Salmonellosis
Salmonella spp. are ubiquitous organisms which reflect contamination of facilities through contact with rodent or wild bird reservoirs. Various Salmonella spp. have been isolated from the gastrointestinal tracts of all ratite species, but the incidence of paratyphoid Salmonella spp. (e.g. S. Typhimurium) is very rare. It must be remembered that certain Salmonella organisms are zoonotic, and precautions should be taken when handling a suspect case. Emus can be infected with S. Pullorum – a pathogen which persists in game fowl – and develop antibodies against this pathogen. The importance of S. Pullorum in ratites is unknown at this time, as no documented field cases have been identified. Salmonella organisms can be transmitted horizontally by infected birds via the faecal/oral route, or through contamination of equipment or the environment. Vertical transmission via faecal contamination of eggs has also been described as a method of Salmonella infection in the poultry industry. As Salmonella bacteria can be transmitted through eggs or contaminated equipment, care must be taken when receiving birds or eggs after interstate or international shipment. Most birds suffering from Salmonella spp. infections show no specific clinical signs, and are diagnosed through microbiological screening at necropsy. Treatment of infected birds with an appropriate antibiotic will generally suppress the clinical infection, but may lead to an asymptomatic carrier state. To reduce the risk of subclinical carriers developing, a whole-blood S. Pullorum agglutination test should be performed prior to shipment, and routine screening of birds by cloacal swabs during quarantine is also suggested.
Erysipelas
Emus have been reported to be susceptible to infection by Erysipelothrix rhusiopathiae. Infection with this soil organism occurs via small skin lacerations, caused by trauma, or insect vectors. Acute deaths usually occur due to a bacterial septicaemic condition, but penicillin or quinolone antibiotics may help mildly-affected birds. If erysipelas is a problem within a region or at a particular production facility, ratites should be immunized using a commercial, formalin-inactivated bacterin (with aluminium hydroxide adjuvant) licensed for turkeys. No adverse reaction has been noted in emus vaccinated with this inactivated turkey vaccine. In areas where erysipelas is endemic, birds should receive the first vaccine subcutaneously at six weeks of age, a second dose at six months of age, and an annual booster.
Colibacillosis
Escherichia coli serotypes are widely distributed; the degree of pathogenicity depends on the condition of the bird(s) exposed. In general, emus seem to be more susceptible to E. coli gastroenteritis infection than other ratite species.
Transmission usually occurs via the faecal/oral route, and the agent may be identified via culturing of cloacal swabs. Appropriate antibiotics are essential in treating an E. coli infection in ratite species. Autogenous bacterins are available, which may be used when colibacillosis becomes a health problem on a farm. These bacterins use cultures isolated from affected birds to help boost immunity in the resident animals. The efficacy of these bacterins in ratite and other avian species is unknown at present. The best prevention measures for colibacillosis infections are proper management and nutrition, and stress reduction in the flock or transported birds.
Pasteurellosis
There have been rare occurrences of Pasteurella spp. isolation in ratite species.
Intensive farming may increase occurrence, and this organism should therefore be monitored closely. Environmental exposure and direct contact with recovered Pasteurella carriers provide ample opportunity for acquisition of this bacterium in an immune suppressed ratite flock. Non-specific respiratory signs may be noted in the clinically-diseased bird, while generalized vascular congestion is seen on gross necropsy specimens. At present, no vaccination measures are recommended, but high standards of biosecurity are required to prevent introduction of infections into flocks.
Mycoplasmosis
Mycoplasma cloacale has been isolated from tracheal swabs of ostriches and emus, while there has been no isolation from these species of the three pathogenic Mycoplasma spp. found in commercial poultry. Intensification of the ratite industry, and concentration of birds in feedlots, may lead to the emergence of mycoplasmosis as a disease of economic significance due to the ease of transmission of this pathogen. Clinical signs accompanying mycoplasmal infection include nonspecific upper respiratory conditions and/or arthritis (27). Identification of Mycoplasma in other avian species is performed through isolation of the organism from joint aspirates or respiratory discharge, or through serological screening using the serum plate agglutination test. At present, a highly-sensitive polymerase chain gene probe assay can be used for identification of Mycoplasma galliseptium and M. synoviae in a few diagnostic laboratories (27). Treatment of confirmed cases is usually accomplished using tylosin or tetracycline antibiotics. Producers and transporters are encouraged to identify potential cases before the animals are placed in holding facilities, to reduce the risk of exposure of non-infected birds.
Tuberculosis
Mycobacterium avium has been diagnosed in ostriches and emus in the USA and Canada, and in emus in the USA. M. avium persists in wild bird populations and can infect pigs, cattle and immunosuppressed humans; it is therefore classified as a zoonotic disease. Transmission of M. avium occurs through infected faeces shed by clinically-ill birds. The organism can remain viable in the soil for up to twelve months, making sanitation after a clinical case difficult for the owner. The highly-mobile ratite industry enables dissemination of the organism via transport, holding facilities, quarantine houses and auction barns.
As M. avium generally affects the avian gastrointestinal system, clinical signs are usually those of non-specific wasting. Emus may develop leukocytosis with or without cloacal prolapse. Confirmation of the infection is usually accomplished at necropsy, unless an intensive ante-mortem physical examination is performed, isolating the acid-fast organism from a bacterial granuloma or a faecal screen. Screening tests using faecal acid-fast methods are unreliable; intradermal testing is therefore recommended, together with the maintaining of closed flocks, examination of newly-acquired breeding stock and good management. Tuberculosis is a potential zoonotic disease for which no treatment is available; a flock maintained within a production facility must therefore be free from tuberculosis.
Chlamydiosis
Chlamydia psittaci is an intracellular bacterium which has been identified as the causative agent in deaths of commercial rheas. Infected rheas usually die peracutely, while emus seem to be refractory to the organism isolated from species flocks. Pigeon strains of C. psittaci have been identified in outbreaks of the disease in Texas, and may have caused other rhea deaths in the southern USA. Diagnosis is made at necropsy through bacterial isolation. The gross pathological signs of psittacosis include splenomegaly, hepatomegaly, pericarditis and fibrinous airsacculitis. Extreme care should be taken by the veterinarian during treatment and/or necropsy of a C. psittaci case, in view of the zoonotic potential of the organism. The psittacosis bacterium is highly infectious to humans and causes severe pneumonia and death if not treated appropriately. Treatment of ratites and humans is best achieved with the tetracycline class of antibiotics. Reduction of wild bird access to feed and water areas will reduce the exposure of ratites to potential carriers of the Chlamydia organism.
Clostridial enteritis
A number of clostridial organisms have been isolated from various ratite species, including Clostridium perfringens, C. colinum, C. chauvoei and C. difficile. There is no published information on the frequency of isolation of Clostridium spp. from the intestinal tract of normal ratites, but clostridial enteritis usually occurs following proliferation of a toxin-forming Clostridium spp. in other avian species. Diagnosis of clostridial enteritis is usually made at necropsy through microbiological identification. Anaerobic culture methods should be recommended by the clinical veterinarian if such procedures are not commonly performed on bacterial culture specimens by the diagnostic laboratory. Outbreaks of clostridial infections can be treated with the addition of zinc bacitracin in feed at a rate of 30 g/ton (27).
Infectious coryza
Haemophilus spp. are transmitted horizontally and have been isolated from ostriches in Israel. Clinical signs are concentrated in the upper respiratory system and are treated with appropriate antibiotics from microbiological culture, and antibiotic sensitivity results. Proper management and quarantine of newly-acquired birds will reduce the risk of exposure and infection from this bacterial organism.
Anthrax
Although rare, Bacillus anthracis has been diagnosed in South African ostriches. In areas where anthrax has been identified as a cause of livestock deaths, ratite producers are advised to have any bird which dies peracutely necropsied by a veterinarian or pathologist, due to the highly zoonotic nature of this organism. Diagnosis is usually made at necropsy. Affected birds have extreme splenomegaly, hepatomegaly and vascular congestion (27). There is no treatment for this disease, and ostriches or other ratite species should not be maintained on farms with a history of anthrax.