Guanarito virus: a virus that causes the disease Venezuelan hemorrhagic fever in humans. Guanarito virus is a member of the arenavirus family of RNA viruses. These viruses typically live in rodent hosts and spread among the rodents without causing apparent disease. Humans can become infected when they come in contact with rodent secretions or droppings. Guanarito virus is found only in Venezuela in a south American rodents. It is not clear if this virus could live in North American rodents. It is also not spread from person to person.