For the first time since 1994, the polio virus has been detected in Brazil, the World Health Organization said Monday. The virus — minute amounts of which can be detected — was found in a sewage sample from an airport near Campinas, in southeastern Brazil. It was collected in March and matched a strain recently found in Equatorial Guinea on the central African coast. There are no reports of any cases of paralysis; for every child paralyzed by polio, health authorities estimate that 200 more are carrying and shedding the virus with few or no symptoms. Because about 95 percent of Brazilian children are immunized against polio, the W.H.O. says it is very unlikely that the virus will spread widely and has not suggested any restrictions on travel to or from the country.