Epidemiological and environmental investigations of Legionella pneumophila infection in cattle and case report of fatal pneumonia in a calf

Abstract

A fatal pneumonia due to Legionella pneumophila was diagnosed in a young calf reared in a dairy herd located in northern Italy. Clinical symptoms consisted of watery diarrhea, hyperthermia, anorexia, and severe dyspnea. The pathological and histological findings were very similar to those observed in human legionellosis. Legionella pneumophila serogroup 1 (SG1) and SG10 were isolated from the calfs lung, and L. pneumophila SG1 was isolated from the calfs liver. L. pneumophila SG1 was also demonstrated in the lung tissue by immunofluorescence and immunohistochemical examinations. Nine of 10 L. pneumophila SG1 isolates belonged to the Olda subtype, and 1 belonged to the Camperdown subtype. A very low prevalence of antibodies to Legionella was detected in cows and calves reared in the same herd. Cultures of aqueous sediment of an old electric water heater which supplied hot water for the feeding of the calves yielded L. pneumophila SG1. Four of the colonies tested belonged to the Olda subtype. Ten clinical and four environmental isolates were examined for the presence of plasmids. Nine of them were also examined by pulsed-field gel electrophoresis assay, and the same patterns were found for L. pneumophila SG1 Olda strains isolated from the calf and from the electric heater. This is the first report of a documented case of a naturally occurring Legionella pneumonia in an animal. Cattle probably act as accidental hosts for legionellae, much the same as humans.

FIG. 1

Electric water heater used to supply hot water for the feeding of the calves.

FIG. 2

Calf lung. Fibrin and inflammatory cells fill the alveolar lumina (arrowheads). Purulent exudate is present in the lumen of a bronchiol (arrow). Hematoxylin-eosin stain was used. Bar, 125 μm.

FIG. 3

Calf lung. L. pneumophila SG1 antigen is detectable at the edge of a necrotic area (lower part). Immunohistochemical staining for L. pneumophila SG1 and hematoxylin counterstaining were performed. Bar, 55 μm.

FIG. 4

Photomicrograph of lung tissue from the pneumonic calf stained by indirect immunofluorescence with L. pneumophila SG1 antiserum. Single and clumped legionellae are indicated by arrows. Magnification, ×560.

FIG. 5

PFGE of genomic DNA from L. pneumophila strains isolated from calf clinical samples and from the associated environment digested with NotI. Lanes: 1, size marker (Saccharomyces cerevisiae YPH 755 chromosomes; Boehringer Mannheim); 2, L. pneumophila SG1 isolated from the electric water heater; 3, L. pneumophila SG1 isolated from liver; 4 and 5, L. pneumophila SG1 isolated from lung; 6, L. pneumophila SG10 isolated from lung; 7, size marker (bacteriophage λ ladder concatemers; Bio-Rad).