Susceptibility of cats to infection with Ehrlichia risticii, causative agent of equine monocytic ehrlichiosis.

The research study explores the susceptibility of cats to infection with Ehrlichia risticii, a bacterium that causes equine monocytic ehrlichiosis, a disease predominantly affecting horses. The researchers investigated this by inoculating eight adult cats with E. risticii and observing the clinical signs.

Methodology

• The researchers used a group of eight adult cats for the study.
• These cats were inoculated, either intravenously (IV) (6 cats) or subcutaneously (SC) (2 cats) with Ehrlichia risticii-infected P388D1 cells, or with the Ehrlichia risticii bacterium released from these cells.
• For control purposes, three additional cats were inoculated with organism-free P388D1, a murine macrophage cell line, and one cat was inoculated with a balanced salt solution.

Observations

• Ehrlichia risticii could be isolated from cats inoculated intravenously. They displayed clinical signs of illness.
• One cat developed intermittent diarrhea between post-inoculation days (PID) of 8 and 18.
• Another cat showed symptoms of lymphadenopathy (enlarged lymph nodes), acute depression, and anorexia between PIDs of 20 and 24.
• However, no Ehrlichia risticii was isolated from the cats that were inoculated subcutaneously or from the control cats.
• All eight cats that were inoculated with Ehrlichia risticii seroconverted (or developed antibodies against Ehrlichia risticii) between PIDs of 10 and 23.

Pony Inoculation

• In an extended part of the study, a pony was inoculated with Ehrlichia risticii isolated from one of the inoculated cats.
• The pony showed clinical signs of equine monocytic ehrlichiosis, such as fever, anorexia, depression, and mild colic. These symptoms are consistent with the disease in its typical host, the horse.
• Ehrlichia risticii was then successfully isolated from the blood of this pony on PIDs 7, 9, 11, and 16.

Conclusion

This study suggests that cats can potentially serve as a host for Ehrlichia risticii, the bacteria that cause equine monocytic ehrlichiosis, expanding the range of potential hosts for this bacterium beyond horses. The findings essentially highlight the potential for interspecies transmission of this pathogen. However, further studies are needed for definitive conclusions.