[Epidemiological investigation of predominance tick and the infectious status of severe fever thrombocytopenia syndrome virus in Penglai and Laizhou counties, Shandong province].

OBJECTIVE:To investigate the predominance ticks and the infectious status of severe fever with thrombocytopenia (SFTSV) in Penglai and Laizhou counties, Shandong province. METHODS:Two towns with high incidence rate were selected in Penglai and Laizhou, respectively, then three villages were selected in each towns. Parasitic ticks were collected from the host skin by hand manually and free ticks manually with white cloth from the grassland, monthly, during April to December in 2011. Samples were classified by original, varieties, developmental stages, then extracted RNA, using Realtime RT-PCR to test severe fever thrombocytopenia syndrome virus, S fragments were amplified with nested PCR, then isolated virus. By neighbor joining method in the phylogenetic tree, the minimum infection rate (MIR) was used to represent the infection status of ticks in novel bunyavirus. RESULTS:A total of 3 145 ticks were collected totally from 5 categories, there were 3 048(96.92%) of Haemaphysalis longicornis, 73(2.32%) of Rhinpicephalus sanguineus, 10(0.32%) of microplus Boophilus, 9(0.29%) of Haemaphysalis campanulata, 5(0.16%) of Dermacentor sinicus, respectively. The positive rate of nucleic acid of 2 044 samples was 6.16% (126/2 044), minimum infection rate (MIR) was 4.01%, there were 122(96.83%) of Haemaphysalis longicornis, 3(2.38%) of Rhinpicephalus sanguineus, and 1(0.79%) of microplus Boophilus, MIR was 4.00%, 4.11%, and 10.00%, respectively. There were no nucleic acid positive samples in Haemaphysalis campanulata and Dermacentor sinicus. The 11 S segments were amplified in 126 positive samples, the homology of S fragment was 95.6%-99.9% with 11 strains isolated from the identified SFTS cases in local area, 3 strains isolated from animals, and 11 strains isolated from other areas. There was no significant difference among original, varieties and developmental stages. CONCLUSION:Haemaphysalis longicornis was the predominant species in Penglai and Laizhou counties, it could be propagation medium with Rhipicephalus sanguineus and microplus Boophilus, S sequence in ticks was higher homology with virus isolated from local SFTS cases.