Environmental Stability of Swine and Human Pandemic Influenza Viruses in Water under Variable Conditions of Temperature, Salinity, and pH

Abstract

The movement of influenza A viruses (IAVs) from wild bird reservoirs to domestic animals and humans is well established, but the transmission mechanisms that facilitate efficient movement across and within these host populations are not fully defined. Although predominant routes of transmission vary between host populations, the extent of environmental stability needed for efficient IAV transmission also may vary. Because of this, we hypothesized that virus stability would differ in response to varied host-related transmission mechanisms; if correct, such phenotypic variation might represent a potential marker for the emergence of novel animal or human influenza viruses. Here, the objective was to evaluate the ability of eight swine and six human IAV isolates to remain infective under various pH, temperature, and salinity conditions using a preestablished distilled water system. Swine and human viruses persisted longest at near-neutral pH, at cold temperatures, or under "freshwater" conditions. Additionally, no significant differences in persistence were observed between pandemic and nonpandemic IAVs. Our results indicate that there have been no apparent changes in the environmental stability of the viruses related to host adaptation. IMPORTANCEThis study assessed the environmental stability of eight swine and six human influenza A viruses (IAVs), including viruses associated with the 2009 H1N1 pandemic, in a distilled water system. The important findings of this work are that IAV persistence can be affected by environmental variables and that no marked changes were noted between human and swine IAVs or between pandemic and nonpandemic IAVs. Influenza A viruses (IAVs) have been isolated from numerous avian and mammalian hosts, and cross-species transmission commonly occurs between wild bird reservoirs, domestic animals, and humans (1). Swine are susceptible to infection by IAVs of both avian and mammalian origin (2) and are recognized as an intermediate host for the evolution and adaptation of IAVs with pandemic potential (1, 2). From 1930 to 1990, classic H1N1 swine influenza virus (SIV) underwent little genetic change, but by the late 1990s, the "triple-reassortant" SIV viruses H1N1, H3N2, and H1N2 had become predominant in swine in North America (3, 4).The pandemic H1N1 influenza A virus (pH1N1) was first detected in April 2009 in two human cases in California (2009), and it quickly spread across the world. The emergence of this virus was subsequently traced to the reassortment of recent North American avian/human/swine triple-reassortant viruses with Eurasian swine viruses (5). This virus has since infected swine and continues to reassort with other SIVs (6, 7); pH1N1 is now a part of the endemic human influenza pool (8).The potential for viruses such as pH1N1 to emerge as a result of reassortment between human, swine, and avian viruses involves unlikely transmission events. Transmission mechanisms for IAVs not only are poorly understood in all of these host systems but also vary between them. With b...

Two genetically diverse H7N7 avian influenza viruses isolated from migratory birds in central China

“…To date, many studies have evaluated the environmental factors (temperature, salinity, and pH) that influence the stability of different AIVs under variable conditions. Overall, the persistence of AIVs was negatively associated with the temperature and acidity of the environment, and it has been suggested that AIVs remains infective for the longest time between a pH of 7.2 and 8.4 at low temperature 46 , 48 , 49 . In line with previous studies on viral persistence, our study also showed that both HH179/H7N7 and CH1228/H7N7 were more stable under the condition of near-neutral pH (7.2) and cold temperature (4 °C) than under other conditions.…”

“…In line with previous studies on viral persistence, our study also showed that both HH179/H7N7 and CH1228/H7N7 were more stable under the condition of near-neutral pH (7.2) and cold temperature (4 °C) than under other conditions. In addition, Poulson et al 46 . evaluated the ability of eight swine (H1N1 and H3N2) and six human (H1N1 and H3N2) strains to remain infective under various pH, temperature, and salinity conditions.…”

HA stability regulates H1N1 influenza virus replication and pathogenicity in mice by modulating type I interferon responses in dendritic cells

“…At pH 7.0, the titers of both viruses dropped from approximately 5.7 log 10 to 1.7 log 10 TCID 50 /mL over a period of 72 h. When virus aliquots were incubated at pH 6.4, the titer of Y17H virus decayed at an accelerated rate compared to that of WT virus. The 90% reduction time (Rt value) is the time required for a 90% (1 log 10 ) decrease in the viral titer (56). At pH 7.0, the Rt values for the WT and Y17H viruses were similar (21.7 ± 1.5 h and 20.4 ± 2.1 h, respectively); however, at pH 6.4, the Rt values for the WT and Y17H viruses were 26.6 ± 1.8 h and 7.4 ± 0.6 h, respectively.…”

“…Extracellular environments with acidic pH (pH <6.6), warmer temperature, and/or higher salinity decrease the environmental persistence of IAVs (56, 60). Environmental stability can also be decreased by destabilizing HA mutations (41), i.e., those that increase the pH at which the HA protein becomes activated to undergo irreversible structural changes (16, 30).…”

Potential for Waterborne and Invertebrate Transmission of West Nile Virus in the Great Salt Lake, Utah

“…A 20-fold reduction in titer of feline calicivirus (FCV), a nonenveloped RNA virus, was reported when introduced into artificial seawater (18). In contrast to nonenveloped RNA virus, lower survival of human and swine influenza viruses (enveloped RNA viruses) was reported when the virus was incubated in saline solutions up to 30 ppt salinity (19). Similarly, survival of avian influenza virus was inhibited when the virus was incubated in Ͼ25 ppt saline (20).…”