Coronaviruses are a major cause of the common cold. They gained notoriety in 2002 due to the SARS (severe acute respiratory syndrome) pandemic, which had a case fatality rate of up to 50%. The virus has a high frequency of recombination. Its replicative cycle is unique because it obtains its envelope from the endoplasmic reticulum, not the plasma membrane. The receptor for SARS-CoV is angiotensin converting enzyme 2.
Clinical features: The common cold presents with nasal discharge, mild fever, cough, sore throat, and malaise. Coronaviruses can also cause gastroenteritis in infants. SARS causes severe pneumonia with fever, cough, and dyspnea, with hypoxia resulting from pulmonary edema. Leukopenia and thrombocytopenia may be seen.
Laboratory diagnosis of Coronavirus infections: Infection can be detected by ELISA, electron microscopy of stool samples, PCR, and cell culture.
Rotavirus is in the Reovirus family. It is the only medically important RNA virus that is double stranded. It has a wheel-like morphology. Depending on the outer viral hemagglutinin, it is divided into six serotypes. Antibody to hemagglutinin is protective against further infection. Beta adrenergic receptors are the receptors the virus uses to attach to human cells. Calcium ions play an important role in the Rotavirus replicative cycle. The Rotavirus protein NSP 1 functions as an interferon antagonist.
Mechanism of Rotavirus diarrhea: Rotavirus causes watery diarrhea with minimal intestinal inflammation. It primarily infects intestinal villus enterocytes, while crypts are spared. Several mechanisms contribute to diarrhea:
Rotavirus infection can spread extra intestinally also.
Clinical features: Patients are typically infants and children under 2 years of age. They present with vomiting and greenish yellow, non-bloody, watery diarrhea. It may cause dehydration.
Laboratory diagnosis of Rotavirus diarrhea: Detection of Rotavirus in stool samples by electron microscopy, immunoassay, or ELISA are preferred methods. IgM and IgG antibodies can be detected in blood by ELISA.
Norwalk virus belongs to the family Calicivirus and is also called Norovirus. It causes outbreaks of viral gastroenteritis in long-term healthcare facilities, restaurants (lettuce, fresh fruit, and shellfish being the main culprits), schools and childcare facilities, and cruise ships. It presents with fever, abdominal cramps, nausea, vomiting, and non-bloody diarrhea. Headache and photophobia can occur.
Laboratory diagnosis is made by viral antigen detection in stool by RT PCR or electron microscopy. Antibodies can be detected by ELISA. In stool microscopy, remember that no pus cells or RBCs are seen.
Human astroviruses (HAtVs) are positive-sense single-stranded RNA viruses. They are star shaped, hence the name. Classic HAstVs contain 8 serotypes and account for 2 to 9% of all acute nonbacterial gastroenteritis in children worldwide. Infections are usually self-limiting but can also spread systemically and cause severe infections in immunocompromised patients. The diarrhea is mild and watery, with fever and abdominal pain. It is a zoonosis.
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