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At least 847 records · Page 47Linked to original sources
PubMed1990

Serological study of louse borne and flea borne typhus in Addis Ababa.

A total of 500 subjects (288 males and 212 females) were tested in Addis Ababa, Ethiopia, in Virology and Rickettsiology Division of the National Research Institute of Health, in 1987, for anti R. prowazekii using Complement Fixation Test (CFT). Out of these 58 subjects (41 males and 17 females) were also tested for anti R. typhi using the same test. The study population included three groups. Group I included 200 patients referred to the National Research Institute of Health (NRIH) for the Weil-Felix test for the diagnosis of typhus. Group II consisted of 200 patients with febrile illness visiting the Outpatient Department (OPD) of St. Paul's Hospital. Group III included 100 blood donors' serum samples included from previous collections. The blood donors had no sign of febrile illness during the collection of the blood samples. The results showed that anti R. prowazekii was detected in 38 subjects (7.6%). The sex ratio among the positive subjects indicated that there were 32 males (22%) and 6 females (2.8%). From the 58 subjects who were also tested for anti R-typhi only 7 (5 males and 2 females) (12%) were found to be positive. Only one person was found to be positive both for anti R. prowazekii and anti R-typhi. From 200 samples (Group-I) tested both by the Weil-Felix test and by Complement Fixation Test for anti R. prowazekii only 4 samples were positive by both test, thus showing very low percent agreement.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1997

Effects of estrogenic xenobiotics on molting of the water flea, Daphnia magna.

The effects of five xenobiotics, 2,4,5-trichloribiphenyl (PCB29), the polychlorinated biphenyl (PCB) Aroclor 1242, diethyl phthalate, lindane, and 4-octylphenol, on molting of Daphnia magna were investigated. All except PCB29 are known to have unexpected estrogenicity in vertebrates. Daphnids exposed to PCB29, Aroclor 1242, and diethyl phthalate took significantly more time to complete four molts than did the controls. The inhibitory effects of these ortho-chlorinated PCBs suggest that certain structural features, most probably including ortho-chlorination, are related to the ability of a PCB to affect molting. Agents with multicyclic structures, such as PCBs, are more effective in inhibiting molting than are single-ringed xenobiotics, such as diethyl phthalate, which suggests that hydrophobicity may be a requirement for binding to the ecdysteroid receptor. These molt-inhibiting agents with multiple rings appear to bear more structural resemblance to the steroidal molting hormones of arthropods, the ecdysteroids, than do the single-ringed ones. While the possibility of alternative mechanisms, such as impairment of ecdysteroidogenesis exists, the results obtained herein support the hypothesis that some xenobiotics which disrupt endocrine processes in vertebrates can also interfere with the hormonally regulated molting process in arthropods through acting as antagonists of endogenous ecdysteroids by binding to and thereby blocking the ecdysteroid receptor.

Animals↗
PubMed1983

The fine structure of the gill epithelium of a fresh-water flea, Daphnia magna (Crustacea: Phyllopoda) and changes associated with acclimation to various salinities. I. Normal fine structure.

Two kinds of epithelial cells, dark and light types, are alternately arranged in the gill of Daphnia magna. The dark cell has numerous mitochondria and an elaborate tubular system containing two kinds of cytoplasmic tubules, small about 70 nm in diameter, and large about 130 nm in diameter. The former occur in bundles and seem to be smooth-surfaced endoplasmic reticulum. The latter, lined with a ridged surface coat and frequently open at the lateral and basal cell membrane, are regarded as extensions of the cell membrane. The atypical cell membrane of the dark cell is modified by repeated subunits of a cytoplasmic coat on the inner leaflet of the unit membrane. The light cell exhibits a high degree of basal infoldings of the cell membrane, which represent a magnification of the surface area of the cell. Large mitochondria between the infoldings often come into intimate association with the infolded cell membrane to form a regular array of parallel mitochondria interposed with the double cell membranes. The results suggest that at least the dark epithelial cells play an important role in the osmoregulation of this animal.

Animals↗
PubMed2002

Circulatory oxygen transport in the water flea Daphnia magna.

To determine the contribution of circulatory convection to tissue oxygen supply in animals of Daphnia magna, heart rate ( f(H)), in-vivo Hb oxygen-saturation ( S(Hb)) and NADH fluorescence intensity ( I(NADH)) as a measure of the tissue oxygenation state were simultaneously measured using digital motion analysis, microabsorption spectroscopy and fluorescence microscopy. In addition, the relationship between stroke volume and body size was established. Groups of differently sized animals (small: 1.4-1.6 mm, medium: 2.7-2.9 mm, large: 3.3 mm) with either low (Hb-poor) or high Hb concentration (Hb-rich) in the hemolymph were exposed to a gradual decrease in ambient oxygen partial pressure ( P(O2amb)) between normoxia and anoxia. In all groups, f(H) increased in response to progressive hypoxia. The hypoxic maximum in f(H) was highest in medium-sized Hb-poor animals, whereas perfusion rate increased continuously with increasing body size in Hb-poor and Hb-rich animals. The P(O2amb) at which Hb in the heart region was half-saturated (in-vivo P(50)) was higher in medium-sized (Hb-poor: 3.2 kPa, Hb-rich: 2.0 kPa) than in small (Hb-poor: 2.1 kPa, Hb-rich: 1.5 kPa) and large animals (Hb-poor: 1.9 kPa). The in-vivo P(50) was always lower in Hb-rich than in Hb-poor animals. The I(NADH) indicated an impairment of tissue oxygenation starting at higher critical P(O2amb) with increasing body size and with lower Hb concentration. Model calculations suggest that at the respective critical P(O2amb), circulatory convection delivers less than half of the oxygen demand in Hb-poor animals. In contrast, in Hb-rich animals, the contribution of circulatory convection to tissue oxygen supply at respective critical P(O2amb) was much greater due to the higher concentration of Hb.

Animals↗