The concept of vector in parasitology, ecology of agents, epidemiology and epizootology

The concepts of "host" and "vector" are compared in application to arthropods which are capable to transmit pathogens to man and animals. The paper shows that these concepts are not identical. The function of such arthropods as hosts of microorganisms, as well as their possible importance in population ecology, epidemiology and epizootology are discussed. The system of different concepts corresponding to the tasks of these scientific disciplines is also considered.     

Control of lettuce big-vein disease by application of fungicides and crop covers

One of the economically important diseases of lettuce is lettuce big-vein disease (LBVD), which leads to severe yield losses. LBVD is associated with a complex of two viruses, Lettuce big-vein associated virus (LBVaV) and Mirafiori lettuce big-vein virus (MLBVV). These viruses are transmitted by motile zoospores of Olpidium spp. fungi, which persist in the soil for decades through resting spores. In greenhouse and field experiments, this study tested whether changing plant and soil temperatures together with fungicide application would have a significant effect on controlling LBVD in lettuce. Soil fumigation with metam sodium was not effective at controlling the disease, as opposed to treatment with chloropicrin and methyl bromide. Moreover, the fungicides carbendazim and fluazinam were effective in reducing the incidence of Olpidium virulentus. Nevertheless, control of the fungal vector did not seem to be sufficient to control the disease due to the transition ability of the virus under low vector abundance. Crop covers, which affect the favourable environmental conditions for the viruses by lowering soil temperature and raising air temperature, reduced the disease symptoms. Combining fungicides with crop cover had a synergistic effect on reducing disease symptoms, thus providing a sustainable solution for LBVD.     

Evolutionary implications of two rainbow trout growth hormone genes

The primary structures of two rainbow trout growth hormone mRNAs (GH1 and GH2) have been deduced by direct sequencing of their respective cDNA clones and portions of the mRNA. Both GH1 and GH2 mRNA contain open reading frames comprised of 630 nucleotides and encode 210 amino acid residues of which 11 are variant. The translated regions of both mRNA are flanked by a short but rather conserved 5′-end, and a relatively long but highly diverged 3′-end. The differences at translated and 3′-untranslated regions suggest that the GH1 and GH2 mRNA originate from different loci. The GH1 and GH2 mRNA are likely transcribed from two distinct loci which were duplicated during tetraploidization of salmonid genome between 50 to 100 million years ago. The GH2 gene has been isolated and sequenced from a rainbow trout genomic library. This gene spans a region of approximately 4 kilobases. The trout GH gene is comprised of 6 exons and 5 introns, in contrast to 5 exons and 4 introns in mammals. The additional intron in the trout gene interrupts the translated regions that are analogous to the last exon of the mammalian counterpart. The alleged internally repeating sequences in mammalian GH, prolactin (Pr1) and placental lactogen (PL) are not observed in the predicted polypeptide sequence of trout GH. In addition, direct repeats that flank exons I, III and V of mammalian GH, Pr1 and PL genes are absent in trout gene. These findings indicate that the rainbow trout GH gene structure does not support the current hypothesis that internally repeated regions in GH, Pr1 and PL arose from a small primordial gene.     

Seasonal and size-related changes in the diet of perch,Perca fluviatilis L., in the shallows of an Australian river,and their implications for the conservation of indigenous teleosts

1. Perca fluviatilis was sampled monthly over 2 years from the shallow waters (<2 m deep) of the Collie River in south-western Australia to determine the diet of this introduced species and the extent to which it comprised indigenous fish species. 2. As P. fluviatilis increased in size, its diet shifted from predominantly planktonic crustaceans to benthic invertebrates, with decapod crustaceans constituting between 55% and 88% of the volume of the food ingested by larger fish (> 120 mm long) in spring, summer and autumn. 3. All size groups of P. fluviatilis fed on the small indigenous teleosts Edelia vittata and Bostockia porosa. 4. The prevalence with which the different size groups of P. fluviatilis ingested indigenous fish species in the main channel of the river was as high as 14% in fish < 50 mm long in summer, 25% in fish 50–120 mm long in spring and 17% of fish > 120 mm long in autumn. 5. Despite appreciable predation and a relatively high prevalence of P. fluviatilis, indigenous fish species have coexisted with perch in the Collie River since the early 1900s. Such coexistence has apparently been facilitated by a high density of invertebrate prey (as a result of eutrophication) and limited interspecific dietary overlap. 6. The absence of E. vittata in those parts of a nearby river system now occupied by P. fluviatilis and the extremely high prevalence of fish that is sometimes found in P. fluviatilis stomachs, suggest that under certain extreme conditions, such as when a marked depletion in alternative food sources occurs, the presence of perch could pose a threat to the conservation of indigenous fish species in certain river systems in south-western Australia.     

A clinicopathological study of 52 feline epulides

A retrospective study was performed to characterize 52 new cases of feline epulides between 1995 and 2001, with clinical and pathological results classified according to Head's histopathologic criteria for canine epulides. The incidence of the fibromatous, acanthomatous, ossifying, and giant cell epulis were respectively 57.7% (30/52), 7.7% (4/52), 5.8% (3/52), and 28.8% (15/52). Giant cell epulides presented significant differences in clinical behavior compared with the fibromatous type, including rapid growth (P < .0001), presence of ulcerative changes (P < .01), and rapid recurrence after surgery (P < .01) from which euthanasia was judged necessary in 4 cases. Fifteen giant cell epulides were additionally examined in order to characterize the lesion both histochemically and immunohistochemically and to investigate the origin of the multinucleated giant cells (MGCs). Van Gieson staining showed osteoid and woven bone formation in 11 cases. Both the MGCs and a fraction of the mononuclear cells were positive for vimentin, tartrate-resistant acid phosphatase (TRAP), a commonly accepted marker for osteoclasts, and the polyclonal antibody receptor activator of nuclear factor kappabeta (RANK), a cytokine leading to the differentiation of osteoclast progenitors into mature osteoclasts in presence of its ligand. MGCs were negative for smooth muscle actin, MIB-1, and factor VIII. The giant cell epulis may be a variant of the fibromatous and ossifying epulis in which extensive ulceration and inflammation results in increased osteoclastic activity. The osteoclast-like giant cells are most likely formed from a monocyte/macrophage-like osteoclast precursor that differentiates into osteoclasts under the influence of mononuclear osteoblast-like stromal cells.     

Pharmacokinetics of a single intravenous dose of marbofloxacin in adult donkeys

Six donkeys each received 2 mg/kg marbofloxacin as a 10 per cent aqueous solution administered intravenously. Principal pharmacokinetic parameters were determined and two efficacy indices were computed by using pharmacokinetic parameters and selected mic90 values of marbofloxacin against pathogenic equine strains to predict the efficacy of the drug at this dose. The pharmacokinetics of marbofloxacin in donkeys was characterised by a large mean volume of distribution at a steady state (1.15 [0.09] l/kg) and a long mean (sd) elimination half-life of 9.24 (1.96) hours. It was also characterised by a relatively slow total body clearance of 0.10 (0.02) l/kg/hour, slower than in horses. Using mic90 values of marbofloxacin against pathogenic equine strains with a daily dose of 2 mg/kg, appropriate values of efficacy indicators were obtained only for Enterobacteriaceae. Daily intravenous doses of 0.33, 2.62 and 20 mg/kg were calculated for evaluation in clinical trials of infections due to Enterobacteriaceae, Staphylococcus aureus and Streptococci, respectively.     

Biological control of the Western flower thripsFrankliniella occidentalis in cucumber using the entomopathogenic fungusMetarhizium anisopliae

Biological control of the western flower thrips (WFT)Frankliniella occidentalis, using the entomopathogenicMetarhizium anisopliae-7 (M. a-7) strain was studied in three consecutive seasons under greenhouse conditions. Cucumber plants infested with WFT were sprayed with spore suspension of the fungusM. a-7 (0.5 g m^-2), or the soil was treated with dry powder of the fungus (0.5 g m^-2); the control was without fungus application. In the 1997 spring experiment, when the cucumber plants were initially infested with only three or four insects per leaf, the spore suspension spray caused a significant reduction in growth of the thrips population compared with the other treatments and the control. However, in the 1997 summer experiment, when the plants were initially heavily infested with WFT (10–15 insects per leaf), the spray treatment caused only a modest reduction in WFT population growth, and only after 4 weeks of treatment was the reduction significant. In the 1999 experiment, with a low initial WFT population of three or four insects per leaf, the spray treatment was effective in reducing the population growth to a lower level than in the other treatments or control. TheM. a-7 strain was found to be effective in reducing the population growth of WFT under greenhouse conditions, particularly when the initial thrips population was low to moderate. http://www.phytoparasitica.org posting Nov. 4, 2001.