The World Health Organization (WHO) has declared that COVID-19 is a pandemic, caused by the new human coronavirus (SARS-CoV-2) that has already infected more than 20 million people and cause more than 700 thousand deaths worldwide by August 2020 [1
]. Person-to-person contact and contact with contaminated surfaces have been identified as the most common modes of transmission [2
]. The length of infectivity time of SARS-CoV-2 was recently evaluated on several inanimate surfaces, and it ranges from hours to several days [3
]. The efficiency of surface disinfectant has been investigated and it has been shown to inactivate SARS-CoV-2 in a few minutes [3
]. However, these virus inactivation agents rapidly evaporate, are flammable, become inefficient soon after application and, consequently, the sanitized surfaces can become a new transmission source following novel contamination. These products are also hard to find or expensive in underdeveloped countries, which are the new hotspots for the disease. Methods for prevention of transmission by contact, through washing hands with soaps and sanitization with alcohols, have been implemented in several countries [5
]. However, these procedures are only efficient at eliminating contamination that happened before the sanitization and the hands might be contaminated shortly after these sanitization procedures. Therefore, there is an urgent need for a simple, low-cost and efficient antiviral procedure that is able to maintain virus inactivation efficiency up to several hours.
Our hypothesis was that the use of a long-lasting dry film, made with dishwashing detergent, has the ability to reduce viral infectivity by several orders of magnitude in few minutes on inanimate surfaces. A similar film, applied on hands, could also reduce the risk of contamination when hand washing and/or sanitization are reduced, especially in locations where water is not easily available, which is a common scenario in developing countries where the majority of the population has low socioeconomic status.
Detergents have a high concentration of surfactants such as sodium dodecyl sulfate (SDS), also known as sodium lauryl ether sulfate (SLES) or sodium lauryl sulfate (SLS), which is a well-known protein-denaturing agent [6
], and linear alkylbenzene sulfonates (LAS). Therefore, surfactants could denature or induce small conformational changes in the supramolecular structure of S (spike protein) of SARS-CoV-2 that binds to the ACE-2 (angiotensin-converting enzyme 2) receptor of the epithelial cells in the host [2
], reducing the virus infectivity. Surfactants may also inactivate enveloped viruses (like SARS-CoV-2), acting on the lipidic layer [7
]. Scientific reviews by the independent Cosmetic Ingredient Review (CIR) initiative concluded that SDS is safe and it is not a cause for concern to the consumer [8
], the same conclusion was confirmed by another study [9
]. In order to verify the potential inactivation efficiency of the detergent dry film on SARS-CoV-2, we have used the avian coronavirus (ACoV), also known as avian infectious bronchitis virus, as model of this challenge, since the chemistry and structure are very similar between coronaviruses [10
]. Both viruses are enveloped, single-strand, positive-sense RNA viruses. ACoV belongs to the Gammacoronavirus genus, while SARS-CoV-2 is classified in the Betacoronavirus genus [11
]. ACoV was the first coronavirus to be reported in 1937, from chickens with respiratory disease [12
]. Due to the huge economic impact caused by this virus, ACoV is one of the most studied coronaviruses in recent decades [13
]. Among the main advantages of using ACoV as a model of this challenge is the non-zoonotic nature of this virus (the infectivity is restricted to chickens), which can be cultivated under lower biosafety levels. Additionally, there are numerous attenuated virus vaccines that are commercially available, allowing the experiments to be reproduced worldwide. Therefore, this study aimed to evaluate the chemical stability and the ability to inactivate ACoV infectivity of two proposed detergent based films, one for applying to inanimate surfaces and one to be used on hands.
In view of the current arising worldwide pandemic distribution of COVID-19, there is a realization that mortality of SARS-CoV-2 is inequitably distributed among vulnerable populations, especially related to lower socioeconomic status. Unlike the high-income countries of Europe, Northern Asia and North America, most countries of lower economic status face limited mitigation capacity, poor access to high quality public health and medical care, dense population and also have scarce access to commercial sanitizers and running water. Alternative formulations, such as the here proposed film for virus inactivation, characterized by easy access, low cost and simple preparation, may constitute a powerful and important tool for COVID-19 prophylaxis in these vulnerable populations.
In the present study, the antiviral activity of a simple and low-cost semi-permanent film was tested on a plastic surface, using ACoV as model. A recent review about the persistence of animal and human coronaviruses on different types of inanimate surfaces showed that coronaviruses remain infectious on a plastic surface for the same time or longer than other surfaces (steel, aluminum, wood, paper, glass, silicon rubber, latex, disposable gown, ceramic and teflon) [20
]. The longest viral viability time (9 days) was found on a plastic surface [21
]. Together, these results indicate that hard and non-porous plastic surfaces, as used in this study, are a good choice to screen the inactivation effects of disinfectants. Equally, despite the fact that this study has used ACoV as a virus model, the obtained findings may be extended to SARS-CoV-2, as similar chemical composition and structure were verified for the viruses of the Coronaviridae
]. Similar environmental resistance was observed between these two viruses. At 56 °C, SARS-CoV-2 was viable after 10 min and inactivated after 30 min [3
], while nine different ACoV strains were inactivated after 15 min at the same temperature [13
]. Both, SARS-CoV-2 and ACoV were extremely stable in a wide range of pH values (3–10) at room temperature [3
The presence of SARS-CoV-2 on surfaces is always a concern. In this study, film on a plastic surface was able to inactivate the ACoV at all tested challenge doses. As result, no RNA detection (RT-qPCR) or virus activity in chicken embryos was observed in treatments previously exposed to the film (Figure 1
and Table 2
), while all positive controls (challenged and not previously exposed to the film) presented virus replication observed by macroscopic lesions and RNA virus detection in the embryos.
The antiviral activity of the film can be attributed, in large part, to the biocidal action of the surfactants present in the detergent. Surfactants (surface active agents) are the single most important ingredients in laundry and household cleaning products [9
], comprising 1% to 30% in cleaning products formulation [9
]. SLS surfactant could be a potent inhibitor of the infectivity of different types of pathogens without causing marked toxicity to skin and/or mucosae [23
]. The mechanism by which SLS inactivates enveloped and non-enveloped viruses probably involves the denaturation of envelope or capsid proteins. These proteins may play different roles in the viral replicative cycle such as adhesion receptors, proteins involved in the encapsulation of viral genome [23
]. Protein denaturation involves an initial rapid process where protein and SLS produce aggregates, followed by two slower processes, where the complexes first disaggregate into single protein structures situated asymmetrically on the SLS micelles, followed by the isotropic redistribution of the protein [6
Although the viral load of coronaviruses on inanimate surfaces is not clearly known to contribute as a source of contamination, during an outbreak, it seems plausible that reduction in the viral load on surfaces by disinfection, especially those frequently touched by infected patients, may constitute an efficient tool for minimizing the virus spread [20
]. The prevalence of face-touching behavior in students was determined as, on average, 23 times per hour, whereas for mucosae (eye, mouth and nose) touching it was 10 times per hour [24
]. Consequently, sanitization of both surfaces and hands are essential and inexpensive preventive methods for breaking the transmission cycle. Several biocidal agents, such as 0.5% hydrogen peroxide, 62–71% ethanol or 0.1% of sodium hypochlorite, were able to inactivate coronavirus from inanimate surfaces within one minute [20
]. However, these biocidal agents rapidly evaporate or become inefficient in a short period and, consequently, these sanitized surfaces can become a new transmission source following novel contamination.
The results of the chemical stability evaluation of the films here tested showed that SDS and LAS compounds are highly stable in dry film casted on a plastic surface for at least seven days. The chemical stability of the proposed films indicates that the compounds properties, including antiviral activity, will be preserved for the same period, and may keep a residual protective effect. Our proposal is that the detergent film, applied on plastic, metal, glass, ceramic, laminated and other inanimate surfaces, in public areas, can be an efficient alternative to prevent SARS-CoV-2 spread, especially in locations where methods of prophylaxis are scarce. Besides, diluted hand soap (1:49), which is well known to contain surfactants in the composition, was able to reduce 3.6 Log10
SARS-CoV-2 after 5 min and reached undetected levels after 15 min [3
], reinforcing the role of these substances in virus inactivation.
Therefore, the dry film might effectively maintain virus inactivation ability through hours to days, reducing the use of hazardous chemicals and the need for frequent sanitization procedures with the chemical compounds normally dissolved in water, which generate large amounts of toxic waste that may contaminate ecosystems. New detergent film can be applied to inanimate surfaces without removing the previous detergents, this reduces the need for water and consequently reduces environmental contamination. Hand lotion prepared with detergent/vegetable oil could also reduce the risk of contamination, especially in locations where water is not easily available for hand washing, which is a common scenario in populations in underdeveloped countries.