Replication capacity and adaptability of a severe fever with thrombocytopenia syndrome virus at different temperatures

<div><p>Severe fever with thrombocytopenia syndrome (SFTS) is an emerging disease caused by the SFTS virus (SFTSV). Although fever and thrombocytopenia are the typical manifestations of SFTS, a specific SFTS case with no fever was observed in Zhejiang, China. In this report, we aimed to explore the probable reason for the absence of fever by analyzing the genetic characteristics and temperature sensitivity (ts) of the SFTSV strain ZJ2013-06, which was isolated from the specific case. Phylogenetically, different clusters of SFTSV strains circulated in Zhejiang. ZJ2013-06 was farthest from ZJ2014-02, an isolate belonging to a Chinese dominant cluster, and nearest to the coastal strain NB24/CHN/2013. Ts tests, performed on Vero cells at 37°C and 39°C, indicated that ZJ2013-06 had restricted replication at 39°C. Its viral loads were substantially reduced at 39°C compared with that at 37°C (approximately 100-fold reduction) and were significantly lower than that of ZJ2014-02 at 39°C (<i>P</i> < 0.01). By adaptive culture at 39°C, the induced strain ZJ2013-06-P7 was obtained. Owing to a reverse mutation (S1616), ZJ2013-06-P7 lost the ts of the original strain, displaying similar replication processes with NB24/CHN/2013. The results indicated that the amino acid residue 1616 was related to the ts characteristics of ZJ2013-06. Our study revealed that ZJ2013-06 was temperature-sensitive and may be related to the absence of fever in our case.</p></div

Proliferation curves of ZJ2013-06 and ZJ2014-02 in Vero cells at different temperatures.

<p>Proliferation curves of ZJ2013-06 and ZJ2014-02 in Vero cells at different temperatures.</p

Replication capacities of ZJ2013-06 at different temperatures.

<p>Replication capacities of ZJ2013-06 at different temperatures.</p

Temperature sensitivity of NB24/CHN/2013 and ZJ2013-06-P7.

<p>Temperature sensitivity of NB24/CHN/2013 and ZJ2013-06-P7.</p

Specific amino acid sites possessed by the ZJ2013-06 strain.

<p>Specific amino acid sites possessed by the ZJ2013-06 strain.</p

Prediction of linear B cell epitopes for nucleocapsid protein from different SFTSV strains.

<p>Prediction of linear B cell epitopes for nucleocapsid protein from different SFTSV strains.</p

Sero-prevalence of SFTSV in healthy individuals from different villages of Daishan.

<p>A: IFA detection of IgG antibodies to SFTSV in healthy individuals. B: ELISA detection result of IgG and IgM antibodies to SFTSV in healthy individuals from different districts of Daishan.</p

Homology comparison of the target nucleocapsid gene sequences from different SFTSV strains.

<p>A: The similarities of the target nucleocapsid gene sequences from the SFTSV strains of China (Henan, Liaoning, Shandong, Jiangsu, Hubei, Zhejiang and Anhui), Japan (Yamaguchi and Miyazakj), and South Korea (Gangwon) were 94.2–100%. B: Phylogenetic tree showed the phylogenetic positions of SFTSV strains in Zhejiang (Daishan), compared with other known SFTSV strains.</p

Surveillance results for SFTS in Daishan, Zhejiang Province.

<p>A: Age distribution of diagnosed SFTS patients in Daishan from 2011 to 2014. B: Seasonality distribution of identified SFTSV infection cases in Daishan from 2011 to 2013.</p