Are bed bug bites dangerous if left untreated?

Bite marks on body
Some people are allergic to the salivary gland injection made by a bed bug and thus show "mosquito" like welts on their body where the insect has fed.

No visible bite marks on body
Not everyone is allergic to the bed bug salivary gland excretion, therefore, one person may show signs while a partner sleeping in the same bed at the same time shows no signs on their body, when in fact the bug has fed on them too.

Quoted from: http://www.bedbug.com/Page-Bed-Bug-Bites_45.aspx