Infectious diseases are primarily a problem in chicks <6 mo old. Infective agents associated with disease in chicks include bacterial, fungal, viral, and parasitic agents. However, the isolation of disease agents in a sick chick must be considered in conjunction with a review of nutritional, environmental, management, and genetic factors.
Diarrhea is the most common clinical sign in ratite chicks. Many chicks will have diarrhea when the yolk sac is absorbed and the chick starts eating well, at 8–12 days of age. If the chicks are alert and active, no treatment is needed. Chicks will also develop diarrhea after a sudden change in diet for which treatment with probiotics is indicated. Bacterial causes of diarrhea include Escherichia coli, Salmonella spp, Pseudomonas spp, Campylobacter jejuni, Klebsiella spp, Clostridium perfringens, Clostridium colinum, Mycobacterium spp (adults), Streptococcus spp, and Staphylococcus spp. The appropriate antibiotic should be determined by culture and subsequent microorganism isolation and sensitivity, and the source of bacteria identified (eg, barn, hatcher, inadequate hygiene, airborne vectors). Viral agents (suspected pathogens) that may cause diarrhea include paramyxovirus, reovirus, herpesvirus, birna-like virus, enterovirus, adenovirus, and coronavirus. Treatment for viral diarrhea is supportive only, and any potential source of the virus (eg, wild birds, infected hens, people) should be eliminated. GI obstruction is another cause of diarrhea; treatment is surgical, and any changes in environment or feed should be made slowly to prevent recurrence. In cases of fungal candidiasis, antibiotic treatment should be discontinued and a dry environment maintained. Although the pathogenicity of protozoa relating to diarrhea diagnosed in ostrich chicks is unknown, metronidazole is considered the treatment of choice. Enteritis may also be caused by management errors, including overmedication and excess electrolyte supplementation in drinking water during hot weather.
The incidence of yolk sac infection and retention generally is low in naturally hatched chicks. However, this condition often occurs when owners assist to hatch a chick or tie off the omphalomesenteric vessels and bandage the abdomen. The yolk sac may also be contaminated through the ostium at the ileal opening when absorption of the yolk material by the vitelline membrane (yolk sac lining) is delayed. Bacteria commonly isolated from the yolk sac are gram-negative; however, yolk sac retention secondary to noninfectious causes also occurs.
Poxvirus infections are more frequent in ostrich chicks and produce typical, crusty granulomatous lesions on the face, ears, and neck. Poxvirus is transmitted by insect vectors, primarily mosquitoes. The disease is self-limiting, and mortality is low. Vaccination of a flock during an outbreak with fowlpox vaccine may stop the spread of disease. The vaccine is a cutaneous fowlpox vaccine administered by dipping a large needle with reservoirs near the tip that allow inoculation when a puncture is made through the propatagium. Staphylococcal dermatitis occurs as a secondary problem in debilitated chicks, especially when external parasites disrupt the epithelial integrity.
Eastern equine encephalomyelitis can cause death in ostrich chicks as a fading chick syndrome and as a violent and fatal gastroenteritis in emus of all ages. Vaccination of emus for this disease is necessary in areas where the virus exists.
Avian influenza has been diagnosed in rheas and other ratite species. Routine testing for avian influenza is required for most intrastate shipments of ratites.
A number of intestinal protozoa, including Hexamita, Giardia, Trichomonas spp, Cryptosporidium, and Toxoplasma spp, have been isolated from ratite chicks. The pathogenicity of these parasites in all ratite species is unknown, and immunosuppression may be required for disease to develop. Metronidazole at 10 mg/kg, PO, bid, is recommended for protozoal parasite infections diagnosed in ratite species. Coccidiosis is common, and although not believed to be pathogenic, it can be treated with sulfa drugs. If coccidiosis is causing clinical signs (eg, diarrhea), the underlying immunosuppressive disease condition(s) must be diagnosed to effectively treat the protozoal disease.
The wireworm Libostrongylus douglassii is the most economically significant GI parasite of ostriches. Mature worms and late larval stages live in the crypts of the glandular portion of the stomach. Diagnosis is based on finding trichostrongyloid-type eggs in the feces. The recommended treatment for the ostrich wireworm is ivermectin at 0.2 mg/kg or fenbendazole at 15 mg/kg. Another nematode with clinical significance for ratite species is Baylisascaris spp, which is transmitted from skunks or raccoons through feed. This neurotropic parasite causes CNS lesions and signs. Restricting exposure to raccoon and skunk feces is the best prevention. Chandlerella quiscali is a nematode identified in emus that results in cerebral larval migrans. The common grackle is the definitive host for C quiscali, and emus are exposed to the parasite through the bite of Culicoides crepuscularis. Birds infected with C quiscali develop profound torticollis and incoordination that leads to emaciation, scoliosis, and death. Ivermectin is the treatment of choice for C quiscali infections in emus.
Three types of arthropods can affect ratites: lice, ticks, and quill mites. Lice can be a problem, especially in ostriches. Biting lice (Struthioliperurus struthionis) cause skin and feather damage. Treatment with permethrin spray (poultry concentration) is effective, as is injectable ivermectin at 1 mL /110 lb, IM. Several species of ticks have been identified on ratite species; their main significance is as vectors of disease. Feather mites live in the vein on the underside of the feather and feed on blood. Ratite feather mites can be visualized as small, reddish, dust-like particles in the feather vein. Treatment for ticks and mites is ivermectin at 0.2 mg/kg at 30-day intervals.