The Topic of This Month Vol. 32, No. 8 (No. 378)
National Epidemiological Surveillance of Infectious Diseases (NESID): Lyme disease is Category IV infectious disease under the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (Infectious Diseases Control Law). Doctors who diagnosed the disease are obliged to notify. For the notification, required is either isolation/identification of the pathogen, detection of the pathogenfs genome, or detection of the antibody to bacterial antigen by the Western blot (http://www.mhlw.go.jp/bunya/kenkou/kekkaku-kansenshou11/01-04-35.html). While notifiable initially, in April 2006 when the notification criteria were amended, EIA antibody test positives were excluded from the notification on account of false-positives, and cases positive for the confirmatory Western blot antibody test were included in the notification. After the amendment in April 2011, cases positive for the bacterial genome in the PCR assay are also included in the notification.
Since April 1999 when the Infectious Diseases Control Law entered in force, 124 cases were reported till December 2010 under NESID (Table 1). Since April 2006 when the notification criteria were amended, 49 cases were reported till December 2010. Among the 49 cases, 41 cases (male 25 cases and female 16 cases) were domestic cases (Fig. 1) and 21 (51%) of them were those older than 60 years. The number of reported cases is highest in July and almost absent in winter seasons (from December to March of the next year) (Fig. 2). Among domestic cases, 19 were suspected to have acquired infection in Hokkaido, followed by infection in Nagano (5 cases) and in Kanagawa, Niigata, Gifu and Fukuoka (2 cases each) (Fig. 3). There were 8 cases infected abroad, such as in the United States (4 cases), Germany (3 cases) and Switzerland (1 case). The clinical symptoms were erythema migrans (30 cases, 73%) followed by myalgia (29%), arthritis/arthralgia (27%), fever (24%) and neural symptoms (22%), such as radiculitis and facial palsy. The Lyme incidence rate per 100,000 population is 0.008 in Japan. Among prefectures, the rate is highest in Hokkaido (0.069).
Route of Infection: Ticks inhabiting hills and fields transmit the Lyme disease-causing Borrelia (see p. 226 of this issue). Ixodes scapularis is the vector in the North America and I. ricinus in Europe. In Asia and Russia, I. persulcatus is considered to be the vector. Actually, the responsible pathogen B. garinii was detected in I. persulcatus captured in Japan (see p. 224 of this issue). The house dust mite does not transmit the disease. No human-to-human infection is known.
In Japan, the vector tick is found in the mountainous area of the northern part of the mainland Honshu and Hokkaido. In Hokkaido, it is found even in flatlands. Actually in Japan, the Lyme disease cases have been reported from these areas since it was first confirmed in 1986 (see p. 218 of this issue). The carrier rate of the tick is geographically variable and is in the range of 6.7-22%. Similar level of carrier rate was reported from Europe and Russia where B. garinii is endemic as in Japan.
Diagnosis: Diagnosis should take into account epidemiological background, clinical pictures and laboratory data. Epidemiological consideration should include the place of residence (whether the Lyme disease endemic area or not), the history of travel to the endemic area and the tick bite history. Clinically important sign is erythema migrans (see p. 219 of this issue). However, even for erythema migrans-negative cases, if there is a possibility of Lyme disease based on the epidemiological background or other clinical symptoms (see p. 218 of this issue), laboratory diagnosis, such as pathogen isolation/detection or antibody detection, should be conducted. Though rare, a case associated with acute hepatitis has been reported (see p. 221 of this issue).
Laboratory Diagnosis: For antibody test, selection of antigen is important, because both domestic and oversea infection cases are seen in Japan. The antigen should be identical to that of Borrelia that caused the disease. For selection of antigens, information on the probable geographical site of infection is useful. In acute phase of Lyme disease, antibody test often gives negative results, and very often the antibody level remains low during 2-3 weeks post-infection. Antibody test using paired sera is required for obtaining meaningful results.
Laboratory diagnosis includes isolation of the pathogen and/or detection of genome DNA from skin specimens of the affected part or cerebrospinal fluid. The Department of Bacteriology I in National Institute of Infectious Diseases conducts the laboratory examination and provides the reagents for testing on request (see p. 223 of this issue).
Therapy: Lyme disease is generally treated with antibiotics, such as, penicillin, amoxicillin, ceftriaxone, minocycline, doxycycline and tetracycline. In case of neurologic involvement, ceftriaxone that easily enters the cerebrospinal fluid is the first choice. For infant cases amoxicillin is often used. Up to now no drug-resistant strains have been reported.
Global Situation: In Europe and North America, tens of thousands of Lyme disease cases are reported annually, and the number is on the rise. Lyme disease is becoming an object of public concern in some countries. In Delaware, Connecticut and other east-northern part of the United States, the incidence rate per 100,000 population is 50-100. In Austria, Slovenia and other nearby countries in Europe the rate is over 25 (see p. 222 of this issue). In Africa and South America, the existence of Lyme disease is suspected but it is not confirmed because pathogen isolation is not conducted in these regions.
For the time being, travelers should pay special attention concerning Lyme disease in Europe and the North America where infections of Japanese travelers have been reported.
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