Viruses are microscopic entities that replicate within living cells. Their discovery and characterization are ongoing processes, crucial for understanding infectious diseases. Scientists continuously work to identify new viral threats, including coronaviruses, to address potential public health impacts.
The First Sightings
Coronavirus infections were first reported in the late 1920s, causing a respiratory illness in chickens in North America. The causative agent, infectious bronchitis virus (IBV), was isolated in 1933. In the mid-1960s, researchers identified the first human coronaviruses, HCoV-229E and HCoV-OC43, which caused common cold symptoms.
In 1967, electron microscopy revealed the distinctive appearance of these early human and animal coronaviruses. Scientists noted spike-like projections on their surface, giving them a crown-like or “corona” appearance. This led to their collective name “coronavirus” and established them as a distinct viral group with shared structural characteristics.
Unveiling New Threats
For decades, human coronaviruses were largely associated with mild respiratory illnesses. This perception shifted dramatically with the emergence of severe acute respiratory syndrome (SARS) in late 2002. SARS-CoV, identified in 2003, caused a severe pneumonia outbreak that spread across multiple countries. It likely originated in bats, then crossed the species barrier into civet cats before infecting humans.
In 2012, Middle East Respiratory Syndrome Coronavirus (MERS-CoV) emerged in Saudi Arabia. MERS-CoV caused severe respiratory illness and was linked to dromedary camels as a primary source of transmission to humans. These outbreaks demonstrated the potential for coronaviruses to cause severe disease in humans and to jump from animal hosts.
The Global Impact Discovery
The most recent and widespread global impact came with the identification of SARS-CoV-2, the virus causing COVID-19. Cases of atypical pneumonia were first reported in Wuhan, China, in December 2019. Scientists quickly identified a novel strain of coronavirus as the cause, with its genome sequence made publicly available by early January 2020.
The rapid sharing of genetic information allowed for quick development of diagnostic tests and accelerated research efforts worldwide. The World Health Organization declared COVID-19 a pandemic in March 2020, underscoring the swift global recognition and spread of this novel virus.
Identifying Viral Features
Scientists employ various methods to discover and identify coronaviruses, relying on their unique structural and genetic characteristics. Electron microscopy is a fundamental tool, allowing researchers to visualize the virus’s distinctive morphology. These images reveal the spherical or pleomorphic shape of the virus particles, typically ranging from 60 to 140 nanometers in diameter. The characteristic “crown-like” appearance, formed by spike proteins protruding from the viral envelope, is a key visual identifier.
Genomic sequencing plays a central role in precisely identifying and classifying new coronaviruses. By decoding the virus’s genetic material, scientists can determine its specific strain, track its evolution, and understand its relationship to other known viruses. The spike protein, located on the virus’s surface, facilitates the virus’s entry into host cells and is often a target for diagnostic tests and vaccine development.