UNCLASSIFIED TOXOPLASMA GONDII-LIKE ORGANISM

UNCLASSIFIED TOXOPLASMA GONDII-LIKE ORGANISM

UNCLASSIFIED TOXOPLASMA GONDII-LIKE ORGANISM (Figures 1-15 to 1-17) <a href="https://www.aavp.org/wp-content/uploads/2016/06/fig01-15-3.jpg"><img width="300" height="196" class="aligncenter size-medium wp-image-3343" alt="fig01-15" src="https://www.aavp.org/wp-content/uploads/2016/06/fig01-15-3-300x196.jpg" /></a> ETYMOLOGY: This organism has not been named. HISTORY: This parasite was first reported in the early 1990's (Dubey et al., 1992; Dubey and Carpenter, 1993; Dubey and Fenner, 1993). It closely resembles Toxoplasma gondii, but the tissue cysts of this organism are about twice as large as those of T. gondii. GEOGRAPHIC DISTRIBUTION AND PREVALENCE: Dubey and Carpenter (1993) found this organism in 3 of 103 cats examined in a retrospective study of feline toxoplasmosis. The subjects had been examined at necropsy at the Angell Memorial Animal Hospital, Boston, Massachusetts between 1952 to 1991. DIAGNOSIS: A tentative diagnosis can be made on the large size of the tissue cysts. Transmission electron microscopy is needed to confirm the diagnosis. Bradyzoites of the unclassified organism have numerous micronemes that are arranged in rows, while micronemes in bradyzoites of T. gondii are fewer in number and arranged randomly (Dubey et al., 1992; Dubey and Fenner, 1993). Infected cats may be T. gondii antibody positive and tissue cysts may react weakly with anti-T. gondii serum in immunohistochemical tests. CLINICAL SIGNS AND PATHOGENESIS: Infected cats have ranged in age from 3 to 17 years. Clinical signs attributable to parasitism have been associated with only 1 of 6 cats reported to have been infected with this organism (Dubey and Fenner, 1993). The cat was three years-old and was presented for lameness. Neurologic and ophthalmologic abnormalities were present on physical examination. The neurologic examination indicated lesions in the spinal cord at C6-T2. A complete necropsy was done and gross and microscopic lesions were confined to the spinal cord. Grossly, a focal translucent grayish area 1 x 0.3 cm laterally between cervical nerve roots C5 and C6. In addition, the spinal cord widened unilaterally from C4 to C6. Microscopic lesions consisted of focal granulomatous myelitis involving both gray and white matter and focal nonsuppurative meningitis including radiculoneuritis. Numerous protozoal tissue cysts were associated with the lesions. Three of the other 5 infected cats have had concurrent lymphoid disorders and may have been suffering from varying degrees of immunosuppression. The association of this parasite and the immune status of the host needs to be better defined. REFERENCES: Dubey JP, Peters D, Brown C. 1992. An unidentified Toxoplasma-like tissue cyst-forming coccidium in a cat (Felis catus). Parasitol Res 78:39-42. Dubey JP, Carpenter JL. 1993. Unidentified Toxoplasma-like tissue cysts in the brains of three cats. Vet Parasitol 45:319-321. Dubey JP, Fenner WR. 1993. Clinical segmental myelitis associated with an unidentified Toxoplasma-like parasite in a cat. J Vet Diagn Invest 5:472-480. Figure 1-15. Toxoplasma-like organism. Brain of a cat with a large cyst of this Toxoplasma- C:\Aa Old D\Dwight\CATBOOK\complete\chap1\chap1-with figs.doc Page 35 of 112 Feline Clinical Parasitology – Chapter 1 like organism. Figure 1-16. Toxoplasma-like organism. Higher power view of the cyst in which can be seen the many bradyzoites that are present. Figure 1-17. Toxoplasma-like organisms. Electron micrograph of the Toxoplasma like organism showing the many micronemes and rhoptries present in this organism.