Pathology Case of the Month – Red Crossbills and American Goldfinches

Gross Findings: Gross findings were similar in all examined birds. On external examination, abundant light green fecal material was present in the feathers around the vent. On internal examination, there was no subcutaneous, visceral, or epicardial fat. Pectoral muscle was atrophied in some birds. There were multiple variably sized thick tan plaques or seed-like plaques on the mucosal surface of the crop; the largest measured 1 x 0.7 x 0.3 cm. There were multiple round tan nodules in the liver and spleen, measuring up to 1 mm and 2.5 cm in diameter, respectively.  The ventriculus contained crushed seeds.

Diagnostic Test Results:

• Culture of the crop or spleen yielded Salmonella sp.
• Sequencing showed Salmonella enterica
• Serotyping showed serovar Typhimurium

Conditions:

1. Salmonellosis
2. Emaciation

Etiology: Salmonella enterica serovar Typhimurium

Salmonellosis is caused by bacteria in the genus Salmonella. There are over 2,500 different strains or “serovars” of salmonellae. Serovars are variants of two species, S. enterica and S. bongori. Pullorum disease, (S. enterica serovar Pullorum) and fowl typhoid (S. enterica serovar Gallinarum) are well known diseases of poultry but also infect wild birds. However, wild birds are more commonly infected by paratyphoid forms, of which S. enterica serovar Typhimurium is a prominent representative.

Geographic distribution: No restrictions.

Time: No restrictions; in songbirds, outbreaks at feeders occur at times of heavy use; in colonial nesting species, outbreaks occur in the summer after young are hatched.

Host range: All avian species; increased index of suspicion in passerines frequenting bird feeders and in colonial nesting waterbirds such as gulls, terns, herons, egrets, cormorants, and pelicans. Juvenile birds are more susceptible than adults.

Transmission: Fecal-to-oral is the major route of transmission since salmonellae are primarily enteric bacteria.

Clinical signs: Infection may result in: 1) asymptomatic intestinal carrier stage; 2) acute, fatal septicemia with or without enteritis; or 3) chronic localized infections with or without clinical signs. Signs of illness are nonspecific and may include lethargy, ruffled feathers, drooping head, ocular discharge, joint swelling, diarrhea, fecal staining of vent feathers, or emaciation.

Pathology: In acute cases, there may be few lesions such as pulmonary and renal congestion, and swollen and congested liver and spleen with or without small hemorrhagic or necrotic foci. Chronic cases may have esophagitis and ingluvitis, enteritis, typhlitis with necrotic cores and necrosis or inflammation in the liver, spleen, pectoral muscle, subcutis, brain, or other sites. Other chronic changes include depletion of fat stores, pectoral muscle atrophy, or arthritis. Histopathological findings include a combination of necrosis and inflammation usually with abundant Gram-negative bacilli.

Diagnosis: Histopathology; culture and identification of bacteria and serotype.

Public health concerns: Salmonellosis is a zoonotic disease that causes gastroenteritis. Any persons handling dirty bird feeders, bird baths, or equipment should wear gloves and practice careful personal hygiene including washing their hands after touching infected materials and promptly removing and washing any clothing that has become contaminated with bird feces.

Wildlife population impacts: Salmonellosis is unlikely to threaten wild bird populations as it does not often cause extensive mortality.

References:

• Daoust PY, Prescott JF. 2007. Salmonellosis. In: Infectious Diseases of Wild Birds, Thomas NJ, Hunter DB, Atkinson CT, editors. Blackwell Publishing, Oxford, England, pp 270–288. https://doi.org/10.1002/9780470344668.ch13
• Friend M. 1999. Salmonellosis. In Field Manual of Wildlife Diseases: General Field Procedures and Diseases of Birds, Friend M, Franson JC, editors. U. S. Geological Survey: Reston, VA. pp 99–110. Available online: https://pubs.usgs.gov/itr/1999/field_manual_of_wildlife_diseases.pdf#page=111. Accessed 20 Sept 2021.