Understanding Infectious Diseases and Immunity
Infectious Diseases and Immunity
2. Transmission of Infectious Diseases
2.1. Diseases Transmitted by Bites
- Rabies: Transmitted by the bite of dogs, cats, and bats. The virus attacks the nervous system, and symptoms appear three to eight weeks after the bite. These include fever, hyperactivity, hallucinations, and confusion.
- Tetanus: Causes violent involuntary muscle contractions, such as in the neck and jaw.
- Gas Gangrene: The exotoxin secreted causes tissue degeneration and releases a large amount of hydrogen gas.
- Dermatomycoses: More or less circular lesions on the skin or dermis.
2.2. Airborne Diseases
Microorganisms transmitted through the air usually infect the respiratory tract.
- Common Cold: Infection of the nasal epithelium and pharynx. Symptoms include nasal congestion, sneezing, slight fever, and cough.
- Influenza: Infection of the upper respiratory tract and sometimes the lungs. Symptoms include high fever, headache, chills, and fatigue.
- Measles: Infection of the respiratory tract and, in severe cases, other tissues.
- Mumps: Infection of the upper respiratory tract and inflammation of the salivary glands. The infection can progress to the testes, brain, and pancreas.
- Chicken Pox: Infection of the respiratory tract and lymph nodes.
- Pharyngitis: Intense throat inflammation, slight fever, malaise, and infection of the middle ear and tonsils.
- Tuberculosis: Infection of the lungs and other organs.
- Pneumonia: Infection of the lungs.
- Diphtheria: Infection of the throat and tonsils.
2.3. Sexually Transmitted Diseases
- AIDS: The virus attacks and destroys T cells, significantly decreasing the patient’s immune defenses.
- Genital Herpes: Blisters and infections around the anus, urethra, and vagina in females, and the penis in males.
- Hepatitis B: General weakness, nausea, frequent vomiting, fever, and yellowing of the skin. It can also be acquired through contaminated blood transfusions.
- Gonorrhea: The bacterium produces a potent endotoxin, causing inflammation of the vaginal mucosa in women and urethral infection with painful urination and pus discharge in men.
- Syphilis: Initial skin lesions on the genitals and other body parts, followed by a widespread rash. If the infection spreads, the nervous system and blood vessels may be affected.
- Vaginal Candidiasis: Inflammation of the vaginal lining with pasty vaginal discharge.
- Trichomoniasis: Vaginitis with vaginal discharge and painful urination in women, infection of the urethra in both sexes, and the prostate and seminal vesicles in men.
2.4. Waterborne and Foodborne Diseases
- Poliomyelitis: Initial infection of the pharynx and intestine, followed by fever, muscle pain, and stiffness of the neck and back.
- Hepatitis A: Infection of the liver, fever, loss of appetite, fatigue, and yellowing of the skin.
- Salmonellosis: Gastroenteritis caused by bacterial proliferation in the gut.
- Cholera: Transmitted mainly through contaminated water.
- Staphylococcal Poisoning: Enterotoxin causes diarrhea, nausea, and vomiting.
2.5. Diseases Transmitted by Animals
- Yellow Fever: Transmitted by mosquito bites. Infection of the liver, kidneys, and other organs.
- Plague: Transmitted by fleas from rats. Infection of the lymph nodes, lumps, dark patches on the skin due to bleeding, shock, and death within days.
- Sleeping Sickness: Transmitted by the tsetse fly. Infection of blood vessels, then the parasite can invade the central nervous system, causing inflammation of brain and spinal cord tissue.
3. Immunity
Immunology is the science that studies the molecular and cellular mechanisms involved in defending the body against microorganisms.
3.1. Natural Immunity
Animals acquire natural immunity when exposed to microbial invasion. The immune system produces specific antibodies against these microbes. If the invasion is defeated, the animal is immunized for as long as the antibodies remain in the blood. Active immunity is when the animal’s own immunological mechanisms achieve immunity. Passive immunity is when the antibodies are acquired from an external source.
3.2. Artificial Immunity
Immunity can also be acquired artificially through techniques outside the body. Vaccination involves injecting dead or attenuated microbes to activate the immune system and produce specific antibodies. Vaccines are preventive, not curative, as they take effect after a few days.
4. Nonspecific Defense Mechanisms
4.1. Primary Barriers
- Skin
- Mucosa
- Tears
- Acidic sweat
- Bacterial flora
4.2. Secondary Barriers
These mechanisms activate when microbes bypass primary barriers and penetrate the body.
5. The Immune System
The immune system comprises cells, tissues, and molecules involved in immunization. Its most important feature is recognizing foreign molecules. It plays a crucial role in defending against bacterial infections and cellular disorders like tumors. Two types of responses are related to blood cells called lymphocytes.
5.1. Lymphocytes
Lymphocytes are immunocompetent cells found in blood and lymph, forming the basis of humoral and cellular immunity. They originate from pluripotent stem cells, which also give rise to erythrocytes, leukocytes, and platelets.