Why this course

• Fungi are a leading cause of Hospital infections.

• Fungal infections are a major problem in immune suppressed people.

• Fungal infections are often mistaken for bacterial infections, with fatal consequences.

Mycoses: Clinical Classification of diseases

cause by fungi

• Superficial • Cutaneous• Subcutaneous • Systemic • Opportunistic

Medically important fungi (Pathogenic ) , fungi that cause

systemic mycoses retain several factors which allow their growth in adverse conditions provided by the

host, leading to the establishment of the parasitic relationship and

contributing to disease development.

The symbiotic-parasitic relationship produces an infectious process leading to lesions of the host tissues

and

establishment of disease due to a direct imbalance in parasite-host interaction.

EYE

SKIN

UROGENITAL TRACT

ANUS

MOUTHRESPIRATORY TRACT

PORTAL OF ENTRY

•SKIN

•HAIR

•NAILS

•RESPIRATORY TRACT

•GASTROINTESTINAL TRACT

•URINARY TRACT

EYE

SKIN

UROGENITAL TRACT

ANUS

MOUTHRESPIRATORY TRACT

COLONIZATION

Multiplication of an organism at a given site without harm to the host

EYE

SKIN

UROGENITAL TRACT

ANUS

MOUTHRESPIRATORY TRACT

INFECTION

Invasion and multiplication of organisms in body tissue resulting in local cellular injury..

Mycologists estimate that there are 100,000 species of fungi in nature.

These fungi inhabit different niches, a number of them are symbiotic and may live in commensalism, mutualism or parasitism with other organisms.

However, only some of the fungal species are pathogenic to man, a fact that has led to several studies providing a better understanding of the relationship among parasite, host and virulence factors

The host provides conditions for growth that usually differ markedly from the ecological niche that the fungus normally inhabits.

In order to survive in this new environment,

potential pathogens must withstand high temperatures, hormonal influences and attacks by phagocytes cells of the immune system

Factors that affect the transition from the saprophytic to parasite form in host-fungus relationship.

Cutaneous Mycoses

Skin, hair and nailsRarely invade deeper

tissue

Dermatophytes

Superficial Cutaneous Infection

Malassezia, Tinea nigra, Piedra

SUPERFICIAL MYCOSES 

• The superficial (cutaneous) mycoses are usually confined to the outer layers of skin, hair, and nails, and do not invade living tissues. The fungi are called dermatophytes. Dermatophytes, or more properly, keratinophilic fungi, produce extracellular enzymes (keratinases) which are capable of hydrolyzing keratin.There are three genera of dermatophytes:

• Malassezia furfur• Trichophyton species (19 species)• Microsporum species• Epidermophyton floccosum.

Infection requires a large inoculum and a susceptible

host

1. infection often occurs in endemic areas

2. most infections are asymptomatic or self-limiting

3. in immune-compromised hosts, infections are more often fatal (AIDS)

4. Most fungal infections affect our surface not our contents

Superficial Cutaneous Mycoses

• Malassezia infections• Tinea nigra--gray to black macular lesions often on

palms• White piedra--soft whitish granules along hair shaft• Black piedra--dark gritty deposits on hair

• All are diagnosed by microscopy and are easily treated by topical preparations.

• Malassezia infections

• Description:• Malassezia furfur is the causative agent of Pityriasis

versicolor, Pityriasis folliculitis and it has recently been implicated as a causative agent of seborrhoeic dermatitis and dandruff. It has also been recovered in blood cultures from neonate and adult patients undergoing lipid replacement therapy. M. furfur is a lipophilic yeast living on the skin as part of the normal flora.

• Clinical manifestations

• Pityriasis versicolor showing hyperpigmented lesions in a Caucasian and hyphopigmented lesions .

• Pityriasis versicolor: This is a chronic, superficial fungal disease of the skin characterised by well-demarcated white, pink, fawn, or brownish lesions, often coalescing, and covered with thin furfuraceous scales. The colour varies according to the normal pigmentation of the patient, exposure of the area to sunlight, and the severity of the disease. Lesions occur on the trunk, shoulders and arms, rarely on the neck and face, and fluoresce a pale greenish colour under Wood's ultra-violet light. Young adults are affected most often, but the disease may occur in childhood and old age.

• Pityriasis folliculitis: This is characterised by follicular papules and pustules localised to the back, chest and upper arms, sometimes the neck, and more seldom the face. These are itchy and often appear after sun exposure. Scrapings or biopsy specimens show numerous yeasts occluding the mouths of the infected follicules. Most cases respond well to topical imidazole treatment, however patients with extensive lesions often require oral treatment with ketoconazole or itraconazole. Once again, prophylactic treatment once or twice a week is mandatory to prevent relapse.

•

• Pityriasis folliculitis.

• Seborrhoeic dermatitis and dandruff: Current evidence suggests M. furfur, combined with multifactorial host factors is also the direct cause of seborrhoeic dermatitis, with dandruff being the mildest manifestation. Host factors include genetic predisposition, an emotional component (possible endocrine or neurologically mediated factors), changes in quantity and composition of sebum (increase in wax esters and a shift from triglycerides to shorter fatty acid chains), increase in alkalinity of skin (due to eccrine sweating) and external local factors such as occlusion. Patients with neurological diseases such as Parkinson's disease and those with AIDS are commonly affected. Clinical manifestations are characterised by erythema and scaling in areas with a rich supply of sebaceous glands ie the scalp, face, eyebrows, ears and upper trunk. Lesions are red and covered with greasy scales and itching is common in the scalp. The clinical features are typical and skin scrapings for a laboratory diagnosis are unnecessary. Once again, the use of a topical imidazole is recommended, especially ketoconazole which has proved to be the most effective agent. Relapse is common and retreatment when necessary is the simplest approach for long term management.

• Laboratory diagnosis:• 1. Clinical material: Skin scrapings from patients with superficial lesions,

blood and indwelling catheter tips from patients with suspected fungaemia.

• 2. Direct Microscopy: Skin scrapings taken from patients with Pityriasis versicolor stain rapidly when mounted in 10% KOH, glycerol and Parker ink solution and show characteristic clusters of thick-walled round, budding yeast-like cells and short angular hyphal forms up to 8um in diameter (ave. 4um diam.). These microscopic features are diagnostic for Malassezia furfur and culture preparations are usually not necessary.

•

• GMS stained skin biopsy showing characteristic spherical yeast cells and short pseudohyphal elements typical of M. furfur.

•

• 10% KOH with Parker ink mount showing characteristic spherical yeast cells and short pseudohyphal elements typical of the fungus.

• 3. Culture: Culture is only necessary in cases of suspected fumgaemia. M. furfur is a lipophilic yeast, therefore in vitro growth must be stimulated by natural oils or other fatty substances. The most common method used is to overlay Sabouraud's dextrose agar containing cycloheximide (actidione) with olive oil or alternatively to use a more specialized media like Dixon's agar which contains glycerol mono-oleate (a suitable substrate for growth).

•

• Culture of M. furfur on Dixon's agar.• 4. Serology: There are currently no commercially available serological

procedures for the diagnosis of Malassezia infections.• 5. Identification: Microscopic evidence of inipolar, broad base budding

yeast cells and special lipid requirements for growth in culture are usually diagnostic.

• Causative agents:• Malassezia furfur

• Management:• The most appropriate antifungal treatment for pityriasis

versicolor is to use a topical imidazole in a solution or lathering preparation. Ketoconazole shampoo has proven to be very effective. Alternative treatments include zinc pyrithione shampoo or selenium sulfide lotion applied daily for 10-14 days or the use of propylene glycol 50% in water twice daily for 14 days.

• In severe cases with extensive lesions, or in cases with lesions resistant to topical treatment or in cases of frequent relapse oral therapy with either ketoconazole [400 mg single dose or 200 mg/day for 5-10 days] or itraconazole [200 mg/day for 5-7 days] is usually effective. Mycologically,

• yeast cells may still be seen in skin scrapings for up to 30 days following treatment, thus patients should be monitored on clinical grounds.

• Patients also need to be warned that it may take many months for their skin pigmentation to return to normal, even after the infection has been successfully treated. Relapse is a regular occurrence and prophylactic treatment with a topical agent once or twice a week is often necessary to avoid recurrence.

• Tinea nigra• Description:• A superficial fungal infection of skin characterised by

brown to black macules which usually occur on the palmar aspects of hands and occasionally the plantar and other surfaces of the skin. World-wide distribution, but more common in tropical regions of Central and South America, Africa, South-East Asia and Australia. The aetiological agent is Hortaea (Phaeoannellomyces) werneckii a common saprophytic fungus believed to occur in soil, compost, humus and on wood in humid tropical and sub-tropical regions.

• Clinical manifestations:• Skin lesions are characterised by brown to black macules

which usually occur on the palmar aspects of hands and occasionally the plantar and other surfaces of the skin. Lesions are non-inflammatory and non-scaling. Familial spread of infection has also been reported.

•

• Typical brown to black, non-scaling macules on the palmar aspect of the hands. Note there is no inflammatory reaction.

• Laboratory diagnosis:• 1. Clinical Material: Skin scrapings.• 2. Direct Microscopy: Skin scrapings should be

examined using 10% KOH and Parker ink or calcofluor white mounts.

•

• Skin scrapings mounted in 10% KOH showing pigmented brown to dark olivaceous (dematiaceous) septate hyphal elements and 2-celled yeast cells producing annelloconidia typical of Hortaea werneckii.

• 3. Culture: Clinical specimens should be inoculated onto primary isolation media, like Sabouraud's dextrose agar.

• 4. Serology: Not required for diagnosis.• 5. Identification: Characteristic clinical, microscopic and

culture features.• Causative agents:• Hortaea werneckii (syn. Phaeoannellomyces werneckii). • Management:• Usually, topical treatment with Whitfield's ointment

(benzoic acid compound) or an imidazole agent twice a day for 3-4 weeks is effective.

• White piedra

• Description:• White piedra is a superficial cosmetic fungal infection of

the hair shaft caused by Trichosporon beigelii. Infected hairs develop soft greyish-white nodules along the shaft. Essentially no pathological changes are elicited. White piedra is found worldwide, but is most common in tropical or subtropical regions.

• Infections are usually localised to the axilla or scalp but may also be seen on facial hairs and sometimes pubic hair. White piedra is common in young adults. The presence of irregular, soft, white or light brown nodules, 1.0-1.5 mm in length, firmly adhering to the hairs is characteristic of white piedra.

• Laboratory diagnosis:• 1. Clinical Material: Epilated hairs with white soft

nodules present on the shaft.• 2. Direct Microscopy: Hairs should be examined using

10% KOH and Parker ink or calcofluor white mounts. Look for irregular, soft, white or light brown nodules, 1.0-1.5 mm in length, firmly adhering to the hairs.

• 3. Culture: Hair fragments should be implanted onto primary isolation media, like Sabouraud's dextrose agar. Colonies of Trichosporon beigelii are white or yellowish to deep cream colored, smooth, wrinkled, velvety, dull colonies with a mycelial fringe.

• 4. Serology: Not required for diagnosis.• 5. Identification: Characteristic clinical, microscopic and

culture features.

• Causative agents:• Trichosporon beigelii

• Management:• Shaving the hairs is the simplest method of treatment.

Topical application of an imidazole agent may be used to prevent reinfection.

• Black piedra• Description:• Black piedra is a superficial fungal infection of the hair

shaft caused by Piedra hortae, an ascomycetous fungus forming hard black nodules on the shafts of the scalp, beard, moustache and pubic hair. It is common in Central and South America and South-East Asia.

• Clinical manifestations:• Infections are usually localised to the scalp but may also

be seen on hairs of the beard, moustache and pubic hair. Black piedra mostly affects young adults and epidemics in families have been reported following the sharing of combs and hairbrushes. Infected hairs generally have a number of hard black nodules on the shaft. Black piedra may be confused with trichorrhexis nodosa and trichonodosis but mycological examination will always confirm the diagnosis.

• Laboratory diagnosis:• 1. Clinical Material: Epilated hairs with hard black

nodules present on the shaft.• 2. Direct Microscopy: Hairs should be examined using

10% KOH and Parker ink or calcofluor white. Look for darkly pigmented nodules that may partially or completely surround the hair shaft. Nodules are made up of a mass of pigmented with a stroma-like centre containing asci.

• 3. Culture: Hair fragments should be implanted onto primary isolation media, like Sabouraud's dextrose agar. Colonies of Piedra hortae are dark, brown-black and take about 2-3 weeks to appear.

• 4. Serology: Not required for diagnosis.• 5. Identification: Characteristic clinical, microscopic and

culture features.• Causative agents:• Piedra hortae

• Management:• The usual treatment is to shave or cut the hairs short, but

this is often not considered acceptable, particularly by women. In-vitro susceptibility tests have shown that Piedra hortae is sensitive to terbinafine and it has been successfully used, at a dose of 250 mg a day for 6 weeks, to treat a 23 year old Swedish Caucasian man following a 4 month visit to India (Gip, 1994).

THERAPY

Because they are eukaryotic, fungi are biochemically similar to the human host. Therefore it is difficult to develop chemotherapeutic agents that will destroy the invading fungus without harming the patient.

PROBLEM

Finding an agent that will selectively injure fungal cell walls without damaging the host cell.

PRIMARY ANTI-FUNGAL AGENTS

1. Polyene derivatives– Amphotericin B– Nystatin

2. Azoles– Ketoconazole– Fluconazole– Itraconazole– Voriconazole– Posaconazole

PRIMARY ANTI-FUNGAL AGENTS

3. Griseofulvin4. 5-fluorocytosine (5-FC)5. Allylamines

-Terbinafine (Lamasil)6. Echinocandins

- Caspofungin