Fungal Organisms Flashcards
What are the characteristics of fungi?
How do they reproduce?
- eukaryotic organisms
- they range from single-celled to macroscopic (multicellular)
- growth forms are mainly hyphal or yeast
- they have a glucan-chitin cell wall
- they reproduce asexually and/or sexually through spore formation
What are the 3 types of lifestyle of a fungus?
- saprophytes - decay organic matter
- plant pathogens
- animal pathogens (small number)
What are the 3 types of fungal disease?
- superficial infection
- subcutaneous infection
- systemic infection
What is meant by a superficial infection?
What 3 types of organism cause this?
it affects skin, hair, nails and mucosal surfaces
it is caused by:
- dermatophytes
- Malassezia
- Candida
What is meant by subcutaneous infection?
this affects subcutaneous tissue, usually following traumatic implantation
it is common in tropical countries
What is meant by a systemic infection?
What types of organisms cause this?
it affects deep-seated organs
it is caused by:
- Candida
- Aspergillus
What are dermatophytes?
a group of slow growing moulds seen as causes of disease in skin, hair and nails
What are the 3 types of dermatophytes and where do they originate?
geophilic - originate in soil
zoophilic - originate in other animals
anthropophilic - originate in other humans
What is shown in the images?
Trichophyton interdigitale
This is a dermatophyte that occurs between the toes
What are the following dermatophyte infections?
What is the % rate of fungal nail infections?
In which group are they more common?
they are common in the general adult population - probably 5-25% rate
there is an increasing incidence in elderly people
What types of people are most commonly affected by Athlete’s foot?
it is more common in adults (not younger people) and sportsmen as it is acquired from communal changing areas
In which group is scalp ringworm more common?
prepubertal children
What are the typical signs of tinea pedis (Athlete’s foot)?
it is unilateral or bilateral
it features itching, flaking or fisuring of the skin
the soles of the feet are dry and scaly
What is it called if Athlete’s foot affects the whole of the foot?
Moccasin foot
there is a fine scale over the plantar surface of the foot
What symptom may increase the severity of Athlete’s foot?
hyperhidrosis (secondary to infection)
this is excess sweating which may increase severity of infection
What may tinea pedis lead to?
- secondary bacterial infection
- it may spread to infect the toe nails
What organism typically causes Tinea pedis?
Trichopyton rubrum
What characterises tinea unguium?
What is an alternative name for it?
Thickening, discolouring and dystrophy of the nails
It is also known as onychomycosis
What are the 4 types of tinea unguium?
the type depends on where on the nail the infection starts
- lateral/distal subungual
- superficial white (usually in immunocompromised)
- proximal
- total nail dystrophy (takes over the whole nail)
What organisms typically cause tinea unguium?
Trichophyton rubrum
Trichophyton interdigitale
What is tinea cruris?
What are the typical features of it?
itching, scaling, erythematous plaques with distinct edges
the active fungus is present at the edges of the plaque
satellite lesions are sometimes present
What are the typical causes of tinea cruris?
Where is it usually found?
T. rubrum
This can spread from the nails or foot
It is found in the groin region but may extend to the buttocks, back and lower abdomen
Where is tinea capitis usually seen?
What does it look like?
it is mainly seen in pre-pubescent children
it ranges from slight inflammation, scaly patches with alopecia, “black dots”, “grey patches” to severe inflammation
What does severe inflammation in tinea capitis lead to?
Kerion celsi
these are boggy inflamed lesions with hair loss and permanent scarring
usually from zoophilic dermatopytes
What is a more rare result of tinea capitis?
Favus
this is the presence of cup shaped crusts or scutula
What is an alternative name for tinea corporis?
What does it look like?
Ringworm
It involves circular, single or multiple erythematous plaques
It may extend from the scalp or groin
What is it called when tinea corporis invades a hair follicle?
Majocci’s granuloma
What is the typical cause of tinea corporis?
a wide range of dermatophytes
either anthropophilic or zoophilic
What is involved in the investigation of dermatophyte infection?
microscopy and culture
sample can come from a hair follicle, piece of nail or skin scraping etc.
What are the 2 types of treatment for a dermatophyte infection?
Mild disease:
- topical antifungal therapy with terbinafine or clotrimazole
- usually self-diagnosis and treatment
Severe disease:
- systemic antifungal therapy
What should all cases of tinea capitis be treated with?
Why?
systemic antifungals
e.g. griseofulvin, terbinafine, itraconazole
topical therapy has a role in reducing spread but will NOT be curative
What are Malassezia?
Where are they found?
they are a genus of yeasts
they are part of normal skin flora in all humans from shortly after birth
they are most frequent on the head and trunk
What diseases are caused by Malassezia?
- pityriasis versicolor
- they have a role in seborrhoeic dermatitis and atopic eczema
What does pityriasis versicolor look like?
What types of people are usually affected?
hyper- or hypopigmented lesions on the upper trunk
it affects people between puberty and middle age
it is more common in the tropics
Why is pityriasis versicolor relapsing?
it is caused by a commensal organism which is always present on the skin
How is pityriasis versicolor diagnosed?
microscopy
it is a dimorphic fungi so yeast cells and hyphal segments are seen (“spaghetti and meatballs”)
culture is difficult and not interpretable
What is the treatment for pityriasis versicolor?
topical antifungals e.g. clotrimazole
if this fails then oral fluconazole or itraconazole is given
What is shown in this image?
Candida albicans
They are dimorphic fungi
The hyphal form is often seen in infected tissues
What types of patients tend to be affected by acute pseudo-membranous oral candidiosis?
- low CD4 count (<200 cells/ul)
- younger patients
- asthma with steroid inhalers
What types of patients tend to be affected by chronic atrophic oral candidiosis?
older patients
this is characterised by erythema and angular cheilitis (in corners of mouth)
What organs are typically affected by candida spp.?
How are they usually acquired?
candida spp. can infect almost any organ in the body
it is usually acquired from colonised skin or mucosal sites or from the GI tract
How is candida oesophagitis diagnosed?
What symptoms are present?
it cannot be picked up on blood culture so is diagnosed by endoscopy with biopsy
it causes pain/difficulty on eating/swallowing
Why is candida endophthalmitis difficult to treat?
it requires intravitreal antifungals (injecting into the eye)
How is candida endocarditis treated?
it is difficult to treat without valve replacement
What causes renal candidosis?
What group of people are usually affected?
candida from the blood lodges in kidney tissue during filtration
it is most common in immunocompromised premature neonates
What is shown?
bullseye sign
abcess in the spleen seen in hepatosplenic candidosis
What is shown here?
Aspergillus fumigatus
In which types of patients is an aspergilloma common in?
patients with cavities from previous TB, sarcoid, surgery
involves formation of solid balls of fungus
What is chronic pulmonary aspergillosis?
What are the symptoms and what does it look like on CT?
it is seen in COPD
- chronic respiratory symptoms such as cough, wheezing, breathlessness and chest pain
- consolidation and cavitation on CT
What signs are seen on CT scans in invasive aspergillosis?
Halo sign and air cresent signs
