BackgroundBlood-sucking lice (suborder Anoplura) parasitize eutherian mammals with 67% of the 540 described species found on rodents. The five species of blood-sucking lice that infest humans and pigs have fragmented mitochondrial genomes and differ substantially in the extent of fragmentation. To understand whether, or not, any life-history factors are linked to such variation, we sequenced the mt genomes of Polyplax asiatica and Polyplax spinulosa, collected from the greater bandicoot rat, Bandicota indica, and the Asian house rat, Rattus tanezumi, respectively.ResultsWe identified all of the 37 mitochondrial genes common to animals in Polyplax asiatica and Polyplax spinulosa. The mitochondrial genes of these two rat lice are on 11 circular minichromosomes; each minichromosome is 2–4 kb long and has 2–7 genes. The two rat lice share the same pattern for the distribution of the protein-coding genes and ribosomal RNA genes over the minichromosomes, but differ in the pattern for the distribution of 8 of the 22 transfer RNA genes. The mitochondrial genomes of the Polyplax rat lice have 3.4 genes, on average, on each minichromosome and, thus, are less fragmented than those of the human lice (2.1 and 2.4 genes per minichromosome), but are more fragmented than those of the pig lice (4.1 genes per minichromosome).ConclusionsOur results revealed distinct patterns of mitochondrial genome fragmentation within the genus Polyplax and, furthermore, indicated a possible inverse link between the extent of mitochondrial genome fragmentation and the length of life cycle of the blood-sucking lice.

During a survey lasting from 1990 to 2008, we captured 4,113 Asian house rats, Rattus tanezumi Temminck 1844 (Rodentia: Muridae) from 28 counties of Yunnan Province in southwestern China. From these rats, a total of 19,304 gamasid mites (Acari: Mesostigmata) were collected and identified as comprising 50 different species. The species diversity of gamasid mites from this single rat species is higher than that reported previously from multiple hosts within a given geographical region. Of the 50 mite species, 31 species belonged to ectoparasites and 19 species belonged to free-living mites. The species diversity of the mites from rats trapped outdoors was much higher than from rats trapped indoors. The parameter K from the negative binomial distribution was used to measure the spatial distribution patterns of the dominant mite species and revealed that all the mites had an aggregated distribution among the rat hosts. Most mite species showed a predominantly female-biased population structure with many more females than males.

There are several main vectors of scrub typhus in China, and Leptotrombidium rubellum Wang et Liao, 1984 is one of them, which was previously considered to be restricted to the coastal regions of Changle to Xiamen, Fujian province of east China. Ecological investigation of chigger mites in recent years demonstrated the presence of L. rubellum also in Yunnan province. Chigger mites were collected from 34 counties, in which 127,460 larval mites were collected from 14,381 small mammal hosts. A total of 277 species belonging to 26 genera and three subfamilies were identified. A total of 705/127,460 (0.55%) L. rubellum were collected from eight counties. Leptotrombidium rubellum was collected mainly at low elevations in southern Yunnan. A total of 663/705 (94.04%) of L. rubellum were collected from Rattus flavipectus (Milne-Edwards, 1871) found in outdoor habitats with relatively high infestation prevalence and mean intensity. Although it was collected from several hosts, the primary host was Rattus tanezumi. This represents a new distribution record of L. rubellum for Yunnan province.