Chlamydia psittaci induced pneumonia in a horse.

The research paper covers a disease-causing agent lethal to chicken embryos, identified as Chlamydia psittaci, which is isolated from a horse’s tissue exhibiting fatal respiratory disease symptoms. The researchers then confirm the disease in the horse and experimentally infect two Shetland ponies leading to subsequent reisolation from the lung tissues in one pony.

Identification of Chlamydia psittaci

• The investigation started with the dissection of a quarter horse mare that had succumbed to a severe respiratory illness. The lung tissues of the horse had an agent that was lethal to embryonated chicken eggs, disrupting their development.
• Through microscopical tests of the lesions caused by the disease on chicken embryos, the particular staining properties (tinctoral properties), and the visual observation of the agent’s ultrastructure, the scientists could conclude that it belonged to the family Chlamydiaceae.
• The particular strain of bacteria also proved resistant to sodium sulfadiazine, a type of sulfonamide antibiotic typically active against a wide range of bacteria.
• The study further detected a chlamydial complement fixing antigen, a protein produced in response to Chlamydia psittaci, supporting the agent’s identification as this specific type of bacteria.

Infection of Shetland Ponies

• Following the identification of Chlamydia psittaci, the researchers used the isolated bacteria to infect two Shetland ponies experimentally to confirm its disease-causing abilities.
• Even though these ponies developed subclinical infections, meaning they did not show apparent symptoms, an increase in complement-fixing antibody titers was observed. This response demonstrated that the organism incited an immune response, confirming the agent’s pathological nature.

Post-mortem Examination

• The researchers conducted a post-mortem examination on one of the ponies, confirming a widespread chlamydial infection.
• Microscopic evidence revealed signs of interstitial pneumonia, a type of lung disease characterized by inflammation and fibrosis of the lung tissue, and focal hepatic necrosis, a condition involving the death of liver cells.
• The investigation also managed to re-isolate Chlamydia psittaci from the lung tissues of the affected pony, providing undeniable proof of the infectious nature of this bacteria, particularly its role in causing respiratory disease.