Mycology and parasitology

Microbiology (B.Sc) · Microbes · free study notes for exams, placements and interviews

In short

Mycology is the study of fungi — eukaryotic, chitin-walled, heterotrophic organisms ranging from unicellular yeasts to filamentous moulds — and parasitology is the study of protozoa and helminths that live at a host's expense. Together they cover the non-bacterial, non-viral agents of human disease: dermatophytoses, candidiasis, aspergillosis, mucormycosis, malaria, amoebiasis, kala-azar, filariasis and soil-transmitted worms. These are high-weightage units in B.Sc Microbiology medical-microbiology papers, CSIR-UGC NET/GATE Life Sciences (XL/BT), ICMR and DBT-BET, and in entrance tests for M.Sc Medical Microbiology. In practice the knowledge is used in NABL-accredited diagnostic labs, ICMR institutes (NIMR, NIRT, RMRC), NCDC, state Vector Borne Disease Control programmes, pharma antifungal R&D and agricultural/food mycology (mycotoxin testing).

Explained

Fungi: structure, nutrition and classification

Defining features: eukaryotic, non-photosynthetic, cell wall of chitin and glucans (not peptidoglycan, not cellulose), membrane sterol is ergosterol (the target of most antifungals), storage carbohydrate glycogen, mostly aerobic, absorptive (osmotrophic) nutrition after secreting extracellular enzymes.
Morphological forms: yeast (single cells, budding, pasty colonies — *Candida*, *Cryptococcus*); mould/filamentous (branching hyphae forming a mycelium; hyphae septate or aseptate/coenocytic); dimorphic (mould at 25 °C in soil, yeast at 37 °C in tissue — *Histoplasma*, *Blastomyces*, *Sporothrix*, *Talaromyces marneffei*, *Coccidioides* which is mould/spherule).
Reproduction — asexual (anamorph): budding, fission, fragmentation, sporangiospores (in sporangia, Mucorales), conidia (free: blastoconidia, phialoconidia, arthroconidia, chlamydoconidia, macro- and microconidia in dermatophytes).
Reproduction — sexual (teleomorph): zygospore (Zygomycota), ascospore in an ascus (Ascomycota), basidiospore on a basidium (Basidiomycota); Deuteromycota / "fungi imperfecti" is an artificial form-class for fungi with no known sexual stage — most medically important moulds were placed here before molecular reclassification.
Modern phyla: Chytridiomycota (motile zoospores), Mucoromycota/Zoopagomycota (replacing Zygomycota; aseptate hyphae — *Rhizopus*, *Mucor*, *Lichtheimia*), Ascomycota (largest; *Aspergillus*, *Candida*, dermatophytes, yeasts), Basidiomycota (*Cryptococcus*, *Malassezia*, mushrooms), Glomeromycota (mycorrhizal), Microsporidia (now fungal, obligate intracellular).
Beneficial fungi: *Saccharomyces cerevisiae* (bread, ethanol), *Aspergillus niger* (citric acid), *Penicillium chrysogenum* (penicillin), *Rhizopus* (fermented foods), mycorrhizae and biocontrol agents (*Trichoderma*).

Medical mycology: mycoses by depth of invasion

Superficial: confined to outermost keratin/hair. Pityriasis versicolor (*Malassezia furfur*) — hypo/hyperpigmented macules, "spaghetti and meatballs" short hyphae with round yeasts in KOH; lipid-dependent, needs olive-oil overlay to grow. Also tinea nigra, black and white piedra.
Cutaneous (dermatophytoses, "tinea"): keratinophilic genera Trichophyton, Microsporum, Epidermophyton (Epidermophyton never infects hair; Microsporum rarely infects nails). Clinical types: tinea capitis, corporis, cruris, pedis, unguium (onychomycosis), barbae, manuum. Ecological grouping: anthropophilic, zoophilic, geophilic (zoophilic cause more inflammation). India now has a large burden of recalcitrant, terbinafine-resistant *Trichophyton indotineae* (squalene epoxidase mutations), driven by irrational steroid–antifungal–antibiotic combination creams — a current, well-documented Indian problem.
Subcutaneous: follow traumatic implantation of soil fungi. Sporotrichosis (*Sporothrix schenckii*, "rose gardener's disease", lymphocutaneous nodular chain); chromoblastomycosis (sclerotic/medlar bodies); eumycetoma (*Madurella mycetomatis* — "Madura foot", first described from Madurai; discharging sinuses with grains; actinomycetoma is the bacterial counterpart caused by *Nocardia*/*Actinomadura*); phaeohyphomycosis, rhinosporidiosis (*Rhinosporidium seeberi*, now a protist).
Systemic/endemic: dimorphic fungi inhaled as conidia. Histoplasmosis (*H. capsulatum* — bird/bat guano; Gangetic West Bengal is an Indian endemic focus; intracellular yeasts in macrophages, tuberculate macroconidia in culture); blastomycosis, coccidioidomycosis (not endemic to India), paracoccidioidomycosis, *Talaromyces marneffei* (NE India, HIV-associated).
Opportunistic: the clinically dominant group in India. Candidiasis (*C. albicans* plus *C. tropicalis*, *C. parapsilosis*, *C. glabrata*, and multidrug-resistant *Candidozyma (Candida) auris* — a major Indian ICU problem); aspergillosis (*A. fumigatus*, *A. flavus* — invasive, aspergilloma, ABPA, chronic pulmonary; *A. flavus* predominates in Indian sino-orbital disease); mucormycosis (*Rhizopus arrhizus* — rhino-orbito-cerebral in uncontrolled diabetes; India has the world's highest burden and saw a large post-COVID-19 surge in 2021, after which many states made it a notifiable disease); cryptococcosis (*C. neoformans* var. *grubii* in HIV, capsulated, urease and melanin positive); pneumocystosis (*Pneumocystis jirovecii*).
Fungal allergy and mycotoxins: ABPA, allergic fungal sinusitis; aflatoxin B1 (*A. flavus/parasiticus*, hepatocarcinogen), ochratoxin, fumonisin, ergot alkaloids. Aflatoxin limits in Indian food are set under the FSS (Contaminants, Toxins and Residues) Regulations, 2011 made under the Food Safety and Standards Act, 2006 — commonly 15 µg/kg total aflatoxin in most foods and 0.5 µg/kg aflatoxin M1 in milk; verify the current amendment as limits are revised periodically.

Laboratory diagnosis and treatment of mycoses

Specimens: skin scrapings/hair/nail clippings, sputum/BAL, pus, tissue biopsy, CSF, blood, corneal scraping. Collect from the active margin after cleaning with 70% alcohol.
Direct microscopy: 10% KOH (skin/sputum), 20–40% KOH for nails, KOH + DMSO or calcofluor white with fluorescence (most sensitive); India ink/nigrosin negative stain for *Cryptococcus* capsule; Gram stain for *Candida*; lactophenol cotton blue (LPCB) for mould morphology; Giemsa for *Histoplasma*.
Histopathology stains: PAS, Gomori methenamine silver (GMS), mucicarmine (cryptococcal capsule), H&E. Aseptate, wide, ribbon-like, right-angle-branching hyphae = Mucorales; septate, narrow, acute-angle (45°) branching = *Aspergillus*.
Culture: Sabouraud dextrose agar (SDA) at 25 °C and 37 °C; SDA with chloramphenicol/gentamicin to suppress bacteria and cycloheximide to suppress saprophytes (never for *Cryptococcus*/Mucorales, which it inhibits); Dermatophyte Test Medium (phenol red turns pink); CHROMagar Candida; birdseed/niger seed agar (brown *Cryptococcus*); BHI with blood for dimorphics; incubate up to 4 weeks.
Yeast identification: germ tube (Reynolds–Braude) test in serum — positive for *C. albicans*/*C. dubliniensis*; chlamydospores on cornmeal–Tween 80; sugar assimilation/fermentation; urease; growth at 42 °C and on CHROMagar; definitive identification by MALDI-TOF MS or ITS/D1-D2 sequencing.
Non-culture tests: galactomannan (serum/BAL, aspergillosis), (1→3)-β-D-glucan (pan-fungal, negative in Mucorales and *Cryptococcus*), cryptococcal antigen (CrAg) latex/LFA, *Histoplasma* antigen, panfungal PCR.
Susceptibility: broth microdilution to CLSI M27 (yeasts)/M38 (moulds) or EUCAST; MIC against azoles, amphotericin B, echinocandins.
Antifungal drug classes: polyenes (amphotericin B, nystatin — bind ergosterol, pore formation; AmB is nephrotoxic, lipid formulations safer); azoles (fluconazole, itraconazole, voriconazole, posaconazole, isavuconazole — inhibit lanosterol 14α-demethylase/CYP51); echinocandins (caspofungin, micafungin, anidulafungin — inhibit β-1,3-glucan synthase, fungicidal for *Candida*); allylamines (terbinafine — squalene epoxidase); flucytosine (pyrimidine analogue, with AmB for cryptococcal meningitis); griseofulvin (disrupts microtubules, for tinea capitis). Mucormycosis management = control diabetes/acidosis + surgical debridement + liposomal amphotericin B.

Parasitology: scope, classification and host relationships

Definitions: parasite lives on/in a host at its expense; ectoparasite (lice, mites) vs endoparasite; obligate vs facultative; accidental; opportunistic (*Cryptosporidium*, *Toxoplasma* in HIV).
Hosts: definitive host harbours the adult/sexual stage; intermediate host harbours larval/asexual stage; paratenic (transport) host carries larvae without development; reservoir host maintains infection in nature; vector — biological (develops in it) or mechanical.
Terms: zoonosis, anthroponosis, infective stage, diagnostic stage, prepatent period, autoinfection (*Enterobius*, *Strongyloides*, *H. nana*), carrier.
Classification — Protozoa (unicellular): Amoebae/Sarcodina (*Entamoeba histolytica*, *Acanthamoeba*, *Naegleria fowleri*); Flagellates/Mastigophora — intestinal/genital (*Giardia lamblia*, *Trichomonas vaginalis*) and haemoflagellates (*Leishmania*, *Trypanosoma*); Ciliates (*Balantidium coli*); Apicomplexa/Sporozoa (*Plasmodium*, *Toxoplasma*, *Cryptosporidium*, *Cystoisospora*, *Cyclospora*, *Babesia*).
Classification — Helminths: Platyhelminthes (flatworms) — Cestoda (tapeworms: *Taenia solium/saginata*, *Echinococcus granulosus*, *Hymenolepis nana*, *Diphyllobothrium*) and Trematoda (flukes: *Fasciolopsis buski*, *Fasciola hepatica*, *Schistosoma*, *Paragonimus*); Nemathelminthes (Nematoda, roundworms) — intestinal (*Ascaris lumbricoides*, *Trichuris trichiura*, hookworms *Ancylostoma duodenale*/*Necator americanus*, *Enterobius vermicularis*, *Strongyloides stercoralis*) and tissue/blood (*Wuchereria bancrofti*, *Brugia malayi*, *Trichinella*, *Dracunculus*).
Nematode vs cestode vs trematode: nematodes are cylindrical, unsegmented, with a complete gut and separate sexes; cestodes are segmented, ribbon-like, hermaphrodite with a scolex and no gut; trematodes are leaf-like, unsegmented, mostly hermaphrodite (except *Schistosoma*, which has separate sexes) with two suckers and a blind gut.

Major Indian parasitic diseases: life cycles and control

Malaria: *P. falciparum*, *P. vivax* (the two dominant in India), *P. malariae*, *P. ovale*, *P. knowlesi*. Vector: female *Anopheles* (*An. culicifacies* rural, *An. stephensi* urban, *An. fluviatilis*, *An. minimus*/*An. baimaii* in the NE). Man is the intermediate host; the mosquito is the definitive host (sexual cycle occurs in it). Human cycle: sporozoites → liver (pre-erythrocytic schizogony; *vivax*/*ovale* form dormant hypnozoites causing relapse) → merozoites → erythrocytic schizogony (ring → trophozoite → schizont → merozoites; periodicity 48 h tertian, 72 h quartan in *malariae*) → gametocytes. Mosquito cycle: gametocytes → ookinete → oocyst on the midgut wall → sporozoites to salivary glands (sporogony).
Malaria diagnosis and policy: thick film (screening/parasite density) and thin film (species ID) with Giemsa/JSB stain; rapid diagnostic tests (HRP-2 for *falciparum* — note HRP-2 gene deletions give false negatives — plus pan-LDH); QBC; PCR. Treatment in India follows the National Drug Policy on Malaria — ACT (artesunate + sulfadoxine–pyrimethamine; AL = artemether–lumefantrine in the North-East) for *falciparum* with single-dose primaquine as gametocytocidal, and chloroquine + 14-day primaquine for *vivax* radical cure (G6PD caution). Control under the National Center for Vector Borne Diseases Control (NCVBDC, formerly NVBDCP) with IRS, LLINs, larvivorous fish, source reduction; India's goal is malaria elimination by 2030 (National Framework for Malaria Elimination 2016–2030). Confirm current drug-policy details against the latest NCVBDC guideline before quoting.
Amoebiasis: *E. histolytica* — faecal–oral, quadrinucleate cyst is the infective stage, trophozoite is invasive (flask-shaped ulcers in caecum/sigmoid colon, amoebic liver abscess with "anchovy sauce" pus). Trophozoite has ingested RBCs; must be distinguished from non-pathogenic *E. dispar* by antigen detection/PCR. Treatment: metronidazole/tinidazole plus a luminal amoebicide (diloxanide furoate/paromomycin).
Giardiasis: *G. lamblia*, "falling-leaf" motility, pear-shaped trophozoite with 4 pairs of flagella and a ventral sucking disc; steatorrhoea and malabsorption; ELISA/string test; metronidazole/tinidazole.
Visceral leishmaniasis (kala-azar): *Leishmania donovani*, vector female *Phlebotomus argentipes* sandfly; amastigote (LD body) in human macrophages, promastigote in the vector. Fever, splenomegaly, pancytopenia, PKDL. Diagnosis: splenic/bone marrow aspirate, rK39 rapid test, culture in NNN medium. Treatment: single-dose liposomal amphotericin B, miltefosine. Endemic in Bihar, Jharkhand, West Bengal, eastern UP; targeted for elimination as a public health problem (<1 case per 10,000 population per block).
Lymphatic filariasis: *W. bancrofti* (~98% of Indian cases, vector *Culex quinquefasciatus*) and *B. malayi* (*Mansonia*); nocturnally periodic microfilariae in night blood smear (collect 20:00–24:00); ICT antigen card test. Mass Drug Administration of IDA (ivermectin + DEC + albendazole) or DA under the national programme.
Soil-transmitted helminths: *Ascaris* (ingestion of embryonated egg; Löffler's syndrome during lung migration), hookworm (filariform larva penetrates skin, iron-deficiency anaemia), *Trichuris* (rectal prolapse), *Strongyloides* (autoinfection, hyperinfection on steroids). Controlled by National Deworming Day albendazole to children.
Cestodes and cysticercosis: *T. solium* — man is definitive host for the adult worm, but ingesting eggs makes man an intermediate host giving neurocysticercosis, India's commonest cause of adult-onset seizures. Hydatid disease (*E. granulosus*: dog definitive, sheep/man intermediate; Casoni test obsolete, imaging + serology used; avoid spillage during surgery — anaphylaxis).
Other: toxoplasmosis (cat definitive host; congenital triad), cryptosporidiosis (modified Ziehl–Neelsen/Kinyoun acid-fast oocysts, chronic diarrhoea in HIV), trichomoniasis (STI, motile trophozoite on wet mount).

Parasitological laboratory methods and biosafety

Stool examination: macroscopic (consistency, blood, mucus, proglottids); saline wet mount (motile trophozoites, larvae) and iodine mount (cyst nuclei/glycogen); concentration — sedimentation (formol-ether, best overall) and flotation (zinc sulphate, saturated salt for hookworm/*Ascaris* eggs).
Quantitation: Kato-Katz thick smear (eggs per gram) and McMaster/Stoll methods for intensity of STH infection; used in national deworming surveys.
Stains: Giemsa/JSB/Leishman (blood parasites), trichrome and iron-haematoxylin (intestinal protozoa), modified acid-fast (*Cryptosporidium*, *Cystoisospora*, *Cyclospora*), modified trichrome (microsporidia), Delafield's haematoxylin (microfilariae).
Other techniques: NIH cellophane tape swab for *Enterobius* eggs; Baermann funnel and agar plate culture for *Strongyloides*; Harada–Mori filter paper culture for hookworm larvae; NNN (Novy–MacNeal–Nicolle) medium for *Leishmania*; duodenal aspirate/string test; serology (IHA, ELISA, rK39, ICT) and molecular PCR/LAMP.
Biosafety and quality: most of this work is BSL-2; cultures of dimorphic fungi (*Histoplasma*, *Coccidioides*) and mould handling need a biosafety cabinet Class II / BSL-3 practice; sharps and culture waste segregated under the Bio-Medical Waste Management Rules, 2016 (as amended) — yellow category for microbiology cultures (incineration), blue for glass, white translucent for sharps. Diagnostic labs are regulated under the Clinical Establishments (Registration and Regulation) Act, 2010 in adopting states and accredited to ISO 15189 by NABL.

Key points

Fungal cell wall — chitin + glucans + mannoproteins; membrane sterol is ergosterol, the basis of polyene and azole action.
Dimorphism — mould at 25 °C, yeast at 37 °C; seen in *Histoplasma*, *Blastomyces*, *Sporothrix*, *Talaromyces marneffei*.
Mycosis levels — superficial, cutaneous, subcutaneous, systemic (endemic) and opportunistic.
Dermatophytes — *Trichophyton*, *Microsporum*, *Epidermophyton*; keratinophilic; *Epidermophyton* spares hair.
KOH mount is the first-line direct test for skin/nail; LPCB for mould identification; India ink for *Cryptococcus*.
SDA is the basic fungal medium; cycloheximide suppresses saprophytes but also inhibits *Cryptococcus* and Mucorales.
Hyphal clue — aseptate, right-angle, ribbon-like = Mucorales; septate, acute-angle = *Aspergillus*.
Germ tube test positive identifies *C. albicans*/*C. dubliniensis*.
Antifungal targets — polyenes bind ergosterol; azoles inhibit CYP51; echinocandins inhibit β-1,3-glucan synthase; terbinafine inhibits squalene epoxidase.
India-specific — world's highest mucormycosis burden, terbinafine-resistant *Trichophyton indotineae*, multidrug-resistant *Candidozyma auris* in ICUs.
Host definitions — definitive host carries the sexual/adult stage; for malaria that host is the mosquito, not man.
Plasmodium stages — sporozoite (infective), schizogony in man, gametocyte, sporogony in mosquito; hypnozoites cause *vivax* relapse.
Thick film for detection and density, thin film for species identification; Giemsa/JSB stain.
Infective stages — *E. histolytica* quadrinucleate cyst (ingested); hookworm filariform larva (skin); *Ascaris* embryonated egg (ingested); *Leishmania* promastigote (sandfly bite).
Kala-azar — *L. donovani* via *Phlebotomus argentipes*; amastigote (LD body) in macrophages; rK39 test.
Filariasis — night blood smear 20:00–24:00 for nocturnally periodic microfilariae; MDA with IDA/DA.
Concentration methods — formol-ether sedimentation (general), zinc sulphate flotation (light eggs/cysts), Kato-Katz for egg counts.
Programmes and rules — NCVBDC (ex-NVBDCP) for malaria/filaria/kala-azar, National Deworming Day, Bio-Medical Waste Management Rules 2016, NABL/ISO 15189 accreditation.

Formulas and examples

Parasite density (per µL) = (parasites counted × 8,000) ÷ WBC counted — thick film, assuming 8,000 leucocytes/µL
Parasitaemia (%) = (parasitised RBCs ÷ total RBCs counted) × 100; with RBC = 5 × 10⁶/µL, 1% ≈ 50,000 parasites/µL
Eggs per gram (EPG) = eggs counted on Kato-Katz slide × 24 (for the standard 41.7 mg template)
Prevalence (%) = (number infected ÷ number examined) × 100; Intensity = mean parasite load per infected host
Annual Parasite Incidence API = (confirmed malaria cases in a year ÷ population under surveillance) × 1,000
Slide Positivity Rate SPR (%) = (positive slides ÷ slides examined) × 100
Generation time / doubling: N = N₀ × 2^t/g for asexual parasite multiplication (g = cycle time, 48 h for *P. falciparum*)
Fractional Inhibitory Concentration Index FICI = (MIC of A in combination ÷ MIC of A alone) + (MIC of B in combination ÷ MIC of B alone); ≤0.5 synergy, >4 antagonism

Example 1 — Parasite density from a thick film. A thick Giemsa film shows 320 *P. falciparum* asexual parasites against 200 WBCs.

Density = (320 × 8,000) ÷ 200 = 2,560,000 ÷ 200 = 12,800 parasites/µL.
As parasitaemia with RBC 5 × 10⁶/µL: 12,800 ÷ 5,000,000 × 100 = 0.256% — a moderate, uncomplicated-range load; hyperparasitaemia is conventionally >5%.

Example 2 — Multiplication over 48-hour cycles. Starting from 12,800/µL with no treatment and a 48 h erythrocytic cycle in which each schizont releases 16 merozoites (take an effective 8-fold rise per cycle after host clearance):

After one cycle: 12,800 × 8 = 102,400/µL (≈2.05%).
After two cycles: 102,400 × 8 = 819,200/µL (≈16.4%) — above the severe-malaria threshold, which is why *falciparum* must be treated immediately rather than observed.

Example 3 — Kato-Katz egg count and intensity class. A 41.7 mg Kato-Katz smear from a child shows 210 *Ascaris* eggs.

EPG = 210 × 24 = 5,040 eggs per gram.
WHO intensity classes for *Ascaris*: light 1–4,999, moderate 5,000–49,999, heavy ≥50,000 EPG → this child is moderate intensity, the target group for albendazole 400 mg on National Deworming Day.

Example 4 — API in a district. A district with a population of 1,250,000 under surveillance reports 375 confirmed malaria cases in a year; 60,000 slides were examined, of which 375 were positive.

API = (375 ÷ 1,250,000) × 1,000 = 0.30 per 1,000 — below the API 1 threshold used to classify low-transmission areas.
SPR = (375 ÷ 60,000) × 100 = 0.625%.

Example 5 — Antifungal MIC and combination index. Against a *Candida* isolate, amphotericin B alone MIC = 1 µg/mL, fluconazole alone MIC = 16 µg/mL; in combination AmB MIC falls to 0.25 and fluconazole to 2 µg/mL.

FICI = (0.25 ÷ 1) + (2 ÷ 16) = 0.25 + 0.125 = 0.375 → synergy (FICI ≤ 0.5). The fluconazole MIC of 16 µg/mL alone would be reported with reference to the current CLSI M27 breakpoints/ECVs for that species.

Feature	Fungi	Protozoa	Helminths
Cells	Uni- or multicellular eukaryote	Unicellular eukaryote	Multicellular metazoan
Multiply in host	Yes	Yes (so low dose can cause disease)	No (except Strongyloides, H. nana)
Diagnostic material	Skin/sputum/tissue, KOH, SDA culture	Stool, blood, aspirate; stains, antigen	Stool eggs/larvae, blood microfilariae
Eosinophilia	Usually absent	Usually absent	Characteristic
Chief drugs	Azoles, polyenes, echinocandins, terbinafine	Metronidazole, ACT, antimonials, miltefosine	Albendazole, mebendazole, DEC, ivermectin, praziquantel

Fungus	Key microscopy	Classic disease
Candida albicans	Budding yeast + pseudohyphae; germ tube positive	Oral thrush, candidaemia
Cryptococcus neoformans	Capsulated yeast, India ink halo; urease +	Meningitis in HIV
Aspergillus fumigatus	Septate hyphae, acute-angle branching; uniseriate vesicle	Invasive/ABPA/aspergilloma
Rhizopus arrhizus	Broad aseptate hyphae, rhizoids, sporangia	Rhino-orbito-cerebral mucormycosis
Trichophyton rubrum	Pencil-shaped macroconidia, tear-drop microconidia	Tinea corporis, onychomycosis
Histoplasma capsulatum	Tuberculate macroconidia; intracellular yeast	Histoplasmosis

Where it is used

Diagnostic microbiology labs (NABL/ISO 15189, hospital and chains such as SRL, Metropolis, Dr Lal PathLabs): KOH mounts, fungal culture, blood smears, stool concentration, antigen tests — roles of Lab Technologist, Microbiologist, Section In-charge.
Public health programmes: NCVBDC and state VBD cells, NCDC, district malaria/filaria offices — slide cross-checking, API/SPR reporting, MDA and National Deworming Day coverage surveys.
ICMR research institutes: NIMR (malaria, Delhi), RMRI Patna (kala-azar), NIRT, NIE Chennai, VCRC Puducherry (vector control and filariasis) — JRF/Project Scientist roles in entomology, drug resistance monitoring and molecular diagnostics.
Pharma and biotech: antifungal and antiparasitic screening, formulation of liposomal amphotericin B and miltefosine (Cipla, Sun, Bharat Serums), diagnostic kit manufacture (rK39, HRP-2 RDTs) and sterility/mycology QC in sterile manufacturing under Schedule M GMP.
Food, feed and agriculture: mycotoxin (aflatoxin) testing by HPLC/ELISA for FSSAI compliance and export certification, spoilage mould identification, *Trichoderma*/mycorrhizal biofertiliser production, plant-pathogen diagnostics.
Veterinary and One Health: zoonotic hydatid and cysticercosis surveillance in abattoirs, dermatophytosis in livestock and pets, dog-mediated transmission control.

Interview questions

Q: Why is ergosterol the main antifungal target? A: It is the principal sterol of the fungal membrane but absent in human cells, which use cholesterol — so polyenes that bind it and azoles that block its synthesis are relatively selective, though overlap with human CYP enzymes still causes toxicity.
Q: How do you distinguish *Aspergillus* from Mucorales on histology? A: *Aspergillus* shows narrow, septate hyphae branching at acute (about 45°) angles; Mucorales show broad, ribbon-like, aseptate (or sparsely septate) hyphae branching at right angles.
Q: Which host is the definitive host in malaria and why? A: The female *Anopheles* mosquito, because the sexual cycle (gametogony, fertilisation, sporogony) completes in it; man harbours only asexual schizogony and is the intermediate host.
Q: Why must *P. vivax* be treated with primaquine for 14 days? A: Only primaquine (or tafenoquine) kills the dormant liver hypnozoites that cause relapse; chloroquine clears only the blood stages. G6PD status matters because primaquine causes haemolysis in deficiency.
Q: What does a thick film give you that a thin film does not? A: Greater sensitivity — more blood per field, so low parasitaemia is detected and density can be counted against WBCs; the thin film preserves RBC and parasite morphology for species identification.
Q: Why is a 40% KOH used for nails but 10% for skin? A: Nail keratin is far thicker and denser, so a stronger alkali (and longer digestion, sometimes with DMSO) is needed to clear it enough to see hyphae.
Q: Why did mucormycosis surge in India during COVID-19? A: The combination of uncontrolled or steroid-induced hyperglycaemia, ketoacidosis, high-dose corticosteroids and immune dysregulation on a background of very high diabetes prevalence and heavy environmental spore load — iron availability in acidosis also favours *Rhizopus*.
Q: How would you tell *Entamoeba histolytica* from *E. dispar*? A: They are morphologically identical; only *E. histolytica* trophozoites typically contain ingested RBCs, and definitive separation needs antigen detection (adhesin ELISA), isoenzyme analysis or PCR.
Q: Why is blood for microfilariae collected at night? A: *W. bancrofti* microfilariae show nocturnal periodicity, appearing in peripheral blood mainly between about 22:00 and 02:00, matching the biting time of the *Culex* vector; a DEC provocation test can be used by day.
Q: Which fungal infections does β-D-glucan testing miss? A: Mucormycosis and cryptococcosis, because Mucorales walls have little β-1,3-glucan and *Cryptococcus* has a thick capsule masking it — so a negative result cannot exclude these.
Q: What is *Candida auris* and why does it worry hospitals? A: A multidrug-resistant yeast, first reported widely from Indian ICUs, that resists fluconazole (often amphotericin and echinocandins too), survives on surfaces, is misidentified by conventional systems and causes outbreaks of candidaemia — requiring MALDI-TOF/molecular ID and strict contact precautions.
Q: Why do helminth infections cause eosinophilia but protozoal ones usually do not? A: Tissue-invasive and migrating multicellular helminths drive a Th2 response with IL-5, which expands eosinophils; most protozoa are intracellular or luminal and elicit Th1/macrophage-based responses instead.

Common mistakes

Reversing the malaria hosts — writing that man is the definitive host; the mosquito is, because sexual reproduction occurs there.
Treating "Deuteromycota" as a true phylum, or still calling *Rhizopus* infection "zygomycosis"; the accepted term is mucormycosis and the group is Mucorales/Mucoromycota.
Confusing infective with diagnostic stages — the *E. histolytica* cyst infects while the trophozoite in dysenteric stool is diagnostic; the hookworm filariform larva infects while eggs are diagnostic.
Using cycloheximide-containing media for every specimen, thereby failing to grow *Cryptococcus* and Mucorales, or reporting a mould from a single skin culture without correlating with KOH microscopy.
Calling any yeast in urine or sputum "infection" — *Candida* is a commensal; significance needs quantitation, repeat isolation and clinical correlation.
Arithmetic slips in parasite density — forgetting the 8,000 WBC/µL factor, or quoting EPG without multiplying the Kato-Katz count by the template factor (24 for 41.7 mg).
Prescribing or recommending steroid–antifungal combination creams for tinea, which drive the terbinafine-resistant *T. indotineae* problem, and omitting the mandatory dose duration for onychomycosis.