This is the first time such "prions" have been biochemically detected.
The discovery is expected to lead to a much more effective detection method for the infectious proteins responsible for brain-destroying disorders, such as bovine spongiform encephalopathy (BSE) in cattle and variant Creutzfeldt-Jakob disease (vCJD) in humans.
The blood test would make it much easier to keep BSE-infected beef out of the human food supply.
It would also ensure that blood transfusions and organ transplants do not transmit vCJD, and would give researchers their first opportunity to work out how many people may be incubating the disease.
UTMB neurology professor Claudio Soto, senior author of the study, says that the concentration of infectious prion protein in blood is far too small to be detected by the usual methods but is still enough to spread the disease.
They were it seems successful in developing a technique that amplifies the quantity of the protein more than 10 million-fold, raising it to a detectable level.
Soto along with UTMB assistant professor of neurology Joaquin Castilla and research assistant Paula Saá, applied a method they call protein misfolding cyclic amplification (PMCA) to blood samples.
Successive rounds of PMCA led to the discovery of prions in the blood of 16 of 18 infected hamsters, while no prions were found in blood samples that were taken from 12 healthy control hamsters and subjected to the same treatment.
Soto and team have spent four years optimizing and automating the process and are currently working on detecting prions in the blood of animals before they develop clinical symptoms, and then applying the technology to human blood samples.
Because current tests require post-slaughter brain tissue for analysis, tests for infectious prions in cattle and human blood are badly needed.
In the United States, only cattle already showing clinical symptoms of BSE (so-called "downer cows"), are tested for the disorder, even though vCJD has the potential to be transmitted by animals not yet showing symptoms of the disease.
To date only two cases of BSE have been found in American cows, and although British BSE cases have been in decline since 1992, scientists believe the British BSE epidemic of the 1980s could have exposed millions of people in the UK and Europe to infectious prions.
The extent of the vCJD epidemic is yet unknown.
So far the disease has killed around 180 people worldwide, but numbers could reach thousands or even hundreds of thousands in the coming decades.
Prions have also been shown to be transmissible through blood transfusions and organ transplants.
The research appears in Nature Medicine online.