Identification of a mouse-virulent recombinant type I/III Toxoplasma gondii strain in liver cytology of an immunosuppressed cat infected with FeLV-C subgroup.

Toxoplasma gondii infection is common in cats, though clinical disease is uncommon and typically occurs in immunocompromised individuals. Till now, there is no specific genotype that can be associated with a certain clinical outcome. A 5-year-old Siamese cat, diagnosed as Feline Leukemia Virus (FeLV)-positive and classified within the FeLV-C subgroup, presented with a two-month history of progressive lethargy, hyporexia, weight loss, and non-regenerative anemia. The cat, a rescued stray with ongoing outdoor access, had previously responded to doxycycline and prednisolone for presumed Mycoplasma spp. infection, but relapsed and began showing signs of discomfort in head and neck regions, consistent with peripheral neuropathy/ encephalitis. Despite treatment with raltegravir, prednisolone, darbopoetin alfa, cyclosporine and clindamycin (although unknown effectiveness of oral administration), clinical deterioration occurred. The cat developed fever, severe anemia, neutropenia, hyperbilirubinemia, hypoglycaemia and elevated ALT activity. Imaging revealed diffuse hepatic changes and a pulmonary interstitial pattern. Liver FNA identified T. gondii organisms, confirmed by qPCR. Despite the initiation of intravenous clindamycin and trimethoprim-sulfamethoxazole, the cat developed seizures, acute respiratory distress, and septic shock, leading to euthanasia. Genotyping of the hepatic T. gondii isolate via targeted NGS at 13 loci revealed a strain with a recombinant type I/III profile. This mosaicism was previously associated with high virulence in mice and also detected in human patients from the same geographical region. This case highlights the variable presentation of toxoplasmosis in cats and contributes to the scarce knowledge of circulating strains in animals. Characterizing the genetic background of strains could identify sources during zoonotic outbreaks and identify genotypes associated with specific clinical manifestations.