Mycoses 1 Flashcards
Dermatopytosis ( mycoses superficial infections)
superficial infections of keratinized tissues ( hair, nail and skin) and athletes foot Less common in face/ areas exposed to air. Caused by closely related group of moulds - ( dermatophytes). Key virulence factor: ability to digest keratin the compound that waterproofs our skin. Only organisms able to infect intact keratinized tissues, yet penetrate no further due to inability to acquire iron from host cell. Commonly ringworm or tinea. Infections occur in both humans and animals ( cross over in vets and farm workers)
- Common infection is Athletes foot ( ringworm of the foot) known as Tinea pedis ( named by its location not by the bacteria causing it), also common in the nail, scalp, groin and less commonly on the face and areas exposed to outside air
Types of Fungal Infection
Fungal infection types: 250k Fungal species 180 cause disease.
Superficial Mycoses (skin, mucosal regions): most common. Subcutaneous Mycoses: rare, equatorial, requires trauma. Systemic Mycoses: most serious (initial infection then immunosuppression). Often soil located.
Mycoses: difficult to control: lack of specific antifungal drugs, ubiquitous nature of the pathogens.
Cause serious systemic disease, often in impaired immunity: AIDS patients, immunosuppression. Treated with wide range of anti-fungal drugs with low resistance incidence.
but also many other forms of immunosuppression.
- Wide range of anti-fungal drugs treat infections with little incidence of resistance.
Mycoses superficial infections Pathology
- Fungi digest keratin and push hyphae into newly keratinized cells created to replace those damaged. Limited inflammatory response focussed on the surface unless other organisms take advantage in the breach in the skin and infect more deeply since they have iron scavenging systems.
Detection of Mycoses superficial infections
Direct microscopy requires KOH added to remove fungi from biopsy. Culture uses Sabouraud agar medium to grow the organisms and then identify mould on colonial appearance and microscopy. Specific media uses phenol red as a dye: yellow to red as nitrogenous material broken down by fungi making media alkali. Skill needed to learn structures associated with each species to confirm identification microscopically. Woods Lamp/UV Lamp causing both fluorescent fungi to glow and showing presence of dead skin cells.
Subcutaneous Mycoses infections
- Caused by various different species typically requiring host trauma for skin penetration. Infections of subcutaneous connective tissue (fascia), muscle, and deeper epidermal layers. an take years to develop, eventually spread along lymphatic channels.
Subcutaneous Mycoses infections: Chromomycossis and chromoblastomycosis
- Soli fungi form dark brown nodules , encrusted abscess and lesion development along lymphatics as infection spreads.
- Caused by organisms such as
Organisms e.g Fonsecaea pedrosoi gain entry to legs of feet via minor injury from thorns or sharp stones. Largely limited to tropical areas (Madagascar and Brazil)
Subcutaneous Mycoses - Mycetoma (Madura Foot)
Caused by Madurella mycetomatis. Endemic in Mexico, India and countries in africa. Causes destruction of subcutaneous tissue leading to deformities again typically in feet and legs. can spread through lymphatic system
Subcutaneous Mycoses- Sporotrichosis (Sporothrix schenkii)
Fungus found worldwide on various plants, associated with hay bales, soil. Injury allows entry via skin, spread through lymphatic systems.
Subcutaneous Mycoses treatment/prevention
Antifungal drugs or debridement of tissue (amputation of infected tissue)
- Avoided by protective clothing .Debilitating rather than fatal.
Candida from superficial to systemic mycoses
Candida: opportunistic fungi typically existing as commensals but can cause superficial, cutaneous, systemic mycoses.
Superficial infection on mucosal tissue causing : vaginal (thrush), oral and rectal disease: white patches. Usually caused by Candida Albian’s but other species observed (C. glabrata and C. parapsilosis).
Causes of systemic infection
- Switch to a systemic infection due to either alteration to normal microflora allowing extensive growth or by alteration of the immune system.
- ## Superficial infections can be prolonged despite topical antifungal therapy leading to systemic invasion due to prolonged immunosuppression .
Causes of prolonged immunosuppression.
Age: continued reduction in bacterial flora (broad spectrum antibiotics), Surgery or transplantation, T-cell reduction or other immuno-suppressions e,g: neutropenia, cancer or HIV. Damage to epithelial cells e.g from a contaminated catheter: localised infection, easily treated (amphotericin B), requires removal of catheter to remove contamination source.
Signs of systemic infection
- More serious pathology and often seen as a patient with persistent fever who fails to respond to antibiotics.
- Candida was the most common cause of systemic fungal injections in AIDS but its now replaced by Aspergillum species
- Candida spread causes: Meningitis, Renal abscess, Myocarditis, Osteomyelitis, Arthritis
Systemic infection detection and treatment
- Antibodies present in uninfected due to commensal nature of fungus: serology rarely use. Pathogens identified in sterile locations (blood, lung, CNS) or higher than normal levels in non-sterile locations (10000/ml shows signs of fungal UTI)
: - Treatments: range of antifungal drugs or amphotericin taken intravenously followed by fluconazole orally.
- Other risk factors: Immunosuppression, Intravenous drug abuse, Low birth weight ( in neonatal infections only) bacterial sepsis,
Prolonged hyperalimentation ( for example intravenous nutrient supply), systemic broad spectrum antibiotic therapy, Corticosteroid therapy, Recent abdominal surgery, Malignancy, Alcoholism, Diabetes mellitus, Trauma, and Hemodialysis
