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Isolation of Chlamydia psittaci from naturally infected African clawed frogs (Xenopus laevis)
Abstract:
An inclusion-forming agent was isolated from the livers of commercially raised African clawed frogs (Xenopus laevis) involved in an epizootic of high morbidity and mortality. Original isolation was made in McCoy cells. This agent was identified as Chlamydia psittaci based on the formation of typical intracytoplasmic inclusions which developed within 48 h, were not stained by iodine, and were resistant to sulfadiazine. The isolate from one particular frog (designated as strain 178) was further studied and found to be lethal for 7-day-old embryonated chicken eggs after intra-yolk sac inoculation. This strain was demonstrated not to be pathogenic for mice when inoculated intraperitoneally. The cell culture isolate of C. psittaci was transmitted to uninfected X. laevis, causing disease and death.
Insights
Chlamydia psittaci was identified as the cause of a disease outbreak in African clawed frogs (Xenopus laevis). This frog pathogen caused mortality in frogs and chicken eggs but was not pathogenic in mice.
Area of Science:
- Veterinary Pathology
- Microbiology
- Amphibian Diseases
Background:
- An epizootic characterized by high morbidity and mortality occurred in commercially raised African clawed frogs (Xenopus laevis).
- Inclusion-forming agents were suspected as the causative agents of the disease outbreak.
Purpose of the Study:
- To isolate and identify the causative agent responsible for the epizootic in Xenopus laevis.
- To characterize the pathogenicity of the isolated agent.
Main Methods:
- Isolation of the agent in McCoy cell culture.
- Identification of the agent based on morphological and biochemical characteristics (intracytoplasmic inclusions, iodine staining, sulfadiazine resistance).
- Pathogenicity testing in embryonated chicken eggs and mice, and transmission studies in Xenopus laevis.
Main Results:
- An inclusion-forming agent, identified as Chlamydia psittaci (strain 178), was successfully isolated from diseased Xenopus laevis.
- The isolated Chlamydia psittaci formed typical intracytoplasmic inclusions, was iodine-negative, and sulfadiazine-resistant.
- Strain 178 was lethal to embryonated chicken eggs but not pathogenic to mice via intraperitoneal inoculation.
- The isolate was transmissible to healthy Xenopus laevis, causing disease and death.
Conclusions:
- Chlamydia psittaci is identified as the etiological agent responsible for the epizootic in African clawed frogs.
- The study highlights the susceptibility of Xenopus laevis to Chlamydia psittaci and its potential impact on amphibian populations.
- The findings contribute to understanding Chlamydia infections in amphibians and their potential zoonotic or economic implications.