This chapter discusses some DNA viruses and RNA viruses. They lead to infectious diseases. Human adenoviruses are transmitted through the fecal-oral route or through inhalation of respiratory droplets and are very common, with most individuals demonstrating evidence of prior infection by the age of ten. Infections are typically subclinical, mild, or self-limiting and can result in a variety of symptoms depending on the type, including respiratory tract infection, urinary tract infection, gastroenteritis, and conjunctivitis. Herpesviruses affect a wide range of animal species, including insects, fish, mollusks, reptiles, birds, and mammals. Herpes simplex viruses (HSV) include two types: HSV-1 and HSV-2. Both can cause oral and genital ulcerations characterized by an initial infection and latency with recurrent infections. Oropouche virus infection is typically a self-limiting disease with symptoms of fever, headache, myalgia, nausea, arthralgia, and less commonly, meningitis. It is characterized by both an urban and a sylvatic cycle.