Influenza D virus is a recently identified member of the Orthomyxoviridae family. It has a segmented, negative‑sense RNA genome and primarily infects cattle and pigs, where it causes mild respiratory disease. Influenza D viruses have not been shown to cause disease in humans.
Virology & Pathogenesis
Influenza D viruses were first isolated from pigs in 2011 and later recognized as a distinct genus, Deltainfluenzavirus. Their genome contains seven RNA segments and encodes a hemagglutinin‑esterase‑fusion (HEF) glycoprotein analogous to that of influenza C virus. The HEF protein mediates receptor binding, receptor destruction and membrane fusion; it recognizes 9‑O‑acetylated sialic acid on host respiratory epithelial cells. After attachment and endocytosis, the viral genome replicates in the nucleus, and progeny virions bud from the cell surface. Influenza D viruses display limited genetic diversity compared with influenza A viruses and have been found predominantly in cattle, with serologic evidence suggesting wide circulation among bovines in many countries. Experimental infections in pigs and cattle cause mild respiratory signs, nasal discharge and occasional cough. According to the CDC, influenza D viruses primarily affect cattle and are not known to infect people to cause illness.
Host range and significance
Cattle appear to be the main reservoir for influenza D viruses, and viral RNA has been detected in respiratory secretions and dairy cattle herds worldwide. Serologic studies indicate that a high proportion of cattle have antibodies to influenza D virus, suggesting endemic infection. Swine can also be infected experimentally and in the field, and seropositivity has been reported in small ruminants such as sheep and goats. Human serologic surveys have shown low or absent antibody prevalence, and there are no confirmed cases of human disease. Nevertheless, occupational exposure to livestock may result in asymptomatic infection, and ongoing surveillance is important to assess zoonotic potential. There are currently no licensed vaccines for influenza D virus, and control in cattle relies on general biosecurity and management practices.
Influenza D virus represents a distinct branch of the orthomyxoviruses with a host range centered on cattle and swine. While its impact on human health appears negligible at present, continued monitoring of animal reservoirs and people with close livestock contact will help identify any changes in host range or pathogenicity.
Related Terms: Orthomyxoviridae, Hemagglutinin‑esterase‑fusion, Cattle, Influenza C virus, Pigs