Avian influenza in ostriches: epidemiological investigation in the Western Cape Province of South Africa.

An H5N2 avian influenza virus was isolated from ostriches in the Eastern Cape Province of South Africa in July 2004. During a subsequent national survey to determine the possible presence of the disease in other areas of South Africa, specific antibodies against H5 avian influenza were detected by the haemagglutination inhibition test in ostrich sera collected in the Western Cape Province. However, the sampling strategy used in the initial survey was developed to accommodate practical constraints but did not truly reflect the prevalence of the sero-reactor entities. A follow-up survey was therefore conducted from March to May 2005 to obtain more representative samples. None of the 15 126 serum samples collected from ostriches aged 0-4 months was positive, while 2.4% of the 14 664 serum samples collected from slaughter ostriches aged 5-14 months and 3.66% of the 8 791 samples collected from breeder ostriches aged over 14 months were positive. Fourteen farms were inspected in particular to identify relevant risk factors and risk mitigation procedures that could minimise the spread of the disease. It was concluded that biosecurity measures should be improved on ostrich farms, in particular to minimise possible contact between ostriches and wild birds.