Introducing Influenza D: International Committee on Taxonomy of Viruses Names New Virus

The International Committee on Taxonomy of Viruses recently approved the naming of influenza D virus as a new species. The committee announced the new species and assigned it a new genus in the Orthomyxoviridae family, distinct from influenza A, B and C viruses. The virus was first identified and characterized by researchers at South Dakota State University, including Drs. Ben Hause, Feng Li, and Radhey Kaushik.

Although it was first isolated from a diseased pig in 2011, this virus is notable for being the first influenza virus identified in cattle. Cattle from the same farm as the original pig isolate were tested and showed evidence of past infection, and additional scientific sleuthing revealed cows as the primary reservoir. Since then, influenza D virus has been isolated from cattle in several countries including China, France, and the United States, and antibodies against the virus have been found in sheep and goats. Surveillance of cattle in Mississippi by Dr. Richard Webby and colleagues at SJCEIRS resulted in several virus isolates and multiple positive serum samples. Researchers at SJCEIRS also demonstrated that the virus could be transmitted between cattle in close contact, which supports the hypothesis that cattle are a natural reservoir. Unlike influenza A, influenza D virus does not infect poultry and appears to have only limited spillover to pigs. Much of the origin and ecology of influenza D virus remains unknown. Researchers do not yet know how or when it first emerged, but analysis of archived serum samples by SJCEIRS suggests that influenza D virus has been circulating in cattle since at least 2004. Influenza D virus infections in cattle also tend to be associated with other respiratory infections, particularly pneumonia, but the significance is not known.

From the limited number samples collected so far, researchers identified two distinct viral lineages which vary in their specificity for binding the sialic acid receptors found throughout the airway. The bovine-lineage viruses have much broader specificity, binding both α-2,6 and α-2,3 sialic acids in the upper and lower respiratory tract. The other lineage has more narrow specificity, though it is unclear how the viruses’ binding specificity impacts virus pathology or transmission.

Perhaps the greatest unknown is whether influenza D virus poses an emerging public health concern, though it is not known to cause disease in humans. However, it is distantly related to influenza C virus, which does cause mild infections in people. Studies in animal models are currently underway to compare outcomes of infection between bovine influenza D and human influenza C virus. Ultimately, little known about the biology of the virus, leaving many unanswered questions ripe for future research.

Links to other sources about the newly named influenza D virus: