during january  august 2013 , we collected rodents and shrews in jiaonan county , shandong province , china ( 1193012030e , 35353608 n ) .
the animals were trapped once a month by using mouse traps baited with peanuts ; a different trap site was used each month .
the traps were set before sunset outside human dwellings in rural areas and collected the next morning .
we classified the rodents and shrews according to appearance ( hair color ) and body structures ( i.e. , shape of mouth , teeth , tail , ratio of tail length to body length , cheek pouch ) .
after the animals were euthanized , we collected blood samples from their hearts onto absorbent paper strips ( 10 mm  30 mm ) .
animal use and sample collection protocols were approved by the bioethics committee of the school of public health , shandong university . before testing the serum samples for the presence of sftsv
, we evaluated the sensitivity and specificity of a double - antigen sandwich elisa kit ( wuxi xinlianxin biotech co , wuxi city , china ) for detecting sftsv in rodent serum . to do this
, we used an indirect immunofluorescence assay ( ifa ) as a standard to test rodent serum samples for sftsv and compared the results with those from the elisa .
a total of 68 kunming albino mice ( shandong university experimental animal center , jinan , china ) were used for the tests : 36 were injected with sftsv , and 32 ( controls ) were injected intraperitoneally with saline solution . on days 7 , 12 , 17 , and 21 after injection , 9 infected and 8 control mice were euthanized , and serum samples from the mice were tested for sftsv antibody by ifa and elisa .
of the 36 serum samples from the sftsv - inoculated mice , 33 were positive for sftsv by ifa and elisa and 3 were positive by ifa only .
all 32 serum samples from the control mice were negative for sftsv by ifa and elisa .
thus , under these laboratory conditions and compared with the ifa , the elisa had a sensitivity of 91.7% and specificity of 100% , suggesting that the elisa could be used to test serum samples from the field - collected rodents .
kits for shrews were not commercially available in china , so we were unable to test the sensitivity and specificity of the elisa for detecting sftsv in serum from shrews .
we collected 89 asian house shrews ( suncus murinus ) and 666 rodents in the field during january 
the rodents included 186 striped field mice ( apodemus agrarius ) , 182 house mice ( mus musculus ) , 156 brown rats ( rattus norvegicus ) , 125 greater long - tailed hamsters ( cricetulus tyiton ) , and 17 chinese hamsters ( cricetulus barabensis ) .
serum samples from the rodents and shrews were tested for igg and igm to sftsv by using the elisa as described previously ( 810 ) .
serum samples on absorbent paper were each reconstituted by adding 150 l of phosphate - buffered saline , and 75 l of each sample was added to a well of the elisa plate .
elisa results showed that sftsv seroprevalence was higher among asian house shrews ( 4.5% , 4/89 ) than among rodents ( 0.9% , 6/666 ) ( p = 0.014 ) . among the rodents , sftsv seropositivity was higher in house mice ( 1.1% , 2/182 ) and striped field mice ( 1.1% , 2/186 ) than in other rodent species ( table ) .
however , the seropositivity rate was not significantly different among the rodent species ( p = 0.691 ) .
in addition , the seropositivity rate did not differ significantly by month ( p = 0.411 ) .
total rna was extracted from homogenized animal spleens by using the rneasy mini kit ( qiagen , hilden , germany ) , which was used as a template for sftsv amplification performed by using the access rt - pcr system ( promega , madison , wi , usa ) .
primers for reverse transcription pcr ( rt - pcr ) were designed from the m segments of the sftsv genome .
outside pcr primers were 5-tctgcagttcagactcaggga-3 and 5-gacgtgtattgctgttttccc-3 ; nested pcr primers were 5-tgttgcttgtcagcctatgac-3 and 5-caaccaatgatcctgagtgga-3. the pcr products ( 674 bp ) were cloned and sequenced for both strands at least 3 times .
amplification results showed that the sftsv positivity rate was higher among shrews ( 2.6% , 2/77 ) than among rodents ( 0.7% , 3/440 ) , but the difference was not significant ( p = 0.162 ) ( table ) .
the pcr positivity rate differed by month : the rate was 4.7% ( 4/86 ) for animals trapped in march , 1.6% ( 1/62 ) for animals trapped in june , and 0 for animals collected during the other 6 months ( p = 0.043 ) .
phylogenetic analysis indicated that the sftsv sequences from the rodents and shrews were closely related to each other ( 98.5% 99.7% homology ) and highly homologous ( 95.3% to 99.7% ) to the corresponding sequences of sftsv from a human ( genbank accession no .
jf267784 ) , and ticks ( genbank accession nos . kc473541 and jq684872 ) ( figure ) .
phylogenetic analysis of severe fever with thrombocytopenia syndrome virus ( sftsv ) amplified from the spleens of asian house shrew and rodents .
the neighbor - joining phylogenetic tree was constructed by using mega 5.2 software(http://www.megasoftware.net/).genbank accession numbers precede isolate names on the right side of the figure .
two previous studies demonstrated that rodents in china were seronegative for sftsv ( 7,12 ) .
however , negative results might have been caused by small sample sizes or by using rodents that were collected from sites where sftsv was not endemic .
the serologic and rt - pcr results in our study show that rodents and shrews in eastern china are seropositive for sftsv .
we also attempted to amplify s segments of the genomes of sftsv isolates , but results were positive for only 1 animal .
it is possible that in our study , the primer for the s segment was not as sensitive as that for the m segment .
most animal species that have been investigated for the presence of sftsv have been positive for the virus , including rodents , shrews , goats , cattle , dogs , and chickens ( 5,810 ) .
goats have usually shown high seroprevalence to sftsv but very low virus loads and short periods of sftsv viremia ( 9 ) .
rodents experimentally infected with sftsv usually have long periods of viremia and high virus loads in the blood ( 13,14 ) .
cross - sectional analysis indicated that the sftsv infection rate among rodents and shrews did not differ substantially by month during the 8-month study period , but the pcr positivity rate was highest for animals collected during march .
the variation between months can probably be explained by the fact that the animals were collected from different sites each month ; the rates of infection among animals at the different sites may have differed . in conclusion ,
our findings show that the asian house shrew and different varieties of rodents are potential animal hosts of sftsv .
further studies are needed to determine which of the many animal hosts of sftsv can most effectively transmit the virus to ticks , the probable vector of sftsv transmission to humans .
 to evaluate the role of small mammals as hosts of severe fever with thrombocytopenia syndrome virus ( sftsv ) , we tested serum samples from rodents and shrews in china , collected in 2013 . 
 sftsv antibodies and rna were detected , suggesting that rodents and shrews might be hosts for sftsv . 
The Study
Conclusions