Jpn. J. Infect. Dis., 52, 1999

Laboratory and Epidemiology Communications

Malaria Infections in Japan

Kenji Yagita and Takuro Endo*

Department of Parasitology, National Institute of Infectious Diseases, 
1-23-1 Toyama, Shinjuku-ku, Tokyo, Japan

Communicated by Hiroshi Yoshikura

(Accepted February 15, 1999)

     The western part of Japan, Okinawa in particular, was once heavily infested with malaria.
In 1925, as many as 90,000 indigenous malaria cases were reported, while by 1935 
the number of patients had decreased to 20,000. In 1962, the mosquito-borne infection of
malaria was considered eradicated, and malariasis was categorized as a national notifiable
disease whose report to local health authorities was obligated.
     The National Institute of Infectious Diseases (NIID) has been conducting confirmatory 
diagnoses of malariasis based on the examination of blood smear specimens sent from 
local health authorities. Up to the present, cases of malaria diagnosed in Japan were mostly
imported from regions abroad where mosquito-borne transmission was known to occur. 
One congenital infection and five infections resulting from exposure to infected blood have
been reported in Japan.
     Thirty to sixty specimens have been sent to NIID each year since 1982. About 70 percent
of the specimens were derived from those of Japanese nationality, and the rest from non-
Japanese. However, since 1995, the number of patients of Japanese nationality has tended
to increase (Fig. 1).
     As shown in Fig. 2, most cases were Plasmodium falciparum and P. vivax. Only on rare 
occasions were P. malariae and P. ovale detected. It was noted that incidences of 
P. falciparum whose infection often results in fulminant type have gradually increased
from 1994, though it was rather in the minority until 1992. It is not known whether or not 
this tendency reflects the current status of global malaria infection.
     On our confirmation examination, the diagnoses made by local laboratories were found
to be very accurate; only a few misdiagnoses were found. However, the specimens were
sent to NIID only when the specimens were found positive for the protozoa. In addition,
the institutions which sent the specimens to NIID were restricted to a limited number of
hospitals and laboratories. Therefore, the data shown in Figs. 1 and 2 give only a partial 
indication of the range of plasmodium infection in Japan. Further strengthning of the
surveillance activity on malariasis is needed.

REFERENCE
1.  Warrell, D.A., Molyneux, M.E. and Beales, P.F. (1990) : Severe and complicated Malaria
     (2nd Ed.) WHO Division of Control of Tropical Diseases, Trans. Roy. Soc. Trop. Med. 
     Hyg. 84, Suppl. 2, 1-65.

*Corresponding author: E-mail: tendo@nih.go.jp, Fax: +81-3-5285-1173

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