A new, heavily disputed theory says that the BSE outbreak in Europe during the 1980s has its origins in the rivers of the Indian subcontinent. This adds another element to the ongoing controversy about the source of the first BSE cases.

A new hypothesis published by Alan and Nancy Colchester in the Lancet proposes that human TSE-contaminated material was the cause of BSE. In the 1960s and 1970s, the UK imported hundreds of thousands of tons of bones to be used as fertilizer and for the production of animal feed from Bangladesh, India, or Pakistan. Gathering large bones and carcasses from the land and from rivers was, for a long time, an important source of income for local peasants in India and Pakistan. Given the religious custom to consign their deceased to rivers (preferably the Ganges) the collectors came across not only animal bones but also human remains. The Colchesters estimate that 150 cases of CJD per year have occurred in India. So, on a stochastic basis, CJD-infected cadavers were likely to be amongst these remains from time to time.

Why did BSE start in the UK? The UK was the most important purchaser of animal by-products coming from India and Pakistan during the 1960s and 1970s. Furthermore Britain was up front when it came to feeding meat and bone meal to one- or two-week old calves. The Colchesters argue that their hypothesis is consistent with the fact that the comparison of human TSE and BSE strain characteristics shows sufficient similarities.

Hypothesis is controversial
In a comment in the Lancet, Susarla K Shankar, an Indian scientist, put the Cholchesters' hypothesis into perspective: The Colchesters have drawn heavily from pictures from the internet and other sources. Furthermore, no study has been done to establish whether or not putrefied human cadavers from the Indian rivers contained CJD, and an experimental transmission from the human source into animals has not been attempted. So far, not a single case of BSE or scrapie has been reported for India. Shankar concludes that scientists must be cautious when hypothesizing about a disease that has such wide geographic, cultural and religious implications.

Scrapie-theory still most widely accepted
The most widely accepted theory for the source of BSE is that it originated from a transmission of scrapie through meat and bone meal from sheep to cattle. Most authorities agree that the main route of propagation of the BSE epidemic was via the recycling of contaminated meat and bone meal of BSE-infected cattle into cattle feed. However, hypotheses about the source of mad cow disease remain controversial and the fact that cows born after the ban for meat and bone meal in cattle feed still get infected with BSE suggests that other sources for infection may exist. Therefore testing remains the appropriate measure to prevent BSE from entering the food chain.