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Susceptibility of ponies to infection with Streptococcus pneumoniae (capsular type 3)
A S Blunden1, D Hannant, G Livesay
1Department of Infectious Diseases, Animal Health Trust, Newmarket, Suffolk, UK.
Abstract:
Welsh Mountain ponies were inoculated with an isolate of Streptococcus pneumoniae, SPE 1618 (capsular type 3) recovered from the equine respiratory tract: 10 ml of a suspension of 10(8) or 10(9) cfu/ml were instilled intratracheally. Fever was observed after either dose but the greater concentration also produced coughing, ocular and nasal discharge, depression and enlargement of submandibular lymph nodes. Cytological evidence of infection was also observed in tracheal washings during the first week after inoculation and corresponded with isolation of S. pneumoniae from the washes. Morbid anatomical and histopathological examinations of selected animals revealed focal pneumonia affecting the ventral lung, especially the cardiac area and accessory lobe, with a propensity to affect the right lung. S. pneumoniae was isolated directly in pure culture from these lesions or was demonstrable by immunostaining of macrophages bearing specific capsular type 3 antigen. By 10 days after inoculation, the ponies were healthy and had developed antibodies to S. pneumoniae. S. pneumoniae was therefore a primary pathogen in the horse under the conditions of the challenge.
Insights
Streptococcus pneumoniae causes respiratory illness in horses. This study shows the bacterium is a primary pathogen in ponies, leading to pneumonia and other symptoms.
Area of Science:
- Veterinary Medicine
- Microbiology
- Equine Health
Background:
- Equine respiratory disease is a significant concern in horses.
- Streptococcus pneumoniae has been isolated from the equine respiratory tract, but its pathogenicity requires further investigation.
Purpose of the Study:
- To determine if Streptococcus pneumoniae acts as a primary pathogen in horses.
- To characterize the clinical and pathological effects of experimental Streptococcus pneumoniae infection in ponies.
Main Methods:
- Welsh Mountain ponies were intratracheally inoculated with Streptococcus pneumoniae (capsular type 3).
- Clinical signs, tracheal wash cytology, bacterial isolation, and post-mortem examinations were performed.
- Antibody responses were assessed post-inoculation.
Main Results:
- Inoculation with Streptococcus pneumoniae caused fever, coughing, nasal discharge, and lymph node enlargement.
- Focal pneumonia, particularly in the ventral lung, was observed.
- Streptococcus pneumoniae was isolated from lesions and tracheal washes.
- Ponies developed antibodies to Streptococcus pneumoniae by 10 days post-inoculation.
Conclusions:
- Streptococcus pneumoniae is a primary respiratory pathogen in horses under experimental conditions.
- The study demonstrates the capacity of Streptococcus pneumoniae to induce pneumonia and systemic signs in ponies.
- Successful recovery and antibody development indicate a host response to infection.