Human Health and Disease – CBSE NCERT Study Resources

The immune response involves innate and adaptive mechanisms. B-cells produce antibodies, while T-cells mediate cellular immunity.

• B-cells recognize viral antigens and differentiate into plasma cells, secreting neutralizing antibodies (e.g., IgG).
• Cytotoxic T-cells (CD8+) destroy infected cells by releasing perforins and granzymes.
• Helper T-cells (CD4+) activate B-cells and macrophages via cytokines.

Our textbook shows memory B and T-cells ensure long-term immunity, as seen in COVID-19 survivors.

Understanding these mechanisms aids vaccine development, like mRNA vaccines targeting spike proteins.

Zoonotic diseases jump from animals to humans due to ecological disruptions. The One Health model integrates human, animal, and environmental health.

• Example 1: COVID-19 likely originated from bats via intermediate hosts.
• Example 2: Nipah virus spreads from pigs or fruit bats to humans.

Our textbook highlights deforestation and wet markets as key risk factors.

One Health policies, like surveillance in wildlife, can prevent outbreaks, as proposed by WHO.

Mycobacterium tuberculosis causes TB, primarily affecting lungs. Granulomas wall off bacteria but may also harbor latent infection.

• Macrophages engulf bacteria but fail to kill them, forming caseous necrosis.
• MDR-TB arises from mutations due to incomplete antibiotic courses.

Our textbook shows India accounts for 27% of global MDR-TB cases (WHO 2022).

New diagnostics like GeneXpert and adherence to DOTS can curb resistance.

Active immunity involves memory cells, while passive immunity provides temporary protection.

• Active: Vaccination (e.g., polio vaccine) induces long-term immunity.
• Passive: Maternal antibodies or antivenom offer immediate but short-lived defense.

Herd immunity (e.g., 70% vaccination for measles) protects unvaccinated individuals by breaking transmission chains.

COVID-19 demonstrated its importance, though natural herd immunity risks high mortality.

Oncogenes (e.g., RAS) promote cell division, while tumor suppressors (e.g., p53) inhibit it. Mutations disrupt this balance.

• Genetic: BRCA1 mutations increase breast cancer risk by 70%.
• Lifestyle: Tobacco use causes 90% of lung cancers via carcinogens.

Our textbook shows only 5-10% cancers are purely hereditary; most involve gene-environment interactions.

Early screening (e.g., mammograms) and lifestyle changes can reduce incidence.

Malaria is caused by Plasmodium, transmitted via Anopheles mosquitoes. The parasite targets liver cells and RBCs.

• Sporozoites infect hepatocytes, multiplying into merozoites (exo-erythrocytic cycle).
• Merozoites lyse RBCs, causing cyclic fever (e.g., P. falciparum).

Our textbook shows antigenic variation in Plasmodium evades immunity, complicating vaccine design.

Research on RTS,S vaccine highlights partial protection, urging novel strategies.

Autoimmune diseases arise from immune system attacking self-antigens due to genetic/environmental triggers.

• Type 1 diabetes: T-cells destroy pancreatic β-cells, reducing insulin.
• Rheumatoid arthritis: Autoantibodies (e.g., RF) attack joint synovium.

Our textbook shows immunosuppressants (e.g., methotrexate) manage symptoms but lack cures.

Stem cell therapy and biologics (e.g., anti-TNFα) offer promising treatments.

Unhealthy diets, smoking, and stress contribute to CVDs by damaging blood vessels.

• Atherosclerosis: LDL cholesterol forms plaques, obstructing arteries.
• Hypertension: High salt intake increases blood pressure, straining the heart.

Our textbook shows Mediterranean diets reduce CVD risks by 30%, as per WHO data.

Public health campaigns (e.g., Fit India) promote preventive lifestyles.

HIV, a retrovirus, integrates its RNA into host DNA via reverse transcriptase, targeting CD4+ cells.

• Viral RNA converts to DNA, merging with host genome (e.g., provirus).
• CD4+ depletion weakens immunity, leading to AIDS (opportunistic infections).

Our textbook shows ART drugs (e.g., zidovudine) delay progression but don’t eradicate HIV.

Research on CRISPR-based therapies aims to excise viral DNA.

Vaccines induce herd immunity by stimulating antibody production without causing disease.

• Smallpox: Live-attenuated vaccine (e.g., vaccinia virus) eradicated it by 1980.
• Polio: Oral polio vaccine (OPV) reduced global cases by 99%.

Our textbook shows challenges like vaccine hesitancy delayed polio eradication in some regions.

Lessons from these programs guide COVID-19 vaccination drives.

Tuberculosis (TB) is caused by Mycobacterium tuberculosis, which survives in macrophages.

• The bacteria evade lysosomal destruction by inhibiting phagosome-lysosome fusion.
• Host defenses include granuloma formation, isolating the pathogen.

Our textbook shows latent TB reactivates when immunity weakens, e.g., in HIV patients.

BCG vaccine boosts immunity, but drug-resistant strains demand new therapies.

Cancer arises from mutations in oncogenes (e.g., RAS) and tumor suppressor genes (e.g., p53).

• Oncogenes promote cell proliferation when mutated (e.g., HER2 in breast cancer).
• Tumor suppressors like p53 regulate apoptosis; their loss causes uncontrolled growth.

Our textbook shows BRCA1 mutations increase ovarian cancer risk.

Targeted therapies, like trastuzumab for HER2+, exemplify precision medicine.

Vector-borne diseases like malaria (Plasmodium) and dengue (Flavivirus) spread via mosquitoes.

• Malaria transmits via Anopheles; dengue via Aedes aegypti.
• Prevention includes insecticide-treated nets (ITNs) and larval source reduction.

Our textbook shows India’s NVBDCP reduced malaria cases by 50% since 2000.

Vaccines like RTS,S for malaria highlight progress in disease control.

The gut microbiome aids digestion, immunity, and vitamin synthesis. Dysbiosis disrupts this balance.

• Firmicutes/Bacteroidetes ratio shifts in obesity.
• Probiotics (e.g., Lactobacillus) restore microbial balance.

Our textbook links dysbiosis to IBD and type 2 diabetes.

Personalized diets and fecal transplants emerge as therapeutic options.

HIV targets CD4+ T-cells, weakening immunity. ART suppresses viral replication but doesn’t cure.

• Drug resistance arises from non-adherence or mutations (e.g., M184V in reverse transcriptase).
• Combination ART (e.g., tenofovir + emtricitabine) reduces resistance risk.

Our textbook shows 95% viral suppression in adherent patients.

Long-acting injectables (e.g., cabotegravir) may improve compliance.

The Human Immunodeficiency Virus (HIV) primarily targets the CD4+ T-lymphocytes, which are crucial for immune response. The replication mechanism involves the following steps:

• Attachment and Entry: HIV binds to the CD4 receptors and co-receptors (CCR5 or CXCR4) on the host cell surface using its gp120 envelope protein. The viral envelope fuses with the host membrane, releasing viral RNA and enzymes into the cytoplasm.
• Reverse Transcription: The viral reverse transcriptase converts single-stranded RNA into double-stranded DNA.
• Integration: The viral DNA is integrated into the host genome by the enzyme integrase, forming a provirus.
• Replication and Assembly: The host machinery transcribes viral DNA into mRNA, which is translated into viral proteins. New virions are assembled and bud out from the host cell.
• Maturation: The enzyme protease cleaves viral polyproteins into functional components, forming mature infectious viruses.

Over time, HIV destroys CD4+ T-cells, weakening the immune system and leading to Acquired Immunodeficiency Syndrome (AIDS), where the body becomes vulnerable to opportunistic infections like tuberculosis and pneumonia.

Preventive measures include:

• Using sterile needles and avoiding sharing syringes.
• Practicing safe sex with condoms.
• Screening blood before transfusion.
• Preventing mother-to-child transmission through antiretroviral therapy (ART).
• Promoting awareness and education about HIV/AIDS.

Early diagnosis and adherence to ART can significantly slow disease progression and improve quality of life.

A vaccine contains weakened or inactivated pathogens (e.g., polio virus) or their components (e.g., tetanus toxoid), which stimulate the immune system without causing disease. The response occurs in two phases:

• Primary Response: Antigen-presenting cells (APCs) detect the vaccine antigen and activate B-cells and T-cells. B-cells produce antibodies, while T-cells eliminate infected cells.
• Memory Formation: Some B- and T-cells differentiate into memory cells, which persist long-term.

Upon future exposure to the actual pathogen, memory cells mount a rapid, stronger secondary response, preventing infection. For example, the MMR vaccine provides lifelong immunity against measles, mumps, and rubella due to robust memory cell formation.

Value-added insight: Vaccines like COVID-19 mRNA vaccines (e.g., Pfizer) use viral genetic material to train the immune system, showcasing modern advancements.

The Human Immunodeficiency Virus (HIV) primarily targets the CD4+ T-lymphocytes, which are crucial for immune function. The replication mechanism involves the following steps:

1. Attachment and Entry: HIV binds to the CD4 receptors and CCR5/CXCR4 co-receptors on the host cell surface using its gp120 and gp41 envelope proteins.
2. Reverse Transcription: The viral RNA genome is converted into DNA by the enzyme reverse transcriptase.
3. Integration: The viral DNA integrates into the host genome using the enzyme integrase, forming a provirus.
4. Transcription and Translation: The host cell machinery produces viral proteins and RNA copies.
5. Assembly and Budding: New viral particles assemble and bud out from the host cell, maturing into infectious virions.

Preventive Measures:

• Use of sterile needles and safe blood transfusion practices.
• Promoting protected sex through condoms and awareness programs.
• Prevention of mother-to-child transmission via antiretroviral therapy (ART).
• Regular HIV testing and early diagnosis to manage the infection.
• Public education to eliminate stigma and encourage healthy practices.

Understanding HIV replication helps in developing targeted therapies like ART, which suppresses viral load and improves quality of life.

The HIV (Human Immunodeficiency Virus) primarily targets the CD4+ T-lymphocytes, which are crucial for immune function. The replication mechanism involves the following steps:

1. Attachment and Entry: The virus binds to the CD4 receptor and CCR5/CXCR4 co-receptors on the host cell surface, followed by fusion and entry of viral RNA into the cell.
2. Reverse Transcription: The viral reverse transcriptase enzyme converts viral RNA into DNA.
3. Integration: The viral DNA integrates into the host genome using the integrase enzyme, forming a provirus.
4. Replication and Assembly: The host machinery transcribes viral DNA into RNA, which is translated into viral proteins. New virions assemble and bud out from the host cell.

The progression from HIV to AIDS (Acquired ImmunoDeficiency Syndrome) occurs in three stages:

1. Acute Infection: Flu-like symptoms appear as the virus replicates rapidly.
2. Chronic Phase (Clinical Latency): The virus remains active but reproduces at low levels, gradually depleting CD4+ cells.
3. AIDS: When CD4+ count drops below 200 cells/mm³, severe immunodeficiency leads to opportunistic infections (e.g., tuberculosis, candidiasis) and cancers (e.g., Kaposi’s sarcoma).

Preventive Measures:

• Using sterile needles and practicing safe sex with condoms.
• Promoting awareness programs and regular testing for early detection.

The HIV (Human Immunodeficiency Virus) primarily targets the T-lymphocytes (specifically CD4+ cells), which are crucial for immune response. The replication mechanism involves the following steps:

1. Attachment and Entry: The virus binds to CD4 receptors and co-receptors (CCR5 or CXCR4) on the host cell surface, followed by fusion and entry of viral RNA into the cell.
2. Reverse Transcription: The viral RNA is converted into DNA by the enzyme reverse transcriptase.
3. Integration: The viral DNA integrates into the host genome using integrase, forming a provirus.
4. Replication and Assembly: The host cell machinery produces viral proteins and RNA, which assemble into new virions.
5. Budding: Mature viruses bud out from the host cell, destroying it in the process.

As HIV replicates, it destroys CD4+ T-cells, leading to a weakened immune system and eventually AIDS (Acquired Immunodeficiency Syndrome).

Preventive measures include:

• Using barrier methods (condoms) during sexual intercourse.
• Avoiding sharing of needles and ensuring sterile medical equipment.
• Screening blood before transfusion.
• Promoting awareness about HIV transmission and prevention.
• Administering Antiretroviral Therapy (ART) to infected individuals to control viral load.

Vaccination is a crucial medical intervention that helps prevent infectious diseases by stimulating the body's immune system to recognize and combat pathogens. It works on the principle of adaptive immunity, where the immune system is exposed to a weakened or inactivated form of a pathogen (or its components), triggering the production of antibodies and memory cells. This prepares the body to fight future infections efficiently.

The concept of herd immunity arises when a significant portion of a population becomes immune to a disease (through vaccination or prior infection), reducing its spread and protecting those who are not immune, such as individuals with compromised immune systems.

• Example 1: The polio vaccine has nearly eradicated polio globally by inducing immunity and reducing transmission.
• Example 2: The MMR vaccine (measles, mumps, rubella) prevents outbreaks by maintaining high herd immunity.

Vaccination not only safeguards individuals but also contributes to public health by controlling epidemics and eradicating diseases, as seen with smallpox. It is a cost-effective and scientifically proven method to ensure long-term disease prevention.

Vaccination is a crucial preventive measure against infectious diseases. It involves administering a vaccine, which contains weakened or inactive pathogens or their components, to stimulate the immune system to produce antibodies and memory cells. This prepares the body to fight future infections effectively.

The principle of herd immunity states that when a significant portion of a population (usually 70-90%) is vaccinated, the spread of the disease is minimized, protecting even those who are not vaccinated (e.g., immunocompromised individuals). This occurs because the pathogen cannot find enough susceptible hosts to sustain transmission.

For example, the polio vaccine has been instrumental in nearly eradicating polio worldwide. Due to widespread vaccination campaigns, the virus has been eliminated in most countries, demonstrating the success of herd immunity.

Key benefits of vaccination include:

• Prevents outbreaks of deadly diseases
• Reduces healthcare burden
• Protects vulnerable populations
• Contributes to global disease eradication efforts

The Human Immunodeficiency Virus (HIV) primarily targets the CD4+ T-lymphocytes, which are crucial for immune response. The replication mechanism involves the following steps:

1. Attachment and Entry: HIV binds to the CD4 receptors and co-receptors (CCR5 or CXCR4) on the host cell surface using its gp120 and gp41 envelope proteins. The viral envelope fuses with the host membrane, releasing viral RNA and enzymes into the cytoplasm.

2. Reverse Transcription: The viral reverse transcriptase enzyme converts single-stranded RNA into double-stranded DNA.

3. Integration: The viral DNA is integrated into the host genome by the integrase enzyme, forming a provirus.

4. Replication and Assembly: The host machinery transcribes viral DNA into mRNA, which is translated into viral proteins. New virions are assembled and bud out from the host cell.

5. Maturation: The protease enzyme cleaves viral polyproteins into functional components, forming mature infectious HIV particles.

HIV gradually destroys CD4+ T-cells, weakening the immune system. When the CD4 count drops below 200 cells/mm³, the individual develops AIDS (Acquired Immunodeficiency Syndrome), making them susceptible to opportunistic infections like tuberculosis and pneumonia.

Preventive Measures:

• Using barrier methods (e.g., condoms) during sexual intercourse.
• Avoiding sharing of needles and ensuring sterile medical equipment.

Vaccination is a preventive measure that stimulates the immune system to recognize and combat pathogens like viruses or bacteria. It involves administering a weakened or inactive form of the pathogen (or its components) to trigger an immune response without causing the disease.

The concept of herd immunity arises when a significant portion of a population becomes immune to a disease, either through vaccination or prior infection, reducing its spread. This indirectly protects unvaccinated individuals, such as those with compromised immune systems.

• Public Health Benefits: Vaccination programs eradicate or control deadly diseases (e.g., smallpox, polio).
• Economic Impact: Reduces healthcare costs by preventing outbreaks.
• Community Safety: Protects vulnerable groups (newborns, elderly) who cannot be vaccinated.

For example, the COVID-19 vaccination drive significantly lowered transmission rates, showcasing herd immunity in action.

The Plasmodium parasite has a complex life cycle involving two hosts: humans and the Anopheles mosquito.

1. Transmission to Humans:
When an infected female Anopheles mosquito bites, it injects sporozoites into the bloodstream.
These travel to the liver, multiply asexually (forming merozoites), and infect red blood cells (RBCs).

2. Asexual Reproduction in Humans:
Inside RBCs, merozoites replicate, causing cell rupture and releasing toxins, leading to fever/chills (malaria symptoms).

3. Sexual Reproduction in Mosquitoes:
When another mosquito bites an infected human, it ingests gametocytes.
These fuse in the mosquito’s gut, forming sporozoites that migrate to its salivary glands, continuing the cycle.

Preventive Measures:

• Use of insecticide-treated nets (ITNs) and indoor residual spraying (IRS).
• Antimalarial drugs like chloroquine (where effective).
• Eliminating stagnant water to reduce mosquito breeding.

Understanding this cycle helps in targeting interventions, such as vaccines (e.g., RTS,S) and mosquito control programs.