Virome of Giant Panda-Infesting Ticks Reveals Novel Bunyaviruses and Other Viruses That Are Genetically Close to Those from Giant Pandas

Abstract

Tick infestations have been reported as one of the factors threatening the health of giant pandas, but studies of viral pathogens carried by ticks feeding on the blood of giant pandas are limited. To assess whether blood-sucking ticks of giant pandas can carry viral pathogens and if so, whether the viruses in ticks are associated with those previously detected in giant panda hosts, we determined the viromes of ticks detached from giant pandas in a field stocking area in Sichuan Province, southwest China. Using viral metagenomics we identified 32 viral species in ticks, half of which (including anellovirus [n = 9], circovirus [n = 3], and gemycircularvirus [n = 4]) showed homology to viruses carried by giant pandas and their associated host species (such as red pandas and mosquitoes) in the same living domain. Remarkably, several viruses in this study phylogenetically assigned as bunyavirus, hepe-like virus, and circovirus were detected with relatively high abundance, but whether these newly identified tick-associated viruses can replicate in ticks and then transmit to host animals during a blood meal will require further investigation. These findings further expand our understanding of the role of giant panda-infesting ticks in the local ecosystem, especially related to viral acquisition and transmission, and lay a foundation to assess the risk for giant panda exposure to tick-borne viruses. IMPORTANCE Ticks rank only second to mosquitoes as blood-feeding arthropods, capable of spreading pathogens (including viruses, bacteria, and parasites) to hosts during a blood meal. To better understand the relationship between viruses carried by ticks and viruses that have been reported in giant pandas, it is necessary to analyze the viromes of giant panda-parasitic blood-sucking ticks. This study collected 421 ticks on the body surface of giant pandas in Sichuan Province, China. We characterized the extensive genetic diversity of viruses harbored by these ticks and reported frequent communication of viruses between giant pandas and their ticks. While most of the virome discovered here are nonpathogenic viruses from giant pandas and potentially tick-specific viruses, we revealed some possible tick-borne viruses, represented by novel bunyaviruses. This research contributes to the literature because currently there are few studies on the virome of giant panda-infesting ticks.

Keywords: cross-species transmission; giant pandas; phylogenetic analysis; tick-borne viruses; ticks.

FIG 1

Taxonomic analyses of eukaryotic viral reads at the level of family or species. The heatmap (A) and bar graph (B) show the read counts of each viral family in each tick library. Viral types or viral families are shown with corresponding colors (see color legend). (C) The read abundance (node color) of each viral species. The viral species is indicated in the same color of node outline for each tick library.

FIG 2

Phylogenetic analyses of STHEV and STTV sequences. (A) Bayesian phylogenetic tree for STHEV and other representative members from the families Hepeviridae, Matonaviridae and Benyviridae based on the amino acid sequences for RNA-dependent RNA polymerase protein (RdRp) domain. Nodes with bootstrap values ≥70 are indicated. (B) Bayesian phylogenetic tree for STTV and other representative members from the family Totiviridae based on the amino acid sequences for RdRp domain. Each scale bar indicates the amino acid substitutions per site.

FIG 3

Phylogenetic relationship of Bunyavirales. (A) Phylogenetic tree based on RdRp domain amino acid sequences of the 10 families in the order Bunyavirales. (B) Pairwise genetic distance heatmap of Orthonairovirus and nairo-like virus RdRp domain protein sequences. (C) Pairwise genetic distance heatmap of Phlebovirus, Banyangvirus, Uukuvirus, and phlebo-like virus RdRp domain protein sequences. (D) Phylogenetic tree for STPV and members of the same or closely related genera in the family Phenuiviridae. (E) Phylogenetic tree for STNV, orthonairoviruses, and other nairo-like viruses in the family Nairoviridae. Each scale bar indicates the amino acid substitutions per site.

FIG 4

Phylogenetic analysis of the anelloviruses based on the ORF1 amino acid sequences. The newly identified viruses in ticks and previously identified in giant pandas are marked with blue and red dots, respectively. Putative cross-species transmission events between ticks and giant pandas are pointed with red pentagrams. Each scale bar indicates the amino acid substitutions per site.

FIG 5

Phylogenetic analysis of the CRESS-DNA viruses based on the Rep amino acid sequences. The viruses identified from ticks in this study and other five different host species are marked with corresponding colors (see color legend). Each scale bar indicates the amino acid substitutions per site.