Norichika H. Kumazawa

Seroprevalence of Antibodies against Spotted Fever Group Rickettsia among Dogs and Humans in Okinawa, Japan

We evaluated serum antibodies against Rickettsia japonica in 517 dogs (430 stray dogs and 87 pet dogs) and 164 humans in Okinawa, Japan, by indirect immunofluorescence assay. The seropositive rate in stray dogs was significantly higher than that in pet dogs (30.7 versus 4.6%, P<0.01). This high prevalence rate is attributed to the understandably frequent environmental exposure of stray dogs to tick infestation. Human samples obtained from Okinawa and Sapporo also showed a significant difference in seropositive antibody percentages (45.1 and 12.0%, respectively, P<0.01). This result suggests that there has been preexposure to spotted fever group rickettsia in humans in Okinawa.

Distribution of marine birnavirus (MABV) in marine organisms from Okinawa, Japan, and a unique sequence variation of the VP2/NS region

Distribution of marine type of Aquabirnavirus (MABV) was examined in shellfish and fish from Okinawa and Ishigaki Islands, Japan, where water temperature is higher than 25°C through the year. Genome detection and virus isolation were performed for shellfish and fish samples, and the results revealed the prevalent distribution of MABV in diverse species in the area, although isolation was not frequently. Detection rate of MABV genome in bivalves was higher than gastropods, which was similar result to former report in mainland of Japan. Furthermore, the unique five-nucleotide deletion was found with a high rate of occurrence in the MABV genome from shellfish and fish. This study showed distribution status of MABV in organisms in subtropical waters by wide monitoring, and discovered new genome variation in VP2/NS region of this virus.

Characterization of Spotted Fever Group Rickettsiae Detected in Dogs and Ticks in Okinawa, Japan

Spotted fever group (SFG) rickettsial DNAs were detected in 2.4% of 340 canine blood samples and a pool of 84 tick pool samples (229 ticks) collected in Okinawa, Japan by PCR using a citrate synthase and an SFG rickettsial 190‐kDa surface antigen gene primer pair. The sequences of both genes from canine blood and tick samples showed high levels of similarity with those of Rickettsia japonica and several SFG rickettsiae (R. aeschlimannii, R. massiliae, R. rhipicephali and Bar‐29 strain). Phylogenesis of canine blood and tick samples was closely related to that of reference SFG rickettsiae. Serological evidence of SFG rickettsial infection in dogs and humans in Okinawa, where no clinical human cases have been reported, has been obtained. In this study, genetical characterization of SFG rickettsia in Okinawa was investigated phylogenetically.

Quantification of Thermostable Direct Hemolysin-Producing Vibrio Parahaemolyticus from Foods Assumed to Cause Food Poisoning Using the LightCycler Instrument

Vibrio parahaemolyticus isolated from the feces of patients with food poisoning contains in most cases either thermostable direct hemolysin (TDH) and/or TDHrelated hemolysin (TRH), both important pathogenic factors carried by this microorganism [1–3]. However, most organisms from brackish water, estuary mud or fish that cause food poisoning have neither the TDH production gene (tdh) nor the TRH production gene (trh) [1]. This seems to be because TDH-producing V. parahaemolyticus occurs in only small amounts in nature or foods compared to other Vibrio spp. In addition, it is difficult to grow in artificial media, since TDH-producing V. parahaemolyticus is in the viable but nonculturable (VNC) state due to nutrient limitation, low temperature, etc. [4, 5]. Therefore, TDH-producing V parahaemolyticus is rarely isolated from foods assumed to cause food poisoning that have a high probability of containing TDH-producing V. parahaemolyticus Accordingly, it is very difficult to quantitate TDH-producing V. parahaemolyticus by culture. In order to estimate the content of TDH-producing V. parahaemolyticus in suspect foods, we have developed a LightCycler assay to quantitate tdh.