Researchers Discover New Virus Called Influenza D

We hear a lot about influenza types A and B every year when flu season approaches, and occasionally about the less severe type C. Now researchers have identified a new form of the virus—influenza D.

The announcement of this new flu comes from the South Dakota State University research team who first isolated the virus in a diseased pig in Oklahoma in 2011. A study on their findings now appears in the American Society for Microbiology journal. Five years after their initial discovery of the new genus in the Orthomyxoviridae family, with a single species the team dubbed influenza D, and the executive committee of the International Committee of Taxonomy of Viruses has given their approval to the naming.

Funding for the research on the biology, genetics, and evolution of the new virus came from a nearly $400,000 grant from the National Institutes of Health, secured by university professors Feng Li, PhD, DVM, and Radhey Kaushik, BV Sc., AH, PhD. In their initial findings, the research team noted pigs exhibiting symptoms such as mild respiratory illness, from what they observed to be an influenza C-like virus. Humans are the natural reservoir for type C flu, which on rare occasions has been found in pigs and dogs, so the study authors say their initial findings raised many questions about whether current understanding of influenza C is correct.

“It is unclear why influenza D virus was found only in 2011, not earlier,” says study author Dr. Li. “This virus has been around for some time. It can be traced back as early as in 2002 but may have been with us for hundreds of years already. Since 2011, the new virus has been frequently detected in worldwide bovines or pigs with influenza-like symptoms.”

Although the initial finding of the novel influenza virus appeared in a pig, routine testing of nasal swabs from pigs challenged the researchers’ early theory that swine is the primary host of the virus. After taking nasal swab samples from 45 animals in six states, the scientists traced the primary reservoir for the virus back to cattle, making this the first influenza type detected in cattle. Analysis of samples taken from cows, sheep, and goats showed that eight samples from Oklahoma and Minnesota came up positive for the new virus. Through genome sequencing of samples taken from the bovine herds, they discovered that the virus was genetically and antigenically distinct from influenzas type A, B, and C, though it has about a 53% similarity to type C.

In their study, the researchers note that poultry are not affected by the new virus, though it is surprisingly widespread in bovine herds. The study authors emphasize that while influenza D has not been found in humans, they don’t yet know if the virus could impact human health. Modeling for human influenza virus pathogenesis studies suggests this pathogen has the potential to cause disease in humans, say the authors. The presence of this new virus in cattle and its presumptive spillover to swine, both of which live in close proximity to humans, further highlights its potential threat to human health, which the authors say merits further studies.

“Viruses such as influenza D viruses with bovine origin to which humans have no preexisting immunity may pose a potential risk to human health if jumping to humans,” says Dr. Li. “A recent human study provided serological evidence of influenza D virus infections in humans, or zoonosis, especially in those who were exposed to bovines infected with the virus. However, little is still known whether influenza D virus can cause disease in humans.”