There is an
infection called Bartonellosis, caused by a Bartonella bacteria. In some people, it causes a scratch rash (looks like fingernail scratches or stretch marks) that are reddish, usually on the trunk, but other places, too. It is transmitted by over two dozen different kinds of insects. It was believed in the past to be a very mild infection that didn't require antibiotics, but in the last 10 years, doctors are beginning to discover that it is worse than previously realized.