Multiplication of bluetongue virus in culicoides nubeculosus (Meigen) simultaneously infected with the virus and the microfilariae of Onchocerca cervicalis (Railliet & Henry).
01 Aug 1980-Annals of Tropical Medicine and Parasitology (Ann Trop Med Parasitol)-Vol. 74, Iss: 4, pp 463-469
TL;DR: It is suggested that C. nubeculosus can act as a vector of BTV when simultaneously infected with virus and the microfilariae of a filarial worm.
Abstract: Culicoides nubeculosus under normal experimental conditions was found incapable of supporting multiplication of bluetongue virus (BTV) after infection via the oral route. Simultaneous infection with BTV and the microfilariae of Onchocerca cervicalis, a filarial worm of the horse, transformed this situation. A small proportion of infected midges subsequently developed high titres of virus, which persisted until the termination of the experiment at day 13 post infection. C. nubeculosus intrathoracically inoculated with BTV were found to transmit the virus after 7, 8 and 14 days incubation at 26°C, with no evidence for a ‘salivary gland barrier’. It is therefore suggested that C. nubeculosus can act as a vector of BTV when simultaneously infected with virus and the microfilariae of a filarial worm.
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16 May 1991
TL;DR: This chapter discusses the evolution of the blood-sucking habit, feeding preferences, host-insect interactions, and the transmission of parasites by blood-Sucking insects.
Abstract: Part 1 The importance of blood-sucking insects. Part 2 The evolution of the blood-sucking habit: prolonged close association with vertebrates morphological pre-adaptation for piercing. Part 3 Feeding preferences of blood-sucking insects: host choice host choice and species complexes. Part 4 Location of the host: the behavioural framework of host location appetitive searching activation and orientation attraction movement between hosts. Part 5 Ingestion of the blood meal: vertebrate haemostasis insect anti-haemostatic factors probing stimulants phagostimulants mouthparts blood intake. Part 6 Managing the blood meal: midgut anatomy the blood meal gonotrophic concordance nutrition host hormones in the blood meal partitioning of resources from the blood meal autogeny. Part 7 Host - insect interactions: insect distribution on the surface of the host morphological specializations for life on the host host immune responses to insect salivary secretions behavioural defences of the host density dependent effects on feeding success. Part 8 Transmission of parasites by blood-sucking insects: transmission routes specificity in vector-parasite relationships origin of vector parasite relationships.
772 citations
Cites background from "Multiplication of bluetongue virus ..."
...In relation to the gut barrier, it is notable that mosquitoes are more easily infected with arboviruses when they are concurrently infected with microfilariae, which probably assist the passage of the virus through the intestinal barriers (Mellor and Boorman, 1980; Turell et al., 1984a)....
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TL;DR: Recently the virus causing this disease has extended its range northwards into areas of Europe never before affected and has persisted in many of these locations causing the greatest epizootic of the disease on record.
Abstract: Bluetongue (BT) exists around the world in a broad band covering much of the Americas, Africa, southern Asia, northern Australia and, occasionally, the southern fringe of Europe. It is considered to be one of the most important diseases of domestic livestock. Recently the virus causing this disease has extended its range northwards into areas of Europe never before affected and has persisted in many of these locations causing the greatest epizootic of the disease on record. The reasons for this dramatic change in BT epidemiology are complex but are linked to recent extensions in the distribution of its major vector, Culicoidesimicola, to the involvement of novel Culicoides vector(s) and to an apparent ability of the virus to overwinter in the absence of adult vectors. In addition, the effects of these changes have been exacerbated by problems in control, particularly in relation to vaccination. This paper explores these areas and highlights prospects for the future.
367 citations
TL;DR: The ability of the virus to infect Culicoides persistently and be transmitted by them is restricted to a relatively small number of species, and in essence, the world distribution map of BTV is little more than a distributed map of competent insect vectors.
Abstract: Bluetongue virus (BTV) has long been known to be transmitted biologically by certain species of biting midge belonging to the genus Culicoides (Latreille). Du Toit (1944) in South Africa was the first to implicate a Culicoides species in the transmission of this virus when he showed that C. imicola (pallidipennis) was able to transmit bluetongue from infected to susceptible sheep. Since that time numerous authors have confirmed his observations (Walker and Davies 1971; Braverman and Galun 1973; Braverman et al. 1981, 1985; Mellor et al. 1984a). However, although there are well over 1000 species of Culicoides in the world (Boorman 1988), only 17 have been connected with BTV and to date only six, C. variipennis, C. imicola, C. fulvus, C. actoni, C. wadai and C. nubeculosus, have been proven to transmit the virus (Table 1). This number may soon be increased to eight since on the basis of epidemiological evidence and virus isolations it is
Table 1
Field and laboratory BTV infections of Culicoides
Subgenus
Species
Virus isolation
Laboratory infection
Transmission
Avaritia
C. actoni
−
+
+
C. brevipalpis
−
+
−
C. brevitarsis
+
+
−
C. fulvus
+
+
+
C. imicola
+
+
+
C. obsoletus
+
−
−
C. tororoensis
+
−
−
C. wadai
−
+
+
Culicoides
C. peregrinus
−
±
−
Diphaeomia
C. debilipalpis
−
+
−
Hoffmania
C. insignis
+
−
−
C. milnei
+
-
-
C. venustus
−
+
−
Monoculicoides
C. variipennis
+
+
+
C. nubeculosus
−
+
+
Oecacta
C. oxytoma
−
+
−
Pulicaris
C. impunctatus
−
±
−
likely that C. insignis and C. brevitarsis will also prove to be competent BTV vectors (Greiner et al. 1985; Standfast et al. 1985). Although some of the remaining species of Culicoides may eventually be shown to be fully competent BTV vectors most species will be refractory to infection. Why this should be is not yet entirely clear, but it is known that the mechanism or mechanisms controlling the oral infection of Culicoides with BTV operate chiefly at the level of the mid-gut wall (Jennings and Mellor 1988), a single layer of cells of epithelial origin supported by a basement lamina (Hardy et al. 1983; Megahed 1956).
177 citations
TL;DR: This work presents the first definitive identification of the vectors of AHSV in Spain during the 1987, 88 and 89 epizootics as well as suggesting the significance of these findings with regard to the epidemiology of African horse sickness in Spain.
Abstract: This paper describes the first isolations of African horse sickness virus (AHSV) from insects in Spain. Seven isolations of AHSV serotype 4 were made; four from Culicoides imicola a known vector of the virus elsewhere, two from mixed pools of Culicoides species not including C. imicola and one from blood engorged mosquitoes. Three further isolations of AHSV serotype 4 were also made from horses kept adjacent to the insect collecting sites. This work presents the first definitive identification of the vectors of AHSV in Spain during the 1987, 88 and 89 epizootics. Suggestions are also made concerning the significance of these findings with regard to the epidemiology of African horse sickness in Spain.
138 citations
TL;DR: 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.
Abstract: 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 γδ 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 γδ T-cells with antibody to the γδ 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 γδ T-cells. The interaction of persistently infected γδ 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.
137 citations
Cites background or methods from "Multiplication of bluetongue virus ..."
...Virus titres were determined in 96-well plates using BHK cells (Mellor & Boorman, 1980) and expressed as TCID50 ml 21....
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...The survival of virus from one ‘vector season’ to the next is popularly termed ‘overwintering’ (Yonguc et al., 1982; Taylor & Mellor, 1994; Mellor & Boorman, 1980; Mellor, 1998)....
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References
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178 citations
161 citations
TL;DR: The studies here described aim at the elucidation of the action of a plant virus within the insect that is its specific vector by the method of mechanical inoculation of the virus into the insect.
Abstract: The studies here described aim at the elucidation of the action of a plant virus within the insect that is its specific vector. It is widely held that insect transmission is not normally a mechanical process; but of the nature of the biological relation, into which virus and insect are supposed to enter, little is definitely known. By the use of the method of mechanical inoculation of the virus into the insect I have obtained certain direct evidence bearing upon this problem. The virus studied is that which causes streak disease in the maize plant. A single strain has been used, maintained in the course of my experiments by repeated transfers to maize seedlings in the greenhouse. Conceivably this strain is a complex of viruses, but if so it has shown no sign of splitting into its components during the period of the work now described.
116 citations
99 citations
TL;DR: Kieff as discussed by the authors described a method by which Culicoides variipennis (Coq), C. nubeculosus (Mg) and C. riethi Kieff have been maintained as laboratory colonies for over five years.
Abstract: A method is described by which Culicoides variipennis (Coq.), C. riethi Kieff. and C. nubeculosus (Mg.) have been maintained as laboratory colonies for over five years. Techniques are given for the maintenance of adults, larvae and pupae; with some modifications these could probably be applied to a range of other species. Adult midges were held in waxed card pill boxes, and provided with sugar solution. Anaesthetised mice provided a blood-meal source. Larvae were reared in pans on a substrate of glass fibre in a medium which contained nutrient broth, grass meal and Bemax. The life-cycle of these species occupies 10–21 days at 23–25°C.
90 citations