No pleading on behalf of the plaintiff shall be necessary except the petition mentioned in § 8.01-537. The principal defendant, and any other defendant who seeks to defeat the petitioner’s attachment, may demur to the petition, issue on which demurrer shall be deemed to be joined; but if such demurrer be overruled, such defendant shall answer the petition in writing. No replication shall be necessary to such answer. The answer shall be sworn to by such defendant, or his agent. Any other defendant may answer the petition, under oath, and the cause shall be deemed at issue as to him, if he denies any of the allegations of the petition, without any replication. Answers under this section shall not have the effect of evidence for the defendant.