West Nile virus infection of Thoroughbred horses in South Africa (2000-2001)

REASONS FOR PERFORMING STUDY

West Nile virus (WNV) infection is endemic in southern Africa. With the recent emergence of WNV infection of horses in Europe and the USA the present study was performed to estimate the risk of seroconversion to WNV in a cohort of 488 young Thoroughbred (TB) horses.

OBJECTIVES

To estimate the risk of seroconversion to WNV among a cohort of South African TB yearlings sold at the 2001 National Yearling Sales (NYS) and to determine whether the risk varied geographically. Two horses were also infected with a recent South African isolate of WNV to evaluate its virulence in horses.

METHODS

Serum samples were collected from the cohort of 488 TB yearlings at the 2001 NYS. Serum samples that were collected from the same horses at the time that they were identified were sourced from our serum bank. Sera from 243 of the dams that were collected at the time that the foals were identified were also sourced from our serum bank. These sera were subjected to serum neutralisation (SN) tests for antibody to WNV.

RESULTS

Approximately 11% of yearlings seroconverted to WNV on paired serum samples collected from each animal approximately 12 months apart. Studfarms with WNV-seropositive yearlings were widely distributed throughout South Africa and SN tests on sera from their dams indicated that exposure to WNV was even more prevalent (75%) in this population. Neurological disease was not described in any of the horses included in this study and 2 horses inoculated with a recent lineage 2 South African isolate of WNV showed no clinical signs of disease after infection and virus was not detected in their blood.

CONCLUSIONS

Infection of horses with WNV is common in South Africa, but infection is not associated with neurological disease.

POTENTIAL RELEVANCE

In contrast to recent reports from Europe, North Africa, Asia and North America, the results of our field and experimental studies indicated that exposure of horses to the endemic southern African strains of WNV was not associated with neurological disease.

A comparison of the vector competence of the biting midges, Culicoides (Avaritia) bolitinos and C. (A.) imicola, for the Bryanston serotype of equine encephalosis virus

Equine encephalosis virus (EEV) is widespread and prevalent in southern Africa. In this study, the oral susceptibility of Culicoides (Avaritia) imicola Kieffer (Diptera: Ceratopogonidae) to EEV was confirmed. In addition, C. (A.) bolitinos Meiswinkel, collected in the high-lying eastern Free State, South Africa, was systemically infected with the Bryanston serotype of EEV after feeding through a membrane on artificially infected equine blood containing 4.7 log10 PFU/mL of EEV. The mean infectivity of Bryanston virus in C. bolitinos increased from 1.2 log10 PFU/midge, in midges assayed for virus immediately after feeding on the blood-virus mixture, to 3.1 log10 PFU/midge in midges assayed after 10 days' incubation at 23.5 degrees C. Elevated virus infectivity titres, found in individual infected C. bolitinos, suggested that this Culicoides species is a vector of EEV. This bovine dung-breeding Culicoides species may play an important role in transmitting EEV in the cooler parts of southern Africa, where it can be the most abundant Culicoides species collected near livestock. In the present study the prevalence of infection obtained for C. bolitinos (2.2%) with the Bryanston serotype of EEV was significantly lower than that of C. imicola (18.4%). After incubation, the Bryanston serotype of EEV was also isolated from one of 110 C. onderstepoortensis Fiedler assayed. However, the virus titre in this midge was 1.2 log10 PFU/midge, which is not different from the titre that would be expected immediately after feeding on the blood-virus mixture. Culicoides species that survived the incubation period and that were negative for the presence of Bryanston virus were C. magnus Colaço (96), C. bedfordi Ingram & Macfie (95) and C. pycnostictus Ingram & Macfie (45).

The living conditions of elderly black people in a typical rural area in the Free State

The proposed policy in respect of the care of older persons places much emphasis on the involvement and responsibility of the community. Majwemasweu is a typical rural black community in the Free State where an active Committee for the care of older persons is already in place and has already largely taken the responsibility for caring for its older persons on itself. This research scrutinizes the living conditions of this community's older persons and, wherever possible, compares it with those of black urban and rural research groups in the Multidimensional Survey of Elderly South Africans, 1990-1991. Bearing in mind the time lapse between die two surveys, the situation of the Majwemasweu group is in many aspects much better than those of the two groups with which it is compared. Their socio-economic position is, in many respects, more favourable as a result of political change, when compared with the two other groups, while the unremitting zeal of the local Committee for the care of older persons has undoubtedly contributed to their more favourable position. It would appear that the community is ready for the implementation of the new policy for the care of older persons. Internal political disputes which have already been responsible for the retraction of sponsorship for upgrading the community health clinic, will, however, have to be settled immediately. Sustained intervention through dialogue on the side of the researchers continues to attempt to stimulate the development potential of the community with a view to successfully implementing the new policy.