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The clinical, virological and pathological findings observed in a natural outbreak of highly pathogenic avian influenza in intensively farmed ostriches (Struthio camelus) are reported. Clinical signs characterized by anorexia, depression, nervous and enteric signs were observed in young birds, which resulted in death of 30% of the affected birds. Virus isolation performed in accordance with the guidelines listed in European Union Directive 92/40/EEC yielded an influenza A virus of the H7N1 subtype with a deduced cleavage site motif containing multiple basic amino acids, typical of highly pathogenic viruses. Gross lesions, mainly haemorrhagic enteritis and liver degeneration and necrosis, were confirmed by histopathology and immunohistochemistry, resulting in the detection of necrotic lesions and influenza A nucleoprotein in selected organs. The findings reported indicate that ostriches are susceptible to highly pathogenic avian influenza.

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.

A retrospective study of bursa of Fabricius from 90 necropsied ostriches from Florida farms was performed. Eighty-five bursas showed lymphoid necrosis and/or depletion, and acute to chronic inflammation. Rounded cytoplasmic inclusions were noted within bursal macrophages of 17 birds. Ultrastructurally, these inclusions comprised arrays of icosahedral virions with a diameter of 60 to 65 nm, suggesting possibly reovirus or birnavirus. Further work is needed to classify and determine the pathogenic significance of this virus in the ostrich.

Virus excretion, immune response, and, for chickens, deaths were recorded in 3-week-old ostriches and chickens inoculated by either the intramuscular or intranasal route with one of two influenza A viruses of subtype H5. One of the viruses, A/turkey/England/50-92/91 (H5N1) (50/92), was highly pathogenic for chickens causing 5/5 deaths by each route of inoculation. The other virus, A/ostrich/Denmark-Q/72420/96 (H5N2) (72420/96), isolated from ostriches in quarantine in Denmark during 1996, was of low pathogenicity for chickens, causing no clinical signs by either route of inoculation. No significant clinical signs were seen in any of the ostriches infected with either of the viruses by either route of infection. Both viruses were recoverable from both species up to 12 days post-infection, and low serological responses were detected in surviving infected ostriches and chickens at 21 days after inoculation.

Summary An influenza A virus of the H7 N1 subtype was isolated from young ostriches which died after developing a syndrome characterized by a green discolouration of the urine, weakness and signs of respiratory distress. Mortality varied, depending on the age of the ostriches, the presence of other infectious agents and the amount of stress to which they were exposed. Using the haemagglutination inhibition test, an amnestic response was recorded in ostriches which recovered from the disease. Pathogenicity tests indicated that the isolate was of low virulence for chickens.

Summary The production of a white urine by ostriches can be indicative of illness or water deprivation. A metabolic renal study was carried out by dehydrating young, healthy ostriches for 2 days, the period during which urine was still excreted. It was found that the normally copious colourless urine changed to a thick, white excretion after 2 days dehydration and no fluid was excreted after 3 days. From the blood and urine analyses it is concluded that the ostrich conserves body water by an excellent renal concentrating mechanism which excretes urates. This excretion is a useful sign to the fanner that for some reason the animals are not drinking, be it due to a lack of drinking water or to illness.

Summary Clinical signs suggesting pox were observed in a flock of ostrich chicks (Struthio camelus), 10 to 60 days old. The disease was confirmed by isolation of the agent from affected ostriches and reproduction of typical pox lesions in turkeys. Further infection of young ostriches was prevented by vaccination with fowl pox vaccine.

Summary Haematological reference values according to age and sex, were obtained from healthy ostriches (Struthio camelus) held under intensive conditions. Erythrocytic parameters and indices demonstrated an age‐related trend: the packed cell volume, haemoglobin concentration and erythrocyte count were lowest in ostriches of 1 to 3 months of age. The mean corpuscular volume increased with age until adulthood. No sex‐linked differences were demonstrated in regard to the erythrocytic parameters. Leukocyte counts were higher in younger ostriches; changes also being detected in the differential count with age. The erythrocyte sedimentation rate was both sex‐ and age‐related. Young birds had the fastest rate of sedimentation and females had a faster rate than males.