An incursion of classical swine fever virus (CSFV) into the domestic pig population in South Africa, identified in 2005, raised the concern that infection might spread to wildlife species and be maintained in these hosts. This study sought to determine whether two wildlife Suidae species present in South Africa, the bushpig (Potamochoerus larvatus) and the common warthog (Phacochoerus africanus), could support productive CSFV infection. Both species could be infected with CSFV and transmitted infection to in-contact animals of the same species. Viral antigen and RNA genome were detected in blood/serum and animals that survived initial infection seroconverted approximately 10-14 days post-inoculation. Viral RNA remained detectable in nasal and saliva secretions for prolonged periods until monitoring ended at 42-44 days after initial challenge. These data suggest that both Suidae species could serve to spread circulating CSFV within wild populations, with implications for disease control.

W. VOSLOO, S.P. SWANEPOEL, M. BAUMAN, B. BOTHA, J.J. ESTERHUYSEN, C.I. BOSHOFF, D.F. KEET, A. DEKKER Transboundary Animal Diseases Programme, ARC-Onderstepoort Veterinary Institute, Private Bag X05, Onderstepoort, 0110, South Africa Department of Tropical Veterinary Diseases, Faculty of Veterinary Medicine, University of Pretoria, South Africa Deltamune, PO Box 14167, Lyttelton, 0140, South Africa Department of Biomedical Sciences, Tshwane University of Technology Private Bag X680, Pretoria, 0001, South Africa Office of the State Veterinarian, Kruger National Park, P.O. Box 12, Skukuza, 1350, South Africa

The potential role of giraffe (Giraffa camelopardalis) in the epidemiology and spread of foot-and-mouth disease (FMD) SAT types was investigated by experimental infection and detection of virus in excretions using virus isolation on primary pig kidney cell cultures. In two experiments separated by a period of 24 months, groups of four animals were needle infected with a SAT-1 or SAT-2 virus, respectively and two in-contact controls were kept with each group. Viraemia was detected 3-9 days post-infection and virus isolated from mouth washes and faeces only occasionally up to day 13. The SAT-1 virus was transmitted to only one in-contact control animal, probably via saliva that contained virus from vesicles in the mouth of a needle-infected animal. None of the animals infected with the SAT-2 virus had any vesicles in the mouth, and there was no evidence of transmission to the in-contact controls. No virus was detected in probang samples for the duration of the experiments (60 days post-infection), indicating that persistent infection probably did not establish with either of these isolates. Giraffe most likely do not play an important role in FMD dissemination. Transmission of infection would possibly occur only during close contact with other animals when mouth vesicles are evident.

A longitudinal study was performed in the Kruger National Park, South Africa to investigate the role of impala (Aepyceros melampus) in maintaining SAT serotypes of foot-and-mouth disease (FMD) virus. Three sampling sites with different histories of FMD outbreaks in impala and also of varying ecology were chosen. At three monthly intervals approximately 40 impala were bled and examined for clinical FMD at each of these sites for a period of 6 years, followed by 4 years of less frequent sampling. During the 10 years of the study, clinical disease was only observed once at a single sampling site, while at two of the three locations, serological evidence of infection was detected; in one locality this was a frequent occurrence. The discrepancy between clinically evident disease and serological evidence of infection indicated that sub-clinical infection with these viruses may be more regular than previously suspected. Furthermore, there was evidence that either SAT-serotype infection is maintained within local impala populations for prolonged periods or that re-infection of impala by buffalo occurs repetitively, sometimes at frequent intervals. A mixed-effects logistic regression model showed that females and older animals had a higher risk of seropositivity, while summer and autumn also represent periods when there is a heightened risk of seropositivity (as opposed to winter and spring which previous studies had shown to be associated with clinical disease). Comparison of impala and buffalo ratios in the three sampling regions indicated that the higher the impala density, the more likely disease transmission is from buffalo to impala, and that this is independent of buffalo numbers (presumably above an undetermined threshold). This study confirmed the potential role of impala for propagating FMD in southern Africa and this factor should therefore be considered when designing control strategies where wildlife and domestic animals interact.

African buffalo (Syncerus caffer) play an important role in the maintenance of the SAT types of foot-and-mouth disease (FMD) in southern Africa. These long-term carriers mostly become sub-clinically infected, maintaining the disease and posing a threat to other susceptible wildlife and domestic species. During an unrelated bovine tuberculosis experiment using captive buffalo in the Kruger National Park (KNP), an outbreak of SAT-1 occurred and was further investigated. The clinical signs were recorded and all animals demonstrated significant weight loss and lymphopenia that lasted 100 days. In addition, the mean cell volume and mean cell haemoglobin values were significantly higher than before the outbreak started. Virus was isolated from several buffalo over a period of 167 days post infection and the molecular clock estimated to be 3 × 10−5 nucleotide substitutions per site per day. Seven amino acid changes occurred of which four occurred in hypervariable regions previously described for SAT-1. The genetic relationship of the outbreak virus was compared to buffalo viruses previously obtained from the KNP but the phylogeny was largely unresolved, therefore the relationship of this outbreak strain to others isolated from the KNP remains unclear.

A population of domestic pigs in northern Mozambique with increased resistance to the pathogenic effects of African swine fever (ASF) virus was identified by the high prevalence of circulating antibodies to ASF virus. An attempt was made to establish whether the resistance in this population was heritable. Some of these pigs were acquired and transported to a quarantine facility and allowed to breed naturally. Offspring of the resistant pigs were transferred to a high security facility where they were challenged with two ASF viruses, one of which was isolated from one of the Mozambican pigs and the other a genetically closely-related virus from Madagascar. All but one of the 105 offspring challenged developed acute ASF and died. It therefore appears that the resistance demonstrated by these pigs is not inherited by their offspring, or could not be expressed under the conditions of the experiment. The question remains therefore as to the mechanism whereby pigs in the population from which the experimental pigs were derived co-existed with virulent ASF viruses.