Bovine spongiform encephalopathy (BSE) belongs to a group of fatal, transmissible protein misfolding diseases known as transmissible spongiform encephalopathies (TSEs). It incubates for years before the disease is discovered and then it it usually only evident when the cow can no longer walk straight or stand up on its own.

Research published in March this year, co-authored by Heather Greenlee, associate professor of biomedical sciences at Iowa State's College of Veterinary Medicine, has found that BSE may be detectable in animals through an examination of their retinas up to 11 months before the emergence of the usual symptoms.

The authors of the report say the retina "is the most accessible part of the central nervous system, and retinal pathology in TSE affected animals has been previously reported. Here we describe antemortem (before death) changes in retinal function and morphology that are detectable in BSE inoculated animals several months prior to the appearance of any other signs of clinical disease."

The scientists used electroretinography and optical coherence tomography, non-invasive procedures, to measure changes in the retinas of the animals both prior and after inoculation with BSE.

Post-inoculation, the cows infected with BSE showed changes in retinal thickness and function, with differences in function emerging in correlation with the difference in the type of BSE, whether a-typcial or typical.

The typical or classical BSE, which is foodborne, and was the type of BSE diagnosed on a dairy farm in Co Louth this week, caused retinal changes 11 months before the emergence of more classical symptoms, which came after 22 months. The a-typical BSE caused retinal changes five months before the emergence of the symptoms, which came 17 months after inoculation.

The authors concluded that while the screening methods used in this research could be used as a means of identifying BSE sooner than conventional methods, the suitability of retinal assessment for diagnosis of TSE diseases in animals or humans "remains an open question".

The research was published in the peer-reviewed academic journal PLOS ONE and the full details of it can be accessed here.