The Topic of This Month Vol.26 No.8(No.306)

Zoonoses in Japan

(IASR 2005; 26 : 193-194)

R. Virchow, known as the father of pathology, labeled the term "zoonosis" as an animal disease transmissible to man. The Joint WHO/FAO Expert Committee Meeting (1958) defined zoonoses as "those diseases and infections which are naturally transmitted between vertebrate animals and man".

Zoonoses in Japan: Approximately 60% of microorganisms that are infectious to humans, representing over 800 species, originate from animals. In recent years, various species of animals have been identified as reservoir hosts or sources of infection for many emerging and re-emerging disease pathogens worldwide, highlighting the public health importance of zoonoses.

Japan has succeeded in controlling many zoonotic diseases, such as rabies and plague. This success has largely been due to inherent geographic and climatic advantages as an island country, with resulting limitations of direct invasion of terrestrial animals and decreases in activity of animals and vectors during the winter season. Efforts have thus focused on domestic countermeasures. Recently, however, many animals and livestock products have been imported from all over the world, and the introduction of animals from overseas under natural conditions, such as migratory birds, is a current reality. These factors suggest that the possibilities of introductions of new zoonoses into Japan are high, and are likely to occur through various routes of introduction.

National surveillance system: The National Epidemiological Surveillance of Infectious Diseases (NESID), in compliance with the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (the Infectious Diseases Control Law) enacted in April 1999, requires physicians to report 86 different infectious diseases, of which about 40% are zoonoses. By the amendment of the Infectious Diseases Control Law enacted in November 2003 (see IASR 25:1-4, 2004), leptospirosis, tularemia, lyssavirus infection, Nipah virus infection, monkeypox, avian influenza (AI) virus infection, and hepatitis E have been added as Category IV infectious diseases. Infectious diseases that require measures against animals and goods are classified as Category IV disease, particularly diseases that involve wildlife (including exotic pets and urban-type wild animals) as reservoir hosts or sources of infections. Infectious diseases related to livestock (livestock products) with high breeding densities are included among diseases that can cause large-scale outbreaks.

According to the Infectious Diseases Control Law, when there is suspicion that a person may have been infected by an animal, the prefectural governor or the national government has the authority to conduct active epidemiological investigations in order to determine the extent, trends, and cause of the infection.

Veterinarians who diagnose infected animals are required to report monkeys with Ebola hemorrhagic fever or Marburg disease, prairie dogs with plague, palm civet cats, Melogale and raccoon dogs with SARS, and since October 2004, monkeys with dysentery, birds with West Nile fever, and dogs with echinococcosis.

Restriction of animal import: Until now, measures have been taken to quarantine certain imported animals (monkeys, dogs, cats, foxes, raccoons, and skunks) and to prohibit other animals (some species of monkeys, prairie dogs, palm civet cats, Melogale, raccoon dogs, Mastomys, and bats).

However, no public health measures had been taken against the hundreds of thousands of other various vertebrate species imported every year, leaving importations of wild animals largely unchecked. Therefore, as countermeasures against the introduction of infectious diseases, importation of monkeys as pets has become prohibited since July 2005. Furthermore, from September 2005, animals allowed to be imported must be accompanied by a health certification issued by a government agency of the exporting country (see p. 196 of this issue). On the health certification, regardless of the purpose of importation, documentation is required verifying that rodents and their carcasses are free from infection with plague, rabies, monkey pox, hemorrhagic fever with renal syndrome, hantavirus pulmonary syndrome, tularemia, or leptospirosis, that lagomorphs are free of rabies or tularemia, that other terrestrial mammals are free from rabies, and that all species of birds are free of West Nile fever or AI virus infection.

NESID: Among cases of zoonoses shown in Table 1, newly assigned Category IV infectious diseases included leptospirosis (one case in 2003, 18 cases in 2004) and hepatitis E (30 cases in 2003, 36 cases in 2004), were reported. In particular, cases of hepatitis E infected after consuming raw liver of wild boars or raw meat of wild deer have been reported and continue to increase. Among pork liver sold commercially, hepatitis E virus genes have been detected, thereby requiring thorough cooking prior to consumption. No other new Category IV infectious diseases (tularemia, lyssavirus infection, Nipah virus infection, monkeypox, or AI virus infection) have been reported.

Of the infections which veterinarians are required to report after October 2004, 10 cases of shigellosis (in monkeys imported for research purposes) and 2 cases of echinococcosis (in dogs) have been reported.@Every year, 470-840 shigellosis cases are reported (Table 1), with most of them thought to have been infected from non-animal sources. In contrast, echinococcosis (Echinococcus multilocularis ) is prevalent in Hokkaido, with 10-25 new cases being reported annually since 2000. The infection rate in red foxes, the dead-end host of echinococcosis, is about 40% in Hokkaido. Beside countermeasures against this species of host animal, prevention of spread of echinococcosis to south of Honshu has become an important issue.

Conclusion: Zoonoses involve various animal reservoir hosts or sources of infection, such as wild animals, livestock, and pets (Table 1), as well as complex routes of transmission. In the future, surveillance systems that promote diagnostic pathogen surveillance of animals in Japan and abroad, together with prevention and outbreak control measures, need to be strengthened. Furthermore, based on outbreaks of threatening emerging zoonoses in Asian countries in recent years, efforts to control zoonoses from a global perspective will be necessary.

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