Newcastle disease in ostriches (Struthio camelus) - a review

Newcastle disease (ND) in ostriches was first reported in zoo birds in the 1950s. An outbreak of ND in commercial ostriches in Israel was reported in 1989, but of more significance were the ND infections of ostriches in southern Africa during the 1990s as a result of assumed spread from commercial domestic fowl. The latter outbreaks were of particular concern due to the boom in international trade in ostriches and their products at that time. ND virus appeared to spread only slowly through affected ostrich flocks, and the clinical signs and mortality seen varied considerably with age. In field and experimental infections, morbidity, mainly in the form of nervous signs, and mortality could be extremely high in young birds but low or absent in adults. Characterization of ND viruses isolated during outbreaks in ostriches has shown them to be indistinguishable from viruses infecting chickens in the locality. Experimental challenge has shown ND poultry vaccines to be protective in ostriches, and several workers have proposed vaccine regimens employing both live and inactivated vaccines, usually given more frequently and employing much higher doses than recommended for chickens. Indirect and blocking enzyme-linked immunosorbent assay (ELISA) tests have been developed for the detection of ND antibodies in ostrich sera. Although some reports have suggested problems using the haemagglutination inhibition(HI)tests, others have recorded good correlation between ELISA, HI and virus neutralization tests. Because of their size and, as a consequence, the method of rearing, ostriches are quite different to conventional poultry and respond differently, in terms of disease and spread, when infected with ND virus. However, at present, for the international control of ND, there would appear to be little alternative to treating ostriches as poultry for the purposes of trade.