Date of Award
8-2017
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biological Sciences
Committee Member
Xiuping Jiang, Committee Chair
Committee Member
Simon Scott, Co-Chair
Committee Member
Angela Fraser
Committee Member
Charles Pettigrew
Abstract
Worldwide, enteric viruses are the main cause of acute gastroenteritis (AGE). Among these viruses, human noroviruses (HuNoV) are leading cause of AGE and account for ca. 20% of all diarrheal cases, a top-five cause of death worldwide. In humans, these viruses spread via person-to-person contact, food, water, and/or the environment. Person-to-person contact is the most common mode of HuNoV transmission. Yet, environmental transmission has been linked to several outbreaks and prolonged others. HuNoV survival and inactivation on hard environmental surfaces have been extensively studied. However, nonlaunderable soft surfaces, such as carpet, have received little attention despite epidemiological evidence suggesting their role in transfer and transmission of HuNoV. Currently there are no commercially available products for sanitizing these surface after a contamination event. Documenting the efficacy of sanitizers intended for virally contaminated soft surfaces is also compounded by no standardized method for the recovery of viruses. Therefore our aims for this study, using the environmentally relevant soft surface, carpet, were to (i) determine factors that influence the survival and inactivation of enteric viruses on nonlaunderable soft surfaces (ii) determine survival of HuNoV surrogates on an carpet, (iii) compare sampling methods to determine their ability to recover HuNoV surrogates from carpet, and (iv) to assess two sanitizing technologies, silver dihydrogen citrate (SDC) and steam vapor, against a HuNoV surrogate, FCV, on carpet. A systematic review of the literature was conducted to determine factors that influence the survival and inactivation of enteric viruses on nonlaunderable soft surfaces. EBSCO and Web of Science were searched for experimental studies published between 1965 and 2015 using Preferred Reporting Items for Systematic Reviews and Meta-Analyses methods. Titles and abstracts were screened using 3 eligibility criteria. The quality of all study methods was also assessed. Our search yielded 12 articles. Viruses survived between 0 hours and 140 days depending on surface and environment conditions. Virus survival was influenced by temperature, relative humidity, organic content, and deposition method. A variety of chemistries were tested across studies and were shown to have a varied effect on enteric viruses. Chlorine, glutaraldehyde, vaporous ozone, and hydrogen peroxide were the most efficacious against enteric viruses (> 3-log reduction). The efficacy of liquid and vaporous chemistries are associated with surface and virus type The survival profile of HuNoV surrogates, FCV and murine norovirus (MNV), as studied on carpet. First, we measured the zeta potential and absorption capacity of wool and nylon carpet fibers, developed a mini-spin column elution method (MSC), and characterized the survival of HuNoV surrogates, FCV and MNV over 60 days under 30 and 70% relative humidity (RH) on carpets and a glass surface. Carpet surface charge was negative at a typical buffer pH while wool could absorb ca. 2X more liquid than nylon. Percent recovery efficiency with the MSC ranged from 4.34 to 20.89% and 30.71 to 54.14% for FCV and MNV on carpet fibers, respectively. Moreover, elution buffer type did not significantly affect recovery of either surrogate virus. Infectious FCV or MNV survived between <1 and 15 or 3 and 15 days, respectively. However, MNV survived longer under some conditions and at significantly higher titers compared to FCV. Albeit, surrogates followed similar survival trends, i.e. both survived longest on wool followed by nylon and glass while 30% RH provided a more hospitable environment compared to 70% RH. qRT-PCR signals for both surrogates were detectable for the entire study but FCV genomic copies experienced significantly higher reductions (<3.80 log10 copies) on all surfaces compared to MNV (<1.10 log10 copies). Virus recovery methods were compared to evaluate their ability to recover FCV and MNV from carpet. Specifically, we assessed and compared three recovery methods, i.e. bottle extraction (BE), macrofoam-tipped swabbing (MS), and the microbial vacuum (MVAC), using HuNoV surrogates, FCV and MNV, inoculated on wool and nylon. We also investigated detection issues for FCV after environmental recovery, i.e. inhibition. Infectious FCV and MNV percent recovery efficiency (% RE) of BE ranged from 0.44 to 48.44 and 40.77 to 68.83%, respectively, compared to MS % RE, which was 0.02 to 0.82% and 1.54 to 2.87%, respectively. The MVAC % RE of infectious FCV and MNV ranged from 7.30 to 18.29% and 52.58 to 74.67%, respectively. Percent RE of genomic copies of FCV and MNV with BE ranged from 0.36 to 2.53% and 3.34 to 14.97%, respectively, while MS % RE ranged from 1.03 to 2.24 and 2.02 to 4.25%, respectively. The MVAC % RE of genomic copies of FCV and MNV ranged from 2.49 to 23.72% and 28.78 to 79.15%, respectively. Significantly more plaque-forming units and genomic copies were recovered using BE and MVAC compared to MS, while buffer type played a significant role in recovery of infectious FCV. Additionally, qRT-PCR analysis indicated recovery from tested carpet types inhibited amplification of FCV RNA and required dilution after nucleic acid extraction Two sanitizing technologies, SDC and steam vapor, were evaluated against FCV on wool and nylon carpet carriers. First, we evaluated both technologies effect on aesthetic appearance on carpet, developed a neutralizer for SDC, evaluated SDC’s efficacy in suspension with and without 5% fetal bovine serum (FBS), SDC and steam vapor’s efficacy on glass, each with and without 5% FBS, and finally tested both sanitizers on carpets. Wool and nylon carpet carriers exhibit no obvious color changes or abrasions after both treatments, however SDC treatment left a residue while steam left minor abrasions to the surface fibers. A sodium thioglycolate-based solution was found to adequately neutralize and eliminate SDC cytotoxicity. SDC in suspension and on glass reduced FCV by 4.65 and >4.66 log10 pfu, respectively, but demonstrated reduced efficacy in the presence of serum. However, SDC was only efficacious against FCV on nylon (3.62 log10 pfu reduction). Steam vapor reduced FCV by >4.93 log10 pfu on glass in 10 sec, with no observed difference among serum treatments, and >3.68 log10 pfu on wool and nylon carpet carriers in 90 sec. There was limited reduction to FCV RNA under both sanitizer treatments, but RNA reductions were higher in treatments with serum. In this Ph.D. dissertation, I characterized wool and nylon carpet fibers based on their absorptive capacity and zeta potential while demonstrating that HuNoV surrogates, feline calicivirus (FCV) and murine norovirus (MNV), can survive for at least 15 days on carpets under some conditions. Additionally, we evaluated three methods’ recovery efficiency with FCV and MNV on wool and nylon carpets that provides key data and analysis of methods intended for efficacy testing and environmental monitoring. Finally, we assessed two sanitizing technologies, silver dihydrogen citrate (SDC) and steam-vapor with thermo-accelerated nano-crystal sanitation (TANCS) technology, against FCV, in suspension, glass, and wool and nylon carpet carriers of an experimental design for assessing efficacy of sanitizer intended for viruses on carpets. Results suggest SDC and steam-vapor with TANCS are efficacious against FCV but steam-vapor provides the highest level of inactivation. Ultimately, this is the first comprehensive study of HuNoV on carpet, an understudied fomite. Specifically, these studies estimate the survival characteristic of HuNoV on carpet, provide a comprehensive comparison of potential virus recovery methods from carpet, demonstrate the efficacy of two acceptable and reasonable virucidal sanitizers on carpet, and establish a much-needed experimental design for assessing virucidal sani tizers on carpets.
Recommended Citation
Buckley, David, "Survival, Recovery, and Inactivation of Human Norovirus Surrogates, Feline Calicivirus and Murine Norovirus, on Carpets" (2017). All Dissertations. 1979.
https://tigerprints.clemson.edu/all_dissertations/1979