Dental work releases many millions of bacteria into the blood.

People getting joint replacement, often are given prophylaxis with antibiotics to prevent joint infections. This is being modified now. But people with heart replacement valves still are given antibiotics before dental procedures.

Strep is well known to travel to the heart and cause vegetations on healthy valves. Rheumatic heart disease, killed my mother.

Also the risk of bacterial endocarditis is higher for women who have just delivered their babies.

Bacteria do get into the blood somehow, it is just that intestinal ones are still controversial. I'd like to see some studies showing results of cultures done with blood sera to see if they really do.

Parasites? Well, some of them do move around. Toxoplasmosis will get into the retina and brain.
Hook worms will get from the feet (where larva live in soil) and end up in the GI mucosa. Pork tapeworms will end up in the brain and cause holes in the brain tissue!

There is a show from TV called The Monsters Inside Me....
I can't get it to load right now, you might Google it after all the hurricaine servers open up.
edit to add... I finally got thru to this link:
Monsters Inside Me | Animal Planet

I think alot depends on the virulence of any organism that gets into the blood. Some organisms are more likely to establish disease in mammals and humans than others.
Candida ( a fungus) does create aldehyde congeners which are irritating to nerves. I have seen claims that up to 50% of adults carry this fungus(a yeast) in the gut. The congeners are similar to those in alcoholic drinks like wine and beer. They are byproducts of the fermentation process and everyone consumes them as adults in one form or another (they are in vinegars except the distilled white). The metabolism of aldehydes relies on vitamin B1.