Vetnuus | September 2024 7 3. Diagnostic tests Only the ARC Onderstepoort Veterinary Research (ARC-OVR) Rabies Laboratory and the Allerton Provincial Veterinary Laboratory (PVL) are SANAS accredited and Director Animal Health (DAH) approved to conduct animal rabies diagnostic testing using the fluorescent antibody test (FAT) – This test is conducted on fresh/ glycerosaline brain samples (that include the hippocampus portion). Formalinised seal brain samples (retrospective samples) that were submitted for histopathology were available at the Pathology Section of the Faculty of Veterinary Science, University of Pretoria, Onderstepoort. The DAH allowed rabies testing of these samples using an immunohistochemistry (IHC) test at the Pathology Section, Onderstepoort, as these samples cannot be tested using the FAT. For diagnostic purposes for all suspect rabies cases, fresh/ glycerosaline brain samples should be submitted to either ARC-OVR or Allerton PVL. Any suspected case of rabies must immediately be reported to the responsible state veterinary office. Samples that have tested positive on FAT at the ARC-OVR Rabies Laboratory are being sequenced through the ARC-OVR. Samples that have tested positive on IHC testing at the Pathology Section, Onderstepoort, are being sequenced through the Centre for Viral Zoonosis (CVZ), University of Pretoria. The first FAT positive case was reported to the World Organisation for Animal Health (WOAH) and all additional FAT positive cases are reported to the WOAH as well. IHCpositive cases are not reported to the WOAH, as this method is not SANAS accredited and DAH approved for official diagnostic use in South Africa. The IHC test’s current value is limited to adjunct use in rabies diagnosis for brain tissue that is fixed in formalin (FAT testing cannot be conducted on formalin-fixed brain tissue). 4. Epidemiology Sequencing of positive seal samples (prospective and retrospective) has been initiated to better understand the epidemiology of the disease. Initial sequencing results have revealed that the rabies strain involved is a canid strain, possibly of dog- or jackal-cycle origin, indicating a potential introduction from other canid dog and/or jackal rabies cycles to Cape fur seals. The closest links identified to date are to a canid rabies strain from a black-backed jackal from Namibia, and a separate link to a canid rabies strain from a bat-eared fox from the Western Cape. Some of the sequences that have been obtained to date cluster together and in some cases the sequences are similar, indicating that this rabies virus is very likely circulating within the Cape fur seal population, and may already be established in this population, i.e. representing a canid rabies Cape fur seal cycle. On the other hand, at least one sample seems to have yielded a distinctly separate sequence, thus indicating that there may have been more than one introduction into the Cape fur seal population. Additionally, the dog from Cape Town that tested positive in May 2024 was likely infected by a rabid Cape fur seal, indicating that rabies transmission from seals is possible. Further investigations and comparisons are required to consolidate any theory around the origin of the current Cape fur seal cycle with the note that phylogenetic trees can only be drawn from other available sequences. There are vast areas in Namibia and the Northern Cape Province of South Africa that are sparsely populated and some areas are restricted due to mining activities. Observational surveillance in such areas is limited, and hence samples from these areas for rabies testing in animals will be limited. In addition, it has not been possible to date to obtain and sequence all rabies strains from dog cases in South Africa either, not even in the Western Cape Province in which dog rabies remains a relatively rare occurrence. The table below provides a summary of all reported rabies cases in Cape fur seals. To date, positive Cape fur seal rabies cases have only been reported from the Western Cape Province. Cape fur seals occur along the coast of Africa between southern Angola and Algoa Bay, South Africa. The Eastern Cape and Northern Cape Provinces are aware of the outbreaks and surveillance in Cape fur seals will be enhanced to detect any possible cases. Information has also been extended to the neighbouring countries of Namibia and Angola. >>> 8 Leading Article Sample collection date Areas where the sample was collected FAT or IHC 2022/08/05 Kommetjie IHC + 2023/05/24 Noordhoek Beach IHC + 2023/07/30 Kalk Bay IHC + 2023/08/09 Melkbosstrand FAT + and IHC + 2023/10/12 Fish Hoek IHC + 2024/01/07 Plettenberg Bay FAT + and IHC + 2024/02/23 Pringle Bay IHC + 2024/04/08 Plettenberg Bay FAT + 2024/05/15 Strand IHC + 2024/05/22 Blouberg FAT + and IHC + 2024/05/26 Muizenberg IHC + 2024/06/13 Die Dam (between Gansbaai and Cape Agulhas) FAT + 2024/06/26 Muizenberg FAT + and IHC + 2024/06/27 Glencairn FAT + and IHC + 2024/07/15 Yzerfontein (2 CAPE FUR SEAL) FAT + 2024/07/17 Mossel Bay FAT + Total no. of positive cases = 17 Table 1 Summary of rabies-positive Cape fur seals from Western Cape Province
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