In mid 60s, syphilis recurred in many countries including Japan. In USA, epidemics occurred with a peak in 1990; followed by decrease in number of reports (CDC, MMWR, Vol. 50, No. 7, 2001). In UK, patients increased in number in London and Greater Manchester in 1999 and surveillance for infectious syphilis was enhanced from January 2001 (CDSC, CDR, Vol. 12, No. 5, 2002).
Etiological agent and modes of transmission: The etiological agent, Treponema pallidum (Tp) of Spirochaetaceae , is a bacterium in a form of spiral coil of 6-14 rotations with a diameter of 0.1-0.2 ƒÊm and a length of 6-20 ƒÊm. Isolation of Tp on a culture medium has not been succeeded. The bacterium can not be observed under an ordinary light microscope, but were observed under a dark-field microscope or with a Parker-ink stained preparation. Complete genome sequence of Tp was determined in 1998 (Science 281: 375-388, 1998). No penicillin-resistant strain of Tp has emerged so far. The serological test for syphilis comprises two methods; one uses the treponema antigen and the other the lipid antigen (cardiolipin) (see p. 87-89 of this issue).
Infection occurs by Tp penetration of mucous membranes or entering through a break in the epidermis principally by risky sexual contacts or mockeries. Infected persons possess Tp in their blood and also in the tissue fluid or exudate of the lesions of the skin and mucous membrane (including insensible intrarectal, perianal, and oral lesions) in an early stage. They serve as sources of infection. Tp is easily killed outside of a living body. Although indirect contact with Tp in daily life may not cause infection, medical staffs must be careful not to contact directly with any source of infection containing a large amount of Tp, particularly to accidental needle-stick injury. Infection through blood transfusion has never been reported since all donated blood is subjected to screening tests. Nevertheless, infection seems possible by emergency transfusion with fresh blood of antibody-negative asymptomatic carriers during their incubation period. In addition, mother-to-child transmission may occur from a pregnant syphilitic woman to her fetus, causing abortion, stillbirth, or congenital syphilis. Since a large number of Tp are present in placenta, umbilical cord, amnion fluid, and fetal nasal fluid in congenital syphilis, they must be disposed with great care. Transmission in the birth canal during delivery is also possible.
Case notification: In Japan, notification of syphilis cases began in 1950 under the Venereal Disease Prevention Law and increased during 1981-1987. The subsequent decrease is regarded as the influence of the "AIDS panic" in 1987, when the first female AIDS patient was reported (Fig. 1).
Syphilis has been placed under the category IV notifiable infectious diseases under the National Epidemiological Surveillance of Infectious Diseases since April 1999. The physician who has diagnosed a syphilis case must notify it to the nearby health center within 7 days. The disease is classified into four types depending on the stage; early symptomatic (primary and secondary syphilis), late symptomatic, asymptomatic and congenital syphilis (see p. 87 and p. 92 of this issue). During April-December 1999, 735 cases, during January-December 2000, 769 cases (0.61 cases per 100,000 population), and during January-December 2001, 581 cases (0.46 cases per 100,000 population) were reported, totaling at 2,085 cases. Of these cases, 754 were early symptomatic (342 primary and 412 secondary), 131 late symptomatic, 1,177 asymptomatic, and 23 congenital syphilis cases. Male cases numbered at 1,385 and female ones at 700; male cases exceeded female ones in early and late symptomatic syphilis (Fig. 2). Cases reported in Osaka, Tokyo, Fukuoka, and Hyogo prefectures accounted for 47% of all cases; early symptomatic cases were outstanding also in Osaka and Tokyo prefectures (Table 1). The ages of the cases were widely spread; there were many young adult cases of early symptomatic syphilis, with a peak at 25-29 years (Fig. 3). Many asymptomatic cases may have been found by syphilis testing at examinations for other STIs, blood donation, health check-up for the pregnant women, examinations before surgical operation, etc. Of 5,774,269 instances of blood donation during January-December 2001, there were 11,309 antibody positives (about 0.2%) by the Tp particle agglutination test (Japanese Red Cross Society). There were particularly a large number of asymptomatic cases among the aged persons due to the finding in the tests at the time of entering the facilities for the aged.
Prevention and control: For prevention, it is important to avoid risky sexual contact. The use of a condom is highly effective. It has been pointed out, however, that its use is limited among youths (the Study Group on Socio-epidemiology of HIV infection by the Ministry of Health and Welfare (MHW), 1999, see IASR Vol. 21, No. 7, 2000) and we must direct our attention to infected person's future increase. Since contraceptive pills can not prevent STIs, it is necessary to educate young people that they must use the condom consistently as a powerful tool for prevention of STIs. Since congenital syphilis increases by infection of Tp to fetus later than formation of placenta in the 16th weeks of gestation, it is important to instruct females before pregnancy to receive the syphilis testing in an early stage of the pregnancy to be able to prevent congenital syphilis. Physicians must educate patients to help recognize the facts that syphilis, like chancroid and herpes simplex, causes genital ulcer disease (GUD), increases the risk of HIV infection or other STIs, may sometimes be worsened when complicated with HIV infection (see p. 91 of this issue), and is transmissible by both oral and anal sex, and that syphilis-antibody positives might be infected again.
At most medical institutions, screening tests for hepatitis B and C virus infections and syphilis of patients are routinely performed in advance as preventive measures for infection by occupational exposure to blood such as the surgical operation.
Subjects of discussion: Reports of syphilis cases (897) from sentinel clinics for STIs (about 600 medical institutions) in 1998 outnumbered the notified syphilis cases (553) in the same year under the Venereal Disease Prevention Law. According to the report by the Study Group on Basic Trial of Sentinel Surveillance for STIs in Japan by MHW, the annual incidence in 1998 in seven prefectures (Hokkaido, Iwate, Ibaraki, Aichi, Hyogo, Hiroshima, and Fukuoka prefectures) was estimated at 3.6 cases per 100,000 population. The number of cases after enactment of the Infectious Diseases Control Law has considerably been underreported, presumably hiding a considerable number of cases (see p. 89 of this issue). To grasp the trend of incidence to serve as the basic data for infectious disease control, it is necessary to enlighten physicians on the notification of all cases.
A basis of confirmatory diagnosis is the detection of the etiological agent, nevertheless Tp can be detected microscopically from lesions only for a short period of time and diagnosis of syphilis must often depend on the clinical findings and syphilis antibody testing (see p. 87-88 of this issue). Tp detection becomes difficult soon after the start of chemotherapy, which deprives of the infectivity of Tp. Judgment of recovery takes a long time because it is necessary to see the fall of the antibody titer. It is desired to develop a laboratory method to find whether the antibody positives keep the infectivity, possessing the pathogenic microbes or have been cured loosing the infectivity.