Ostrich diseases.

Abstract

Scientific knowledge of ostrich diseases is incomplete and very fragmented, with specific details on technical aspects of diagnostic and/or screening tests completely absent in most cases. Salmonella Typhimurium is common in multispecies collections and causes mortality in chicks younger than three months on commercial farms, but is rarely found in chicks older than six months, or slaughter birds of twelve to fourteen months in southern Africa. Campylobacter jejuni and Chlamydia psittaci are occasionally reported, mainly in young ostriches, but both remain a diagnostic challenge. Crimean-Congo haemorrhagic fever is transmitted to domestic animals including ostriches, principally by ticks of the genus Hyalomma. In the ostrich, the disease causes no clinical symptoms during a viraemia of approximately four days. Spongiform encephalopathy has not been reliably reported in ostriches, while anthrax has occurred rarely in modern times but was reportedly an important cause of death approximately 100 years ago in South Africa. Salmonella Gallinarum and S. Pullorum are unknown in ostriches. Pasteurella multocida occurs but is easily contained with antibiotics. Mycoplasma spp. are regularly found in an upper respiratory disease syndrome complicated by opportunistic bacterial pathogens. Ostriches of all ages are susceptible to challenge by velogenic Newcastle disease virus (NDV), but standard inactivated La Sota poultry vaccines can stimulate protective immunity lasting over six months. The viraemic period in vaccinated slaughter ostriches is between nine and eleven days and there are no indications of a carrier state or presence of the virus in the meat or any other tissues after this period, with peak immunoglobulin G response reached on day fourteen post infection. Haemagglutination inhibition tests are significantly less sensitive and less specific than enzyme-linked immunosorbent assays. Cloacal and choanal swabs used for direct virological screening in clinically affected cases (field and experimental) could not detect NDV. All avian influenza isolates reported from ostriches have been non-pathogenic to poultry, even the H5 and H7 subtypes. Some of the latter have been associated with mortality of ostrich chicks in localised outbreaks during periods of inclement weather and with significant wild bird (waterfowl) contact. Borna disease causes a nervous syndrome in ostrich chicks, but to date, has only been reported in Israel. Eastern and Western equine encephalomyelitides cause fatal disease in ostriches and other ratites, with mortality ranging from less than 20% to over 80% in affected flocks. These diseases are present in North, Central and South America where the associated ornithophilic mosquito vectors occur. Equine and human vaccines are apparently safe and efficacious in ratites. Wesselsbron disease, infectious bursal disease (type 2), adenovirus and coronavirus infections have been reported from ostriches but the significance of these diseases is unclear. Due to the paucity of data regarding ostrich diseases and the unvalidated state of most poultry tests in this unique group of birds, strict observation of a pre-slaughter quarantine of thirty days is strongly advised, whilst live exports and fertile eggs should be screened through the additional use of sentinel chickens and/or young ostriches.