Host Range, Biology, and Species Specificity of Seven-Segmented Influenza Viruses—A Comparative Review on Influenza C and D

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.

Antiviral Susceptibilities of Distinct Lineages of Influenza C and D Viruses

“…Influenza C virus was first isolated from humans in 1947 [ 36 ] and is widely distributed throughout the world. It infects humans, dogs, swine, camels, horses, and bovines, although humans are the primary host [ 37 ]. Influenza C virus causes relatively mild respiratory illness; however, it can cause bronchitis and pneumonia, particularly in children younger than 2 years or patients with underlying illnesses [ 38 , 39 , 40 , 41 , 42 ].…”

“…Since then, the virus has been detected in bovines in several countries including USA, Mexico, France, Japan, Italy, China, and Ireland [ 43 , 44 , 45 , 46 , 47 , 48 ]. Global serological studies have shown that influenza D virus has a broad host range, including humans, swine, sheep, goats, camels, horses, and bovines, although the primary host of influenza D virus is bovines [ 37 ].…”

Existing Evidence for Influenza B Virus Adaptations to Drive Replication in Humans as the Primary Host

“…ICV and IDV also bind to a chemically different receptor than IBV or IAV [ 103 , 104 , 105 ]. Wider natural host ranges for ICV and IDV compared to IBV have been described [ 106 ]. Unfortunately, little is known mechanistically about the host restriction factors for ICV or IDV.…”

Time-resolved characterization of the innate immune response in the respiratory epithelium of human, porcine, and bovine during influenza virus infection

“…Both ICV and IDV utilize the same receptor determinant to enter the host cell, however both viruses have distinct host reservoirs; human for ICV and bovine for IDV (8,9,12,(16)(17)(18). Nonetheless, despite the common receptor determinant usage, IDV has shown to have a broader host tropism compared to ICV, suggesting that other factors might play a dominant role in cross-species virus transmission (7).…”

“…Interestingly, both the ICV and IDV HEF glycoproteins can bind to the luminal surface of human, porcine, and bovine respiratory epithelium, although both viruses noticeably differ in their respective host tropism (7). ICV is predominantly a human pathogen, causing respiratory diseases in infants and children, and has sporadically been associated with respiratory infections in swine and cattle (8)(9)(10)(11). In contrast, IDV exhibits an intrinsic broad host tropism among different livestock (12)(13)(14)(15), with cattle as the main host reservoir (12,(16)(17)(18), and was shown to have a zoonotic potential (19)(20)(21)(22)(23)(24).…”