Introduction Fungal Infections:
Many Patients worldwide are troubled by Fungal infections. Most of them are usually Non-serious but they can turn Serious in immunocompromised individuals.
Various agents are implicated in the causation of different Diseases. One of the emerging trends is an increase in the incidence of fungal infections.
Medical Students, MBBS doctors, DM Aspirants, NEET Aspirants preparing for Medical Examinations in India like FMGE, NEET-PG, AIIMS Exams, NEET DM Examinations, NEET DM Medicine and NEET DM Infectious diseases Examinations in addition to USMLE Exams, PLAB Exams, Australian Board, Canadian Board Examinations and MRCP get loads of questions on Fungal infections.
They form an important set of questions in medicine, microbiology especially. Medical Students and Students preparing for NEET PG and Especially NEET DM Examinations get a lot of Questions from Fungal infections.
Classifying Fungal infections:
Dermatophytes are also called as the Ring Worm (Tinea) infection. Dermatophytes include a distinct group of fungi that under most conditions have the ability to infect & survive only one the dead (stratum corneum or keratin layer), hair & nails. They cannot survive on mucosal surfaces (eg mouth or vagina) where the keratin layer does not form. Infections are not usually serious.
Serious infections, Deep invasion & multisystem dissemination is very rarely seen in immunocompromised hosts.
Trichophyton Infects skin, hair & nail.
There are Several infecting species include
- Trichophyton rubrum
- Trichophyton Mentangrophyte
- Trichophyton Violaceum
- Trichophyton Verrucosum
- Trichophyton schoenleini.
Clinical patterns of Fungal Infections. A patient with Fungal Infections can present at different sites.
- Non- inflammatory Human or Epidemic type
- Most common & most difficult to diagnose because it resembles dandruff.
- Most commonly caused by anthropophilic ectothrix eg. audouinii or M. canis , M.ferrugineum & T. tonsurans.
- In this Condition, the Hairs turn gray & lusterless secondary to the sheath of arthroconidia associated with a hyperkeratotic, scaly plaque of alopecia (gray patch type) usually on occiput giving the appearance of the mowed wheat field
- . Often there is adenopathy & no hair loss.
- Culture is often necessary because only 30% have positive KOH examination
- Inflammatory (Kerion) type
- It is a hypersensitivity reaction to infection usually seen with M. cannis & M. gypseum, audouinii, M. nanum, T. mentagrophytes, T.schoenleinii, T. tonsurans, T. verrucosum
- Ranges from pustular folliculitis to keroin, which is boggy inflammatory tender mass studded with broken hairs, follicular orifice oozing with pus & easily pluckable hair.
- Pruritis, pain, fever, occipital & posterior cervical lymphadenopathy & scarring alopecia may occur.
- Black dot
- Caused by anthropophilic endothrix T.tonsurans & T.violaceum
- It is least inflammatory form resembling scaly variety but with less scaling, itching; & hair is broken at or below that scalp surface resulting in <2 mm long stump & I/t black dot appearance.
- Favus or Tinea favosa
- schoenleinii is the most common cause of human favus, T. violaceum, & M. gypseum are also causative.
- It is a chronic infection of the scalp, glabrous skin, & nails. There is a Typical Presentation of thick yellow honeycomb crust (scutula) within the hair follicles.
Onychomycosis & Tinea Unguium
- Nails can be Target of Fungal infections. Usually mire resistant to Treatment.
- Onychomycosis (most prevalent nail disease) is an infection of the nail caused by a dermatophyte or nondermatophyte fungi or yeast. However, Tinea unguium refers strictly to dermatophyte infection of the nail plate.
It is also named as Jack itch and in India as Dhobi Itch
It is a common dermatophytosis worldwide involving anatomic sites like the groin, pubic, perianal skin & genitalia. It is more common in males than in females, & adults are affected more commonly than children.
Most tenia cruris is caused by Trichophyton rubrum & epiderophyton floccosum (most often responsible for epidemics) .
The warm, moist environment is a predisposing factor.
In clinical Examination, the Lesions are mostly unilateral & begin in crural folds. A semilunar plaque forms as a well-defined scaling, & sometimes a vesicular border advances out of crural fold onto the thigh. The skin within the border turns red-brown, is less scaly & may develop red papules.
The involvement of scrotum & genitalia is unusual – unlike Candida; which is more extensive, often bilateral involves scrotum & shows typical fringe of scale at border & satellite pustules.
§ Amphotericin B is selective in its fungicidal effect because it exploits the difference in the lipid composition of fungal and mammalian cell membranes.
§ Ergosterol, a cell membrane sterol, is found in the cell membrane of fungi, whereas the predominant sterol of bacteria and human cells is cholesterol.
§ Amphotericin B binds to ergosterol and alters the permeability of the cell by forming amphotericin B-associated pores in the cell membrane. is a polyene antibiotic similar to nystatin. It is not absorbed orally so administered by slow I .v. infusion. It is widely distributed except in the CNS. It binds to ergosterol and causes the formation of artificial pores in the fungal cell membranes.
§ Amphotericin B has the widest antifungal spectrum and is the drug of choice or co-drug of choice for most systemic fungal infections.
§ It can be used intrathecally in fungal meningitis and locally for corneal ulcers and keratitis. Drugs used are diverse. Usually, Topical treatment alone can be sufficient
- Ciclopirox is effective against Tinea unguium, candida.
- Amorolfine is effective against dermatophytes, yeasts & molds when applied once weekly.
Oral antifungals may be used for refractory, severe, or non-dermatophyte onychomycosis, or when shorter treatment regimen or higher chances for clearance or cure is desired.
- Terbinafine is the most effective oral t/t for fungally infected toenails available today. It is effective against dermatophytes, Aspergillus.
- Itraconazole is fungistatic against dermatophytes, non-dermatophytes & yeasts at 400 mg daily for 1 week /month pulse dose or 200 mg daily continuous dose for 2 months (fingernails) or 3 months (toenails).
- Fluconazole is fungistatic against dermatophytes, some non-dermatophytes & candida at 150-300mg once/week for 3-12 months
- Griseofulvin is rarely considered nowadays.
- Terbinafine is a common most antifungal used. It is effective against dermatophytes, Itraconazole is fungistatic against dermatophytes, non-dermatophytes & yeasts Fluconazole is fungistatic against dermatophytes, some non-dermatophytes & candida at 150-300mg once/week for 3-12 months. Griseofulvin is used treatment for Onychomycosis &T. unguium.
Mechanism of Action of Antifungals
- Flucytosine Interferes with DNA and RNA synthesis selectively in fungi
- Ketoconazole Blocks fungal P450 enzymes and interferes with ergosterol synthesis
- Itraconazole Same as for ketoconazole
Medical Graduates, MBBS Students, Microbiologists and Medical Students aspiring for Examinations like FMGE, NEET-PG, AIIMS Exams, PGI Exams, NEET DM Examinations, NEET DM Medicine and NEET DM Infectious diseases Examinations in addition to USMLE Exams, PLAB Exams, Australian Board, Canadian Board Examinations and MRCP Examinations would tremendously benefit from the Topic.