Prion diseases can have long incubation periods of up to 30 to 40 years and one route of transmission for infectious prions is through the blood. As there was an outbreak of prion disease in the UK in the 1980s we would need to know if someone lived in the UK during this time since they might have been exposed to, and infected by, an infectious prion. As the incubation period is so long infected individuals would not yet have shown symptoms. Transfusion of blood from an infected individual would guarantee that the recipient would be exposed to the infectious prion. Therefore, individuals who may possibly have been infected would be rejected as potential blood donors.
The overall health of the potential target of infection plays a major role in the infection process and poor socio-economic conditions can lead to the compromise of a person’s overall health and their ability to defend themselves against infection. Emerging infectious pathogens are ones that have not been seen before and for which there is no herd immunity to them within the population. This, in combination with compromised overall health due to poor socio-economic conditions, makes the potential for infection even greater.
There were two obvious connections between the pandemics of Spanish flu in 1918, Asian flu in 1957, and Hong Kong flu in 1968. First, there is a similarity in the genetic makeup of the influenza viruses that were involved in these three separate cases, and second, there was the establishment of heard immunity with each infection. The herd immunity that occurred in the population of people exposed to the Spanish flu of 1918 made the Asian flu pandemic of 1957 (39 years later) less serious. The same kind of herd immunity existed when the third pandemic occurred in 1968 (11 years after the Asian influenza pandemic). In each case there were enough people who had been exposed to the previous infection so that the following infections had fewer potential targets to infect.