When pathogens escape the body defenses and colonize in the host, disease results. Disease is an observable change in health or malfunction of any body part of the host. Signs of disease usually are related to the observable presence of microbes; and the term "signs" is most commonly used to describe plant infestations. For example, there were signs (evidences) of spider mites on the lilac bushes or signs of smut on the corn.

Usually we use the term "symptoms" to describe changes that are observed in diseased animals. Plants do also show symptoms such as wilted leaves, loss of green color, etc. There are many disease symptoms that you have experienced during you life. Digestive changes are frequently related to disease. The loss of appetite (anorexia), nausea, vomiting (emesis), diarrhea, and constipation are some symptoms of disease. Listlessness, fatigue, dehydration, and loss of weight may also be observed.

Body temperature fluctuates between 95 and 99,5 degrees Fahrenheit; but low grade fever and high grade fever (above 101 degrees) are often related to pathogenic infections. Fever may be also be caused by the presence of tumors or certain medications; and still other fevers have unknown origins (FUO).

Patients who report disease symptoms to clinic staff are often required to have blood and urine tests because changes in the blood and urine are often associated with disease. Low red blood cell counts (anemia), reduced or elevated white blood cell counts, and wastes in the blood (azotemia) may indicate disease. Urine changes include cloudiness or turbidity, color, hematuria (blood in the urine), glucosuria (glucose or sugar in the urine), and albumenuria (protein in the urine).

Changes in the skin and nervous system are also related to disease. Symptoms including change in skin color (jaundice, reddening, cyanosis); development of rash, carbuncles or petechiae--broken blood vessels under the skin; and sweats or dry skin are some indicators of infection or disease. Also diseased humans may be confused, irritable, nervous, or even comatose.

Some examples of pathogens that produce disease symptoms in humans include Mycobacterium (anorexia, fever), E.coli (diarrhea), Bordetella (cough, emesis), Neisseria (burning urination in males), Staphylococcus (sore throat, fever, reddening of skin), Staphylococcus, Bacteroides, Chlamydia and Pseudomonas (small skin pustules), Legionella (fever, headache, pneumonia, confusion), and Proteus (rash, blood in urine).