Picobirnaviruses were initially discovered by the finding of two nucleic acid segments through PAGE during investigations of acute gastroenteritis in children and from feces of black-footed pigmy rice rats [9Pereira HG, Fialho AM, Flewett TH, Teixeira JM, Andrade ZP. Novel viruses in human faeces. Lancet 1988; 2(8602): 103-4.
[http://dx.doi.org/10.1016/S0140-6736(88)90032-3] [PMID: 2898672] , 10Pereira HG, Flewett TH, Candeias JA, Barth OM. A virus with a bisegmented double-stranded RNA genome in rat (Oryzomys nigripes) intestines. J Gen Virol 1988; 69(Pt 11): 2749-54.
[http://dx.doi.org/10.1099/0022-1317-69-11-2749] [PMID: 3053986] ]. The virus has subsequently been detected in faecal samples from domestic and wild animal species, including rats, giant anteaters, guinea pigs, rabbits, chickens, pigs, calves, foals, cat and dogs [4Li L, Giannitti F, Low J, et al. Exploring the virome of diseased horses. J Gen Virol 2015; 96(9): 2721-33.
[http://dx.doi.org/10.1099/vir.0.000199] [PMID: 26044792] , 9Pereira HG, Fialho AM, Flewett TH, Teixeira JM, Andrade ZP. Novel viruses in human faeces. Lancet 1988; 2(8602): 103-4.
[http://dx.doi.org/10.1016/S0140-6736(88)90032-3] [PMID: 2898672] -34Volotäo EM, Soares CC, Albuquerque MC, et al. First evidence of a trisegmented double-stranded RNA virus in canine faeces. Vet J 2001; 161(2): 205-7.
[http://dx.doi.org/10.1053/tvjl.2000.0532] [PMID: 11243690] ]. Epidemiological studies on PBVs in India are still in its early stages, with limited reports only. Here, we converse with the epidemiological studies carried out as on date in India on PBVs and present the current knowledge of PBVs in different hosts emphasizing the Indian perspective.

The actual journey of PBV discovery started in 1988, when Pereira and colleagues described a novel virus in human faeces serendipitously [9Pereira HG, Fialho AM, Flewett TH, Teixeira JM, Andrade ZP. Novel viruses in human faeces. Lancet 1988; 2(8602): 103-4.
[http://dx.doi.org/10.1016/S0140-6736(88)90032-3] [PMID: 2898672] ]. Subsequently, in 1995 PBVs were detected as co-infecting agents with Cryptosporidium in human faeces [15Gallimore CI, Green J, Casemore DP, Brown DW. Detection of a picobirnavirus associated with Cryptosporidium positive stools from humans. Arch Virol 1995; 140(7): 1275-8.
[http://dx.doi.org/10.1007/BF01322752] [PMID: 7646357] ] and the virus was characterized by two extraction methods i.e. phenol/chloroform and guanidinium thiocyanate (GTC)/silica method followed by electron microscopy to know its physical properties [35Gallimore CI, Appleton H, Lewis D, Green J, Brown DW. Detection and characterisation of bisegmented double-stranded RNA viruses (picobirnaviruses) in human faecal specimens. J Med Virol 1995; 45(2): 135-40.
[http://dx.doi.org/10.1002/jmv.1890450204] [PMID: 7775930] ]. In 2000, two prototype strains for GG-I (1-CHN-97) and GG-II (4-GA-91) were cloned and sequenced, obtained from human HIV infected patient and non-HIV infected patient from China and USA respectively [2Rosen BI, Fang Z-Y, Glass RI, Monroe SS. Cloning of human picobirnavirus genomic segments and development of an RT-PCR detection assay. Virology 2000; 277(2): 316-29.
[http://dx.doi.org/10.1006/viro.2000.0594] [PMID: 11080479] ]. Their presence has been reported in human faeces from Argentina [5Giordano MO, Martinez LC, Rinaldi D, et al. Diarrhea and enteric emerging viruses in HIV-infected patients. AIDS Res Hum Retroviruses 1999; 15(16): 1427-32.
[http://dx.doi.org/10.1089/088922299309937] [PMID: 10555105] , 8Giordano MO, Martinez LC, Rinaldi D, et al. Detection of picobirnavirus in HIV-infected patients with diarrhea in Argentina. J Acquir Immune Defic Syndr Hum Retrovirol 1998; 18(4): 380-3.
[http://dx.doi.org/10.1097/00042560-199808010-00010] [PMID: 9704944] , 36Martínez LC, Giordano MO, Isa MB, et al. Molecular diversity of partial-length genomic segment 2 of human picobirnavirus. Intervirology 2003; 46(4): 207-13.
[http://dx.doi.org/10.1159/000072429] [PMID: 12931028] , 37Giordano MO, Masachessi G, Martinez LC, et al. Two instances of large genome profile picobirnavirus occurrence in Argentinian infants with diarrhea over a 26-year period (1977-2002). J Infect 2008; 56(5): 371-5.
[http://dx.doi.org/10.1016/j.jinf.2008.02.017] [PMID: 18403022] ], Brazil [38Barreto ML, Milroy CA, Strina A, et al. Community-based monitoring of diarrhea in urban Brazilian children: incidence and associated pathogens. Trans R Soc Trop Med Hyg 2006; 100(3): 234-42.
[http://dx.doi.org/10.1016/j.trstmh.2005.03.010] [PMID: 16303156] ], USA [7Grohmann GS, Glass RI, Pereira HG, et al. Enteric viruses and diarrhea in HIV-infected patients. N Engl J Med 1993; 329(1): 14-20.
[http://dx.doi.org/10.1056/NEJM199307013290103] [PMID: 8099429] , 39Cunliffe NA, Glass RI. Gastrointestinal manifestations of HIV infection. Lancet 1996; 348(9033): 1037.
[http://dx.doi.org/10.1016/S0140-6736(05)64970-7] [PMID: 8855890] , 40Zhang T, Breitbart M, Lee WH, et al. RNA viral community in human feces: prevalence of plant pathogenic viruses. PLoS Biol 2006; 4(1): e3.
[http://dx.doi.org/10.1371/journal.pbio.0040003] [PMID: 16336043] ], Venezuela [41Ludert JE, Liprandi F. Identification of viruses with bi- and trisegmented double-stranded RNA genome in faeces of children with gastroenteritis. Res Virol 1993; 144(3): 219-24.
[http://dx.doi.org/10.1016/S0923-2516(06)80032-4] [PMID: 8356343] , 42González GG, Pujol FH, Liprandi F, Deibis L, Ludert JE. Prevalence of enteric viruses in human immunodeficiency virus seropositive patients in Venezuela. J Med Virol 1998; 55(4): 288-92.
[http://dx.doi.org/10.1002/(SICI)1096-9071(199808)55:4<288::AID-JMV6>3.0.CO;2-X] [PMID: 9661837] ], Hungary [43Bányai K, Jakab F, Reuter G, et al. Sequence heterogeneity among human picobirnaviruses detected in a gastroenteritis outbreak. Arch Virol 2003; 148(12): 2281-91.
[http://dx.doi.org/10.1007/s00705-003-0200-z] [PMID: 14648286] ], Italy [44Cascio A, Bosco M, Vizzi E, Giammanco A, Ferraro D, Arista S. Identification of picobirnavirus from faeces of Italian children suffering from acute diarrhea. Eur J Epidemiol 1996; 12(5): 545-7.
[http://dx.doi.org/10.1007/BF00144011] [PMID: 8905320] ], Netherlands [45van Leeuwen M, Williams MM, Koraka P, Simon JH, Smits SL, Osterhaus AD. Human picobirnaviruses identified by molecular screening of diarrhea samples. J Clin Microbiol 2010; 48(5): 1787-94.
[http://dx.doi.org/10.1128/JCM.02452-09] [PMID: 20335418] ], Russia [46Novikova NA, Epifanova NV, Fedorova OF, Golitsyna LN, Kupriianova NV. [Detection of picobirnaviruses by electrophoresis of RNA in polyacrylamide gel]. Vopr Virusol 2003; 48(6): 41-3.
[PMID: 14708231] ], Thailand [47Wakuda M, Pongsuwanna Y, Taniguchi K. Complete nucleotide sequences of two RNA segments of human picobirnavirus. J Virol Methods 2005; 126(1-2): 165-9.
[http://dx.doi.org/10.1016/j.jviromet.2005.02.010] [PMID: 15847933] ] and Australia [48Finkbeiner SR, Allred AF, Tarr PI, Klein EJ, Kirkwood CD, Wang D. Metagenomic analysis of human diarrhea: viral detection and discovery. PLoS Pathog 2008; 4(2): e1000011.
[http://dx.doi.org/10.1371/journal.ppat.1000011] [PMID: 18398449] ] that advocates circulation of the virus in several developed and developing countries of the world.

The available reports from India on PBVs in humans specify one geographical location i.e. Kolkata [49Bhattacharya R, Sahoo GC, Nayak MK, et al. Molecular epidemiology of human picobirnaviruses among children of a slum community in Kolkata, India. Infect Genet Evol 2006; 6(6): 453-8.
[http://dx.doi.org/10.1016/j.meegid.2006.02.005] [PMID: 16616879] ], the eastern part of the country. It was first reported in faecal specimens of children from a slum community [49Bhattacharya R, Sahoo GC, Nayak MK, et al. Molecular epidemiology of human picobirnaviruses among children of a slum community in Kolkata, India. Infect Genet Evol 2006; 6(6): 453-8.
[http://dx.doi.org/10.1016/j.meegid.2006.02.005] [PMID: 16616879] ], where out of the 56 diarrheic and 607 non-diarrheic samples screened, around 3.57% and 1.64% samples were found positive for PBV, respectively. Among the positive faecal specimens, both large (n=11) and small (n=1) genome pattern were observed in the PAGE analysis. Subsequently, from the same region, sporadic occurrence of this virus in humans was reported from 1999 to 2003 with detection of 21 (2.47%) positive out of 850 tested [50Bhattacharya R, Sahoo GC, Nayak MK, et al. Detection of Genogroup I and II human picobirnaviruses showing small genomic RNA profile causing acute watery diarrhoea among children in Kolkata, India. Infect Genet Evol 2007; 7(2): 229-38.
[http://dx.doi.org/10.1016/j.meegid.2006.09.005] [PMID: 17049316] ].All the positive samples were mostly taken from children which were showing acute watery diarrhea. These two reports showed the presence of both short genome profile as well as large genome profile PBV strains in India. Additionally, both reports showed diversity in human PBVs. In 2007, a report confirmed PBV infection in 2.06% of samples collected from children aged below 5 years [51Ganesh B, Nataraju SM, Rajendran K, et al. Detection of closely related Picobirnaviruses among diarrhoeic children in Kolkata: evidence of zoonoses? Infect Genet Evol 2010; 10(4): 511-6.
[http://dx.doi.org/10.1016/j.meegid.2010.02.008] [PMID: 20178864] ]. Majority of the PBVs however, showed large genomic profile (n=22) as compared to the virus with small profile (n=1). These diverse sequence heterogeneity among the human PBVs belongto both GG-I and GG-II.

On molecular characterization of PBV positive samples from India in different studies, it was evident that PBV genogroup I is predominant in humans. Initial report of PBV in India, confirmed that genogroup I was more in asymptomatic (n=4) and symptomatic (n=1) cases and genogroup II was only diarrheic case [49Bhattacharya R, Sahoo GC, Nayak MK, et al. Molecular epidemiology of human picobirnaviruses among children of a slum community in Kolkata, India. Infect Genet Evol 2006; 6(6): 453-8.
[http://dx.doi.org/10.1016/j.meegid.2006.02.005] [PMID: 16616879] ]. Whereas, the subsequent study showed almost equal distribution of genogroup I (n=6) and genogroup II (n=5) but the study performed in 2007 showed higher prevalence of genogroup I (13/23) than genogroup II [50Bhattacharya R, Sahoo GC, Nayak MK, et al. Detection of Genogroup I and II human picobirnaviruses showing small genomic RNA profile causing acute watery diarrhoea among children in Kolkata, India. Infect Genet Evol 2007; 7(2): 229-38.
[http://dx.doi.org/10.1016/j.meegid.2006.09.005] [PMID: 17049316] ]. Although the presence of genogroup I as mixed infection was also reported from a diarrheic sample PBV/Human/INDIA/GPBV6/2007, in which 4 strains were from genogroup I and one strain from genogroup II was observed, suggesting intricate genetic reassortment and recombination episodes within the human PBV population [52Ganesh B, Nagashima S, Ghosh S, et al. Detection and molecular characterization of multiple strains of Picobirnavirus causing mixed infection in a diarrhoeic child: Emergence of prototype Genogroup II-like strain in Kolkata, India. Int J Mol Epidemiol Genet 2011; 2(1): 61-72.
[PMID: 21537403] ]. Further, based on the sequence analysis and phylogenetic studies of several human PBV of genogroup I origin, it was found that they are closely related to the genogroup I strains of porcine origin which were earlier reported from Hungary, Venezuela and Argentina. This report also pointed towards the possibility of viral zoonoses from different animal species to human [52Ganesh B, Nagashima S, Ghosh S, et al. Detection and molecular characterization of multiple strains of Picobirnavirus causing mixed infection in a diarrhoeic child: Emergence of prototype Genogroup II-like strain in Kolkata, India. Int J Mol Epidemiol Genet 2011; 2(1): 61-72.
[PMID: 21537403] ]. The presence of PBV as co-infection was also reported in the Indian studies discussed above, where PBV was associated with rotavirus (n = 3) or astrovirus (n = 3) or both (n=1) [49Bhattacharya R, Sahoo GC, Nayak MK, et al. Molecular epidemiology of human picobirnaviruses among children of a slum community in Kolkata, India. Infect Genet Evol 2006; 6(6): 453-8.
[http://dx.doi.org/10.1016/j.meegid.2006.02.005] [PMID: 16616879] , 50Bhattacharya R, Sahoo GC, Nayak MK, et al. Detection of Genogroup I and II human picobirnaviruses showing small genomic RNA profile causing acute watery diarrhoea among children in Kolkata, India. Infect Genet Evol 2007; 7(2): 229-38.
[http://dx.doi.org/10.1016/j.meegid.2006.09.005] [PMID: 17049316] ] and Salmonella spp. (n = 1) [50Bhattacharya R, Sahoo GC, Nayak MK, et al. Detection of Genogroup I and II human picobirnaviruses showing small genomic RNA profile causing acute watery diarrhoea among children in Kolkata, India. Infect Genet Evol 2007; 7(2): 229-38.
[http://dx.doi.org/10.1016/j.meegid.2006.09.005] [PMID: 17049316] ]. However, no co-infection with norovirus, sapovirus or adenovirus or with parasites (Cryptosporidium spp., Giardia spp., Entamoeba spp., helminths) or bacteria (Vibrio spp., Shigella spp., Escherichia coli) was seen.

Though first report of PBV infection in bovines emerged from Russia in the year 1989 [22Vanopdenbosch E, Wellemans G. Birna-type virus in diarrhoeic calf faeces. Vet Rec 1989; 125(24): 610.
[PMID: 2609497] ], reports on their prevalence remained obscured for a long time. PBVs were found in neonatal calves as sub-clinical infections along with Cryptosporidium parvum [53Villacorta I, Peeters JE, Vanopdenbosch E, Ares-Mazás E, Theys H. Efficacy of halofuginone lactate against Cryptosporidium parvum in calves. Antimicrob Agents Chemother 1991; 35(2): 283-7.
[http://dx.doi.org/10.1128/AAC.35.2.283] [PMID: 2024962] ]. In the year 2003, Buzinaro and colleagues while determining the incidence of group A rotavirus (RVA) in dairy herds of Sao Paulo Brazil came to know the existence of this bi-segmented virus in four samples [23Buzinaro MG, Freitas PP, Kisiellius JJ, Ueda M, Jerez JA. Identification of a bisegmented double-stranded RNA virus (picobirnavirus) in calf faeces. Vet J 2003; 166(2): 185-7.
[http://dx.doi.org/10.1016/S1090-0233(03)00031-5] [PMID: 12902184] ]. In 2003, Novikova and co-workers discovered this virus from faeces of a calf along with 3 cases of diarrhea in children in Russia [46Novikova NA, Epifanova NV, Fedorova OF, Golitsyna LN, Kupriianova NV. [Detection of picobirnaviruses by electrophoresis of RNA in polyacrylamide gel]. Vopr Virusol 2003; 48(6): 41-3.
[PMID: 14708231] ]. A recent study in the year 2016 in Brazil reported small genome profile and the first sequence report from the American continent in bovine host [29Takiuchi E, Macedo R, Kunz AF, et al. Electrophoretic RNA genomic Profiles of Brazilian Picobirnavirus (PBV) strains and molecular characterization of a PBV isolated from diarrheic calf. Virus Res 2016; 211: 58-63.
[http://dx.doi.org/10.1016/j.virusres.2015.09.022] [PMID: 26435337] ].

The first detection of bovine PBV from India is attributed to the unanticipated discovery of this bi-segmented dsRNA virus strain, RUBV-P, in a one month old diarrheic calf. Molecular characterization of the strain RUBV-P for its full length gene segment 2 revealed distant genetic relatedness to other genogroup I PBVs of other animal species. Due to lack of sequence availability it was not possible to assess the genetic heterogeneity among bovine PBVs [24Ghosh S, Kobayashi N, Nagashima S, Naik TN. Molecular characterization of full-length genomic segment 2 of a bovine picobirnavirus (PBV) strain: evidence for high genetic diversity with genogroup I PBVs. J Gen Virol 2009; 90(Pt 10): 2519-24.
[http://dx.doi.org/10.1099/vir.0.013987-0] [PMID: 19587136] ]. Subsequently, in one of our study carried out during 2007-2010 from subtropical (central India) and western Himalayan area of Uttarakhand, 136 faecal samples from buffalo (n=122) and cow calves (n=14) were screened for PBV. Among the five PBV samples identified, three were from buffalo calves and one from cow calf exhibiting acute diarrhea, while one sample was from a non-diarrheic buffalo calf. This report of PBV infection in diarrheic calves was based on RNA-PAGE analysis therefore sequence based assessment cannot be established with these samples [25Malik YS, Chandrashekar KM, Sharma K, et al. Picobirnavirus detection in bovine and buffalo calves from foothills of Himalaya and Central India. Trop Anim Health Prod 2011; 43(8): 1475-8.
[http://dx.doi.org/10.1007/s11250-011-9834-0] [PMID: 21479844] ]. Later on, we detected a buffalo PBV isolate from Maharashtra, India (PBV-B18) of genogroup I exhibiting very less homology of 44.5% and 45.1% at nucleotide and amino acid levels, respectively, with the prototype human PBV strain of GG I (1-CHN-97/AF246939). To note, this buffalo PBV isolate (B18) showed less homology with the previously reported bovine PBV strain from India (RUBV-P/GG-I/2005/GQ221268) suggesting this unique PBV isolate may represent an emerging heterogeneous group of virus with a new lineage [26Malik YS, Kumar N, Sharma K, et al. Molecular characterization of a genetically diverse bubaline picobirnavirus strain, India. Wetchasan Sattawaphaet 2013; 43: 609-13.]. In 2013, Mondal and co-workers also reported the presence of PBV infection in diarrheic buffalo and cattle calves along with co-infection of rotavirus though RNA-PAGE analysis [27Mondal A, Chakravarti S, Majee SB, Bannalikar AS. Detection of picobirnavirus and rotavirus in diarrhoeic faecal samples of cattle and buffalo calves in Mumbai metropolis, Western India. Vet Ital 2013; 49(4): 357-60.
[PMID: 24362776] ]. The same author described the presence of GG-I type PBV in diarrheic calves from West Bengal, India [28Mondal A, Joardar SN. Detection of Genogroup I Picobirnavirus in Diarrhoeic Faecal Samples of Calves from West Bengal, India. J Immunol Immunopathol 2014; 16: 40-3.
[http://dx.doi.org/10.5958/0973-9149.2014.01076.4] ]. These reports of PBV infection in diarrheic buffalo calves expanded our knowledge regarding the host range and their geographical distribution. In March 2012, a surveillance study on enteric viruses reported a unique bovine PBV isolate (HP-7) from diarrheic calves which carried dual infection of GG-I and GG-II genogroup [54Malik YS, Sharma AK, Kumar N, Sharma K, Ganesh B, Kobayashi N. Identification and characterisation of a novel genogroup II picobirnavirus in a calf in India. Vet Rec 2014; 174(11): 278.
[http://dx.doi.org/10.1136/vr.102065] [PMID: 24570405] ]. Upon sequence analysis, it was found that HP-7-I was closer to Hungarian human PBV (Accession number AJ504796) and Brazilian canine PBV (Accession number FJ164032) isolates respectively. Whereas, HP-7-II was alike Indian human PBV (Accession number AB517738). This report supported the fact of finding frequent mixed infection of PBVs comprising both genotypes in humans and porcine population [52Ganesh B, Nagashima S, Ghosh S, et al. Detection and molecular characterization of multiple strains of Picobirnavirus causing mixed infection in a diarrhoeic child: Emergence of prototype Genogroup II-like strain in Kolkata, India. Int J Mol Epidemiol Genet 2011; 2(1): 61-72.
[PMID: 21537403] , 55Smits SL, Poon LL, van Leeuwen M, et al. Genogroup I and II picobirnaviruses in respiratory tracts of pigs. Emerg Infect Dis 2011; 17(12): 2328-30.
[http://dx.doi.org/10.3201/eid1712.110934] [PMID: 22172405] ].

The earliest report of PBV infection in pigs dates back in 1989 when this dsRNA virus was discovered by polyacrylamide gel electrophoresis in Brazil [17Gatti MS, de Castro AF, Ferraz MM, Fialho AM, Pereira HG. Viruses with bisegmented double-stranded RNA in pig faeces. Res Vet Sci 1989; 47(3): 397-8.
[PMID: 2687991] ]. Bi-segmented banding pattern confirmed the presence of PBV infection which was also observed during the investigation of intestinal content from human, pigmy rice rats and guinea pig. Consecutively, in successive years detection of this bi-segmented pathogen was also observed in different diagnostic labs of UK [18Chasey D. Porcine picobirnavirus in UK? Vet Rec 1990; 126(18): 465.
[PMID: 2356603] ] followed by various Latin American studies on porcine PBV in Venezuela [19Ludert JE, Hidalgo M, Gil F, Liprandi F. Identification in porcine faeces of a novel virus with a bisegmented double stranded RNA genome. Arch Virol 1991; 117(1-2): 97-107.
[http://dx.doi.org/10.1007/BF01310495] [PMID: 2006903] , 56Carruyo GM, Mateu G, Martínez LC, et al. Molecular characterization of porcine picobirnaviruses and development of a specific reverse transcription-PCR assay. J Clin Microbiol 2008; 46(7): 2402-5.
[http://dx.doi.org/10.1128/JCM.00655-08] [PMID: 18508933] , 57Núñez GMC, Aristiguieta ACA, Fraire FL, Leon JEL. Porcine picobirnavirus infection in Venezuelan farms 2014; 24], Brazil [58Alfieri AA, Alfieri AF, de Freitas JC, et al. Ocurrence of Escherichia Coli, rotavirus, picobirnavirus and Cryptosporidium Parvum in a postweaning diarrhoea focus in swine. Semin Cienc Agrar 1994; 15: 5-7.], Argentina [59Martínez LC, Masachessi G, Carruyo G, et al. Picobirnavirus causes persistent infection in pigs. Infect Genet Evol 2010; 10(7): 984-8.
[http://dx.doi.org/10.1016/j.meegid.2010.06.004] [PMID: 20601172] , 60Giordano MO, Martinez LC, Masachessi G, et al. Evidence of closely related picobirnavirus strains circulating in humans and pigs in Argentina. J Infect 2011; 62(1): 45-51.
[http://dx.doi.org/10.1016/j.jinf.2010.09.031] [PMID: 20888858] ] which has also reported this virus in due course of detecting various other enteric pathogens or working specifically for PBV diagnosis. A study in Hungary also elaborated the possibility of interspecies transmission among the porcine and human PBV strains [20Bányai K, Martella V, Bogdán A, et al. Genogroup I picobirnaviruses in pigs: Evidence for genetic diversity and relatedness to human strains. J Gen Virol 2008; 89(Pt 2): 534-9.
[http://dx.doi.org/10.1099/vir.0.83134-0] [PMID: 18198385] ]. The PBV isolates detected in Venezuela, Argentina and Hungary were closely related to human GG-I PBVs [20Bányai K, Martella V, Bogdán A, et al. Genogroup I picobirnaviruses in pigs: Evidence for genetic diversity and relatedness to human strains. J Gen Virol 2008; 89(Pt 2): 534-9.
[http://dx.doi.org/10.1099/vir.0.83134-0] [PMID: 18198385] , 56Carruyo GM, Mateu G, Martínez LC, et al. Molecular characterization of porcine picobirnaviruses and development of a specific reverse transcription-PCR assay. J Clin Microbiol 2008; 46(7): 2402-5.
[http://dx.doi.org/10.1128/JCM.00655-08] [PMID: 18508933] , 60Giordano MO, Martinez LC, Masachessi G, et al. Evidence of closely related picobirnavirus strains circulating in humans and pigs in Argentina. J Infect 2011; 62(1): 45-51.
[http://dx.doi.org/10.1016/j.jinf.2010.09.031] [PMID: 20888858] ]. In 2011, Smits and colleagues reported the PBV infection in respiratory tracts of pigs, signifying their role as respiratory pathogens [55Smits SL, Poon LL, van Leeuwen M, et al. Genogroup I and II picobirnaviruses in respiratory tracts of pigs. Emerg Infect Dis 2011; 17(12): 2328-30.
[http://dx.doi.org/10.3201/eid1712.110934] [PMID: 22172405] ]. While working on a Porcine PBV strain 221/04-16, Banyai and co-workers also demonstrated that due to high degree of insertions/deletions in the PBV genome are responsible for short and long type of genome segments resulting in sequence length heterogeneity [61Bányai K, Potgieter C, Gellért Á, et al. Genome sequencing identifies genetic and antigenic divergence of porcine picobirnaviruses. J Gen Virol 2014; 95(Pt 10): 2233-9.
[http://dx.doi.org/10.1099/vir.0.057984-0] [PMID: 24584476] ]. These reports regarding the presence of multiple PBV strains present in pigs also emerged from China in the year 2014 [62Chen M, Sun H, Lan D, et al. Molecular detection of genogroup I and II picobirnaviruses in pigs in China. Virus Genes 2014; 48(3): 553-6.
[http://dx.doi.org/10.1007/s11262-014-1058-8] [PMID: 24682937] ]. Reports emerged in Thailand where diarrheic and non-diarrheic piglets were found to possess the PBV infection along with co-infection of group A rotavirus (RVA) and bocavirus (BoV), all PBV strains were belonged to GG-I genogroup and phylogenetically they were close to Chinese PBV strains [63Wilburn L, Yodmeeklin A, Kochjan P, et al. Molecular detection and characterization of picobirnaviruses in piglets with diarrhea in Thailand. Arch Virol 2017; 162(4): 1061-6.
[http://dx.doi.org/10.1007/s00705-016-3190-3] [PMID: 28032197] ].

The first detection and molecular characterization of porcine PBV (BG-Por-2/2010 and BG-Por-7/ 2010) was reported from a piggery located in an urban slum at Kolkata, India [64Ganesh B, Bányai K, Kanungo S, Sur D, Malik YS, Kobayashi N. Detection and molecular characterization of porcine picobirnavirus in feces of domestic pigs from kolkata, India. Indian J Virol 2012; 23(3): 387-91.
[http://dx.doi.org/10.1007/s13337-012-0106-z] [PMID: 24293831] ]. The phylogenetic analysis revealed genetic similarity to different porcine and human GG-I PBVs from different geographical regions. In 2016, Porcine PBV infection was reported from North Eastern Region of India with strains having varied diversity and were not found to be closely associated with any other Indian isolates of PBVs so far [21Kylla H, Dutta TK, Roychoudhury P, Malik YS, Mandakini R, Subudhi PK. Prevalence and molecular characterization of porcine Picobirnavirus in piglets of North East Region of India. Trop Anim Health Prod 2017; 49(2): 417-22.
[http://dx.doi.org/10.1007/s11250-016-1210-7] [PMID: 27987110] ]. The study also claims that PBV infections are higher in acute summer and winter seasons compared to spring and autumn seasons with high prevalence recorded in cross breed pigs in contrast to local breeds.

With the availability of high end instruments and state-of-art techniques, PBVs have been detected in several un-common animal species throughout the world. In 2015, researchers explored the virome of 458 rhesus macaques collected from different geographical areas of neighboring country Bangladesh [65Anthony SJ, Islam A, Johnson C, et al. Non-random patterns in viral diversity. Nat Commun 2015; 6: 8147.
[http://dx.doi.org/10.1038/ncomms9147] [PMID: 26391192] ]. They applied the combination of consensus PCR (cPCR) along with High Throughput Sequencing (HTS) to characterize 184 viruses from 14 virus families. Out of them all, 120 were PBV of the 184 viruses found in these animals which showed the presence of this bipartite virus in the population of nearby primate population. Moreover these free ranging macaques are usually found near the human settlements and therefore the risk of zoonoses cannot be ruled out. Earlier, high incidence of PBV infection in asymptomatic primates was also observed in Argentina where individually caged orangutans were diagnosed with persistent PBV infections over the span of three years [66Masachessi G, Ganesh B, Martinez LC, et al. Maintenance of picobirnavirus (PBV) infection in an adult orangutan (Pongo pygmaeus) and genetic diversity of excreted viral strains during a three-year period. Infect Genet Evol 2015; 29: 196-202.
[http://dx.doi.org/10.1016/j.meegid.2014.11.019] [PMID: 25435283] ]. Application of metagenomics sometime reveals unknown pathogens in unusual hosts and gives a comprehensive picture regarding genetic map of those pathogens, similar study was performed in Portugal in 2015 where PBV infection was found in wolves [67Conceição-Neto N, Mesquita JR, Zeller M, et al. Reassortment among picobirnaviruses found in wolves. Arch Virol 2016; 161(10): 2859-62.
[http://dx.doi.org/10.1007/s00705-016-2987-4] [PMID: 27438074] ]. This study also described the reassortment events going among PBVs in which identical capsid segments together with diverse RdRp segments were found.

Alike, a PBV strain, PBV/Horse/India/BG-Eq-3/2010, was identified in the faeces of a 10 month old weaned female foal with diarrhoea in January 2010 from Kolkata, India [31Ganesh B, Banyai K, Masachessi G, et al. Genogroup I picobirnavirus in diarrhoeic foals: can the horse serve as a natural reservoir for human infection? Vet Res (Faisalabad) 2011; 42: 52.
[http://dx.doi.org/10.1186/1297-9716-42-52] [PMID: 21414192] ]. Surprisingly, sequence comparison and phylogenetic analysis revealed close genetic relatedness to a human genogroup I PBV strain (Hu/GPBV1) detected earlier from the same part of India.

Using RT-PCR assay, PBV has been detected in 2.4% (3/125) and 3% (3/100) diarrheic kids and lambs fecal samples, respectively, from July, 2013 – February 2014 in Northern parts of India. Three PBV isolates, each from caprine and ovine species were typed as genogroup I (GGI) while two ovine isolates were typed as genogroup II (GGII). Even in one of the ovine samples both genogroups were found as a mixed infection (Unpublished data).

PBVs have also been defined to be present as persistent infection in captive animal species which expanded our knowledge regarding the host range of this virus [68Masachessi G, Martínez LC, Giordano MO, et al. Picobirnavirus (PBV) natural hosts in captivity and virus excretion pattern in infected animals. Arch Virol 2007; 152(5): 989-98.
[http://dx.doi.org/10.1007/s00705-006-0900-2] [PMID: 17245535] ]. Although the diagnosis method applied in that study was RNA-PAGE which has lower sensitivity then RT-PCR therefore the number of PBV positive species could have been more if RT-PCR assay would have been applied. Similarly, PBV infection in captive feline species was also described in 2012 in Uruguay where four different feline species were found to possess the PBV infection [69Gillman L, Sánchez AM, Arbiza J. Picobirnavirus in captive animals from Uruguay: identification of new hosts. Intervirology 2013; 56(1): 46-9.
[http://dx.doi.org/10.1159/000338275] [PMID: 22759924] ]. In 2009, a report emerged from Brazil in which further investigation on captive species like Wistor rats, snakes and domestic dogs was carried out to characterize PBV from these species and they applied the RT-PCR diagnosis method to diagnose the infection [70Fregolente MCD, de Castro-Dias E, Martins SS, Spilki FR, Allegretti SM, Gatti MSV. Molecular characterization of picobirnaviruses from new hosts. Virus Res 2009; 143(1): 134-6.
[http://dx.doi.org/10.1016/j.virusres.2009.03.006] [PMID: 19463731] ]. This study shed more light on co-circulation of PBV in different hosts and identified snakes as a new host for PBVs. Following reports of PBV infection in different hosts Woo and colleagues discovered a novel PBV in feces of Calfornia Sea Lions and prosed a new species as otarine PBV for which they published the whole genome [71Woo PC, Lau SK, Bai R, et al. Complete genome sequence of a novel picobirnavirus, otarine picobirnavirus, discovered in California sea lions. J Virol 2012; 86(11): 6377-8.
[http://dx.doi.org/10.1128/JVI.00686-12] [PMID: 22570247] ]. These reports contributed in the understanding that PBV infections are persistent in symptomatic as well as asymptomatic animals which includes both mammals and birds [72Masachessi G, Martinez LC, Ganesh B, et al. Establishment and maintenance of persistent infection by picobirnavirus in greater rhea (Rhea Americana). Arch Virol 2012; 157(11): 2075-82.
[http://dx.doi.org/10.1007/s00705-012-1400-1] [PMID: 22782138] ]. Studies on domesticated birds like turkey and broilers have also reported the diagnosis of PBV infection in USA and Brazil [73Verma H, Mor SK, Erber J, Goyal SM. Prevalence and complete genome characterization of turkey picobirnaviruses. Infect Genet Evol 2015; 30: 134-9.
[http://dx.doi.org/10.1016/j.meegid.2014.12.014] [PMID: 25530436] , 74Ribeiro Silva R, Bezerra DAM, Kaiano JHL, et al. Genogroup I avian picobirnavirus detected in Brazilian broiler chickens: a molecular epidemiology study. J Gen Virol 2014; 95(Pt 1): 117-22.
[http://dx.doi.org/10.1099/vir.0.054783-0] [PMID: 24108140] ]. In 2014, a thorough NGS study on camel feces revealed huge abundance of PBV infection co-infecting the camel population along with other viral pathogens [75Woo PC, Lau SK, Teng JL, et al. Metagenomic analysis of viromes of dromedary camel fecal samples reveals large number and high diversity of circoviruses and picobirnaviruses. Virology 2014; 471-473: 117-25.
[http://dx.doi.org/10.1016/j.virol.2014.09.020] [PMID: 25461537] ]. Keeping in mind the findings of Woo and colleagues, in 2016 we diagnosed PBV infection in captive camel population of Gujarat state where 93.10% of samples were found positive with no diarrheic symptoms (Unpublished data). Likewise, a comprehensive molecular epidemiological study was conducted in several mammalian species of terrestrial and marine habitat in Hong Kong revealed high diversity among different mammals [76Woo PC, Teng JL, Bai R, et al. High diversity of genogroup I picobirnaviruses in mammals. Front Microbiol 2016; 7: 1886.
[http://dx.doi.org/10.3389/fmicb.2016.01886] [PMID: 27933049] ]. These studies expanded our knowledge regarding the increase in host range of PBV’s and their greater susceptibility to domesticated, terrestrial as well as marine mammalian species. The risk of species jumping among different PBV strains is an alarming condition which can be addressed by continuous surveillance of this virus in different mammalian and avian species.

The total number of nucleotide submission of PBV from different species are very few from India (n=87) (Table 1). Out of the 87 sequences only one sequence is having complete information of RdRp gene (Segment 2).

Table 1
Total number of nucleotide submissions in GenBank for picobirnavirus from India.

Sequences from different species of Indian PBV population were phylogenetically analyzed using the MEGA 6.0 software applying the General Time Reversible model along with Gamma distribution which was used to model evolutionary rate differences among sites [77Tamura K, Stecher G, Peterson D, Filipski A, Kumar S. MEGA6: molecular evolutionary genetics analysis version 6.0. Mol Biol Evol 2013; 30(12): 2725-9.
[http://dx.doi.org/10.1093/molbev/mst197] [PMID: 24132122] ]. The analysis included 53 sequences comprising the reference sequences of PBV for GG-I and GG-II (Fig. 1). Huge diversity was observed within the Indian PBV sequences when they were phylogenetically analyzed suggesting species jumping with no specific host among the Indian PBV population. Although the available GG-I and GG-II sequences had formed a separate clade (Fig. 1). The bipartite nature of PBVs renders them as possible candidates for further recombination and reassortment among the different isolates [20Bányai K, Martella V, Bogdán A, et al. Genogroup I picobirnaviruses in pigs: Evidence for genetic diversity and relatedness to human strains. J Gen Virol 2008; 89(Pt 2): 534-9.
[http://dx.doi.org/10.1099/vir.0.83134-0] [PMID: 18198385] , 43Bányai K, Jakab F, Reuter G, et al. Sequence heterogeneity among human picobirnaviruses detected in a gastroenteritis outbreak. Arch Virol 2003; 148(12): 2281-91.
[http://dx.doi.org/10.1007/s00705-003-0200-z] [PMID: 14648286] ]. A recent report has also confirmed and speculated that animal and human PBV strains can re-assort independently [67Conceição-Neto N, Mesquita JR, Zeller M, et al. Reassortment among picobirnaviruses found in wolves. Arch Virol 2016; 161(10): 2859-62.
[http://dx.doi.org/10.1007/s00705-016-2987-4] [PMID: 27438074] ].

Fig. (1) Phylogram display genetic diversity between different Picobirnavirus populations in India.

Further, to confirm the species diversity among Indian PBV isolates, the dataset was analyzed using the SplitsTree4 software package [78Huson DH, Bryant D. Application of phylogenetic networks in evolutionary studies. Mol Biol Evol 2006; 23(2): 254-67.
[http://dx.doi.org/10.1093/molbev/msj030] [PMID: 16221896] ]. The Minimum Spanning Network applied to the dataset bifurcated the isolates into two major Indian PBV populations which shows a bigger network comprising of human, bovine, porcine and equine isolates reported till date whereas, the smaller population comprises majorly of human PBV isolates with only one bovine PBV strain RUBV-P also clustering along with these human strains (Fig. 2). The recently proposed GG-III genogroup isolate from Netherlands (VS6600008) also clustered within this bunch of human origin PBV isolates.

Fig. (2) Minimum spanning network exhibiting diversity between Indian Picobirnavirus isolates.

Interestingly, in this analysis a bovine PBV (PTN-P120) isolate emerged as a pivotal strain from where two major clusters were seemed to have emerged in the Indian PBV population. The reference strain for GG-II PBV (4-GA-91) was again distantly placed beside the Indian human PBV strain (GPBV6G2) from Kolkata which also belong to GG-II genogroup. Rest all other strains pertaining to GG-I and GG-II were clustered inside the major constellation of Indian PBV isolates. The analysis suggested that these all isolates are resultant of species jumping, where GG-I and GG-II sequences were seemed to have co-evolved with each other having no clear ancestor among them.

Nevertheless, due to limited epidemiological data available on PBVs in Indian human and animal population we can’t approach to a concrete conclusion regarding the evolution, host-virus relationship and the infection pattern of PBV in Indian perspective.