First Confirmation of Canine Echinococcosis in Honshu in Japan
Echinococcosis is an important parasitic zoonosis around the world. Humans are infected with it when they ingest the parasite eggs which are contained in feces of foxes and dogs. All owners of dogs had better keep this infectious disease in mind because echinococcosis has a long incubation period before and is difficult to treat. The incidence of echinococcosis used to be limited in Hokkaido where many North Foxes live. The North Foxes which were introduced from Northern Territories for the purpose of exterminating field mice and gaining fur, were already infected with the parasite that they had developed in Rebun Island. Then, these infected foxes are presumed to have come to Hokkaido on drifting ice. Recently, it was reported that genes of echinococcosis were detected in feces of 3 of 56 homeless dogs captured in Aichi Prefecture. It was not clarified if these dogs discharged live eggs of the parasite or not, however, it indicates that echinococcosis is expanding from Hokkaido to Honshu. The infectious rate of canine echinococcosis in Hokkaido is estimated around 1 %.
This parasitic disease is most commonly caused by Echinococcus multilocularis, yet sometimes caused by Echinococcus granulosus. The number of human infectious cases in Japan are approximately 500, almost all of them occurring in Hokkaido. Both foxes and dogs are definitive hosts of the adult parasite. These animals discharge eggs into their feces, and then, humans are infected by ingesting the eggs orally through contaminated river water or eating raw vegetables grown in a contaminated area. Humans are intermediate hosts with symptoms of cyst’s forming primarily in the liver mainly. Not only wild mice but also swine, horses, sheep, goats, and camels are regarded as the other intermediate hosts. Intermediate hosts do not infect others with this disease even if they have contact each other, and foxes or dogs are mainly infected with it when they eat infected wild mice. Humans show no symptoms for 5 to 10 years after ingesting parasitic eggs. Echinococcus makes lesions in the liver and causes hepatic dysfunction to progress. In general, infected humans may develop severe hepatic dysfunction with jaundice, hydroperitoneum and edema within 6 months and finally died after metastasis to various organs. Lesions of echinococcus are sometimes discovered when humans are misdiagnosed as a liver cancer by image diagnosis. There is no effective medicine for this disease, and surgical resection of lesions is the only effective treatment. Once humans show symptoms, however, the prognosis is poor. On the other hand, foxes and dogs show no symptoms generally. They occasionally suffer from diarrhea or discharged mucous and bloody feces when they ingest a large number of parasitic eggs. Diagnosis of echinococcus for them can be possible by fecal examinations or detection of antigens in feces, however, the facilities where examinations can be performed are limited.
Praziquantel preparations are effective for treatment of infected dogs. Moreover, unleashing dogs in polluted areas of Echinococcus is not recommended. The rate of infection for wild mice in Hokkaido is considered around 30%. Dogs show no symptoms even if they are infected, and we cannot see parasitic eggs with the naked eyes. We recommend the owners to consult a veterinarian if your dogs may eat wild mice, or may be infected with Echinocossus. Dogs can be diagnosed accurately and administered parasiticides. We recommend avoiding contact with foxes in polluted areas such as Hokkaido, and to paying attention to ingesting food and drink that may be polluted with parasitic eggs.