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At least 37 records · Page 2Linked to original sources
PubMed1998

Anticoagulant activity in salivary glands of the insect vector Culicoides variipennis sonorensis by an inhibitor of factor Xa.

Blood feeding by the insect vector Culicoides variipennis sonorensis involves laceration of superficial host tissues, an injury that would be expected to trigger the coagulation cascade. Accordingly, the salivary glands of C.v. sonorensis were examined for the presence of an antihemostatic that prevents blood coagulation. Assays using salivary gland extracts showed a delay in the recalcification time of plasma devoid of platelets, indicating the presence of anticoagulant activity. Retardation in the formation of a fibrin clot was also observed after the addition of tissue factor to plasma that was preincubated with salivary gland extracts. Similarly, an inhibitory effect by salivary gland extracts was detected in assays that included factors of the intrinsic pathway. Inhibition of the catalytic activity of purified factor Xa toward its chromogenic substrate suggested that it was the target of the salivary anticoagulant of C.v. sonorensis. This was corroborated by the coincidence of anticoagulant and anti-FXa activities obtained by reverse-phase HPLC. The depletion of anti-FXa activity from salivary glands during blood feeding suggests that the FXa inhibitor functions as anticoagulant. Molecular sieving HPLC yielded an apparent molecular mass of 28 kDa for the salivary FXa inhibitor of C.v. sonorensis. Preventing the formation of thrombin through the inhibition of FXa likely facilitates blood feeding by maintaining the pool of blood fluid at the feeding site. The salivary FXa inhibitor of C.v. sonorensis could impair the network of host-defense mechanisms in the skin microenvironment by avoiding blood coagulation at the site of feeding.

Animals↗
PubMed2003

A possible overwintering mechanism for bluetongue virus in the absence of the insect vector.

Bluetongue virus (BTV) and several other Orbivirus species are transmitted between mammalian hosts via bites from adults of certain species of Culicoides midges. However, BTV can survive for 9-12 months (typically during the winter), in the absence of adult vectors, with no detectable cases of viraemia, disease or seroconversion in the host. The survival of the virus from one 'vector season' to the next is called 'overwintering' but the mechanism involved is not fully understood. It is demonstrated that BTV can persistently infect ovine gammadelta T-cells in vitro, a process that may also occur during infection and viraemia in mammalian hosts, thus providing a mechanism for virus persistence. Interaction of persistently BTV-infected gammadelta T-cells with antibody to the gammadelta T-cell-specific surface molecule WC-1 resulted in conversion to a lytic infection and increased virus release. Skin fibroblasts induce a similar conversion, indicating that they express a counter ligand for WC-1. Feeding of Culicoides midges induces skin inflammation, which is accompanied by recruitment of large numbers of activated gammadelta T-cells. The interaction of persistently infected gammadelta T-cells with skin fibroblasts would result in increased virus production at 'biting sites', favouring transmission to the insect vector. This suggested mechanism might also involve up-regulation of the WC-1 ligand at inflamed sites. It has been shown previously that cleavage of virus surface proteins by protease enzymes (which may also be associated with inflammation) generates infectious subvirus particles that have enhanced infectivity (100 times) for the insect vector.

Animals↗
PubMed1997

Detection of Xylella fastidiosa in potential insect vectors by immunomagnetic separation and nested polymerase chain reaction.

A sensitive and specific assay for detecting Xylella fastidiosa in potential insect vectors was developed. This assay involves immunomagnetic separation of the bacteria from the insect, followed by a two-step, nested polymerase chain reaction (PCR) amplification using previously developed oligonucleotide primers specific to X. fastidiosa. A total of 347 leafhoppers representing 16 species were captured and sampled from American elm (Ulmus americana L.) trees growing in a nursery where bacterial leaf scorch caused by X. fastidiosa occurs. Two of these leafhopper species, Graphocephala coccinea and G. versuta, regularly tested positive for X. fastidiosa using this technique. These insects are therefore potential vectors of X. fastidiosa. Using immunocapture and nested PCR, it was possible to detect as few as five bacteria per sample.

Animals↗
PubMed2002

Manipulation of medically important insect vectors by their parasites.

Many of the most harmful parasitic diseases are transmitted by blood-feeding insect vectors. During this stage of their life cycles, selection pressures favor parasites that can manipulate their vectors to enhance transmission. Strategies may include increasing the amount of contact between vector and host, reducing vector reproductive output and consequently altering vector resource management to increase available nutrient reserves, and increasing vector longevity. Manipulation of these life-history traits may be more beneficial at some phase of the parasite's developmental process than at others. This review examines empirical, experimental, and field-based evidence to evaluate examples of changes in vector behavior and physiology that might be construed to be manipulative. Examples are mainly drawn from malaria-infected mosquitoes, Leishmania-infected sandflies, and Trypanosoma-infected tsetse flies.

Animals↗
PubMed2002

Expression of the movement protein of Tomato spotted wilt virus in its insect vector Frankliniella occidentalis.

Tomato spotted wilt virus (TSWV) is able to infect both its botanical hosts and its insect vector (thrips). In plant tissue the NS(M) protein of TSWV functions as viral movement protein (MP), aggregating into plasmodesma-penetrating tubules to establish cell-to-cell movement. As upon heterologous expression NS(M) was able to form similar tubules on the surface of insect (Spodoptera frugiperda) cells, we have now investigated the expression and cellular manifestation of this protein in infected thrips tissue. It is shown that NS(M), though detectably expressed in both the L2 larval and adult thrips stages, does not aggregate into tubules, indicating that this requirement is associated to its function as MP in plants, and raising the question if NS(M) has a function at all during the insect life cycle of TSWV.

Animals↗
PubMed2000

Sequence analysis of Pns11, a nonstructural protein of rice gall dwarf virus, and its expression and detection in infected rice plants and vector insects.

The nucleotide sequence of genome segment S11 of rice gall dwarf virus (RGDV), a member of Phytoreovirus, was determined. The segment encodes a putative protein of 40 kDa that exhibits approximately 37% homology at the amino acid level to the nonstructural proteins Pns10 of rice dwarf and wound tumor viruses, which are other members of Phytoreovirus. A band of a protein with an apparent molecular mass of 40 kDa was specifically detected in an analysis of cells transfected with S11 cDNA. An antiserum raised against this protein reacted with a protein of approximately 40kDa after fractionation by SDS-PAGE of materials prepared from infected plants and from viruliferous vector insects. However, the antiserum did not react with purified viral proteins. These results suggest that S11 encodes a nonstructural protein of RGDV. This protein was named Pns11.

Amino Acid Sequence↗
PubMed1997

[Individual protection against insect vectors].

Many diseases for which no vaccine is available are transmitted by insect and arthropod vectors, the main exceptions being yellow fever and Japanese encephalitis B. Treatment is less and less effective due to the development of chemoresistance to therapeutic and prophylactic drugs as is well-illustrated by malaria. One of the best methods of preventing these diseases is personal protection against insect bites. Personal protection measures can be divided into three categories which can be used separately or in combination : application of repellents to the skin, wearing clothes impregnated with insecticides, and use of bed nets and other barriers impregnated with insecticides. The choice of method depends on the type of insect vector involved. For insects that are active during the day or at dusk, application of repellents to the skin gives good short-term protection and wearing impregnated clothes is useful. Bed nets that have been properly impregnated with pyrethroids are highly effective for night-time protection. Since personal protection methods are not 100% effective, they must be used in association with chemoprophylaxis according to medical guidelines. Medical advice should be sought if fever should occur especially after returning from a trip in the tropics.

Animals↗
PubMed2002

Targeted deletion of the gp72 gene decreases the infectivity of Trypanosoma cruzi for mice and insect vectors.

The infective behavior of a mutant Trypanosoma cruzi clone, carrying a targeted deletion of the gp72 gene, was studied in the insect vector Triatoma infestans and in mice. After feeding T. infestans with complement-resistant forms (CRF) of Ynull and wild-type clones, it was observed that the number of parasites released in the bug's feces was reduced to less than 1% in the mutant clone. Both gp72-null and wild-type clones had a low infectivity for mice in comparison with other T. cruzi isolates, probably as a consequence of prolonged in vitro culture. Therefore, the behavior of both clones was tested in highly susceptible BALB suckling mice and immunodeficient athymic mice. After infecting the animals with 10(5) CRF, wild-type parasites could be detected in fresh blood mounts of most mice, but mutants were never found by this method. However, in 4 of 22 hemocultures from 11 athymic mice, gp72-null epimastigotes carrying the mutant phenotype were reisolated by day 29 of infection. Serological and polymerase chain reaction determinations performed on the blood of animals inoculated with the mutants indicated the possibility of temporary infections, which were extinguished after 90 days. The intact GP72 gene seems essential for sustaining latent infections in immunocompetent animals.

Animals↗
PubMed1997

Resistance to insecticides in insect vectors of disease: est alpha 3, a novel amplified esterase associated with amplified est beta 1 from insecticide resistant strains of the mosquito Culex quinquesfasciatus.

Vector control programmes in many countries face the dual problems of parasite drug resistance and insecticide resistance in the insect vectors of the disease. Here we report for the first time a new esterase-based insecticide resistance mechanism in the filariasis vector Culex quinquefasciatus. The field collected COL strain of C. quinquefasciatus from Columbia was heterogeneous for organophosphorus insecticide resistance. On native polyacrylamide gels it had an elevated beta-naphthyl acetate specific esterase with the same Rf as that for the Est beta 1s involved in insecticide resistance in other strains of this mosquito species. After five generations of temephos insecticide selection, both the esterase specific activity with p-nitrophenyl acetate and the temephos LC50 values were increased, suggesting that elevation of esterase activity was the underlying mechanism of resistance. Western blots with antisera raised to Est alpha 2(1) and Est beta 2(1) from C. quinquefasciatus indicated that the COL strain had an elevated Est alpha 3 enzyme which co-migrated on native gels with Est beta 1. Southern blots indicated that an est alpha 3 gene was amplified in the COL strain and a Cuban mosquito strain (MRes), although the restriction digest patterns of the est beta 1 genes in these two strains are different. In contrast, the Californian TEMR strain, with the amplified est beta 1(1) gene, had no associated elevated Est alpha. Restriction digest patterns for COL and TEMR DNA suggest that they contain an identical est beta 1(1) gene, but our data suggest that the est alpha 3 gene occurs on the same amplicon as an est beta 1 gene although the genes are probably > 10 kb apart. Hence, either the COL strain has two est beta 1 genes or the est beta 1(1) amplicon in TEMR has been disrupted at some stage during the long colonisation of this strain and the amplified est alpha has been lost.

Animals↗