Magic In Biology

Clinical Presentation

Coronaviruses cause acute, mild upper respiratory infection (common cold).

Structure

Spherical or pleomorphic enveloped particles containing single-stranded (positive-sense) RNA associated with a nucleoprotein within a capsid comprised of matrix protein. The envelope bears club-shaped glycoprotein projections.

Classification

Coronaviruses (and toroviruses) are classified together on the basis of the crown or halo-like appearance of the envelope glycoproteins, and on characteristic features of chemistry and replication. Most human coronaviruses fall into one of two serotypes: OC43-like and 229E-like.

Multiplication

The virus enters the host cell, and the uncoated genome is transcribed and translated. The mRNAs form a unique “nested set” sharing a common 3′ end. New virions form by budding from host cell membranes.

Pathogenesis

Transmission is usually via airborne droplets to the nasal mucosa. Virus replicates locally in cells of the ciliated epithelium, causing cell damage and inflammation.

Host Defenses

The appearance of antibody in serum and nasal secretions is followed by resolution of the infection. Immunity wanes within a year or two.

Epidemiology

Incidence peaks in the winter, taking the form of local epidemics lasting a few weeks or months. The same serotype may return to an area after several years.

Diagnosis

Colds caused by coronaviruses cannot be distinguished clinically from other colds in any one individual. Laboratory diagnosis may be made on the basis of antibody titers in paired sera. The virus is difficult to isolate. Nucleic acid hybridization tests (including PCR) are now being introduced.

Control

Treatment of common colds is symptomatic; no vaccines or specific drugs are available. Hygiene measures reduce the rate of transmission.

Every nucleus in the human body has DNA of 6 feet long.

Our bone marrow produces 260 billion red blood cells (RBCs) and 135 billion white blood cells (WBCs) per day.