In early 2013 researchers reported their findings of a novel influenza virus detected in swine from Oklahoma - initially classified as a novel Influenza C virus - but which was later designated as Influenza D.
Their research – published PLoS Pathogens – was called Isolation of a Novel Swine Influenza Virus from Oklahoma in 2011 Which Is Distantly Related to Human Influenza C Viruses, and it immediately caused a stir in the flu research community.
The authors wrote:
Based on its genetic organizational similarities to influenza C viruses this virus has been provisionally designated C/Oklahoma/1334/2011 (C/OK).
Phylogenetic analysis of the predicted viral proteins found that the divergence between C/OK and human influenza C viruses was similar to that observed between influenza A and B viruses. No cross reactivity was observed between C/OK and human influenza C viruses using hemagglutination inhibition (HI) assays.Additionally, the authors found that this new (provisional) influenza C virus could infect, and transmit, in both ferrets and pigs. The authors described this new discovery as:
. . . a new subtype of influenza C viruses that currently circulates in pigs that has not been recognized previously. The presence of multiple subtypes of co-circulating influenza C viruses raises the possibility of reassortment and antigenic shift as mechanisms of influenza C virus evolution.
A little over two years ago, in mBio: Characterizing A Novel Influenza C Virus In Bovines & Swine we looked at a second paper by these same researchers, which added cattle to the list of hosts found to carry this novel virus. While still calling it an Influenza C, they wrote:
Detailed genetic, biological, and antigenic characterization suggests that C/OK viruses in cattle and swine are distinct from human ICV and likely represent a new genus in the Orthomyxoviridae family, with C/OK virus as the type species of influenza D virus.
Additionally, widespread and high antibody titers to C/OK virus and relative ease of virus isolation in cattle indicate that bovines may represent the reservoir to this novel influenza virus. The finding of C/OK virus in both swine and bovine indicates that this new virus may spread and establish infection in other mammals, including humans.
Since then, researchers have found evidence of a much wider spread of this virus (now provisionally called Influenza D) than just in the American Midwest. (see EID journal’s Influenza D Virus in Cattle, France, 2011–2014 and EID Journal: Influenza D In Cattle & Swine – Italy).
Last April, in JVI: Pathogenesis Of Influenza D in Cattle, we saw more evidence suggesting that cattle are the natural reservoir for Influenza D, and a limited test showing that ferrets exposed to contaminated fomites were not readily infected with the virus.
Still, questions remain over the zoonotic potential for Influenza D, along with its ability to reassort with other influenza viruses.
Shedding some new light on all of this, we've a study appearing in the Journal of Clinical Virology, which finds a high prevalence of antibodies against Influenza D among people with cattle exposure.
What we don't know at this time is whether human infection with Influenza D produces a symptomatic illness, or what its impact on human health is likely to be in the future.
Serologic evidence of exposure to influenza D virus among persons with occupational contact with cattle
Sarah K. White, Wenjun Ma, Clinton J. McDaniel, Gregory C. Gray, John A. Lednicky correspondenceemail
DOI: http://dx.doi.org/10.1016/j.jcv.2016.05.017 |
•Influenza D virus antibodies were detected in 34 of cattle-exposed persons (Total = 35).
•Influenza D virus antibodies were detected in 2 non-cattle exposed persons (Total = 11).
•86% of cattle-exposed individuals reported exposure to calves (Total = 35).
•Half of seropositive cattle-exposed persons reported work with sick cattle.
Influenza D virus (IDV), a novel influenza virus with proposed classification: family Orthomyxoviridae, genus Influenzavirus D, species Influenza D virus, has been associated with influenza-like illness in cattle and swine. More recently, anti-IDV antibodies have also been detected in small ruminants. A seroprevalence of approximately 1.3% has been estimated for the general human population.
To gain insights on the zoonotic potential of IDV to human adults with occupational exposure to cattle in north central Florida.
A cross-sectional serological study was performed on human serum samples from 35 cattle-exposed and 11 non-cattle-exposed adults to screen for IDV antibodies using hemagglutination inhibition (HI) and microneutralization (MN) assays.
A seroprevalence of 91% was detected via HI assay, and 97% by MN assay among individuals working with cattle in Florida. Among non-cattle-exposed individuals, seropositivity determined via MN assay (only) was lower (18%).
IDV poses a zoonotic risk to cattle-exposed workers, based on detection of high seroprevalence (94–97%). Whereas it is still unknown whether IDV causes disease in humans, our studies indicate that the virus may be an emerging pathogen among cattle-workers.