Is it possible to infect yourself?

[zapatos]

Is it possible for someone to carry a virus or bacteria in their body without it causing a disease in them, then later infect themselves? For example, cold virus will typically infect a person when a person transmits the virus on their hand to the nose or eye. Is it possible to eat something with the virus on the surface of the food, have the virus pass harmlessly through the gut, end up on the person's hand, then finally make to the eye or nose where the person then gets a cold?

 

There are also many bacteria in the digestive system that cause no problem to humans. Could that bacteria pass through the intestines, encounter a tear in the skin on the way out of the body, and cause some kind of infection in the person now that is is out of the digestive tract and into the blood stream?

 

And an add-on question, why is bacteria allowed in the digestive tract? Does the body recognize the bacteria as 'self', or is the digestive tract somehow not covered by the immune system?

[Acme]

snip...

And an add-on question, why is bacteria allowed in the digestive tract? Does the body recognize the bacteria as 'self', or is the digestive tract somehow not covered by the immune system?

 

I don't know the answers to the snipped bit, but I do know something on the add on question in regard to bacteria in the human gut . I hope a wiki article will suffice; if not there are other links there to more in depth expositions. :

 

 

Gut flora

Gut flora consists of microorganisms that live in the digestive tracts of animals and is the largest reservoir of human flora. In this context, gut is synonymous with intestinal, and flora with microbiota and microflora.The human body, consisting of about 100 trillion cells, carries about ten times as many microorganisms in the intestines.^[1][2][3][4] The metabolic activities performed by these bacteria resemble those of an organ, leading some to liken gut bacteria to a "forgotten" organ.^[5] It is estimated that these gut flora have around 100 times as many genes in aggregate as there are in the human genome.^[6]

 

Bacteria make up most of the flora in the colon^[7] and up to 60% of the dry mass of feces.^[2] Somewhere between 300^[2] and 1000 different species live in the gut,^[3] with most estimates at about 500.^[4][5][8] However, it is probable that 99% of the bacteria come from about 30 or 40 species.^[9] Fungi and protozoa also make up a part of the gut flora, but little is known about their activities.

 

Research suggests that the relationship between gut flora and humans is not merely commensal (a non-harmful coexistence), but rather a symbiotic relationship. ...

[Suxamethonium]

Um, firstly the digestive tract is a lumen, it is not the "inside" of the body... its the "outside". Think like a donut. So, the bacteria inside the digestive tract are effectively outside our bodies, the same as if they were on our skin. As such, perforating the bowel commonly leads to serious bacterial infections and toxicity (Escherichia coli is well known). So in that respect, yes you could say a person could infect themselves. However, if they have already contracted the pathogen (inside their body) but its dormant, asymptomatic, etc, they are still 'infected', and depending on the pathogen and its stage of developement, possibly 'infectious' to others.

[Mrs Zeta]

One could argue that the activation of the varicella zoster (Chickenpox) virus that causes herpes zoster (shingles) is a typical example of 'infecting' yourself.