Medical Microbiology & Immunology
Time: 3 hrs
Max. Marks: 75
Section –A
Answer any Five questions of the following (5 x 3 = 15 Marks)
1. Cholera: Cholera is an acute diarrheal disease caused by Vibrio cholerae. The bacteria produce cholera toxin, which leads to severe diarrhea and dehydration. The infection is typically spread through contaminated water or food. Symptoms include watery stools, vomiting, and muscle cramps. It can be treated with oral rehydration therapy (ORT) and antibiotics like doxycycline.
2. Bacterial Toxins: Bacterial toxins are harmful substances produced by bacteria that can damage host tissues or interfere with normal cell function. They are mainly classified into two categories:
- Exotoxins: Proteins secreted by bacteria (e.g., tetanus toxin, botulinum toxin).
- Endotoxins: Lipopolysaccharides found in the cell wall of Gram-negative bacteria (e.g., E. coli, Salmonella).
Exotoxins are more potent and are often heat-labile, while endotoxins are heat-stable and usually cause fever and inflammation.
3. Amoebiasis: Amoebiasis is an intestinal infection caused by Entamoeba histolytica, a protozoan parasite. It can lead to symptoms such as dysentery, abdominal pain, and weight loss. Severe infections may result in liver abscesses. Transmission occurs through the ingestion of cysts from contaminated water or food. Treatment involves anti-amoebic drugs like metronidazole or tinidazole.
4. SARS: Severe Acute Respiratory Syndrome (SARS) is a viral respiratory illness caused by the SARS coronavirus (SARS-CoV). The disease emerged in 2002-2003 and caused severe pneumonia. Symptoms include fever, cough, shortness of breath, and respiratory distress. SARS is transmitted via respiratory droplets, and treatment focuses on supportive care. The outbreak was controlled through stringent quarantine measures.
5. MHC Molecule: Major Histocompatibility Complex (MHC) molecules are cell surface proteins that play a crucial role in the immune system. MHC molecules present peptide fragments to T-cells, enabling the immune system to recognize and respond to pathogens. There are two classes of MHC molecules:
- MHC Class I: Found on all nucleated cells, presenting antigens to CD8+ cytotoxic T cells.
- MHC Class II: Found on antigen-presenting cells (e.g., macrophages, dendritic cells), presenting antigens to CD4+ helper T cells.
6. Epitope: An epitope, also known as an antigenic determinant, is the part of an antigen that is recognized by the immune system. It is the specific region of an antigen to which an antibody or T-cell receptor binds. Epitopes can be linear (a sequence of amino acids) or conformational (a specific three-dimensional structure).
7. RIA (Radioimmunoassay): Radioimmunoassay (RIA) is a sensitive laboratory technique used to measure the concentration of antigens or antibodies in a sample. It involves the use of radioactively labeled molecules and a competitive binding assay. RIA is used in clinical diagnostics, hormone assays, and drug testing.
8. Autoimmune Disorders: Autoimmune disorders occur when the body’s immune system mistakenly attacks its own tissues. Common autoimmune diseases include:
- Rheumatoid arthritis: The immune system attacks joint tissues.
- Type 1 diabetes: The immune system destroys insulin-producing cells in the pancreas.
- Multiple sclerosis: The immune system attacks the myelin sheath of neurons. These disorders are treated using immunosuppressive drugs.
Section-B
Answer all questions of the following (4 x 15 = 60 Marks)
9. a) Host-Pathogen Interactions: Host-pathogen interactions refer to the dynamic relationship between the host organism and a pathogen. Successful pathogens must evade the host’s immune system, adhere to host cells, and sometimes invade tissues to cause disease. Factors influencing these interactions include:
- Virulence factors: Bacterial toxins, adhesion molecules, and enzymes that facilitate tissue invasion.
- Immune evasion: Strategies like antigenic variation, capsule formation, and immune suppression.
- Host immunity: The host’s innate and adaptive immune responses attempt to eliminate or control the infection.
(OR)
b) Nosocomial Infections: Nosocomial infections are infections acquired in a hospital or healthcare setting. These infections are typically caused by multidrug-resistant organisms like Methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile. Nosocomial infections can spread through contaminated surfaces, medical equipment, or person-to-person contact. Common types include urinary tract infections, surgical site infections, and pneumonia. Prevention includes strict hygiene practices, sterilization of medical instruments, and isolation of infected patients.
10. a) Zoonotic Infections – Rabies: Zoonotic infections are diseases that can be transmitted from animals to humans. Rabies is a viral disease caused by the rabies virus, primarily transmitted through the bite of infected animals like dogs, bats, or raccoons.
- Etiological agent: Rabies virus (a negative-sense RNA virus).
- Pathogenesis: The virus enters the body through the bite, travels via nerves to the central nervous system, causing encephalitis.
- Diagnosis: Diagnosis is confirmed through laboratory tests like PCR, immunofluorescence, or brain tissue analysis post-mortem.
- Treatment: Rabies is fatal once symptoms appear, but post-exposure prophylaxis (PEP) with a rabies vaccine and rabies immune globulin can prevent disease if administered before symptoms.
(OR)
b) Hepatitis-B: Hepatitis B is a viral infection caused by the Hepatitis B virus (HBV), affecting the liver. The virus is transmitted through contact with infected bodily fluids (blood, semen).
- Replication: HBV replicates in liver cells using reverse transcription.
- Pathogenesis: It causes liver inflammation and can lead to cirrhosis, liver cancer, or liver failure.
- Diagnosis: Diagnosis is made through serological tests (HBsAg, anti-HBs, HBV DNA).
- Treatment: Antiviral drugs such as lamivudine, entecavir, or tenofovir are used. A vaccine is available for prevention.
11. a) Immunoglobulins: Immunoglobulins (Ig) are antibodies produced by B-cells that help the immune system recognize and neutralize foreign invaders like bacteria, viruses, and toxins. There are five main classes of immunoglobulins:
- IgG: Most abundant, provides long-term immunity.
- IgA: Found in mucosal areas (e.g., saliva, tears).
- IgM: The first antibody produced in response to an infection.
- IgE: Involved in allergic reactions and responses to parasitic infections.
- IgD: Functions primarily in the initiation of immune responses.
Diagrams:
- IgG structure: Y-shaped with two heavy chains and two light chains.
- IgA structure: Dimeric with two Y-shaped units.
(OR)
b) Immunity: Immunity is the ability of an organism to resist harmful microorganisms or viruses. Types of immunity include:
- Innate immunity: The body’s first line of defense, including physical barriers (skin), phagocytosis, and natural killer cells.
- Adaptive immunity: A specific immune response involving T-cells (cell-mediated immunity) and B-cells (humoral immunity).
- Active immunity: Acquired through exposure to pathogens or vaccination.
- Passive immunity: Acquired through the transfer of antibodies, such as from mother to child.
12. a) Hybridoma Technology: Hybridoma technology involves fusing a specific antibody-producing B-cell with a myeloma (cancer) cell, creating a hybrid cell that can both produce antibodies and divide indefinitely. This technology is used to produce monoclonal antibodies, which have wide applications in medicine, including:
- Cancer therapy
- Diagnostic kits
- Immunotherapy
(OR)
b) Hypersensitivity: Hypersensitivity refers to an exaggerated immune response to harmless antigens. There are four types:
- Type I (Immediate hypersensitivity): Caused by IgE antibodies (e.g., allergies, asthma).
- Type II (Cytotoxic hypersensitivity): Involves IgG/IgM antibodies attacking cells (e.g., hemolytic anemia).
- Type III (Immune complex-mediated hypersensitivity): Involves the formation of immune complexes that deposit in tissues (e.g., systemic lupus erythematosus).
- Type IV (Delayed-type hypersensitivity): T-cell mediated (e.g., contact dermatitis, tuberculosis skin test).