Young polio victims receiving physiotherapy in the 1950s The<unk>  describes the influence of<unk>  and viral infections on human history. Epidemics caused by<unk>  began when human behaviour changed during the Neolithic period, around 12,000 years ago, when humans developed more densely populated agricultural communities. This allowed<unk>  to spread rapidly and subsequently to become endemic.<unk>  of plants and livestock also increased, and as humans became dependent on agriculture and farming, diseases such as potyviruses of potatoes and rinderpest of cattle had devastating consequences. Smallpox and measles<unk>  are among the oldest that infect humans. Having evolved from<unk>  that infected other animals, they first appeared in humans in Europe and North Africa thousands of years ago. The<unk>  were later carried to the New World by Europeans during the time of the Spanish Conquests, but the indigenous people had no natural resistance to the<unk>  and millions of them died during epidemics. Influenza pandemics have been recorded since 1580, and they have occurred with increasing frequency in subsequent centuries. The pandemic of 1918–19, in which 40–50 million died in less than a year, was one of the most devastating in history. Louis Pasteur and Edward Jenner were the first to develop vaccines to protect against viral infections. The nature of<unk>  remained unknown until the invention of the electron microscope in the 1930s, when the science of virology gained momentum. In the 20th century many diseases both old and new were found to be caused by<unk> . There were epidemics of poliomyelitis that were only controlled following the development of a vaccine in the 1950s. HIV is one of the most pathogenic new<unk>  to have emerged in centuries. Although scientific interest in them arose because of the diseases they cause, most<unk>  are beneficial. They drive evolution by transferring genes across species, play important roles in ecosystems and are essential to life.
Social history of viruses
History of virology
History of dermatology
History of medical diagnosis
History of neuroscience
History of neurology and neurosurgery
History of dental treatments
Timeline of sexual orientation and medicine