That deals with both symptoms and infectivity.
Even for diseases in which it may protect individuals, isolation will often have little effect on the general epidemic; this may be, as in measles, because infectivity precedes the appearance of the characteristic feature, the rash, by a few days, or, as in polio virus infections, because a number of persons are carriers, harbouring the disease agent without discernible illness.
The core confers infectivity, and the capsid provides specificity to the virus.
Each serotype includes a number of strains having different degrees of infectivity, virulence, and pathogenicity.
In several large outdoor tests, scientists drifted clouds of tularemia over cages of live monkeys to evaluate the infectivity.
"There are hundreds of strains of cold viruses, and they have different rates of infectivity," said Dr. Jacobson, an internist and allergist.
Then they jacked up the viral infectivity so that a few days into the fictional epidemic dozens of unrecognized cases already dot the globe.
Many other sub-Saharan countries, Botswana (35%), Zimbabwe (25%), Lesotho (23%), Zambia (20%), and Namibia (19%) have higher rates of infectivity among adults.
"I wince every time I see the TV images with people in space suits because it gives an impression about the infectivity of the virus that is not realistic, it is an overreaction," he said.
Every three months his blood is tested to keep a check on his immune system and viral load - the measure of infectivity.
If the H.I.V.-contaminated fluid dries, its infectivity may decrease.
