[Epidemiological analysis of influenza B virus belonging to B/Victoria/2/87 lineage isolated in off-season of 1998 and late epidemic season in Shizuoka Prefecture]

In Shizuoka Prefecture, influenza B viruses belonging to B/Victoria/2/87 lineage caused an outbreak among school children in the off-season of 1998, and the same B viruses were mainly isolated during the following epidemic. Low titer of HI antibody among children for influenza B virus belonging to the same lineage was a recognized factor in the causation of the distinctive epidemic. The herald virus strains seemed to be antigenically similar to the late epidemic virus strains, but the former strains were not genetically close to the latter. This indicates that the herald viruses are not always the parental viruses for the following influenza season.

[Clinical analysis on an outbreak of SRSV-gastroenteritis with 644 patients emerged in Shizuoka Prefecture]

Small round structured viruses (SRSV) are the major cause of acute non-bacterial enterogastritis and have a characteristic of breaking out with mass victims as food poisoning. The outbreak usually occurs among school children from school lunches in Japan. A case in adults is relatively rare. The SRSV food poisoning with 644 adult victims carried through lunch box broke out, which may be the biggest number in adult cases in the world. This is the report describing its outlines, analytical result of clinical symptoms and fecal microbial examination. The average latent period was 37 hours, the time was mostly (47%) between 24-36 hours. The most emerged symptom was diarrhea and followed nausea, abdominal pain, vomiting and high fever. The older patients showed a higher rate of diarrhea and fewer one of nausea and fever. 15 patients complained of eye symptom. This number should not be neglected. It may be a characteristic of the disease. SRSV detection test with PT-PCR method of feces was done on 36 patients and 24 patients were positive. The most sensitive primer was Yuri/nested/22F/R. In Japan, lunch-service has become a industry advancing monopolization and wide areazation. SRSV make easily contamination to food, therefore if mass victim food-poisoning occurs, this should be considered initially.

Detection of Norwalk-like virus genes in the caecum contents of pigs

Norwalk-like virus genes were detected by RT-PCR in the caecum contents of pigs. Positive PCR products were produced from four out of 1,117 samples by nested PCR using human SRSV primers. Nucleotide sequences between 4,561 and 4,852 numbered according to the Norwalk virus genomic RNA in the RNA polymerase region were determined. Between the Norwalk virus sequence and the sequences detected in pigs, there was 58.2% to 59.9% sequence homology. The swine sequences were located on genogroup II of human SRSVs, but formed a subgroup in the phylogenetic tree of caliciviruses.

Sequence analysis of SRSV in fecal specimens from an epidemic of infantile gastroenteritis, October to December 1995, Japan

From October to December in 1995, an epidemic of infantile gastroenteritis occurred all over Japan except in Hokkaido and Okinawa prefectures. The number of infected infants and young children was estimated to be over 5 million cases [Editorial, IASR 1996]. The stool specimens from patients were examined for the presence of small round structured viruses (SRSVs) by reverse transcription-polymerase chain reaction (RT-PCR) and nucleotide sequencing of parts of the RNA-dependent RNA polymerase region. Thirty-five of 87 stool specimens examined gave positive results. Genomic variation was investigated by sequence analysis of a 327 bp cDNA region. The nucleotide and deduced amino acid sequences of the ten strains segregated into two distinct groups; one showed 96.0-100% nucleotide and 99.1-100% amino acid identity, the others showed 91.4-99.7% nucleotide and 93.5-100% identity. The main mechanism of transmission remains unknown. However, these data suggest the possibility of person-to-person spread by two or more kinds of SRSV.

Outbreaks of Norwalk-like virus-associated gastroenteritis traced to shellfish: coexistence of two genotypes in one specimen

We determined the nucleotide sequences of Norwalk-like viruses in 10 PCR products from stool or oyster specimens obtained from four outbreaks of gastroenteritis in which shellfish was suspected as the cause in Shizuoka prefecture in Japan between 1987-94. The sequences were determined from nucleotide positions 4561-4852 (292 bp) in the polymerase region. Two types of sequences were detected. One (genotype 1) had 87% sequence homology with the prototype Norwalk virus, and the other (genotype 2) had 59% sequence homology. The sequences from isolates belonging to the same genotype were almost the same regardless of the year of isolation. Because sequences of 2 genotypes were detected in 2 of the 4 outbreaks, nested PCR was performed with genotype-specific primers to detect the presence of 2 genotypes in the same specimen. In 5 of 10 specimens, PCR bands were detected with both genotype-specific primers, indicating the coexistence of 2 genotypes in 1 specimen. We also detected two genotypes of Norwalk-like virus in an oyster from a sample implicated in one of the outbreaks which may provide direct evidence of oysters as the cause of the gastroenteritis.

Isolation of Coxiella burnetii from children with influenza-like symptoms in Japan

The prevalence of Coxiella burnetii antibodies was investigated by indirect immunofluorescence (IF) test in 55 paired sera (acute and convalescent phases) of school children who had influenza-like symptoms. Of the convalescent serum samples examined, 18 (32.7%) sera reacted positively to phase II antigen of C. burnetii. Coxiella-like organism was isolated from the sera of 13 children after injection of the 18 acute phase sera into mice. The organism was identified as C. burnetii by Giemsa staining and the IF antigen test of mouse spleen smears, the polymerase chain reaction (PCR) method, electron microscopic observations of the mouse spleen cells, and the IF antibody test of mouse sera. This is the first report of isolation of C. burnetii from serum specimens of children having influenza-like symptoms. The evidence that C. burnetii was isolated from people indigenous to Japan at a considerably high incidence suggested that C. burnetii may be widespread as a cause of influenza-like symptoms in Japan.

Two-step polymerase chain reaction for diagnosis of scrub typhus and identification of antigenic variants of Rickettsia tsutsugamushi

Two-step polymerase chain reaction (nested PCR) method was examined for the diagnosis of scrub typhus. Primers were derived from the type-specific antigen (TSA) gene DNA sequences of Rickettsia tsutsugamushi, Gilliam strain. These primers served to produce rickettsia-specific products in the amplification of template DNA prepared from all serovariants, Gilliam, Karp, Kato, Kawasaki, Kuroki and Shimokoshi strains, and the fragments of product after digestion with several kinds of restriction endonuclease showed the respective patterns to strain in acrylamide or agarose gel electrophoresis. The rickettsia-specific DNAs were also derived, by this nested PCR, by amplifying DNA from patients' bloods and mites from endemic areas, and the serotype of rickettsiae infected to these hosts could be identified from fragment patterns of the amplified products observed after endonuclease treatment. These results indicate that this PCR is sensitive and specific method not only for detection of rickettsial DNA in patient specimens and in mites, but also for the typing of rickettsiae infected to these hosts.

Epidemiology of Tsutsugamushi disease in relation to the serotypes of Rickettsia tsutsugamushi isolated from patients, field mice, and unfed chiggers on the eastern slope of Mount Fuji, Shizuoka Prefecture, Japan

A total of 59 strains of Rickettsia tsutsugamushi were isolated from patients (24 isolates), Apodemus speciosus mice (30 isolates), and unfed larvae of Leptotrombidium scutellare (2 isolates) and Leptotrombidium pallidum (3 isolates) in the Gotenba-Oyama District, Shizuoka Prefecture, Japan. All these isolates were classified into the three serotypes Karp, Kawasaki, and Kuroki based on reactivity with strain-specific monoclonal antibodies. Kawasaki- and Karp-type rickettsiae were isolated from L. scutellare and L. pallidum, respectively, and the geographic distribution of patients and rodents infected with these two types of rickettsiae coincided with the areas densely populated by the respective chiggers. From these results, we conclude that Kawasaki-type rickettsiae are transmitted by L. scutellare and Karp-type ones are transmitted by L. pallidum. Kawasaki-type rickettsial infections were prevalent in early autumn, and Karp-type infections showed a peak of occurrence in the late autumn, reflecting the seasonal fluctuations of L. scutellare and L. pallidum. Isolates of Kuroki-type rickettsiae were obtained only from four patients in October and November, and the relationship between this type of rickettsia and its vector species could not be fully defined.