By the 2003 amendment of the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (the Infectious Diseases Control Law), leptospirosis has been placed as a category IV notifiable infectious disease of the National Epidemiological Surveillance of Infectious Diseases (NESID). The physicians who have diagnosed leptospirosis must notify promptly the near-by health center (see the criteria for reporting; http://www.mhlw.go.jp/bunya/kenkou/kekkaku-kansenshou11/01-04-40.html).
Trend of notified cases: Since November 2003, a total of 93 cases including domestic and imported ones have been reported from 19 prefectures (as of December 10, 2007). Of 87 domestic cases, 40 (46%) were suspected to have been infected in Okinawa Prefecture (Fig. 1, Table 1). The suspected areas of infection of the other six imported cases are Borneo Island, Malaysia (three cases), Bali Island, Indonesia (one case), Thailand (one case), and Fiji (one case) (see Table 1 and p. 8 of this issue).
Cases occurred often during summer toward autumn; 76% of domestic cases (66 cases) were concentrated to three months from August through October (Fig. 2). Eighty-seven percent of all cases (81 cases) were males. The median age was 52 years (11-82 years); 21 cases (23%), the largest in number, were at the age of 50s followed by 30s and 60s, accounting for 15 cases (16%) and 14 cases (15%), respectively (Fig. 3). There were five cases of teenaged, all of which were infected in Okinawa Prefecture, and all but one case infected at unknown place were estimated to have been infected at rivers or water falls during summer season. Fatal cases were reported one each from Okinawa and Shizuoka Prefectures (see p. 10 & 13 of this issue).
Suspected cause of infection: Leptospira is carried most often by rodents and many other kinds of mammals, being harbored in the kidney and excreted in urine. Therefore, the infection sources of Leptospira are occupational or recreational exposure in environment contaminated with urine of carrier animals, and occupation having a chance of direct contact with urine or blood of infected animals. The estimated sources of infection of 93 notified cases were as follows, based upon the notified information of NESID and the information obtained by the Department of Bacteriology I, the National Institute of Infectious Diseases (NIID) when requesting directly by medical institutions (Table 1), (1) farm work (including work in highland); 31 cases from 10 prefectures, (2) leisure activities and labor at river; 23 cases (19 cases from four prefectures, one case in Kyushu district and three overseas cases), (3) contact with fresh water of other than river (labor); 16 cases (15 cases from six prefectures, and an imported case), (4) direct and indirect contacts with rodents (including incidents of witness of rats at houses or working places); 17 cases from six prefectures, (5) contact with animals of other than rats; four cases from three prefectures, (6) unknown; six cases. The contact with river water or fresh water other than rivers was suspected to be the source of infection (correspond to items 2 and 3 above), 70% or 56% of which were the cases occurring in Okinawa Prefecture. In Okinawa Prefecture, outbreaks due to leisure and labor at rivers or ponds have been reported (see p. 10 of this issue). Of four cases in which the source of infection was estimated to be contact with animals other than rats (item 5 above), two were professional animal importers infected from American flying squirrels imported from USA for pets in Shizuoka Prefecture in 2005 (IASR 26: 209-211, 2005). In one case in Ehime Prefecture in 2004 and two other cases in Miyazaki Prefecture in 2005, the infection might have occurred during the labor at rivers and agricultural labor after floods caused by typhoons.
Laboratory diagnosis and typing of Leptospira serovars (see p. 7 of this issue): Laboratory diagnosis of leptospirosis depends on isolation of leptospires, Leptospira gene detection by PCR, or serodiagnosis by microscopic agglutination test (MAT) (seroconversion or significant rise in agglutination titer between paired sera). Laboratory diagnoses of the 93 cases described above were accomplished by the following procedures: 60 cases were by MAT only, 16 cases by MAT+isolation, five cases were by MAT+PCR, two cases were by MAT+isolation+PCR, one case was by MAT+darkfield microscopic observation, six cases were by isolation only, one case was by PCR only, and two cases were by other serological tests (latex agglutination test and Dipstick test).
The serovars of the causative Leptospira estimated by MAT numbered 13; Australis, Autumnalis, Canicola, Copenhageni, Grippotyphosa, Hebdomadis, Icterohaemorrhagiae, Javanica, Kremastos, Poi, Pyrogenes, Rachmati and Sejroe. The serovars Grippotyphosa, Javanica and Pyrogenes were detected from only cases infected in Okinawa Prefecture (excluding cases of animal importers).
Treatment: For antibiotics for serious cases, penicillin has been indicated. For antibiotics for milder cases, amoxicillin, ampicillin, doxycycline and erythromycin have been indicated (WHO, Human leptospirosis: guidance for diagnosis, surveillance and control, 2003; http://www.who.int/csr/don/en/WHO_CDS_CSR_EPH_2002.23.pdf).
Notification based on the Domestic Animal Infectious Diseases Control Law: The incidence of leptospirosis among domestic animals during 2003-2006 involved 144 dogs in 25 prefectures in 2003, 158 in 30 prefectures in 2004, 71 in 13 prefectures in 2005, and 40 in 19 prefectures in 2006. Nine pigs were reported in Okinawa Prefecture in 2004 (http://niah.naro.affrc.go.jp/disease/fact/42.html).
Problems of leptospirosis: Although until the beginning of 1970s, 50 or more deaths used to be reported annually, however due to the recent conspicuous decrease in cases, leptospirosis is recognized as merely a past disease by many medical professionals. In areas where no human case has been reported, rats carrying leptospires and dogs infected with leptospires are found (see p. 5 of this issue), it is considered to be possible that infected cases are overlooked. In severe cases, such typical symptoms as jaundice, hemorrhage or renal failure may appear, so Weil's disease, a kind of leptospirosis, may be an object of differential diagnosis. In mild cases, however, only atypical clinical symptoms may appear and clinical diagnosis of leptospirosis is very difficult. Even if only nonspecific clinical symptoms have appeared, there have been instances of actual cases diagnosed from suspicion of leptospirosis by referring to history of contact with soil or water or overseas travel history (see p. 8 of this issue).
For diagnosis of leptospirosis, special culture media and serological methods are required, therefore at present, it is inevitable to depend on certain prefectural and municipal public health institutes (PHIs) or NIID for laboratory tests. To reveal epidemiology of leptospirosis in Japan, it is necessary to construct infrastructure for laboratory examination at various laboratories through development of simple and easy diagnostic tests.