1. Introduction
The black-necked crane (
Grus nigricollis) is a vulnerable species and the only one that inhabits the plateau. It is classified as a vulnerable species (VU) by the International Union for Conservation of Nature (IUCN), with a global population ranging from 6,600 to 6,800 individuals [
1]. The Tibet Plateau is one of the main habitats for black-necked cranes and has one of the largest populations of this species in the world. However, human activities, including agriculture, mining, and tourism, are increasingly threatening the black-necked crane population [
2,
3,
4]. Additionally, viruses that infect birds and other crane species potentially endanger their lives. In recent years, emerging and re-emerging viruses such as avian influenza virus, Marek's disease virus, West Nile virus, and Crane hepatitis herpesviruses. have been found to infect cranes and pose health risks [
5,
6,
7,
8]. Some of these viruses may also have the potential to cross species barriers and infect humans. However, there have been limited virological studies conducted on black-necked cranes.
Viral metagenomics is a powerful tool for exploring both new and known viruses, and it has been widely utilized to understand viral compositions in diverse samples [
9,
10]. However, the viral composition in fecal samples from black-necked crane remains poorly understood. Therefore, the objective of this study is to investigate the viral composition of fecal samples collected from black-necked cranes in their natural habitat in Sa'gya County, Tibet Province, China, using a viral metagenomics approach. The findings of this study will provide valuable information for the prevention and treatment of viral diseases in this vulnerable species.
4. Discussion
The black-necked crane, as a vulnerable species, is highly susceptible to viral diseases. Previous studies have identified various viruses that can infect cranes and cause diseases. For instance, Lee and co-workers isolated a low pathogenic H7N7 avian influenza virus from a red-crowned crane in a zoo in South Korea [
5]. Ozawa and co-workers reported the widespread prevalence of crane-associated adenovirus 1 in cranes overwintering on the Izumi plain, Japan [
16]. Taniguchi and co-workers demonstrated that crane herpesvirus can induce hemagglutination [
17]. In our previous study, viral metagenomics revealed the presence of multiple viruses in the fecal samples of red-crowned cranes [
18]. However, limited research has been conducted on viral diseases in black-necked cranes. Hence, in this study, we employed high-throughput sequencing to investigate the virome of black-necked crane fecal samples. Our results showed that multiple viruses were firstly detected in black-necked crane and classified into novel virus species.
Members of the
Picornaviridae family are small, single-stranded RNA viruses with genome lengths ranging from approximately 7.2 to 9.4 kb. The
Picornaviridae family currently consists of 158 species grouped into 68 genera [
19]. Different genera of
Picornaviridae infect various animals and humans, leading to a variety of diseases [
20,
21,
22,
23,
24]. For instance, Enterovirus is the most common genus of
Picornaviridae virus and can cause diseases such as hand, foot, and mouth disease, poliomyelitis, and myocarditis [
25,
26,
27]. Hepatovirus includes human hepatitis A virus, which can cause acute hepatitis [
28]. Recently, viruses in the genus
Senecavirus have garnered attention from both veterinary and public health communities because they have been found to cause swine hand, foot, and mouth disease [
29].
Grusopivirus is a novel genus of the
Picornaviridae family, which was first discovered in the fecal sample of a red-crowned crane in 2014 by our lab [
18]. In this study, a novel grusopivirus was detected for the first time from fecal samples of black-necked cranes. This virus has a similar genomic structure and potential cleavage sites to the members of avihepatoviruses, which can cause poultry diseases. It suggests that the novel grusopivirus has the potential to be pathogenic to black-necked cranes. By amino acid sequence alignment, we found that P1 of grusopivirus D only had amino acid sequence identity of 40.81% with that of Grusopivirus A1 strain (NC_075281), while P2 and P3 of grusopivirus D shared over 96% amino acid sequence identity with that of Grusopivirus A1. Considering that the capsid protein, encoded by P1 of picoranvirus, plays an important role as a ligand in virus infection within the body, we speculate that these differences in the P1 polypeptide are related to differences in host receptors. Currently, all discovered grusopiviruses have been isolated from members of the
Gruiforms family. This prompts us to think that grusopiviruses can only infect cranes. However, the epidemiological and pathological characteristics of Grusopiviruses are not well understood. Therefore, further experimental and epidemiological studies are needed to understand its pathogenesis and transmission mechanisms.
Parvovirus is non-enveloped, icosahedral, single-stranded DNA virus with a genome approximately 4 kb and 6 kb in length [
30]. Historically, the
Parvoviridae family has two subfamilies including
Densoviridae and
Parvovirinae, which infect vertebrates and invertebrates, respectively. Recently, a new subfamily called
Hamaparvovirinae has been identified, which includes the genera
Brevihamaparvovirus,
Chaphamaparvovirus,
Hepanhamaparvovirus,
Ichthamaparvovirus, and
Penstylhamaparvovirus [
31]. Members of the genus
Chaphamaparvovirus can infect various animals, including dogs, wolves, chickens, pheasants, Larus delawarensis (a species of gull), bats, Sarcophilus harrisii (Tasmanian devil), Pavo cristatus (peacock), Cebusimitator (white-headed capuchin), parrots, and rodents [
32,
33,
34,
35,
36,
37]. Some of these infections can cause diseases in their respective hosts. For example, a study by Michael et al. reported that chaphamaparvovirus is the cause of hepatitis outbreaks in pheasants (Phasianus colchicus), which are characterized by high mortality [
34]. Subir Sarker also found that galliform chaphamaparvovirus is associated with spotty liver disease in chickens [
38]. Additionally, dogs, especially puppies infected with carnivore chaphamaparvovirus, exhibit clinical signs such as diarrhea, fever, and cough [
39]. In this study, four novel chaphamaparvoviruses were characterized for the first time. They were classified into four different novel species within the genus
Chaphamaparvovirus of the subfamily
Hamaparvovirinae. Surprisingly, phylogenetic analysis and pairwise alignment indicated that these four chaphamaparvoviruses have a higher genetic relationship with representative strains that were detected from fecal samples of red-crowned cranes. We speculate that chaphamaparvovirus is widely distributed among members of the
Gruiforms family. Further epidemiological investigation is needed to determine whether these viruses can cause black-necked crane disease and whether interspecies transmission is possible.
Members of the family
Genomoviridae are small, icosahedral, non-enveloped single-stranded circular DNA viruses. Their genomes are approximately 1.8-2.4 kb in length and encode a rolling-circle replication initiation protein (Rep) and a capsid protein (CP) in an ambisense orientation [
40]. The family
Genomoviridae is currently classified into nine genera:
Gemycircularvirus,
Gemyduguivirus,
Gemygorvirus,
Gemykibivirus,
Gemykolovirus,
Gemykrogvirus,
Gemykroznavirus,
Gemytondvirus, and
Gemyvongvirus [
15]. The first discovered genomovirus was Sclerotinia sclerotiorum hypovirulence-associated DNA virus 1 (SsHADV-1), which infects phytopathogenic fungus
Sclerotinia sclerotiorum [
41]. Recently, multiple genomoviruses have been detected in diverse samples taken from various organisms, including Actinopterygii, Arachnida, Aves, Embryophyte, Gastropoda, Insecta, Leotiomycetes, Mammalia, Reptilia, and the environment [
15,
42,
43,
44,
45,
46]. In the present study, we detected four novel genomoviruses for the first time in fecal samples from black-necked cranes. From a genome evolution perspective, these four genomoviruses are genetically related to strains isolated from nest material of finches in the USA, or from feces of Pteropus tonganus in Tonga. This indicates that the same species of genomovirus can infect different bird species, even if they live in different locations. However, since our samples were collected from healthy individuals, we cannot be certain if these novel genomoviruses will cause disease in black-necked cranes. It is also possible that these novel genomoviruses originated from foodborne insects. Therefore, further epidemiological investigations, including large-scale collection of blood samples, will be beneficial to clarify whether these genomoviruses are true pathogens of black-necked cranes. For genomovirus, the three conserved PCR motifs (I, II, and III) in Rep protein is crucial important for its replication. To our surprise, only PCR motif I was found, not motif II and III in the Rep protein of Gemycircularvirus c1. However, all other genomoviruses have three conserved PCR motifs. It is unknown whether the absence of two PCR motifs will affect the proliferation of Gemycircularvirus c1. Further experiments on virus proliferation in infected cells will help answer this question. Additionally, phylogenetic analysis based on the Rep proteins revealed that Gemycircularvirus c1 and Gemycircularvirus c2 are located in different branches. Therefore, we believe that phylogenetic trees constructed based on the Rep proteins can be effectively utilized for clustering virus genera, but may not be suitable for determining virus species.
Although multiple new viruses were identified in black-necked crane fecal samples using viral metagenomic method in this study, we are unable to determine whether these new viruses can cause disease in black-necked cranes. This limitation stems from the small number of samples collected and the exclusive focus on fecal samples. Moreover, we are uncertain about the exact sources of these viruses and their potential for cross-species transmission. Consequently, conducting a comprehensive epidemiological investigation in the region is crucial, necessitating the collection of various sample types from numerous animals on a larger scale