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Title: Life cycle of Hammondia hammondi (Apicomplexa: Sarcocystidae) in cats

item Dubey, Jitender
item FERGUSON, DAVID - Oxford Radcliffe Hospitals

Submitted to: Journal of Eukaryotic Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2014
Publication Date: 10/1/2014
Citation: Dubey, J.P., Ferguson, D. 2014. Life cycle of Hammondia hammondi (Apicomplexa: Sarcocystidae) in cats. Journal of Eukaryotic Microbiology. 62:346-352.

Interpretive Summary: Only members of the cat family excrete the environmentally resistant stage of Toxoplasma gondii, an important foodborne parasite, but cats also shed cysts of a morphologically similar parasite, Hammondia hammondi, leading to frequent misdiagnosis. Although molecular tools can discriminate between them, a detailed comparison of the how these parasites develop in cats might assist in their differential diagnosis, and shed light on why only one of these parasites, T. gondii, has become a ubiquitous and zoonotic parasite, infecting a vast range of vertebrate hosts and infecting approximately one-third of the global human population. We found many similar aspects of their development in cats, but were able to identify nuanced differences that may assist pathologists, parasitologists, and mammalogists better understand how these two parasites differ.

Technical Abstract: Hammondia hammondi and Toxoplasma gondii are feline coccidian that are morphologically, antigenically, and phylogenitically related. Both parasites multiply asexually and sexually in feline intestinal enterocytes but H. hammondi remains confined to enterocytes whereas T. gondii also parasitizes extra-intestinal tissues of the cat. Here, we studied multiplication of H. hammondi in feline intestine and compared with T. gondii cycle. Five parasite–free cats were inoculated orally with tissue cysts and free bradyzoites from skeletal muscles of gamma interferon gene knock out mice and killed at 1, 3, 4, 6, and 7 days later. At 1 and 3 day post inoculation (DPI) numerous individual intracellular bradyzoites were detected in histological sections of small intestine. At 4 DPI only schizonts were found and they were located in enterocyte cytoplasm above the host cell nucleus. At 6 and 7 DPI both schizonts and gamonts were seen and they were located in enterocytes. Ultrastucturally, schizogonic and gametogonic development of H. hammondi was similar to T. gondii. However, in H. hammondi merozoites rhoptries were longer, and coiled and contained more micronemes than in T. gondii. Ultrastructural development is illustrated in detail.