Showing papers in "Advances in Parasitology in 1972"

Intramolluscan inter-trematode antagonism: a review of factors influencing the host-parasite system and its possible role in biological control.

Abstract: Publisher Summary The study of intramolluscan single and double trematode infections has proved to be a useful approach in better understanding host–parasite relationship Modification and disruption of snail infection with trematodes is reviewed and the parameters and characteristics of various infection combinations are described Biologically, however, the inter-trematode reactions and the responses of the snail host offer remarkable opportunities to examine and isolate various aspects of this host–parasite relationship The single species infection patterns differ widely between the pure sporocyst type, exemplified by S mansoni, and the redial type, typified by P segregatum Characteristics of each are reviewed Their interaction is then reviewed, based on original data and comparison with other studies Redial predation (“direct antagonism”) is discussed in terms of relative activity, efficiency, and predatory response to triggering stimuli in the snail Possible mechanisms of indirect antagonism are reviewed, with a fuller consideration of snail immunity as induced by these infections and measured experimentally The parameters or characteristics of single-species infection are described and related to one another in a preliminary fashion as an “adaptation index” (AI), which includes such parameters as infection rate, period for 50% snail death, and period to cercarial shed The trematode method is locally applicable, using indigenous strains supplied and sustained at a high level by continual reseeding with eggs of the controlling trematode (or processed faeces from the appropriate final hosts) Effective biocontrol as a self-sustaining life-cycle appears highly improbable, as is the expectation that this method can be adopted on a wide scale with the same controlling agent

Taeniasis and cysticercosis (Taenia saginata).

Abstract: Publisher Summary This chapter summarizes all significant matters concerning Taenia saginata (T. saginata) taeniasis and cysticercosis—that is, nomenclature, host relationships, structure and biology, clinical and therapeutic features, epidemiology and epizootiology, and prevention of infection. It considers some taxonomic problems and the hosts of T. saginata. The structure and biology of the adult worm, egg, onchosphere, and cysticercus is discussed. The clinical aspects of taeniasis are dealt in terms of symptomatology, clinical pathology, diagnosis, and treatment. Yomesan is the drug of choice for T. saginata infection in Man at present, and some suggestions are made for treatment with this and other drugs. The chapter discusses epidemiology, epizootiological, and losses due to taeniasis and cysticercosis. Losses are difficult to estimate, because infection is rarely fatal, but some figures are available for European, African, and American areas. Meat inspection is dealt with as a means of prevention, likewise serological diagnosis and the immunization of cattle. Sanitation is a matter discussed, its improvement, expensive but connected with higher standards of living.

The Pathogenesis of Mammalian Malaria

Abstract: Publisher Summary This chapter examines two principal features of mammalian malaria: the pathophysiology of malaria as an inflammation and the possible initiating and maintaining factors involved. Intravascular coagulation has often been blamed for the obstruction of the cerebral circulation in falciparum malaria. In fact, clotting has rarely been demonstrated and there is very little evidence that coagulation thrombosis or embolus play significant roles in producing the vascular lesions (as distinct from being associated with them). When they occur they represent developments following and not preceding the reduction of blood flow. The “plugging” of the small cerebral vessels by parasitized erythrocytes continues to be the common pathological pattern described at autopsy findings in fatal P. falciparum cases. The function of the endothelial membranes of the brain is examined in the laboratory in P. knowlesi and P. berghei infections. The methods for demonstrating the escape of protein across the cerebral vascular endothelium, choroid plexus, ventricular walls, and other parts of the brain are used. The changes in membrane permeability and some of the circulatory disturbances noted are induced by physiologically active peptides, such as kinins. The intravascular coagulation in malaria is also discussed. Many factors are involved in creating the environment that leads to cellular damage in malaria. At some stage in the development of a malaria infection, the pathogenic processes must be initiated by the parasite, either during its development in the erythrocyte or at schizogony. One possible link between the parasite and the host may be the soluble factor, which is capable of inhibiting mitochondria1 respiration and phosphorylation. This and possibly other factors may be involved, acting at various strategic points in the host and influencing its physiological and biochemical balance.

The Aspidogastrea, Especially Multicotyle purvisi Dawes, 1941

Abstract: Publisher Summary The Aspidogastrea are trematodes with a ventral disc (Baer's disc) divided into one to four longitudinal rows of alveoli or represented by a single row of ventral suckers. The ultrastructure of the tegument is examined in Multicotyle purvisi only. It corresponds in all details to the tegument of Digenea. The basal cell membrane is located above a well-developed basal lamina and has extensive invaginations which, however, never reach the surface and are partly lamellar. The tegument contains mitochondria and numerous ovoid bodies, in some areas also vacuoles and lamellated bodies. The intestinal tract of aspidogastrids is a simple tube, consisting of mouth cavity, pharynx, and caecum. The feature distinguishing the genital system of Aspidogastrea most clearly from that of other trematodes is the structure of the oviduct. All larval Aspidogastrea examined have a mouth cavity, prepharynx, pharynx, simple caecum, and a postero-ventral disc without alveoli. The digestive tract is examined with the electron microscope only in the larva of Multicotyle purvisi. Multicotyle, just as the other examined species , has an ectolecithal egg. However, the yolk cells do not lie at one pole as in Cotylogaster and Macraspis but surround the egg cell located in the centre of the egg as in Cotylaspis.

A phylogeny of life-cycle patterns of the Digenea.

Abstract: Publisher Summary A comparison of helminth life-cycles reveals a number of singular features in the digenean pattern. Thus, in addition to the most singular feature, alternation of generations, there is the ubiquity of the cercaria, a stage designed for escape from the molluscan first host and for swimming, two patterns of behavior that are not called for in many life-cycles. To explain the ubiquity of the cercaria, it is postulated that the present molluscan first intermediate host was the original host of the proto-digenean and that escape of the cercaria from this host is primitive. And to explain the occurrence in many life-cycles of a free-swimming miracidium that penetrates the integument of the molluscan host, it is postulated that in an earlier stage the proto-digenean was an ectoparasite of the mollusc. Assuming that the proto-digenean was a visceral parasite of a mollusc and that it escaped from its host as an adult, presumably tailed, to lay its eggs, then the known life-cycles of contemporary digeneans may be interpreted as suggesting the following order in the acquisition of hosts: (i) vertebrate definitive (two-host life-cycle) and (ii) invertebrate second intermediate (three-host life-cycle). With regard to the succession of generations, it is postulated that the present adult was the original adult, that the mother sporocyst generation was the first of the new generations, that the redia was the second, and that daughter sporocysts have been derived from rediae several times.

The structure of the helminth cuticle.

Abstract: Publisher Summary This chapter discusses the structure of helminth cuticle. The following groups and species are considered: Turbellaria (Kronborgia amphipodicola), Monogenea (various species), Digenea (Fasciola hepatica and various other species), Cestodaria (Gyrocotyle urna), Cestoda (various species), Nematoda (various species), and Acanthocephala (Polymorphus minutus). In the Digenea, the change from miracidium to sporocyst also involves shedding of the ciliated epidermal cells and the formation of a syncytial epidermis from cells, which lie below the muscles. Cestodaria are either monogeneans or occupy a phylogenetic position between the monogeneans and the cestodes. The development of the epidermis of adult cestodes still needs much work to clarify the situation, especially from the embryological point of view. The epidermis of adult cestodes has been confirmed as an outer cytoplasmic syncytial epidermis, which is covered with microvilli bearing electron-dense spine-like tips, and in cytoplasmic continuity with nucleated cell-like bodies in the parenchyma. The cuticle of many different stages and species of nematode is examined with the electron microscope, and a certain type of cuticle structure appears to be common to most larval nematodes and also to some adults. Several examples of moulting in nematodes have been described, and it would appear that moulting differs in different types of nematode and sometimes in different stages of the life cycle. The body wall of some larval stages of two acanthocephalans has been described by means of electron microscopy and shown to be rather similar to that of the adult.

Avian Blood Coccidians

Abstract: Publisher Summary This chapter discusses avian blood coccidians focusing on two distinct groups of blood-dwelling stages of coccidia: (1) small nonpigmented nucleophilic parasites of mononuclear cells in the viscera and peripheral circulation and (2) typical adeleine haemogregarines, such as those that parasitize the blood cells of vertebrates during the course of the life cycle. Check-list of avian hosts of both groups of parasites is given. These parasites are considered in separate sections as atoxoplasms and adeleine haemogregarines. There are considerable morphological differences between the atoxoplasms seen in avian monocytes and the classical Lankesterella minima, which inhabits erythrocytes of frogs. Atoxoplasms have been studied by electron microscopy. The ultrastructure revealed is markedly similar to that of Toxoplasma and the other einieriid coccidian, such as Eimeria species and Isospora. In some instances, especially where the host red blood corpuscle was partly disintegrated, the haemogregarine could clearly be seen to have a sharply reflected “tail.”

The Metabolism of the Malaria Parasite and its Host

Abstract: Publisher Summary This chapter discusses considerations that are necessary in the metabolic investigations of Plasmodia. It discusses some current research trends that seem to advance the knowledge of fundamental biochemical processes occurring in parasites and are involved in the host–parasite relationship. The pentose phosphate pathway (PPP) for which the malaria parasite could have an absolute requirement is probably the principal pathway for the production of pentose sugars necessary for nucleic acid synthesis. There is now evidence that the most of the malaria parasites studied up to the present are dependent on the glucose-6-phosphate dehydrogenase (G-CPD), the initial enzyme of the PPP, the parasites being unlikely to thrive in enzyme-deficient cells and thus unable to produce an overwhelming infection. Further metabolism remains enigmatical, but current trends in research with mammalian species are discussed. Other topics considered are carbon dioxide fixation by malaria parasites, aerobic mechanisms, and the metabolism of chloroquine-resistant malaria parasites. The chapter also considers the metabolism of the host during infection—namely, biological changes in erythrocytes—the effects of acute infection on host–tissue metabolism and host–lipid metabolism. Such studies are enabling some advances to be made in an understanding of the pathological process involved in malaria.