Human Health and Disease

Learning Outcomes:

1. Understand the concepts of health and disease.
2. Learn the mechanisms of common diseases caused by bacteria, viruses, fungi, and parasites.
3. Understand the body’s defense systems, including innate and acquired immunity.
4. Recognize the causes, transmission, and prevention of HIV/AIDS and cancer.
5. Recognize the consequences of drug and alcohol abuse.

Health and Disease

For centuries, health was defined based on the balance of “humors” or bodily fluids, an idea that originated from Greek philosophers such as Hippocrates and was also embraced by Ayurveda. Individuals with an excess of black bile were believed to have a “hot personality” and prone to fever. This theory was later refuted with the advent of modern science, particularly through William Harvey’s discovery of blood circulation and experiments that demonstrated normal body temperature in individuals.

Later, scientific advancements demonstrated that the mind, through the neural and endocrine systems, significantly influences the immune system. Hence, physical, mental, and social factors play a role in health. These include:

• Genetic disorders: Conditions passed from parents at birth.
• Infections: Diseases caused by microorganisms.
• Lifestyle: Factors such as diet, exercise, rest, and habits.

Health is more than the absence of disease. It’s a state of complete physical, mental, and social well-being. Healthy individuals contribute to societal productivity and economic prosperity while ensuring longer lifespans and reduced infant and maternal mortality. Key to maintaining health are:

1. Balanced diet, personal hygiene, and regular exercise.
2. Awareness of diseases and the impact on bodily functions.
3. Immunization and hygiene practices such as proper waste disposal, vector control, and safe food and water handling.

Common Diseases in Humans

Humans can suffer from various infectious and non-infectious diseases. Infectious diseases, transmitted from one person to another, are often caused by pathogens such as bacteria, viruses, protozoans, and fungi. Non-infectious diseases, such as cancer and those stemming from drug and alcohol abuse, can severely impact health.

Pathogenic Organisms

1. Bacterial Infections:

• Typhoid: Caused by Salmonella typhi, this infection is transmitted through contaminated food and water. It can lead to high fever, weakness, and intestinal perforation. The Widal test confirms the presence of the bacteria.
• Pneumonia: Streptococcus pneumoniae and Haemophilus influenzae infect the lungs, causing fluid build-up in the alveoli. Symptoms include cough, fever, and difficulty in breathing.

1. Viral Infections:

• Common Cold: Rhino viruses attack the nose and respiratory passages. This highly contagious infection spreads through direct contact or inhaling infected droplets.

1. Protozoan Infections:

• Malaria: Caused by Plasmodium species, malaria is transmitted by the female Anopheles mosquito. The parasite enters the body, multiplies in the liver, and attacks red blood cells, causing chills, fever, and fatigue.
• Amoebiasis: Entamoeba histolytica causes amoebic dysentery, resulting in abdominal cramps and stools containing blood. Contaminated food and water are the main sources.

1. Helminth Infections:

• Ascariasis: Ascaris lumbricoides leads to intestinal obstruction, fever, and anemia, usually transmitted through contaminated food and water.
• Filariasis: Caused by Wuchereria bancrofti, it results in elephantiasis, characterized by chronic inflammation and swelling of body parts.

1. Fungal Infections:

• Ringworm: Fungi like Microsporum and Trichophyton cause ringworms, leading to itchy, dry patches on the skin. These fungi thrive in moist areas and are contagious through contact with infected individuals or objects.

Important Note: Maintaining personal and public hygiene is crucial in preventing infectious diseases. Clean drinking water, proper food handling, and avoiding contact with infected individuals are essential.

Immunity

The body’s ability to protect itself from pathogens is known as immunity. This can be broadly divided into two categories:

1. Innate Immunity: The body’s natural, non-specific defense against pathogens. It includes:

• Physical Barriers: Skin and mucus trap and prevent pathogens from entering the body.
• Physiological Barriers: Acids in the stomach and enzymes in tears and saliva inhibit microbial growth.
• Cellular Barriers: Certain white blood cells like macrophages and neutrophils ingest pathogens.
• Cytokine Barriers: Virus-infected cells produce interferons that block further viral infection.

1. Acquired Immunity: A specific response to pathogens, characterized by memory. It includes:

• Humoral Immunity: B-lymphocytes produce antibodies to neutralize pathogens.
• Cell-Mediated Immunity: T-lymphocytes help destroy infected cells directly or assist in antibody production. Important Concept: Vaccines stimulate the production of memory cells that recognize pathogens upon subsequent exposure, ensuring a faster and stronger immune response.

Comparison of Innate and Acquired Immunity

AIDS

AIDS (Acquired Immuno Deficiency Syndrome) is caused by the HIV virus, which attacks the immune system, leading to the failure of defense against infections. HIV primarily infects macrophages and helper T-lymphocytes. Over time, the body’s immune system weakens, making the individual susceptible to opportunistic infections. The virus spreads through:

1. Sexual contact with an infected person.
2. Contaminated blood transfusions.
3. Sharing of needles among intravenous drug users.
4. Mother-to-child transmission during pregnancy or breastfeeding.

HIV can remain dormant in the body for several years before symptoms such as fever, weight loss, and opportunistic infections become apparent. ELISA is a common diagnostic test for detecting HIV.

Important Note: HIV/AIDS can only be prevented, as there is no definitive cure. Safe practices like using disposable needles and protected sex are essential in preventing the spread.

Cancer

Cancer is characterized by uncontrolled cell growth, often leading to the formation of tumors. Tumors can be:

1. Benign: Confined to their original location and less harmful.
2. Malignant: Aggressively spread to other body parts through the bloodstream—a process known as metastasis.

Carcinogens, including radiation, chemicals like tobacco smoke, and oncogenic viruses, can trigger the transformation of normal cells into cancerous ones. Early detection through biopsy, CT scans, and MRI helps in effective treatment. Common cancer treatments include:

1. Surgery: Removing the tumor.
2. Radiation therapy: Targeting cancer cells with radiation.
3. Chemotherapy: Using drugs to kill cancer cells.

Important Concept: Some cancers can evade the immune system, and treatments like immunotherapy can help by stimulating the body’s immune response to target cancer cells.

Drug and Alcohol Abuse

The misuse of drugs and alcohol, especially among youth, is a growing concern. Commonly abused substances include:

1. Opioids: Derived from the poppy plant, opioids like heroin slow down body functions.
2. Cannabinoids: Extracted from Cannabis sativa, these chemicals affect the cardiovascular system.
3. Cocaine: Derived from the coca plant, this stimulant creates a sense of euphoria but can cause hallucinations and heart failure.

Nicotine in tobacco is another addictive substance that increases heart rate and blood pressure, and smoking is linked to various cancers.

Adolescents are particularly vulnerable to drug and alcohol use due to curiosity, peer pressure, and stress. Early intervention, education, and counseling are essential in preventing addiction.

Prevention and Control of Drug Abuse

To prevent drug and alcohol abuse:

1. Avoid undue peer pressure: Recognize personal limits and avoid yielding to pressure.
2. Education and counseling: Proper guidance can help individuals cope with stress and avoid turning to substances.
3. Seek help: Professional counseling and support from trusted friends or family can prevent further substance abuse.

MCQ: What is the primary mode of HIV transmission?
Answer: Sexual contact with an infected person.