Coronaviruses are enveloped RNA viruses from the Coronaviridae family and part of the Coronavirinae subfamily. With its characteristic surface, the virions appear as a crown like image under the electron microscope and so the viruses are named after the Latin word corona, meaning 'crown' or 'halo'.
In animals the viruses infect the respiratory and gastrointestinal systems as well as occasionally affecting the liver and the neurological systems.
The human coronaviruses mainly infect the upper respiratory and gastrointestinal tract. They often result in upper respiratory tract infections (simple colds) in humans, causing mild illnesses usually of short lasting nature with a rhinitis, cough, sore throat, as well as fever.
Occasionally, the viruses are able to cause more significant lower respiratory tract infections in human with pneumonia; this is more likely in immunocompromised individuals, people with cardiopulmonary illnesses, as well as the elderly and young children. Only very rarely do the humans viruses cause severe disease, like severe acute respiratory syndrome (SARS).
In general, SARS begins with a high fever (temperature greater than 100.4°F [>38.0°C]). Other symptoms may include headache, an overall feeling of discomfort, and body aches. Some people also have mild respiratory symptoms at the outset. About 10 percent to 20 percent of patients have diarrhea. After 2 to 7 days, SARS patients may develop a dry cough. Most patients develop pneumonia.
Most people infected with MERS-CoV have developed severe acute respiratory illness with symptoms of fever, cough, and shortness of breath. About half of them have died. Some people were reported as having a mild respiratory illness.
Please see the WHO Global Alert and Response page "Revised interim case definition for reporting to WHO – Middle East respiratory syndrome coronavirus (MERS-CoV)" for more information about identification of MERS-CoV and MERS-CoV interim case definitions.
The five coronaviruses types which affect humans are alpha (229E and NL63), beta (OC43), HKUI1 and SARS-CoV - although the latter is best considered an animal virus that has only rarely infected humans.
Severe acute respiratory syndrome (SARS) is a viral respiratory illness caused by a coronavirus, called SARS-associated coronavirus (SARS-CoV). SARS was first reported in Asia in February 2003. Over the next few months, the illness spread to more than two dozen countries in North America, South America, Europe, and Asia before the SARS global outbreak of 2003 was contained.
There is also an emerging novel coronavirus which is now called the Middle East respiratory syndrome coronavirus (MERS-CoV). This new beta virus strain of an animal coronavirus was identified in September 2012 in individuals with severe acute respiratory illness occurring in the Arabian Peninsula, some of whom were transferred for care to hospitals in Europe. Retrospectively some infections have also been detected in humans with severe acute respiratory illness in Jordan in the spring of 2012. This coronavirus differs from the previously identified coronaviruses such as the SARS coronavirus (SARS-CoV), which caused the 2003 SARS outbreaks. There is still much to be investigated, but it is considered likely that this virus originated from an animal source. Surveillance guidance, case definition and other advice for this novel virus has been provided by WHO, as well as Public Health England (UK) and the Robert Koch Institute (Germany). Further information is provided by ECDC in its risk assessments and epidemiological updates.
Laboratory tests can be done to confirm whether an illness may be caused by human coronaviruses. However, these tests are not used very often because people usually have mild illness. Also, testing may be limited to a few specialized laboratories.
Specific laboratory tests may include:
Nose and throat swabs are the best specimens for detecting common human coronaviruses. Serological testing requires collection of blood specimens.
Several laboratory tests can be used to detect SARS-CoV. A reverse transcription polymerase chain reaction (RT-PCR) test can detect SARS-CoV in clinical specimens such as blood, stool, and nasal secretions. Serologic testing also can be performed to detect SARS-CoV antibodies produced after infection. Finally, viral culture has been used to detect SARS-CoV.
Many studies have been undertaken or are underway to evaluate whether there are specific laboratory and/or clinical parameters that can distinguish SARS-CoV disease from other febrile respiratory illnesses. Researchers are also working on the development of laboratory tests to improve diagnostic capabilities for SARS-CoV and other respiratory pathogens. To date, however, no specific clinical or laboratory findings can distinguish with certainty SARS-CoV disease from other respiratory illnesses rapidly enough to inform management decisions that must be made soon after the patient presents to the healthcare system. Therefore, early clinical recognition of SARS-CoV disease still relies on a combination of clinical and epidemiologic features.
In the absence of person-to-person transmission of SARS-CoV anywhere in the world, the diagnosis of SARS-CoV disease should be considered only in patients who require hospitalization for radiographically confirmed pneumonia and who have an epidemiologic history that raises the suspicion of SARS-CoV disease. The suspicion for SARS-CoV disease is raised if, within 10 days of symptom onset, the patient:
Once person-to-person transmission of SARS-CoV has been documented in the world, the diagnosis should still be considered in patients who require hospitalization for pneumonia and who have the epidemiologic history described above. In addition, all patients with fever or lower respiratory symptoms (e.g., cough, shortness of breath, difficulty breathing) should be questioned about whether within 10 days of symptom onset they have had
Persons with such an exposure history should be evaluated for SARS-CoV disease according to the algorithm in Figure 2.
Lab tests (polymerase chain reaction or PCR) for MERS-CoV are available at state health departments, CDC, and some international labs. Otherwise, MERS-CoV tests are not routinely available. There are a limited number of commercial tests available, but these are not FDA-approved.
For more information about investigating confirmed and probable cases of MERS-CoV, please see the WHO guidelines for investigation of cases of human infection with Middle East Respiratory Syndrome Coronavirus (MERS-CoV) (July 2013). As described in the introduction, "This document provides a standardized approach for public health authorities and investigators at all levels to plan for and conduct investigations around confirmed and probable cases of MERS-CoV infection. It should be read in conjunction with other detailed guidance reference throughout the text, such as current laboratory testing guidelines and study protocols. It will be updated as necessary to reflect increased understanding of MERS-CoV transmission and control."
In humans, the transmission of coronaviruses between an infected individual and others can occur via respiratory secretions. This can happen either directly through droplets from coughing or sneezing, or indirectly through touching contaminated objects or surfaces as well as close contact, such as touching or shaking hands.
The main way that SARS seems to spread is by close person-to-person contact. The virus that causes SARS is thought to be transmitted most readily by respiratory droplets (droplet spread) produced when an infected person coughs or sneezes. Droplet spread can happen when droplets from the cough or sneeze of an infected person are propelled a short distance (generally up to 3 feet) through the air and deposited on the mucous membranes of the mouth, nose, or eyes of persons who are nearby. The virus also can spread when a person touches a surface or object contaminated with infectious droplets and then touches his or her mouth, nose, or eye(s). In addition, it is possible that the SARS virus might spread more broadly through the air (airborne spread) or by other ways that are not now known.
The original source(s), route(s) of transmission to humans, and the mode(s) of human-to-human transmission have not yet been determined; however there is clear evidence of person-to-person transmission. The efficiency of person-to-person transmission of MERS-CoV is not well characterized but appears to be low, given the small number of confirmed cases since the discovery of the virus. As of July 2013, no evidence of sustained community transmission beyond small clusters has been reported in any country. Transmission has occurred between patients in a hospital setting.
It is important to stress that the mode of transmission of MERS-CoV is still not fully understood, as discussed in this media statement released by WHO on July 3, 2013.
The incubation period for SARS is typically 2 to 7 days, although in some cases it may be as long as 10 days. In a very small proportion of cases, incubation periods of up to 14 days have been reported.
While the incubation period is still being investigated, the current case definition uses an onset of illness within 14 days for travel to the Arabian Peninsula or neighboring countries.
Available information suggests that persons with SARS are most likely to be contagious only when they have symptoms, such as fever or cough. To date, no cases of SARS have been reported among persons who were exposed to a SARS patient before the onset of the patient's symptoms. Patients are most contagious during the second week of illness. However, as a precaution against spreading the disease, CDC recommends that persons with SARS limit their interactions outside the home (for example, by not going to work or to school) until 10 days after their fever has gone away and their respiratory (breathing) symptoms have gotten better.
The period of communicability for MERS-CoV is unknown at this time. Until further guidance is available, follow isolation recommendations used for SARS; persons with MERS should be isolated (for example, by not going to work or to school) until 10 days after fever has resolved, provided respiratory symptoms are absent or improving.
There are currently no vaccines or specific treatments for the coronaviruses. Hence, in order to reduce the risk and prevent the spread of infections, simple preventative measure are: good respiratory hygiene, including washing hands; avoiding touching one's eyes, mouth and nose; sanitary disposal of oral and nasal discharges as well as avoiding contact with sick people.
The Centers for Disease Control and Prevention (CDC) recommends the following guidelines for individuals to prevent respiratory illnesses such as SARS-CoV:
For more detailed information, please visit the Centers for Disease Control and Prevention (USA) SARS Infection Control page.
The Centers for Disease Control and Prevention (CDC) recommends the following guidelines for individuals to prevent respiratory illnesses such as MERS-CoV:
For healthcare workers, the CDC recomends standard, contact, and airborne precautions for management of hospitalized patients with known or suspected MERS-CoV infection, based on CDC's case definition for patient under investigation.
These recommendations are consistent with those recommended for the coronavirus that caused severe acute respiratory syndrome (SARS). As information becomes available, these recommendations will be re-evaluated and updated as needed.
The European Center for Disease Prevention and Control (ECDC) recommends the following infection control guidelines for healthcare workers: