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PubMed1999

[Physiology of ticks (Ixodida) in non-parasitic phase of life cycle].

Non-parasitic phase of ticks is the most critical period of their life cycle. During off host period the ticks must maintain the water homeostasis and must find a host for feeding. Body water homeostasis is one of the most important processes that influences tick survival in nature and transmission of pathogens. Structure of intergument, particularly the waxy lipids in the epicuticle, and structure of peritremes restrict the loss of water from tick body. The water losses may be compensated by uptake of water vapour from the atmosphere. The critical equilibrium humidity of tick species of Ixodidae family range from 70 to 96% r.h. During non-feeding period, behaviour of ticks contributes to the maintenance of body water. The ticks aviod the microhabitats where loss of water may be accelerated.

Animals↗
PubMed1999

Cloning of the SmSPO-1 gene preferentially expressed in sporocyst during the life cycle of the parasitic helminth Schistosoma mansoni1.

Schistosomes are parasitic helminths with a complex life cycle in human and snail hosts. They express stage-specific genes that conceivably determine distinct properties of the parasite at different developmental stages. Here we report the stage-specific gene SmSPO-1, which is preferentially expressed in sporocysts residing in the snail host. The cDNA and the gene were cloned and sequenced. The cDNA, from cap site to the poly(A) addition site, is 498 bp long. It encodes a protein of 117 amino acids with a hydrophobic signal peptide of 18 residues, indicating that SmSPO-1 is a secreted or a membranal protein. In the gene the cDNA is split into four exons spread over 2.1 kb of chromosomal DNA.

Amino Acid Sequence↗
PubMed1997

Toxicity of 4-nonylphenol in a life-cycle test with the midge Chironomus tentans.

A life-cycle test with the macroinvertebrate Chironomus tentans was conducted with 4-nonylphenol. The chironomids were exposed to a series of concentrations of 4-nonylphenol via the water, in an intermittent (2 times/day) water renewal system. The test included evaluation of a number of developmental (e.g., growth) and reproductive (e.g., emergence, fecundity, viability) endpoints through parental and into F1 generations. Reductions in survival were observed in 20-day-old larvae at the highest test concentration, which corresponded to no-observable- and lowest-observable-effect concentrations of 42 and 91 microg/liter, respectively. No significant effects on larval growth (20 days), organism survival past 20 days, emergence success or pattern, sex ratio, fecundity, or egg viability were observed at any treatment level. Qualitative observations indicated an increase in deformed egg masses at the highest test concentrations; however, the biological significance of this is uncertain.

Animals↗
PubMedDate not supplied

The life-cycle of human immunodeficiency virus type 1.

The life-cycle of human immunodeficiency virus type 1 (HIV-1) has been studied using several techniques including immunoelectron microscopy and cryomicroscopy. The HIV-1 particle consists of an envelope, a core and the region between the core and the envelope (matrix). Virus particles in the extracellular space are observed as having various profiles: a central or an eccentric round electron-dense core, a bar-shaped electron-dense core, and immature doughnut-shaped particle. HIV-1 particles in the hydrated state were observed by high-resolution electron cryomicroscopy to be spherical and the lipid membrane was clearly resolved as a bilayer. Projections around the circumference were seen to be knob-like. The shapes and sizes of the projections, especially the head parts, were found to vary with each projection. HIV-1 cores were isolated with a mixture of Nonidet P40 and glutaraldehyde, and were confirmed to consist of HIV-1 Gag p24 protein by immunogold labelling. On infection, the HIV-1 virus was found to enter the cell in two ways: membrane fusion and endocytosis. After viral entry, no structures resembling virus particles could be seen in the cytoplasm. In the infected cells, positive reactions by immunolabelling suggest that HIV-1 Gag is produced in membrane-bound structures and transported to the cell surface by the cytoskeletons. A crescent electron-dense layer is then formed underneath the cell membrane. Finally, the virus particle is released from the cell surface and found extracellularly to be a complete virus particle with an electron-dense core. However, several cell clones producing defective mature, doughnut-shaped (immature) or teardrop-shaped particles were found to be produced in the extracellular space. In the doughnut-shaped particles, Gag p17 and p24 proteins exist facing each other against an inner electron-dense ring, suggesting that the inner ring consists of a precursor Gag protein showing a defect at the viral proteinase.

Cell Line↗
PubMed2003

Characterization of the Mucor circinelloides life cycle by on-line image analysis.

AIMS: The life cycle of the dimorphic fungus Mucor circinelloides was studied in a temperature-controlled flow-through cell, which constitutes an ideal tool when following the development of individual cells, with a view to understanding the growth and differentiation processes occurring in and between the different morphological forms of the organism. METHODS AND RESULTS: Mycelial growth and the transformation of hyphae into chains of arthrospores were characterized by image analysis techniques and described quantitatively. The influence of the nature (glucose and xylose) and concentration of the carbon source on specific growth rate and hyphal growth unit length were studied. The organism branched more profusely on xylose than on glucose while the specific growth rates determined were rather similar. Methods were developed to study the yeast-like growth phase of M. circinelloides in the flow-through cell, and combined with fluorescent microscopy which allowed new insights to bud formation. Additionally, numbers and distribution of nuclei in arthrospores, hyphae and yeasts were studied. CONCLUSIONS: The results give essential information on the morphological development of the organism. SIGNIFICANCE AND IMPACT OF STUDY: Development of any industrial process utilizing this organism will be dependent on the information obtained here for effective process optimization.

Cell Nucleus↗
PubMed2005

Evolutionary implications of the adaptation to different immune systems in a parasite with a complex life cycle.

Many diseases are caused by parasites with complex life cycles that involve several hosts. If parasites cope better with only one of the different types of immune systems of their host species, we might expect a trade-off in parasite performance in the different hosts, that likely influences the evolution of virulence. We tested this hypothesis in a naturally co-evolving host-parasite system consisting of the tapeworm Schistocephalus solidus and its intermediate hosts, a copepod, Macrocyclops albidus, and the three-spined stickleback Gasterosteus aculeatus. We did not find a trade-off between infection success in the two hosts. Rather, tapeworms seem to trade-off adaptation towards different parts of their hosts' immune systems. Worm sibships that performed better in the invertebrate host also seem to be able to evade detection by the fish innate defence systems, i.e. induce lower levels of activation of innate immune components. These worm variants were less harmful for the fish host likely due to reduced costs of an activated innate immune system. These findings substantiate the impact of both hosts' immune systems on parasite performance and virulence.

Adaptation, Physiological↗
PubMedDate not supplied

Ultrastructural observations on life cycle stages of Pneumocystis carinii.

An ultrastructural study of life cycle stages of Pneumocystis carinii in infected rat lungs in situ was undertaken utilizing 8 different modes of fixation. Three of the fixatives employed gave good fixation of cysts and intracystic bodies, but for the trophic forms fixation was only fair. Both the trophic forms and intracystic bodies have nuclear pores. The mitochondria of the organism have cristae that appear lamellar. One of the fixation modes revealed a thin, electron-dense layer on the outer surface of the cell wall, a "fuzzy coat" that had not been described previously. This material appears to mediate tight adhesion of trophic forms with other trophic forms, cysts, and with pneumocytes of the lung alveolus.

Animals↗
PubMed1991

The life cycle of Echinostoma bolschewense (Kotova, 1939) (Trematoda: Echinostomatidae).

The life cycle of E. bolschewense, the species with 37 collar spines and closely related to E. revolutum, was experimentally studied. The following developmental stages are described: mother and daughter rediae, cercaria, metacercaria, and adult. The freshwater prosobranchiate snail Viviparus contectus was found to be the first intermediate host in nature. Under experimental conditions, the miracidia developed in V. contectus. They did not, however, penetrate into Bithynia tentaculata or into any of the pulmonate snails tested. The cercariae encysted in various Prosobranchia and Pulmonata. Adult worms were commonly obtained from hamsters (Mesocricetus auratus) and only exceptionally from chickens (Gallus gallus f. dom.). The species studied is considered to be conspecific with Cercaria bolschewensis described by Kotova (1939).

Animals↗
PubMed1999

Human papillomavirus type 31 oncoproteins E6 and E7 are required for the maintenance of episomes during the viral life cycle in normal human keratinocytes.

The E6 and E7 oncoproteins of the high-risk human papillomavirus (HPV) types are able to immortalize human keratinocytes in vitro and likely contribute to the development of anogenital malignancies in vivo. The role of these oncoproteins in the productive viral life cycle, however, is not known. To begin to examine these possible roles, mutations in E6 were introduced in the context of the complete HPV 31 genome. Although transfected wild-type HPV 31 genomes, as well as genomes containing an E6 translation termination linker, an E6 frameshift mutation, and a point mutation in the p53 interacting domain were able to replicate in transient assays, only the wild-type genome was stably maintained as an episome. Interestingly, mutant genomes in either the E6 splice-donor site or splice-acceptor site were reduced in replication ability in transient assays; however, cotransfection of E1 and E2 expression vectors restored this function. In a similar fashion, genomes containing mutant HPV 31 E7 genes, including a translation termination mutant, two Rb-binding site mutants, a casein kinase II phosphorylation site mutant, and a transformation deficient mutant, were constructed. Although transient replication was similar to wild type in all of the E7 mutants, only the casein kinase II mutant had the ability to maintain high copies of episomal genomes. These findings suggest a role for E6 and E7 in the viral life cycle beyond their ability to extend the life span of infected cells.

Casein Kinase II↗
PubMed1983

A weather-based prediction model for the life-cycle of the sheep tick, Ixodes ricinus L.

The incidence of sheep tick activity depends not only on the climatic conditions within the tick habitat, but also on the rates of fecundity, development, activity, engorgement and mortality of each stage of the life-cycle. Use of existing experimental results on the effect of these factors enables a model of the life-cycle to be formulated for the purpose of predicting the occurrence of tick activity in the field where climatic conditions vary. The components of such a model are described and the predicted results compared with field studies carried out in Ireland. It is hoped that the model presented will show the potential of formulating a system for predicting tick activity. Such a system could be used to enhance the control of tick-transmitted diseases.

Animals↗
PubMed2000

The life-cycle of Echinostoma friedi n. sp. (Trematoda: Echinostomatidae) in Spain and a discussion on the relationships within the 'revolutum' group based on cercarial chaetotaxy.

The morphology of the different stages and life-cycle of Echinostomna friedi n. sp. are described and figured. The freshwater snail Lymnaea peregra (Gastropoda: Lymnaeidae) serves as the natural and experimental first intermediate host and L. corvus and Gyraulus chinensis (Gastropoda: Planorbidae) as experimental first intermediate hosts. These, and Physella acuta (Gastropoda: Physidae), also serve as second intermediate hosts. Adult worms, possessing 37 collar spines, were obtained from naturally infected Rattus norvegicus and experimentally from albino rats, golden hamsters and chickens. Mice were not suitable experimental definitive hosts. E. friedi differs from the most closely related species in the 'revolutum' group mainly in terms of several morphological and biological features of the life-cycle stages and in its cercarial chaetotaxy. The chaetotaxy patterns of the species of the 'revolutum' group are analyzed and the results show that a taxonomic comparison of these species may be carried out on the basis of the number of sensilla in the clusters CIII VI, CIII V2 (or CIII V1 + CIII V2), CIV DL and UVb. These clusters appear adequate to establish taxonomic relationships between different species within the 'revolutum' group.

Animals↗
PubMed2005

Life cycle assessment of municipal solid waste management methods: Ankara case study.

Different solid waste management system scenarios were developed and compared for the Municipal Solid Waste Management System of Ankara by using the life cycle assessment (LCA) methodology. The solid waste management methods considered in the scenarios were collection and transportation of wastes, source reduction, Material Recovery Facility (MRF)/Transfer Stations (TS), incineration, anaerobic digestion and landfilling. The goal of the study was to determine the most environmentally friendly option of MSWM system for Ankara. The functional unit of the study was the amount of solid waste generated in the system area of concern, which are the districts of Ankara. The life cycle inventory analysis was carried out by IWM Model-1. The inputs and outputs of each management stage were defined and the inventory emissions calculated by the model were classified in to impact categories; non-renewable energy sources exhausting potential, final solid waste as hazardous and non-hazardous, global warming, acidification, eutrophication and human toxicity. The impacts were quantified with the weighing factors of each category to develop the environmental profiles of each scenario. In most of the categories, Source Reduction Scenario was found to be the most feasible management method, except the global warming category. The lowest contribution to GWP was calculated for the anaerobic digestion process. In the interpretation and improvement assessment stage, the results were further evaluated and recommendations were made to improve the current solid waste management system of Ankara.

Costs and Cost Analysis↗
PubMedDate not supplied

Coping, satisfaction, and the life cycle in families with mentally retarded persons.

The study focused on the variables influencing the functioning of 62 families with MR (mentally retarded) persons, living at home, in various stages of the life cycle. Results demonstrated the importance of some father characteristics to maternal coping skills in two-parent households. Although mean maternal coping scores were not statistically different between two-parent and single-parent households, single mothers' coping skills showed strong negative associations with both the number of children in the household and the age of the mother. This was not true of mothers in two-parent households. Single-parent mothers also appeared to be considerably more dissatisfied with family functioning than mothers in two-parent households. The supportive role of older fathers in mothers' coping in two-parent households also was apparent. Clinical implications of the study point to the need for greater support for mothers of young children with MR, mothers who are sole caregivers, and parents with many children. Differential support to mothers and fathers of an MR person may be required over the life cycle.

Adaptation, Psychological↗
PubMed1998

Identification of a Theileria annulata antigen expressed in multiple stages of the parasite life cycle.

In order to identify sporozoite surface molecules which may be involved in invasion and could act as potential vaccine candidates, a number of Mabs were raised in mice against T. annulata sporozoites. These were assayed for their ability to block sporozoite invasion of bovine peripheral blood mononuclear (PBM) cells in vitro. One of these, Mab 4B11, was found to neutralize sporozoite invasion to a high degree and to recognize a group of sporozoite antigens on Western blots. A T. annulata lambdagt11 genomic expression library was screened with Mab 4B11 and a positive clone containing a 900-bp insert (KP8) analysed further. Data from Southern and Northern blotting indicated that the gene containing the KP8 sequence, termed sporozoite and macroschizont gene 2 (spm2), was expressed both in T. annulata sporozoites and in later parasite life-cycle stages, macroschizont-infected leucocytes and piroplasms. The KP8 sequence was expressed in E. coli as a fusion protein with glutathione-S-transferase (GST) using the vector pGEX1lambdaT. Bovine antiserum raised against GST-KP8 recognised a single high molecular weight molecule on Western blots corresponding to one of the antigens recognised by Mab 4B11, expressed in sporozoites, macroschizont-infected leucocytes, and piroplasms. While our evidence suggests that the spm2 molecule alone is not responsible for sporozoite neutralization, it is a multistage antigen likely to function both in T. annulata sporozoites and in subsequent parasite life-cycle stages.

Amino Acid Sequence↗
PubMed1998

HIV-1 gag proteins: diverse functions in the virus life cycle.

The Gag proteins of HIV-1, like those of other retroviruses, are necessary and sufficient for the assembly of virus-like particles. The roles played by HIV-1 Gag proteins during the life cycle are numerous and complex, involving not only assembly but also virion maturation after particle release and early postentry steps in virus replication. As the individual Gag domains carry out their diverse functions, they must engage in interactions with themselves, other Gag proteins, other viral proteins, lipid, nucleic acid (DNA and RNA), and host cell proteins. This review briefly summarizes our current understanding of how HIV-1 Gag proteins function in the virus life cycle.

Amino Acid Sequence↗
PubMed2002

Does inhibition of Trypanosoma cruzi key enzymes affect parasite life cycle and geographic distribution?

The hemoflagellate protozoan parasite Trypanosoma cruzi is the causative agent of the Chagas disease, a progressive fatal cardiomyopathy that afflicts more than 20 million people in Central and South America. The T. cruzi life cycle is affected by changes in temperature and pH, the parasite replication being facilitated in mammalian hosts rather than in insect vectors. Here, we postulate that the modulation of key enzymes by pH- and temperature-dependent substrate inhibition may affect the T. cruzi life cycle and limit the geographic range covered by the parasite.

Animals↗
PubMed1989

The SV40 nucleosome-free region is detected throughout the virus life cycle.

The structures of SV40 intracellular chromatin complexes and of extracellular virus particles were examined by photolabeling with a radioactive psoralen derivative in order to determine the fate of the exposed origin region during the virus life cycle. We have previously shown that the origin region of intracellular SV40 chromatin is preferentially accessible to psoralen derivatives in vivo, whereas psoralen adducts are uniformly distributed when purified virus particles are photoreacted. We demonstrate here that when virion is photoreacted prior to a freeze-thaw cycle, the exposed regulatory region detected in intracellular nucleoprotein complexes is also found in mature virus particles. In contrast, if the virion is frozen and thawed prior to the photoreaction, the origin is not preferentially exposed to photoaddition. Virus particles that have not been subjected to a freeze-thaw cycle were found to exhibit preferential labeling in the origin region whether they were irradiated intracellularly, in culture medium, or following purification. Banding the virus in CsCl had no significant effect on the relative accessibility of the origin region to psorealen. Our findings indicate that the open regulatory region found on intracellular SV40 chromatin persists throughout the virus life cycle.

Animals↗