Infectious Organisms: Chlamydia, Rickettsia, Viruses

• Common infectious organisms include chlamydia, rickettsia, viruses, fungi, protozoa, and helminths.

Chlamydia

• Extremely small bacteria with complex life cycles.
• Grow inside living cells.
• Susceptible to antibiotics.
• Cause conjunctivitis, trachoma, pelvic inflammatory disease (PID), and other sexually transmitted infections (STIs).

Rickettsia

• Extremely small bacteria that grow in living cells.
• Susceptible to antibiotics.
• Cause typhus and Rocky Mountain spotted fever.

Viruses

• Submicroscopic infectious agents.
• Can live and reproduce only within living cells.
• Cause colds, herpes, hepatitis, measles, varicella (chickenpox), influenza, and AIDS.

Fungi

• Simple, nongreen plants, some of which are parasitic.
• Includes yeasts and molds.
• Cause candidiasis, skin infections (tinea, ringworm), and valley fever.

Protozoa

• Single-celled animals.
• Cause dysentery, Trichomonas infection, and malaria.

Helminths

• Worms.
• Cause trichinosis and infestations with roundworms, pinworms, and hookworms.
• The body can be infected through damaged skin, the respiratory tract, digestive system, and urinary and reproductive tracts.
• An infected person's bodily discharges can spread infection.
• Microorganisms can produce disease through toxins.
• Sepsis refers to the presence of harmful microorganisms or their toxins in the body.

Bacteria

• Bacteria occur in various shapes: round (cocci), rod-shaped (bacilli), and curved (vibrios and spirochetes).
• Bacteria are named according to their shape and arrangement.
• They are also described by the dyes they take up when stained.
• Chlamydia and rickettsia are bacterial groups smaller than typical bacteria and grow only within living host cells.

Responses to Disease: Inflammation

• Inflammation is a common response to infection or injury.
• Injured cells release chemicals, resulting in increased blood flow and fluid to the tissues.
• The four signs of inflammation are:
  • Heat
  • Pain
  • Redness
  • Swelling
• The suffix "-itis" indicates inflammation.
• Edema is swelling or fluid accumulation in tissues. Edema can result from inflammation, fluid blockage, heart failure or body imbalance.

Phagocytosis

• Phagocytosis is the process used by the body to eliminate microorganisms, damaged cells, and harmful debris
• White blood cells engulf and destroy these materials internally.
• Phagocytic cells are found in the blood, tissues, and lymphatic system
• Pus consists of fluid and white blood cells remaining after phagocytosis.

Immunity

• Immunity refers to defenses against infectious disease.
• Inflammation and phagocytosis are inborn protective mechanisms.
• Innate mechanisms don't require previous exposure to disease.
• Intact skin, mucous membranes, stomach acid, saliva and tears are mechanical barriers against disease.
• Adaptive (acquired) immunity develops from exposure to disease organisms.
• Is specific for particular diseases from natural exposure or vaccines.
• Adaptive immunity consists of cells that recognize and eliminate foreign invaders using antibodies.
• The immune system monitors for abnormal cells, but can overreact produce allergies or react to one's tissues and cause autoimmune diseases.

Neoplasia

• Neoplasm: abnormal, uncontrolled tissue growth (tumor).
• Benign neoplasm: does not spread but may cause local damage.
• Malignant neoplasm: invasive, can metastasize (cancer).
• Carcinoma: malignant tumor of epithelial tissue.
• Adenocarcinoma: cancer arising in glandular epithelium.
• Melanoma: cancer of pigmented epithelial cells (melanocytes).
• Sarcoma: neoplasm that involves connective tissue or muscle.
• Cancers of the blood, lymphatic system, and nervous system are classified by cell type and clinical features.
• Cyst: a sac or pouch filled with fluid or semisolid material, abnormal but not cancerous.