Jpn.J.Infect.Dis., 52, 1999

Laboratory and Epidemiology Communications

Serotypes of Astrovirus Isolated from Children in Sporadic Gastroenteritis Cases in Ehime Prefecture 1981-1997

Mitsuaki Oseto*, Yasutaka Yamashita, Kimi Yoshida, Reiko Kondo, Tadao Asai, Hiroo Inouye, Shozo Nakano1 and Yoshiro Ishimaru1

Ehime Prefectural Institute of Public Health and Environmental Science, Sanban-cho 8-234, Matsuyama, Ehime 790-0003 and 1Ishimaru Clinic, Sanban-cho 6-5-1, Matsuyama, Ehime 790-0003, Japan

Communicated by Hiroo Inouye

(Accepted July 8, 1999)

Astrovirus is known to cause diarrhea in young children. At least seven serotypes have been reported (1,2). Though the detection rate of astrovirus is lower than that of rotavirus or calicivirus in the infectious agents surveillance, astrovirus requires close surveillance from a public health viewpoint. Actually, a large outbreak of astrovirus-related diarrhea occurred in Osaka in 1991 (3).

The distribution of different serotypes of astrovirus has been almost unkown in Japan, though such studies have been come out in the UK (2,4). We report here the distribution of serotypes among astrovirus isolates from central Ehime Prefecture in the years 1981-1997.

The standard astrovirus strains were obtained from Dr. R.I. Glass, CDC, USA. The virus was replicated in Caco-2 cells maintained in medium supplemented with trypsin (Trypsin Type III, SIGMA) at a concentration of 5 mg/ml. The standard diagnostic sera were prepared by inoculating rabbits with the purified virions.

For serodiagnosis, we applied the sandwich ELISA. The antisera were fixed in 96-well plates. Ten percent stool suspensions or medium of the infected cultures were put into the wells, which served as an antigen trap. Astrovirus antigens trapped by the fixed antibodies were detected by the biotin-labelled serotype-specific antibodies. When tested with the standard astrovirus strains, this method was shown to have a high serotype specificity (Fig. 1). Our method appeared to be more specific than Noel et al's ELISA test (5).

The method was applied for the sero-typing of 99 samples derived from gastroenteric patients treated in a pediatric clinic in Matsuyama City, Ehime Prefecture. The samples consisted of 74 stool specimens that had been found astrovirus-positive in electronmicroscopical examination and 25 virus isolates in CaCo-2 cells. All the samples were sero-typed without any ambiguity except for one, which was positive for both type 4 and type 5 antisera.

As shown in Table 1, type I was the most frequent strain (50 cases, 50.5%). Type 4 (24 cases, 24.2%) and type 3 (15 cases, 15.2%) were moderately frequent. Types 2, 5, and 6 were few, and type 7 was absent. Type 1 and type 4 were detected almost every year, though the frequency fluctuated. Types 2, 5, and 6 were detected only sporadically. When the incidence was followed monthly, type 1 could be detected widely from December to June, while the other types tended to be clustered in the period from April to July.

Our data agreed well with the data from Oxford (2) and London (5) in the UK, which showed type 1 as the most frequent strain (> 60%). In the UK, there was an outbreak of the type 4 strain in 1993 (6). Interestingly, in Ehime Prefecture, we also encountered a clustered occurrence of type 4 infection in the same year (Table 1).

Table 2 shows the age distribution of the patients from whom the astrovirus was detected. With the exception of one case, all the patients were younger than 10 years old. Half of the type 1 cases were under 2 years old, while 80% of the cases of types 3 and 4 were over 2 years old. The clinical symptoms, such as fever, diarrhea, vomiting, abdominal pain, were similar for all the astrovirus serotypes.

REFERENCES

  1. Kurtz, J.B. and Lee, T.W. (1984): Human astrovirus serotypes. Lancet, II, 1405.
  2. Lee, T.W. and Kurtz, J.B. (1994): Prevalence of human astrovirus serotypes in the Oxford region 1976-92, with evidence for two new serotypes. Epidemiol. Infect., 112, 187-193.
  3. Oishi, I., Yamazaki, K., Kimoto, T., Minekawa, Y., Utagawa, E., Yamazaki, S., Inoue, S., Grohmann, G.S., Monroe, S.S., Stine, S.E., Carcamo, C., Ando, T. and Glass, R.I. (1994): A large outbreak of acute gastroenterisis associated with astrovirus among students and teachers in Osaka, Japan. J. Infect. Dis., 170, 439-443.
  4. Noel, J.S. and Cubitt, D. (1994): Identification of astrovirus serotypes from children treated at the hospitals for sick children, London 1981-93. Epidemiol. Infect., 113, 153-159.
  5. Noel, J.S., Lee, T.W., Kurtz, J.B., Glass, R.I. and Monroe, S.S. (1995): Typing of human astroviruses from clinical isolates by enzyme immunoassay and nucleotide sequencing. J. Clin. Microbiol., 33, 797-801.
  6. Willcocks, M.M., Kurtz, J.B., Lee, T.W. and Carter, M.J. (1995): Prevalence of human astrovirus serotype 4: capsid protein sequence and comparison with other strains. Epidemiol. Infect., 114, 385-391.

*Corresponding Author: Fax:+81-89-947-1262, E-mail: mi-oseto@pa2.so-net.ne.jp

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