Abstract
Other than genome structure, influenza C (ICV), and D (IDV) viruses with seven-segmented genomes are biologically different from the eight-segmented influenza A (IAV), and B (IBV) viruses concerning the presence of hemagglutinin–esterase fusion protein, which combines the function of hemagglutinin and neuraminidase responsible for receptor-binding, fusion, and receptor-destroying enzymatic activities, respectively. Whereas ICV with humans as primary hosts emerged nearly 74 years ago, IDV, a distant relative of ICV, was isolated in 2011, with bovines as the primary host. Despite its initial emergence in swine, IDV has turned out to be a transboundary bovine pathogen and a broader host range, similar to influenza A viruses (IAV). The receptor specificities of ICV and IDV determine the host range and the species specificity. The recent findings of the presence of the IDV genome in the human respiratory sample, and high traffic human environments indicate its public health significance. Conversely, the presence of ICV in pigs and cattle also raises the possibility of gene segment interactions/virus reassortment between ICV and IDV where these viruses co-exist. This review is a holistic approach to discuss the ecology of seven-segmented influenza viruses by focusing on what is known so far on the host range, seroepidemiology, biology, receptor, phylodynamics, species specificity, and cross-species transmission of the ICV and IDV.
Highlights
Influenza viruses, first documented in the late 16th century [1], have evolved into four major types—alphainfluenza virus, betainfluenza, gammainfluenza, and deltainfluenza viruses
This review describes the ecology of ICV and IDV by discussing the cross-species transmission, host range, phylodynamics, virus biology, species specificity, and receptor preferences
3/76 samples from 12 cattle herds in Turkey (3 weeks–6 months) affected with respiratory disease tested positive for IDV and phylogenetic analyses of hemagglutinin esterase fusion protein (HEF) protein showed that these Turkish strains shared 95% sequence identity to the European and US sequences, indicating the intercontinental transmission of IDV [92]
Summary
First documented in the late 16th century [1], have evolved into four major types—alphainfluenza virus (influenza A), betainfluenza (influenza B), gammainfluenza (influenza C), and deltainfluenza (influenza D) viruses. Domestic ruminant animals of bovine, ovine, and caprine species were unaffected, and these species are considered refractory to eight-segmented influenza A and B viruses, irrespective of a few isolated reports on isolation/seroprevalence of human/swine IAV [10,11] and IBV from cattle in the past [12]. Despite the co-circulation of several influenza strains and the growing host range of IAV that included most of the terrestrial/marine mammals over the last century, influenza A virus could not breach the avian–bovine or human–bovine, species barriers, and it can be inferred that influenza A evolution witnessed an unfavorable stance in bovine species. The ruminant species were quite susceptible to the seven-segmented influenza viruses, ICV and IDV, of which cattle have been considered as the primary reservoir for influenza D viruses. This review describes the ecology of ICV and IDV by discussing the cross-species transmission, host range, phylodynamics, virus biology, species specificity, and receptor preferences
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