Practice 3 structured short- and long-answer medical questions on Principles of Medical Microbiology and Parasitology LAQs & SAQs. Review model answers f...
Answer: - **Alternative agents**: Dapsone, atovaquone, or aerosolized pentamidine may be used in TMP-SMX-intolerant patients. - **CD4 Monitoring**: Regular CD4+ T-cell count assessment to guide initiation and discontinuation of prophylaxis. - **ART initiation**: Early antiretroviral therapy helps restore immunity and prevent opportunistic infections. - **Adherence counseling**: Ensures compliance with prophylactic regimens and ART. - **Leucovorin (folinic acid) supplementation**: To prevent bone marrow suppression from pyrimethamine. - **Regular hematologic monitoring**: Monitor CBC for neutropenia, anemia, and thrombocytopenia. - **Renal function monitoring**: Sulfadiazine can cause crystalluria or renal toxicity. - **Hydration**: Ensure adequate fluid intake to prevent renal complications. - **Allergy surveillance**: Watch for hypersensitivity reactions or rash, especially from sulfonamides. - **Cutaneous lesions**: Ulcerated or nodular skin lesions at the site of sandfly bite, often painless. - **Regional lymphadenopathy**: Enlargement of nearby lymph nodes. - **Disfiguring scars**: Chronic or healing lesions may result in visible scarring. - **Secondary bacterial infection**: May complicate ulcerated lesions. - **Systemic symptoms** *(in some cases)*: Low-grade fever and malaise, depending on the species and immune status. - **Bactericidal effect** occurs when an antibiotic kills bacteria directly. This is typically seen:At higher drug concentrations. - In rapidly dividing bacterial populations. - In infections where immune clearance is inadequate (e.g., endocarditis, meningitis, neutropenia). - **Bacteriostatic effect** inhibits bacterial growth and replication without killing, relying on the host immune system to eliminate the organism. - **Effect depends on the drug, dose, organism, and host immunity.**For example, chloramphenicol may be bacteriostatic for some organisms and bactericidal for others. - **Avoid in immunocompromised patients**: These patients may require bactericidal agents due to reduced immune clearance. - **Avoid combination with bactericidal drugs**: Some combinations (e.g., bactericidal + bacteriostatic) can lead to antagonism and reduced efficacy. - **Pathogenesis**:Prions are misfolded proteins (PrP^Sc) that induce conformational changes in normal cellular prion proteins (PrP^C) to the abnormal form. - PrP^Sc accumulates in neural tissue, forming amyloid plaques. - This accumulation leads to neuronal death, spongiform degeneration, and progressive neurodegeneration. - There is no immune response or inflammation due to the host-derived nature of prions. - **Human prion diseases**:**Creutzfeldt-Jakob disease (CJD)** – the most common prion disease, often sporadic. - **Variant CJD** – associated with consumption of BSE (mad cow disease)-infected beef. ##### **A. Life Cycle** *(Illustration-friendly — include with diagram if submitting)* . Click to see Life Cycle - **Mosquito stage (Definitive host)**Female *Anopheles* mosquito inoculates **sporozoites** during a blood meal. - **Human liver stage (Pre-erythrocytic)**Sporozoites enter hepatocytes → multiply asexually → form **schizonts** → release **merozoites** into bloodstream. - **Human blood stage (Erythrocytic cycle)**Merozoites invade RBCs → mature into **trophozoites** → form **schizonts** → rupture RBCs, releasing more merozoites. - Some trophozoites form **gametocytes** (sexual forms). - **Back to mosquito (sexual cycle)**Mosquito ingests gametocytes → gamete fusion → **zygote** → **ookinete** → **oocyst** → sporozoites → cycle continues. **Illustration tip**: Use a circular flow chart with human and mosquito phases clearly labeled. --- ##### **B. Pathogenesis** - **RBC Destruction** → Hemolytic anemia, jaundice. - **Cytoadherence** → *P. falciparum* causes infected RBCs to adhere to endothelium (via PfEMP1) → **microvascular obstruction**, **cerebral malaria**, **placental malaria**. - **Immune response** → Fever, chills, cytokine release. - **Sequestration** → In spleen/liver; can lead to organomegaly and immune evasion. --- ##### **C. Treatment** - **Uncomplicated malaria**:**Artemisinin-based combination therapies (ACTs)**: e.g., artemether-lumefantrine, artesunate-amodiaquine. - **Severe malaria**:**IV artesunate** (preferred), followed by oral ACT. - **Supportive care**:Manage hypoglycemia, anemia, renal failure, cerebral edema. Note: Chloroquine is **ineffective** due to resistance. --- ##### **D. Control and Prevention** - **Vector control**: Insecticide-treated nets (ITNs), indoor residual spraying (IRS). - **Chemoprophylaxis**: E.g., atovaquone-proguanil, doxycycline (travelers). - **Surveillance**: Rapid diagnostic tests (RDTs), microscopy. - **Vaccination**: RTS,S/AS01 (Mosquirix) approved for children in endemic regions. - **Public education**: Elimination of breeding sites, early diagnosis. **A. Molecular Diagnostics** - **PCR and RT-PCR**: High sensitivity/specificity for *Plasmodium*, *Toxoplasma*, *Leishmania*, *Trypanosoma*. - **Loop-mediated isothermal amplification (LAMP)**: Field-friendly alternative to PCR. **B. Immunodiagnostics** - **ELISA**: Detection of parasite antigens or antibodies (e.g., *Entamoeba histolytica*, *Toxoplasma gondii*). - **Rapid diagnostic tests (RDTs)**:E.g., *Plasmodium falciparum* HRP2 detection. - *Cryptosporidium* antigen tests in stool. **C. Point-of-care testing (POCT)** - Handheld or dipstick tests with visual results.E.g., *Trypanosoma cruzi* (Chagas) lateral flow assays. **D. Imaging and Serology** - **MRI/CT**: *Neurocysticercosis*, *toxoplasmosis*. - **Western blot**: Confirmatory for *T. gondii*, *T. solium*, *Leishmania*. **E. AI and Digital Microscopy** - Image recognition tools to automate parasite detection in blood films or stool samples. **F. Metagenomics and NGS** - **Next-generation sequencing** for rare or mixed infections (e.g., intestinal protozoa). **G. Biosensor and Nanotech** - Experimental tools for real-time detection using parasite-derived DNA/proteins. **(a)**
Answer: - Converts viral **ssRNA** into **dsDNA**. - Has **RNA-dependent DNA polymerase** and **RNase H** activity. - Critical for forming a **DNA provirus** from HIV RNA. - Error-prone → high mutation rate → rapid resistance development.
Answer: - Facilitates **integration of viral DNA** into host genome. - Steps:Viral DNA is processed by integrase. - Integrase binds host DNA. - Catalyzes insertion of proviral DNA. - Allows viral genome to become part of host DNA → **persistent infection**. **Mechanism of Action of Zidovudine (ZDV/AZT)** **(10 Marks)** - **Nucleoside Reverse Transcriptase Inhibitor (NRTI)**. - **Structural analogue of thymidine**. - Enters host cells → phosphorylated to active triphosphate form. - **Competitively inhibits reverse transcriptase**. - Incorporates into viral DNA chain → **terminates elongation** (lacks 3’-OH group). **Effect on Integrase** - **No direct effect on integrase**. - **Indirect impact**: By blocking DNA synthesis, ZDV prevents substrate formation for integration. **Clinical Relevance** - One of the first ARVs developed. - Used in **combination therapy** (HAART). - Prevents **mother-to-child transmission** effectively. - Side effects: Anemia, neutropenia, lactic acidosis (rare). **a) Psychrophile**Organisms that thrive in extremely cold environments, typically at temperatures below 15°C.*Example:* *Pseudomonas fluorescens* found in Arctic soils. **b) Peritrichous**Bacteria that have flagella uniformly distributed over the entire cell surface.*Example:* *Escherichia coli.* **c) Koch’s Postulates**A set of four criteria used to establish a causative relationship between a microbe and a disease: - The microorganism must be found in all organisms suffering from the disease. - It must be isolated and grown in pure culture. - The cultured microbe should cause disease when introduced into a healthy organism. - The same microbe must be re-isolated from the experimentally infected host. **d) Thermodimorphism**The ability of certain fungi to exist in two morphological forms depending on temperature: mold at lower temperatures (25°C) and yeast at body temperature (37° C).*Example:* *Histoplasma capsulatum.* **e) Microaerophile**Microorganisms that require oxygen for growth but at lower concentrations than those in the atmosphere (typically 2–10% O₂).*Example:* *Helicobacter pylori.* **a) Endospores**Highly resistant, dormant structures formed by certain bacteria (e.g., *Bacillus*, *Clostridium*) during nutrient deprivation. They allow bacteria to survive extreme heat, desiccation, chemicals, and radiation. **b) Lipopolysaccharide (LPS) Layer of Gram-Negative Bacteria**LPS contains Lipid A, which acts as an endotoxin. When released during cell lysis, it can trigger septic shock, fever, and inflammation. **c) Plasmid**Small, circular DNA molecules separate from chromosomal DNA. Plasmids often carry genes for antibiotic resistance and virulence, and can be transferred via conjugation. **d) Capsule**A gelatinous outer layer that protects bacteria from phagocytosis by host immune cells. Enhances virulence.*Example:* Capsule of *Streptococcus pneumoniae.* **e) Fimbriae and Pili**Fimbriae help bacteria adhere to host tissues, aiding colonization. Pili (especially sex pili) are involved in genetic exchange through conjugation. - Dry heat sterilizes by **oxidizing cellular components** and denaturing microbial proteins. - It requires **higher temperatures and longer exposure times** than moist heat (e.g., 160°C for 2 hours or 180°C for 1 hour). - Effective for **moisture-sensitive materials** such as powders, oils, and petroleum-based products. - Suitable for **metal instruments**, glassware, and sharp tools as it does not cause corrosion. - Used in **hot air ovens** for sterilizing syringes, forceps, and lab glassware. **a) Light Microscopy:** - Uses **visible light** to illuminate the specimen. - Magnification is up to **1,000–1,500×**. - Lower resolution (~200 nm); suitable for observing **living or stained organisms**. - Types include **bright field, dark field, phase contrast, and fluorescence**. - Commonly used in **clinical labs** for quick diagnostics. **b) Electron Microscopy:** - Uses a **beam of electrons** for imaging. - Magnification can reach up to **500,000×**. - Very high resolution (up to 0.2 nm); useful for observing **ultrastructure of cells and viruses**. - Types include **transmission (TEM)** and **scanning (SEM)**. - Requires fixed, dehydrated, and metal-coated specimens. **a) Roles of Pili (2 marks):** - **Adherence to host cells** – helps bacteria attach to epithelial surfaces. - **Genetic exchange** – sex pili facilitate **conjugation**, transferring resistance genes. **b) Morphological Forms of Fungi (1 mark):** - **Yeast** – unicellular, reproduce by budding (e.g., *Candida albicans*). - **Mold** – multicellular, form hyphae and spores (e.g., *Aspergillus*). **c) Steps in Peptidoglycan Biosynthesis (2 marks):** - **Synthesis of precursors** – N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) with peptide chains are formed in the cytoplasm. - **Transport** – precursors are carried across the membrane by **bactoprenol**. - **Polymerization** – transglycosylation links sugar chains; transpeptidation forms **cross-links** between peptide chains for strength. - **Eukaryotic organisms** – have a true nucleus and membrane-bound organelles. - **Heterotrophic nutrition** – absorb nutrients from organic matter, often as saprophytes or parasites. - **Cell wall contains chitin** – provides structural rigidity and protection. - **Reproduce by spores** – either sexually or asexually, depending on species. - **Can exist as unicellular (yeasts) or multicellular (molds)** – with dimorphic species able to switch forms depending on environment. *Note:* Deuteromycota (Fungi Imperfecti) is a classification used for fungi whose sexual stages have not been observed. **i) Morphology (4 Marks)** - *Ancylostoma duodenale* is a **hookworm** with a curved anterior end resembling a hook. - **Adult male** measures about **8–11 mm**, and the **female** is about **10–13 mm** long. - The buccal capsule contains **two pairs of ventral teeth** used for attachment to the intestinal mucosa. - The posterior end of the **male** has a **copulatory bursa**, while the **female** has a pointed tail. **ii) Pathophysiology (5 Marks)** - Infection begins when **filariform larvae** penetrate the skin, migrate via blood to lungs, then to the pharynx, are swallowed, and reach the small intestine. - In the **intestine**, they attach to the mucosa and **suck blood**, causing **mechanical damage** and **blood loss**. - Chronic blood loss leads to **iron-deficiency anemia** and **hypoproteinemia**. - **Tissue invasion** during larval migration can cause **pneumonitis** and **eosinophilia**. - The parasite also induces a **chronic inflammatory response**, impairing nutrient absorption and contributing to **growth retardation** in children. **iii) Signs and Symptoms (4 Marks)** - **Localized pruritic rash** (“ground itch”) at the site of skin penetration. - **Cough and wheezing** during pulmonary migration phase. - **Abdominal pain**, **diarrhea**, **nausea**, and **anorexia** during intestinal phase. - **Pallor, fatigue, and weakness** due to chronic iron-deficiency anemia. **iv) Diagnosis (3 Marks)** - **Microscopic examination** of stool for characteristic **oval eggs with thin shells**. - **Concentration techniques** (e.g., formalin-ether) may increase sensitivity. - **Complete blood count** may show **eosinophilia** and **microcytic hypochromic anemia**. **v) Treatment (Drug of choice) (4 Marks)** - **Albendazole 400 mg orally as a single dose** is the drug of choice. - Alternative: **Mebendazole 100 mg twice daily for 3 days**. - Iron supplementation and nutritional support are important in managing anemia. - Good hygiene and wearing shoes help prevent reinfection. **i) Etiology (2 Marks)** - Schistosomiasis is caused by blood flukes of the genus **Schistosoma**. - Key species affecting humans include:*S. haematobium* (urinary), - *S. mansoni* (intestinal), - *S. japonicum* (intestinal). **ii) Pathogenesis (5 Marks)** - **Cercariae** penetrate human skin and transform into **schistosomula**, migrating through lungs to the liver. - In the liver, they mature into adult worms and migrate to **venous plexuses** (e.g., mesenteric or pelvic veins). - **Eggs** produced by adults elicit intense **granulomatous inflammation** as they lodge in tissues. - Chronic egg deposition leads to **fibrosis**, **obstruction**, and **organ dysfunction** (e.g., hepatosplenic disease in *S. mansoni*/*japonicum*, bladder fibrosis in *S. haematobium*). - Immunologic response to eggs contributes to **morbidity**, including **portal hypertension** or **bladder calcification**. **iii) Life Cycle (4 Marks)** - Eggs are excreted in **urine (S. haematobium)** or **feces (S. mansoni, S. japonicum)**. - In freshwater, eggs hatch into **miracidia**, which infect **snail intermediate hosts**. - Inside the snail, they develop into **sporocysts** and release **cercariae** into the water. - **Cercariae** penetrate human skin, completing the cycle. **iv) Diagnosis (3 Marks)** - **Microscopic detection of eggs** in stool (*S. mansoni*, *S. japonicum*) or urine (*S. haematobium*). - **Serological tests** (e.g., ELISA) useful in low-burden or chronic infections. - **Ultrasound** or **cystoscopy** may reveal organ damage (e.g., bladder wall changes). **v) Control (3 Marks)** - **Mass drug administration** with **Praziquantel** in endemic areas. - **Improved sanitation** to prevent contamination of water sources. - **Snail control** and **safe water access** to reduce transmission. ### **Explain the roles of the following in the life cycle of a virus and give an example of a virus that exhibits it:** #### A. **Membrane Fusion** - **Definition**: A process used by **enveloped viruses** to gain entry into the host cell by fusing their lipid envelope with the host’s plasma membrane. - **Mechanism**: Viral envelope glycoproteins interact with specific host cell receptors, triggering fusion and release of the viral nucleocapsid into the cytoplasm. - **Example**: **HIV**, **Herpes Simplex Virus (HSV)** **Key Points**: - Involves enveloped viruses - Fusion between viral envelope and host cell membrane - Requires specific viral glycoproteins - Example: HIV --- #### B. **Reverse Transcriptase** - **Definition**: An enzyme that synthesizes **complementary DNA (cDNA)** from an **RNA template**. - **Function**: Enables **retroviruses** to integrate viral DNA into the host genome, allowing replication via host machinery. - **Example**: **HIV** **Key Points**: - RNA to DNA conversion - Essential in retroviral replication - Allows genome integration - Example: HIV - **Production of β-lactamases**Enzymes that hydrolyze the β-lactam ring of penicillin, inactivating the antibiotic. - **Alteration of Penicillin-Binding Proteins (PBPs)**Mutated PBPs have reduced affinity for penicillin, preventing its action. - **Efflux Pumps**Transport systems that expel penicillin from the bacterial cell, reducing intracellular concentration. - **Reduced Permeability**Altered porin channels in Gram-negative bacteria limit drug entry. **Key Points**: - β-lactamase production - Altered PBPs - Efflux pumps - Reduced permeability (optional fourth) - **Histoplasma capsulatum** - **Blastomyces dermatitidis** - **Coccidioides immitis / posadasii** - **Paracoccidioides brasiliensis** - **Cryptococcus neoformans** **Key Points**: - Dimorphic fungi (except *Cryptococcus*) - Cause deep/systemic infections - Often affect lungs and CNS - Opportunistic in immunocompromised hosts - **Parasite Entry**: Sporozoites injected by **Anopheles** mosquito travel to the liver, infect hepatocytes. - **Erythrocytic Phase**: Merozoites infect red blood cells, multiply, and cause **cyclic hemolysis**. - **Cytokine Storm**: Inflammatory response leads to fever, chills, and systemic symptoms. - **Microvascular Sequestration**: *Plasmodium falciparum* causes infected RBCs to adhere to endothelium, leading to **ischemia**. - **Organ Damage**:**Cerebral malaria**: Seizures, coma due to blockage in cerebral capillaries - **Renal failure**: From hemoglobinuria (blackwater fever) - **Severe anemia**: Due to RBC destruction **Key Points**: - Hepatic and erythrocytic stages - Cytoadherence and sequestration - Inflammatory cytokines - Multiorgan involvement (brain, kidneys, blood) - **Ingestion of Eggs**: Humans (accidental intermediate host) ingest eggs from dog feces. - **Larval Migration**: Oncospheres penetrate the intestinal wall and migrate to **liver, lungs, or other organs**. - **Hydatid Cyst Formation**: Larvae develop into fluid-filled **hydatid cysts** surrounded by a host-derived fibrous capsule. - **Mass Effect**: Cysts enlarge, causing pressure effects on nearby organs. - **Complications**:Cyst rupture may cause **anaphylactic shock** - Secondary cyst formation due to spillage **Key Points**: - Human as accidental host - Hydatid cysts in liver/lungs - Mass effect and rupture complications - **Group VI (ssRNA-RT viruses)**:Single-stranded RNA viruses that replicate through a DNA intermediate using **reverse transcriptase**. - **Example**: Retroviridae (e.g., **HIV**) - **Group VII (dsDNA-RT viruses)**:Double-stranded DNA viruses with a partial DNA genome that replicates via an **RNA intermediate** using **reverse transcriptase**. - **Example**: Hepadnaviridae (e.g., **Hepatitis B virus**) **Key Points**: - Group VI: ssRNA → RT → DNA - Group VII: dsDNA → RNA → RT → DNA - Use of reverse transcriptase - Examples: HIV, HBV - **Group VI (Retroviruses):**Viral RNA enters the host cell. - **Reverse transcriptase** synthesizes cDNA from RNA. - cDNA integrates into host genome. - Host machinery transcribes and translates viral genes. - New virions are assembled and bud from the cell. - **Group VII (Hepadnaviruses):**Partial dsDNA genome enters nucleus and completes to full dsDNA. - Transcribed into **pregenomic RNA (pgRNA)**. - **Reverse transcription** converts pgRNA into DNA in cytoplasm. - DNA is packaged into new virions. **Key Points**: - Group VI: RNA → DNA → integration - Group VII: DNA → RNA → reverse transcribed back to DNA - Use of reverse transcriptase - Intracellular replication strategies differ **Differences between yeast and mold (8 marks)** **Key Points**: - Unicellular vs. multicellular - Budding vs. spore formation - Different colony morphology **Roles of fungi in the environment (3 marks)** - **Decomposition**: Break down organic matter. - **Food production**: Fermentation (e.g., bread, beer). - **Antibiotic production**: Penicillin from *Penicillium* spp. - **Symbiosis**: Mycorrhizae with plant roots. **Treatment of mycoses (3 marks)** - **Superficial infections**: Topical antifungals (e.g., clotrimazole) - **Systemic infections**: Oral/IV antifungals (e.g., fluconazole, amphotericin B) - **Prophylaxis**: In immunocompromised patients (e.g., posaconazole) **Asexual reproduction in fungi (6 marks)** - **Mechanisms**:**Budding**: Common in yeasts. - **Binary fission**: Some unicellular fungi. - **Spore formation**: Via mitosis (conidiospores, sporangiospores) - **Importance**: Rapid propagation, survival under stress. **Key Points**: - Budding and spore formation - Mitosis-based - Found in both yeast and molds - **Antonie van Leeuwenhoek:** First to observe microorganisms (“animalcules”) using a simple microscope. - **Louis Pasteur:** Disproved spontaneous generation; proposed germ theory; developed vaccines (rabies, anthrax). - **Robert Koch:** Developed Koch’s postulates; linked microbes to specific diseases. - **Edward Jenner:** Introduced smallpox vaccine using cowpox. - **Joseph Lister:** Introduced antiseptic surgical techniques using carbolic acid. - **Yeasts:** Unicellular; reproduce by budding (e.g., *Candida*). - **Moulds:** Multicellular; filamentous hyphae form a mycelium (e.g., *Aspergillus*). - **Dimorphic fungi:** Exist as yeast (37°C) and mould (25° C) forms (e.g., *Histoplasma*). - **Pseudohyphae:** Elongated yeast cells (e.g., *Candida albicans*). - **Spores:** Asexual or sexual structures for reproduction and dispersal. - **Mediates viral attachment** to host cells. - **Determines host and tissue specificity** (tropism). - **Facilitates viral entry** via fusion or endocytosis. - **Influences severity** of infection (more receptors = higher risk). - **Target for antiviral drugs** (e.g., Maraviroc blocks HIV co-receptor CCR5). - **Early proteins:**Synthesized soon after viral entry and uncoating. - Involved in **viral genome replication** and **host manipulation**. - Include **non-structural proteins** (e.g., polymerases, regulatory proteins). - Suppress host immune responses. - Prepare host machinery for viral replication. - **Late proteins:**Synthesized **after genome replication**. - Mainly **structural proteins** (e.g., capsid, envelope proteins). - Involved in **assembly and packaging** of new virions. - Essential for **virus maturation and release**. **Definition:** - Chemical agents used to **destroy or inhibit microorganisms** on non-living surfaces. - Important in **infection control**, **hospital hygiene**, and **public health**. **Classification Based on Level:** - **High-level disinfectants:**Kill all microbes including spores. - E.g., Glutaraldehyde, Peracetic acid. - **Intermediate-level disinfectants:**Kill bacteria, most viruses, and fungi, but not spores. - E.g., Alcohols (70%), Iodophors. - **Low-level disinfectants:**Kill vegetative bacteria and some viruses. - E.g., Quaternary ammonium compounds. **Common Types and Actions:** - **Alcohols (Ethanol, Isopropanol):**Denature proteins and dissolve lipids. - Used on skin, thermometers. - **Chlorine compounds (e.g., Sodium hypochlorite):**Oxidize cellular components. - Used for surfaces, blood spills. - **Aldehydes (e.g., Glutaraldehyde):**Crosslink proteins and DNA. - Used in high-level disinfection of surgical instruments. - **Phenolics:**Disrupt cell walls and membranes. - Used in environmental cleaning. - **Hydrogen peroxide:**Produces free radicals that damage cell components. - Effective for surfaces and instruments. - **Quaternary ammonium compounds:**Disrupt membrane permeability. - Used for non-critical surfaces. **Applications in Disease Prevention:** - **Hospital disinfection:** Operating theatres, instruments. - **Community settings:** Water treatment, surface disinfection. - **Sterilization of critical items:** Endoscopes, surgical tools. - **Prevention of nosocomial infections.** **Advantages:** - Rapid action. - Broad-spectrum activity. - Easy to apply and cost-effective. **Limitations:** - Inactivation by organic matter. - Toxicity (some agents). - Limited sporicidal activity (for many). **Overview:** - **Cell wall inhibitors** target **peptidoglycan synthesis**, weakening bacterial cell walls and causing **cell lysis**. - Effective **only on actively growing bacteria**. - Mostly **bactericidal**. --- **Major Classes of Cell Wall Inhibitors:** - **Beta-lactams:**Include **Penicillins, Cephalosporins, Carbapenems, Monobactams**. - **Mechanism:** Bind to **penicillin-binding proteins (PBPs)** → inhibit transpeptidation → prevent cross-linking of peptidoglycan. - **Examples:**Penicillin G – gram-positive infections. - Ceftriaxone – broad-spectrum cephalosporin. - Imipenem – broad spectrum, β-lactamase resistant. - **Glycopeptides:**e.g., **Vancomycin**, **Teicoplanin**. - **Mechanism:** Bind to D-Ala-D-Ala terminals → inhibit polymerization and cross-linking. - Effective against **gram-positive bacteria** (e.g., MRSA). - **Reserved for resistant infections**. - **Fosfomycin:**Inhibits early peptidoglycan precursor synthesis. - Used in **urinary tract infections**. - **Bacitracin:**Blocks transport of peptidoglycan precursors across membrane. - Topical use only. --- **Clinical Relevance:** - First-line agents in **respiratory infections, skin infections, meningitis, septicemia, UTI**, etc. - **Beta-lactam antibiotics** are commonly prescribed due to broad-spectrum activity and safety. - **Glycopeptides** used when resistance (e.g., MRSA) is suspected. --- **Resistance Mechanisms:** - **Beta-lactamase production** (e.g., by *Staph aureus*). - **Altered PBPs** (e.g., MRSA). - **Efflux pumps** and **reduced permeability** in gram-negatives. --- **Combination Therapy:** - Use of **beta-lactam + beta-lactamase inhibitors** (e.g., Amoxicillin + Clavulanic acid) to overcome resistance. **A. Interferons (IFNs)** - **Type I IFNs (IFN-α, IFN-β):**Produced by virus-infected cells. - Induce **antiviral state** in neighboring cells. - Activate **RNase L** and **PKR** → degrade viral RNA, block protein synthesis. - Enhance **NK cell** activity and **MHC I** expression. - Used therapeutically (e.g., IFN-α in hepatitis B/C). **B. AZT (Zidovudine / ZDV / Azidothymidine):** - **Nucleoside Reverse Transcriptase Inhibitor (NRTI)**. - **Mechanism:**Mimics thymidine → incorporated into viral DNA by **reverse transcriptase**. - Causes **chain termination** → halts viral DNA synthesis. - Used in **HIV treatment** and **prevention of mother-to-child transmission**. - Reduces **viral load**, slows disease progression. - Contain **live but weakened viruses** that replicate in host without causing disease. - Stimulate **strong immune response**, including:**Cell-mediated immunity** (T cells). - **Humoral immunity** (B cells → antibodies). - Mimic natural infection → formation of **memory cells**. - Provide **long-lasting protection**. - Can induce **herd immunity** by reducing virus transmission. - Example: **Measles vaccine** protects by inducing high antibody titers and T-cell response. **A. Laboratory Diagnosis (8 marks)** - **Stool Microscopy****Proglottids or Eggs Detection**: Identification of characteristic *Taenia* eggs (spherical, radially striated shell) or motile gravid proglottids in feces. - Eggs of *T. saginata* are indistinguishable from *T. solium*, so further analysis is required. - **Proglottid Examination**Count the number of uterine branches in gravid proglottids:*T. saginata*: **>12–30 lateral branches**. - *T. solium*: **<13 branches**. - **Scolex Recovery (Rare)**Post-treatment, recovery of the scolex (unarmed in *T. saginata*) may help confirm species. - **Serological Tests (Not routine)**Used occasionally to detect circulating antigens or antibodies, especially in unclear cases. **B. Treatment (7 marks)** - **First-Line Therapy****Praziquantel**: Single dose of **5–10 mg/kg orally**. - Causes spastic paralysis and detachment of the worm. - **Alternative Therapy****Niclosamide**: 2 g orally (adults); chewable tablet followed by laxative to expel worm. - **Supportive Measures**Laxatives may be used to aid in worm expulsion. - Patient education on hygiene and proper cooking of beef to prevent reinfection. - **Public Health Note**Meat inspection, proper cooking (≥57°C), and sanitation are essential to control transmission. **A. Pathogenesis of Severe Malaria (8 marks)** - **Causative Agent**Most commonly *Plasmodium falciparum*. - **Cytoadherence and Sequestration**Infected RBCs adhere to endothelium via **PfEMP1**, causing microvascular obstruction and tissue hypoxia (e.g., cerebral malaria). - **RBC Destruction and Anemia**Hemolysis of infected and non-infected RBCs leads to **severe anemia** and hemoglobinuria ("blackwater fever"). - **Immune Activation and Cytokine Storm**TNF-α, IL-1 release contributes to fever, inflammation, and endothelial damage. - **Metabolic Derangements****Hypoglycemia**, **acidosis**, **hyperlactatemia**, and **renal failure** due to parasite metabolism and host response. - **Cerebral Malaria**Neurological symptoms due to sequestration in cerebral microvasculature (confusion, seizures, coma). **B. Treatment of Severe Malaria (7 marks)** - **Antimalarial Therapy (Parenteral)****Artesunate IV** (preferred): 2.4 mg/kg at 0, 12, 24 hrs, then daily. - **Quinine dihydrochloride** IV if artesunate unavailable. - **Follow-up Oral Therapy**Complete course with **ACT** (artemisinin-based combination therapy) once oral therapy is tolerated. - **Supportive Treatment**IV fluids, correction of hypoglycemia, antipyretics, anticonvulsants (for seizures), dialysis if needed. - **Monitoring**Frequent monitoring of parasitemia, renal function, blood glucose, and neurological status. **A. Life Cycle Stages (7 marks)** - **Vector**Transmitted by **tsetse fly** (*Glossina* spp). - **Infective Stage****Metacyclic trypomastigote** injected into human host during fly bite. - **Bloodstream Stage**Parasite transforms into **bloodstream trypomastigotes**, multiplying by binary fission in blood, lymph, and cerebrospinal fluid. - **Lymphatic and CNS Invasion**Progression leads to **sleeping sickness** with neurological involvement (late stage). - **Transmission to Vector**Tsetse fly ingests trypomastigotes during blood meal. - **Procyclic Stage in Fly Midgut**Transform into **procyclic trypomastigotes**, multiply, then migrate to salivary glands. - **Epimastigote to Metacyclic Forms**Develop into **epimastigotes**, then into **infective metacyclic trypomastigotes**. **B. Treatment (8 marks)** - **Stage I (Hemolymphatic stage)****Pentamidine**: 4 mg/kg IM/IV daily for 7 days. - Effective with minimal CNS penetration. - **Stage II (CNS involvement)****NECT regimen**: