Pathogens steal our genes to mask their presence
Did you know? That microbes have ‘stolen’ some of our genes? Yes, over the course of evolution, microbes closely associated with eukaryotes (basically non-bacteria, non-archaea, non-virus) such as humans have been known to assimilate bits and pieces of the host DNA.
(Image from Montana State University)
While it may not always confer something useful, every once in a while they may pick up a gene that encodes human cell surface proteins, which when expressed masks the microbe’s cell surface, causing the host to ‘believe’ that the microbe is in fact part of itself, hence ignoring it.
This is why some microbial infections are hard to treat. While the human immune system is generally pretty good at fighting off bacterial infections, it can’t really do anything if it can’t find the pathogens in question. D: Similarly with DNA viruses that embeds themselves in human DNA (retroviruses). Kind of hard to get rid of them when they’re actually a part of yourself.
Current research is focused on better understanding the microbial ability to dodge host responses, although it’s still early work. Until more can be discovered, chronic bacterial infections will unfortunately persist. :/