Pathogenesis Coronaviruses tend to be highly species specific. Most of the known animal coronaviruses display a tropism for epithelial cells of the respiratory or gastrointestinal tract. Corona virus infections in vivo may be disseminated, such as with mouse hepatitis virus, or localized. Coronavirus infections in humans usually, but not always, remain limited to the upper respiratory tract.

In contrast, the outbreak of SARS-CoV in 2003 was characterized by serious respiratory illness, including pneumonia and progressive respiratory failure. Virus could also be detected in other organs, including kidney, liver, and small intestine, and in stool. The SARS virus probably originated in a nonhuman host, most likely bats, was amplified in palm civets, and was transmitted to humans in live animal markets. Chinese horseshoe bats are natural reservoirs of SARS like coronaviruses. In rural regions of southern China, where the outbreak began, people, pigs, and domestic fowl live close together, and there is widespread use of wild species for food and traditional medicine—conditions that promote the emergence of new viral strains.

The MERS-CoV outbreak beginning in 2012 was also characterized by pneumonia and respiratory failure, though most patients who died had medical comorbidities. MERS CoV likely originated in bats and became widespread in camels as shown by seropositivity in animals in the region. It is likely that contact with either bats or camels leads to initial human infections, which can then be transmitted from per son to person.

Coronaviruses are suspected of causing some gastroenteritis in humans. There are several animal models for enteric coronaviruses, including porcine transmissible gastroenteritis virus (TGEV). Disease occurs in young animals and is marked by epithelial cell destruction and loss of absorptive capacity. It is of interest that a novel porcine respiratory coronavirus (PRCV) appeared in Europe in the 1980s and caused widespread epizootics in pigs. Sequence analysis showed that PRCV was derived from TGEV by a large deletion in the S1 glycoprotein.

Clinical Findings

The human coronaviruses produce “common colds,” usually afebrile, in adults. The symptoms are similar to those produced by rhinoviruses, typified by nasal discharge and malaise. The incubation period is from 2 to 5 days, and symptoms usually last about 1 week. The lower respiratory tract is seldom involved, although pneumonia may occur. Asthmatic children may suffer wheezing attacks, and respiratory symptoms may be exacerbated in adults with chronic pulmonary disease. SARS-CoV causes severe respiratory disease. The incubation period averages about 6 days. Common early symptoms include fever, malaise, chills, head ache, dizziness, cough, and sore throat, followed a few days later by shortness of breath. Many patients have abnormal chest radiographs. Some cases progress rapidly to acute respiratory distress, requiring ventilatory support. Death from progressive respiratory failure occurs in almost 10% of cases, with the death rate highest among the elderly. SARS involves a cytokine storm, with elevated levels of multiple chemokines and cytokines in the peripheral circulation for about 2 weeks.

MERS-CoV causes mild to severe respiratory illness in children and adults. Patients with comorbidities are more severely affected, as are the elderly. The incubation period is 2–13 days, with extended illness in some cases leading to pneumonia and death. Laboratory findings include leukopenia, lymphopenia, thrombocytopenia, and elevated lactate dehydrogenase levels. The mortality rate is stated as up to 30%, but this is likely to be an overestimate as mild cases are not typically reported.

Clinical features of coronavirus-associated enteritis have not been clearly described. They appear to be similar to those of rotavirus infections.

Immunity

As with other respiratory viruses, immunity develops but is not absolute. Immunity against the surface projection anti gen is probably most important for protection. Resistance to reinfection may last several years, but reinfections with simi lar strains are common.

Most patients (>95%) with SARS or MERS developed an antibody response to viral antigens detectable by a fluorescent antibody test or enzyme-linked immunoassay (ELISA).

Laboratory Diagnosis

 A. Antigen and Nucleic Acid Detection Coronavirus antigens in cells in respiratory secretions may be detected using the ELISA test if a high-quality antiserum is available. Enteric coronaviruses can be detected by examination of stool samples by electron microscopy. Polymerase chain reaction (PCR) assays are the preferred methods to detect coronavirus nucleic acid in respiratory secretions and in stool samples. Viremia with SARS and MERS coronaviruses is detectable in the plasma by PCR.

B. Isolation and Identification of Virus

Isolation of human coronaviruses in cell culture has been difficult. However, the SARS and MERS viruses have been recovered from oropharyngeal specimens using Vero monkey kidney cells.

C. Serology

 Because of the difficulty of virus isolation, serodiagnosis using acute and convalescent sera is one means of confirming coronavirus infections for epidemiologic purposes. ELISA, indirect immunofluorescent antibody assays, and hemagglutination tests may be used. Serologic diagnosis of infections with strain 229E is possible using a passive hemagglutination test in which red cells coated with coronavirus antigen are agglutinated by antibody-containing sera.

Epidemiology

Coronaviruses are distributed worldwide. They are a major cause of respiratory illness in adults during some winter months when the incidence of colds is high, but the isolation of rhinoviruses or other respiratory viruses is low. They tend to be associated with well-defined outbreaks.

It is estimated that coronaviruses cause 15–30% of all colds. The incidence of coronavirus infections varies markedly from year to year, ranging in one 3-year study from 1% to 35%.

Antibodies to respiratory coronaviruses appear in childhood, increase in prevalence with age, and are found in more than 90% of adults. It appears that reinfection with symptoms can occur after a period of 1 year. However, antibodies to SARS and MERS coronaviruses are uncommon, showing that they have not circulated widely in humans.

Coronaviruses are commonly associated with acute respiratory disease in the elderly, along with rhinoviruses, influenza virus, and respiratory syncytial virus. The frequency of coronavirus infection is estimated to be about half that of rhinoviruses and equivalent to those of the latter two viruses.

Coronaviruses are transmitted by contact with respiratory droplets, contaminated surfaces, and fomites (contaminated inanimate objects). There is a risk of transmission in the health care setting, with documented hospital outbreaks.

The outbreak of SARS erupted in southern China in late 2002 and, by the time it waned in mid-2003, had resulted in over 8000 cases in 29 countries, with over 800 deaths (case fatality rate of 9.6%). In almost all cases, there was a history of close contact with a SARS patient or of recent travel to an area where SARS was reported. International air travel allowed SARS to spread around the world with unprecedented speed. The experience with SARS illustrated that in a globalized world, an infectious disease outbreak anywhere places every country at risk.

Interestingly, a few persons with SARS were identified as “super spreaders”; each appeared to have infected more than 10 contacts. Super spreaders have been described for other diseases such as rubella, Ebola, and tuberculosis and presumably reflect a certain constellation of host, viral, and environ mental factors.

The MERS coronavirus was identified in 2012 as the cause of a patient who died of respiratory failure in Saudi Arabia. Subsequently, it was determined to be the cause of multiple outbreaks of respiratory disease from several countries in the Arabian Peninsula. The virus appears to be endemic in bats and camels in the region. Infected travelers have spread the virus in other countries, and it remains a risk for transmission from pilgrims returning from the annual Hajj in Mecca.

Very little is known about the epidemiology of enteric coronavirus infections.

Treatment, Prevention, and Control

 There is no proven treatment for coronavirus infections and no vaccine. Protease inhibitors used in the treatment of human immunodeficiency virus infections (eg, lopinavir) have in vitro activity against SARS coronavirus. SARS and MERS vaccines are under development.

Control measures that were effective in stopping the spread of SARS included isolation of patients, quarantine of those who had been exposed, and travel restrictions, as well as the use of gloves, gowns, goggles, and respirators by health care workers. There remains a high suspicion for MERS-CoV in patients returning from the Arabian Peninsula, which requires appropriate testing and infection control precautions to prevent further spread.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم شؤون المعارف يصدر كتابًا حول قصيدة الفرزدق في مدح الإمام زين العابدين (عليه السلام)

الأمين العام للعتبة العباسية المقدسة يشارك في حفل افتتاح مشروع تجديد الإيوان الذهبي بحرم أمير المؤمنين (عليه السلام)

المجمع العلمي يطلق ورشًا تطويرية لقرّاء الختمات الرمضانية في بابل

سماحة السيد الصافي يشيد بجهود دار علوم نهج البلاغة ويوجه باعتماد أحد مناهجها وتوسيع طباعة كراس عهد مالك الأشتر

المزيد

الآخبار الصحية

هل توقيت نشاطك اليومي يؤثر على صحة دماغك؟.. العلماء يجيبون

"مشروب محبوب" يخفي فوائد لا يعرفها كثيرون

طبيب يكشف 5 أنواع للسعال.. بعضها خطير

نقص فيتامينات "خفي".. قد يفسّر التعب والتنميل وقلة التركيز

المزيد

الآخبار التكنلوجية

دراسة: تغيّرات في أسلوب القيادة قد تكشف مبكرا عن الخرف !

عمرها 773 ألف سنة.. اكتشاف أقدم أحافير بشرية في المغرب

"اختراق علمي".. اختبار دم في منزلك قد يكشف ألزهايمر

ماذا يحدث للجسم عند قطع الكافيين فجأة؟

المزيد

مواضيع ذات صلة

Pathogenesis and Pathology of Rabies Virus

Properties of the Rabies Virus

Properties of Coronaviruses

Congenital Rubella Syndrome

Postnatal Rubella

Hendra Virus and Nipah Virus Infections

Measles (Rubeola) Virus Infections

Rhabdoviruses

Retroviruses

Reoviruses

Poxviruses

Role of Biomarkers in COVID-19