Merck Manual

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Professional Version

Candidiasis in Poultry

(Thrush, Crop Mycosis, Sour Crop)


Jenny Nicholds

, DVM, DACPV, Poultry Diagnostic and Research Center, Department of Population Health, College of Veterinary Medicine, University of Georgia

Last review/revision Apr 2021 | Modified Oct 2022
Topic Resources

Candidiasis is an opportunistic mycotic disease of the digestive tract of various avian species, including, but not limited to, chickens, turkeys, and quail, that is caused by the fungus Candida albicans. It commonly develops after use of therapeutic levels of various antimicrobials or when using unsanitary drinking facilities. Heavy parasitism and malnutrition (vitamin A deficiency) have also been implicated.

Lesions are most frequently found in the crop and consist of thickened mucosa and whitish, raised pseudomembranes. The same lesions may be seen in the mouth and esophagus. Occasionally, shallow ulcers and sloughing of necrotic epithelium may be present. Listlessness and inappetence may be the only signs. A presumptive diagnosis may be made on observation of gross lesions. Depending on the locations of lesions, differential diagnoses that are important to consider include wet pox, vitamin A deficiency Vitamin A Deficiency Vitamin deficiencies are most commonly due to inadvertent omission of a complete vitamin premix from the birds’ diet. Multiple signs are therefore seen, although in general, signs of B vitamin... read more , and infectious laryngotracheitis Infectious Laryngotracheitis in Poultry Infectious laryngotracheitis (ILT) is an economically important respiratory disease of poultry. This highly contagious disease is caused by Gallid alpha herpesvirus type 1 (GaHV-1), commonly... read more Infectious Laryngotracheitis in Poultry .

Candidiasis in Poultry

Diagnosis can be confirmed by demonstrating tissue invasion histologically. Microscopic lesions are characterized by epithelial hyperplasia, ballooning degeneration, and visualization of pseudohyphae and blastospores consistent with Candida spp. It is important to note that culture alone is not diagnostic of disease; Candida spp are commensal organisms and can be commonly isolated from clinically normal birds. Young chicks and poults are most susceptible.

The removal of contributing factors will help to reduce the incidence of candidiasis, (eg, improving sanitation and judicious antimicrobial use in poultry). Candidiasis may be treated or prevented with addition of copper sulfate at a concentration of 1:2,000 dilution in the drinking water; however, the effectiveness of this intervention is controversial. Administration of nystatin, an antifungal medication, in the feed (220 mg/kg of feed) or in drinking water (62.5–250 mg/L with sodium lauryl sulfate, a surfactant, at 7.8–25 mg/L) for 5 days may be effective for the treatment of affected turkeys. However lack of an approved product for this application in some countries, may render this a nonviable option.

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