by Albie Graham (Editor) Human respiratory viral infections are diseases caused by a range of viruses having similar characteristics, which negatively affect the respiratory system and respiratory tract. The viruses that cause respiratory viral infections encompass parainfluenza viruses, respiratory adenoviruses, influenza viruses and respiratory syncytial virus (RSV). These spread directly through coughing or sneezing, which results in the transmission of viruses when they are inhaled. They can also spread indirectly by coming in contact with contaminated surfaces, hands, handkerchiefs, toys, etc. Some common symptoms of respiratory viral infections are fever, headache, chills, loss of appetite, body ache and weakness.