The aim of this study was to identify commonly available inactivation methods or disinfection agents that might be used for public protection against the novel avian influenza A (H7N9) virus or the decontamination methods at laboratory or field conditions. The results indicated that the novel avian influenza H7N9 viruses can be effectively inactivated by temperature treatment under 56°C for 30 min, 65°C for 10 min, 70°C, 75°C and 100°C for 1 min. But, it should be noted that the H7N9 viruses still could survive after treatment under 56°C for 15 min or 65°C for 5 min. Similar results were demonstrated with highly pathogenic avian influenza (HPAI) H5N1 virus, which was inactivated after exposure at 56°C for 30 min . However, a significant amount of information is available on the resistance at high and low temperatures of AIVs but not all data are in agreement. Such as the H5N1 viruses were completely inactivated at 70°C for 60 min or at 75°C for 45 min . Low pathogenic avian influenza (LPAI) H7N2 viruses were completely inactivated at 56°C after 60 min or at 60°C after 10 min, while retained their infectivity in a water bath at 56°C after 30 min [5, 6]. Additional study on AIV H7N3 indicated that the virus remained infectious after being treated at 56°C condition for 30 min, but its infectivity was lost after for 60 min . Our study suggested that the novel avian influenza A (H7N9) virus has not presented more tolerance to high temperature treatments.
AIV inactivation through UV light irradiation has a potential sterilizing application in the laboratories. The present study showed that UV light irradiation on the novel H7N9 virus is effective under the UV light exposure for 30 min or longer within 75 cm distance. However, the virus can survive if exposed to UV for shorter than 20 min. The result suggested that enough UV exposure time is necessary for avoiding cross-contamination on lab-works. In addition, other disinfection measures should be implemented after lab works since only microbes on the surface of material and in the air can be killed by UV light . UV irradiation could be considered an appropriate method only when the surfaces are well cleaned and the source of light is positioned very close to the surfaces to be disinfected .
Orthomyxoviridae viruses are considered to be sensitive to acid pH values, although their retention of infectivity is dependent on degree of acidity and virus strain . Our study indicated that the novel avian influenza H7N9 viruses may present a strong tolerance to both moderately acidic and higher alkali conditions. The H7N9 viruses lost their infectivity when exposed to less pH 2 for 30 min or pH 3 overnight conditions, while infectivity remained under pH 4–12 conditions for all contact times. However, previous studies suggested that different subtypes of influenza could present different tolerance to acidic or alkali conditions. LPAI H7N2 virus lost 100% infectivity under pH 2 condition for 5 min, but no effect exposure to pH 5, 7, 10 or 12 for 15 min . LPAI H7H3 was unable to maintain their infectivity after exposure to pH 1, 3, 10 and 14 for 48 h . The study on Thailand AIV H5N1 suggested that all ranges of pH 3, 5, 7, 9 and 12 could not inactivate the tested viruses after exposure for 5 and 10 min respectively .
In general, on the basis of their resistance to chemical agents, viruses can be divided into three categories (A, B and C) according to the presence/absence of lipids on the virus particle and size of virus. AIVs belong to category A, which can be inactivated easily by all major classes of disinfectants if used properly . Commercially available disinfectant products evaluated in this study, including Sodium Hypochlorite, Virkon®-S and ethanol, effectively disinfect the novel avian influenza H7N9 viruses at the recommended concentrations for 5 min at room temperature. Study demonstrated that the viral RNA of two LPAI strains H5N9 and H7N3 was completely damaged after exposure to Sodium Hypochlorite at recommended concentration . AIV H5N1 was completely inactivated after treatment with acid hypochloride for 10 min . The efficacy of Virkon®-S against AIVs has been evaluated on H5N9 and H7N3, the results showed that the fresh Virkon®-S solution at the recommended dilution was able to destroy the viral genome making it undetectable by real time RT-PCR . 0.5% Virkon®-S was able to fully inactivate AIV after 90 min while 1% or 2% Virkon®-S achieved virucidal activity after 30 min . Ethanol is efficacious against AIVs and other enveloped viruses, our results demonstrated that the novel avian influenza H7N9 viruses were completely inactivated after 75% ethanol treatment for only 5 min. As AIV H7N2, which lost its infectivity after treatment with 70% ethanol for 5 min or 15 min [5, 6]. However, the disinfection efficacy also depends upon the strain of the virus, exposure time, quantity of the virus and nature of the medium used.