The Hood River County Health Department says it is investigating three cases of the rare brain disorder Creutzfeldt-Jakob Disease in Hood River County.  CJD is a serious brain disorder caused by a misfolded protein called a prion, and there are about 500 new cases per year according to the Creutzfeldt-Jakob Disease Foundation.  Symptoms include issues with memory, walking, coordination, speech, and behavior changes.  A statement from the health department says these three local cases have been found in the past eight months, and at this time, it is not known if the cases are linked.  The department emphasizes the risk of CJD to the public is extremely low.  It cannot be spread through the air, touch, social contact, or water.  Most cases happen without a known reason.  It can be inherited and run in families, and in very rare cases, it may be spread through certain medical exposures to infected brain or nervous tissue or by eating infected beef.  The health department says it is closely monitoring the situation.