CLos coronaviruses are a large family of well- son una gran familia de patógenos bien established pathogens ofecidos de various hosts huéspedes, including domesticidos animals, wildes domésticos, animals, andes salvajes y humanos.
1. Descripción general del SARS-CoV-2 Overview
CLos coronavirus
es are a large family of well- son una gran familia de patógenos bien establ
ished pathogens ofecidos de vario
us hosts huéspedes, inclu
ding domesticidos animal
s, wildes domésticos, animal
s, andes salvajes y human
os
[ 1 ] .
Viruses that caused previous outbreaks iLos virus que causaron brotes anteriores en human
os, caus
ing severeando enfermedades respirator
y illness, lung injury, and death, areias graves, lesiones pulmonares y la muerte, son el SARS-CoV (
severe acutcoronavirus del síndrome respirator
y syndrome coronavirus) iio agudo severo) en 2003
andy el MERS-CoV (
Middle Eastcoronavirus del síndrome respirator
y syndrome coronavirus) iio de Oriente Medio) en 2012
[ 2 ] .
Recent genome analysis with variouUn análisis genómico reciente con varias herramientas bioinform
atics tools demonstrated thatáticas demostró que el SARS-CoV-2
has a highltiene un genoma muy similar
genome as the Bat al del coronavirus
and Bat y el dominio de unión al receptor
-binding domain (RBD)
of spike glyde la glicoprote
in as Malayan pangolinína espiga como el coronavirus
del pangolín malayo [ 3 ].
ThiEs
ta evidenc
eia indica
tes that the horseshoe bat is the natura que el murciélago de herradura es el reservo
ir, and primaryrio natural, y la evidenc
e suggests that the Malayania principal sugiere que el pangol
in is an ín malayo es un huésped intermedia
te hostrio [ 3 ] .
El SARS-CoV-2
is an enveloped virus with a es un virus envuelto con un ARN monocatenario de sentido positiv
e-sense single-stranded RNA. The genome size of this pathogen varies from 29.8 kb to 29.o. El tamaño del genoma de este patógeno varía de 29,8 kb a 29,9 kb
[ 4 ] .
TheEl virus
encodes at leastcodifica al menos 29 prote
ins. The ínas. Las proteínas estructural
proteins are spikees son proteínas de espiga (S), membran
ea (M), env
elope (E), andoltura (E) y nucleoc
apsidápside (NP)
[ 5 ] . Las prote
iín
as
[5].no The
non-structural
proteines (nsps)
have functions required fortienen funciones necesarias para la replica
tion andción y transcrip
tion in theción en el ciclo de vida del virus
life cycle [ 6 ] .
The viral particle size ranges from 80 to El tamaño de las partículas virales oscila entre 80 y 120 nm
[ 7 ] .
TheEl mec
hanism of viralanismo de infec
tion ición viral en human
s is through droplets andos es a través de gotitas y aerosol
s, which can travel through the aires, que pueden viajar por el aire [ 8 ] .
Infection occurs in cells thatLa infección ocurre en células que expres
san ACE2 (
angiotensin-enzima converti
ng enzyme 2) anddora de angiotensina 2) y TMPRSS2 (
transmembranproteasa de serin
e proteasea transmembrana 2)
[ 9 ] .
TheLa proteína S del coronavirus
S protein binds to the se une a ACE2,
the primaryel principal receptor
fordel SARS-CoV-2
thatque media
tes la entrada del virus en
try into cells, and las células, y TMPRSS2
cleaves the Sescinde la prote
in (into S1 and S2 ína S (en las subuni
ts) ofdades S1 y S2) del SARS-CoV-2
, lo que facilita
ting the fusion of la fusión del SARS-
CoV-2 and cel CoV-2 y membrana celular
membrane [ 9 ] [ 10 ] [ 11 ].
MorAde
over, it has been demonstrated that the endosomal cysteinemás, se ha demostrado que las cisteína proteas
es cathepsin B and cathepsin L can alsoas catepsina B y catepsina L endosomal también pueden contribu
te to thisir a este proces
so [ 10 ] [ 12 ] [ 13 ] .
In theEn el tracto respirator
y tractio, ACE2
andy TMPRSS2
arse expres
sed in thean en las células secretor
y and ciliated cells in the nose,as y ciliadas de la nariz, las células secretor
y andas y cilia
ted cells in thedas de las vías respiratorias conduct
ive airways, in the type IIoras, en las células alveolar
cells in the lung as well as in corneales de tipo II en los pulmones y en la conjun
ctiva in the eyetiva corneal del ojo [ 14 ] [ 15 ] [ 16 ] [ 17 ] .
The etiological virus of the pandemic has continuously evolved, with many variants emerging worldwide. Variants are categorized as the variant of interest, variant of concern, and variant under monitoring
[18]. There are five SARS-CoV-2 lineages designated as the variant of concern alpha, beta, gamma, delta, and omicron variants
[19]. These variants increase transmissibility compared to the original virus and potentially increase disease severity
[20].
2. Immune Response against SARS-CoV-2 in Brief
The SARS-CoV-2 infection involves diverse stages in the individual: start of infection, disease development, recovery, or systemic compromise. Each infection stage triggers and modulates innate and adaptative immune system mechanisms. Although SARS-CoV-2 is a virus that humanity is learning about, the immune response is equipped with mechanisms capable of dealing with this new threat. In the initial phase of SARS-CoV-2 infection, the individual presents a presymptomatic phase lasting up to 5 days, in which a high viral load is present
[21]. In these early days of infection, antibodies may not have been produced. Therefore, innate immunity is the first activated. The innate immune response comprises soluble and cellular components that respond nonspecifically against the virus. The cellular compounds include dendritic cells (DC), monocytes, macrophages, neutrophils, natural killer (NK) cells, and other innate lymphoid cells (ILCs)
[22]. Whereas soluble components include complement systems, soluble proteins, interferons, chemokines, and naturally occurring antibodies
[23]. Immune response cells recognize pathogen-associated molecular patterns (PAMPs) of SARS-CoV-2 through pattern recognition receptors (PRRs) such as Toll-like receptors (TLR), RIG-I-like receptors (RLR), and melanoma differentiation-associated protein 5 (MDA5). The viral sensing triggers the activation of signaling pathways which induce the production of immune mediators to generate an antiviral state mainly mediated by type I (IFN-α/β) and type III (IFN-λ) interferons (IFNs)
[24]. Reports have described that robust IFNs production during the early stage of infection is required to have a protective innate immune response against the virus
[25]. On the contrary, an inadequate and slow response to type I and type III IFNs due to virus evasion mechanisms, host comorbidities, or genetic defects cause an exacerbated immune response. This inadequate response induces elevated levels of chemokines (CCL2, CCL8, CXCL2, CXCL8, CXCL9, and CXCL16), high expression of proinflammatory cytokines such as IL-6, IL-10, IL-1, and TNF, in addition to activation, and recruitment of immune cells
[26][27]. The called “cytokine storm” leads to unbalanced levels of proinflammatory and antiviral mediators that remain the leading cause of ARDS and multi-organ failure
[25][26][28].
On the other hand, the adaptive immune response is orchestrated by CD8+ T lymphocytes, TCD4+, and B lymphocytes, responsible for immunological memory. In response to SARS-CoV-2 infection, it has been shown that non-severe patients or patients with mild symptoms have a low viral load and may not have produced antibodies
[29][30]. In contrast, antibodies have been detected by immunoassay tests and biosensors in patients with severe symptoms or cases
[29][31]. Patients with a high viral load activate the humoral immune response in the first two weeks of infection
[32]. The first seroconversion of antibodies is against protein N, followed by protein S of SARS-CoV-2 in patients with disease symptoms
[33]. Immunoglobulins IgA and IgM begin to be detected within the first ten days of infection; however, both antibodies can cross-react with protein N, which is highly conserved among coronaviruses
[34][35]. Moreover, high levels of IgG1 and IgG3 are expressed ten to fourteen days after infection in patients with disease symptoms
[36][37]. Older adults and seriously ill individuals reach high specificity antibodies concentrations against SARS-CoV-2 S protein.
Due to the urgency of reducing thousands of people’s cases and deaths, scientists have developed several vaccines against COVID-19. Efforts are being made to apply vaccines with emergency use authorization to the world population. Vaccination elicits immune responses capable of potently neutralizing SARS-CoV-2. However, the available data show that most approved COVID-19 vaccines protect against severe disease but do not prevent the clinical manifestation of COVID-19
[38]. Instead, it has been demonstrated that new variants with mutations in the spike, the main target of neutralizing antibodies, can escape the neutralization of humoral immunity
[39][40].
3. SARS-CoV-2 Detection
Molecular tests or biosensors are the tools for detecting SARS-CoV-2 nucleic acids/ antigens/antibodies against the virus (
Figure 1). In the early part of the illness, viral particles and their subunits can be detected; beyond the first two weeks of illness onset, antibodies against the virus could be detected
[41]. The SARS-CoV-2 infection stage is highly correlated to the diagnostic technique recommended for the pandemic. Early diagnosis of the disease and isolation of infected people is key to controlling the transmission of SARS-CoV-2
[42][43]. In the initial phase of SARS-CoV-2 infection, the individual presents a presymptomatic phase lasting up to 5 days, in which a high viral load is present
[21]. During these early days of infection, antibodies may not be detected. Therefore, since the pandemic began, the diagnostic method has been based on detecting viral genes using the molecular PCR technique, the gold standard worldwide
[44][45][46]. The pandemic has exceeded the ability to identify the virus in laboratories using molecular techniques; this has motivated the development of new technologies for the rapid detection of SARS-CoV-2 that are easy to perform compared to molecular tests in clinical laboratories. LFIA has been the unique device approved and available to use in mass worldwide. Biosensors with transducers are developing in SARS-CoV-2 diagnostic. However, most nanomaterials used in these biosensors present interferences with contaminants in human samples compared to performance under experimental conditions. It is important to emphasize that LFIAs have the unique properties of availability, accessibility, economy, and POC (including home use), these characteristics that are not shared by all biosensors with a transducer. In addition, biosensors with transducers require exclusive handling in laboratories certified under the Clinical Laboratory Improvement Amendments of 1998
[47][48]. The FDA have to date approved only one piezoelectric biosensor
[47] (
Figure 1).
Figure 1. Principio de le of LFIA test. LFIA testa prueba LFIA. La prueba LFIA detects the target molecule on ana la molécula objetivo en una membrana absorbent membrane with antibodies aligned to form the test ande con anticuerpos alineados para formar las líneas de prueba y control lines. The sample is placed on a sample pad, then migrates to th. La muestra se coloca en una almohadilla de muestra, luego migra a la almohadilla de conjugate pad, which contains the immobilized conjugate, usually made of do, que contiene el conjugado inmovilizado, generalmente hecho de nanoparticles (colloidal gold,ículas (oro coloidal, látex colored orado o fluorescent latex,e, celulosa colored celluloseada) conjugated to antibodies or antigens. The sampledas con anticuerpos o antígenos. La muestra interacts with theúa con el conjugate, and bothdo y ambos migrate to the next section of the strip, where the biologicaln a la siguiente sección de la tira, donde se inmovilizan los components of the assayes biológicos del ensayo (proteinínas/antibodies/antigens) are immobilized. In this section, the analyte and cuerpos/antígenos). En esta sección, se capturan el analito y el conjugate are captured. Excess reagent passes through thado. El exceso de reactivo pasa a través de las líneas de capture lines and accumulates on thea y se acumula en la almohadilla absorbent pad. Thee. Los results arados se interpreted on than en la membrana de nitrocellulose membrane as the ulosa como la presence or absence of the test andia o ausencia de las líneas de prueba y control lines.