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PubMedDate not supplied

Cryptosporidium parvum life cycle in suckling mice: a Nomarski interference-contrast study of a human-derived strain.

Cryptosporidiosis has emerged as one of the life-threatening opportunistic enteric infections in HIV-infected persons. To date, Cryptosporidium parvum is known to infect man via person-to-person or zoonotic transmission. We studied the sequential stages of the life cycle of C. parvum by Normarski interference-contrast microscopy in fresh gut specimens of newborn mice, infected with a strain derived from an AIDS patient with cryptosporidial diarrheal enteritis. Many 4- to 5-day-old suckling BALB/C mice were orally inoculated with 1 x 10(6) oocysts, obtained by acid flocculation of the patient's stools. The animals were sacrificed from 4 to 96 h post-infection and the ileum was examined microscopically. All stages of the asexual life cycle of C. parvum, from excysted sporozoites in the intestinal lumen through the development of type II mature meronts, 12- to 72-h post-infection, were documented by extemporaneous microscopic evaluation of fresh gut samples. The sexual cycle, characterized by the appearance of micro- and macrogametocytes, followed by a zygote developing into a sporulated oocyst, was documented as early 48-h post-infection. Our Nomarski interference-contrast observations on the life cycle of C. parvum yielded data comparable with those originally published by Current and Reese, and confirm the results of previous electron microscopic studies performed by several other authors.

Acquired Immunodeficiency Syndrome↗
PubMed1999

Adding the third dimension to virus life cycles: three-dimensional reconstruction of icosahedral viruses from cryo-electron micrographs.

Viruses are cellular parasites. The linkage between viral and host functions makes the study of a viral life cycle an important key to cellular functions. A deeper understanding of many aspects of viral life cycles has emerged from coordinated molecular and structural studies carried out with a wide range of viral pathogens. Structural studies of viruses by means of cryo-electron microscopy and three-dimensional image reconstruction methods have grown explosively in the last decade. Here we review the use of cryo-electron microscopy for the determination of the structures of a number of icosahedral viruses. These studies span more than 20 virus families. Representative examples illustrate the use of moderate- to low-resolution (7- to 35-A) structural analyses to illuminate functional aspects of viral life cycles including host recognition, viral attachment, entry, genome release, viral transcription, translation, proassembly, maturation, release, and transmission, as well as mechanisms of host defense. The success of cryo-electron microscopy in combination with three-dimensional image reconstruction for icosahedral viruses provides a firm foundation for future explorations of more-complex viral pathogens, including the vast number that are nonspherical or nonsymmetrical.

Cryoelectron Microscopy↗
PubMed1986

The life-cycle of Syphacia muris Yamaguti (Nematoda: Oxyuroidea) in the laboratory rat.

The life-cycle of Syphacia muris is described in primary infections of Wistar rats. The life-cycle of S. muris is completed within seven days and no moults were discovered inside the egg. Instead each of two moults were observed outside the egg up to 24 and 40 hours after infection, and TEM studies suggest a third moult occurs up to 64 hours. The development and maturation of the larval stages are described for the first time using both light and electron microscopy. Differences in the size and growth of female S. muris compared with previously published figures could be due to differences in the strains of rats used.

Animals↗
PubMed1995

Developmental genes as a potential tool in population ecology of complex animal life cycles?

Many aquatic invertebrates possess complex life cycles, which include a switch from a vegetative to a sexual mode of reproduction. While sexual reproduction is usually linked to slow rates of propagation, vegetative reproduction leads to high rates of clonal propagation and a fast increase in population size. I have attempted to identify developmental genes which are differentially expressed between sexually and vegetatively reproducing individuals. quantitative assays of the expression of those diagnostic genes could be applied to field samples to gain information on the reproductive status of the sample. Here I outline a general strategy for identifying and testing the usefulness of homeobox genes as candidates for regulatory genes whose expression patterns are indicative of a sexual or vegetative developmental phase.

Animals↗
PubMed2003

Geographical scenario uncertainty in generic fate and exposure factors of toxic pollutants for life-cycle impact assessment.

In environmental life-cycle assessments (LCA), fate and exposure factors account for the general fate and exposure properties of chemicals under generic environmental conditions by means of 'evaluative' multi-media fate and exposure box models. To assess the effect of using different generic environmental conditions, fate and exposure factors of chemicals emitted under typical conditions of (1). Western Europe, (2). Australia and (3). the United States of America were compared with the multi-media fate and exposure box model USES-LCA. Comparing the results of the three evaluative environments, it was found that the uncertainty in fate and exposure factors for ecosystems and humans due to choice of an evaluative environment, as represented by the ratio of the 97.5th and 50th percentile, is between a factor 2 and 10. Particularly, fate and exposure factors of emissions causing effects in fresh water ecosystems and effects on human health have relatively high uncertainty. This uncertainty is mainly caused by the continental difference in the average soil erosion rate, the dimensions of the fresh water and agricultural soil compartment, and the fraction of drinking water coming from ground water.

Australia↗
PubMed1993

Diploid Paragonimus westermani: the experimental completion of its life-cycle.

Experimental completion of the life-cycle of Paragonimus westermani (Trematoda: Troglotrematidae) (diploid type) from egg to adult has been achieved in the laboratory for the first time. A dog was fed metacercariae of P. westermani from naturally infected freshwater crabs. Geothelphusa dehaani. The adult flukes were recovered and their eggs were incubated in water at 28 degrees C, hatching after 20 days. Laboratory reared marsh snails, Semisulcospira libertina, were exposed to miracidia from embryonated eggs. One of 47 snails became infected with a large number of 2nd generation rediae containing fully mature cercariae 245 days after exposure. Paragonimus-free crabs (G. dehaani) were then infected with the intramolluscan larvae. Of the 40 crabs examined 34-70 days after infection, 17 were infected with a total of 84 metacercariae. A cat and 4 dogs were fed with 55 metacercariae obtained. Eighty to 100 days later, a total of 40 flukes was recovered; 39 flukes were adults with eggs in their uteri.

Animals↗
PubMed2004

System boundary selection in life-cycle inventories using hybrid approaches.

Life-cycle assessment (LCA) is a method for evaluating the environmental impacts of products holistically, including direct and supply chain impacts. The current LCA methodologies and the standards by the International Organization for Standardization (ISO) impose practical difficulties for drawing system boundaries; decisions on inclusion or exclusion of processes in an analysis (the cutoff criteria) are typically not made on a scientific basis. In particular, the requirement of deciding which processes could be excluded from the inventory can be rather difficult to meet because many excluded processes have often never been assessed by the practitioner, and therefore, their negligibility cannot be guaranteed. LCA studies utilizing economic input-output analysis have shown that, in practice, excluded processes can contribute as much to the product system under study as included processes; thus, the subjective determination of the system boundary may lead to invalid results. System boundaries in LCA are discussed herein with particular attention to outlining hybrid approaches as methods for resolving the boundary selection problem in LCA. An input-output model can be used to describe at least a part of a product system, and an ISO-compatible system boundary selection procedure can be designed by applying hybrid input-output-assisted approaches. There are several hybrid input-output analysis-based LCA methods that can be implemented in practice for broadening system boundary and also for ISO compliance.

Certification↗
PubMed1989

Life cycle of Eimeria coecicola Cheissin, 1947.

Life cycle of Eimeria coecicola was studied in experimentally infected rabbits by light microscopy and by transmission and scanning electron microscopy. First and second generation meronts developed in the vermiform appendix; third and fourth generation meronts were located in the epithelium of the ileum. Gametogony developed again in the vermiform appendix. The prepatent period was 9 days. New data were obtained by the study of asexual reproduction. First generation meronts were first observed 4 days post infection (DPI), which is relatively late in comparison with other species of rabbit coccidia. Sporozoites were found in lymphatic follicles of the vermiform appendix at 4 DPI by transmission electron microscopy. This suggests, together with selective location of first generation meronts in the epithelium adjacent to these follicles, that major part of sporozoites enter the epithelium cells through lymphatic follicles and not through the lumen of the vermiform appendix. The process of development of first generation merozoites is similar to endodyogeny. The differences are in formation of apical parts of daughter merozoites which is not coincidental with nuclear division and in formation of the outer membrane of pellicle which arises within the mother cell. Some first generation merozoites have 2-3 nuclei, second and fourth generation merozoites are only uninucleate, while third generation merozoites are only multinucleate. We found that further merozoites are formed in multinucleate third generation merozoites by endopolygeny.

Animals↗
PubMed1996

Ultrastructural morphology of intermediate forms and forms suggestive of conjugation in the life cycle of Pneumocystis carinii.

The intrapulmonary life cycle of Pneumocystis carinii has been proposed to include asexual reproduction of haploid trophic forms and sexual reproduction to form cysts or ascospores containing 8 intracystic bodies or spores. This study presents the ultrastructural morphology of trophic forms and developing ascospores. Nuclear-associated organelles (NAO) were observed in these various forms and in a binucleated trophozoite. The unique configuration of the nuclei and NAO in this binucleated trophic form were similar to ultrastructural features observed in conjugation of Saccharomyces cerevisiae. NAOs in developing ascospores were present in pairs and were associated with multiple nuclei. In more mature ascospores, NAO were associated with individual spores. The intermediate forms described in this study support an asexual and sexual reproductive process in P. carinii.

Animals↗
PubMed2004

Essential role for OspA/B in the life cycle of the Lyme disease spirochete.

The molecular basis of how Borrelia burgdorferi (Bb), the Lyme disease spirochete, maintains itself in nature via a complex life cycle in ticks and mammals is poorly understood. Outer surface (lipo)protein A (OspA) of Bb has been the most intensively studied of all borrelial molecular constituents, and hence, much has been speculated about the potential role(s) of OspA in the life cycle of Bb. However, the precise function of OspA (along with that of its close relative and operonic partner, outer surface [lipo]protein B [OspB]) heretofore has not been directly determined, due primarily to the inability to generate an OspA/B-deficient mutant from a virulent strain of Bb. In this study, we created an OspA/B-deficient mutant of an infectious human isolate of Bb (strain 297) and found that OspA/B function was not required for either Bb infection of mice or accompanying tissue pathology. However, OspA/B function was essential for Bb colonization of and survival within tick midguts, events crucial for sustaining Bb in its natural enzootic life cycle.

Animals↗
PubMed2005

Life cycle of Coitocoecum plagiorchis (Trematoda: Digenea: Opecoelidae).

The life cycle of Coitocoecum plagiorchis Ozaki, 1926 (Coitocaecum is an incorrect subsequent spelling) was studied in the field and laboratory. The study was conducted at the Futatsu River and the Chikugo River, Kyushu, Japan. Adults of C. plagiorchis were obtained from fishes Coreoperca kawamebari, Rhinogobius spp. and Odontobutis obscura. Cotylomicrocercous cercariae with a two-point stylet (=Cercaria distyloides Faust, 1924) were detected in pleurocerid snails (Semisulcospira spp.). Metacercariae with a cyclocoel were obtained from shrimp (Neocaridina denticulata). The cercariae were experimentally exposed to the shrimp, and subsequently metacercariae with a cyclocoel were recovered from the shrimp within 24 days after exposure. These metacercariae were identified as C. plagiorchis. The sporocysts, cercariae, metacercariae and adults are briefly described.

Animals↗
PubMed1978

Defective life cycle and low antibiotic production in submerged cultures of Streptomyces fradiae.

The life cycle of a Streptomyces fradiae strain producing high amounts of neomycin under industrial conditions has been investigated in liquid soybean medium where the production of antibiotic proved to be comparatively low. The changes occurring in the main macromolecular components and the enzyme activities of the mycelium during the life cycle and cytological observations proved that there was a block in the normal proecess of reproductive differentiation and a lack of exocellular alkaline phosphatase activity was found.

Alkaline Phosphatase↗
PubMed2005

The life cycle of Paraquimperia tenerrima: a parasite of the European eel Anguilla anguilla.

Previous studies on the life history of the nematode eel specialist Paraquimperia tenerrima (Nematoda: Quimperiidae) have failed to determine whether an intermediate host is required in the life cycle. In the laboratory, eggs failed to hatch below 10 degrees C, hatching occurring only at temperatures between 11 and 30 degrees C. Survival of the free-living second stage larvae (L2) was also temperature dependent, with maximal survival between 10 and 20 degrees C. Total survival of the free-living stages (eggs and L2) is unlikely to exceed a month at normal summer water temperatures, confirming that parasite could not survive the 6 month gap between shedding of eggs in spring and infection of eels in early winter outside of a host. Eels could not be infected directly with L2, nor could a range of common freshwater invertebrate species. Third stage larvae (L3) resembling P. tenerrima were found frequently and abundantly in the swimbladder of minnows Phoxinus phoxinus from several localities throughout the year and were able to survive in this host in the laboratory for at least 6 months. Third stage larvae identical to these larvae were recovered from minnows experimentally fed L2 of P. tenerrima, and eels infected experimentally with naturally and experimentally infected minnows were found to harbour fourth stage larvae (L4) and juvenile P. tenerrima in their intestines. Finally, the whole life cycle from eggs to adult was completed in the laboratory, confirming that minnows are an obligate intermediate host for P. tenerrima.

Anguilla↗
PubMed2004

Observations on life cycle of certain spiders from Western Ghats of Tamil Nadu.

Survey was conducted, in the different forests ecosystems of Western Ghats of Tamil Nadu in Nilgris, Coimbatore, Erode, Virudhunagar and Tirunelveli districts to collect the adult spiders and study them taxonomically. Fifty-six species of spider collections were made. From the fifty six, biology was studied for six spider species, such as Micrommata virescens n.sp., Oxyopes javanus, Peucetia virridana, Agelena kariansholensis n.sp., Heteropoda venatoria and Olios hampsoni. Biology studies with Peucetia virridana and Micrommata virescens showed that both species took more than 350 days to complete their life cycles. Heteropoda venetoria and Oxyopes javanus took more than 250 days to complete their life cycle. Agelena kariansholensis took 381 days and Olios hampsoni took 345 days to complete their life cycles. 30% of Peucetia virridana and more than 20% of Heteropoda venatoria and Micrommata virescens and 7% of Oxyopes javanus developed into adults in captivity.

Animals↗
PubMed1987

Population dynamics in echinococcosis and cysticercosis: mathematical model of the life-cycles of Taenia hydatigena and T. ovis.

It is shown that under the conditions that prevailed in New Zealand in the late 1950s, Taenia hydatigena was hyperendemic, the life-cycle being regulated by a density-dependent constraint in the form of acquired immunity, and T. ovis was rare. The control measures that caused Echinococcus granulosus, which was endemic at the time, to decline towards extinction reduced T. hydatigena and T. ovis to endemic status only. A non-linear integrodifferential equation model, which was previously linearized to describe the life-cycle of E. granulosus in dogs and sheep in New Zealand, is used to describe the life-cycles of T. hydatigena and T. ovis. The model is then used to compare and contrast the population dynamics of these three species. The model is used to demonstrate that the endemic steady state is structurally unstable, and may be asymptotically unstable to small perturbations. It is also shown that despite the lower infection pressure experienced by the intermediate host in the endemic state, the numbers of larvae in sheep may be higher than in the hyperendemic state. Finally it is shown that the partial success of the control measures against T. hydatigena may have caused an increase in the numbers and prevalence of T. ovis larvae in sheep due to the reciprocal immunity between the two species.

Age Factors↗
PubMed2000

[Ploidy of somatic nuclei during life cycle of Myxosporean (Myxozoa, Grasse, 1970)].

Results of the author's investigation on the ploidy of somatic nuclei in various myxosporean species, throughout different stages of their complicated life cycles, have been summarized. A comparative analysis of data on the ploidy in somatic and generative nuclei of Kudoa quadratum (Multivalvulida) has been given for the first time. Representatives of the Multivalvulida order differ from those of the earlier studied Bivalvulida order in the structure of their myxospore. It has been found that during the myxosporean life cycle alteration of haploid, diploid and polyploid somatic nuclei occurs, and that differentiation of somatic cells and nuclei takes place in both haploid and diploid phases of the life cycle.

Animals↗
PubMed2001

Microsporidian life cycles and diversity: the relationship between virulence and transmission.

The microsporidia are obligate intracellular parasites which have diverse life cycles involving both horizontal and vertical transmission and parasitise a wide range of vertebrate and invertebrate hosts. In this paper we consider the life cycles and diversity of the microsporidia. We focus in particular on the relationship between parasite transmission and virulence and its implications for host-parasite coevolution. The use of horizontal and vertical routes of transmission varies between species and there is a strong link between transmission and virulence. Horizontal transmission is characterised by a high parasite burden and associated pathogenicity. In contrast, vertical transmission is characterised by low virulence, which has led to under-reporting of this important transmission route. Vertically transmitted microsporidia may also cause male killing or feminisation of their host, with implications for host population sex ratio and stability. Phylogenetic analysis shows that vertical transmission occurs in diverse branches of the Microspora. We find that there is evidence for vertical transmission in both vertebrate and invertebrate hosts and conclude that it is a common or possibly even ubiquitous transmission route within this phylum.

Animals↗