The Topic of This Month Vol.21 No.4(No.242)
The new Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (the new Infectious Diseases Control Law) was enacted in April 1999, and acute viral hepatitis was classified into category IV notifiable infectious diseases. (It was 1987 when the National Epidemiological Surveillance of Infectious Diseases recognized the disease in its targets; monthly incidents, therefore, were reported from over 500 sentinel hospitals by March of 1999.) Any diagnose of this disease must be reported to the nearby health center within a week by physicians in this country. The notification aims at keeping track of new infections of acute hepatitis; chronic cases, asymptomatic virus carriers, or acute aggravating cases of hepatitis B or C are not targeted. Cases of acute viral hepatitis reported during the 9 months period from enactment of the new Infectious Diseases Control Law through December 1999 totaled at 1,455, which included 713 cases of hepatitis A (49%), 497 cases of hepatitis B (34%), 138 cases of hepatitis C (9%), two cases of hepatitis E, 70 cases of others (5%), and 35 cases of unknown type (2%) (Fig. 1).
Hepatitis A: The etiological agent of hepatitis A is hepatitis A virus (HAV), a member of the Picornaviridae family. The illness is usually caused by peroral infection with HAV excreted in stools of patients. Chronic HAV infection has not been observed. Children often experience inapparent infection; adults are more liable to develop symptoms and occasionally take serious courses. In the surveillance made before enactment of the new Infectious Diseases Control Law, 353-1,881 cases were reported each year from sentinel hospitals. After reaching a peak in 1990, reports have been decreasing (see IASR, Vol. 18, No. 10, 1997).
Of the 713 cases reported during April-December 1999 under the new law, there were 456 (64%) male cases and 257 (36%) female cases. A greater part of male cases occurred in their 20s and 30s and that of female cases in their 30s and 40s (Fig. 2-a). Only 40 cases (6%) were presumably infected in foreign countries, 625 cases (88%) within the country, and other 48 cases (7%) unknown. Imported cases were infected mainly in India, China, or other Asian countries. Cases of domestic infection per 100,000 population by prefecture were the largest in number in Tokushima, followed by Yamanashi and Tokyo in this order. In Tokushima, clustering of hepatitis A cases was seen during November-December 1999. Comparatively a large number of reported cases occurred also in Kinki districts (Fig. 3). As a route of infection, consumption of raw oysters was ascribed in some cases but because of a long incubation period (4 weeks in average) and the difficulty to isolate HAV from environmental and food specimens, the source of infection has seldom been identified. As another route of infection, 15 male cases infected through homosexual contact have been reported.
Chances in Japan of infection have decreased due to development of clean water supply and sewage systems, and consequently antibody-negative population is increasing among those under 50 years old (see IASR, Vol. 18, No. 10, 1997). HAV is excreted into stools during the long incubation period and is relatively resistant to various environmental conditions (acids, detergents, heating, etc.). Once it enters vulnerable population (household members, welfare facilities, male homosexuals, etc.), infection tends to spread (see IASR, Vol. 18, No. 10, 1997 and Vol. 17, No. 3, 1996). Such incidents in which transmission from food handlers (a sushi bartender or a chef in a restaurant) to the customers continuing for several weeks were reported (see IASR, Vol. 15, No. 5, 1994 and Vol. 16, No. 10, 1995). PCR can amplify the genes in not only patients' stool specimens but also in serum specimens, and comparison of nucleotide sequence homology will provide useful information for identifying the source of infection (see p. 74 of this issue).
Prevention can be relied on administration of hepatitis A vaccine. In the USA, vaccination is recommended to not only those travelling to endemic areas but also to homosexuals, intravenous drug users, those who possibly have chances of occupational exposure, and some states have started to recommend regular vaccination of children (CDC, MMWR, 49, No. 2, 35, 2000). WHO has recently presented a guideline for hepatitis A vaccination (WHO, WER 75, No. 5, 38, 2000).
Hepatitis B: Hepatitis B virus (HBV) belongs to Hepadnaviridae and is transmitted through blood and sexual contact. After showing transient symptoms, the patients will recover by eliminating the virus. If infected from its HBe antigen-positive mother, a newborn baby will tend to become an asymptomatic carrier. Asymptomatic carriers may eventually develop cirrhosis and hepatocellular carcinoma when they are grown up. In Japan, "a project toward prevention of mother-to-child infection of hepatitis B" was started in 1985 (to infants born after 1986). Anti-HBs immunoglobulin and hepatitis B vaccine were administered to infants born of HBe antigen-positive mothers until 1995 and since then to those born of HBs antigen-positives, resulting in dramatic decrease in development of asypmptomatic carries through mother-to-child infection (see p. 74 of this issue).
The 497 cases reported during April-December 1999 included 325 males (65%) and 172 females (35%). Patients in their 20s accounted for the largest percentage in both sexes (Fig. 2-b). As the route of infection with HBV, sexual contact was reported in 213 cases accounting for 43%. Although few cases would take chronic courses in adults with normal immune functions, 1-2% of patients may take fulminant courses. It is necessary to reconsider the disease as a sexually transmitted disease and to emphasize the importance of education for prevention.
Hepatitis C: Develpment of reagents for detecting the antibody revealed that hepatitis C virus (HCV) is the principal cause of non-A, non-B hepatitis. Later, HCV was classified into Flaviviridae. The route of transmission is not yet fully understood, but HCV is regarded as transmitted through blood and other body fluid. The 138 cases reported during April-December 1999 included 72 males (52%) and 66 females (48%), and both sexes were of relatively advanced ages (Fig. 2-c). The criteria for notification complying with the new Infectious Diseases Control Law require reporting cases of primary infection of acute viral hepatitis, but unintentional confusion with chronic hepatitis and acute aggravating cases of asymptomatic carriers seems inevitable. Cases of infection through blood transfusion have decreased in number as have hepatitis B cases owing to the screening of donated blood, nevertheless five cases of accidental infection due to needlestick injuries have been reported.
Other kinds of hepatitis: Hepatitis D tends to cause aggravation of hepatitis B patients by co-infection or superinfection. Hepatitis E is often caused by waterborne infection. There were no reports of hepatitis D during April-December 1999, but two cases of hepatitis E infected presumably in China were reported. Seventy cases of hepatitis due to other viruses were reported including 41 cases infected with Epstein-Barr virus and 14 cases infected with cytomegalovirus.