Life-history parameters of Culicoides (Avaritia) imicola Kieffer in the laboratory at different rearing temperatures

This laboratory study investigates the sub-adult developmental cycle of field collected Culicoides (Avaritia) imicola Kieffer (Diptera; Ceratopogonidae). The period required from blood-feeding field-collected females to the production of progeny adults occupied 34–56 days at 20 °C, 15–21 days at 25 °C and 11–16 days at 28 °C, demonstrating clear temperature dependence. When reared at 28 °C, C. imicola demonstrated higher variability in fecundity (between 2.4 and 20.6 eggs/female) and lower hatching rates (50.0–62.2%), although larval survival rates to pupation were low at all temperatures (20–30%). Similarly, the mean emergence rate from pupae was the highest at lower temperatures. These results highlight the difficulty in establishing and maintaining a laboratory colony of this species from field-collected material and results are discussed in reference to future research directions that may aid this process.     

Determination of 'irritant' threshold concentrations for intradermal testing with allergenic insect extracts in normal horses

Abstract Sixteen healthy horses with no history of skin or respiratory disease were used for an intradermal testing (IDT) threshold study, in order to determine the concentrations of 13 commercial allergenic insect extracts most appropriate for IDT. Five dilutions of each extract were used, which included the manufacturer's recommended concentrations for equine IDT, plus one dilution higher and three lower than these standard concentrations. Allergens tested included caddisfly ( Trichoptera spp.), mayfly ( Ephemeroptera spp.), horsefly ( Tabanus spp.), deerfly ( Chrysops spp.), fire ant ( Solenopsis invicta ), black ant ( Camponotus pennsylvanicus ), cockroach mix ( Periplaneta americana and Blattella germanica ), mosquito ( Aedes aegypti ), house fly ( Musca domestica ), moth ( Heterocera spp.), flea ( Ctenocephalides canis / C. felis ), Culicoides variipennis and Culicoides nubeculosis. Two separate methods were used to calculate the allergen concentration for each insect extract where the normal horses, as a group, ceased to show false-positive ('irritant') reactions. 'Irritant' threshold concentrations were determined for 9/13 of these allergens, whereas the other 4 were undetermined due to either insufficient reactivity (flea, C. variipennis ) or excessive reactivity (black ant, moth) to the concentrations tested. Recommended concentrations for future use in equine patients with suspected insect hypersensitivity include: 125 pnu mL⁻¹ (mayfly); 250 pnu mL⁻¹ (caddisfly, horsefly, deerfly, fire ant, house fly); 500 pnu mL⁻¹ (cockroach); 1000 pnu mL⁻¹ (mosquito); and 1:10 000 w/v ( C. nubeculosis ).     

Effects of altitude, distance and waves of movement on the dispersal in Australia of the arbovirus vector, Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae)

The dispersal of the biting midge and arbovirus vector Culicoides brevitarsis in the Bellinger, Macleay and Hastings river valleys and up the escarpment of the great dividing range (GDR) of mid-northern coastal New South Wales, Australia, from 1995 to 2003 was studied. The midge moved up these valleys from the endemic coastal plain in at least two waves between October and May, and both waves were modelled. Dispersal time can be explained by direct distance from the coast and the altitude of the sites. Dispersal times due to distance were similar at 18.2 ± 2.2 (S.D.) and 15.9 ± 2.6 weeks per 100 km for first- and second-occurrences at fixed altitude. Time of the first wave was extended 0.48 ± 0.22 weeks for every 100-m rise in altitude and the second by 1.14 ± 0.24 weeks for every 100-m rise for a set distance. Although C. brevitarsis can move up the escarpment of the GDR (and possibly transmit virus), vector dispersal, survival and establishment at and beyond the top of the range are limited. A third model showed that previously described slower movement of C. brevitarsis up the more-southerly Hunter valley relative to movements down the coastal plain also was related to increasing altitude.     

Uromyces Viciae-fabae Haustorium Formation in Susceptible and Resistant Faba Bean Lines

Haustorium formation by the faba bean rust (Uromyces viciae-fabae) was studied on susceptible and resistant faba bean lines. The resistant lines showed incomplete resistance, based on late acting hypersensitivity or on non-hypersensitive resistance acting before haustorium formation. Histological observations on infected leaves showed that both the number of haustoria per infection unit and their developmental stage was reduced in both resistant lines. Isolation of haustoria confirmed that both the number and the size of haustoria were reduced in resistant lines, irrespective of whether the resistance was associated with hypersensitivity. Plant age had no detectable effect on both parameters.     

Development and evaluation of a real-time quantitative PCR assay for Culicoides imicola, one of the main vectors of bluetongue (BT) and African horse sickness (AHS) in Africa and Europe

The current microscopy method for identifying the Culicoides imicola Kieffer, 1913 species can be time and labour intensive. There is a need for the development of a rapid and quantitative tool to quantify the biting midges C. imicola ss in light trap catches. A reproducible and sensitive real-time polymerase chain reaction method that targets the internal transcribed spacer (ITS-1) of ribosomal DNA of C. imicola ss species was developed. This real-time PCR assay was first performed on 10-fold serial dilutions of purified plasmid DNA containing specific C. imicola ss ITS-1. It was then possible to construct standard curves with a high correlation coefficient (r2=0.99) in the range of 10(-2)-10(-8) ng of purified DNA. The performances of this PCR were evaluated in comparison with morphological determination on Culicoides trapped along the Mediterranean coastal mainland France. ROC statistical analysis was carried out using morphology as gold standard and the area under the ROC curve had a satisfactory value of 0.9752. The results indicated that this real-time PCR assay holds promise for monitoring C. imicola ss population in both surveillance and research programmes because of its good specificity (92%) and sensitivity (95%).     

Culicoides (Diptera: Ceratopogonidae) associated with horses at Mogoditshane,Gaborone, Botswana

Veterinary Research Communications -     

Systemic granulomatous disease in dairy cattle during a dicyandiamide feeding trial

CASE HISTORY: Mature, in-calf, non-lactating, Friesian or Friesian-cross cows were fed dicyandiamide (DCD) at daily doses of 0.15 g/kg (Group 1; n=31), 0.45 g/kg (Group 2; n=21) and 0.75 g/kg (Group 3; n=12), as part of a safety trial, which also included a control group (n=15). Daily health observations were carried out on each cow until Day 86 of the study. On Day 28 one cow from Group 3 was observed with signs of disease, and subsequently disease was noted in other cows.

CLINICAL FINDINGS: Clinical signs in the first case included depression, pyrexia (40.9°C), salivation and dehydration, in addition to progressive weight loss, followed by death on Day 32. Other cows from all treatment groups developed clinical signs of disease resulting in euthanasia of seven animals. Disease occurred in 10/12 (83%) cows in Group 3, 11/21 (52%) cows in Group 2, and 7/31 (23%) cows in Group 1. Clinical signs were variable and included dermatitis and pruritus of the head and neck, petechial haemorrhages, pyrexia, weight loss, thrombocytopenia, neutropenia, and regenerative anaemia.

PATHOLOGICAL FINDINGS: Gross findings included generalised lymphadenopathy, subcutaneous oedema, petechiation of mucosal and serosal surfaces, and gastrointestinal haemorrhage. Histologically, multiple organs and tissues contained inflammatory foci characterised by infiltrates of lymphocytes, plasma cells, macrophages and occasionally prominent multinucleated giant cells and eosinophils.

DIAGNOSIS: Multisystemic granulomatous and haemorrhagic syndrome resembling cell-mediated hypersensitivity, associated with DCD ingestion.

CLINICAL RELEVANCE:: This is the first report of toxicity in cattle associated with ingestion of DCD. The proportion of affected cows increased with increasing dose of DCD, but not all cattle in the high dose group developed disease, therefore additional factors may determine whether or not an individual cow will develop DCD-associated disease.