CORONAVIRUS

CORONAVIRUS

"Coronavirus" is derived from Latin corona, meaning "crown" or "wreath",The name refers to the characteristic appearance of virions . 

"A virus is a small infectious agent that replicates only inside the living cells of an organism.  Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria    and archaea by electron microscopy".  

Here we provide a brief introduction to coronaviruses, discussing their replication,transmission and pathogenicity, and current prevention, treatment strategies. We will also discuss the outbreaks of the highly pathogenic Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and the recently identified Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV).

Coronaviruses constitute the subfamily Orthocoronavirinae, in the family Coronaviridae

•     Alphacoronavirus
•   Betacoronavirus
•    Gammacoronavirus
•   Deltacoronavirus 

Coronaviruses are a group of viruses that cause diseases in mammals and birds. In humans, coronaviruses cause respiratory tract infections that are typically mild, such as some cases of the common cold (among other possible causes, predominantly rhinoviruses), though rarer forms such as SARS, MERS, and SARS-CoV-2 can be lethal. 

Coronaviruses (CoVs), enveloped positive-sense RNA viruses, are characterized by club-like spikes that project from their surface, an unusually large RNA genome, and a unique replication strategy.

RNA VIRUS

 RNA virus is a virus that has RNA (ribonucleic acid) as its genetic material. This nucleic acid is usually single-stranded RNA (ssRNA) but may be double-stranded RNA (dsRNA).^[2] Notable human diseases caused by RNA viruses include Ebola virus disease, SARS, rabies, common cold, influenza, hepatitis C, hepatitis E, West Nile fever, polio, measles, and COVID-19.

• Single-stranded RNA viruses and RNA Sense

RNA viruses can be further classified according to the sense or polarity of their RNA into negative-sense and positive-sense, or ambisense RNA viruses. Positive-sense viral RNA is similar to mRNA and thus can be immediately translated by the host cell. Negative-sense viral RNA is complementary to mRNA and thus must be converted to positive-sense RNA by an RNA-dependent RNA polymerase before translation.

• Double-stranded RNA viruses 

The double-stranded (ds)RNA viruses represent a diverse group of viruses that vary widely in host range (humans, animals, plants, fungi, and bacteria), genome segment number (one to twelve), and virion organization (Triangulation number, capsid layers, spikes, turrets, etc.).

• Mutation rates 

RNA viruses generally have very high mutation rates compared to DNA viruses, because viral RNA polymerases lack the proofreading ability of DNA polymerases.

REPLICATION

 fig- replication of coronavirus.

TRANSMISSION

Human to human transmission of coronaviruses is primarily thought to occur among close contacts via respiratory droplets (In medicine, public health, and biology, transmission is the passing of a pathogen causing communicable disease from an infected host individual or group to a particular individual or group, regardless of whether the other individual was previously infected. generated by sneezing and coughing.

PATHOGENESIS

Coronaviruses cause a large variety of diseases in animals, and their ability to cause severe disease in livestock.In addition, there has been intense interest in identifying novel bat CoVs, since these are the likely ultimate source for SARS-CoV and MERS-CoV, and hundreds of novel bat coronaviruses have been identified over the past decade.These viruses are endemic in the human populations.

DIAGNOSIS, TREATMENT, AND PREVENTION

In most cases of self-limited infection, diagnosis of coronaviruses is unnecessary, as the disease will naturally run its course. However, it may be important in certain clinical and veterinary settings or in epidemiological studies to identify an etiological agent. Diagnosis is also important in locations where a severe CoV outbreak is occurring, such as, at present, in the Middle East, where MERS-CoV continues to circulate. The identification of cases will guide the development, of public health measures to control outbreaks. It is also important to diagnose cases of severe veterinary CoV-induced disease, such as PEDV and IBV, to control these pathogens and protect food supplies. RT-PCR has become the method of choice for diagnosis of human CoV, as multiplex real-time RT-PCR assays have been developed, are able to detect all four respiratory HCoVs and could be further adapted to novel CoVs . Serologic assays are important in cases where RNA may be difficult to isolate, is  no longer present, and for epidemiological studies.

Sign and symptoms 

Symptoms of COVID-19 are non-specific and those infected may either be asymptomatic or develop flu-like symptoms such as fever, cough, fatigue, shortness of breath, or muscle pain. The typical signs and symptoms and their prevalence, are shown in the corresponding table.

Further development can lead to severe pneumonia, acute respiratory distress syndrome, sepsis, septic shock and death. Some of those infected may be asymptomatic, returning test results that confirm infection but show no clinical symptoms, so researchers have issued advice that those with close contact to confirmed infected people should be closely monitored and examined to rule out infection. 

The usual incubation period (the time between infection and symptom onset) ranges from one to fourteen days; it is most commonly five days. In one case, it may have had an incubation period of 27 days.

Prevention 

Infographic by the United States CDC, describing how to stop the spread of germs.

Strategies for preventing transmission of the disease include overall good personal hygiene, hand washing, avoiding touching the eyes, nose or mouth with unwashed hands, coughing/sneezing into a tissue and putting the tissue directly into a dustbin. Those who may already have the infection have been advised to wear a surgical mask in public. Social distancing measures are also recommended to prevent transmission.

Many governments have restricted or advised against all non-essential travel to and from countries and areas affected by the outbreak. However, the virus has reached the stage of community spread in large parts of the world. This means that the virus is spreading within communities whose members have not travelled to areas with widespread transmission.

Health care providers taking care of someone who may be infected are recommended to use standard precautions, contact precautions and airborne precautions with eye protection.

Contact tracing is an important method for health authorities to determine the source of an infection and to prevent further transmission. Misconceptions are circulating about how to prevent infection, for example: rinsing the nose and gargling with mouthwash are not effective.

As of 13 March 2020, there is no COVID-19 vaccine though a number of organizations are working to develop one. 

• Hand washing

Hand washing is recommended to prevent the spread of the disease. The US Centers for Disease Control and Prevention (CDC) recommends that people wash hands often with soap and water for at least 20 seconds, especially after going to the toilet or when hands are visibly dirty; before eating; and after blowing one's nose, coughing, or sneezing. It further recommended using an alcohol-based hand sanitizer with at least 60% alcohol by volume when soap and water are not readily available. The WHO advises people to avoid touching the eyes, nose, or mouth with unwashed hands.

• Respiratory hygiene

Health organizations recommended that people cover their mouth and nose with a bent elbow or a tissue when coughing or sneezing (the tissue should then be disposed of immediately).Surgical masks are recommended for those who may be infected, as wearing a mask can limit the volume and travel distance of expiratory droplets dispersed when talking, sneezing and coughing. The WHO has issued instructions on when and how to use masks.

Masks have also been recommended for use by those taking care of someone who may have the disease. WHO has recommended the wearing of masks by healthy people only if they are at high risk, such as those who are caring for a person with COVID-19, although masks may help people avoid touching their faces.

Surgical masks are the lowest grade of protection, and are designed mainly to protect others from the wearer. Masks designed to protect the wearer are technically "respirators", though calling them "masks" is common. Only China has specifically recommended the use of masks by healthy members of the public. Nevertheless, face masks have been widely used by healthy people in Hong Kong, Japan, Malaysia,and india.

• Social distancing

Social distancing includes infection control actions intended to slow the spread of disease by minimizing close contact between individuals. Methods include quarantines; travel restrictions; and the closing of schools, workplaces, stadiums, theatres, or shopping centres. Individuals may also apply social distancing methods by staying at home, limiting travel, avoiding crowded areas, using no-contact greetings, and physically distancing themselves from others.  Many governments are now mandating or recommending social distancing in regions affected by the outbreak.The high-risk group includes older adults (60 years of age and older), those with a weak immune system (i.e. due to cancer treatment, treatment for autoimmune diseases, HIV, organ transplant or bone-marrow transplant), smokers and those with serious underlying medical conditions (such as heart disease, diabetes, lung disease.

• Self-isolation

Self-isolation at home has been recommended for those diagnosed with COVID-19 and those who suspect they have been infected. Additionally, individuals who have recently travelled to a country with widespread transmission or who have been in direct contact with someone diagnosed with COVID-19 have also been asked by some government health agencies to self-quarantine or practise social distancing for 14 days from the time of last possible exposure.

The National Health Service in the UK has recommended that those with symptoms of COVID-19 should stay at home for 14 days, taking precautions to avoid infecting others within the household. As long as symptoms do not significantly worsen, health services should not be contacted.

CONCLUSION

Over the past 50 years the emergence of many different COVID-19 that cause a wide variety of human and veterinary diseases has occurred. It is likely that these viruses will continue to emerge and to evolve and cause both human and veterinary outbreaks owing to their ability to recombine, mutate, and infect multiple species and cell types.

Future research on COVID-19 will continue to investigate many aspects of viral replication and pathogenesis. First, understanding the propensity of these viruses to jump between species, to establish infection in a new host, and to identify significant reservoirs of COVID-19 will dramatically aid in our ability to predict when and where potential epidemics may occur. As bats seem to be a significant reservoir for these viruses, it will be interesting to determine how they seem to avoid clinically evident disease and become persistently infected. Second, many of the non-structural and accessory proteins encoded by these viruses remain uncharacterized with no known function, and it will be important to identify mechanisms of action for these proteins as well as defining their role in viral replication and pathogenesis. These studies should lead to a large increase in the number of suitable therapeutic targets to combat infections. Furthermore, many of the unique enzymes encoded by COVID-19 such as ADP-ribose-1”-phosphatase, are also present in higher eukaryotes, making their study relevant to understanding general aspects of molecular biology and biochemistry. Third, gaining a complete picture of the intricacies of the RTC will provide a framework for understanding the unique RNA replication process used by these viruses. Finally, defining the mechanism of how COVID-19 cause disease and understanding the host immunopoathological response will significantly improve our ability to design vaccines and reduce disease burden.