Epidemics from Viruses

Other viruses can cause chronic and lifelong infections, in which the host is infective and has the virus replicating continually inside them. There are a number of individuals chronically infected with the hepatitis B and hepatitis C viruses, leading to a carrier status, in which the person does not get particularly ill but can pass the virus on. A high rate of carriers in a population will lead to an endemic viral infection.

Most viruses get passed horizontally, through droplets, casual touch, blood, stool, contaminated food, contaminated water, and secretions. The degree of infection depends on how many susceptible individuals there are in the community, the means of transmission of the virus, and how virulent the virus is. Vaccines and improved sanitation will help reduce the means of infection as well as the number of susceptible individuals. People (and plants and animals) get quarantined when sick in order to prevent disease. Sometimes animals are destroyed to thin out the numbers of diseased organisms, such as happened to thousands of cows in Great Britain.

Often with viral infections, there is an overlap between the incubation period and the symptomatic period, in which the individual is able to infect other people, called the communicative period. This is what makes it sometimes very difficult to prevent infections entirely. This will lead to epidemics, in which large numbers of people is infected, or pandemics, in which the entire world is affected by the presence of infection.

EPIDEMICS FROM VIRUSES

There have been numerous epidemics and pandemics from viral infections throughout history. Smallpox, for example, killed about 70 percent of the Native American population because it was brought over from the Old World to the New World by Christopher Columbus’ crew. Another serious pandemic was the 1918 influenza pandemic caused by the influenza A virus, it killed about 5 percent of the population of the world. HIV has been a more recent pandemic, starting in sub-Saharan Africa, killing about 25 million people since it was first recognized as a viral infection in 1981. Very popularized viral epidemics have come from filoviruses, such as Ebola and Marburg viruses, leading to viral hemorrhagic fever.