Microbiology

- AIDS defining condition (CD4 <50mm3)- Acquired by ingestion or inhalation. Clinical features:- Night sweats, fever, weight loss- Lymphadenopathy- Abdominal pains, diarrhea- Anemia, leukocytosis - Acid-fast bacilli staining and culture Prophylaxis with azithromycin

Nematode - Larvae in soil penetrate skin; swallowing and autoinfection; rarely, some larvae may penetrate the intestinal wall to enter bloodstream. Incubation period: 1-4 weeks Clinical features: - Cutaneous phase: Swelling, erythema, maculopapular rash, serpiginous lesions (larva currens is pathognomonic), pruritus- Pulmonary phase: Dry coughing and wheezing- Intestinal phase: Abdominal pain, diarrhea, anorexia, nausea and vomiting Diagnosis- Eosinophilia- Mobile rhabditiform larvae seen in feces under microscope Treatment: Ivermectin or bendazoles

Nematode- Most common helminth infection worldwide Transission: Fecal-oralOral ingestion of eggs → eggs hatch to release larvae → larvae invade intestinal walls → migration to lungs via portal vein → migration into alveoli, trachea (“tracheal migration”), larynx → larvae are swallowed back into the intestine → larvae returning to the intestine mature into adult worms, which then lay new eggs. Clinical features:- Early: Dry cough, blood-tinged sputum, wheezing- Late: Abdominal discomfort, anorexia- Obstruction at ileocecal valve, biliary obstruction, intestinal perforation Diagnosis:- Eosinophilia- Knobby-coated oval eggs seen in feces under microscope. Treatment: Bendazoles

Nematode- Most common helminthic infection in the US (vs Ascaris lumbricoides worldwide) - Primarily children aged 5-10 Transmission: Fecal-oral Clinical features:- Anal pruritus - Vulvovaginitis Diagnosis: Seeing egg via the tape test Treatment: Pyrantel pamoate or bendazoles

Nematode Transmission: percutaneous penetration of larvae - Common in warm, moist climates, i.e. the tropicsPenetration of larvae into skin (usually the feet) → larvae migrate to lungs via blood and lymphatic vessels → migration via the bronchi and trachea to the larynx → larvae are swallowed back into the intestine → larvae mature into adult worms that colonize the intestinal tract Clinical features:- Cutaneous larva migrans – pruritis, serpiginous rash from walking barefoot on contaminated beach.- Cause microcytic anemia by sucking blood from the intestinal wall. Treatment: Bendazoles or pyrantel pamoate

Nematode Transmission: Fecal-oral; consumption of undercooked meat (especially pork)Larve enter bloodstream, encyst in striated muscle → muscle inflammation.  Clinical features:- Intestinal phase: Abdominal pain, diarrhea, nausea and vomiting- Muscle phase: → Myositis – myalgia, muscle swelling, weakness→ Periorbital edema Diagnosis: Eosinophilia, ↑ creatinine kinase, serological detection of antibodies Treatment: Bendazoles

Nematode (roundworm) Transmission: Fecal-oral- Ingestion of Toxocara eggs from infected dog or cat feces, e.g., in contaminated playground sand or garden soil. Clinical features:- Visceral larva migrans – Affects heart (myocarditis), liver, and CNS (seizures, coma)- Ocular larva migrans – Unilateral vision loss and resulting strabismus Diagnosis: Eosinophilia, ELISA Treatment: Bendazoles

Nematode (roundworm) Transmission: Female blackfly Clinical features:- Skin nodules, loss of elastic fibers, and river blindness. (black flies, black skin, black sight)- Allergic reaction to microfilaria possible.  Treatment: Ivermectin (ivermectin for river blindness)

Nematode (roundworm) Transmission: Deer fly, horse fly, mango fly Clinical features:- Swelling in skin- Worm in conjunctivaTreatment: Diethylcarbamazine

Cestode (tapeworm) Transmission:- Intestinal taeniasis: Ingestion of larvae encysted in undercooked pork→ Intermediate host: cattle/pigs; definitive host: humans- Cysticercosis: Ingestion of eggs in food contaminated with human feces. Clinical features:- Intestinal taeniasis: Often asymptomatic, abdominal pain, anorexia, nausea, and vomiting- Cysticercosis: Palpable subcutaneous cysts, myalgia, neurocysticercosis – increased intracranial pressure, neurological deficits, seizures Diagnosis:- MRI/CT showing multiple, small (<1 cm) cystic ring-enhancing lesions in the brain with a membranous wall+ often an invaginated scolex during earlier stages+ calcified cyst remnants in later stages Treatment: - Intestinal taeniasis: Praziquantel- Neurocysticercosis: Albendazole 

Cestode (tapeworm) Transmission: Ingestion of larvae in raw or undercooked freshwater fish Clinical featues:- Vitamin B12 deficiency (tapeworm competes for B12 in the intestine) → megaloblastic anemia Diagnosis:- Eosinophilia, megaloblastic anemia- Stool examination for eggs or proglottids Treatment: Praziquantel

Trematode (fluke) Transmission: - Snails are intermediate host- Cercariae penetrate skin of humans in contact with contaminated fresh water (eg, swimming or bathing) Clinical features:- Early: Local reaction (swimmer's itch): pruritic maculopapular rash at point of entry of cecaria- Liver and spleen enlargement (S mansoni, egg with lateral spine), fibrosis, inflammation, portal hypertension.- Chronic infection with S haematobium (egg with terminal spine) can lead to squamous cell carcinoma of the bladder and pulmonary hypertension.Treatment: Praziquantel

Spore-forming, exotoxin-producing, gram ⊕ bacterium- Normal commensal of the GI tract - Breakdowns in the GI mucosa can lead to invasion with subsequent hematogenous dissemination to healthy muscle tissue, resulting in spontanous gas gangrene (nontraumatic vs Clostridium perfringens).- Rapid-onset muscle pain- Fever- Hemorrhagic bullae with dusky surrounding skin- Tissue edema/crepitus - Most cases of spontaneous gas gangrene are triggered by an underlying colonic malignancy - IBD and immunosuppression are risk factors

Curved, gram-negative bacterium that grows in marine environments.- Free-living in salt water- High concentrations in warm months Transmission: Ingestion (raw oysters) or wound infection- ↑ Risk in those with liver disease & iron overload Clinical features:- Rapidly progressive (often <12 hours)- Septicemia – Septic shock, bullous lesions- Cellulitis – Hemorrhagic bullae, necrotizing fasciitis