Interspecies transmission and emergence of novel viruses: lessons from bats and birds

Abstract

As exemplified by coronaviruses and influenza viruses, bats and birds are natural reservoirs for providing viral genes during evolution of new virus species and viruses for interspecies transmission. These warm-blooded vertebrates display high species biodiversity, roosting and migratory behavior, and a unique adaptive immune system, which are favorable characteristics for asymptomatic shedding, dissemination, and mixing of different viruses for the generation of novel mutant, recombinant, or reassortant RNA viruses. The increased intrusion of humans into wildlife habitats and overcrowding of different wildlife species in wet markets and farms have also facilitated the interspecies transmission between different animal species.

Keywords: RNA virus; coronavirus; emerging infectious disease; influenza; virus evolution.

Figure 1

The divergence of coronaviruses into Alphacoronavirus, Betacoronavirus, Gammacoronavirus, and Deltacoronavirus is estimated to have occurred approximately 5000 years ago. This tree was generated by analyzing RNA-dependent RNA polymerase (RdRp) genes under the relaxed-clock model with an uncorrelated log-normal distribution in Bayesian evolutionary analysis sampling trees (BEAST) software. Values at branch points represent the estimated timing of divergence events in numbers of years before the present. Adapted from .

Figure 2

Bats and birds as probable gene sources for the evolution of (A) coronaviruses and (B) influenza viruses, based on epidemiological, virological, and phylogenetic evidence. ‘A’, ‘B’, ‘C’, and ‘D’ represent groups A, B, C, and D in Betacoronavirus. * denotes the undetermined role of bats as reservoirs for emerging influenza viruses. † denotes the undetermined source of A(H1N1)pdm09 virus found in American badger, black-footed ferret, Bornean binturong, and skunk.? with dotted line denotes the unproven direct wild bird-to-human transmission of influenza viruses. Figure 2A is adapted from . Abbreviations: [], host receptor utilized by coronavirus; (), animal host; ACE2, angiotensin converting enzyme 2; AntlopeCoV, sable antelope coronavirus; APN, aminopeptidase N; ASA, 9-O-acetylated sialic acid; BCoV, bovine coronavirus; BuCoV HKU11, bulbul coronavirus HKU11; BWCoV-SW1, beluga whale coronavirus SW1; CCoV, canine coronavirus; CMCoV HKU21, common moorhen coronavirus HKU21; DCoV, duck coronavirus; ECoV, equine coronavirus; FIPV, feline infectious peritonitis virus; GCoV, goose coronavirus; GiCoV, giraffe coronavirus; HCoV-229E, human coronavirus 229E; MERS-CoV, Middle East respiratory syndrome coronavirus; HCoV-HKU1, human coronavirus HKU1; HCoV-NL63, human coronavirus NL63; HCoV-OC43, human coronavirus OC43; Hi-BatCoV HKU10, Hipposideros bat coronavirus HKU10; IBV, infectious bronchitis virus; MHV, murine hepatitis virus; Mi-BatCoV 1A, Miniopterus bat coronavirus 1A; Mi-BatCoV 1B, Miniopterus bat coronavirus 1B; Mi-BatCoV HKU7, Miniopterus bat coronavirus HKU7; Mi-BatCoV HKU8, Miniopterus bat coronavirus HKU8; MRCoV HKU18, magpie robin coronavirus HKU18; MunCoV HKU13, munia coronavirus HKU13; My-BatCoV HKU6, Myotis bat coronavirus HKU6; NHCoV HKU19, night heron coronavirus HKU19; PCoV, pigeon coronavirus; PEDV, porcine epidemic diarrhea virus; PhCoV, Pheasant coronavirus; PHEV, porcine hemagglutinating encephalomyelitis virus; Pi-BatCoV HKU5, Pipistrellus bat coronavirus HKU5; PorCoV HKU15, porcine coronavirus HKU15; PRCV, porcine respiratory coronavirus; RCoV, rat coronavirus; RbCoV HKU14, rabbit coronavirus HKU14; Rh-BatCoV HKU2, Rhinolophus bat coronavirus HKU2; Ro-BatCoV HKU9, Rousettus bat coronavirus HKU9; Ro-BatCoV HKU10, Rousettus bat coronavirus HKU10; Sc-BatCoV 512, Scotophilus bat coronavirus 512; TEGV, transmissible gastroenteritis virus; SARS-CoV, severe acute respiratory syndrome coronavirus; SARSr-CiCoV, SARS-related civet coronavirus; SARSr-CoV-CFB, SARS-related Chinese ferret badger coronavirus; SARSr-Rh-BatCoV HKU3, SARS-related Rhinolophus bat coronavirus HKU3; TCoV, turkey coronavirus; SpCoV HKU17, sparrow coronavirus HKU17; ThCoV HKU12, thrush coronavirus HKU12; Ty-BatCoV HKU4, Tylonycteris bat coronavirus HKU4; WECoV HKU16, white-eye coronavirus HKU16; WiCoV HKU20, wigeon coronavirus HKU20.