Publisher Summary The chapter focuses on the experimental studies on Entamoeba with reference to speciation. Species of Entamoeba can be divided into three groups based on the number of nuclei in the mature cyst, the number being eight, four, or one. The best known species of the 8- and 4-nucleate cyst groups are the human parasites E. coli and E. histolytica respectively. The species illustrated in the chapter are 8-nucleate cyst group, E. coli from man and E. gallinarum from fowl; 4-nucleate cyst group, E, histolytica and E. hartmanni from man; 1-nucleate cyst group, E. chattoni from monkey, E. bovis from cow and E. debliecki from goat. The morphological studies discussed have concentrated on three aspects: (1) the relationship of the large and small races of E. histolytica (known as E. histolytica and E. hartmanni respectively); (2) the occurrence in man of a different species of Entamoeba, which forms 1-nucleate cysts, E. polecki; and (3) the electron microscopy of amoebae and cysts. Electron microscopy has revealed some differences of subcellular organization between Entamoeba and metazoan cells. A great deal of research effort has been devoted to studying the immunology of the human species, E. histolytica. Various immunological methods have been adapted for use with Entamoeba antigens, for example precipitins, indirect haemagglutination, complement fixation, inhibition of red blood cell phagocytosis by specific antisera, inhibition of amoebic growth, and fluorescent antibody. These are described in the chapter. The results of DNA distribution are also discussed.

The post-embryonic developmental stages of cestodes.

Abstract: Publisher Summary This chapter discusses the advances in knowledge made in some aspects of the biology of post-embryonic stages of cestodes in the past 15 years. It summarizes the information on development and structure, emphasizing overall similarities (or differences) among the major groups of cestodes, and indicating some areas in which further research is deemed essential or profitable. Some of the factors, which form the basis of the physiological host specificity or susceptibility are suggested in this chapter. These include (1) enzyme concentration in the host intestine, which determines the hatching of the oncosphere; (2) intestinal emptying time in relation to time required for the hatching and establishment of the oncosphere; (3) the thickness or consistency of the host intestinal wall to be penetrated by the embryo, and (4) the environment of the host's body cavity which may permit or inhibit continued growth after the initiation of post-embryonic development.

Some tissue reactions to the nematode parasites of animals.

Abstract: Publisher Summary This chapter reviews some recent work conducted on the reactions of the mammalian animal to its nematode parasites. The associations between the parasite and host are of various kinds. In some, presumably those where the two organisms have been in association for long periods of time, there is little reaction, but in others, the reactions are acute and are associated with disease. Foreign body and irritant responses are common, while eosinophils are of such regular occurrence that their presence in the tissues of a domestic animal leads to a suspicion of parasitism. Hyperplastic reactions occur and metaplasia is reported, but true neoplasia seems rare. Susceptible animals do not react like immune ones in which the responses are enhanced and lymphocytic and plasma cell proliferation may occur. Many nematode parasites inhabit the lung; some are merely temporary but others reside there as adults. Although some nematodes may not reach adulthood in an unusual host they do nevertheless gain entrance to the tissues, where the reaction to them may be so pronounced that disease results. This is especially true in visceral larva migrans. The chapter illustrates the changing environment in which a nematode may have to live.

Malaria in Mammals Excluding Man

Abstract: Publisher Summary This chapter discusses malaria parasites of mammals other than man, focusing on the members of the genus Plasmodium , and various haemoproteids, for example, important forms such as Hepatocystis kochi ; Polychromophilus marinus , and Plasmodium brodeni . The methods for the purification and characterization of antigens have progressed from precipitation in gel, to paper and cellulose acetate membrane chromatography, to starch gel, and finally to polyacrylamide gel disk electrophoresis. The whole subject of immunity in malaria is in a state of flux today and it is important to keep the following two principal objectives clearly in mind: the identification and origin of the antibodies available for combating the infection and its results, and the antigenic differences between stages of a parasite and between strains, subspecies, and species. The malaria parasite in the course of its life cycle undergoes so many transformations and is exposed to such different environments that its susceptibility to the immune response of the host is naturally diverse.

Problems in the Cultivation of some Parasitic Protozoa

Abstract: Publisher Summary Trypanosomiasis of animals is a disease of great economic importance in Africa because it makes animal husbandry impossible in enormous tracts of country where the population is chronically deficient in protein, and although trypanosomiasis of man in that continent has been largely reduced by the control of the insect vector and by the use of prophylactic drugs, outbreaks still occur. Little is known of the mechanisms by which trypanocidal drugs produce their inhibitory effects upon the parasite and, with the exception of proguanil and pyrimethamine, which have been shown to interfere at different levels with folic acid metabolism in the malaria parasite, the mode of action of antimalarial drugs is not understood. Drug resistance also occurs in malaria parasites and the development, in South America and South-East Asia, of resistance to chloroquine, a drug used extensively in prophylaxis and treatment of the disease, has focused attention upon this problem. As yet, little is known of the changes occurring in trypanosomes when they become resistant to trypanocidal drugs and nothing is known of the changes associated with drug resistance in malaria parasites. For the solution of problems, whether they be mechanisms of drug action, the development of drug resistance, or the transformation of one morphological type into another with the accompanying physiological changes associated with change of host, a greater knowledge of the physiology and biochemistry of these organisms is necessary, and for this, methods of cultivation of all the stages of the life cycle are essential.