Authors: Paula Marco and Nerea Larrañaga
Human prion diseases (such as Creutzfeldt-Jakob disease (CJD), fatal familial insomnia (FFI) and Gerstmann-Sträussler-Scheinker syndrome (GSS), among others) are a group of rapidly progressive, fatal and potentially transmissible neurodegenerative disorders caused by the misfolding of the physiological protein PrPCwhich results in a pathological form (PrPSc) or prion, the accumulation of which in the body (mainly in the central nervous system) leads to neuronal death and the development of the pathology.
This group of diseases are extremely rare and therefore little known, with an estimated incidence of 1-2 cases per million people per year. However, they have had a significant impact on public health due to their potential transmissibility, severity and difficulty to diagnose, highlighting the importance of constant epidemiological monitoring (i.e. active surveillance of the number of cases and their global distribution). A new study published in June 2024 entitled "Updated global epidemiology atlas of human prion diseases"presents an updated overview of the global situation of human prion diseases, revealing important facts about their distribution and the challenges faced by health systems in monitoring them.
Main findings of the study
Epidemiological data on human prion diseases from 1993 to 2020 from international and national surveillance programmes from various sources have been analysed and collected for this study.
1) Increase in the number of cases of human prion diseases
From 1993 to 2020, an annual increase in cases of these diseases has been observed, especially in the last decades, which could be related to the development of better diagnostics and increased surveillance. In total, over the 27 years studied, 27,872 cases of human prion diseases were reported in 34 countries, of which 24,623 are sporadic CJD. The majority of these cases are concentrated in seven countries: the United States, France, Germany, Italy, China, the United Kingdom and Spain.
2) Decrease in cases of acquired human prion diseases
The study also highlights cases of acquired prion diseases (those resulting from infection with prions from external sources), including kuru (a disease endemic to the fore people of Papua New Guinea associated with cannibalistic rituals), which has been virtually eradicated; as well as iatrogenic CJD (iCJD), which results from infections due to hospital interventions such as neurosurgery, and variant CJD (vCJD), caused by ingestion of bovine prions, with 485 and 232 cases, respectively, reported worldwide. However, the two most common forms of iCJD, associated with growth hormone administration and dura mater grafts from cadavers, have decreased significantly following the ban on their administration. On the other hand, cases of variant CJD (vCJD), associated with the consumption of meat contaminated with the bovine spongiform encephalopathy agent (better known as "mad cow disease"), peaked in the early 2000s and have since declined significantly due to strict control measures in the food chain.
3) Global distribution, epidemiological surveillance and underestimation of cases
Although surveillance programmes have improved the identification and reporting of these diseases, there are still regions with limited understanding of prion disease trends. Most prion disease surveillance programmes are in high- and upper-middle-income countries, so it is not surprising that the United States, France, Germany, Italy, China, the United Kingdom and Spain are the countries with the highest number of reported cases. In fact, this could be an indication that global cases may be significantly underestimated, especially in low- and lower-middle-income countries, where prion diseases are underreported or not even detected.
Importance of global epidemiological surveillance
Although prion diseases remain rare, we live in a world where geographical barriers do not stop the spread of biological threats. Consequently, given the potential impact of these diseases and the possibility of new epidemic outbreaks such as mad cow disease, there is a clear need for continuous surveillance to better understand their distribution and mitigate their impact on public health. However, for such surveillance to be effective and to avoid underestimation of cases, it is essential to expand monitoring networks globally and to improve diagnostic capacities in countries with fewer resources, where a lack of data may be masking a larger health problem. Only then will it be possible to ensure that all countries, regardless of income level, are equipped to detect and manage these diseases effectively.
Conclusion
In summary, the epidemiological atlas update reminds us that, although we have come a long way in detecting and controlling prion diseases, there is still a long way to go to ensure global health and safety.
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