A woman has died in Spain of the human version of mad cow disease, following the death of her son in February of the same disease, Spain's Ministry of Health says.

This marks the first time that two members of the same family have died of the disease, health researchers say.

The deaths raised the death toll in Spain to four from the human variant of the Creutzfeldt-Jakob Disease (CJD) linked to the bovine spongiform encephalopathy (BSE) or mad cow disease.

Government officials confirmed on Wednesday that the woman, 64, who died in August, had died of the same human variant of CJD that killed her 41-year-old son in April. The names of the victims were not made public.

Investigators say they are searching for the circumstances of transmission of the disease to the pair. Health officials say they believe the son contracted the disease by eating contaminated beef before preventative measures were adopted in 2001.

Spain recorded its first death from mad cow disease in 2005.