Effect of electromagnetic waves on the morphology of pathogenic viruses
The morphological characteristics of viruses can reflect function, such as survival and infectious ability. It has been demonstrated that electromagnetic waves can disrupt the morphology of viruses, especially ultrahigh-frequency (UHF) and extremely high-frequency (EHF) electromagnetic waves.
Bacteriophage MS2 (MS2) is frequently used in a variety of research fields, such as the disinfection evaluation, kinetic modeling (aqueous), and biological characterization of viral molecules [
5,
6]. Wu found that 2450 MHz, 700 W microwaves caused aggregation and significant shrinkage of water-borne MS2 phage after direct radiation for 1 min [
1]. Surface rupture of the MS2 phage was also observed after further investigation [
7]. Kaczmarczyk [
8] exposed a coronavirus 229E (CoV-229E) sample suspension to a 95 GHz millimeter wave with a power density between 70 and 100 W/cm
2 for 0.1 s. Large holes could be detected on the rough spherical envelope of the virus, which caused loss of their content. Electromagnetic wave exposure can be destructive to viral morphology. However, the changes in morphological properties, such as shape, diameter, and surface smoothness, after the exposure of a virus to electromagnetic radiation are not yet well understood. Therefore, it is important to analyze the relationship between the disruption of morphological features and functions, which might provide a valuable and convenient indicator for evaluating virus inactivation [
1].
Effect of electromagnetic waves on the activity of pathogenic viruses
The activity of a virus can be characterized by its ability to infect, replicate, transcribe, and so on. Viral infectivity or activity is usually evaluated by measuring viral titers using quantitative plaque assay analysis, median tissue culture infectious dose (TCID50), or luciferase reporter gene activity. However, it can also be directly evaluated by the isolation of live virus or the analysis of viral antigens, virus particles density, viral survival rate, and so on.
It has been reported that UHF, SHF, and EHF electromagnetic waves can directly inactivate viral aerosols or water-borne viruses. Wu [
1] exposed MS2 phage aerosols, generated by a laboratory nebulizing device, to 2450 MHz and 700 W electromagnetic waves for 1.7 min, and the survival rate of the MS2 phage was only 8.66%. Similar to MS2 virus aerosols, 91.3% of waterborne MS2 was inactivated within 1.5 min after exposure to electromagnetic waves at the same dose. Moreover, the ability of electromagnetic radiation to inactivate MS2 virus was positively associated with power density and exposure time. However, when the inactivation efficiency reached its maximum, it could not be improved by extending the exposure time or increasing the power density. For example, the minimum survival rate of the MS2 virus was between 2.65% and 4.37% after exposure to 2450 MHz and 700 W electromagnetic waves, and no significant alteration could be detected by increasing the exposure time. Siddharta [
3] radiated cell culture suspensions containing hepatitis C virus (HCV)/human immunodeficiency virus type 1 (HIV-1) with electromagnetic waves at 2450 MHz and 360 W. They found that the virus titers were significantly reduced after 3 min of exposure, indicating that electromagnetic wave radiation is effective against HCV and HIV-1 infectivity and could contribute to the prevention of virus transmission even in the context of coexposure. When low-power electromagnetic waves at 2450 MHz, 90 W, or 180 W were used to radiate HCV cell cultures and HIV-1 suspensions, there was no alteration in virus titer as determined by luciferase reporter gene activity and no significant change in virus infectivity. Even at 600 and 800 W for 1 min, there was no significant loss of infectivity for either virus, which is thought to be related to the electromagnetic wave radiation power and critical temperature action time.
Kaczmarczyk [
8] first demonstrated the lethality of EHF electromagnetic waves against water-borne pathogenic viruses in 2021. They exposed coronavirus 229E or poliovirus (PV) samples to 95 GHz electromagnetic waves with power densities varying between 70 and 100 W/cm
2 for 2 s. There two pathogenic viruses were inactivated with efficiencies of 99.98% and 99.375%, respectively, which indicated that EHF electromagnetic waves had promise in the field of virus inactivation.
The efficiency of UHF electromagnetic wave-mediated virus inactivation was also evaluated on different media, such as breast milk and some materials commonly used in life. Researchers exposed anesthesia masks contaminated with adenovirus (ADV), poliovirus type 1 (PV-1), herpes virus 1 (HV-1), and rhinovirus (RHV) to electromagnetic radiation at 2450 MHz and 720 W. They reported that ADV and PV-1 antigen detection changed to negative, and the titers of HV-1, PIV-3, and RHV decreased to zero, indicating that all of the viruses were completely inactivated after exposure for more than 4 min [
15,
16]. Elhafi [
17] exposed swabs contaminated with avian infectious bronchitis virus (IBV), avian pneumovirus (APV), Newcastle disease virus (NDV), and avian influenza virus (AIV) directly to 2450 MHz, 900 W microwaves for 20 s, and all of these viruses lost their infectivity. Among them, APV and IBV were further tested in tracheal organ cultures prepared from chicken embryos after five passages. Although the virus could not be isolated, viral nucleic acids were still detectable by RT‒PCR. Ben-Shoshan [
18] directly exposed 15 cytomegalovirus (CMV) antigen-positive breast milk samples to electromagnetic waves at 2450 MHz and 750 W for 30 s. Antigen detection using the Shell-Vial method showed complete inactivation of CMV. However, complete inactivation was not achieved in 2 out of 15 samples at 500 W, indicating a positive relationship between the inactivation efficiency and the power of the electromagnetic waves.
It is also noteworthy that Yang [
13] predicted the resonant frequency between electromagnetic waves and viruses according to the established physical model. A suspension of H3N2 virus particles with a density of 7.5 × 10
14 m
− 3, generated by virus-susceptible Madin Darby canine kidney (MDCK) cells, was directly exposed to electromagnetic waves at 8 GHz and 820 W/m² for 15 min. The inactivation rate of the H3N2 virus was up to 100%. However, only 38% of the H3N2 virus was inactivated at the theoretical threshold of 82 W/m
2, which indicated that the efficiency of electromagnetic radiation-mediated inactivation of the virus was closely related to the power density. Based on this study, Barbora [
14] calculated the resonant frequency range (8.5–20 GHz) between electromagnetic waves and SARS-CoV-2 and deduced that the exposure of 7.5 × 10
14 m
− 3 SARS-CoV-2 virus particles to electromagnetic waves with frequencies of 10–17 GHz and a power density of 14.5 ± 1 W/m
2 for approximately 15 min would result in 100% inactivation. A recent study by Wang [
19] clarified that the resonant frequencies of SARS-CoV-2 are 4 and 7.5 GHz, confirming the existence of resonant frequencies independent of virus titer.
In summary, electromagnetic waves can affect virus activity both in aerosols and in suspensions, as well as on the surfaces of objects. The inactivation efficiency was found to be closely associated with the frequency and power of the electromagnetic waves and with the medium used for virus growth. Furthermore, physical resonance-based electromagnetic frequencies are prominent in the field of virus inactivation [
2,
13]. Until now, electromagnetic waves’ effects on pathogenic viruses’ activity have mainly focused on the alteration of infectious ability. Due to the complex mechanisms, few studies have reported the effects of electromagnetic waves on the replication and transcription of pathogenic viruses.