Severe fever with thrombocytopenia syndrome virus among domesticated animals, China

Abstract

To investigate the infections of severe fever with thrombocytopenia syndrome virus (SFTSV) in domesticated animals, we sampled a total of 3,039 animals in 2 counties in Shandong Province, People's Republic of China, from April to November 2011. SFTSV-specific antibodies were detected in 328 (69.5%) of 472 sheep, 509 (60.5%) of 842 cattle, 136 (37.9%) of 359 dogs, 26 (3.1%) of 839 pigs, and 250 (47.4%) of 527 chickens. SFTSV RNA was detected in all sampled animal species, but the prevalence was low, ranging from 1.7% to 5.3%. A cohort study in 38 sheep was conducted to determine when seroconversion to SFTSV occured. SFTSVs were isolated from sheep, cattle, and dogs and shared >95% sequence homology with human isolates from the same disease-endemic regions. These findings demonstrate that natural infections of SFTSV occur in several domesticated animal hosts in disease-endemic areas and that the virus has a wide host range.

Keywords: China; Phlebovirus; SFTSV; domesticated animals; family Bunyaviridae; host; infection; pathogenic disease; prevalence; severe fever with thrombocytopenia syndrome virus; transmission; viruses; zoonoses.

Figure 1

Serum severe fever with thrombocytopenia syndrome virus RNA detection rate in domestic animals from Laizhou and Penglai counties, China, April–November 2011. Viral RNA copies were detected by real-time reverse transcription PCR in serum samples from sheep, cattle, dogs, pigs, and chickens collected from Laizhou and Penglai counties in different months. The viral RNA detection rates are shown. Black bars indicate samples from Laizhou; gray bars indicate samples from Penglai. The viral RNA detection rate in 2 counties was compared (*p<0.05, †p>0.05).

Figure 2

Serum antibody detection rate in domestic animals from Laizhou and Penglai counties, China, April–November 2011. Severe fever with thrombocytopenia syndrome virus N protein-specific antibodies were detected by double-antigen sandwich ELISA in serum samples of sheep, cattle, dogs, pigs, and chickens collected from Laizhou and Penglai counties in different months, and the antibody detection rates are presented. Black bars indicate samples from Laizhou; gray bars indicate samples from Penglai. The antibody detection rates in the 2 counties were compared (*p<0.05, †p>0.05).

Figure 3

Detection of serum severe fever with thrombocytopenia syndrome virus (SFTSV) RNA and antibodies in a cohort of 38 sheep, China. Serum samples in a cohort of 38 sheep were collected from Laizhou and Penglai on the dates indicated on the x-axis from June 21 through November 29, 2011. SFTSV N protein–specific antibodies were measured by using a double-antigen sandwich ELISA, and the cumulative positive percentage in Laizhou and Penglai counties is presented along the timeline.

Figure 4

Time course of serum viral RNA and neutralizing antibodies in 17 sheep positive for severe fever with thrombocytopenia syndrome virus RNA, China. Detection of virus specific antibodies in Laizhou and Penglai is indicated by the dashed line and the bold line, respectively. The numbers on the lines indicate viral RNA copies (×10³/mL) in serum samples detected on the indicated dates. Neutralizing antibody levels in the initial samples collected on June 21, 2011, in the samples positive for viral RNA, and in the samples collected at the late stage on October 20, were measured by using a microneutralization assay. Neutralizing antibody titers are shown with different symbols: *neutralizing antibodies not detected; †neutralizing antibody titers = 4; ‡neutralizing antibody titers = 16; §neutralizing antibody titers >64.

Figure 5

Time course of serum severe fever with thrombocytopenia syndrome virus (SFTSV) RNA and antibody in a naturally infected dog, China, 2011. SFTSV RNA copies and virus-specific antibodies were detected in serum samples from a dog on day 0, once every sample period of 2 days from day 8 to day 22, and on day 90. The gray open squares indicate viral copies; black circles indicate virus-specific IgG. The dashed lines indicate predicted time course of viral RNA and antibodies due to lack of data during day 1–day 7.

Figure 6

Phylogenetic analysis of severe fever with thrombocytopenia syndrome virus (SFTSV) isolates from domesticated animals. The evolutionary relationship of small segments of SFTSV isolated from domesticated animals, SFTS patients and ticks was calculated by using the neighbor-joining method with MEGA 5 (8). Sequences are labeled with the order of GenBank accession number/name of viral strain/year of isolation. Black circles indicate the original sequences of SFTSV strains obtained from domesticated animals in this study; black triangles indicated the original sequences of SFTSV strains obtained from SFTS patients in 2011 in this study; blank triangles indicate the previously published sequences of SFTSV strains obtained from 11 SFTS patients in 2010 (1); and open diamonds indicate the previously published sequences of SFTSV strains obtained from H. longicornis ticks in 2010 (3).