Virus Types

After years of searching for a single, elusive common cold virus, scientists have discovered not one virus, but eight different groups including more than 200 viruses that can cause the illness called a cold—and sometimes flu or worse. All eight groups share one insidious trait: an affinity for the human respiratory tract. In every other way they vary widely, as can be seen from these photographs, in which each virus is magnified about 200,000 times.
Two viral groups, rhino virus (belo4.id corona virus (right), account for about half of all colds; the other six groups cause only about 10 per cent, leaving the cause of the remainder about two out of every five colds a mystery yet to be solved. Meanwhile, the full roles of the known cold viruses are still being explored. One discovery: Respiratory syncytial virus (opposite, top left) causes colds in adults, but pneumonia and bronchiolitis in infants and small children.

CORONA VIRUS
The second largest cause of colds, corona viruses were discovered in 1965 and named for their crownlike circlets, which resemble a solar corona. They are spread in airborne droplets from coughs and sneezes, and tend to strike in midwinter.

RHINO VIRUS
Named from the Greek for nose,” where its effects are felt, but looking like geodesic domes, rhino viruses spread by direct contact. More than 100 types infect human hosts the year round, causing more colds than any other group of viruses.

INFLUENZA VIRUS
Three types of influenza virus, subdivided into many strains, cause colds and flu. All are round, about four billionths of an inch in diameter (medium size for a virus) and studded with spikes. Type A, the most common and dangerous, is shown above.

RESPIRATORY SYNCYTIAL VIRUS
Generally spherical and always covered with spiky projections, this cold virus strikes in winter. It produces lower respiratory tract illness in infants and small children.

PARAINFLUENZA VIRUS
Largest of cold viruses (up to 12 billionths of an inch in diameter), parainfluenza viruses cause colds that in infants and children may lead to croup or pneumonia. These particles broke open as they were prepared for viewing, and hereditary material poured out.

ADENO VIRUS
Intricate assemblages offacets and knob- tipped rods, adeno viruses produce late winter, spring and early-summer colds, but rarely attack people over 15.

ECHO VIRUS
Close cousins of the coxsackie viruses and identical in structure, echo viruses cause colds accompanied by fever, sore throats and severe coughs, especially in children.

COXSACKIE VIRUS
These viruses have 20 facets, invisible even at 200,000-times magnification. Named for New York town where they were discovered, they cause colds with fever.