Recent State of Parasitoses in Japan —Epidemiology for Clinicians—
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Ⅵ Parasitoses Recent State of Parasitoses in Japan —Epidemiology for clinicians— JMAJ 48(3): 148–154, 2005 Yoshiya SATO Professor, University of the Ryukyus Abstract: The recent profile of parasitic diseases in Japan has changed dramati- cally from public health problems with high community prevalence of classic soil-transmitted parasitoses (ascariasis, hookworm disease, etc) to epidemics of various new types of parasitoses (larva migrans, zoonotic parasitoses, imported parasitoses, opportunistic parasitoses, etc). Against this background of change are factors such as the diversification of lifestyles and dietary habits, recent changes in values including the return-to-nature movement and the pet boom, the global- ization of parasitoses due to the development of transportation, and the increase in compromised hosts reflecting the rapid increase in the number of aged citizens. These new types of parasitoses are generally characterized by fragile host-parasite relationships, and disruption of these relationships tends to cause the serious manifestation of parasitoses. They also frequently present difficulties in diagnosis and treatment. As a result, we need to shift emphasis from the public health aspects of these diseases that require conventional mass control to respective clinical interventions requiring individualized care for diversified pathogeneses. Key words: Parasitoses; Host-parasite relationship; Parasitic zoonosis; Imported parasitoses Introduction hookworms, and whipworms. It was taken for granted that almost everyone in Japan at that Japan was once called a “paradise for para- time had a roundworm infection. Subsequently, sites” because it was an agricultural country, parasite control associations were organized and the people ate raw foods. In particular, nation-wide, and their efforts dramatically re- the shortage of food directly following World duced these soil-transmitted parasitoses by the War II encouraged the consumption of home latter half of the 1960s. While parasitoses have grown vegetables cultivated using human ex- been a problem in the past for over 30 years, creta, and this resulted in the wide spread of they are now reemerging as a new medical soil-transmitted parasites including roundworms, problem. This article is a revised English version of a paper originally published in the Journal of the Japan Medical Association (Vol. 131, No. 11, 2004, pages 1715–1720). 148 JMAJ, March 2005—Vol. 48, No. 3 RECENT PARASITOSES IN JAPAN even utilize them for their own survival. In the Host specificity (Host spectrum) case of schistosomiasis, for instance, infection Virulence induces strong immune responses in the host to Facultative prevent re-infection. The worms that invaded Adaptive parasitism evolution during initial infection, however, are not elimi- as parasites Host dependence nated by the immune responses elicited, and Obligate parasitism the defense system only prevents subsequent re-infection that may otherwise increase the AdvAdvancedanced host-parasitehost-parasite interactionsinteractions worm burden. Consequently, the defense sys- tem ensures that the host does not suffer heavy Fig. 1 Adaptive evolution of host-parasite interactions infection and may be profitable for the survival and virulence of worms of the initial infection for a period of several years. Similarly, in the case of toxo- plasmosis, the protozoa evade the host’s de- fense responses by forming cysts and fall into a This article introduces the recent state of dormant state. This mechanism is believed to parasitoses in Japan, focusing on new problems prevent the uncontrolled proliferation of the associated with them. parasite and protects host from fatal infection. A similar mechanism is also assumed in Parasites and Parasitism Trichinella infection, in which adult parasites are rapidly eliminated from the digestive tract In considering new problems of recent para- by host immune mechanisms. The early expul- sitoses in Japan, we first need a basic under- sion of adult worms reduces the output of standing of parasitism and the resulting viru- larvae parasitizing in muscle tissues. lence. Parasites are defined as animals that These observations suggest that host-parasite dwell in other animals (hosts), causing them relationships are maintained over a long period harm. At the same time, parasites cannot under a delicate balance in the presence of the survive without hosts. Interaction between the host’s immune responses. The problems we are parasite and the host (host-parasite relation- facing now are the emergence of new types of ship) has been established in the long process parasitoses (e.g. larval migrans) with poorly of evolution. If a certain type of parasite exerts established host-parasite interaction that are very strong pathogenicity in the host, such a strongly affected by host factors, as is the case host-parasite relationship is eliminated by natu- with opportunistic parasitoses. ral selection in the process of evolution. There- fore, well-established host-parasite relation- Recent Trends in Parasitoses in Japan ships tend to be characterized by relatively low pathogenicity, high host specificity, and strong As mentioned above, soil-transmitted para- host dependency, as shown in Fig. 1. sitoses including ascariasis and hookworm dis- On the other hand, parasitism elicits strong ease comprised the large majority of parasitoses defense responses of host against parasites. in Japan in the past. Because these classic par- However, defense responses, such as inflamma- asitoses generally reveal weak pathogenicity tion and other immune responses, are generally and high host specificity, epidemics were quickly weak in host-parasite relationships that are brought under control through changes in well established through the process of evolu- farming practices and lifestyle, as well as tion. On the other hand, it is believed that some thoroughgoing mass screening and the mass parasites evolve to evade these responses and treatment of infected patients. The only epi- JMAJ, March 2005—Vol. 48, No. 3 149 Y. SATO Table 1 Parasites from Humans Reported in Okinawa (1981-2003) Cases of Imported cases domestic origin Japanese Foreigners Protozoa Plasmodium vivax ࠗࠗ Plasmodium falciparum ࠗࠗ Entamoeba histolytica ࠗࠗࠗ Entamoeba coli ࠗ⅙ ࠗ⅙ Endolimax nana ࠗ⅙ ࠗ⅙ Giardia lamblia ࠗ⅙ ࠗ⅙ Toxoplasma gondii ࠗ Trichomonas vaginalis ࠗ Isospora belli ࠗ Acanthamoeba sp. ࠗ Cryptosporidium parvum ࠗ Flukes Schistosoma japonicum ࠗ Schistosoma mansoni ࠗ Schistosoma haematobium ࠗ Clonorchis sinensis ࠗ Opisthorchis viverrini ࠗ Fasciolopsis buski ࠗ Metagonimus yokogawai ࠗ Heterophyes heterophyes nocens ࠗ Dicrocoelium dendriticum ࠗ Flatworms Diphyllobothrium nihonkaiense ࠗ⅙ Diphyllobothrium yonagoense ࠗ Diplogonoporus grandis ࠗ Sparganum mansoni ࠗ Taenia saginata ࠗࠗࠗ Taenia solium ࠗ Cysticercus cellulosae ࠗ⅙ Hymenolepis nana ࠗࠗ Raillietina celebensis ࠗ Dipylidium caninum ࠗ Nematodes Ascaris lumbricoides ࠗࠗ⅙ Anisakis sp. ࠗ⅙ Enterobius vermicularis ࠗ⅙ ࠗ Ancylostoma duodenale ࠗ⅙ Necator americanus ࠗࠗ⅙ Trichostrongylus colubriformis ࠗ Trichuris trichiura ࠗࠗ⅙ Strongyloides stercoralis ࠗ⅙ ࠗ⅙ Rhabditis hominis ࠗ⅙ Capillaria hepatica ࠗ Angiostrongylus cantonensis ࠗ⅙ Wuchereria bancrofti ࠗ Dirofilaria immitis ࠗ Dirofilaria repens ࠗ Loa loa ࠗ (ࠗϽ10 cases, ࠗ ˘10 cases) 150 JMAJ, March 2005—Vol. 48, No. 3 RECENT PARASITOSES IN JAPAN Table 2 Types of Parasitoses and Number of Case Reports Presented at the Meetings of the Japanese Society of Clinical Parasitology Since 1990 Parasitosis No. of reports Parasitosis No. of reports Protozoan disease Teniasis (tapeworm infection) Malaria 39 Diphyllobothriasis 16 Amebiasis 33 Sparganosis mansoni 12 Cryptosporidiosis 8 Hydatidosis 10 Giardiasis 7 Diplogonoporus grandis infection 9 Isosporiasis 6 Cysticercosis cellulosae 6 Toxoplasmosis 5 Taeniasis saginata 5 Cyclospora infection 4 Dipylidium caninum infection 3 Acanthamebiasis 3 Nematodiasis (nematode infection) Leishmaniasis 2 Anisakiasis 49 Chagas disease 1 Trichomoniasis 1 Acariasis 30 Dirofilaria immitis infection 16 Trematodiasis (fluke infection) Gnathostomiasis 10 Schistosomiasis 36 Angiostrongyliasis 4 Lung fluke disease 23 Toxocariasis 8 Clonorchiasis 6 Spiruroid infection 7 Fascioliasis 5 Thelazia callipaeda infection 4 Metagonimiasis 3 Trichuriasis 4 Opisthorchis viverrini infection 1 Hookworm disease 2 Heterophyiasis 1 Pinworm infection 4 Lancet fluke infection 1 Other 4 Each figure represents the number of reports rather than the number of cases reported. Cases of parasitoses discussed in the evaluation of diagnostic methods and treatment efficacy are not included. demics of classic parasitoses remaining today types of parasitoses. Globalization and the de- are echinococcosis (alveolar hydatid disease) velopment of transportation allow unfamiliar in Hokkaido, strongyloidiasis in the South- parasitoses to move rapidly across the world. western Islands, Okinawa and Amami, and In addition, medical and social factors, such as pinworm infection among school children in the increase in the number of AIDS patients, urban areas of Japan. the popularization of immunosuppressive ther- Pinworm is normally non-pathogenic and apy and the aging of the population, are dis- does not cause major clinical problems. On the rupting delicately balanced host-parasite rela- other hand, Echinococcus (hydatid) is strongly tionships, resulting in manifestations of dis- pathogenic because the human being is an eases not seen before. Because these new types accidental intermediate host, in which serious of parasitoses