Ecology and epidemiology of avian influenza in ostriches

Avian influenza is important because of its potential devastating effect on poultry health and trade. The ostrich industry of South Africa has not escaped the consequences of control and export restrictions resulting from notifiable virus infections. Ostrich farmers first observed a syndrome of green urine in the early and mid 1980s. An H7N1 subtype, causing high mortality in young ostriches but with a low pathogenicity index for chickens, was first isolated in 1991. The first highly pathogenic subtype affecting ratites was reported during the 2000 epidemic of H7N1 in Italy. Low pathogenic subtypes were isolated in South Africa from 1991 to 2004, with one HPAI isolated in 2004. International research work on ostriches with both H5 and H7 subtypes, in both low and high pathogenic pathotypes, found the severity of clinical disease was not directly correlated to the pathotype. The ecology and epidemiology of infections in ostriches is not well understood. Surveys suggest local migratory water birds may play an important role. They have direct contact with ostrich flocks through the free-range production systems. Seasonal occurrence is seen, with the wet colder months more favourable for virus survival and detection. Management, population density, immune status and age are other important determinants of the severity of disease. Surveillance and monitoring must be implemented to understand the ecology and epidemiology, which extends to the validation and standardisation of diagnostic and serological methods for ostriches. Serious consideration should be given to vaccination, education and the use of separate production zones as part of a control programme.