First Report of Hepatozoon canis Infection in a Dog from Chiba Prefecture, Japan

Abstract

In Japan, Hepatozoon canis is reported to be primarily distributed in western Japan. The present study describes the first confirmed Hepatozoon canis infection in a dog from Chiba Prefecture, located in the Kanto region of eastern Japan. The case involved a female stray dog of unknown age and breed rescued in March 2024. Histopathological examination incidentally revealed meronts of Hepatozoon in the inguinal lymph node, which had been removed during the surgical excision of a mammary tumor. Additionally, Hepatozoon gamonts were identified within neutrophils on peripheral blood smears. Molecular identification using polymerase chain reaction targeting the 18S rRNA gene, followed by sequence analysis, confirmed the organism as H. canis. Clinically, the dog exhibited no significant abnormalities in preoperative blood tests or radiographic examination, nor any clinical signs commonly associated with hepatozoonosis, such as fever or anemia. Nonetheless, the detection of H. canis infection in a previously unaffected geographical area underscores the potential expansion of this parasite's distribution within Japan. Veterinarians should, therefore, consider canine hepatozoonosis as a differential diagnosis in dogs presenting with unexplained fever or anemia, even in regions outside traditionally endemic areas. Further epidemiological studies, including surveillance of tick vectors and wild reservoirs, are warranted to elucidate the transmission dynamics and prevent the spread of this infection.