One of the more intriguing influenza discoveries of the past few years has been the discovery of a previously unknown type of flu - Influenza D - infecting swine, cattle, and possibly even humans as well.
We first learned of this new flu early in 2013 when researchers reported finding a novel influenza virus in swine from Oklahoma - initially classified as a novel Influenza C virus - but which would later be 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 following year, in mBio: Characterizing A Novel Influenza C Virus In Bovines & Swine, cattle were added to the list, and appeared to be the virus's primary reservoir.
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).
And while it isn't known if Influenza D can cause symptomatic illness in humans, last summer in Serological Evidence Of Influenza D Among Persons With & Without Cattle Exposure, researchers reported finding a high prevalence of antibodies against Influenza D among people with cattle exposure. They wrote:
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.
All of which serves as prelude to a new study, just published in the EID Journal, which finds Influenza D circulating widely in Guangdong Province, China, among goats, pigs, cattle, and buffalo.
They also report finding evidence of ongoing evolution of influenza D viruses in their hosts.
I've only included some excerpts from a much longer, detailed, reports. Follow the link to read it in its entirety.
Volume 23, Number 8—August 2017
Influenza D Virus in Animal Species in Guangdong Province, Southern China
Shao-Lun Zhai1Comments to Author , He Zhang1, Sheng-Nan Chen1, Xia Zhou, Tao Lin, Runxia Liu, Dian-Hong Lv, Xiao-Hui Wen, Wen-Kang Wei1, Dan Wang, and Feng Li
Molecular tests revealed influenza D viruses of D/OK lineage widely circulating in farmed animal species in Guangdong Province, southern China. In particular, we found high levels of influenza D virus infection in goats and pigs. We also detected viral RNA in serum specimens and feces of animals with certain severe diseases.
Four types of influenza viruses (A–D) have been confirmed (https://www.cdc.gov/flu/about/viruses/types.htm). The recently discovered influenza D virus is thought to cause respiratory diseases primarily in cattle and to a lesser extent in pigs (1–4). Moreover, serologic evidence for influenza D virus infection in small ruminants and humans has been established (5, 6). Since the initial influenza D virus isolation in the United States in 2011 (1), the virus has been reported in China, Mexico, France, Italy, and Japan (7–11).
Genetic analysis of the hemagglutinin-esterase-fusion gene demonstrated that these viruses had 2 distinct lineages, represented by D/OK and D/660 (12). Recently, a novel influenza D virus that emerged in Japan has been proposed as the third lineage (11). D/OK lineage–related viruses were previously identified in native Luxi yellow cattle in Shandong Province, northern China (7). Despite good progress in identifying domestic cattle as the primary reservoir of influenza D virus, we know little about prevalence in other animals. We conducted a study to clarify the origin and transmission dynamics of influenza D virus in goats, buffalo, and pigs as well as farmed cattle.
When first discovered, influenza D virus was reported in diseased pigs in the United States (1). Later, it was identified in cattle and swine herds in several other countries, with or without clinical manifestation (7–11). Moreover, antibodies to influenza D virus were detected in goats, sheep, and humans (5–6). Under experimental conditions, influenza D virus replicated and transmitted among ferrets and guinea pigs (13).
We confirmed that influenza D virus is widely present in cattle species (dairy cattle, yellow cattle, and buffalo). We also found influenza D virus at a high prevalence (> 30%) in pigs and goats (Table), which is in contrast to the low prevalence found in previous investigations (1,5,10). The high prevalence may be caused by poor biosecurity measures and high-density feeding mode practices in China’s animal industry as well as possible cross-species transmission (13). Taken together, our findings expand the host range of influenza D virus and further emphasize the health concern this virus poses to multiple animal species.
In summary, our study investigating the infection status of influenza D virus in different farmed animal species in Guangdong Province provides novel insights into the epidemiology and evolution of IDV. In particular, we document the molecular evidence for influenza D virus infection in goats and buffalo.