The Topic of This Month Vol.18 No.11(No.213)

Malaria in Japan

Malaria is a disease from which presumably 300 to 500 million people suffer and 1.5 to 2.7 million people die every year in the world (see p. 272 of this issue). Four species of parasites, Plasmodium vivax, P.malariae, P.falciparum and P.ovale, are known as the etiological agents of human malaria and the diseases evoked by these agents are called vivax malaria, quartan malaria, falciparum malaria, and ovale malaria, respectively. Although these four diseases differ from one to another in the clinical picture, they can be divided largely into two groups; one that takes serious courses being fatal if no prompt adequate treatment is given in an early stage, viz.falciparum malaria, and the other that takes relatively mild courses, viz.the other three malarias. The former is called malignant malaria and the latter benign malaria. Malaria is distributed mainly in the tropics and subtropics, and the malaria-endemic areas are rather expanding in some parts of the world. These four malarias are transmitted by infective female anopheline mosquitoes. In this topic, imported malaria cases and cases of domestic infection, very few though, will be overviewed.

Imported malaria means that infection occurs overseas and symptoms develop within the country. In this country, however, mainly vivax malaria used to prevail as an indigenous malaria; in addition, epidemics of falciparum malaria have occurred in certain areas on the Southwest Islands. In Fig.1, shown are the trends of malaria patients based on the Statistics of Communicable Diseases in Japan from the Ministry of Health and Welfare. It is estimated that there were 20,000 cases of indigenous malaria per annum before the World War II. Malaria patients numbered nearly 30,000 in 1946, as a large number of people who had acquired infection overseas during the war time were repatriated. Fortunately no further malaria epidemics occurred within the country and the number of patients soon decreased rapidly until indigenous malaria became extinct in 1960 or so. Therefore, cases arising after that time are regarded as of imported malaria, although a few cases of domestic infection due to some exceptional modes of transmission occurred as described below. In fact, histories of traveling to or staying in malaria-endemic areas are recognized among the malaria patients found recently.

The trends of malaria patients in the last decade based on the investigation by the Research Group on Chemotherapy of Tropical Diseases are shown in Table 1. For the past few years, about 120 patients have been confirmed annually. The cases notified to the Ministry of Health and Welfare are about half of them. Some of falciparum malaria patients were unfortunately fatal. Vivax malaria patients numbered the largest accounting for about 50% of all patients, followed by falciparum malaria accounting for 30 to 40%. It is noticeable that falciparum malaria patients, that are liable to take serious courses, are tending to increase in number. Japanese people traveling to malaria-endemic areas are apparently increasing year by year, and a large number of foreigners enter this country from malaria-endemic areas. Therefore, it is difficult to predict the future trend of malaria patients. The estimated places of acquiring infection for these patients are shown in Table 2.

The recent cases of domestic infection are shown in Table 3. There have been cases infected presumably by transfusion or accidental pricking with a needle, and moreover a case of so-called 'airport malaria, 'which affected an aged woman living near an airport. 'Airport malaria' means such malaria that infects people living near airports by infectious mosquitoes transported very rapidly by aircraft from a malaria-endemic country to a non-endemic country. In European countries, Canada and the United States of America, similar cases have occasionally been reported (see IASR, Vol. 18, No. 3).

Since medical experts who have clinically experienced malaria are very few in Japan, cases taking more serious courses due to delayed diagnosis and treatment have been seen. It is important to examine febrile illness of returnees always taking malaria into consideration as a target disease of differential diagnosis. Some patients show unusually long incubation periods. Patients sometimes see doctors at clinical institutions for common cold-like symptoms such as headache, muscle pain and malaise without such high fever that is characteristic of malaria. The prognosis of the patients will be worsened depending largely on delayed diagnosis or treatment especially in falciparum malaria, so early diagnosis and treatment are musts. If malaria is ever suspected, it will be essential to make Giemsa's staining of the blood film to confirm microscopically the malaria parasites within the red blood cells. The most scrupulous attention must be paid to the handling of the blood specimen in case that infection of other diseases occurs from blood. Although this is a very good method being the easiest to perform and allowing rapid diagnosis, it is a disadvantage to require a certain experience as it is based on morphological diagnosis. If there is any difficulty in identification of a malaria parasite, it will be necessary to ask a nearby expert of infectious or parasitic diseases for his or her advice. Tropical febrile diseases include many kinds of highly contagious bacterial and viral infections that would take serious courses, so even after denial of malaria, other infectious diseases such as typhoid fever, dengue fever, yellow fever, viral hemorrhagic fever, etc. will have to be differentiated.

Only two antimalarial drugs, sulfadoxine/pyrimethamine and quinine are being approved in this country. Other antimalarial drugs can be obtained as medicines under clinical trial from the above-mentioned Research Group on Chemotherapy of Tropical Disease (see p. 263 of this issue). Some malaria parasites are drug resistant, so ups and downs of parasitemia must be pursued very carefully during treating the patient.

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