Introduction
In
December 2019, an outbreak of unidentified pneumonia
characterized
by fever, dry cough, and fatigue happened in Wuhan, Hubei, China
(Zhu et al., 2020). With the spread of
the disease,
the
number of infected patients increased substantially which has become the
most challenging health emergency all over the world. Sequence analysis
of the coronavirus has shown a structure typical to that of other
coronaviruses such as SARS coronavirus and MERS coronavirus
(N. Chen et al., 2020). It also revealed
that the new coronavirus has the smallest genetic distance from bat
coronavirus, and about 80% similarity with SARS-CoV, and 50%
similarity with MERS-CoV (P. Sun, Lu, Xu,
Sun, & Pan, 2020). Thereafter, the coronavirus was designated as
SARS-CoV-2 and the infectious disease was named Coronavirus Disease 2019
(COVID-19) by the World Health Organization (WHO)
(Li-Li et al., 2020;
Sohrabi et al., 2020;
Zhu et al., 2020). Besides, the
nosocomial transmission was detected on January 20, 2020, which
suggested that
COVID-19
can be transmitted from human to human.
Due to the effective prevention and control measures, the epidemic has
been brought under control in China, South Korea, Japan, and more than
90% of patients have recovered and discharged in these countries.
However, the confirmed cases are still
growing
rapidly in American, European and African countries including the United
States, Brazil, Russia, the UK and South Africa
(WHO, 2020a). As experience in
recognition, diagnosis, and treatment of COVID-19 builds, WHO has
launched global megatrial of the four most promising coronavirus
treatments (WHO, 2020b). The present
article is to provide a review of the characteristics of COVID19,
including the epidemiology, etiology, clinical features, pathological
changes, and treatment, and the experience of prevention measures for
this disease.
1. Epidemiology ofCOVID-19
Since
December 2019, the first 27 cases of unidentified pneumonia were
reported by the Wuhan Municipal Health Commission
(Ashour, Elkhatib, Rahman, & Elshabrawy,
2020).
On
January 11, 2020, the pathogen of the pneumonia was initially confirmed
as a novel
coronavirus.
On January 20, 4 confirmed cases of COVID-19 were reported from three
countries outside of China including Thailand (2 cases), Japan (1 case),
and the Republic of Korea (1 case). As the epidemic expanded, daily
confirmed cases increased to 14,109, before falling to 1748 on February
18. And since then, the
number
of daily emerging cases gradually falls below 1000 for the first time in
China.
However,
the number of confirmed cases reported daily increased rapidly abroad.
Data released on February 25, 2020 showed foreign countries had
overtaken China in confirmed cases per day for the first time. And then
the disease spread rapidly in Europe and
in
the
United States (Figure 1a) . Up to this point, there have been
84,543 confirmed cases in China and 6,218,350 cases were confirmed in
212 countries outside of China with 370,100 fatalities(Figure
1b) .
Recently,
the
five countries with the greatest number of patients analyzed were the
United States (1,839,679 cases, 106,261 deaths, case-fatality rate:
5.8%), Brazil (514,992 cases, 29,341 deaths, case-fatality rate:
5.7%), Russia (414,878 cases, 4855 deaths, case-fatality rate: 1.03%),
Spain (286,509 cases, 27,127 deaths, case-fatality rate: 9.5%), and the
United Kingdom (274,762 cases, 38,489 deaths, case-fatality rate:
14.0%) (WHO, 2020a) (Figure
1c) .
Since
the first case of COVID-19 was reported in the U.S., the numbers of
confirmed cases and deaths increase exponentially with steady growth at
20,000-30,000 per day. Though the outbreak of COVID-19 appears at later
stage in Russia and Brazil, the number of confirmed cases has exceeded
most European and American countries. From November 2019 to May 25,
2020, the number of cumulative deaths caused by the COVID-19 was
350,057, and the overall case-fatality rate (CFR) was 6.3% which was
lower than that of the SARS (9.60%) and MERS (34.4%)
(WHO, 2020a)(Figure 1d, Table
1) .
The
transmission of infectious diseases must rely on three requirement
conditions: sources of infection, routes of transmission, and
susceptible hosts. A growing body of scientific evidence suggests that
COVID-19 is a zoonotic disease as with SARS and MERS, and originated
from the wild bat (Evans, 2013;
Keeling & Rohani,
2011).
Though the strands of evidence suggest the possibility of an initial
zoonotic emergence, the role of intermediate hosts such as
pangolins,
snakes, turtles,
hamster,
ferret, and other wild animals in the origin of
SARS-CoV-2
still remains controversy (Tiwari et al.,
2020). Close contact with symptomatic cases and asymptomatic cases with
silent infection are the main transmission routes of 2019-nCoV
infection. It
suggested
that SARS-CoV-2 can be transmitted through respiratory aspirates,
droplets, contacts, and digestive tract transmission that remained to be
confirmed (Peng et al., 2020).
Vertical
transmission was sporadically reported in some media but not yet
proved(H. Chen et al., 2020). Reports
showed that the basic reproductive values (R0) of COVID-19 were
calculated between 1.5 and 3.5 (Eisenberg,
2020; Natsuko Imai, 2020). Therefore,
SARS-CoV-2 appears to be more infectious than SARS-CoV or MERS-CoV based
on R0 values at the early stage of this outbreak
(Ying, A, Annelies, & Joacim, 2020)
(Table
1. ). Similar to SARS and MERS, nosocomial transmission was a severe
problem. COVID-19 has posed a difficult challenge to healthcare
facilities from both the impact of healthcare-associated transmission
and the resource burden of controlling and preventing further
spread.
It has been reported that a total of 3,019 health workers were infected,
accounting for 4.17% of total cases
(Epidemiology Working Group for Ncip
Epidemic Response & Prevention, 2020).
In
terms of susceptible populations, people are generally susceptible to
COVID-19
regardless of age or gender. And the elderly and those with underlying
chronic diseases (hypertension, diabetes, COPD) are more likely to
become severe cases. A retrospective cohort study by Chao et al. also
demonstrated that patients with hypertension and diabetes accounted for
20-30% of total infected patients and had a higher risk of developing
into acute respiratory distress syndrome (ARDS) or multiple organ
failure, and have a higher case fatality rate than those without
(Chaomin, 2020). The ACE2 receptor, an
important member of the renin-angiotensin system (RAS), is highly
expressed in the cardiovascular/cerebrovascular and lung tissue in the
hypertension patients (Kristensen et al.,
2015). Current reported data revealed that 86.6% of confirmed patients
were aged 30-79 years and 1-2% of the patients were children and
newborns (1.5 months to 17 years). The clinical course of pregnant women
with COVID-19 is similar to patients of the same age
(Schmid & Fontijn, 2020).
2.The
etiology of COVID-19
Coronavirus
is comprised of
single-stranded
positive RNA virus that belongs to an order Nidovirales , familyCoronaviridae , and
subfamilyOrthocoronavirinae (Jie, Fang, &
Zheng-Li, 2019).
Coronavirus
can be divided into four genera: α-, β-, γ-, δ-coronavirus according to
the characteristics of serotype and genome
(P, Xin, P, & Y, 2019). Genome sequences
analysis showed that the novel coronavirus is a new type of coronavirus
(SARS-CoV-2) and belongs to the β-CoV genera
(Li-Li et al., 2020;
Ren et al.,
2020).
Genetics
researchers and scientists worldwide found that the genomes of
SARS-CoV-2 have naturally evolved, thereby rejecting a hypothesis of a
possibility of recent recombination event as the cause of this outbreak
(X. Xu et al., 2020). Since its genome
is similar to bat coronavirus, scientists conjecture SARS-CoV-2 is most
likely to be originating from the bat
(Cui, Li, & Shi;
Rothan & Byrareddy, 2020). Virion spike
(S) protein is the key components which determines the host tropism of
the virus.
S
protein
is
composed of two subunits: S1 and S2, which are responsible for the
receptor binding and fusion of virus with cell membrane respectively
(Shajahan, Supekar, Gleinich, & Azadi,
2020). Current studies have revealed that SARS-CoV-2 shared the same
receptors with SARS-CoV and MERS-CoV for invading the host cells, and
the angiotensin-converting enzyme 2 (ACE2) receptor has been identified
as the main cell entry receptor of ARS-CoV-2
(Kuba et al., 2020). And structural and
biophysical analysis revealed that the affinity of SARS-CoV-2 for ACE2
is 10 to 20 times higher than that of the SARS-CoV
(Xie & Chen, 2020). A vitro study
confirmed that SARS-CoV-2 can survive in human respiratory epithelial
cells for 96 hours in vitro
(Yu,
2020).
SARS-CoV-2
also
shared
the same physical and chemical characteristics with SARS-CoV and
MERS-CoV.
Coronaviruses
are hypersensitive to ultraviolet rays and heat. And it can be killed
easily by exposed to 56 ℃ for 30 mins, 75% ethanol, chlorine
disinfectant, peracetic acid, and chloroform
(Deng & Peng, 2020).
3. Clinical characteristics ofCOVID-19