IM26.1-35 | Infectious Diseases — Glossary

Hypersensitivity reaction to Aspergillus antigens in asthmatic or CF patients; elevated total IgE (>1,000 IU/mL), eosinophilia, central bronchiectasis; not true invasive infection; treated with prednisolone (anti-inflammatory) + itraconazole (reduces fungal antigen load); complications: progressive bronchiectasis and pulmonary fibrosis.

Indolent chronic infection caused by Actinomyces israelii (endogenous oral flora); triggered by mucosal disruption; three forms: cervicofacial (most common), thoracic, and abdominal; characterised by draining sinuses producing sulphur granules; Gram-positive non-acid-fast branching filaments; treated with prolonged penicillin (6–12 months).

A surface molecule on bacteria (e.g., pili/fimbriae, surface proteins) that binds to specific host-cell receptors to facilitate adherence and colonisation; a prerequisite for most bacterial infections.

A CSF finding characterised by elevated protein with normal or near-normal WBC count; the hallmark of Guillain-Barré syndrome; distinguishes GBS from botulism (normal CSF) and bacterial meningitis (both protein and WBC elevated).

Hepatic abscess caused by Entamoeba histolytica; typically single, right lobe, in a young male; characteristic 'anchovy sauce' (chocolate brown) aspirate; positive amoebic ELISA; treated with oral metronidazole 800 mg TID × 10 days; drainage rarely needed.

Extraintestinal complication of E. histolytica infection; usually single right-lobe cavity containing brown 'anchovy sauce' pus (liquefied hepatocytes, not true pus); diagnosed by USS + anti-amoebic serology; only 10–15% have concurrent diarrhoea; treated with metronidazole 10 days + luminal agent; aspiration reserved for large/left lobe/non-responding cases.

Immunological mechanism in secondary dengue infection: cross-reactive non-neutralising antibodies from primary DENV infection facilitate viral entry into Fc receptor-bearing monocytes/macrophages during secondary heterotypic infection → higher viraemia + more intense cytokine storm → explains why secondary infections are more likely to cause DHF/DSS.

Influenza virus evolution mechanisms: drift = gradual point mutations in haemagglutinin (HA) and neuraminidase (NA) — basis of annual epidemics and need for yearly vaccine reformulation; shift = abrupt reassortment of HA/NA RNA segments between human and animal influenza viruses — basis of pandemics (e.g., H1N1 2009); shift produces a novel subtype to which the human population has no pre-existing immunity.

A coordinated programme of interventions to improve appropriate antibiotic use, reduce misuse, and preserve antibiotic effectiveness by optimising drug selection, dose, route, and duration; a critical strategy to combat antimicrobial resistance.

The WHO- and NVBDCP-mandated first-line treatment for P. falciparum malaria in India; combines a short-acting artemisinin derivative (artesunate, artemether) with a partner drug (sulphadoxine-pyrimethamine, lumefantrine) to achieve rapid parasite kill and prevent resistance development; examples: artesunate + SP (3-day course), artemether-lumefantrine (3-day course).

Bacterial infection of the biliary tract due to obstruction (typically gallstones or stricture); Charcot's triad: right upper quadrant pain + fever + jaundice; caused by Gram-negative enteric bacilli and anaerobes; treatment: IV antibiotics covering bile-duct flora (piperacillin-tazobactam) + biliary decompression (ERCP or surgery).

Fungal ball (mass of Aspergillus hyphae + mucus + inflammatory debris) colonising a pre-existing pulmonary cavity (most commonly post-TB in India); CT shows cavity with freely moving soft tissue mass + air crescent above (bell sign); major complication = massive haemoptysis (managed with bronchial artery embolisation); treatment: surgical resection if feasible, voriconazole/itraconazole for non-resectable cases.

Pulmonary and disseminated disease caused by Aspergillus species (predominantly A. fumigatus); three main clinical forms depending on immune context: ABPA (allergic, asthmatic host), CPA/aspergilloma (cavity disease, mild immune compromise), invasive pulmonary aspergillosis (neutropenic/severely immunocompromised host).

Antifungal drug class; mechanism: inhibit ergosterol synthesis (lanosterol 14-α-demethylase); fungistatic; fluconazole for Candida (not C. krusei, reduced activity against C. glabrata); voriconazole for Aspergillus and broad Candida coverage; posaconazole for Aspergillus prophylaxis and Mucor; significant CYP3A4 drug interactions (especially with immunosuppressants).

Bacterial infection of the meninges and subarachnoid space; presents with fever, headache, and neck stiffness (classic triad); characterised by turbid CSF with neutrophilic pleocytosis, very low glucose ratio (<0.4), and very high protein; treated with IV ceftriaxone + dexamethasone.

Pan-fungal cell wall biomarker detected in serum; positive in Candida and Aspergillus infections; NOT positive in mucormycosis (Mucorales lack beta-glucan in their cell walls — an important diagnostic clue); used as a screening test for invasive fungal infection in high-risk patients; false positives with some antibiotics and dialysis membranes.

A community of bacteria encased in a self-produced polysaccharide matrix; 100–1000-fold more resistant to antibiotics than planktonic bacteria; responsible for chronic infections on prosthetic devices, catheters, and heart valves.

A four-drug H. pylori eradication regimen: PPI BD + bismuth subsalicylate QID + metronidazole TID + tetracycline QID × 14 days; eradication rate >90% regardless of clarithromycin resistance; preferred first-line regimen in India where clarithromycin resistance exceeds 15%.

Exotoxin of Clostridium botulinum; a metalloprotease that cleaves SNARE proteins (SNAP-25/syntaxin) at the presynaptic cholinergic NMJ terminal; prevents acetylcholine release → descending flaccid paralysis (cranial nerves first), autonomic dysfunction; no fever, no sensory loss, consciousness preserved.

Systemic infection by Brucella species (B. melitensis, B. abortus, B. suis) acquired from livestock; presents with undulating fever, night sweats, and musculoskeletal symptoms; spondylodiscitis and sacroiliitis are classic focal complications; diagnosis: blood culture + SAT/ELISA; treatment: doxycycline + gentamicin (never monotherapy — relapse universally occurs).

A sign of meningeal irritation: involuntary flexion of the hips and knees when the examiner passively flexes the patient's neck; reflects reflex hip flexion to reduce meningeal traction on the spinal cord.

An acutely tender, swollen lymph node cluster occurring at the site draining the plague flea bite; most commonly inguinal; characteristic of bubonic plague (Yersinia pestis infection); can suppurate; diagnosis by Gram stain and culture of bubo aspirate.

An aerobic, oxidase-positive Gram-negative non-fermenter found in tropical soil and water; intracellular pathogen causing melioidosis; intrinsically resistant to ampicillin, gentamicin, first-generation cephalosporins, and colistin; sensitive to ceftazidime, meropenem, and TMP-SMX.

Cytotoxin-associated gene A protein of H. pylori; injected into gastric epithelial cells via a type IV secretion system; disrupts cell signalling, promotes oncogenic transformation; the key virulence factor driving gastric carcinoma risk.

Ocular complication of candidaemia; Candida disseminates to retina via bloodstream, forming white cotton-ball retinal infiltrates visible on fundoscopy; occurs in 5–10% of candidaemia patients; dilated fundal examination is mandatory in all patients with candidaemia; treated with systemic antifungal (fluconazole or echinocandin) and sometimes intravitreal antifungal injection.

Infection caused by Candida species (predominantly C. albicans); spectrum from mucocutaneous (thrush, VVC, oesophageal) to invasive (candidaemia, disseminated); risk factors: neutropenia, CVC, broad-spectrum antibiotics, HIV, ICU post-abdominal surgery; treatment: azoles (mucocutaneous), echinocandins (invasive).

Secretory diarrhoeal disease caused by Vibrio cholerae O1 or O139; profuse rice-water stools (up to 20 L/day) without blood or pus; cholera toxin activates adenylate cyclase causing massive secretion; treatment: ORS ± IV Ringer's lactate for severe dehydration; doxycycline 300 mg single dose.

Bilateral non-purulent injection of the conjunctival vessels without discharge; a characteristic early sign of leptospirosis; reflects the generalised vasculitis caused by Leptospira interrogans.

The systematic identification, assessment, and management of people who have been exposed to an infectious disease case; aims to break transmission chains by identifying secondary cases early, offering post-exposure prophylaxis or vaccination, and placing contacts under surveillance during their incubation period; the exposure window is defined by the case's period of communicability.

The sequence of pre-malignant gastric changes driven by H. pylori: normal mucosa → H. pylori chronic active gastritis → atrophic gastritis → intestinal metaplasia → dysplasia → gastric adenocarcinoma; H. pylori eradication at any stage before dysplasia halts progression.

Prothrombotic state in SARS-CoV-2 infection; characterised by elevated D-dimer, elevated fibrinogen, mild thrombocytopenia, and in-situ pulmonary and systemic microthrombi; mechanism: endothelial injury + ACE2 downregulation + cytokine-driven coagulation cascade activation; managed with therapeutic-dose anticoagulation in hospitalised patients.

A polysaccharide antigen of Cryptococcus neoformans detectable in CSF and serum; latex agglutination or lateral flow assay; sensitivity >98% for cryptococcal meningitis; point-of-care test available in resource-limited settings.

Fungal meningitis caused by Cryptococcus neoformans; occurs in HIV-infected patients with CD4 <100 cells/µL; subacute presentation with headache; diagnosed by India ink preparation and CSF CrAg; treated with amphotericin B + flucytosine (induction) then fluconazole.

The ratio of CSF glucose to simultaneous blood glucose; normal ≥0.6; <0.4 strongly suggests bacterial or fungal meningitis; viral meningitis characteristically does not lower the CSF glucose significantly.

A severity score for community-acquired pneumonia: Confusion, Urea >7 mmol/L, Respiratory rate ≥30/min, Blood pressure <90/60 mmHg, age ≥65 years; score 0–1 = outpatient; 2 = consider admission; ≥3 = ICU review.

The practice of switching from broad-spectrum empirical antibiotic therapy to a narrower, targeted regimen once microbiological culture results and susceptibilities are available; a core antimicrobial stewardship strategy that reduces resistance selection.

Mosquito-borne flavivirus infection by DENV-1–4 (Aedes aegypti); three stages: febrile (days 1–3), critical/plasma leakage (days 3–6 — when fever breaks), recovery; thrombocytopenia + rising haematocrit = hallmarks; no antiviral; avoid NSAIDs; fluid management is the critical skill.

Severe dengue with plasma leakage (haemoconcentration ≥20% rise in haematocrit) + thrombocytopenia (<100,000/µL) + haemorrhage; pathogenesis: antibody-dependent enhancement (ADE) in secondary DENV infection → cytokine storm → vascular permeability; requires hospitalisation and IV fluid management.

The most severe dengue presentation — plasma leakage leading to circulatory failure; narrow pulse pressure (<20 mmHg), cold clammy extremities, tachycardia, restlessness; managed with rapid IV crystalloid resuscitation (10 mL/kg over 15–20 minutes); monitor haematocrit and urine output.

IV corticosteroid given before or with the first antibiotic dose in suspected bacterial meningitis (0.15 mg/kg 6-hourly × 4 days); suppresses cytokine-mediated cerebral oedema and sensorineural hearing loss; benefit demonstrated in Streptococcus pneumoniae meningitis (de Gans trial, NEJM 2002).

A luminal amoebicidal drug used after metronidazole treatment of amoebic liver abscess to eradicate intestinal cysts and prevent recurrence and person-to-person transmission; 500 mg three times daily × 10 days; acts exclusively in the gut lumen.

Inflammatory diarrhoea characterised by small-volume, bloody, mucoid stools with tenesmus and fever; results from invasion/destruction of colonic epithelium; caused by Shigella, invasive E. coli, Campylobacter, or Entamoeba histolytica; anti-motility agents are contraindicated.

Antifungal drug class (caspofungin, micafungin, anidulafungin); mechanism: inhibit (1,3)-beta-D-glucan synthase → disrupt fungal cell wall; fungicidal against Candida; IV only; first-line for invasive candidiasis; excellent safety profile; NOT effective against Mucor or Cryptococcus; active against Candida biofilm (key advantage over fluconazole for CVC-related candidaemia).

A necrotic skin lesion (black eschar with surrounding erythema) caused by Pseudomonas aeruginosa vascular invasion in neutropenic or immunocompromised patients; pathognomonic of Pseudomonas bacteraemia; represents a dermatological emergency requiring immediate IV anti-pseudomonal therapy.

Severe necrotising renal infection with gas formation in the renal parenchyma or perinephric space; almost exclusively in diabetics; caused by Klebsiella or E. coli fermenting glucose; CT diagnosis; high mortality without prompt IV carbapenem and drainage or nephrectomy.

Lipopolysaccharide, a structural component of Gram-negative bacterial outer cell membranes; released on bacterial death; activates TLR-4 on macrophages, triggering the cytokine storm that underlies septic shock.

Systemic infection caused by Salmonella typhi (typhoid) or paratyphi A/B/C; stepladder fever, relative bradycardia, rose spots, splenomegaly, leucopenia; blood culture gold standard in first week; treated with IV ceftriaxone or oral azithromycin in India (fluoroquinolones unreliable due to widespread resistance).

A histogram plotting the number of cases of an outbreak against the date of symptom onset; the shape of the epi curve provides clues about the transmission pattern: a sharp peaked curve suggests a point-source (common source) outbreak (e.g., food poisoning); a propagating curve with multiple peaks suggests person-to-person transmission; a flat extended plateau suggests continued common source exposure.

Rickettsia prowazekii infection transmitted by the human body louse; associated with war, displacement, and crowded unsanitary conditions; severe febrile illness with macular rash (trunk → extremities, sparing face/palms/soles); Brill-Zinsser disease = recrudescent epidemic typhus years after primary infection; treated with doxycycline.

An enzyme produced by Gram-negative bacteria (most commonly E. coli and Klebsiella pneumoniae) that hydrolyses most penicillins and cephalosporins; organisms producing ESBLs are resistant to these drug classes and require carbapenem therapy for serious infections.

A painless, black, necrotic skin lesion at the site of an arthropod bite; pathognomonic of scrub typhus (Orientia tsutsugamushi bite) and anthrax (cutaneous form); commonly found in the groin, axillae, hairline, and belt-line in scrub typhus.

A painless necrotic skin lesion with a black crust and surrounding erythema at the site of an arthropod bite; in India, the most clinically important eschar is that of scrub typhus (Orientia tsutsugamushi, chigger bite); found in concealed skin folds (groin, axilla, hairline, belt line, popliteal fossa); present in 30–70% of scrub typhus cases.

A secreted bacterial protein that causes disease by enzymatic action or receptor binding at sites that may be remote from the infection focus; examples include cholera toxin, tetanospasmin, and botulinum toxin.

An intraoperative diagnostic technique: a 2 cm incision is made through skin and subcutaneous tissue; if a finger is inserted and the fascial planes dissect easily without resistance or bleeding, necrotising fasciitis is confirmed; the lack of resistance reflects liquefactive necrosis of the fascia.

Cell wall polysaccharide of Aspergillus; released into blood/BAL during active Aspergillus infection; detected by ELISA; serum sensitivity 70–80% in neutropenic IPA patients, lower in non-neutropenic; false positives with piperacillin-tazobactam, some antibiotics; used as a non-culture biomarker for early IPA diagnosis.

Rapidly progressive muscle infection caused by Clostridium perfringens; crepitus (subcutaneous gas), bronzed skin, haemolytic anaemia, extreme systemic toxicity; surgical emergency — immediate debridement/amputation + IV benzylpenicillin + IV clindamycin.

Cartridge-based real-time PCR test for simultaneous detection of Mycobacterium tuberculosis DNA and rifampicin resistance in approximately 2 hours from sputum; the recommended first-line TB diagnostic test in India under NTEP.

CT chest finding of a pulmonary nodule surrounded by a halo of ground-glass opacity; represents haemorrhagic infarction around an Aspergillus-invaded nodule in angio-invasive IPA; highly characteristic but not entirely specific for Aspergillus (also seen in other angio-invasive moulds and sometimes granulomatosis with polyangiitis); in a neutropenic patient, this CT pattern = probable IPA.

A spiral, microaerophilic, urease-producing Gram-negative bacillus; colonises the gastric mucosa; causes peptic ulcer disease, gastric adenocarcinoma, and MALT lymphoma; infects ~50% of the world's population; eradicated with bismuth quadruple or concomitant quadruple therapy.

The most common sporadic viral encephalitis; caused by HSV-1; characteristic temporal lobe and limbic system involvement; diagnosis by CSF HSV PCR and MRI FLAIR temporal hyperintensity; treated with IV aciclovir 10 mg/kg 8-hourly × 14–21 days — must be started empirically before results return.

DNA virus causing primary mucocutaneous infections and establishing latency in sensory ganglia; HSV-1 causes oral/facial/corneal/CNS disease; HSV-2 causes genital herpes; reactivation triggered by fever, stress, UV, immunosuppression; treated with acyclovir/valacyclovir.

VZV reactivation from dorsal root ganglia; unilateral dermatomal vesicular rash; thoracic most common; HZO = ophthalmic branch; Ramsay Hunt = geniculate ganglion; postherpetic neuralgia (pain >90 days) in ~15%; treat with valacyclovir 1g TDS × 7 days within 72h; gabapentin/amitriptyline for PHN.

Short-course ART given after potential HIV exposure to prevent infection; must be started within 72 hours (ideally <2 hours) and continued for 28 days; standard Indian regimen: tenofovir + lamivudine + lopinavir/ritonavir (or dolutegravir); reduces transmission risk by >80%; indicated for needle-stick injury from HIV-positive source, unprotected high-risk sexual exposure, and sexual assault; do not delay awaiting source patient's test result.

The most common sporadic viral encephalitis; caused by HSV-1; preferentially affects temporal and frontal lobes (limbic encephalitis); presents with fever, behavioural change, temporal lobe seizures, aphasia; MRI T2/FLAIR hyperintensity in temporal lobes; diagnosed by CSF PCR; treated with IV acyclovir 10 mg/kg 8-hourly × 14–21 days.

Purified human anti-tetanus antibody; 3000–6000 units IM; neutralises unbound tetanospasmin in the bloodstream; effective only against circulating (unbound) toxin — cannot displace toxin already bound to neural tissue; must be given as early as possible.

Pathognomonic symptom of furious rabies — violent, painful pharyngeal and laryngeal spasms triggered by attempting to swallow water; caused by virus-induced hyperexcitability of the swallowing reflex circuits in the brainstem; together with aerophobia (spasms triggered by air on face) and bite history, is virtually diagnostic of clinical rabies.

Dormant liver-stage forms of P. vivax (and P. ovale) that persist in hepatocytes after primary infection and can reactivate weeks to months later, causing relapse of clinical malaria; the only drug active against hypnozoites is primaquine (requires G6PD testing first); distinguishes vivax malaria (true relapse from hypnozoites) from falciparum malaria (recrudescence from residual blood-stage parasites, no hypnozoites).

India's national disease surveillance system under NCDC; monitors 33 infectious diseases and syndromes across all states; weekly reporting of S (syndromic), P (probable), and L (laboratory-confirmed) cases; triggers rapid response for outbreak-prone diseases; all healthcare providers are mandated to report notifiable diseases to the district surveillance unit.

Candida bloodstream infection (candidaemia) ± multi-organ dissemination; 30-day mortality 30–50% in ICU patients; CVC removal is mandatory; first-line treatment is IV echinocandin (caspofungin, micafungin, anidulafungin); fundal examination required (Candida endophthalmitis in 5–10%).

Acute angio-invasive Aspergillus infection in severely immunocompromised host (neutropenia, transplant, high-dose corticosteroids); CT: halo sign (nodule + ground-glass halo) or air crescent sign; diagnosed by serum/BAL galactomannan + HRCT; first-line treatment: voriconazole; mortality 50–90% despite treatment.

Flavivirus encephalitis transmitted by Culex mosquitoes in agricultural India; presents with parkinsonian features and seizures; MRI shows bilateral thalamic T2 hyperintensity; no specific antiviral — management is supportive; preventable by vaccination.

A sign of meningeal irritation: resistance and pain on attempting to extend the knee with the hip flexed to 90°; positive when the patient cannot fully extend the knee due to meningeal tension on the lumbosacral roots.

Systemic spirochaetal infection caused by Leptospira interrogans; transmitted via skin/mucosal contact with water contaminated by rodent/animal urine; biphasic illness; Weil's disease (jaundice + AKI + haemorrhage) is the severe form; diagnosed by LEPTO IgM ELISA; treated with doxycycline (mild) or IV penicillin/ceftriaxone (severe).

Lipid formulation of amphotericin B; mechanism: binds ergosterol in fungal cell membrane → pores → fungicidal; broadest antifungal spectrum (Candida, Aspergillus, Mucor, Cryptococcus); drug of choice for mucormycosis; L-AmB (3–5 mg/kg/day) has significantly less nephrotoxicity than conventional amphotericin B deoxycholate; first-line for mucormycosis in India.

Bacterial meningitis caused by Listeria monocytogenes; affects adults >50 years, immunocompromised patients, pregnant women, and neonates; critically — Listeria is intrinsically resistant to ALL cephalosporins; empirical ampicillin must be added to ceftriaxone in at-risk patients.

Diffuse alveolar haemorrhage complicating severe leptospirosis; characterised by rapid respiratory failure, haemoptysis, and diffuse pulmonary infiltrates; can occur in anicteric severe disease (without jaundice); mortality up to 50%; requires mechanical ventilation; not prevented by antibiotics alone.

Mosquito-borne nematode infection (Wuchereria bancrofti, transmitted by Culex quinquefasciatus in India); adult worms obstruct lymphatics → lymphoedema → elephantiasis (chronic massive limb swelling); microfilariae show nocturnal periodicity (blood must be sampled 10 PM–2 AM); treated with diethylcarbamazine (DEC) 6 mg/kg × 12 days.

Invasive Pseudomonas infection of the external auditory canal extending to the temporal bone and skull base; occurs almost exclusively in elderly diabetics; presents with severe ear pain, purulent discharge, granulation tissue, and cranial nerve VII (facial) palsy; treated with IV anti-pseudomonal therapy × 6 weeks + surgical debridement.

Mucosa-Associated Lymphoid Tissue lymphoma; a low-grade B-cell lymphoma driven by chronic H. pylori antigen stimulation; H. pylori eradication alone achieves complete remission in 60–80% of Stage I (confined to stomach) cases — one of the few cancers where antibiotics are first-line treatment.

Infection caused by Burkholderia pseudomallei; endemic in tropical Southeast Asia and parts of India; the 'great mimicker' — can present as pneumonia, multiple organ abscesses, or septicaemia; diabetics are at highest risk; intrinsically resistant to gentamicin; treated with IV ceftazidime or meropenem (intensive phase) followed by oral TMP-SMX + doxycycline (eradication phase).

The mechanisms by which a microorganism causes disease in a host, including adherence, invasion, toxin production, immune evasion, and host inflammatory response.

Staphylococcus aureus with an altered penicillin-binding protein (PBP2a, encoded by mecA gene) conferring resistance to all beta-lactam antibiotics; treatment of choice is vancomycin or linezolid.

A carbapenemase enzyme first identified in India; confers resistance to virtually all beta-lactam antibiotics including carbapenems; present in E. coli, Klebsiella, and other Enterobacteriaceae; organisms with NDM-1 require polymyxin-based combination therapy.

A life-threatening bacterial infection of the deep fascial planes with spreading necrosis; Type I is polymicrobial (aerobic + anaerobic); Type II is mononicrobial (Group A Streptococcus); hallmark signs: pain disproportionate to skin appearance, woody induration, haemorrhagic bullae, systemic toxicity; treatment: immediate surgical debridement + IV broad-spectrum antibiotics.

Infection of the brain and spinal cord by Taenia solium larvae (cysticerci); acquired by ingesting T. solium eggs (NOT from eating pork); the most common cause of acquired epilepsy in India; CT brain shows cystic lesion with scolex (pathognomonic) or ring-enhancing lesion (degenerating cyst); treated with albendazole 15 mg/kg × 28 days + dexamethasone; anti-epileptics required.

India's web-based TB notification and monitoring system under the National Tuberculosis Elimination Programme (NTEP); all diagnosed TB cases (new, retreatment, DR-TB) must be notified at diagnosis; tracks treatment outcomes; triggers drug supply, transfer-in/out, and missed-dose follow-up; all private and public sector providers are legally required to notify.

Infection caused by Nocardia asteroides (soil organism, aerobic filamentous bacteria); predominantly pulmonary infection in immunocompromised patients (transplant, HIV, corticosteroids); weakly acid-fast on modified ZN stain; 25% of disseminated cases have brain abscess; treated with TMP-SMX for 6–12 months.

The phenomenon whereby Wuchereria bancrofti microfilariae concentrate in peripheral blood during the night (10 PM–2 AM), coinciding with the biting behaviour of the Culex mosquito vector; microfilaraemia is very low or absent in daytime blood samples; blood films for filariasis diagnosis must be collected at night.

Dengue non-structural protein 1; secreted into the bloodstream by dengue-infected cells; detectable from day 1–5 of illness (febrile phase); used for early dengue diagnosis; sensitivity 90% on day 1, declining after day 5 as viraemia falls; combined with dengue IgM ELISA (positive from day 5+) gives diagnostic coverage throughout the illness.

Extreme arching of the back and neck due to sustained spasm of the paraspinal extensor muscles in severe tetanus; may be severe enough to cause vertebral fractures; reflects disinhibition of spinal extensor motor neurons.

A resistance mechanism in Pseudomonas aeruginosa: loss of the OprD outer membrane channel that carbapenems (especially imipenem) use to enter the bacterial cell; confers imipenem resistance while meropenem (which uses an additional route) may retain activity; explains the common clinical finding of imipenem-resistant but meropenem-sensitive Pseudomonas.

Neuraminidase inhibitor antiviral for influenza A and B; inhibits neuraminidase enzyme on the viral surface → prevents release of new virions from infected cells → reduces viral spread; dose 75 mg twice daily × 5 days; most effective when started within 48 hours of symptom onset; reduces duration of illness by ~1 day and reduces complication rates in high-risk patients.

Skin manifestation of Leishmania donovani appearing 6 months to 3 years after kala-azar treatment; hypopigmented macules or nodules on the face, trunk; reservoir for continued transmission of kala-azar; treated with miltefosine × 12 weeks; important public health significance in the elimination programme.

Persistent neuropathic pain >90 days after herpes zoster eruption; occurs in 10–15% of all zoster patients, rising to ~50% in patients >70 years; one of the most treatment-resistant chronic pain conditions; prevented by early antiviral treatment and by the recombinant zoster vaccine (Shingrix); managed with gabapentin, pregabalin, TCAs, topical agents.

8-aminoquinoline drug used for two distinct indications in malaria: (1) single dose (0.75 mg/kg) to kill P. falciparum gametocytes (reduces transmission); (2) 14-day course (0.25 mg/kg/day) to eliminate P. vivax liver hypnozoites (radical cure, prevents relapse). G6PD testing is mandatory before use — causes haemolytic anaemia in G6PD-deficient patients. Contraindicated in pregnancy.

A biomarker produced by multiple tissues in response to bacterial infection; levels rise markedly in bacterial sepsis (>2 ng/mL in severe sepsis) but remain low in viral infections and non-infectious inflammation; used to guide antibiotic initiation and cessation.

An aerobic, non-fermenting Gram-negative bacillus; ubiquitous environmental organism; causes opportunistic infections (VAP, bacteraemia, burn wound, malignant otitis externa) in immunocompromised and critically ill patients; characterised by blue-green pyocyanin pigment, fruity odour, and robust biofilm formation; intrinsically resistant to many antibiotic classes.

Bacterial liver abscess, typically due to Gram-negative enteric bacilli (Klebsiella, E. coli) from biliary or portal sources; multiple abscesses common; treated with IV piperacillin-tazobactam or meropenem plus percutaneous drainage.

Primary bacterial abscess of skeletal muscle, predominantly caused by Staphylococcus aureus; relatively common in tropical climates (tropical pyomyositis); diagnosis by MRI; treatment: surgical drainage + IV cloxacillin for 4–6 weeks.

Quick Sequential Organ Failure Assessment score; three criteria — respiratory rate ≥22/min, altered mental status, systolic BP ≤100 mmHg; score ≥2 in a patient with suspected infection identifies high risk for sepsis; prompts ICU evaluation.

Passive immunotherapy given for Category III animal exposures; human RIG (HRIG) 20 IU/kg or equine RIG (ERIG) 40 IU/kg; infiltrated at and around the wound site on day 0 only (never on subsequent vaccine days); provides immediate passive protection before vaccine-induced immunity develops; skin test required before ERIG.

Prevention of rabies after animal bite; three WHO categories: I (intact skin lick/touch — no PEP), II (minor scratch/abrasion — wound wash + vaccine), III (transdermal bite/mucous membrane exposure — wound wash + vaccine + RIG); wound washing is the single most important step.

An endoscopy-based H. pylori test; antral biopsy placed in urea-containing pH indicator medium; urease activity produces ammonia → colour change within 30–60 minutes; widely used in India when endoscopy is performed.

A heart rate that is lower than expected for the degree of fever; classically associated with enteric fever (typhoid), intracellular pathogens (rickettsial disease), and viral infections; reflects direct autonomic modulation by intracellular organisms.

The characteristic appearance of cholera stools — copious, colourless or pale grey, watery fluid with flecks of mucus; caused by massive secretion of isotonic fluid from small intestinal epithelium stimulated by cholera toxin; not bloody (no mucosal invasion).

A pathognomonic sign of tetanus — a grotesque fixed grin caused by sustained spasm of facial muscles (platysma and muscles of the mouth); reflects disinhibition of facial motor neurons by tetanospasmin.

Point-of-care immunochromatographic strip test for visceral leishmaniasis using recombinant Leishmania antigen rK39; sensitivity 96–98% for Indian kala-azar; results in 10 minutes; first-line diagnostic tool in India under the national elimination programme; does not require laboratory equipment.

Faint salmon-pink 2–4 mm maculopapular spots on the trunk; transient; appear in the first week of enteric fever in 20–30% of patients; caused by embolisation of Salmonella typhi in dermal vessels; may be visible only in fair-skinned individuals.

The head/attachment organ of a tapeworm; in neurocysticercosis, the scolex of the living cyst is visible on CT/MRI as a bright dot within the cystic cavity — the 'dot-within-cyst' sign is pathognomonic for viable NCC; its presence distinguishes NCC from other ring-enhancing brain lesions (TB tuberculoma, pyogenic abscess, primary CNS tumour).

Rickettsial disease caused by Orientia tsutsugamushi; transmitted by larval mite (chigger) bite; endemic in South and Southeast Asia; presents with fever, headache, eschar, and macular rash; rapidly fatal if untreated; treated with doxycycline 100 mg BD × 7 days — fever resolves in 24–48 hours.

A subset of sepsis in which circulatory, cellular, and metabolic abnormalities cause substantially increased mortality; defined as vasopressor requirement to maintain MAP ≥65 mmHg AND serum lactate >2 mmol/L despite adequate fluid resuscitation.

Life-threatening P. falciparum malaria defined by WHO criteria; any one of: cerebral malaria (coma), severe anaemia (Hb <7), ARDS, hypoglycaemia, AKI, DIC, hyperparasitaemia (>5%), circulatory collapse, haemoglobinuria; treated with IV artesunate (first-line) + ICU supportive care; corticosteroids are contraindicated.

Communication framework for breaking difficult news (originally for cancer diagnosis, applicable to infectious disease counselling): Setting (private, comfortable), Perception (assess what patient knows), Invitation (ask how much information the patient wants), Knowledge (deliver news clearly), Empathy (acknowledge and respond to emotion), Summary/Strategy (plan next steps and support); helps structure sensitive counselling encounters.

Infection of the intervertebral disc and adjacent vertebral bodies; the most common focal complication of brucellosis (lumbar spine, especially L4-L5); presents with severe back pain and elevated ESR/CRP; MRI is the most sensitive imaging modality; treated with triple antibiotic therapy for 3–6 months.

Infection prevention measures applied to ALL patients regardless of diagnosis; include hand hygiene (WHO 5 moments), gloves and gown for blood/body fluid contact, mask and eye protection for splash risk, safe disposal of sharps, respiratory hygiene; the baseline level of care that prevents transmission of both known and unrecognised pathogens.

Yellow macroscopic aggregates of Actinomyces filaments visible in the discharge from actinomycotic sinuses; composed of bacterial filaments surrounded by calcium phosphate deposits; pathognomonic of actinomycosis; yellowish colour, 0.1–3 mm diameter.

Treatment given to people at high risk of developing active TB, to prevent progression from latent TB infection (LTBI) to active disease; indicated for: household contacts of smear-positive TB who are children <5 years, HIV-positive, or have recently converted TST; regimens: isoniazid 6H (daily × 6 months) or 3HP (weekly rifapentine + isoniazid × 12 weeks); dramatically reduces TB risk in HIV-positive contacts (by ~60%).

Health communication technique to verify patient understanding; after providing information, ask the patient to explain what they understood in their own words ('Can you tell me in your own words what you will do at home to prevent spreading this?'); identifies misunderstandings and clarifies them before the patient leaves; significantly improves adherence and infection control at home.

The exotoxin of Clostridium tetani; a zinc-metalloprotease that cleaves synaptobrevin (VAMP) at inhibitory glycinergic and GABAergic interneuron presynaptic terminals in the spinal cord; prevents inhibitory neurotransmitter release → continuous uninhibited motor firing → ascending spastic paralysis and reflex spasms.

A malaria diagnosis technique in which a large volume of blood is concentrated and lysed on a slide, then stained with Giemsa; provides greater sensitivity than thin smear for detecting low-density parasitaemia; essential for diagnosing malaria in febrile travellers and endemic settings.

Additional precautions added to standard precautions for patients with known or suspected infections spread by specific routes: contact precautions (gloves + gown — MRSA, VRE, C. difficile, scabies), droplet precautions (surgical mask within 1 metre — influenza, meningococcal), airborne precautions (N95 respirator + negative-pressure room — TB, measles, varicella/VZV).

Inability to open the mouth due to masseter muscle spasm; the earliest and most characteristic sign of tetanus; caused by tetanospasmin-induced loss of inhibitory control over motor neurons innervating the masticatory muscles.

Hyperimmune response to Wuchereria bancrofti microfilariae sequestered in pulmonary capillaries; presents with nocturnal cough, paroxysmal wheeze, bilateral infiltrates on CXR, marked eosinophilia (>3,000/µL), elevated IgE; microfilariae absent from peripheral blood; treated with diethylcarbamazine 6 mg/kg × 21 days; responds dramatically to DEC.

Asymptomatic chronic excretion of Salmonella typhi in the stool (or urine) for more than 12 months after acute infection; gallbladder is the reservoir (especially with gallstones); occurs in 1–4% of patients; treated with prolonged fluoroquinolone ± cholecystectomy.

Evidence-based HIV prevention concept: a person living with HIV who is on effective ART with an undetectable viral load (<200 copies/mL) cannot sexually transmit HIV to an HIV-negative partner; important for patient counselling, partner notification, and combating HIV stigma; does not eliminate the need for ART adherence monitoring or other prevention strategies.

A fever pattern characterised by temperature rising in waves over several days, followed by a return to baseline, then recurring — the fever 'undulates' over weeks; classically associated with brucellosis; reflects episodic bacteraemia as Brucella organisms escape from macrophages into the bloodstream.

The gold standard non-invasive test for H. pylori; patient ingests ¹³C-labelled urea; H. pylori urease hydrolyses it to labelled CO₂ detected in exhaled breath; requires PPI washout ≥2 weeks; preferred test for confirming eradication (at ≥4 weeks post-treatment).

Vacuolating cytotoxin A of H. pylori; forms pores in gastric epithelial cell membranes causing cytoplasmic vacuolation, mitochondrial damage, and apoptosis; a key mucosal injury factor.

Primary VZV infection; highly contagious via respiratory droplets; polymorphic rash (multiple stages simultaneously — macules, papules, vesicles, crusts); trunk → face → extremities; adults and immunocompromised have more severe disease; avoid aspirin (Reye's syndrome); treat with acyclovir in adults/immunocompromised.

Hospital-acquired pneumonia developing ≥48 hours after endotracheal intubation; Pseudomonas aeruginosa is the most common causative organism; diagnosed by quantitative tracheal aspirate or BAL culture; treated with anti-pseudomonal beta-lactam ± aminoglycoside.

A subunit typhoid vaccine containing Vi capsular polysaccharide of Salmonella typhi; provides ~70% protection for 2–3 years; recommended for travellers and endemic populations; conjugated typhoid vaccine (TCV) now preferred in children under 2 years for longer-lasting immunity.

Systemic infection by L. donovani; transmitted by sandfly P. argentipes in India; concentrated in Bihar, Jharkhand, West Bengal; obligate intracellular macrophage parasite; clinical features: prolonged fever + massive splenomegaly + anaemia + wasting + pancytopenia + hypergammaglobulinaemia; fatal if untreated; diagnosed by rK39 RDT; first-line in India: liposomal amphotericin B single dose 10 mg/kg.

A historical serological test using Proteus OX-2, OX-19, and OX-K antigens as surrogate antigens for rickettsial antibodies; OX-K positive in scrub typhus, OX-19 positive in epidemic/endemic typhus; insensitive (40–60%), non-specific, no longer recommended — replaced by specific IgM ELISA by IFA.

The severe form of leptospirosis; characterised by the triad of jaundice, acute kidney injury, and haemorrhagic manifestations; mortality 5–15% even with treatment; requires ICU management including potential dialysis; pulmonary haemorrhage syndrome (LPHH) is the most feared complication.

Framework for when hand hygiene must be performed in healthcare: (1) before touching a patient; (2) before a clean/aseptic procedure; (3) after body fluid exposure risk; (4) after touching a patient; (5) after touching patient surroundings. Alcohol-based hand rub (ABHR) used for moments 1, 2, 4, 5; soap and water preferred for C. difficile spores and norovirus (spores not killed by alcohol).

A serological test measuring agglutinating antibodies against Salmonella typhi O and H antigens; unreliable as a single-point test in endemic India due to high background seropositivity; a four-fold rise in paired titres (2 weeks apart) has diagnostic value but is rarely practical; blood culture is preferred in the first week.