Microbiology
High-yield MBBS Microbiology question bank — bacteriology, immunology, virology, mycology and parasitology, with laboratory diagnosis, at Ananthanarayan & Paniker / Jawetz depth.
12chapters144questions82High-Yield
Definition
Cestodes (tapeworms) are segmented, ribbon-like intestinal helminths; the two important human species are Taenia solium and T. saginata.
Structure & Life Cycle
- Scolex (head, attaches), neck, and proglottids (segments)
- Hermaphroditic; no alimentary canal — absorb nutrients
- Man = definitive host (adult worm in intestine)
- Pig (T. solium) or cattle (T. saginata) = intermediate host
- Infection by eating undercooked measly meat containing cysticerci
Comparison & Features
- T. solium — armed scolex (hooks + suckers), <13 uterine branches; can cause cysticercosis
- T. saginata — unarmed scolex, >13 branches, longer worm; no cysticercosis
- Usually mild: abdominal discomfort, passage of segments
- Diagnosis: eggs or proglottids in stool (eggs of both are identical)
Man harbours the adult worm after eating infected pork or beef. Feature T. solium T. saginata Source Pork Beef Scolex Armed (hooks) Unarmed Cysticercosis Yes No Applied
- Treatment: praziquantel or niclosamide
- Thorough cooking of meat prevents infection
🔑KEY POINTS TO REMEMBER- Tapeworms have a scolex and proglottids; man is the definitive host.
- T. solium (pork, armed scolex) can cause cysticercosis; T. saginata cannot.
- Acquired from undercooked meat; treated with praziquantel.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Hydatid disease is infection with the larval stage of Echinococcus granulosus, in which man is an accidental intermediate host.
Life Cycle
- Dog = definitive host (adult worm, smallest tapeworm)
- Sheep, cattle = normal intermediate hosts
- Man — accidental intermediate host (dead-end); ingests eggs from dog faeces
- Embryo penetrates gut → portal circulation → liver (commonest), then lung
Cyst & Clinical Features
- Hydatid cyst: outer pericyst, laminated ectocyst, germinal endocyst
- Contains hydatid fluid, brood capsules and hydatid sand (protoscolices)
- Slow-growing; often asymptomatic for years
- Rupture → anaphylaxis and secondary seeding
- Diagnosis: ultrasound/CT, serology (ELISA); Casoni test (historical)
Man is a dead-end host in whom the larva forms a slowly growing cyst. Host Stage Dog Adult worm Sheep Larval cyst Man Accidental cyst Applied
- Treatment: albendazole + surgery or PAIR procedure
- Avoid diagnostic aspiration — risk of anaphylaxis and spread
🔑KEY POINTS TO REMEMBER- Dog is the definitive host; man is an accidental intermediate host.
- Hydatid cyst forms mainly in the liver, containing hydatid sand.
- Rupture causes anaphylaxis; treat with albendazole plus surgery/PAIR.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Ascariasis and hookworm infection are soil-transmitted nematode infections, among the commonest helminthiases worldwide.
Ascariasis (Ascaris lumbricoides)
- Largest intestinal nematode; faeco-oral (ingested eggs)
- Larvae migrate: gut → liver → lung → swallowed back (Löffler’s syndrome — cough, eosinophilia)
- Adult in small intestine
- Complications: intestinal obstruction, biliary/pancreatic obstruction
- Diagnosis: bile-stained mamillated eggs in stool
Hookworm (Ancylostoma duodenale, Necator americanus)
- Infection by filariform larvae penetrating skin (bare feet)
- Ground itch → lung migration → small intestine
- Adults suck blood → chronic iron-deficiency anaemia
- Diagnosis: oval eggs with segmented ovum in stool
Different entry routes, but both migrate through the lungs. Feature Ascaris Hookworm Entry Ingestion Skin penetration Main harm Obstruction Anaemia Applied
- Treatment: albendazole (single dose) for both
- Mass deworming and sanitation; footwear prevents hookworm
🔑KEY POINTS TO REMEMBER- Ascaris is ingested and causes obstruction; larvae migrate via lungs.
- Hookworm larvae penetrate skin and cause iron-deficiency anaemia.
- Both treated with albendazole; prevented by sanitation and footwear.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Lymphatic filariasis is a mosquito-borne nematode infection caused by Wuchereria bancrofti and Brugia malayi, damaging lymphatics.
Parasite & Transmission
- W. bancrofti (>90% of cases in India), B. malayi
- Vector: Culex quinquefasciatus mosquito
- Adults live in lymphatics and lymph nodes
- Microfilariae show nocturnal periodicity — appear in peripheral blood at night (10 pm–4 am)
Clinical Features
- Asymptomatic microfilaraemia (commonest)
- Acute — recurrent fever, lymphangitis, lymphadenitis, funiculitis
- Chronic — lymphoedema → elephantiasis, hydrocele, chyluria
- Tropical pulmonary eosinophilia — nocturnal cough, very high eosinophilia
Repeated lymphatic damage and fibrosis produce irreversible elephantiasis. Test Detail Night blood smear Microfilariae Antigen card test Any time of day Ultrasound Filarial dance sign Applied
- Treatment: DEC (± albendazole); mass drug administration
- Limb hygiene and elevation for established lymphoedema
🔑KEY POINTS TO REMEMBER- W. bancrofti spread by Culex; adults live in lymphatics.
- Microfilariae show nocturnal periodicity — collect blood at night.
- Causes elephantiasis and hydrocele; treated with DEC + albendazole.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Schistosomiasis (bilharziasis) is a trematode infection caused by Schistosoma species, acquired from freshwater containing cercariae.
Species & Life Cycle
- S. haematobium — urinary bladder venous plexus
- S. mansoni and S. japonicum — intestinal/mesenteric veins
- Snail = intermediate host
- Cercariae penetrate skin during contact with fresh water (‘swimmer’s itch’)
- Unlike other flukes, sexes are separate
Clinical Features
- Acute: Katayama fever (fever, urticaria, eosinophilia)
- Urinary — terminal haematuria, bladder fibrosis, squamous cell carcinoma of bladder
- Intestinal — bloody diarrhoea, hepatic fibrosis, portal hypertension
- Damage is caused by granulomatous reaction to eggs, not the worm
Egg-induced granulomas, not the adult worms, cause the chronic damage. Species Site Egg spine S. haematobium Bladder Terminal S. mansoni Colon Lateral S. japonicum Small bowel Rudimentary Applied
- Diagnosis: eggs in urine (haematobium, midday sample) or stool
- Treatment: praziquantel
🔑KEY POINTS TO REMEMBER- Schistosomes have separate sexes; snail is the intermediate host.
- Cercariae penetrate skin; egg granulomas cause fibrosis.
- S. haematobium → haematuria and bladder cancer; treat with praziquantel.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Cysticercosis is infection with the larval stage (cysticercus cellulosae) of Taenia solium, in which man acts as the intermediate host.
Transmission
- Ingestion of T. solium eggs (not larvae) from contaminated food, water or hands
- Autoinfection in a person harbouring the adult worm (faeco-oral or reverse peristalsis)
- Larvae migrate to brain, muscle, subcutaneous tissue, eye
- Pork eating is not required — vegetarians can get it
Neurocysticercosis
- Commonest cause of acquired epilepsy in endemic regions
- Seizures, headache, raised intracranial pressure, focal deficits
- CT/MRI: cysts with scolex; calcified lesions
- Treatment: albendazole + steroids + antiepileptics
- Ophthalmic cysts — assess eye before starting therapy
Eggs, not meat, cause cysticercosis — man becomes the intermediate host. Infection Stage ingested Result Taeniasis Cysticercus in pork Adult worm Cysticercosis Eggs Larval cysts Applied
- Steroids prevent inflammatory worsening when cysts die
- Hand hygiene and safe water prevent infection
🔑KEY POINTS TO REMEMBER- Cysticercosis follows ingestion of T. solium eggs, not pork.
- Neurocysticercosis is a leading cause of acquired epilepsy.
- Treated with albendazole plus steroids and antiepileptics.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Enterobiasis is infection with Enterobius vermicularis (pinworm/threadworm), the commonest helminth infection in children.
Features & Life Cycle
- Small white thread-like worm living in the caecum
- Gravid female migrates to the perianal skin at night to lay eggs
- Eggs become infective within hours → easy autoinfection and family spread
- Nocturnal perianal itching (pruritus ani) is the hallmark
- Irritability, disturbed sleep; vulvovaginitis in girls
Diagnosis & Treatment
- NIH cellophane/adhesive tape swab in the early morning before washing
- Eggs are plano-convex (D-shaped)
- Eggs are rarely found in stool
- Treatment: albendazole/mebendazole, repeated after 2 weeks
- Treat all family members; wash bed linen, cut nails
Night-time egg laying causes itching, which spreads eggs on the fingers. Feature Detail Hallmark Nocturnal perianal itch Test Adhesive tape swab Egg D-shaped Applied
- Repeat dose after 2 weeks because of autoinfection
- Whole-household treatment prevents recurrence
🔑KEY POINTS TO REMEMBER- Enterobius causes nocturnal perianal itching in children.
- Diagnosed by adhesive tape swab showing D-shaped eggs.
- Treat the whole family and repeat the dose after 2 weeks.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Trichuriasis is infection with Trichuris trichiura, the whipworm, a soil-transmitted nematode of the large intestine.
Parasite & Transmission
- Whip-shaped worm — thin anterior threaded into mucosa, thick posterior free
- Faeco-oral transmission of embryonated eggs from soil
- No lung migration (unlike Ascaris and hookworm)
- Lives in caecum and colon
Clinical Features & Treatment
- Light infection usually asymptomatic
- Heavy infection: chronic bloody mucoid diarrhoea, abdominal pain, anaemia
- Rectal prolapse in heavily infected children — classic sign
- Growth retardation, finger clubbing
- Diagnosis: barrel-shaped eggs with bipolar mucus plugs in stool
- Treatment: albendazole/mebendazole (3 days for heavy infection)
Worms burrow into the colonic mucosa, causing chronic dysentery. Feature Detail Shape Whip-like Egg Barrel with bipolar plugs Classic sign Rectal prolapse Applied
- Often coexists with Ascaris (same faeco-oral route)
- Included in mass deworming programmes
🔑KEY POINTS TO REMEMBER- Trichuris is whip-shaped and lives in the colon; no lung migration.
- Heavy infection causes dysentery and rectal prolapse in children.
- Barrel-shaped eggs with bipolar plugs; treat with albendazole.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Strongyloidiasis is infection with Strongyloides stercoralis, unique in its capacity for autoinfection and lifelong persistence.
Life Cycle
- Filariform larvae penetrate skin from soil
- Migrate through lungs → swallowed → small intestine
- Only parthenogenetic females parasitise man
- Autoinfection — rhabditiform larvae become filariform within the gut → infection persists for decades
- Diagnosis: larvae (not eggs) in stool; Baermann technique, agar plate culture
Clinical Features
- Ground itch; larva currens (rapidly migrating serpiginous rash)
- Abdominal pain, diarrhoea, malabsorption; eosinophilia
- Hyperinfection syndrome in steroid therapy or HTLV-1 → massive larval dissemination, Gram-negative sepsis, high mortality
Autoinfection keeps the infection alive for years and can explode on steroids. Feature Detail Stool finding Larvae Skin sign Larva currens Danger Hyperinfection Applied
- Treatment: ivermectin (drug of choice); albendazole alternative
- Screen before starting steroids in endemic areas
🔑KEY POINTS TO REMEMBER- Strongyloides larvae penetrate skin; autoinfection allows lifelong infection.
- Larvae (not eggs) are found in stool; larva currens is characteristic.
- Steroids risk fatal hyperinfection; treat with ivermectin.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Hymenolepis nana, the dwarf tapeworm, is the commonest tapeworm of man and the only one needing no intermediate host.
Features & Life Cycle
- Smallest human tapeworm (dwarf)
- Direct life cycle — egg ingested → adult in the same host
- Internal autoinfection possible → heavy worm burdens
- Faeco-oral spread; common in children, crowded institutions
- Rodents and grain insects may act as reservoirs
Clinical Features & Treatment
- Light infection asymptomatic
- Heavy infection: abdominal pain, diarrhoea, anorexia, weight loss, irritability
- Diagnosis: eggs in stool — oval with polar filaments between the two membranes
- Treatment: praziquantel (single dose, drug of choice)
- Retreat because of autoinfection; improve hygiene
No intermediate host is needed, so infection spreads easily among children. Feature Detail Intermediate host Not required Egg Polar filaments Treatment Praziquantel Applied
- Most common tapeworm infection in children worldwide
- Institutional outbreaks need mass treatment
🔑KEY POINTS TO REMEMBER- H. nana is the commonest and smallest human tapeworm.
- Direct life cycle with no intermediate host; autoinfection occurs.
- Eggs show polar filaments; treated with praziquantel.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Liver and lung flukes are hermaphroditic trematodes acquired by eating raw or undercooked aquatic foods; snails are the first intermediate host.
Liver Flukes
- Fasciola hepatica — sheep liver fluke; from watercress/aquatic plants; bile-duct obstruction, hepatomegaly
- Clonorchis sinensis — from raw freshwater fish; chronic infection → cholangiocarcinoma
- Opisthorchis — similar to Clonorchis
Lung Fluke
- Paragonimus westermani — from raw/undercooked crab or crayfish
- Encysts in lungs → chronic cough, rusty-brown haemoptysis
- Often misdiagnosed as pulmonary tuberculosis
- Diagnosis: operculated eggs in sputum or stool
Two intermediate hosts precede human infection through raw food. Fluke Source Site Fasciola Watercress Bile duct Clonorchis Raw fish Bile duct Paragonimus Raw crab Lung Applied
- Treatment: praziquantel (triclabendazole for Fasciola)
- Consider paragonimiasis in ‘sputum-negative TB’ with haemoptysis
🔑KEY POINTS TO REMEMBER- Flukes need snails as first intermediate host; acquired from raw foods.
- Clonorchis causes cholangiocarcinoma; Paragonimus mimics tuberculosis.
- Praziquantel treats most; Fasciola needs triclabendazole.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).Definition
Anthelminthic drugs eliminate parasitic worms by paralysing them or disrupting their metabolism and structure.
Main Drugs & Mechanisms
- Albendazole/mebendazole — inhibit microtubule (tubulin) polymerisation; broad spectrum
- Praziquantel — ↑ calcium permeability → spastic paralysis; flukes and tapeworms
- Ivermectin — opens glutamate-gated chloride channels → flaccid paralysis
- DEC — filariasis
- Pyrantel pamoate — depolarising neuromuscular blockade
Drug of Choice
- Roundworm, hookworm, whipworm, pinworm — albendazole
- Tapeworm, schistosomiasis, flukes — praziquantel
- Strongyloidiasis, scabies — ivermectin
- Filariasis — DEC; neurocysticercosis — albendazole + steroids
Paralysed or metabolically crippled worms detach and are passed out. Drug Worm group Albendazole Nematodes Praziquantel Cestodes, trematodes Ivermectin Strongyloides Applied
- Mass deworming with albendazole in school children
- Steroid cover needed when treating neurocysticercosis
🔑KEY POINTS TO REMEMBER- Albendazole/mebendazole inhibit tubulin — broad-spectrum for nematodes.
- Praziquantel is the drug of choice for tapeworms and flukes.
- Ivermectin for strongyloidiasis; DEC for filariasis.
📚SOURCES: Textbook of Microbiology (Ananthanarayan & Paniker); Jawetz, Melnick & Adelberg’s Medical Microbiology; Textbook of Medical Parasitology (Paniker).