Natural Japanese encephalitis virus infection among humans in west and east Japan shows the need to continue a vaccination program

Follow-Up Survey of Japanese Encephalitis Virus Infection in Kumamoto Prefecture, South-West Japan: Status during 2009^|^ndash;2011

“…Significant differences were not observed among the male and female subjects in each age group as well as in the overall prevalence in each year. Antibody prevalence increased with age; this was consistent with previous findings (9). Among the total population (2009-2011), the À60 age group showed significantly higher prevalence than other age groups (P º 0.001), and the 50s age group showed significantly higher prevalence than the 10s age group ( P º 0.01).…”

“…The mean annual infection rate estimated from NS1 antibody prevalence in 2009-2011 was 2.2z in male subjects, 1.7z in female subjects, and 1.9z in the total population (Fig. 1B), which was similar to the 2004-2008 results of 1.9z in male subjects, 1.7z in female subjects, and 1.8z in the total population (9). Although the time-related mean annual infection rate during the 2004-2011 period fluctuated, and significant differences were found for some of these years, the rates in 2004-2011 were considered to be approximately 2z, based on the duration of NS1 antibodies (4.2 years).…”

“…Of these, 8 (7.8z) were positive for neutralizing antibodies, indicating natural infection with JEV. Since the average survival period of these subjects was 3.4 years, the annual infection rate was calculated to be 2.3z (2.1z for male subjects and 2.4z for female subjects), which was similar to the 2.6z results obtained in 2004-2008 (2.4z for male subjects and 2.9z for female subjects) (9).…”

“…With the exception of the non-endemic northern areas, annual infection rates in humans ranged from 3 to 17z before 1960, 5 to 10z in the early 1980s and mid-1990s, and 0.2 to 3.4z between 2001 and 2004 (8). We previously reported mean annual infection rates of 1.8-2.6z between 2004 and 2008 among the inhabitants of Kumamoto Prefecture, which is located in south-west Japan and has a relatively high incidence of JE cases (9). This study tracks the status of natural JEV infections in Kumamoto Prefecture between 2009 and 2011.…”

Estimated global incidence of Japanese encephalitis:

“…2 In the intervening two decades, despite major population growth, urbanization, changes in agricultural practices and increased use of the JE vaccine in many countries, this figure has been widely quoted, including very recently. [9][10][11][12][13] In 2000, assuming an annual, age-group-specific incidence of 25 cases per 100 000, Tsai estimated that in the absence of vaccination 175 000 cases of JE would occur annually among Asian children aged 0-14 years living in rural areas. 14 The current study used more recent, published, local or national incidence estimates and current population data to produce an updated estimate of the annual global incidence of JE.…”