Perhaps. But usually hepatitis is caused by a virus or a bacteria.
sewer gas. either your trap has run dry from lack of use or is improperly or not vented causing your line to syphone. this will cause the water in the p-trap to syphone out allowing the sewer gas to ecsape.
Yes, if sewer gas is coming into your home from a backed up drain it can be very harmful to a baby and everyone else inside the home. It can cause hydrogen sulfide poisoning and asphyxiation.
Over time yes as it does cause some type of brain and liver cancers
Awful.
methane gas
Awful.
Yes, sewer gas can be explosive as it is generally a combination of methane, hydrogen sulfide and a variety of other noxious gases.
There is no permanent health effect of sewer gas odors but it can make one nauseated to smell the odor.
Only if the trap fell off and it was not properly vented
Yes and it can cause headaches, cancer, and other health problems such as breathing and such!
The vent terminal is allowing down drafts to enter thus one would have to install a return bend on this pipe to prevent the air from entering but it will allow sewer fumes to escape
If you think you smell sewer gas in your bathroom, it could be that a sewage blockage is in your pipes, causing the sewage to back up in the lines.