What kinds of pathogens cause the damaging chronic diseases we don’t know about? What should we look for? Persistent infections are more likely to cause chronic diseases than short life infections because the more time a pathogen has to gum up the body’s machinery, the more likely it is that it will.
Internal pathogens are more likely to cause problems than external ones because internal tissues are more delicate and more central to life processes, moreover, internal pathogens must cope with the immune system both to survive and to get out and this ups the ante. Their persistence in the host provokes immune logical destruction of infected cells and inevitable casualties from friendly fire.
The tricks that allow a pathogen to avoid immunological destruction can push our immunological systems to the point of self destruction.
These criteria fit those pathogens that have been traditionally classified as sexually transmitted. They also fit pathogens that are transmitted by less hard core sexual contact, such as Epstein-Barr virrus, which causes infectious mononucleosis and is transmitted by intimate kissing.
Sexually transmitted diseases make up only a small fraction of human diseases, but they are major players in the known chronic diseases caused by infection. Syphilis, infertility due to Chlamydia and gonorrhea, arthritis and ectopic pregnancy caused by Chlamydia, and cervical cancer are just a few of the mentally or physically debilitating chronic diseases caused by sexually transmitted pathogens. Sexually transmitted pathogens are likely to cause a disproportionately large number of the infectious chronic diseases yet to be discovered.
We already know of some suspects. Human parvovirus B19, for example, probably contributes to the crises of sickle cell anemia and yo chronic diseases such as arthritis and multiple sclerosis. Some recent evidence indicates that it may be at least partly a sexually transmitted pathogen,
The other infectious causes of chronic diseases will probably be an eclectic collection much like those that have already been discovered a grab bag of pathogens. Some of these pathogens may rely on their persistence for transmission, like H,pylori and the papillomaviruses.
Others may just by chance have characteristics that allow them to persist in the body in places unrelated to transmission. Still other pathogens may cause chronic disease because of long term disturbances of the body’s machinery that persist even after the pathogen is gone. Some autoimmune responses might fall into this category, such as chronic heart disease caused by streptococcal infections.