Vector competence of Culicoides bolitinos and C. imicola for South African bluetongue virus serotypes 1, 3 and 4

Abstract .The susceptibility of field-collected Culicoides bolitinos to infection by oral ingestion of bluetongue virus serotypes 1, 3 and 4 (BLU 1, 3 and 4) was compared with that of field-collected C. imicola and laboratory reared C. variipennis sonorensis . The concentration of the virus per millilitre of bloodmeal was 10^5.0 and 10^6.0TCID₅₀ for BLU 4 and 10^7.2TCID₅₀ for BLU 1 and 3. Of 4927 C. bolitinos and 9585 C. imicola fed, 386 and 287 individual midges survived 10 days extrinsic incubation, respectively. Midges were assayed for the presence of virus using a microtitration assay on BHK-21 cells and/or an antigen capture ELISA. Infection prevalences for the different serotypes as determined by virus isolation ranged from 22.7 to 82.0% in C. bolitinos and from 1.9 to 9.8% in C. imicola; infection prevalences were highest for BLU 1, and lowest for BLU 4 in both species. The mean log₁₀ TCID₅₀ titre of the three BLU viruses per single fly was higher in C. bolitinos than in C. imicola . The results suggested that C. bolitinos populations are capable vectors of the BLU viruses in South Africa. A high correlation was found between virus isolation and ELISA results for the detection of BLU 1, and less for BLU 4; the ELISA failed to detect the presence of BLU 3 in infected flies. The C. v. sonorensis colonies had a significantly lower susceptibility to infection with BLU 1, 3 and 4 than C. bolitinos and C. imicola . However, since infection prevalence of C. v. sonorensis was determined only by ELISA, this finding may merely reflect the insensitivity of this assay at low virus titres, compared to virus isolation.     

Analysis of glycoconjugate saccharides in organelles isolated from castor bean endosperm

The presence of lipid- and protein-bound sugars in the major organelle fractions isolated from germinating castor bean (Ricinus communis L.) endosperm has been established. Microsomes, glyoxysomes and mitochondria were subfractionated into a membrane fraction and a fraction containing peripheral membrane and soluble matrix proteins. The membranes were further subfractionated into monosaccharide lipid, oligosaccharide lipid and lipid-free protein components. The constituent sugars present in the prepared fractions were released and identified by gas-liquid chromatography. While all derived protein fractions contained the N-acetylglucosamine and mannose typically found in the inner core region attached to asparagine residues in many glycoproteins, some differences were noted in the organellar distribution of peripheral sugars such as fucose, arabinose, and xylose.     

Growth and morphological changes in the stomach of newborn pigs during the first three days after birth.

Growth and morphological changes in the stomach of newborn pigs were examined during the first 3 days after birth. The stomach grew disproportionately faster than the body as a whole during this period. The growth was due to hyperplasia and hypertrophy during the first day and mainly to hyperplasia thereafter as gastric DNA content increased progressively after birth, and the protein:DNA and RNA:DNA ratios increased only on the first day. Histological and morphometric analyses revealed that the growth was more pronounced in the gastric body region than in the cardiac and pyloric regions, and more pronounced in the mucosal layer than in other layers. The percentage of mucosal volume occupied by parietal cells (volume density) and the number of parietal cells per unit volume of gastric mucosa (numerical density) increased significantly 3 days after birth in the cardiac and body regions, but not in the pyloric region, of the stomach. The observed morphological changes coincide with the known pattern of functional maturation during the immediate postnatal period. It is suggested that a high level of circulating gastrin and oral ingestion of milk-derived growth factors in the newborn pig contribute to these changes.     

The action of philanthotoxin-343 and photolabile analogues on locust (Schistocerca gregaria) muscle

The effects of philanthotoxin-343 (PhTX-343; tyrosyl-butanoyl-spermine) and photolabile analogues of this synthetic toxin on locust (Schistocerca gregaria) skeletal muscle have been investigated using whole muscle preparations (twitch contractions), single muscle fibres (excitatory postsynaptic currents (EPSCs)) and muscle membrane patches containing single quisqualate-sensitive glutamate receptors (qGluR). Analogues containing an azido group attached to either the butanoyl side-chain of PhTX-343 or as a substitute for the hydroxyl moiety of the tyrosyl residue were about 6 fold more potent antagonists than PhTX-343; those with an azido group located at the distal end of the toxin molecule were generally 2–3 fold less potent than PhTX-343. When these compounds were tested in subdued light, they were reversible antagonists of the muscle twitch, EPSC and qGluR. When a muscle was irradiated with U.V. during application of photolabile toxin combined with either neural stimulation of the muscle orl-glutamate application, antagonism of the twitch, EPSC and qGluR was complete and irreversible.     

Spatial distribution of Culicoides species in Portugal in relation to the transmission of African horse sickness and bluetongue viruses

Surveillance of Culicoides (Diptera: Ceratopogonidae) biting midge vectors was carried out at 87 sites within a 50 x 50 km grid distributed across Portugal, using light trap collections at the time of peak midge abundance. Culicoides imicola (Kieffer) made up 66% of the 55 937 Culicoides in these summer collections. It was highly abundant in the central eastern portion of Portugal, between 37 degrees 5' N and 41 degrees 5' N, and in a band across to the Lisbon peninsula (at around 38 degrees 5' N). Of all the complexes, its distribution was most consistent with that of previous outbreaks of Culicoides-borne disease, suggesting that it may remain the major vector in Portugal. Its distribution was also broadly consistent with that predicted by a recent climate-driven model validating the use of remote sensing datasets for modelling of Culicoides distribution. Adult C. imicola were found to have overwintered at 12 of 20 sites re-surveyed in winter but it did so in very low numbers. Culicoides obsoletus (Meigen) and Culicoides pulicaris (Linnaeus) complex midges were widespread despite their low summer abundance. The observed coincidence of high abundances of C. imicola and high abundances of C. pulicaris in summer lead us to suggest that C. imicola could bring African horse sickness virus or bluetongue virus into contact with C. pulicaris and the latter complex, together with C. obsoletus, could then transmit these viruses across much wider areas of Europe. The fact that adult C. pulicaris are present in high abundances in winter may provide a mechanism by which these viruses can overwinter in these areas.     

Climate change and the recent emergence of bluetongue in Europe

Bluetongue, a devastating disease of ruminants, has historically made only brief, sporadic incursions into the fringes of Europe. However, since 1998, six strains of bluetongue virus have spread across 12 countries and 800 km further north in Europe than has previously been reported. We suggest that this spread has been driven by recent changes in European climate that have allowed increased virus persistence during winter, the northward expansion of Culicoides imicola, the main bluetongue virus vector, and, beyond this vector's range, transmission by indigenous European Culicoides species - thereby expanding the risk of transmission over larger geographical regions. Understanding this sequence of events may help us predict the emergence of other vector-borne pathogens.