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PubMed1982

Cytological examination of Leeuwenhoek's first microbial specimens.

Of the nine packets of specimens sent by van Leeuwenhoek to London in the seventeenth century, and which were recently rediscovered in their original condition, three contained dried aquatic microorganisms. The author has reconstituted portions of this material. Several recognizable organisms have been noted, including portions of this material. Several recognizable organisms have been noted, including water-fleas, chlorophyte and cyanophyte algae, desmids, diatoms and rotifers. These provide evidence for the formation of the 'heavenly paper', which was believed at the time to represent charred notepaper dropped from the skies, but which Leeuwenhoek rightly assumed to be dried algal felts. Photomicrographs reveal many cytological details in the material, and this has been correlated with Leeuwenhoek's descriptions, extracted from the original correspondence.

Eukaryota↗

PubMed1988

Acute toxicity of cresols, xylenols, and trimethylphenols to Daphnia magna Straus 1820.

Twenty-four-hour IC50 values (50% immobilization concentration) for phenol, o-cresol, m-cresol, p-cresol, six xylenols, and three trimethylphenols were determined for Daphnia magna under static conditions. Our results show that cresols are more toxic than phenol, that xylenols do not exhibit significantly higher toxicity than cresols, and that trimethylphenols are less toxic than cresols. Thus, no direct relationship can be found between the number and position of methyl groups on the phenol nucleus and their acute toxicity to the water flea.

Animals↗

PubMed1995

Accidental contamination from uranium compounds through contact with ceramic dinnerware.

Examination of orange-colored dinnerware samples purchased in antique stores and flea markets has revealed the occasional presence of surface uranium compounds that are readily transferred to the hands and clothing. We have further been able to produce soluble uranium compounds on the surfaces of clean dishes by exposing them to household vinegar or bleach. We estimate that handling of a contaminated dish can transfer up to 1-2 becquerels or more of uranium compounds to the hands. Uranium contamination is of concern because the element is not only an alpha emitter but also a chemical nephrotoxin. Although the amount of uranium likely to be ingested as a result of casual handling may be small, it could still exceed by several times the amount occurring in the average diet (about 40 mBq/day). Furthermore, since fresh surface compounds are readily formed, it is possible that a person who regularly handles or eats from uranium-glazed dinnerware can accidentally ingest significant amounts of uranium.

Ceramics↗

PubMed1996

Effect of microwave heating on leaching of lead from old ceramic dinnerware.

When samples of pre-1950s U.S.-made ceramic dinnerware, purchased in antique shops and flea markets, were filled with 4% acetic acid or 0.5% citric acid and heated in a microwave oven for 2-5 min, lead was leached in amounts of up to 5 mg per dish. Concentrations of lead in the leachates were not significantly correlated with, and could not be predicted from, concentrations in leachates measured during 24-h room temperature acid leaching tests. Unsafe lead concentrations (>3 microg/ ml) were found in microwave leachates of dishes with uranium-containing glazes, with copper-containing glazes, and with floral over-the-glaze decals. This evidence suggests that use of such dishes to microwave common foods could result in the ingestion of dangerously large amounts of lead.

Acetic Acid↗

PubMed1985

Toxic impact of effluents from petrochemical industry.

The toxicity of effluents from a petrochemical industry center in southern Finland was tested by conducting bioassays on organisms from three different trophic levels. In fish tests, rainbow trout (Salmo gairdneri) were caged at the discharge site and simultaneously at a reference area. The only clear differences, among the measurements of 25 metabolic parameters, were observed in fish liver where activities of two detoxication enzymes were significantly increased in the exposed group. The water flea (Daphnia magna) was used both in acute (EC50) and long-term reproduction tests. No acute lethal toxicity was detected in any of the wastewater samples investigated. A combined effluent, however, caused a reduction in the reproduction rate with an EC50 of 3%. No mutagenic activity was observed with the Ames test (Salmonella typhimurium, strains TA 97, TA 98, and TA 100) in concentrated effluents, in sediment samples, or in liver samples from predator fish caught from the discharge site.

Acetylcholinesterase↗

PubMed1986

The physiology of itch.

The perception of itch is associated with many parasites and their vectors, especially following penetration of the skin by the parasites themselves, as in cercarial dermatitis of schistosome infections, or penetration of arthropod mouthparts during blood feeding. Many ectoparasites such as scabies, lice and fleas, provoke sensations of itch - even when the insects are no longer (or have never been) present, giving rise to the phenomenon of delusory parasitosis. Itch, and the host 'grooming' responses with which it is associated, is increasingly recognized as an important factor in modulating vector feeding behaviour, which can have profound effects on the transmission dynamics of vector borne parasites. As a background to future reviews of this developing subject, we asked John Alexander, author of the classic Arthropods and Human Skin (Springer-Verlag, 1984), to explain what is itch, and to discuss what is known about its underlying Physiology.

Journal Article↗

PubMed1990

Health aspects of resettlement in Ethiopia.

The literature on health implications and effects of government-sponsored resettlement in Ethiopia is reviewed with the objective of providing an initial evaluation of the health status of settlers and the health hazards of resettlement in western Ethiopia. Emphasis is on the 1984/85 resettlement program, which resulted in the movement of about 600,000 drought victims from northern and central Ethiopia to the western part of the country. Malaria, trypanosomiasis, onchocerciasis, yellow fever, nonfilarial elephantiasis, sand-flea infestation, and psychological stress are identified as immediate and greater health hazards than in the areas of settler origin, based on the geographic distribution and ecology of the major communicable, nutritional, and geochemical diseases in Ethiopia, and on the impact of program deficiencies on settler health. More studies are needed on the epidemiology and ecology of bancroftian filariasis, visceral leishmaniasis, dracunculiasis, eye and skin diseases, tuberculosis, meningitis, intestinal parasitism, diarrhea, and calorie/protein malnutrition before their public health and economic significance in settlements can be evaluated. Schistosomiasis appears to be less common, for the time being, in resettlement areas than in the areas of outmigration. Research needs and constraints in resettlement planning, implementation, and operation are identified, and some recommendations made for disease control programs.

Adult↗

PubMed1994

The occurrence of artemocyanin in Branchiopoda (Crustacea).

Artemocyanin, the extracellular hemolymph biliprotein of Artemia, is demonstrated in the fairy shrimp Streptocephalus, the clam shrimp Leptestheria and the water flea Daphnia. Artemocyanins can be purified from hemolymph as intact polypeptides (Mr 170-190,000), but are degraded upon homogenization of the whole animal by partial proteolysis to polypeptides with Mr 102,000 and 85,000. The aminoterminal sequence of the intact artemocyanin polypeptide was determined, but no clear-cut relationships with arthropod biliproteins or other protein families could be demonstrated.

Amino Acid Sequence↗

PubMed1992

The biology of Ctenocephalides canis in Ireland.

A colony of Ctenocephalides canis was established using dogs as hosts. Two diets were used as media. Fleas reared on cats did not develop beyond the first larval stages. The effects of different temperatures on egg hatching and larval development were examined. Larval survival was poor at 22 degrees C and 25 degrees C at 50% relative humidity, but good at 75% relative humidity at these temperatures. The development from egg to adult took 21 days.

Animals↗

PubMed1992

Arthropoda as zoonoses and their implications.

Some aspects of changing patterns of arthropodal infections and arthropod-borne diseases in Mediterranean areas are briefly discussed. Selected examples are given, with particular emphasis on the phenomenon of the synanthropic flea Ctenocephalides felis felis and on health problems caused by human infections with Argas reflexus, the common tick of urban pigeons in Europe. Finally, the risk of the emergence of Lyme borreliosis (Borrelia burgdorferi) is considered in relation to the increasing spread of environmental infestation with ticks, mainly Ixodes ricinus, an efficacious vector for the spirochaete.

Animals↗

PubMed1977

Evolution of ribosomal RNA.

1. The G + C content of ribosomal RNA of animals seems correlated with the length of periods required for maturation of those organisms. 2. In Protostomes of the animal kingdom, the size of the 28S rRNA molecule does not seem to correlate with the evolutionary stage of the organism. 3. Aphids and water-fleas as well as some protozoa have the 18S rRNA with mol. wt of 0.9 x 10(6) against an overwhelming pressure of evolution to conserve the rRNA molecule of 0.7 x 10(6) daltons. 4. All the Deuterostomes examined were distinguished from Protostomes by having the 28S rRNA's void of the hidden break at the central point. 5. Aphids and nematodes are exceptional Protostomes in that they have the 28S rRNA's without the hidden break. This was discussed in the light of the evolutionary stage of these organisms. 6. Molecular properties of chloroplast rRNA seem to evidence for endosymbiotic origin of this organelle. Mitochondrial rRNA differs considerably from prokaryotic rRNA with respect to molecular size and base composition.

Biological Evolution↗

PubMed1992

Effects of temperature on the anaesthetic potency of halothane, enflurane and ethanol in Daphnia magna (Cladocera: Crustacea).

1. The effects of temperature on the anesthetic potencies of halothane, enflurane and ethanol have been studied in the water flea Daphnia magna. 2. In the absence of anaesthetics, decreasing temperature resulted in decreased activity by the daphnids. 3. Potencies in the gas phase decreased with increasing temperature for all of the anaesthetics, while aqueous potency decreased for halothane and enflurane but increased for ethanol. 4. Enthalpy calculations suggest that the observed potency changes for the inhalational anaesthetics cannot be accounted for in terms of changing solubility in lipid bilayers but most likely reflect more specific interactions with animal target sites.

Animals↗

PubMed1992

Analysis of Yersinia pestis chromosomal determinants Pgm+ and Psts associated with virulence.

The ability to absorb exogenous pigments (Pgm+) has, until now, been considered an established virulence factor of Yersinia pestis, the causative agent of plague. This property correlates with the sensitivity to the bacteriocin pesticin (Psts). Both functions are chromosomally encoded. In the present study, using Hfr donors and isogenic Pgm-Psts and Pgm-Pstr mutants, these functions were shown to be determined by discrete but closely linked genes. These markers designated pgm and psn, respectively, were preliminarily located within a linkage group including 11 loci. It was also found that pigmentation is not essential for mouse virulence but is necessary for survival of Y. pestis in the flea, the plague vector. At the same time, conversion of an avirulent Pstr mutant to pesticin sensitivity restored some degree of virulence.

Animals↗

PubMed2005

Cold temperature-induced modifications to the composition and structure of the lipopolysaccharide of Yersinia pestis.

Following a report of variations in the lipopolysaccharide (LPS) structure of Yersinia pestis at mammalian (37 degrees C) and flea (25 degrees C) temperatures, a number of changes to the LPS structure were observed when the bacterium was cultivated at a temperature of winter-hibernating rodents (6 degrees C). In addition to one of the known Y. pestis LPS types, LPS of a new type was isolated from Y. pestis KM218 grown at 6 degrees C. The core of the latter differs in: (i) replacement of terminal galactose with terminal d-glycero-d-manno-heptose; (ii) phosphorylation of terminal oct-2-ulosonic acid with phosphoethanolamine; (iii) a lower content of GlcNAc, and; (iv) the absence of glycine; lipid A differs in the lack of any 4-amino-4-deoxyarabinose and presumably partial (di)oxygenation of a fatty acid(s). The data obtained suggest that cold temperature switches on an alternative mechanism of control of the synthesis of Y. pestis LPS.

Carbohydrate Sequence↗

PubMed2004

Physiological interactions of silver and humic substances in Daphnia magna: effects on reproduction and silver accumulation following an acute silver challenge.

Silver (Ag) in aquatic environments mediates its toxic actions by inhibiting sodium influx. Humic substances protect against silver toxicity by complexing the toxic, ionic form of the metal, but may also directly stimulate sodium influx in aquatic organisms. This study investigated the effects of silver and humic substances on the water flea Daphnia magna. Acute silver challenge (24 h; 1 microg L(-1)) and the chronic exposure to humic substances (Aldrich humic acid; 7 mg C L(-1)) had considerable influence on daphnid physiology and reproduction. In particular silver exposure in the absence of humic substances stimulated reproduction, resulted in enhanced adult mass, and altered both the response of the animal to subsequent silver exposure and a physiological surrogate measure of silver toxicity (whole body sodium concentration). The presence of humic substances countered the effects on adult mass and reproduction, returning these parameters to control levels. Humic substances also lowered silver body burden, but with significantly improved whole body sodium status than previously silver-exposed animals. These changes may distort the correlation between silver body burden and indicators of toxic action, an important tenet of site-specific risk assessment tools such as the biotic ligand model.

Animals↗

PubMed2005

Production of male neonates in four cladoceran species exposed to a juvenile hormone analog, fenoxycarb.

Previous studies have found that exposure of a cyclic parthenogen, the water flea Daphnia magna (Cladocera, Crustacea), to juvenile hormones and their analogs results in the production of neonates of male sex at concentration-dependent rates. We conducted reproduction experiments in four different species (Moina macrocopa, M. micrura, Ceriodaphnia dubia and C. reticulata) of cladoceran to test for the first time whether the occurrence of this phenomenon after exposure of the parent to such hormones is a generalized phenomenon. In the presence of a juvenile hormone analog, fenoxycarb, all four species produced male neonates and showed reduced rates of reproduction. The estimated median effective concentration (EC50) for the production of male neonates varied with species, ranging from 0.60 x 10(3) to 9.3 x 10(3) ng/l. Although there was a wide range of sensitivity to fenoxycarb, the production of male neonates in all four species demonstrates that this phenomenon is a common response to juvenile hormone analogs and further suggests that these hormones are capable of initiating sexual reproduction in cladocerans, most of which exhibit cyclic parthenogenesis.

Animals↗

PubMed2005

Production of male neonates in Daphnia magna (Cladocera, Crustacea) exposed to juvenile hormones and their analogs.

We exposed the water flea Daphnia magna (Cladocera, Crustacea) to either juvenile hormone I (JH I), juvenile hormone II (JH II), or the juvenile hormone-mimicking insecticides kinoprene, hydroprene, epofenonane, or fenoxycarb. By 21-day reproduction tests, we investigated the effects on the number of neonates born per female and the offspring sex ratio. All six chemicals induced D. magna to produce male neonates; the male sex ratio of the offspring increased as the chemical concentration increased. EC50 values for production of male neonates were estimated as 400 (JH I), 410 (JH II), 190 (kinoprene), 2.9 (hydroprene), 64 (epofenonane), and 0.92 (fenoxycarb) microg/l. The number of neonates produced was reduced with all chemicals at the concentrations investigated. At the EC50 for male production, five of the six chemicals reduced the reproductive rate to less than 50%; the exception was epofenonane, which caused only a slight reduction in reproductive rate. These results were similar to those obtained for five juvenoids studied previously, one of which was studied here again. There are now 10 chemical substances--all juvenile hormones or their analogs-that are known to induce D. magna to produce male neonates. This suggests that juvenile hormone is involved in initiating male production followed by sexual reproduction in D. magna, and probably in most cladocerans that exhibit cyclic parthenogenesis.

Animals↗

PubMed2005

Turning Yersinia pathogenesis outside in: subversion of macrophage function by intracellular yersiniae.

Three bacterial species within the genus Yersinia are causative agents of human disease. Yersinia pestis is transmitted by fleas or in aerosols, infects regional lymph nodes or lungs, and causes the highly lethal disease known as plague. Yersinia enterocolitica and Yersinia pseudotuberculosis are enteric pathogens most commonly associated with self-limiting infections of the mesenteric lymph nodes. Although Y. pestis and the enteropathogenic Yersinia species utilize different modes of transmission and cause different diseases, they rely on a common set of "core" virulence determinants to successfully infect a mammalian host. These virulence factors are encoded on the bacterial chromosome and on an approximately 70-kb plasmid. Once established in lymphoid tissue, all three Yersinia species replicate as aggregates of extracellular bacteria within necrotic lesions or abscesses. At this stage of the infectious process, the bacteria resist phagocytosis by neutrophils, which are able to destroy the bacteria if they are internalized. A type III secretion system encoded on the 70-kb plasmid functions to export multiple proteins (the Yops and LcrV) that are delivered to the extracellular milieu, the plasma membrane, or the cytosol of a host target cell. The Yops and LcrV act in concert to inhibit phagocytosis and downregulate inflammation. Although it is clear that the bulk of bacterial multiplication occurs in an extracellular phase, there is also evidence that all three pathogenic Yersinia survive and multiply in macrophages. Survival and replication of Yersinia in macrophages may occur throughout the infection, but is likely to be of greatest importance at early stages of colonization. That macrophages can serve as permissive sites for bacterial replication in vivo is supported by in vitro experiments, which demonstrate that Y. pestis, Y. peudotuberculosis, and Y. enterocolitica share the ability to survive and multiply in macrophage phagosomes. There is also evidence that the bacteria can subvert the functions of macrophages from within, by inhibiting phagosome acidification (Y. pseudotuberculosis) and the production of nitric oxide (Y. pestis and Y. pseudotuberculosis). Although considerable attention has been focused on how Yersinia subverts the functions of phagocytes from the outside, the study of how these bacteria subvert macrophage functions from the inside will lead to a better overall understanding of Yersinia pathogenesis.

Animals↗