Larva Migrans, Tetanus, Leprosy, Dermatophytes PDF

# Larva Migrans ## Overview: Larva migrans refers to the condition caused by the migration of parasitic larvae in humans, who are accidental hosts. It is primarily categorized into cutaneous larva migrans and visceral larva migrans, each with distinct etiologies and manifestations. ## Etiology:...

# Larva Migrans ## Overview: Larva migrans refers to the condition caused by the migration of parasitic larvae in humans, who are accidental hosts. It is primarily categorized into cutaneous larva migrans and visceral larva migrans, each with distinct etiologies and manifestations. ## Etiology: ### Cutaneous Larva Migrans: Caused by _Ancylostoma_ species (_A. brasiliensis_, _A. caninum_, _A. ceylanicum_) Infective stage: Filariform larva (L3) Transmission: Skin penetration by larvae in contaminated soil. ### Visceral Larva Migrans: Caused by _Toxocara_ species, _Gnathostoma spinigerum_, _Anisakis_ species. ## Manifestations: ### Cutaneous Larva Migrans: Symptoms include "ground itch" and larva currens (migrating rash). ### Visceral Larva Migrans: Symptoms include hepatosplenomegaly, lymphadenopathy, lung involvement, skin lesions (urticaria and nodules), seizures, and ocular issues (chorioretinal granuloma, panuveitis). ## Laboratory Diagnosis: Diagnosis based on clinical features for both types. Serological tests and biopsy may be used for visceral larva migrans. Blood eosinophilia and increased gamma globulin levels are common findings. # Tetanus ## Overview: Tetanus is a serious bacterial infection caused by _Clostridium tetani_, characterized by muscle stiffness and spasms due to neurotoxin production. It often follows wounds contaminated with the bacteria, leading to severe complications if untreated. ## Causative Agent: Bacteria: _Clostridium tetani_ Exotoxins Produced: - Tetanolysin (hemolytic toxin) - Tetanospasmin (neurotoxin responsible for symptoms) ## Pathogenesis: _C. tetani_ produces tetanospasmin which binds to alpha motor neurons. The toxin is internalized and transported retrogradely to inhibitory interneurons in the spinal cord. This leads to loss of inhibition over motor neuron discharge, resulting in hyperreflexia, muscle spasms, and spastic paralysis. ## Laboratory Diagnosis: ### Specimen Collection: Excised tissue from necrotic wounds. ### Microscopy: Gram-positive bacilli with terminal spores (drumstick appearance). ### Culture: Grows in RCM broth (black turbidity) and blood agar (characteristic swarming growth). ### Toxigenicity Tests: - In vitro hemolysis inhibition test for tetanolysin. - Mouse inoculation test for tetanospasmin. ## Prevention: ### Vaccination: Tetanus toxoid (TT) used for active immunization. Administered as monovalent or part of combination vaccines (DPT, Td). Primary immunization schedule includes 7 doses during childhood. ### Post-Injury Prophylaxis: Td booster based on wound classification and vaccination history. ### Neonatal Tetanus Prevention: Promote hospital deliveries to reduce risk. # Leprosy ## Overview: Leprosy, caused by _Mycobacterium leprae_, is a chronic infectious disease primarily affecting the skin and peripheral nerves. It leads to loss of sensation and skin lesions, with two main forms: multibacillary and paucibacillary leprosy. ## Causative Agent: Bacteria: _Mycobacterium leprae_ ### Characteristics: Non-cultivable in artificial media. Requires specific animal models for cultivation (e.g., nine-banded armadillo, footpad of mice). ## Laboratory Diagnosis: ### Sample Collection: Preferred sites: edge of lesions, forehead, cheek, chin, buttock, ear lobe, nasal mucosa. ### Techniques: Slit skin smear, nasal scraping, biopsy from thickened nerves or nodular lesions. ### Microscopy: Acid-fast staining using Ziehl-Neelsen technique. Appearance: Red acid-fast bacilli, often in globi within foamy macrophages (Virchow's cells). ### Grading: - Bacteriological index (BI) based on total number of bacilli per oil immersion field. - Morphological index (MI) indicates treatment response. ### Antibody Detection: FLA ABS test and ELISA for IgM antibodies against PGL-1 antigen. ### Cell-Mediated Immunity Testing: Lepromin test assesses delayed hypersensitivity and CMI status. # Dermatophytes ## Overview: Dermatophytes are a group of fungi that cause superficial infections known as dermatophytosis, commonly referred to as tinea or ringworm. They infect keratinized tissues such as skin, hair, and nails, leading to various clinical manifestations. ## Species: - **Trichophyton species:** Affects skin, hair, and nails (e.g., _T. rubrum_, _T. mentagrophytes_). - **Microsporum species:** Primarily affects skin and hair (e.g., _M. canis_, _M. gypseum_). - **Epidermophyton species:** Affects skin and nails (e.g., _E. floccosum_). ## Clinical Types: - **Tinea capitis:** Scalp infection. - **Tinea corporis:** Infection on non-hairy skin. - **Tinea pedis:** Athlete's foot; involves the first web space between toes and soles. - **Tinea cruris:** Groin area infection. - **Tinea barbae:** Beard and moustache area infection. - **Tinea faciei:** Non-bearded areas of the face. - **Tinea unguium:** Nail bed infection. - **Tinea manuum:** Palm infection. ## Laboratory Diagnosis: ### Specimen Collection: Skin scrapings, hair plucks, nail clippings. ### Woods Lamp Examination: Certain dermatophytes fluoresce under UV light (e.g., _Microsporum_ species). ### Direct Examination: 10% KOH mount reveals thin septate hyaline hyphae with arthroconidia. ### Culture Techniques: Sabouraud Dextrose Agar (SDA) followed by LPCB mount for spore identification (macroconidia and microconidia). ### Other Tests: Hair perforation test, urease test, PCR for species-specific genes. # Gas Gangrene ## Overview: Gas gangrene is a severe, rapidly progressing necrotizing infection of muscle tissue caused primarily by _Clostridium_ species. It typically occurs in traumatic wounds and is characterized by the production of gas within tissues, leading to significant pain and tissue destruction. ## Causative Agents: ### Established Agents: - _Clostridium perfringens_ - _Clostridium septicum_ - _Clostridium novyi_ ### Probable Agents: - _Clostridium histolyticum_ - _Clostridium sporogenes_ - _Clostridium fallax_ - _Clostridium bifermentans_ - _Clostridium sordellii_ - _Clostridium aerofoetidum_ - _Clostridium tertium_ ## Pathogenesis: Trauma introduces bacteria into anaerobic environments. _C. perfringens_ produces alpha and theta toxins, causing: - Phospholipase C and sphingomyelinase activity. - Formation of aggregates that occlude blood vessels. Severe pain and rapid tissue destruction. Late-stage complications include cardiovascular collapse and organ failure. ## Laboratory Diagnosis: ### Specimens: Necrotic tissues, muscle fragments, exudates from deeper wounds. ### Direct Microscopy: Identification of thick, stubby, boxcar-shaped gram-positive bacilli (indicative of _C. perfringens_). ### Culture Techniques: - Robertson cooked meat broth (RCM) - Egg yolk agar ### Identification Tests: - Double zone hemolysis on blood agar. - Nagler's reaction (opalescence around streak line on egg yolk agar). - Reverse CAMP test positive. - Heat tolerance at 45°C for 4-6 hours on RCM broth. - Stormy clot reaction in litmus milk. # Mycetoma ## Overview: Mycetoma is a chronic granulomatous infection of the skin and subcutaneous tissue, characterized by swelling, discharging sinuses, and the presence of grains in discharge. It can be caused by various fungi or bacteria, leading to eumycetoma or actinomycetoma forms. ## Causative Agents: ### Eumycetoma: - _Madurella mycetomatis_ - _Madurella grisea_ - _Curvularia_ species - _Acremonium_ species - _Fusarium_ species ### Actinomycetoma: - _Nocardia_ species - _Streptomyces somaliensis_ - _Actinomadura madurae_ ### Botryomycosis (bacterial): - _Staphylococcus aureus_ - _Escherichia coli_ ## Clinical Features: Triad of symptoms: - Subcutaneous swelling - Discharging sinuses - Presence of granules in discharge Granule color helps identify causative agents: - **Black granules:** _Madurella_ species - **White granules:** _Pseudallescheria boydii_, _Acremonium_ sp. - **Pink to red granules:** _Actinomadura pelletieri_ ## Laboratory Diagnosis: ### Specimen Collection: Clean lesion and collect grains from discharging sinuses. ### Direct Examination: Macroscopic examination of granules for color, size, shape, and texture. ### KOH mount for eumycetoma reveals hyphae; ### Gram stain for actinomycetoma shows filamentous Gram-positive bacilli. ### Histopathological Examination: - **Eumycetoma:** Granulomatous reaction with palisade arrangement of hyphae. - **Actinomycetoma:** Granulomatous reaction with filamentous bacteria. ### Culture: - **Eumycetoma:** Sabouraud Dextrose Agar (SDA). - **Actinomycetoma:** Lowenstein Jensen media (LJ media).