Specie di Culicoides (Diptera: Ceratopogonidae) vettori del virus della Bluetongue in Sud Africa

The aim of this paper is to consolidate vector competence studies on Culicoides midges (Diptera: Ceratopogonidae) as vectors of Bluetongue virus (BTV) done over a period 25 years at the Agriculture Research Council ‑ Onderstepoort Veterinary Institute in South Africa. In 1944, it was demonstrated for the first time in South Africa that Culicoides midges transmit BTV. In 1991, field‑collected Culicoides imicola were fed on blood containing BTV‑3 or BTV‑6 and the infection rates were established as being 31% and 24%, respectively. In 1998, Culicoides bolitinos was shown to have a higher infection prevalence and virus titre/midge than C. imicola. This species was then shown to have a higher transmission potential for BTV‑1 over a range of incubation temperatures wider than the one showed by C. imicola. Attenuation of BTV also does not reduce its ability to infect competent Culicoides species. Oral susceptibility studies, involving 29 BTV isolates of various serotypes, indicated differences between various geographic virus isolates and Culicoides populations evaluated. While low recovery rates of European BTV strains from South African Culicoides species suggest co‑adaptation between orbiviruses and vectors in a given locality, co‑adaption was shown not to be essential for virus transmission. Cumulative results since 1991 provide evidence that at least 13 livestock‑associated Culicoides species are susceptible to BTV. Susceptibility results are supported by field isolations from 5 of these species. This implies that multi‑vector potential for the transmission of BTV will complicate the epidemiology of BT. It must be emphasised that neither oral susceptibility nor virus isolation/ detection from field‑collected specimens is proof that a species is a confirmed field vector.Il presente lavoro ha l’obiettivo di descrivere i risultati degli ultimi 25 anni di ricerca condotta all’Agriculture Research Council ‑ Onderstepoort Veterinary Institute in Sud Africa, sul ruolo dei Culicoides (Ditteri: Ceratopogonidae) come vettori del virus della Bluetongue (BTV). Nel 1944, in Sud Africa, è stato dimostrato per la prima volta il loro ruolo di vettori di BTV. Nel 1991, Culicoides imicola catturati in campo e nutriti con sangue contenente i sierotipi 3 o 6 del BTV hanno evidenziato percentuali di infezione, rispettivamente, del 31% e 24%. Nel 1998 è stato dimostrato che Culicoides bolitinos ha una prevalenza di infezione e un titolo virale per insetto superiori a quelli di C. imicola. È stato quindi dimostrato che C. bolitinos ha un maggior potenziale di trasmissione di BTV-1 in un intervallo di temperatura di incubazione più esteso di quello riportato per C. imicola. L’attenuazione del BTV non riduce la sua capacità di infettare specie competenti di Culicoides. Studi di competenza vettoriale attraverso infezione orale con 29 ceppi diversi appartenenti a vari sierotipi di BTV hanno evidenziato differenze a seconda dell'origine geografica dei ceppi e delle popolazioni di Culicoides esaminate. I bassi livelli di infezione dei ceppi europei di BTV in specie sudafricane di Culicoides suggeriscono l'esistenza di un possibile co-adattamento tra Orbivirus e vettori in una data zona, co-adattamento che tuttavia non è essenziale per la trasmissione del virus. In tutti questi anni è stato possibile dimostrare che almeno 13 specie di Culicoides associate al bestiame sono suscettibili al BTV. Tali risultati sono supportati da isolamenti di campo su 5 di queste specie. Ciò implica che il potenziale multi-vettoriale per la trasmissione di BTV complicherà l'epidemiologia di BT. Va sottolineato che né la suscettibilità orale né l’isolamento/rilevamento del virus da insetti catturati in campo provano che una data specie sia vettore certo del BTV.http://www.izs.it/vet_italiana/issues_vet_it.htmam2016Veterinary Tropical Disease

The virtual absence of Culicoides imicola (Diptera: Ceratopogonidae) in a light-trap survey of the colder, high-lying area of the eastern Orange Free State, South Africa, and implications for the transmission of arboviruses

Altogether 52 078 Culicoides biting midges of 35 species were collected during February 1990 and 1993 in 40 light-trap collections made on 17 cattle and/or sheep farms in the Bethlehem and Fouriesburg districts of the colder, high-lying eastern Orange Free State. Culicoides (Avaritia) bolitinos was by far the most abundant species, representing 50,9% of all specimens collected. Culicoides (A.) imicola, considered to be the most common stock-associated species in the summer rainfall areas of southern Africa, and the only proven vector of bluetongue virus (BTV) and African horsesickness virus (AHSV) in the subregion, was uncommon, comprising only 1,4%. While AHS is apparently absent, BT and bovine ephemeral fever (BEF) are endemic in this cooler, high-lying area of South Africa. The virtual absence of C. imicola implies that other Culicoides species, such as C. bolitinos and C. cornutus, may be involved in transmitting BT virus (and perhaps BEF) in the eastern Orange Free State, and possibly elsewhere in Africa. Virus isolation attempts made on 45 single species pools of C. bolitinos, C. pycnostictus, C. milnei, C. leucostictus, C. zuluensis and C. gulbenkiani were, however, negative. Finally, 20 of 28 blood-engorged Culicoides of 11 species, which were tested against cattle, sheep, horse, pig and bird antisera, tested only positive against cattle antisera.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Seasonal abundance and parity of Culicoides biting midges associated with livestock at Roma, Lesotho (Diptera : Ceratopogonidae)

A light-trap survey was undertaken of the species composition, seasonal abundance and parity of Culicoides at Roma, Lesotho, to establish whether the likely vectors for bluetongue and African horse sickness occur in this area as well as the chance of transmission. A total of 34 catches was made between 21 September 1985 and 24 September 1986; 32 819 Culicoides were caught belonging to 19 species. Culicoides numbers rapidly built up from December to a peak in February which implies that this may also be the optimum time for virus transmission. The number of Culicoides dropped sharply in April with the onset of cooler conditions. C. zuluensis was the dominant species forming 69,6 % of the totalled catches, followed by C. pycnostictus with 11,7%. C. imicola, the only proven vector of bluetongue, was never abundant representing only 4,4% of the midges caught. The parous rate for each of the 2 commonest species was low, implying a low vector capacity.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.lmchunu2014mn2014mn201

Assessment of the Hemotek® system for the in vitro feeding of field-collected Culicoides imicola (Diptera: Ceratopogonidae) in South Africa

The optimising and standardisation of in vitro blood feeding protocols for field-collected Culicoides species (Diptera: Ceratopogonidae) will be of essence for the comparison of the vector competencies of various populations of viruses of veterinary importance and the establishment of laboratory colonies of putative vector species. A custom-made feeding chamber to accommodate the small size of Culicoides imicola Kieffer was designed for the commercially available Hemotek® system and compared to existing membrane and cotton pledge feeding methods. High feeding rates coupled to higher mean blood meal volume than that of the existing OVI device indicated that the Hemotek system will be suitable for the feeding of field-collected Culicoides. The Hemotek system was subsequently used to identify factors that may affect feeding success in the laboratory. Evaluated factors were the source (host) and temperature of the blood meal, time of the day of feeding, the position of the blood reservoir in relation to the midges and exposure time to the blood. While only feeding orientation and the temperature of the blood source seems to significantly affect the feeding rate, all the factors did influence the volume of blood consumed.https://onlinelibrary.wiley.com/journal/13652915hj2022Veterinary Tropical Disease

The use of a membrane feeding technique to determine the infection rate of Culicoides-imicola (Diptera, Ceratopogonidae) for 2 bluetongue virus serotypes in South Africa

Culicoides spp. in the Lowveld of the northern Transvaal, Republic of South Africa, were fed bluetongue virus serotypes 3 and 6 and African horsesickness virus serotype 1 through latex and chicken skin membranes. After an incubation period of 10 days at 25-27 °C, the infection rate of C. imicola for bluetongue virus serotypes 3 and 6 was established at 31% and 24% respectively. No African horsesickness virus could be recovered. The membrane feeding technique and handling procedures proved to be suitable for field studiesThe articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Thermal limits of two biting midges, Culicoides imicola Kieffer and C. bolitinos Meiswinkel (Diptera : Ceratopogonidae)

BACKGROUND : Culicoides imicola Kieffer and Culicoides bolitinos Meiswinkel (Diptera: Ceratopogonidae) are both of veterinary importance, being vectors of Schmallenberg, bluetongue and African horse sickness (AHS) viruses. Within South Africa, these Culicoides species show a marked difference in their abundances according to altitude, with C. imicola highly abundant in lower altitudes, but being replaced as the dominant species by C. bolitinos in cooler, high-altitude regions. METHODS : The thermal physiology of field collected adults of each species was determined to evaluate whether it could account for differences in their distribution and abundance. Critical thermal maxima (CTmax) and minima (CTmin), as well as upper and lower lethal temperatures (ULT and LLT) were assessed after acclimation temperatures of 19°C, 24°C and 29°C. Critical thermal limits were determined using an ecologically relevant rate of temperature change of 0.06°C.min−1. RESULTS : Significant differences in CTmin and CTmax were found between acclimation temperatures for C. imicola and C. bolitinos. In C. bolitinos, the LLT of individuals acclimated at 24°C was significantly improved (LLT50 = −6.01°C) compared with those acclimated at the other temperatures (LLT50 = −4°C). Acclimation had a weak (difference in LLT50 of only 1°C) but significant effect on the LLT of C. imicola. When CTmin, CTmax, LLT and ULT were superimposed on daily maximum and minimum temperature records from locations where each tested Culicoides species is dominant, it was found that temperatures frequently declined below the CTmin and LLT of C. imicola at the location where C. bolitinos was dominant. CONCLUSIONS : The distribution and abundance of C. imicola is likely directly constrained by their relatively poor tolerance of lower temperatures. Results for C. bolitinos suggest that the adult phase is hardy, and it is hypothesised that the thermal biology of other life stages could determine their range.http://www.parasite-journal.org/hb201

Culicoides (Diptera: Ceratopogonidae) associated with livestock in the Onderstepoort area, Gauteng, South Africa as determined by light-trap collections

In 54 light-trap collections made at 28 sites in the Onderstepoort area a total of 178 941 Culicoides midges of 35 species was collected in March 1988; the survey was repeated at 26 sites in September and yielded 19 518 Culicoides of 24 species. The number of Culicoides species collected totalled 38. C. imicola was the most abundant species at 27 of the 28 sites sampled, and accounted for 88% and 67% of all midges collected in the two months respectively. This study not only confirms that C. imicola is widespread and abundant in the greater Onderstepoort area, but also that its numbers correlate positively with the historical prevalence of African horse sickness (AHS) and bluetongue (BT) locally. The high numbers of C. imicola make Onderstepoort the ideal site for the study of its laboratory vector capacity. The relatively low numbers of Culicoides spp. other than C. imicola in the Onderstepoort area, will severely limit studies on their roles in the transmission of arboviruses. The origin of the blood-meals of 1 338 engorged Culicoides belonging to 13 species was determined by means of a cross-over electrophoresis precipitin test; C. imicola fed on cattle, horses, sheep and pigs. Four other Culicoides species showed a similarly wide host range.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat X Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201

Evaluation of light emitting diode suction traps for the collection of livestock-associated Culicoides species in South Africa

Risk analysis of pathogens transmitted by Culicoides (Diptera; Ceratopogonidae) depends on the ability to detect all potential vectors attacking livestock in an area. Onderstepoort 220-V ultraviolet (UV) down-draught light traps are considered the gold standard for this purpose. To improve the flexibility of this trap in the field, in the absence of 220-V power, the possibility of using low-energy light emitting diodes (LEDs) was assessed. The efficiency of a standard 220-V Onderstepoort trap (30 cm 8 W fluorescent UV light tube) was compared to that of 220-V Onderstepoort traps fitted with either two, four or eight individual white LEDs. The Onderstepoort 220-V trap was also compared to a 12-V Onderstepoort trap fitted with an 8 W fluorescent UV light tube, a 12-V Onderstepoort trap with 12 individual white LEDs and 12-V and 220-V Onderstepoort traps fitted with 12 individual UV LEDs. Higher numbers of Culicoides as well as species diversity were collected with a brighter light source. The use of UV LEDs in both the 12-V and 220-V combinations was comparable to the Onderstepoort 220-V light trap with ration to species diversity collected. The Onderstepoort 220-V light trap is recommended if large numbers of Culicoides need to be collected.The Agricultural Research Council—Onderstepoort Veterinary Research, The South African Department of Science and Technology and the National Research Foundation of South Africa.https://onlinelibrary.wiley.com/journal/13652915hj2022Veterinary Tropical Disease

Assessment of the repellent effect of citronella and lemon eucalyptus oil against South African Culicoides species

The use of insect repellents to reduce the attack rate of Culicoides species (Diptera: Ceratopogonidae) should form part of an integrated control programme to combat African horse sickness and other diseases transmitted by these blood-feeding midges. In the present study the repellent effects of a commercially available mosquito repellent, a combination of citronella and lemon eucalyptus oils, on Culicoides midges was determined. The number of midges collected with two 220 V Onderstepoort traps fitted with 8 W 23 cm white light tubes and baited with peel-stick patches, each containing 40 mg of active ingredient, was compared with that of two unbaited traps. Two trials were conducted and in each trial the four traps were rotated in two replicates of a 4 x 4 randomised Latin square design. Although more midges were collected in the baited traps, the mean number in the baited and unbaited traps was not significantly different. This mosquito repellent did not influence either the species composition or the physiological groups of Culicoides imicola Kieffer. The higher mean numbers in the baited traps, although not statistically significant, may indicate that this mosquito repellent might even attract Culicoides midges under certain conditions.http://www.jsava.co.zaam201

Improving the diet for the rearing of Glossina brevipalpis Newstead and Glossina austeni Newstead : blood source and collection - processing - feeding procedures

One of the challenges to maintain tsetse fly (Diptera: Glossinidae) colonies is the sustainable supply of high quality blood meals. The effect of using anticoagulants during collection of the blood, the addition of phagostimulants to the blood meals as well as using mixtures of bovine and porcine blood in different proportions for feeding on colony productivity was assessed. Defibrinated bovine blood was found to be suitable to maintain both the Glossina brevipalpis Newstead and Glossina austeni Newstead colonies. Blood collected with the anticoagulants sodium citrate, citric sodium combination, citrate phosphate dextrose adenine and citric acid did not affect colony performance of both species. Defibrinated bovine and porcine blood in a 1:1 ratio or the feeding of either bovine or porcine blood on alternating days improved pupae production of G. austeni and can be used to enhance colony growth. Bovine blood is appropriate to maintain G. brevipalpis colonies, however, feeding either bovine or porcine blood on alternating days did improve productivity. Adding the phagostimulants inosine tri-phosphate, cytosine mono-phosphate and guanosine mono-phosphate to the blood at a concentration of 10−4 M improved pupae production of the G. brevipalpis colony. The addition of adenosine tri-phosphate and inosine tri-phosphate improved the performance of the G. austeni colony. Decisions on the most suitable rearing diet and feeding protocols will not only depend on the biological requirements of the species but also on the continuous supply of a suitable blood source that can be collected and processed in a costeffective way.The National Assets (000773) at the Agricultural Research Council-Onderstepoort Veterinary Institute and the Joint Food and Agriculture Organization / International Atomic Energy Agency Division of Nuclear Techniques in Food and Agriculture under the coordinated research project (CRP) 12618/R0/RBF Department of Technical Cooperation of the International Atomic Energy Agency under project RAF 5069.http://www.plosone.orgam2017Veterinary Tropical Disease