Fatal Toxoplasmosis in Red Kangaroos () in East China.

Background: As a ubiquitous apicomplexan parasite, causes huge economic losses and poses a great threat to the health of animals, including humans, worldwide. In some kangaroo species, can be fatal. To date, little information is available on infection in the red kangaroos in east China. At a zoo in east China, thirteen red kangaroos consecutively developed clinical signs from July to November 2016, resulting in the deaths of seven, three of which were analyzed in this study.

Methods: In the present study, ascitic fluid, blood and samples from the brain, heart, liver, spleen, lung, kidney, and mesenteric lymph nodes of three dead red kangaroos were collected. The pathogen was explored through microscopic observation, nested PCR, immunofluorescence antibody test (IFAT), hematoxylin-eosin (HE) staining, and immunohistochemistry (IHC) staining, respectively. Meanwhile, the potential source of the infection was also investigated by testing the blood of stray cats in the zoo for using nested PCR.

Results: Three dead red kangaroos were subjected to a necropsy, and organisms resembling were detected in their ascitic fluids under microscope. This infection was further confirmed by a nested PCR assay, which resulted in a successful amplification and sequencing of the 433 bp fragment of the 5.8S rRNA gene in all the dissected tissues, including heart, liver, spleen, lung, kidney, lymph nodes, cecum, and brain, as well as in body fluids (blood and ascitic fluid). Furthermore, the tachyzoites were observed in the heart, liver, spleen, lymph nodes, cecum, and brain through IFAT and HE staining. Administration of classic drugs (sulfadiazine and pyrimethamine) against significantly alleviated the clinical signs of the sick kangaroos. The possible source of this infection was traced to a native stray cat, as DNA was detected in its blood.

Conclusions: In the present study, lethal infection in red kangaroos has been described for the first time in east China, highlighting the necessity and urgency for close and long-term surveillance of this parasite infection in captive animals. The same strain of detected in kangaroos as that found in stray cats wandering in the same area emphasizes the importance of controlling stray cat populations to mitigate the risk of transmission to other animals.