A web-based survey of horse owners' perceptions and network analysis of horse movements relating to African horse sickness distribution in Namibia and South Africa.

Africa horse sickness (AHS) is the most lethal infectious non-contagious horse disease and has accordingly been declared notifiable by the World Organisation for Animal Health. AHS is endemic to sub-Saharan Africa and causes considerable losses to the equestrian industry. The effect of diseases in livestock on socio-economic factors is well researched, but the effect of anthropogenic factors on the distribution of a disease is poorly understood. The purpose of the study was to assess Namibian and South African horse owners' perceptions and the effect of horse movement on AHS distribution. A cross-sectional study was conducted to collect information from horse owners in Namibia and South Africa. To that end 'Fluid survey' was used for survey development. The survey was launched on Facebook and the link shared to horse related focus groups in Namibia and South Africa. A total of 508 responses were collected during the survey period. Of the 417 completed questionnaires received, 22% were from Namibia and 78% from South Africa. The participants comprised of 71% social and 29% professional riders. The most popular precautionary measures used, in addition to vaccination, were chemical repellents (64%) and stabling of horses during dusk and dawn (59%). A network analysis was performed in Gephi 0.8.2.B to illustrate the movement of horses between countries and districts/provinces. Network analysis results indicate that areas with the highest movement of horses corresponded to the areas with a high occurrence of AHS. Although 93% of the participants were aware that AHS is a notifiable and controlled disease, the process and efficiency of reporting is mostly unknown. With this snapshot of horse owners' perceptions and the effect of horse movement on the distribution of AHS, it is clear that a more holistic approach is needed. To that end, all environmental and social factors must be taken into account in effective management strategies.

Detection of African horse sickness virus in Culicoides imicola pools using RT-qPCR.

African horse sickness (AHS) is an infectious, non-contagious arthropod-borne disease of equids, caused by the African horse sickness virus (AHSV), an orbivirus of the Reoviridae family. It is endemic in sub-Saharan Africa and thought to be the most lethal viral disease of horses. This study focused on detection of AHSV in Culicoides imicola (Diptera: Ceratopogonidae) pools by the application of a RT-qPCR. Midges were fed on AHSV-infected blood. A single blood-engorged female was allocated to pools of unfed nulliparous female midges. Pool sizes varied from 1 to 200. RNA was extracted and prepared for RT-qPCR. The virus was successfully detected and the optimal pool size for the limit of detection of the virus was determined at a range between 1 to 25. Results from this investigation highlight the need for a standardized protocol for AHSV investigation in Culicoides midges especially for comparison among different studies and for the determination of infection rate.

Culicoides species composition and environmental factors influencing African horse sickness distribution at three sites in Namibia.

African horse sickness (AHS) is one of the most lethal infectious, non-contagious, vector-borne disease of equids. The causative agent, African horse sickness virus (AHSV) is transmitted via Culicoides midges (Diptera: Ceratopogonidae). AHS is endemic to Namibia but detailed studies of Culicoides communities and influencing environmental parameters are limited. This study aims to determine the Culicoides species composition at three different sites and to assess environmental parameters influencing the geographical distribution of AHS in Namibia. Weekly collections of Culicoides were made during the AHS peak season from January to May for 2013 and 2014 using the Onderstepoort 220V UV-light trap. Out of 397 collections made, 124 collections (3287 Culicoides) were analysed for AHSV presence with RT-qPCR. A total of 295 collections were analysed for total Culicoides (all collected Culicoides individuals) and in 75% of these collections the Culicoides were identified to species level. C. imicola was the dominant species with proportional representation of 29.9%. C. subschultzei, C. exspectator and C. ravus each contribute more than 10% to the species composition. The lowest number of Culicoides was collected at Aus 9980, a total of 21819 at Windhoek and the highest number at Okahandja 47343. AHSV was present at all three sites during 2013 but only in Windhoek and Okahandja during 2014. Multivariate analyses of data from the two year survey indicate the environmental parameters in order of importance for the distribution of AHS in Namibia as precipitation>temperature>clay>relative humidity>NDVI. The implication of these findings is that any precipitation event increases Culicoides numbers significantly. Together with these results the high number of species found of which little is known regarding their vector competence, add to the complexity of the distribution of AHS in Namibia.

Comparing the effect of modeled climatic variables on the distribution of African horse sickness in South Africa and Namibia.

Africa horse sickness (AHS) is a lethal disease of horses with a seasonal occurrence that is influenced by environmental conditions that favor the development of Culicoides midges (Diptera: Ceratopogonidae). This study compared and evaluated the relationship of various modeled climatic variables with the distribution and abundance of AHS in South Africa and Namibia. A comprehensive literature review of the historical AHS reported data collected from the Windhoek archives as well as annual reports from the Directorate of Veterinary services in Namibia were conducted. South African AHS reported data were collected from the South African Department of Agriculture, Forestry, and Fisheries. Daily climatic data were extracted for the time period 1993-2011 from the ERA-interim re-analysis dataset. The principal component analysis of the complete dataset indicated a significant statistical difference between Namibia and South Africa for the various climate variables and the outbreaks of AHS. The most influential parameters in the distribution of AHS included humidity, precipitation, evaporation, and minimum temperature. In South Africa, temperature had the most significant effect on the outbreaks of AHS, whereas in Namibia, humidity and precipitation were the main drivers. The maximum AHS cases in South Africa occurred at temperatures of 20-22° C and relative humidity between 50-70%. Furthermore, anthropogenic effects must be taken into account when trying to understand the distribution of AHS.

The effect of anthropogenic activity on the occurrence of Culicoides species in the South-Western Khomas Region, Namibia.

Certain species of midges in the genus Culicoides (Diptera: Ceratopogonidae) are vectors of several serious orbiviral (Reoviridae) diseases, one of which, African horse sickness (AHS), was reported in the South-Western area of Khomas Region, Namibia, where it had been believed to be absent. Culicoides imicola, AHS principal vector, was collected in several farms in the area during the winter of 2009. The objective of this study was to determine whether Culicoides midges, especially C. imicola, were favoured at anthropogenic impacted/homestead sites in the arid Khomas Region, where they were not expected to occur under natural, veld conditions. The natural 'background' Culicoides communities where determined from collections made at veld sites, which were then compared to corresponding collections made at homestead sites. Altogether, 10,178 Culicoides midges were collected at homesteads and were then compared to 1,733 individuals collected at veld sites. Culicoides midge numbers were likely boosted in anthropogenic impacted areas/homesteads. This was also the case for the Culicoides species that are vector of AHS. This study indicated the significance of human settlement in the Khomas Region in terms of Culicoides midge abundance and distribution and showed the implications that this may have on the transmission of Culicoides-vectored diseases.

Occurrence of Culicoides species Diptera: Ceratopogonidae) in the Khomas region of Namibia during the winter months.

Although African horse sickness (AHS) is considered to be endemic in Namibia, limited data on its Culicoides midge vector (Diptera: Ceratopogonidae) are available. The principal study objective was to determine the presence, species composition and the richness and diversity of Culicoides adults during the colder and drier months in the Khomas region of central Namibia. Five sites were selected, ranging from relatively high to low altitudes with high to low annual rainfall. Onderstepoort suction UV-light traps were used for Culicoides species collection and were run during the winter from 6 July to 21 September 2009. A relatively high diversity of 25 species from 9 091 Culicoides individuals were collected in 34 collections. The abundance of the proven vector of AHS virus, Culicoides imicola, varied from 94% near Windhoek at a high altitude and relatively higher annual rainfall, to 12% at the site situated farthest south-west, with the lowest altitude and annual rainfall. This relatively high Culicoides midge abundance, coupled with the presence of a cycling host (zebra) in the area, imply that AHS virus may overwinter in the Khomas region of Namibia.