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; they can be treated with probiotics. Bacterial causes of diarrhea include Escherichia, Salmonella, Pseudomonas, Campylobacter jejuni, Klebsiella, Clostridium perfringens, Clostridium colinum, Mycobacterium (adults), Streptococcus, and Staphylococcus. The appropriate antibiotic should be determined by culture and sensitivity, and the source of bacteria identified (eg, barn, hatcher, inadequate hygiene, airborne vectors such as flies, etc). Viral agents (suspected pathogens) that may cause diarrhea include paramyxovirus, reovirus, herpesvirus, birna-like virus, enterovirus, adenovirus, and coronavirus. Treatment for viral diarrhea is symptomatic 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 stopped, and a dry environment should be maintained. Although the pathogenicity of protozoa in diarrhea of ostrich chicks is unknown, metronidazole can be administered. Enteritis may also be caused by management errors, including overmedication and excess electrolytes in drinking water during hot weather.

The incidence of yolk sacculitis generally is low in naturally hatched chicks. However, owners often assist the chick in hatching or tie off the omphalomesenteric vessels and bandage the abdomen. These practices often result in yolk sacculitis. 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 pox lesions on the face, ears, and neck. Poxvirus is transmitted by insects. 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. Staphylococcal dermatitis occurs as a secondary problem in debilitated chicks, especially when external parasites are a problem.

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 those areas where the virus exists.

Avian influenza can be a problem in some flocks, and testing is routine for most intrastate shipments of ratites.

Parasitic Diseases

Protozoa

A number of intestinal protozoa, including Hexamita, Giardia, Trichomonas, Cryptosporidium, and Toxoplasma, have been isolated from ratite chicks. Their pathogenicity is unknown, and immunosuppression may be required for disease to develop. Metronidazole at 10 mg/kg, PO, bid is administered. Coccidiosis is common, and although not believed to be pathogenic, it can be treated with sulfa drugs.

Cestodes

The tapeworm Houttuynia struthionis is common in Africa but is seen only sporadically in the USA. The intermediate host is not known. Treatment is fenbendazole, 15 mg/kg, PO, sid for 5 days, used at regular intervals.

Nematodes

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. Treatment is ivermectin at 0.2 mg/kg or fenbendazole at 15 mg/kg. Another nematode with clinical significance is Baylisascaris, which is transmitted from skunks or raccoons through feed. It is a neurotropic parasite that causes CNS lesions and signs. Restricting exposure to raccoon and skunk feces is the best prevention.

Arthropods

Three types of arthropods can affect ratites—lice, ticks, and quill mites. Lice can be a problem, especially in ostriches. Biting lice (Struthioliperurus struthionis) result in skin and feather damage. Treatment with permectrin spray (poultry concentration) is effective, as is injectable ivermectin at 1 mL /110 lb. Several species of ticks affect ratites; their main significance is as vectors of disease. Feather mites live in the vein on the underside of the feather and feed on blood. They 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.

Last full review/revision July 2011 by Karen Hicks-Alldredge, DVM