The risks when using pig organs were considered to be very small but recent research has shown that pig genes contain previously unknown viruses that can infect human cells in vitro . There is also a risk to the animal population being used, a virus which is usually dormant could be activated when in humans and be lethal to that species. The animals used would be reared in a 'germ-free' environment. They would be born by caesarian section and hand reared in a controlled environment. This is one of the reasons non-human primates are no longer considered viable, it would take many years to build up a stock of donors.
Pigs have larger litters and breed quickly.
This means that the organs are technically safer than if they have transplanted from a human cadaver in which case tht environment has not been controlled in any way. This is a point worth considering when looking at risks of infection. In theory the testing of herds of pigs used as donors would be much easier than with human donors where there is very little knowledge of previous contact with diseases. The chief concern has to be for the public as a whole, the patient will be suffering from a life threatening disease, typically end-stage organ failure, so will be prepared to take the risk but if they do contract a serious disease it could be transmitted to others. It is concievable that if a disease was contracted the patient would have to be quarantined to protect others.