Susceptibility of ponies to infection with Streptococcus pneumoniae (capsular type 3).

The research article discusses the susceptibility of Welsh Mountain ponies to infection with a specific bacterial strain Streptococcus pneumoniae, and how these infections affect their health before the ponies eventually recover and develop antibodies against the bacteria.

Methodology

• The researchers used Welsh Mountain ponies for the experiment, inoculating them with different doses of an isolate of Streptococcus pneumoniae (alleged SPE 1618, capsular type 3) that was recovered from the horse respiratory tract.
• The bacteria were instilled intratracheally – directly into the trachea – in two volumes: 10 ml of a suspension containing either 10(8) (100 million) or 10(9) (1 billion) colony-forming units (cfu) per ml.

Observations

• Fever was noticed in all ponies regardless of the dosage they received. However, the ponies that received the higher concentration also displayed other symptoms, such as coughing, ocular and nasal discharge, noticeable low mood, and enlargement of the submandibular lymph nodes (located beneath the jaw).
• Cytological analysis of tracheal washings – samples taken from the trachea – within the first week after inoculation showed evidence of bacterial infection and the bacteria could be successfully cultured from these samples.

Pathological Findings

• Post-mortem examination of selected ponies, in concert with histopathological (tissue-based) investigation, revealed the development of focal pneumonia (infection localized in certain areas) predominantly affecting the ventral (lower) part of the lungs, particularly the cardiac area and the auxiliary lobe. The right lung was more prone to such infections.
• Either Streptococcus pneumoniae was isolated directly from these lung lesions, or macrophages (a type of white blood cell) bearing specific capsular type 3 antigen were confirmed with immunostaining – a technique used to identify specific proteins (antigens) in tissue samples using antibodies that attach to them.

Recovery and Immunity

• By day 10 post-inoculation, the ponies recovered from the disease and appeared healthy. They had also developed antibodies specific to the Streptococcus pneumoniae, pointing towards future resistance against this pathogen.
• The study concluded that Streptococcus pneumoniae was a primary pathogen in these ponies under the circumstances of this particular experiment.