Some theories suggest that a virus or bacteria may trigger the immune system, leading to an attack of the glands.

Based on their observations, Huebner and Rowe hypothesized that these viruses could trigger an unknown gene that would cause cells to grow out of control.

Once ensconced in their lungs, the virus triggered a havoc of inflammation, hemorrhage and cell death.

A symbiotic virus in the plant triggered the change.

Until it is known for sure if certain bacteria or viruses trigger the disease, contact with people with the disease will not change your risk for developing it.

It is not yet known why the virus triggers the release of the protein.

In either case, the altered virus triggers an immune response and imprints an immunological memory.

Acute disseminated encephalomyelitis or ADEM, a closely related disorder in which a known virus or vaccine triggers autoimmunity against myelin.

The research also suggests that the virus triggers the cancer in people directly, rather than indirectly by first causing liver-damaging hepatitis, said the researcher, Dr. Gilbert Jay.

But for those with asthma, it can be an especially stressful time of year because even a simple cold virus can trigger a major asthma event.