An international team of researchers identified two Swiss cows with a new form of mad-cow disease in a study released online Friday.

Bovine spongiform encephalopathy (BSE), more commonly known as mad cow disease, is caused by prion proteins that become tangled up and cause brain damage decades after infection. Humans can become infected by the prion proteins and develop Creutzfeldt-Jakob disease, a neurodegenerative disease, first reported in 1996. Since then, health experts have identified 217 patients from 11 countries with the disease.

Two cows died in the Swiss countryside, an 8-year-old from an accident and a 15-year-old that was put down, and mandatory testing gave a positive result for BSE.

Previously, scientists had uncovered three prion variants, but when the current team examined the prions of the two cows, they found a fourth unknown variant.

The interpretation of these findings remains difficult because neuropathologic and systematic clinical data for the 2 cases are not available, the authors wrote in their paper in the journal Emerging Infectious Diseases, published by the U.S. Centers for Disease Control and Prevention.

The journal released the data Friday online before the article appears in the journal in January.

The new prion variant raised concerns that current testing might miss variants that can cause debilitating and lethal brain damage decades after infection.

Nonetheless, our findings raise the possibility that these cattle were affected by a prion disease not previously encountered and distinct from the known types of BSE, the authors concluded. To confirm this possibility and to assess a potential effect on disease control and public health, in vivo transmission studies using transgenic mouse models and cattle are ongoing. Until results of these studies are available, molecular diagnostic techniques should be used so that such cases are not missed.