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PubMedDate not supplied

Enterocytozoon bieneusi (Microspora): prevalence and pathogenicity in AIDS patients.

Microsporidia are unicellular organisms, which lack mitochondria. They have prokaryotic-like ribosomes and characteristic spores containing an extrusible polar tube which serves as a passage for inoculation of the infectious agent (sporoplasm) into host cells. Clinically apparent infections in man appear to be limited to immunoprivileged sites or immunocompromised patients. One species, Encephalitozoon cuniculi, has been reported several times in patients with neurological disorders and once causing a fatal hepatitis in an AIDS patient. The most recently discovered species, Enterocytozoon bieneusi, is known only from the small intestinal enterocytes of patients with the acquired immunodeficiency syndrome, and is easily differentiated from other microsporidia by the precocious development of spore organelles in the sporont and by the poor development of the endospore layer of the spore wall. Although only about 40 cases have been reported, circumstantial evidence suggests that E. bieneusi may be the cause of a severe watery diarrhoea, which responds only temporarily to treatment with metronidazole.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Antibodies to Plasmodium falciparum sporozoites following a malarial outbreak in a non-endemic area of Sri Lanka.

An enzyme-linked immunosorbent assay (ELISA) based on the synthetic peptide (NANP)40 was used to characterize the sporozoite antibodies in an unusual Plasmodium falciparum outbreak in a non-malarious area in Sri Lanka. A positive antibody response was seen in 62% of patients with their first P. falciparum illness. There was no correlation between sporozoite antibodies and the antibody against blood stages, determined by immunofluorescence assay. The majority (91%) of the patients lost the antibodies to circumsporozoite (CS) protein within one year (in the absence of re-exposure). Three patients had high levels of CS antibodies even after one year, and this persistence was related to the level of the initial antibody response. In the area of the outbreak 10% of schoolchildren had antibodies to the (NANP)40 peptide. 21% of the 42 children with present or past overt malaria were antibody positive. Of the children with no such background, 8% were antibody positive. The corresponding seropositivity rates for asexual blood stages were 31% and 1% for the 2 groups respectively. It is concluded that (NANP)40 ELISA is potentially a valuable tool in sero-epidemiology, particularly in situations of seasonal transmission and recurrences due to drug resistance.

Animals↗
PubMedDate not supplied

Infectivity of Plasmodium vivax and P. falciparum to Anopheles tessellatus; relationship between oocyst and sporozoite development.

The assessment of malarial infectivity, for example in the evaluation of transmission blocking immunity, is generally based on counting oocysts in mosquitoes fed on infected blood. Ultimate transmission of the disease may, however, depend on the sporozoite load in the mosquito and its relationship to the size of the inoculum introduced to man. We conducted a laboratory study on Anopheles tessellatus infected with 108 different natural isolates of Plasmodium vivax from patients and 24 of P. falciparum to determine the relationship between oocyst numbers, sporozoite loads, and the effect of these on mosquito mortality. It was found that the P. vivax parasite density was positively correlated with the proportion of mosquitoes infected by a given feed at both the midgut and gland stages of parasite development (correlation coefficient [r] = 0.77, P < 0.001 and r = 0.6, P < 0.05 respectively). A significant positive linear correlation was observed between the number of oocysts and sporozoites in P. vivax (r = 0.5; P < 0.05); the proportions of mosquitoes infected with oocysts and sporozoites were also similarly related, although in general about 15% of mosquitoes infected with oocysts failed to develop salivary gland infections with sporozoites. The number of mosquitoes infected with P. falciparum parasites was too low for statistical analysis. Infection with either species of parasite did not appear to affect mosquito survival, nor was parasite density in the mosquito correlated with mosquito mortality.

Animals↗
PubMed1975

Ultrastructural analysis of the freeze-etched spore envelope of the microsporidian, Nosema apis Zander.

The outer limiting layer of the spore coat of Nosema apis is relatively smooth. The inner limiting layer shows two fractured faces, the concave face carrying many stud-like projections, 120 nm long and 50 nm high, while the convex face carries numerous depressions which are complementary to the projections. In addition, the convex face bears 7 nm particles. In between the outer and inner limiting layers lies the thick homogeneous portion of spore coat which is comprised of numerous microfibres, each 9 nm in diameter. These microfibres resemble those in the freeze-etched host endocuticle. Next to the inner limiting layer of the spore coat are double spore membranes. The convex faces of these spore membranes have a dense population of particles, each 7 nm in diameter.

Animals↗
PubMed1982

Salivary gland of the tick vector of East Coast fever. IV. Cell type selectivity and host cell responses to Theileria parva.

Responses of cells in the tick salivary gland to parasitism by Theileria parva were studied by electron microscopy. The gland is composed of three distinct types of acini (I, II, III) which together include ten or more different cell types. Of some 30 infected cells observed in the present study, all were E-cells of acinus III. The parasite thus exhibits a high degree of selectivity for acinus and cell type. The glandular cell invaded undergoes massive hypertrophy and accumulates glycogen deposits in its cytoplasm which may serve as an energy source for the growing intracellular parasite. As synthesis of its secretory material declines the product is packaged in progressively smaller secretory granules. The extensive arrays of endoplasmic reticulum are dismantled and eliminated in autophagic vacuoles. Excess secretory granules are also broken down by crinophagy. After 4 days, sporogony is completed and the host cell contains 30,000-50,000 sporozoites in an electron-lucent cytoplasm largely devoid of cytomembranes and secretory granules. Mitochondria are still present and normal in appearance. The loss of basophilia and secretory granules observed heretofore by light microscopy have been attributed to ingestion and destruction of host organelles by the parasite. The pallid appearance of the cytoplasm has been interpreted as a sign of impending degeneration of the host cell. In electron micrographs no ingestion of organelles by the parasite or degenerative changes were found. The host cell clearly remains viable and metabolically active throughout sporogony. The striking changes in its ultrastructure result from active elimination of organelles and inclusions by the host cell itself in response to parasitism.

Animals↗
PubMed1984

Interaction of sporozoites of Theileria parva with bovine lymphocytes in vitro. I. Early events after invasion.

Sporozoites of Theileria parva rapidly enter bovine lymphocytes by a mechanism of passive endocytosis that depends upon progressive circumferential binding of ligands on the parasite to receptors on the host-cell membrane. Within 10 min of entry, the micronemes of the sporozoite discharge their content and the enveloping host-cell membrane is lysed. The host cell responds within 30 min of invasion by polymerization of microtubules arrayed tangential to the sporozoite and converging upon the cytocentrum. Multivesicular bodies and lysosomes are generated and gather around the parasite but are ineffective in the absence of an endocytotic membrane with which they can fuse. Thus Theileria parva can be added to the category of obligate intracellular parasites that ensure their survival by lysis of the parasitophorous vacuole.

Animals↗
PubMed1987

Ultrastructure of the intra-erythrocytic stage of Theileria species from cattle and waterbuck.

A transmission electron microscopic study of the intra-erythrocytic stages of a pathogenic Theileria parva from cattle and a previously uncharacterized Theileria sp. from waterbuck (Kobus defassa) in Kenya revealed several novel ultrastructural features, associated with feeding and multiplication, in these parasites. In trophozoites a connecting channel was observed between the parasite's cytostome and its intracytoplasmic food vacuole. In some cases the limiting membrane of the food vacuole was seen to be continuous with a close-meshed network of membrane-bounded, anastomosing tubules. This labyrinthine structure, which has not been described previously, may function as a digestive organelle in theilerial trophozoites. Electron micrographs also revealed the mode of intra-erythrocytic multiplication of these parasites in vivo. Prior to division, electron-dense cisternae and rhoptries appeared beneath the parasite's plasmalemmal membrane, marking the sites of merozoite formation. From a single parasite, a maximum of four merozoites were formed by schizogonous division and subsequently separated from a residual body by constriction at the base of each merozoite. In addition, observations on two double-membraned organelles seen in trophozoites and the intra-erythrocytic crystalline structures associated with Theileria sp. in waterbuck are reported.

Animals↗
PubMed1986

Immunoglobulin levels of the winter flounder (Pseudopleuronectes americanus) and the summer flounder (Paralichthys dentatus) injected with the microsporidan parasite Glugea stephani.

The microsporidan parasite G. stephani, has been found in the intestine of the American winter flounder Pseudopleuronectes americanus. A quantitative study of total serum immunoglobulin (Ig) levels has shown that an injection of this parasitic spore causes a decrease in serum IgM levels. The level of suppression seems to be related to the number of spores injected into the host, as well as the frequency of injections administered. As the dosage of spores injected into the winter flounder increased from 3 X 10(3)/ml to 3 X 10(8)/ml, the level of serum IgM's decreased proportionally. When a single IM injection of spores (3 X 10(6)/ml) was administered, the initial decrease in serum IgM was followed by a gradual recovery of total Ig levels by day 60. Repeated injections of G. stephani on days 21 and 42 respectively, causes an even greater decrease in total IgM levels. Indomethacin (a drug that inhibits prostaglandin activity), has been shown to negate the decrease in IgM levels caused by the G. stephani spores. When injected twice weekly, the indomethacin inhibited the decrease in serum IgM caused by the spore homogenate, with IgM levels comparable to those observed in control WF. This supports previous observations, that prostaglandins are implicated in the decrease in IgM levels induced by injection of the parasite. The effects of G. stephani on serum Ig levels does not seem to be species-specific. When the spores were injected into summer flounder (Paralichthys dentatus) together with an erythrocyte antigen, horse red blood cells (HRBC), a decrease in total IgM levels occurred, as well as a decrease in hemagglutination titers to HRBC similar to the decrease described in winter flounder.

Animals↗
PubMed1989

The effect of the microsporida Glugea stephani on the immunoglobulin levels of juvenile and adult winter flounder (Pseudopleuronectes americanus).

The microsporida Glugea stephani is an intracellular parasite that causes a decline in the serum IgM levels of both adult and juvenile winter flounder, shortly after introduction. This decline was noted in fish injected with spores or infected via an intermediary vector. The parasite also suppresses the humoral response to other antigens such as horse red blood cells. The suppression of the response to the antigen however, is related directly to the exposure time with regard to the kinetic state of the immune response. Less suppression occurred when the response was already past the initiation stage. The results implicate that the parasite may be interfering with the initiation of the response as well as at other stages. The presence of a soluble serum protein, which may contribute to this immunosuppression, was detected by electrophoresis.

Animals↗