The infected California cow confirmed Tuesday was America's fourth case of mad cow disease.

CNN: STORY HIGHLIGHTS

According to Cancer Research UK some 41, 000 men are diagnosed with prostate cancer every year, but 10, 700 will die of the disease, making it the fourth most common cause of cancer death - and second only to lung cancer in men.

BBC: 'Cinderella cancer' comes in from the cold

Strokes are the fourth biggest killer after cardiovascular conditions, cancers and respiratory disease.

BBC: Stroke campaign by pharmacists to cut number of victims

Step by step, Sara ended up on a fourth round of chemotherapy, one with a minuscule likelihood of altering the course of her disease and a great likelihood of causing debilitating side effects.

NEWYORKER: Letting Go

Epilepsy is the fourth most common neurological disorder in the United States after migraine, stroke and Alzheimer's disease, and yet it is widely misunderstood, according to the Institute of Medicine.

CNN: Seizures: When 'electrical brainstorm' hits