What causes National Hormone and Pituitary Program (NHPP): Information for People Treated with Pituitary Human Growth Hormone (Comprehensive Report) ?
We have not found any particular preparation of pituitary hGH that is especially likely to carry CJD. We believe that CJD did not come from a single infected pituitary gland or preparation. Prior to 1977, in an effort to extract as much hormone as possible from the pituitary glands, the glands were often processed repeatedly. Hormone extracted from the same pituitaries was often included in many hormone preparations. Also, patients who got CJD were treated on average for 8.4 years and received many different hormone preparations. This makes it very difficult to identify any preparation associated with transmitting CJD.
                
Doctors wanted to see if a specific preparation of pituitary hGH could transmit CJD. To try to find the pituitary hGH that could have caused CJD, HHS researchers did two things:
                
1. They set up a test in animals, injecting samples of all available preparations of pituitary hGH directly into the brains of monkeys. CJD develops more rapidly if injected into the brain than under the skin, as hGH was used in people. The animals were watched for 10 years. The brains of all animals were examined for signs of CJD. If an animal got sick with CJD, it would help researchers to understand which vials of pituitary hGH were contaminated with the agent that causes CJD.
                
2. They studied people treated with pituitary hGH to see who got CJD and which hormone preparation they might have received based on which preparations were sent to their doctor.
                
Results:
                
- The animal tests did not help find the pituitary hGH that might have caused CJD. One animal developed the disease 5 years after injection of pituitary hGH. Two other animals that received injections from different vials of the same pituitary hGH preparation did not develop CJD.  - None of the people who developed CJD are known to have received the hormone preparation that made the animal sick. At most, two patients (whose records are incomplete) may have received this pituitary hGH preparation. Because of this, we do not believe that the patients who received the hormone preparation that transmitted CJD to the animal have a greater risk of developing CJD than others treated with pituitary hGH. Because each preparation of pituitary hGH was used to fill multiple vials, it is not known if CJD contamination was spread evenly among all vials of pituitary hGH that came from a particular preparation. It's possible that one vial got more contamination and another got little or none from the same preparation of pituitary hGH. It is believed that multiple preparations of pituitary hGH probably had very low levels of the CJD infectious agent. With such low levels of contamination, some vials of a preparation might carry CJD while other vials would not. Further, most of the people who got CJD received pituitary hGH for long periods of time and received many different preparations. + NIDDK + National Hormone and Pituitary Program (NHPP): Information for People Treated with Pituitary Human Growth Hormone (Comprehensive Report)