We develop symptoms of hay fever and other allergies whenever the immune system wrongly determines pollen, dust, certain foods, insect stings, penicillin, and other innocuous substances to be an enormous threat. When the body detects the pollen in the body for the first time, it mounts an immune response and puts out antibodies that bind to mast cells. The next time you breathe in pollen, certain tissue cells release potent chemicals, like histamine, that alerts other immune cells. All these chemicals floating around cause sneezing, runny eyes, itching, wheezing, or even a life-threatening condition known as anaphylactic shock . Because germs evolve rapidly, they can devise ways to evade the immune system of slower-evolving hosts.
Antibiotics usually fill in the gaps.
For example, antibiotic-resistant tuberculosis and pneumonia caused by Staphylococcus are diseases that already are very serious health problems. Drug companies continue the hunt for novel, stronger antibiotics to help lessen the danger of a serious public health problem in the future. At the same time, a small number of outbreaks of lethal viral diseases have occurred in pockets around the world. Because viral infections cannot be treated with antibiotics, outbreaks must be quickly controlled to reduce the risk to public health. A popular movie and best-selling book recently described the devastation of a community from a lethal virus.