Serologic evidence of exposure to influenza D virus among persons with occupational contact with cattle

Background: 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. Objectives: To gain insights on the zoonotic potential of IDV to human adults with occupational exposure to cattle in north central Florida. Study: 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. Results: 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%). Conclusions: 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.