Common Diseases in Humans

Table of Contents
1. Historical Perspectives on Health
2. Factors Affecting Health
3. Maintenance of Good Health
4. Disease-Causing Organisms (Pathogens)
5. Bacterial Diseases
6. Viral Diseases
7. Protozoan Diseases
8. Helminthic Diseases
9. Fungal Diseases
10. Prevention and Control Measures
View more

Human health is defined as a state of complete physical, mental and social well-being, not merely the absence of disease or physical fitness. This comprehensive definition includes mental and social aspects along with physical wellness. Diseases occur when the functioning of one or more organs or systems is adversely affected, characterized by various signs and symptoms. Diseases are broadly classified into infectious diseases (easily transmitted between persons) and non-infectious diseases (not transmitted between persons).

1. Historical Perspectives on Health

• Humor Theory: Early Greeks (Hippocrates) and Indian Ayurveda proposed that health was a balance of certain 'humors' in the body.
• Blackbile Personality: Persons with blackbile were thought to have hot personality and would develop fevers (based on reflective thought).
• Disproval of Humor Theory: William Harvey discovered blood circulation using experimental method. Use of thermometer showed normal body temperature in blackbile persons, disproving the humor hypothesis.
• Modern Understanding: Mind influences immune system through neural and endocrine systems. Mental state can affect health through this pathway.

2. Factors Affecting Health

• Genetic Disorders: Deficiencies present from birth or inherited from parents.
• Infections: Diseases caused by pathogenic organisms.
• Lifestyle Factors: Food, water quality, rest, exercise, and personal habits.
• Economic Impact: Healthy people are more efficient at work, increasing productivity and economic prosperity. Health increases longevity and reduces infant and maternal mortality.

3. Maintenance of Good Health

• Balanced Diet: Proper nutrition is essential for maintaining health.
• Personal Hygiene: Keeping body clean and maintaining cleanliness.
• Regular Exercise: Physical activity for maintaining fitness.
• Yoga: Practiced since time immemorial to achieve physical and mental health.
• Disease Awareness: Understanding diseases and their effects on bodily functions.
• Vaccination (Immunisation): Protection against infectious diseases.
• Waste Disposal: Proper disposal of wastes to prevent disease spread.
• Vector Control: Managing organisms that transmit diseases.
• Hygiene in Resources: Maintaining cleanliness in food and water sources.

4. Disease-Causing Organisms (Pathogens)

Pathogens are disease-causing organisms that can belong to bacteria, viruses, fungi, protozoans, or helminths. Most parasites are pathogens as they cause harm to the host. Pathogens enter the body through various means, multiply, and interfere with normal vital activities, causing morphological and functional damage.

Types of Pathogens

4.1 Pathogen Adaptation

• Pathogens must adapt to the host environment for survival.
• Example: Gut pathogens must survive low stomach pH and resist digestive enzymes.

5. Bacterial Diseases

5.1 Typhoid Fever

• Causative Agent: Salmonella typhi (pathogenic bacterium).
• Route of Entry: Small intestine through contaminated food and water.
• Pathogen Migration: Migrates to other organs through blood.
• Symptoms: Sustained high fever (39°C to 40°C), weakness, stomach pain, constipation, headache, loss of appetite.
• Severe Cases: Intestinal perforation and death may occur.
• Diagnosis: Confirmed by Widal test.
• Historical Case: Mary Mallon (nicknamed "Typhoid Mary") was a cook and typhoid carrier who spread disease through food she prepared for several years.

5.2 Pneumonia

• Causative Agents: Streptococcus pneumoniae and Haemophilus influenzae (bacteria).
• Site of Infection: Alveoli (air-filled sacs) of the lungs.
• Pathological Change: Alveoli get filled with fluid, leading to severe respiratory problems.
• Symptoms: Fever, chills, cough, headache. In severe cases, lips and fingernails turn gray to bluish in color.
• Transmission: Inhaling droplets/aerosols from infected person or sharing glasses and utensils with infected person.
• Other Bacterial Diseases: Dysentery, plague, diphtheria.

6. Viral Diseases

6.1 Common Cold

• Causative Agent: Rhino viruses.
• Site of Infection: Nose and respiratory passage (not the lungs).
• Most Infectious: One of the most infectious human ailments.
• Symptoms: Nasal congestion and discharge, sore throat, hoarseness, cough, headache, tiredness.
• Duration: Usually lasts 3-7 days.
• Transmission: Droplets from cough or sneezes of infected person are inhaled directly or transmitted through contaminated objects (pens, books, cups, doorknobs, computer keyboard, mouse).

7. Protozoan Diseases

7.1 Malaria

• Causative Agent: Plasmodium (tiny protozoan).
• Species: Different species cause different types of malaria: P. vivax, P. malariae, P. falciparum.
• Most Serious Type: Malignant malaria caused by Plasmodium falciparum (can be fatal).
• Vector: Female Anopheles mosquito (transmitting agent).
• Infectious Form: Sporozoites enter human body through bite of infected female Anopheles mosquito.

Transmission of Malaria

7.1.1 Life Cycle of Plasmodium

1. Entry into Human: Sporozoites (infectious form) enter through bite of infected female Anopheles mosquito.
2. Liver Stage: Parasites initially multiply within liver cells.
3. RBC Stage: Parasites then attack red blood cells (RBCs), resulting in their rupture.
4. Haemozoin Release: Rupture of RBCs releases toxic substance called haemozoin.
5. Symptoms: Haemozoin is responsible for chill and high fever recurring every 3-4 days.
6. Entry into Mosquito: When female Anopheles mosquito bites infected person, parasites enter mosquito's body.
7. Development in Mosquito: Parasites undergo further development and multiply within mosquito to form sporozoites.
8. Storage in Salivary Glands: Sporozoites are stored in mosquito's salivary glands.
9. Transmission to New Host: When mosquito bites human, sporozoites are introduced into body, initiating cycle again.

Two-Host Life Cycle: Malarial parasite requires two hosts to complete life cycle: human and mosquito. Female Anopheles mosquito acts as both host and vector.

Stages of Life Cycle of Plasmodium

7.2 Amoebiasis (Amoebic Dysentery)

• Causative Agent: Entamoeba histolytica (protozoan parasite).
• Site of Infection: Large intestine of human.
• Symptoms: Constipation, abdominal pain and cramps, stools with excess mucous and blood clots.
• Mechanical Carrier: Houseflies act as mechanical carriers, transmitting parasite from faeces of infected person to food and food products.
• Source of Infection: Drinking water and food contaminated by faecal matter.

Entamoeba Histolyica in Human Gut

8. Helminthic Diseases

Helminths are parasitic worms. Two important pathogenic helminths in humans are Ascaris (roundworm) and Wuchereria (filarial worm).

8.1 Ascariasis

• Causative Agent: Ascaris (common roundworm).
• Type: Intestinal parasite.
• Symptoms: Internal bleeding, muscular pain, fever, anemia, blockage of intestinal passage.
• Transmission: Eggs of parasite are excreted with faeces of infected persons, contaminating soil, water, plants.
• Infection Route: Healthy person acquires infection through contaminated water, vegetables, fruits.

8.2 Filariasis (Elephantiasis)

• Causative Agents: Wuchereria bancrofti and Wuchereria malayi (filarial worms).
• Pathology: Slowly developing chronic inflammation of organs where worms live for many years.
• Common Site: Usually lymphatic vessels of lower limbs.
• Symptoms: Gross deformities of affected parts. Genital organs are also often affected, resulting in deformities.
• Transmission: Pathogens transmitted through bite by female mosquito vectors.

9. Fungal Diseases

9.1 Ringworms

• Causative Agents: Fungi belonging to genera Microsporum, Trichophyton, and Epidermophyton.
• Prevalence: One of the most common infectious diseases in man.
• Symptoms: Dry, scaly lesions on skin, nails, and scalp. Lesions accompanied by intense itching.
• Growth Conditions: Heat and moisture help fungi grow. They thrive in skin folds (groin, between toes).
• Transmission: Acquired from soil or by using towels, clothes, or comb of infected individuals.

10. Prevention and Control Measures

10.1 Personal and Public Hygiene

Maintenance of personal and public hygiene is very important for prevention and control of many infectious diseases.

10.1.1 Personal Hygiene Measures

• Keeping the body clean.
• Consumption of clean drinking water.
• Eating clean food, vegetables, fruits.

10.1.2 Public Hygiene Measures

• Proper disposal of waste and excreta.
• Periodic cleaning and disinfection of water reservoirs, pools, cesspools, tanks.
• Observing standard practices of hygiene in public catering.

10.1.3 Disease-Specific Measures

• Food and Water-borne Diseases (Typhoid, Amoebiasis, Ascariasis): Personal and public hygiene measures are particularly essential.
• Air-borne Diseases (Pneumonia, Common Cold): In addition to hygiene measures, avoid close contact with infected persons or their belongings.

10.2 Vector Control Measures

For diseases transmitted through insect vectors (malaria, filariasis), the most important measure is to control or eliminate vectors and their breeding places.

• Avoid Water Stagnation: Prevent stagnation of water in and around residential areas.
• Regular Cleaning: Regular cleaning of household coolers.
• Mosquito Nets: Use of mosquito nets for protection.
• Biological Control: Introducing fishes like Gambusia in ponds that feed on mosquito larvae.
• Chemical Control: Spraying of insecticides in ditches, drainage areas, and swamps.
• Physical Barriers: Doors and windows should be provided with wire mesh to prevent entry of mosquitoes.
• Recent Importance: These precautions are important due to widespread incidences of vector-borne diseases like dengue and chikungunya (transmitted by Aedes mosquitoes) in many parts of India.

10.3 Medical Interventions

10.3.1 Vaccines and Immunisation

• Disease Eradication: Vaccines and immunisation programmes enabled complete eradication of deadly disease smallpox.
• Disease Control: Large number of infectious diseases like polio, diphtheria, pneumonia, and tetanus controlled to large extent by vaccines.
• Future Prospects: Biotechnology is making available newer and safer vaccines.

10.3.2 Antibiotics and Drugs

• Discovery of antibiotics and various other drugs has enabled effective treatment of infectious diseases.
• Advancements in biological science have armed us to effectively deal with many infectious diseases.

Understanding common diseases, their causative organisms, modes of transmission, and prevention strategies is crucial for maintaining public health. Integration of personal hygiene, public health measures, vector control, and medical interventions provides a comprehensive approach to disease management and prevention.