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Certain structures which indicate probable involvement of a filamentous phase in life cycle of M. leprae have been noted in preserved skin biopsy suspensions from lepromatous leprosy cases. These include (i) filaments with empty or pink round spaces within them (ii) conidia-like structures and (iii) membranes with acid fast bacilli. These structures were rare in the fresh material.
The life cycle of Rhipicephalus evertsi evertsi Neumann, 1897, is discussed under the following headings: larval feeding; larval drop; nymphal feeding; nymphal drop; nymphal moulting; adult feeding; adult drop; preoviposition period; oviposition period and incubation. Special attention has also been given to the development of both male and female reproductive organs, gametogensis and mating.
Plasmodium yoelii is a rodent parasite commonly used as a model to study malaria infection. It is the preferred model parasite for liver-stage immunological studies and is also widely used to study hepatocyte, erythrocyte and mosquito infection. We have generated a P. yoelii yoelii 17XNL line that is stably transfected with the green fluorescent protein (gfp) gene. This parasite line constitutively expresses high levels of GFP during the complete parasite life cycle including liver, blood and mosquito stages. These fluorescent parasites can be used in combination with fluorescence activated cell sorting or live microscopy for a wide range of experimental applications.
The varied ultrastructure of the eggshell of Paracapillaria (Crossicapillaria) philippinensis, collected from a human sample, is reported from a scanning electron microscopy study. Two distinct egg shapes were identified: typical peanut-shaped and swollen peanut-shaped. Both thick and thin eggshells were detected. Thick eggshells are either fairly smooth or bear a beam-like network in relation to the pillars in their surface ultrastructure. Thin eggshells are transparent allowing visibility of the coiled larva within. Presence of the thin shell provides supportive evidence of autoinfection involved in the life cycle of this medically important parasite.
The morphology of the different larval stages and life cycle of Hypoderaeum conoideum (Trematoda: Echinostomatidae) are described. The freshwater snail species Lymnaea peregra (Gastropoda: Lymnaeidae) serves as the natural first intermediate host and this and L. corvus serve as experimental first intermediate hosts. These and other freshwater snails, such as Physella acuta and Gyraulus chinensis, in turn serve as second intermediate hosts. Adult worms were obtained from chicks and ducks, but not from rats, mice and golden hamsters. The morphology of the larval stages is compared with previous work on H. conoideum. Several aspects of the biology of the life history stages are described with emphasis on the transmission dynamics of the free-living stages. Differential suitability of the snail species that may act as first and/or second intermediate hosts is studied and discussed.
The genome of Trypanosoma brucei contains about 120 chromosomes, which do not visibly condense during mitosis. We have analyzed the organization and segregation of these chromosomes by in situ hybridization using fluorescent telomere probes. At the onset of mitosis, telomeres migrate from their nuclear peripheral location and congregate into a central zone. This dense group of telomeres then splits into two entities that migrate to opposite nuclear poles. Segregation continues until the double-sized nucleus divides and, before cytokinesis occurs, the telomeres reorganize into the discrete foci observed at interphase. During migration, the telomeres are located at the free end of the mitotic spindle. Treatment with the microtubule polymerization inhibitor rhizoxin prevents telomere clustering and chromosomal segregation. In the insect-specific procyclic form as well as in the non-dividing bloodstream stumpy form, telomeres tend to cluster close to the nuclear periphery at interphase. In contrast, in the proliferative bloodstream slender form the telomeres preferentially locate in the central zone of the nucleus. Thus, telomeres are closer to the nuclear periphery during those life cycle stages where the telomeric expression sites for the variant surface glycoprotein are all inactive, suggesting that transcriptional inactivation of these sites is related to their subnuclear localization.
The completion of the genome sequence for Plasmodium falciparum, the species responsible for most malaria human deaths, has the potential to reveal hundreds of new drug targets and proteins involved in pathogenesis. However, only approximately 35% of the genes code for proteins with an identifiable function. The absence of routine genetic tools for studying Plasmodium parasites suggests that this number is unlikely to change quickly if conventional serial methods are used to characterize encoded proteins. Here, we use a high-density oligonucleotide array to generate expression profiles of human and mosquito stages of the malaria parasite's life cycle. Genes with highly correlated levels and temporal patterns of expression were often involved in similar functions or cellular processes.
Echinostoma trivolvis is a ubiquitous 37-collar-spined echinostome found in aquatic birds and mammals and in the planorbid snail Helisoma trivolvis. This echinostome has not been cycled continuously in the laboratory. The present report provides details on the continuous life cycle of E. trivolvis in dexamethasone-treated ICR mice and laboratory-raised H. trivolvis snails. Previous attempts to obtain patent adult of E. trivolvis in mice hosts failed because of worm injection within 2 weeks of infection. ICR mice infected with encysted metacercariae and injected with 2 mg/kg dexamethasone daily for 28 days yielded gravid worms that produced 250-500 eggs/worms at 21 and 28 days postinfection (p.i.). Miracidia derived from these eggs or eggs containing fully developed miracidia were capable of infecting 3- to 5-mm shell-diameter, laboratory-reared H. trivolvis snails. These snails released cercariae by 35 days p.i. Cercariae encysted in the kidney-pericardium of the snails. Encysted metacercariae could be excysted in vitro in an alkaline trypsin-bile salts medium or in vivo when fed to domestic chicks.
Molecular genetic studies of Drosophila melanogaster have led to profound advances in understanding the regulation of development. Here we report gene expression patterns for nearly one-third of all Drosophila genes during a complete time course of development. Mutations that eliminate eye or germline tissue were used to further analyze tissue-specific gene expression programs. These studies define major characteristics of the transcriptional programs that underlie the life cycle, compare development in males and females, and show that large-scale gene expression data collected from whole animals can be used to identify genes expressed in particular tissues and organs or genes involved in specific biological and biochemical processes.
Small subunit rDNA sequences were obtained from field-collected Amblyospora connecticus (Microsporida: Amblyosporidae) spores isolated from the mosquito, Aedes cantator (Diptera: Culicidae), and from field collected spores isolated from the putative intermediate host, Acanthocyclops vernalis (Copepoda: Cyclopidae). The ribosomal DNA sequences of the spores isolated from the two hosts were identical. These findings corroborate previous laboratory transmission studies and validate the intermediary role of A. vernalis in the life cycle of this microsporidium. These data represent the first comparative sequence analysis of a microsporidium isolated from its definitive and intermediate hosts. The results demonstrate the effectiveness of using rDNA sequence data for screening potential intermediate hosts. Unlike laboratory transmission tests, which can take months or years to complete, this technique can be completed in days and can be performed on a single infected organism.
An all around educational programme for general practice trainees involving a conference and seminar cirriculum was developed, based on a life-cycle concept. In addition to emphasizing the study of usual life stresses and crisee for individuals and families, the programme encouraged the contribution of resource people from many related medical disciplines and also from the non-health sciences. Detailed planning allowed the structuring of the conference over an academic year. Clearly defining the objectives for each meeting led to effective evaluation and enhanced the educational process.
Plasmodium berghei and Plasmodium chabaudi are widely used model malaria species. Comparison of their genomes, integrated with proteomic and microarray data, with the genomes of Plasmodium falciparum and Plasmodium yoelii revealed a conserved core of 4500 Plasmodium genes in the central regions of the 14 chromosomes and highlighted genes evolving rapidly because of stage-specific selective pressures. Four strategies for gene expression are apparent during the parasites' life cycle: (i) housekeeping; (ii) host-related; (iii) strategy-specific related to invasion, asexual replication, and sexual development; and (iv) stage-specific. We observed posttranscriptional gene silencing through translational repression of messenger RNA during sexual development, and a 47-base 3' untranslated region motif is implicated in this process.
In the present report we study the proteolytic activity of the excretion-secretion and crude extracts of different stages of Trichinella spiralis (Owen, 1835) Railliet, 1895, (muscle-stage larvae, adult worms before and after mating, and newborn larvae) using natural substrates (structural and hematic mammalian proteins). The analysis of the results allow us to set up a certain stage-specificity, as well as an important relationship between the protease patterns throughout the parasite life cycle and how the parasite may overcome both mechanical and humoral barriers within the host. Muscle-stage larvae present a great activity against structural proteins (collagen), while newborn larvae and adult worms degrade principally hematic proteins (hemoglobin, fibrinogen and immunoglobulin G).
The life-cycle and taxonomically important properties of the yeast-form of Asterophora lycoperdoides (Nyctalis asterophora Fr.) were investigated. This yeast resembles representatives of some genera of basidiomycetous and imperfect yeasts, especially with respect to some biochemical characteristics.
The effects of tributyltin (TBT) to the life cycle of the estuarine fish Cyprinodon variegatus were examined in a 180-day flow-through exposure. The study was initiated with embryos less than 24 h postfertilization and monitored through hatch, maturation, growth, and reproduction under continuous exposure to mean measured TBT concentrations of 5.4, 3.2, 1.3, 0.66, and 0.41 microg TBT/L. Progeny isolated at the onset of reproduction by the parental generation (F0) were monitored for survival as embryos, survival as fry/juveniles, and growth 30 days postisolation. TBT, at a concentration of 5.4 microg/L, significantly reduced embryo survival of the F0 generation sheepshead minnows. By day 145 of the exposure, significant effects to the survival of this generation increased and included all test concentrations >/=0.66 microg/L. Survival of 0.66 microg/L was reduced 59% relative to control survival by termination of the F0 generation. Growth of F0 generation organisms as measured by standard length was significantly reduced only on day 90 at 3.2 microg/L, however no significant reductions of wet or dry weight related to treatment concentration were detected. Due to complete mortality of organisms exposed to 5.4 microg/L by study day 7, effects to fecundity and progeny were monitored at measured concentrations of 3.2, 1.3, 0.66, and 0.41 microg TBT/L. Fecundity, as measured by the production of viable eggs produced per female per day, was unaffected by any of the test treatments. All F1 generation embryos isolated from treatment chambers into 3.2 microg/L died. Survival, standard length, wet and dry weight of the F1 generation at the remaining treatment concentrations were unaffected. The results of this study indicate that exposure to TBT reduced survival of the F0 generation sheepshead minnow and establishes the lowest observed effect concentration (LOEC) as 0.66 microg TBT/L, and the no observed effect concentration (NOEC) as 0.41 microg TBT/L for this species.http://link.springer-ny. com/link/service/journals/00244/bibs/37n2p258.html
African trypanosome variant surface antigen, which was released from the Trypanosoma brucei parasite at two stages in its life cycle, has been characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of 4 M urea. Variant surface antigen released as exoantigen into the bloodstream of infected rats resembled the soluble form of the surface antigen. Variant surface antigen released from parasites undergoing transformation to the uncoated procyclic stage was detected as two molecular species: soluble variant surface antigen and a cleavage product of variant surface antigen. The data presented are consistent with enzymatic cleavage of the variant surface antigen C-terminal hydrophobic moiety operating to release parasite surface coat from living parasites.
Triiodothyronine (T3) was measured by double antibody radioimmunoassay in the sera of individuals of all stages of the life cycle in the sea lamprey, Petromyzon marinus, and in larval (ammocoetes) and metamorphosing individuals of the brook lamprey, Lampetra lamottenii. There was no significant difference in results from the two species. Although serum T3 concentration did not vary significantly in ammocoetes maintained at the same temperature throughout the year, concentrations in ammocoetes displayed an inverse response to fluctuations in water temperature. Ammocoetes maintained at temperatures of 7 to 10 degrees and 19 to 21 degrees exhibited significantly different circulating T3 levels of 2400 and 1550 ng dl-1, respectively. Therefore, it is expected that there may be some seasonal variation in the levels of the hormone in ammocoetes in their natural environment. A precipitous collapse of the serum levels of T3 was observed by an early stage of metamorphosis (100 ng dl-1) and no significant difference in levels was observed throughout the remaining period of this phase. Young parasitic adults and adult lampreys collected during their spawning migration (upstream migrants) exhibited circulating T3 concentrations of 40 and 30 ng dl-1, respectively. T3 levels in some upstream migrants were below the limit of detection (less than 5 ng dl-1). The metamorphic decline in serum T3 may simply mark the beginning of the lower T3 levels that characterizes the adult serum.
The life cycle of Amblyospora indicola, a parasite of the mosquito Culex sitiens, was revealed by field observations and laboratory infection experiments conducted in Australia. In northern Queensland, infected C. sitiens larvae were often found breeding in association with two cyclopoid copepods: Apocyclops dengizicus and an undescribed species of the same genus. The latter species was found to be an intermediate copepod host of this microsporidium whereas A. dengizicus was not. One complete cycle of the parasite extends over two mosquito generations (by transovarial transmission from females with binucleate spores to their eggs) and by horizontal transmission between mosquitoes and copepods. The latter involves horizontal transmission from mosquitoes to copepods via meiospores produced in larval fat body infections and horizontal transmission from copepods to mosquitoes via uninucleate spores produced within infected copepods. Uninucleate clavate spores were formed in Apocyclops sp. nov. copepods 7-10 days after exposure to larval meiospores and were infectious to larvae of a microsporidian-free colony of C. sitiens. The development of A. indicola within mosquito larvae exposed to infected copepods is similar to that of A. dyxenoides infecting C. annulirostris. It proceeds from stages with a single nucleus to diplokaryotic binucleate cells in oenocytes. These stages persist through pupation to adult emergence after which time a proportion of male mosquitoes and female mosquitoes may develop binucleate spores without the need for a blood meal. A proportion of both male and female larval progeny of infected females with binucleate spores develop patent fat body infections via transovarial transmission and die in the fourth larval instar.(ABSTRACT TRUNCATED AT 250 WORDS)