On December 31, 2019, China alerted WHO about several
cases of unusual pneumonia in Wuhan (a port city of 11 million people in the
central Hubei province) caused by an unknown virus [1-3]. Predominant
potentially affected individuals worked at the city’s Huanan Seafood Wholesale
Market, which was shut down on January 1, 2020. As many health experts worked
hard to identify the virus amid growing alarm, the number of infections
exceeded 40. On January 8, 2020, a newly discovered virus was named as novel
coronavirus 2019 officially by WHO and announced as the causative pathogen of
disease COVID-19 (co- corona, vi-virus, d-disease, 2019-outbreak year) by the
Chinese Centre for Disease Control and Prevention [2-4]. Coronavirus Study
Group (CSG) of the International Committee proposed to name this new
coronavirus as SARS-CoV-2, both issued on 11 February 2020. The Chinese
scientists rapidly isolated a SARS-CoV-2 from a patient within a short time on
7 January 2020 and came out to genome sequencing of the SARS-CoV-2. However,
there is no evidence so far that the origin of SARS-CoV-2 was from the seafood
market. Rather, bats are the natural reservoir of a wide variety of CoVs,
including SARS-CoV-like and MERS-CoV-like virus. Upon virus genome sequencing,
the COVID-19 was analysed throughout the genome to Bat CoV RaTG13 and showed
96.2% overall genome sequence identity, suggesting that bat CoV and human
SARS-CoV-2 might share the same ancestor, although bats are not available for
sale in this seafood market. Besides, protein sequences alignment and
phylogenetic analysis showed that similar residues of receptor were observed in
many species, which provided more possibility of alternative intermediate
hosts, such as turtles, pangolin and snacks [4,5]. Outside mainland China, the
first confirmed case of coronavirus was observed on January 20, 2020 in Japan,
Thailand and South Korea. On January 21, 2020 the first case in US was
identified in Washington State. Also authorities in United States, Nepal,
France, Australia, Malaysia, Singapore, South Korea, Vietnam and Taiwan
confirmed cases over the following days. On January 30, 2020, the World Health
Organization (WHO) announced that this outbreak had constituted a public health
emergency of international concern [6,7]. On March 11, 2020 WHO declared
COVID-19 a pandemic, pointing to the over 118,000 cases of the coronavirus
illness in over 110 countries and territories around the world and the
sustained risk of future global spread. As of 29 April 2020, COVID-19 has been
recognized in over 213 countries, areas or territories, with a total of over
30, 24,059 confirmed cases and over 208,112 deaths. Studies estimated the basic
reproduction number (R0) of SARS-CoV-2 to be around 2.2, or even more (range
from 1.4 to 6.5), and familial clusters of pneumonia outbreaks add to evidence
of the epidemic COVID-19 steadily growing by human-to-human transmission [8,9].
Currently, our understanding about the transmission of COVID-19 are still to be
determined. Based on findings of genetic and epidemiologic research, it seems
that the COVID-19 outbreak started with a single animal-to-human transmission,
followed by sustained human-to-human spread. It is now believed that its
interpersonal transmission (droplets while talking, sneezing, coughing or
direct contact with mucous membrane) occurs mainly between family members,
including relatives and friends who intimately contacted with patients or
incubation carriers. Transmission between healthcare workers occurred in 3.8%
of COVID-19 patients, issued by the National Health Commission of China on 14
February 2020 [10-12]. By contrast, the transmission of SARS-CoV and MERS-CoV
is reported to occur mainly through nosocomial transmission. Infections of
healthcare workers in 33–42% of SARS cases and transmission between patients
(62–79%) was the most common route of infection in MERS-CoV cases. Direct
contact with intermediate host animals or consumption of wild animals was
suspected to be the other main route of SARS-CoV-2 transmission. In addition,
there may be risk of fecal-oral transmission, as researchers have identified
SARS-CoV-2 in the stool of patients from China and the United States [10].
However, whether SARS-CoV-2 can be spread through vertical transmission (from
mothers to their new-borns) is yet to be confirmed [13]. All Dental settings
invariably carry high risk of COVID-19 infection due to unique characteristics
and specificity of its procedures, which involves face-to-face communication
with patients, frequent exposure to saliva, blood, and other body fluids,
handling of sharp instruments and use of equipment’s such ultrasonic scalers,
air-water syringes and air turbine handpieces [14]. While dealing with dental
patients, transmission of virus possibly by any of the following routes: firstly,
through inhalation of airborne microorganisms that can remain suspended in the
air for longer periods, secondly, through direct or accidental contact with
blood, oral fluids, or other COVID 19 affected patient materials, thirdly,
contact of conjunctival, nasal or oral fluids with droplets and aerosols
containing microorganisms generated from an infected persons and propelled a
short distance by coughing and talking without a mask, and last but not the
least by an indirect contact with contaminated instruments and/or environmental
surfaces. Moreover, aerosol transmission of SARS-CoV-2 is also plausible as the
virus can remain viable and infectious in aerosols for at least three hours and
on surfaces for days. Transmission from asymptomatic COVID-19 carriers’
possibility was also reported [14-17]. Considering that COVID-19 was recently
identified in saliva of infected patients, and this outbreak is a reminder that
dental and other health professionals must always be diligent in protecting
against the spread of contagious disease, and it provides a chance to determine
if a non-invasive saliva diagnostic for COVID-19 could assist in detecting such
viruses and reducing its spread [18]. The exact incubation period is not known.
Based on current epidemiological investigation, it is presumed to be between
1–14 days after exposure, with numerous cases occurring within 5 days after
exposure, however, up to 24 days was also reported in some studies. And the
COVID-19 is contagious during the latency period. It is highly transmissible in
humans, especially in the elderly and individuals with underlying medical
problems. The median age of patients is 47–59 years, and 41.9 45.7% of patients
were females [1,4,19,20]. A recent study led by Prof. Nan-Shan Zhong’s team, by
sampling 1099 laboratory-confirmed cases, found that the common clinical
manifestations included fever (88.7%), cough (67.8%), fatigue (38.1%), sputum
production (33.4%), dyspnea (18.6%), sore throat (13.9%), and headache (13.6%).
In addition, a part of patients manifested gastrointestinal symptoms, with
diarrhea (3.8%), vomiting (5.0%), reduced sense of smell and abnormal taste
sensation. Fever and cough were the dominant symptoms whereas upper respiratory
symptoms and gastrointestinal symptoms were rare, suggesting the differences in
viral tropism as compared with SARS-CoV, MERS-CoV, and influenza. The elderly
and those with underlying disorders (i.e., hypertension, chronic obstructive
pulmonary disease, diabetes, cardiovascular disease, immunological disease) developed
rapidly into acute respiratory distress syndrome, septic shock, metabolic
acidosis hard to correct and coagulation dysfunction, even leading to the death
[21,22]. However, on the other hand in April 2020 it is noticeable that, about
80% of the cases have only mild symptoms that resemble flulike symptoms and
seasonal allergies, which might lead to an increased number of undiagnosed
cases. These asymptomatic patients can act as “carriers” and also serve as
reservoir for re-emergence of infection [20]. While the mild COVID-19 cases do
not require specific care, and usually symptomatic treatment and home isolation
are enough. Oxygen therapy is the major intervention for patients with severe
cases. Critical cases management on the other hand is case dependent and will
usually need intensive care. Even after patient recovery, recusancy during the
convalescence period was reported. This is plausible since the presence of some
virus strains in saliva for as long as 29 days have been reported in the
literature.