Defiling the Eucharist, which Catholics believe is the body and blood of Christ, is also considered a and one which is on the increase, the high-ranking members of the tribunal said.
Such sins, which can only be dealt with by the Pope, acting through the tribunal, bring automatic excommunication from the Church. If the Pope decides to grant absolution, the excommunication is lifted.
~ Vatican reveals secrets of worst sins - Telegraph
This illustrates why religious values are a poor guide for human morality. Desecration of a symbol (though Catholic believe the Eucharist IS the body of Christ) is ranked as a worse sin than, say, a priest molesting a child or a man murdering his wife.