National progress in dengue vector control in Vietnam: survey for Mesocyclops (Copepoda), Micronecta (Corixidae), and fish as biological control agents.
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This paper describes the process of expanding a successful dengue control program in 3 provinces in northern Vietnam into a national one and demonstrates the presence of a rich, low-cost resource that could have similar applicability to other countries in the region. The cornerstone of the preventive strategy is larval control of Aedes aegypti (L.), the major vector, using predators such as copepods, Mesocyclops spp., aided by the corixid bug Micronecta quadristrigata Bredd, and fish in large water storage containers. From 1989 to 1998, 9 species of Mesocyclops (M. woutersi Van de Velde, M. aspericornis (Daday), M. ruttneri Kiefer, M. thermocyclopoides Harada, M. affinis Van de Velde, M. ogunnus Onabamiro, M. yenae Holynska, M. cf. pehpeiensis Hu, and M. dissimilis Defaye and Kawabata) were found in natural and artificial habitats in 26 provinces throughout Vietnam. The predatory capacities of 6 of these were evaluated in the laboratory. This indicated that daily consumption/killing averaged between 16 and 41 Ae. aegypti larvae per copepod. From detailed evaluations in 9 provinces, Mesocyclops spp. were surprisingly common in 8,413 artificial containers (concrete tanks, wells, ornamental ponds and in the south, large jars). Because of existing practices for washing and water transfer from ponds and lakes in Ha Tay and Ha Bac, Mesocyclops spp. already occurred in 60-100% of the water storage containers. When the relationship between the presence or absence of Mesocyclops and Aedes larvae in 5,111 containers was analyzed by the chi-square test, their distributions were significantly related, indicating control (odds ratio = 0.56). When 3,426 containers that did not contain Mesocyclops or fish were analyzed in relation to the distribution of Aedes larvae, those with Micronecta also had significantly less Aedes (odds ratio = 0.43). Therefore, this study demonstrates that there is an abundance of local Mesocyclops spp. in Vietnam that can be incorporated into specifically designed community-based control programs aided by Micronecta and fish. (+info)
Propeptide dependent activation of the Antarctic krill euphauserase precursor produced in yeast.
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Euphauserase is a brachyurin type digestive enzyme isolated from Antarctic krill. The brachyurins belong to clan SA of the S1 family of serine endopeptidases. In this study, we demonstrate that the precursor form of recombinant euphauserase, termed pro-r-euphauserase, can be successfully expressed in Pichia pastoris. The presence of most of the 51-residue euphauserase propeptide is essential during expression, under the growth conditions of Pichia. The propeptide may be required either for correct folding or processing of the enzyme. Cod trypsin generates a fully active r-euphauserase from its precursor, which appears to be identical to the native enzyme. The mature r-euphauserase sequence contains 250 amino-acid residues including a 13-residue activation peptide, which seems to be attached to the molecule by a disulfide bond. Euphauserase shares an average sequence identity of 62% with its type I brachyurin analogue, crab collagenase I. However, the identity between these two sequences is much higher in the regions shown to be important for the broad substrate specificity and collagen binding of crab collagenase I. The type I brachyurins share only 30-40% identities with the type II brachyurins and trypsins. The low isoelectric point of euphauserase, with a calculated pI value of 3.9, is typical for the type I brachyurins. (+info)
Life in transition: balancing inertial and viscous forces by planktonic copepods.
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Copepods (1-10 mm aquatic crustaceans moving at 1-1000 mm s(-1)) live at Reynolds numbers that vary over 5 orders of magnitude, from 10(-2) to 10(3). Hence, they live at the interface between laminar and turbulent regimes and are subject to the physical constraints imposed by both viscous and inertial realms. At large scales, the inertially driven system enforces the dominance of physically derived fluid motion; plankton, advected by currents, adjust their life histories to the changing oceanic environment. At Kolmogorov scales, a careful interplay of evenly matched forces of biology and physics occurs. Copepods conform or deform the local physical environment for their survival, using morphological and behavioral adaptations to shift the balance in their favor. Examples of these balances and transitions are observed when copepods engage in their various survival tasks of feeding, predator avoidance, mating, and signaling. Quantitative analyses of their behavior give measures of such physical properties of their fluid medium as energy dissipation rates, molecular diffusion rates, eddy size, and eddy packaging. Understanding the micromechanics of small-scale biological-physical-chemical interactions gives insight into factors influencing large-scale dynamics of copepod distribution, patchiness, and encounter probabilities in the sea. (+info)
Comparison of methods for detection of Erysipelothrix spp. and their distribution in some Australasian seafoods.
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For many years, Erysipelothrix rhusiopathiae has been known to be the causative agent of the occupationally related infection erysipeloid. A survey of the distribution of Erysipelothrix spp. in 19 Australasian seafoods was conducted, and methodologies for the detection of Erysipelothrix spp. were evaluated. Twenty-one Erysipelothrix spp. were isolated from 52 seafood parts. Primary isolation of Erysipelothrix spp. was most efficiently achieved with brain heart infusion broth enrichment followed by subculture onto a selective brain heart infusion agar containing kanamycin, neomycin, and vancomycin after 48 h of incubation. Selective tryptic soy broth, with 48 h of incubation, was the best culture method for the detection of Erysipelothrix spp. with PCR. PCR detection was 50% more sensitive than culture. E. rhusiopathiae was isolated from a variety of different fish, cephalopods, and crustaceans, including a Western rock lobster (Panulirus cygnus). There was no significant correlation between the origin of the seafoods tested and the distribution of E. rhusiopathiae. An organism indistinguishable from Erysipelothrix tonsillarum was isolated for the first time from an Australian oyster and a silver bream. Overall, Erysipelothrix spp. were widely distributed in Australasian seafoods, illustrating the potential for erysipeloid-like infections in fishermen. (+info)
Ontogenetic changes in visual sensitivity of the parasitic salmon louse Lepeophtheirus salmonis.
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The salmon louse, Lepeophtheirus salmonis, is an ectoparasitic copepod of salmonid fishes whose life cycle involves two broadly defined, free-living larval stages, the nauplius and the copepodid. After settling on a host, the copepodid goes through various transformations to become a mobile adult. We recorded swimming responses of free-swimming salmon lice at the naupliar, copepodid and adult stages to the onset (ON) and offset (OFF) of lights of varying spectral irradiance and polarization. Nauplii showed a prominent swim-up OFF response across the spectrum 352-652 nm, but no ON response. Copepodids exhibited a swim-up ON response and a passive (sinking) OFF response across the same spectral range. Adults showed active swim-up responses to both ON and OFF stimuli, although the OFF response was proportionately stronger. The spectral range of the adult ON and OFF responses was the same as that of the copepodids and slightly greater than that of the nauplii, which did not exhibit responses at 652 nm. The absolute sensitivity of copepodids under white light (approx. 10(-13) photons m(2) s(1)) was higher than that of nauplii (approx. 10(-17) photons(-1) m(2 )s, OFF response) and that of adult female lice (approx. 10(-14) photons(-1)m(2)s). This suggests that the naupliar visual system is best suited for detection of shadows (e.g. the host) under a bright light field (daylight hours), while copepodids and adults may be more specialized for host detection at crepuscular periods and during the night, when light levels are low. None of the developmental stages responded to the rotation of the plane of polarized light or exhibited any difference in directed response when polarized light was used in place of diffuse light. (+info)
Crustacean (malacostracan) Hox genes and the evolution of the arthropod trunk.
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Representatives of the Insecta and the Malacostraca (higher crustaceans) have highly derived body plans subdivided into several tagma, groups of segments united by a common function and/or morphology. The tagmatization of segments in the trunk, the part of the body between head and telson, in both lineages is thought to have evolved independently from ancestors with a distinct head but a homonomous, undifferentiated trunk. In the branchiopod crustacean, Artemia franciscana, the trunk Hox genes are expressed in broad overlapping domains suggesting a conserved ancestral state (Averof, M. and Akam, M. (1995) Nature 376, 420-423). In comparison, in insects, the Antennapedia-class genes of the homeotic clusters are more regionally deployed into distinct domains where they serve to control the morphology of the different trunk segments. Thus an originally Artemia-like pattern of homeotic gene expression has apparently been modified in the insect lineage associated with and perhaps facilitating the observed pattern of tagmatization. Since insects are the only arthropods with a derived trunk tagmosis tested to date, we examined the expression patterns of the Hox genes Antp, Ubx and abd-A in the malacostracan crustacean Porcellio scaber (Oniscidae, Isopoda). We found that, unlike the pattern seen in Artemia, these genes are expressed in well-defined discrete domains coinciding with tagmatic boundaries which are distinct from those of the insects. Our observations suggest that, during the independent tagmatization in insects and malacostracan crustaceans, the homologous 'trunk' genes evolved to perform different developmental functions. We also propose that, in each lineage, the changes in Hox gene expression pattern may have been important in trunk tagmatization. (+info)
The complete sequence of the mitochondrial genome of the crustacean Penaeus monodon: are malacostracan crustaceans more closely related to insects than to branchiopods?
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The complete sequence of the mitochondrial genome of the giant tiger prawn, Penaeus monodon (Arthropoda, Crustacea, Malacostraca), is presented. The gene content and gene order are identical to those observed in Drosophila yakuba. The overall AT composition is lower than that observed in the known insect mitochondrial genomes, but higher than that observed in the other two crustaceans for which complete mitochondrial sequence is available. Analysis of the effect of nucleotide bias on codon composition across the Arthropoda reveals a trend with the crustaceans represented showing the lowest proportion of AT-rich codons in mitochondrial protein genes. Phylogenetic analysis among arthropods using concatenated protein-coding sequences provides further support for the possibility that Crustacea are paraphyletic. Furthermore, in contrast to data from the nuclear gene EF1alpha, the first complete sequence of a malacostracan mitochondrial genome supports the possibility that Malacostraca are more closely related to Insecta than to Branchiopoda. (+info)
Effect of salinity on hatching, survival and infectivity of Anguillicola crassus (Nematoda: Dracunculoidea) larvae.
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The effect of salinity on hatching, larval survival and infectivity of Anguillicola crassus was studied under experimental conditions using eggs obtained from naturally infected eels. Egg hatching rate, second-stage larval survival and larval infectivity were maximal in fresh water and declined with increase in salinity. Larvae survived up to 100 d in fresh water, 70 d in 50 % sea water and 40 d in 100% sea water. Infectivity experiments demonstrated that salinity influenced transmission success throughout the life cycle by decreasing total infectivity of the larval population in utero within female A. crassus and when larvae were free-living in the aquatic environment. Infectivity was age-dependent in relation to salinity. Larvae were infective to intermediate and paratenic hosts for up to 80 d in fresh water, 21 d in 50% sea water and up to 8 d in 100% sea water. The data confirm field observations that infection levels decrease with an increase in salinity. The study contributes to experimental verification of the colonization abilities of A. crassus and supports the hypothesis that A. crassus can be disseminated and transmitted in brackish water. The importance of regular monitoring and stringent hygiene practices in the transportation of eels is emphasized. (+info)