Video: Top Five Health Scares

PHILADELPHIA - In the past two decades, fear of viruses and strange illnesses spreading to pandemic proportions made headlines several times.

We take a look back at the top five health scares.

At five, Hantavirus was first recognized in its current form in the early 90s in the southwestern United States.

Rodent control became the strategy for preventing it.

At four is Mad Cow Disease.

By earlier this year, it had killed 164 people in Britain and 42 elsewhere.

The number of cases is expected to rise because of the disease's long incubation period, but is no longer cause of widespread panic.

Number three is 'Avian' or bird flu.

Since it first infected humans in the 1990s, study of the virus has prompted changes in poultry farming, flu vaccination research, and pandemic planning.

Two is SARS (Severe Acute Respiratory Syndrome)

Within a matter of weeks in early 2003, SARS spread from China to 37 countries.

It caused nearly 800 deaths, but now is considered rare.

Number one is West Nile Virus.

In the past decade, we've come to expect hundred of cases a year in this country.

In 2007, there were 3600 cases reported and 124 deaths.