Echinococcosis Risk among Domestic Definitive Hosts, Japan

To the Editor: Echinococcosis is a serious parasitic zoonosis in the Northern Hemisphere. In Japan, it is characterized by alveolar, hepatic, and cerebral disorders in humans caused by the larval form (metacestode) of the tapeworm Echinococcus multiloc-ularis. The life cycle of the parasite is maintained in the wild by gray-backed voles, Clethrionomys rufo-canus, as intermediate hosts, and by red foxes, Vulpes vulpes, as definitive hosts. Humans are infected by inges-tion of the parasite eggs, mainly through water contaminated with the feces of wild red foxes, which have an estimated infection prevalence of 54%–56% (1). The echinococcosis-endemic area in Japan is restricted to the northern island of Hokkaido, although sporadic human cases have been reported on other islands (2), and infected pigs have been documented on the main island of Honshu (3). While the threat of echinococcosis spreading into Honshu had raised fears, an emergent concern is the possible role of domestic dogs in dispersing the disease from disease-endemic areas during reloca-tion of residences by owners or when accompanying owners during domestic travel. In September 2005, a stray dog in Saitama prefecture in mainland Honshu was found to be positive for E. multilocularis infection by PCR (mitochondria 12S RNA gene) (Y. Morishima, pers. comm.). The sequence was identical to the Hokkaido isolate (GenBank accession no. AB244598). This raised an alarm because the area in which the infection was found is adjacent to the Tokyo metropolis, the most populous zone in Japan. Reports also claimed that 2 of 69 dogs moved from Hokkaido to Honshu were positive for E. multilocularis by coproantigen examination (4). Nearly 10,000 pet dogs were estimated to have been transported in 1 year to and from Honshu and Hokkaido by planes and ferries; this presumably included up to 30 E. mul-tilocularis–infected pet dogs per year (5). Even so, no compulsory quarantine or Echinococcus examination is enforced for dogs transported within Japan. A compulsory requirement of a certificate from a veterinarian stating that the animal has been treated with praziquantel 3–4 days before travel-ing would be a helpful preventive measure. As part of an amendment to the Infectious Disease Law in Japan, E. multilocularis infection was included among the 4th Category Diseases (6). Thus, since October 2004, it has been mandatory for veterinarians who have diagnosed echinococcosis in dogs to report each case to health authorities, the first national reporting system of its kind worldwide. Our laboratory established the …