Diseases – Zoonotic, Hereditary, Protozoan, Viral & Bacterial | Science & Technology for UPSC CSE PDF Download

Introduction

• You've provided a comprehensive overview of health and disease. Health is indeed a state of complete well-being that encompasses physical, mental, and social aspects of an individual's life. It goes beyond the absence of disease and involves various factors, including lifestyle, genetics, environment, and access to healthcare.
• Disease, on the other hand, represents a disruption in the normal functioning of the body. It can be caused by a variety of factors, as you've mentioned, including infections, dietary issues, hereditary conditions, environmental factors, and genetic anomalies. Disease can manifest in various ways and affect different parts of the body, leading to both physical and mental health challenges.
• Maintaining good health involves not only preventing and treating diseases but also promoting overall well-being through healthy lifestyle choices, mental and emotional well-being, and social connections. It's a holistic approach that aims to optimize an individual's quality of life.

Causes of Diseases/Disease Agents

A disease agent is an organism, substance, or force which causes disease due to its excessive presence, deficiency, or absence.

• Pathogens/Biological Agents: These are living organisms or entities that cause infectious diseases. They include viruses, bacteria, fungi, protozoa, and helminths. Each type of pathogen can cause specific diseases, ranging from common infections like the flu to more severe illnesses.
• Nutrient Agents: Nutritional deficiencies or imbalances can lead to diseases. Lack of essential vitamins, minerals, or macronutrients like carbohydrates, fats, and proteins can result in conditions such as scurvy, rickets, or malnutrition. Conversely, excessive food intake can lead to obesity.
• Chemical Agents: Diseases can be caused by both endogenous (originating within the body) and exogenous (coming from external sources) chemical agents. Examples include diabetes due to insulin deficiency, exposure to environmental pollutants causing lung diseases, and allergic reactions to various allergens.
• Physical Agents: Physical factors like heat, cold, radiation, sound, and humidity can contribute to diseases. For instance, prolonged exposure to high temperatures can lead to heatstroke, while extreme cold can cause frostbite.
• Mechanical Agents: Mechanical factors such as fractures, sprains, dislocations, and injuries can result in diseases or health conditions. These injuries can lead to long-term health issues if not properly treated.
• Genetic Agents: Genetic factors play a significant role in some diseases. Genetic mutations, chromosomal abnormalities, and the presence of harmful alleles can lead to conditions like color blindness, albinism, or hemophilia.

Classification of Disease

• Physical Diseases: These are diseases that primarily affect the body's physical structure or function. Examples include heart disease, diabetes, and cancer.
• Mental Diseases: Mental illnesses primarily affect a person's thoughts, emotions, and behavior. Conditions like depression, anxiety disorders, and schizophrenia fall into this category.
• Infectious Diseases: These diseases are caused by pathogens (viruses, bacteria, fungi, parasites) and can be transmitted from one person to another. Examples include the flu, tuberculosis, and HIV/AIDS.
• Non-Infectious Diseases: Non-infectious diseases are not caused by pathogens and typically result from genetic, environmental, or lifestyle factors. Examples include diabetes, hypertension, and asthma.
• Deficiency Diseases: These diseases arise from a lack of essential nutrients in the diet. Conditions like scurvy (vitamin C deficiency) and rickets (vitamin D deficiency) are deficiency diseases.
• Inherited Diseases: Inherited or genetic diseases are caused by abnormal genes passed down from parents to their offspring. Examples include cystic fibrosis and Huntington's disease.
• Degenerative Diseases: These diseases involve the gradual breakdown of body tissues or organs over time. Conditions like Alzheimer's disease and osteoarthritis are degenerative diseases.
• Social Diseases: Social diseases often result from societal factors and lifestyle choices. Examples include substance abuse disorders, eating disorders, and gambling addiction.
• Self-Inflicted Diseases: These diseases are a consequence of an individual's own actions or choices, such as smoking-related diseases (e.g., lung cancer) or alcohol-related diseases (e.g., liver cirrhosis).
• Acute Diseases: Acute diseases have a sudden onset, progress rapidly, and typically resolve within a short time frame. Examples include the common cold and acute injuries.
• Chronic Diseases: Chronic diseases have a long-lasting or recurring nature and can persist for months or years. Conditions like diabetes, heart disease, and chronic obstructive pulmonary disease (COPD) fall into this category.
• Communicable Diseases: Communicable diseases are infectious diseases that can be transmitted from one person to another, either directly or indirectly. Examples include COVID-19, tuberculosis, and sexually transmitted infections (STIs).
• Non-Communicable Diseases: Non-communicable diseases are not infectious and do not spread from person to person. They often result from factors like genetics, lifestyle, and environmental exposures. Examples include cancer, diabetes, and cardiovascular diseases.

Infectious Diseases

• Infectious diseases are also known as communicable diseases.
• They are caused by microorganisms or pathogens, which include bacteria, viruses, fungi, protozoans, rickettsia, and worms.
• These diseases can be transmitted from an infected person to a healthy individual through various means, such as sneezing, coughing, contaminated food or water, and direct contact.
• Examples of infectious diseases include cholera, chickenpox, malaria, tuberculosis, and the common cold.
• Infectious diseases are typically characterized by their ability to spread from one person to another.

Non-Infectious Diseases

• Non-infectious diseases are caused by factors other than pathogens, such as genetics, age, nutritional deficiencies, gender, and lifestyle choices.
• They do not spread from one person to another; instead, they remain confined within the individual who has developed the condition.
• Examples of non-infectious diseases include hypertension (high blood pressure), diabetes, cancer, Alzheimer's disease, asthma, cataracts, and heart diseases.
• These diseases are often associated with chronic conditions that develop over time and may be influenced by a combination of genetic predisposition and environmental factors.

Bacterial Diseases

Bacterial diseases are illnesses caused by various types of bacteria. Bacteria are microscopic, single-celled organisms that come in various shapes and sizes. They can thrive in a wide range of environments, including soil, water, and the human body. Bacteria can be classified based on their shape (e.g., cocci, bacilli, spirilla), the composition of their cell walls (e.g., gram-positive, gram-negative), and genetic characteristics.
Some key points about bacterial diseases include:

• Types of Bacteria: There are thousands of bacterial species, and while many are harmless or even beneficial, some can cause diseases in humans, animals, and plants. Examples of disease-causing bacteria include Streptococcus, Staphylococcus, Escherichia coli (E. coli), Salmonella, and Mycobacterium tuberculosis.
• Transmission: Bacterial diseases can be transmitted through various means, such as direct contact with infected individuals, ingestion of contaminated food or water, inhalation of airborne bacteria, or exposure to contaminated surfaces. The mode of transmission varies depending on the specific disease.
• Symptoms: The symptoms of bacterial diseases can range from mild to severe and may include fever, inflammation, pain, fatigue, gastrointestinal issues, respiratory problems, and skin infections. The specific symptoms depend on the type of bacteria involved and the affected body system.
• Treatment: Bacterial diseases are often treated with antibiotics, which are medications designed to kill or inhibit the growth of bacteria. The choice of antibiotic depends on the type of bacteria causing the infection and its susceptibility to specific drugs.
• Prevention: Preventing bacterial diseases involves practicing good hygiene, such as regular handwashing, proper food handling and cooking, and vaccination (for diseases like tetanus, diphtheria, and pertussis). Additionally, some bacterial diseases can be prevented through the use of disinfectants and antimicrobial agents in healthcare settings and food production.

Common bacterial diseases in humans include strep throat, urinary tract infections (UTIs), tuberculosis, cholera, and bacterial pneumonia, among others. Understanding the nature of bacteria and how they cause diseases is essential for diagnosis, treatment, and prevention efforts in healthcare and public health.
Examples are:

• Diphtheria
• Anthrax
• Pneumonia
• Leprosy
• Tuberculosis
• Plague: Plague is caused by the bacteria Yersinia pestis, a zoonotic bacterium usually found in small mammals and their fleas.
• Meningitis: Meningitis — an infection of the tissues that cover and protect the brain and spinal cord — can be caused by viruses, bacteria, or fungi.
• Cholera
• Tetanus
• Typhoid fever
• Lyme disease
• Whooping cough
• Gonorrhea: It is a sexually transmitted disease. It is caused by the gonococcus, Neisseria gonorrhoeae—a bacterium.
• Syphilis: a systemic disease that is caused by the spirochete bacterium, Treponema pallidum. Syphilis is usually a sexually transmitted disease, but it is occasionally acquired by direct nonsexual contact with an infected person, and it can also be acquired by an unborn fetus through infection in the mother.

Viral Diseases

• A viral disease, also known as a viral infection or viral illness, is any medical condition caused by a virus.
• Viral diseases can affect various parts of the body and lead to a wide range of symptoms, from mild to severe. Common symptoms include fever, fatigue, cough, sore throat, and body aches.
• Some viral infections are acute, meaning they have a sudden onset and a relatively short duration. Examples of acute viral diseases include the common cold and influenza (the flu).
• Other viral infections can become chronic, persisting in the body for extended periods. Chronic viral diseases include HIV/AIDS, hepatitis B and C, and herpes.
• Vaccines have been developed to prevent several viral diseases, providing immunity and reducing the risk of infection. Examples of vaccines include those for measles, mumps, rubella, polio, and COVID-19.

Examples are:

• Influenza-Flu by influenza virus
• Common Cold- Rhinovirus
• Hepatitis A– Liver
• Norovirus-Gastro-intestinal illness
• Rotavirus– Diarrhea
• Human Papilloma Virus (HPV)
• Hepatitis B– Inflammation in the liver
• HIV
• Measles
• Rabies
• Smallpox
• Polio
• Rubella
• Chickenpox
• Japanese Encephalitis
• Zika Viral Fever
• Yellow Fever
• MERS-CoV (Middle East respiratory syndrome)
• SARS – Severe Acute Respiratory Syndrome

Protozoan Diseases

• Protozoan diseases are caused by single-celled eukaryotic organisms known as protozoa. These organisms can be parasitic and cause various diseases in humans and animals.
• Protozoan infections are prevalent in many parts of the world, particularly in regions with inadequate sanitation and hygiene practices.
• Transmission of protozoan diseases can occur through various means, including ingestion of contaminated food or water, contact with infected animals, and insect vectors (such as mosquitoes or flies) that transmit protozoa to humans.
• Some common protozoan diseases in humans include malaria (caused by Plasmodium species), amoebic dysentery (caused by Entamoeba histolytica), giardiasis (caused by Giardia lamblia), and trypanosomiasis (caused by Trypanosoma species).

Key Protozoa and Diseases:

• Plasmodium species: Plasmodium parasites are responsible for causing malaria, a mosquito-borne disease that affects millions of people worldwide. Malaria can lead to symptoms such as fever, chills, anemia, and can be life-threatening if not treated promptly.
• Entamoeba histolytica: This protozoan causes amoebic dysentery, a diarrheal illness characterized by severe abdominal pain, bloody stools, and dehydration.
• Giardia lamblia: Giardia is a common cause of giardiasis, a diarrheal disease that leads to symptoms like abdominal cramps, diarrhea, and weight loss.
• Trypanosoma species: These parasites cause diseases such as African trypanosomiasis (sleeping sickness) and Chagas disease. African trypanosomiasis can result in neurological symptoms, while Chagas disease can affect the heart and digestive system.

Examples:

• Malaria
• Amoebiasis
• Trichomoniasis
• African Sleeping sickness or Trypanosomiasis
• Leishmaniasis or Kala-azar
• Giardiasis
• Balantidiasis
• Toxoplasmosis

Zoonotic Diseases

• Zoonotic diseases, as you mentioned, are illnesses that can be transmitted between animals and humans. These diseases can be caused by various pathogens, including viruses, bacteria, parasites, and fungi.
• Zoonoses can be transmitted through direct contact with infected animals, their bodily fluids, or their environment. In some cases, they can also be transmitted through consumption of contaminated food or water.
• Some zoonotic diseases are relatively mild, causing mild flu-like symptoms or gastrointestinal issues in humans. However, others can be severe or even fatal.
• The emergence and spread of zoonotic diseases are influenced by various factors, including changes in land use, wildlife habitat destruction, global travel, and agricultural practices. Close proximity between humans and animals in certain settings, such as farms or live animal markets, can increase the risk of zoonotic disease transmission.

Examples:

• Chikungunya
• Malaria
• Yellow Fever
• Zika Virus Disease
• Dengue Fever
• Ebola
• Hepatitis E
• Rabies
• Japanese Encephalitis
• Filariasis
• Lyme disease
• Babesiosis
• Ehrlichiosis
• Ringworm
• Swine flu, also known as the H1N1 virus – caused by type A influenza virus.
• West Nile virus – causes a viral infection that is typically spread by mosquitoes and can cause neurological disease as well as death.

Neglected tropical diseases

• NTDs are a group of diverse infectious diseases that primarily affect populations in low-resource and tropical regions of the world. These diseases are characterized by their chronic nature and their association with poverty.
• NTDs are often referred to as "neglected" because they have historically received limited attention and funding compared to other global health issues. Despite their significant impact on affected communities, they have been overlooked in terms of research, treatment, and prevention efforts.
• The transmission of NTDs is closely linked to environmental and socioeconomic factors. Factors such as inadequate sanitation, lack of access to clean water, and close proximity to disease vectors (e.g., mosquitoes, flies) contribute to the spread of these diseases.
• The burden of NTDs is substantial, resulting in disability, disfigurement, and social stigma for affected individuals. Some NTDs can lead to long-term health complications if left untreated.
• The World Health Organization (WHO) has been a key player in efforts to combat NTDs. WHO's NTD program aims to provide support to endemic countries in their efforts to control and eliminate these diseases through strategies such as mass drug administration, improved access to healthcare, and vector control measures.

Examples:

• Buruli Ulcer
• Rabies
• Dengue
• Chikungunya
• Leprosy (Hansen’s disease)
• Lymphatic Filariasis
• Yaws
• Trachoma
• Schistosomiasis

West Nile Virus

• West Nile Virus is a vector-borne virus, meaning it is primarily transmitted to humans and animals through the bite of infected mosquitoes. The virus can also be transmitted through blood transfusions, organ transplants, and from mother to child during pregnancy, childbirth, or breastfeeding.
• While many people infected with WNV do not develop any symptoms, others may experience a range of mild to severe symptoms, with fever being the most common. Severe cases can lead to neurological complications, such as encephalitis or meningitis, which can be life-threatening.
• West Nile Virus was first identified in Uganda in 1937 and was named after the West Nile District, where it was discovered. The virus has since spread to various parts of the world.
• Birds are the natural reservoir hosts for WNV, meaning the virus primarily circulates between birds and mosquitoes. Mosquitoes become infected when they feed on infected birds and can then transmit the virus to other birds, animals, or humans during subsequent blood feeds.
• In regions where WNV is endemic, such as parts of North America, there are seasonal outbreaks of the disease, typically occurring during the summer and early fall when mosquito populations are at their peak.
• Prevention measures for WNV include reducing mosquito exposure (e.g., using insect repellent, wearing protective clothing, and eliminating mosquito breeding sites), controlling mosquito populations through insecticide spraying, and monitoring and testing blood donations to prevent transfusion-transmitted infections.
• There is no specific antiviral treatment for WNV. Supportive care and management of symptoms are typically provided to individuals with severe infections.

Leishmaniasis

• Transmission: Leishmaniasis is typically transmitted to humans through the bite of infected female sandflies. These sandflies are most commonly found in tropical and subtropical regions, as well as some parts of southern Europe. The disease can also be transmitted through blood transfusion, organ transplantation, or from mother to child during childbirth.
• Clinical Presentation: Leishmaniasis can manifest in several clinical forms, including cutaneous leishmaniasis, mucocutaneous leishmaniasis, and visceral leishmaniasis (also known as kala-azar). The symptoms and severity of the disease depend on the species of Leishmania involved and the individual's immune response. Cutaneous leishmaniasis primarily affects the skin, causing skin ulcers, while visceral leishmaniasis affects internal organs and can be fatal if left untreated.
• Global Distribution: Leishmaniasis is prevalent in various regions of the world, including parts of Asia, Africa, the Middle East, and Central and South America. The disease affects millions of people in these areas, especially those living in poverty and with limited access to healthcare.
• Treatment: The treatment of leishmaniasis depends on the clinical form and species of Leishmania involved. Antimonial drugs, such as sodium stibogluconate and meglumine antimoniate, have been commonly used for treatment. However, drug resistance has become a concern in some areas. Alternative treatments, including miltefosine and liposomal amphotericin B, have been introduced. Early diagnosis and prompt treatment are crucial to prevent complications.
• Prevention: Preventing leishmaniasis primarily involves controlling the sandfly vector. This can be achieved through measures like using insecticide-treated bed nets, wearing protective clothing, applying insect repellent, and implementing vector control programs. Research into a Leishmaniasis vaccine is ongoing.

Tuberculosis (TB)

• Causative Agent: Mycobacterium tuberculosis is the bacterium responsible for tuberculosis. It is an aerobic, acid-fast bacillus that primarily affects the lungs but can also infect other organs and tissues.
• Transmission: TB is primarily transmitted through the inhalation of respiratory droplets containing the bacteria. When an individual with active TB disease coughs or sneezes, they release these infectious droplets into the air, which can be inhaled by others.
• Global Impact: TB is one of the top infectious disease killers worldwide. In addition to the high-burden countries mentioned, it's important to note that TB can affect people in any part of the world. Efforts to combat TB include early diagnosis, appropriate treatment, contact tracing, and public health measures to prevent its spread.
• Drug-Resistant TB: MultiDrug Resistant Tuberculosis (MDR-TB) and Extensively Drug Resistant Tuberculosis (XDR-TB) are forms of TB that are resistant to multiple anti-TB drugs. Treating drug-resistant TB is more challenging and requires longer and more complex treatment regimens.
• BCG Vaccine: The Bacillus Calmette-Guérin (BCG) vaccine is the only currently available vaccine for TB. While it is not 100% effective at preventing TB, it can provide partial protection, especially against severe forms of TB in children.
• Geographic Variation: As you mentioned, the effectiveness of the BCG vaccine can vary by geographic location. Several factors, including strain differences, genetic factors, and exposure to environmental mycobacteria, can influence the vaccine's efficacy. It's an area of ongoing research and study.

Leprosy

• Symptoms: Leprosy primarily affects the skin, peripheral nerves, mucosal surfaces of the upper respiratory tract, and the eyes. It can present with a wide range of symptoms, including skin lesions, numbness or loss of sensation in affected areas, weakness or muscle paralysis, and in severe cases, damage to the nose and eyes.
• Transmission: The exact mode of transmission of leprosy is not fully understood, but it is believed to occur through prolonged close contact with an untreated person who has the disease. Leprosy is not highly contagious and is not easily transmitted.
• Early Diagnosis and Treatment: Early diagnosis and treatment of leprosy are crucial to prevent disabilities and reduce the risk of further transmission. Multidrug therapy (MDT) is the recommended treatment approach for leprosy. As you mentioned, MDT involves a combination of antibiotics, including rifampicin, clofazimine, and dapsone, based on the classification of the disease.
• Stigma and Discrimination: Leprosy has been historically associated with stigma and discrimination, often leading to social isolation of affected individuals. Efforts have been made to reduce stigma and promote social inclusion for people affected by leprosy.
• Global Efforts: The World Health Organization (WHO) has been actively involved in the global effort to control and eliminate leprosy. The goal is to reduce the burden of the disease and achieve a world free of leprosy-related suffering.

Alzheimer’s Disease

• Prevalence: While Alzheimer's disease predominantly affects individuals older than 65, it can occur in younger individuals, although this is less common. When it occurs in people under 65, it is referred to as early-onset Alzheimer's disease.
• Progressive Nature: Alzheimer's disease is progressive, meaning it worsens over time. It leads to the gradual destruction of brain cells and neural connections, which impairs cognitive function.
• Symptoms: The symptoms of Alzheimer's disease are often categorized into stages. In the early stages, individuals may experience mild memory loss and difficulty with familiar tasks. As the disease progresses, more severe symptoms develop, including confusion, language problems, poor judgment, mood changes, and personality changes. In advanced stages, individuals may lose the ability to recognize loved ones, communicate, or perform basic self-care tasks.
• Neuropathology: Alzheimer's disease is characterized by the accumulation of abnormal protein aggregates in the brain, including beta-amyloid plaques and tau tangles. These abnormal protein deposits disrupt normal brain function and contribute to the cognitive decline seen in Alzheimer's patients.
• No Cure: As you mentioned, there is currently no cure for Alzheimer's disease. Treatment approaches typically focus on managing symptoms and slowing down the progression of the disease. Medications and interventions may be used to alleviate some of the cognitive and behavioral symptoms associated with Alzheimer's.
• Ongoing Research: Research into Alzheimer's disease is ongoing, with a focus on understanding its causes, risk factors, and potential treatment strategies. Early diagnosis and intervention remain important areas of study, as identifying the disease in its early stages may offer the best chances for effective treatment.
• Caregiver Challenges: Alzheimer's disease not only affects individuals diagnosed with the condition but also places significant emotional and physical burdens on caregivers. Caregiver support and resources are important aspects of managing the challenges associated with Alzheimer's disease.

Parkinson’s Disease

• Dopamine Deficiency: Parkinson's disease primarily results from a loss of dopamine-producing nerve cells in a specific region of the brain called the substantia nigra. Dopamine is a neurotransmitter that plays a crucial role in coordinating smooth, controlled movements. The reduction in dopamine levels leads to the motor symptoms associated with Parkinson's disease.
• Motor Symptoms: As you mentioned, the hallmark motor symptoms of Parkinson's disease include tremors (typically a resting tremor), bradykinesia (slowness of movement), rigidity (stiffness of muscles), and postural instability (balance problems). These symptoms can vary in severity and progression from person to person.
• Non-Motor Symptoms: In addition to motor symptoms, Parkinson's disease can also involve non-motor symptoms. These may include cognitive changes, mood disorders (such as depression and anxiety), sleep disturbances, autonomic dysfunction (problems with blood pressure, digestion, and sweating), and sensory changes.
• Age of Onset: While Parkinson's disease is more commonly diagnosed in older adults, it can affect individuals at a younger age as well. Early-onset Parkinson's disease refers to cases diagnosed before the age of 50, and juvenile Parkinson's disease can occur in children and young adults.
• Treatment: While there is currently no cure for Parkinson's disease, several treatment options are available to help manage symptoms. These treatments may include medications to increase dopamine levels, physical therapy, occupational therapy, and in some cases, surgical interventions like deep brain stimulation (DBS).
• Research and Awareness: Ongoing research aims to better understand the underlying causes of Parkinson's disease, develop more effective treatments, and potentially find ways to slow or halt the progression of the disease. Increasing awareness of Parkinson's and supporting those affected by the condition are important aspects of addressing this complex disorder.