The symbiotic bacteria associated with the stomach disc, a large aggregate of bacteriocytes on the ventral side of the midgut, of human body and head lice were characterized. Molecular phylogenetic analysis of 16S rRNA gene sequences showed that the symbionts formed a distinct and well-defined clade in the Gammaproteobacteria. The sequences exhibited AT-biased nucleotide composition and accelerated molecular evolution. In situ hybridization revealed that in nymphs and adult males, the symbiont was localized in the stomach disc, while in adult females, the symbiont was not in the stomach disc but in the lateral oviducts and the posterior pole of the oocytes due to female-specific symbiont migration. We propose the designation "Candidatus Riesia pediculicola" for the louse symbionts.

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We have measured the relaxation time in ferroelectric TAAP near the Curie temperature. The dielectric relaxation in this crystal could be described to a good approximation by the Debye equations. The relaxation time exhibits critical slowing down characteristic of an order-disorder transition.

Although body louse is a well-known vector of trench fever, the growth kinetics of Bartonella quintana in body lice has not been fully understood. We performed a quantitative analysis of bacterial multiplication rate. B. quintana started proliferation in body lice 4 days after ingestion and was constantly excreted in the feces for at least 3 weeks. The number of bacteria in feces reached the maximum 10(7)/louse per day on Day 15. The doubling time of B. quintana estimated from logistic regression formula was 21.3 hours. Scanning electron microscopy showed the presence of bacterial masses in feces. Immunofluorescent study using specific monoclonal antibody confirmed identification of B. quintana. Such an explosive multiplication rate and active excretion of B. quintana from the body lice could be related to epidemics of trench fever in developed countries.