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The topic of This Month Vol.37 No.6(No.436)

Leptospirosis in Japan, January 2007-April 2016

(IASR 37: 103-104, June 2016)

Leptospirosis is a zoonotic infectious disease caused by Leptospira spp. (IASR 29: 5-7, 2008).  The bacteria colonize the renal tubules of rodents and other mammals and are excreted in urine.  Humans are infected by the bacteria through direct contact with the urine of the carrier animal or indirectly through contact with contaminated water and/or soil; occasionally, infection may occur through ingestion of contaminated food and/or water.

Leptospirosis is an acute febrile disease. The incubation period is 3-14 days and the disease onset is sudden with chills and fever. The clinical spectrum is broad, ranging from mild flu-like symptoms to severe disease (Weil’s disease), including jaundice, hemorrhage, and renal failure.

National Epidemiological Surveillance of Infectious Diseases (NESID)

Leptospirosis is a category IV infectious disease that requires immediate notification of all the diagnosed cases under the Infectious Diseases Control Law, amended in November 2003 (see http://www.niid.go.jp/niid/images/iasr/37/436/de4361.pdf for notification criteria).

Notified cases and suspected place of infection: From January 2007 to April 30, 2016, a total of 284 cases were reported from thirty prefectures, among which 258 (91%) cases were domestic cases (as of April 30, 2016, Table 1 in p. 105 of this issue). Annually, there were 15-42 domestic cases reported. There were 25 prefectures that were suspected to be the place of infection; Okinawa was suspected for 142 (55%) cases and Tokyo for 27 (10%) cases (Fig. 1). There were 26 (9%) cases infected abroad, with at least one such case being reported every year (Table 1 in p. 105 of this issue). The suspected places of infection were mostly Southeast Asian countries: 4 cases each from Indonesia (2 cases from Bali Island), Thailand, and Malaysia (3 cases from Borneo Island); 3 cases from Palau; 2 cases each from Vietnam and Laos; and one case each from Cambodia, Panama, Fiji, and the Philippines; there were 3 cases with visit to multiple countries. As Fig. 2 shows, incidence (by month of onset) was highest during summer to autumn; for domestic cases, incidence peaked in September (36% of cases), and 77% of cases occurred during July-October (IASR 29: 1-2, 2008).

Sex and age distribution of cases: Among 284 patients, 87% were male, and 13% female (Fig. 3). Higher incidence (>90%) among males has also been reported from overseas (see p. 110 of this issue). The median age was 44.5 years (range: 8-84 years). There were 6 fatal cases (5 males and 1 female) at the time of report.

Suspected source of infection: Leptospirosis is acquired through direct contact with animal urine or blood or from exposure to an environmental source contaminated by urine of carrier animals. According to the reported NESID data, both for infections in Japan and abroad, most infections were linked to activities (occupational or recrea-tional) related to rivers (47% of domestic cases and 81% of imported cases) (Table 2). As for the infection source, 51 domestic cases were suspected to be contact with rats/mice or their urine and 34 cases to farming-related activities.

There was also a large scale leptospirosis outbreak at a US Military basecamp in Okinawa in 2014 (not included in the NESID data) (see p. 106 of this issue). Countries in the tropics such as the Philippines often experience large scale leptospirosis outbreaks after flooding caused by typhoons or heavy rain (see p. 110 of this issue). Reports of leptospirosis after a typhoon or heavy rain has also been reported in Japan (IASR 32: 368-369, 2011; 33: 14-15, 2012; & 35: 16, 2014).

Signs and symptoms: Among the 284 cases reported to NESID, the frequency of the signs/symptoms were: fever 97%, conjunctival suffusion 60%, myalgia 59%, proteinuria 51%, renal failure 48%, jaundice 45%, and hemorrhage 13%. Other signs/symptoms included respiratory failure, shock syndrome (6 cases each) and DIC (3 cases).

Laboratory diagnosis and serogroups: Laboratory diagnoses of the 284 cases reported were as follows: antibody detection by microscopic agglutination test (MAT) (169 cases, 60%); detection of Leptospira DNA by PCR (118 cases, 42%) from blood (88 cases), urine (48 cases) and/or cerebrospinal fluid (3 cases); isolation of the bacteria (65 cases, 23%) from blood (62 cases), urine (6 cases) and/or other sources (2 cases); and/or other methods (3 cases, 1%) (see http://www.niid.go.jp/niid/images/lab-manual/leptospirosis.ver2015-2-2.pdf ;“Laboratory testing manual for leptospirosis”).

Fifteen serovars from 11 serogroups have been reported in Japan. Identification of serogroups is possible by serotyping the isolates using reference antisera or by the detection of serogroup-specific antibody using MAT. Through such methods, ten serogroups were detected during the period: the predominant serogroup was Hebdomadis (28%, 71/258), followed by Autumnalis (11%, 28/258) and Icterohaemorrhagiae (6%, 15/258). Serogroups Pyrogenes (3%, 7/258) and Ballum (1%, 3/258) were detected only in Okinawa (Table 3).

Notification based on the Domestic Animal Infectious Diseases Control Law

Leptospirosis in domestic animals is notifiable under the Domestic Animal Infectious Diseases Control Law. During 2007-2015, there were 20-52 infected dogs per year, 3 infected cattle (2 in 2007 and 1 in 2014), and 8 infected pigs (6 in 2007 and 2 in 2011) (http://www.maff.go.jp/j/syouan/douei/kansi_densen/kansi_densen.html). As the reporting is limited to certain serovars, however, the reported number of leptospirosis in domestic animals may be underestimates (see p.111 of this issue).

Treatment, prevention and measures to be taken

For milder cases, the first choice for treatment is doxycycline, but for severe cases, penicillin is recommended. As intravenous administration may cause Jarisch-Herxheimer reaction, careful monitoring of the patient is necessary. For prevention, minimizing the chance of contact with the infection source (e.g. blood or urine of the infected animal, contaminated water or soil) is recommended. Although several countries produce leptospirosis vaccines for human use, the effectiveness of the vaccine is serovar-specific. The chemoprophylactic use of doxycycline has been reported.

Further remarks

Most leptospirosis infections are asymptomatic or mild. Clinical diagnosis of such cases is generally difficult, and may be missed outside of endemic areas such as Okinawa (see p. 105 of this issue; IASR 35: 14-15, 2014 & 35: 216-217, 2014). In addition, differential diagnosis from dengue fever or malaria is necessary given similar clinical pictures (see p. 109 of this issue, IASR 34: 111-112, 2013). Inquiring about the patients’ occupation or travel or contact history with potentially contaminated soil or water is thus important and may assist with diagnosis (see p. 107 of this issue).

Laboratory diagnosis of leptospirosis requires special media for pathogen isolation and special methods for sero-diagnosis. The Department of Bacteriology I of the National Institute of Infectious Diseases, along with several prefectural and municipal public health institutes, can perform laboratory diagnosis upon request.

Copyright 1998 National Institute of Infectious Diseases, Japan

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