Viruses are tiny infectious agents that can cause diseases in humans, animals, and plants. They spread when a virus enters a host’s body and uses living cells to reproduce. Common causes of viral infections include contact with an infected person, coughing or sneezing, contaminated food or water, touching infected surfaces, insect bites, and exposure to infected blood or body fluids. Some viruses can also spread from animals to humans. Poor hygiene, close contact, and weakened immunity can increase the risk of infection. Examples of viral diseases include influenza, COVID-19, measles, dengue, and hepatitis. Good hygiene, vaccination, and avoiding exposure help prevent viral infections.