Epidemiology and ecology of
fungal diseases
Healthcare
Focus on:
- individual
- diagnosis
- treatment
Public Health
Focus on:
- population
- prevention
The nature of fungi
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Kingdom Fungi (lat. fungus, -i)
Diverse group of eukaryotic organisms - all must lead
heterotrophic exsistance in nature as parasites or saprobes,
dependent on living or dead organic matter for their nutrition
Among more than 250 000 species of fungi that have been
described, 200 have been associated with human disease
In general these organisms are free-living in nature and are in
no way dependent of humans (or animals) for their survival
Fungal cells are similar to animal cells but are characterized by
the presence of a polysaccharide-based cell wall
Types of fungi
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There are two principal types of fungi:
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I. The yeasts – single cells which reproduce by a process
of bud formation to give rise to single daughter cells
(unicellular organisms – Candida)
II. The mycelial or mould fungi – form chains of
contiguous cells, hyphe (filamentous fungi)
(multicellular organisms – Aspergillus)
Dimorphic fungi – exist as either yeasts or mycelia at
different stages of their life cycles (Histoplasma)
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Mycoses
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Fungi can cause human disease in a number of different ways,
through the production of toxins, sensitizing antigens
(allergens) or by the invasion of tissue
Invasive diseases caused by fungi are known collectively as the
mycoses (fungal infections) › medical mycology
The fungi are recognized causes of disease in all parts of the
world
The distribution of mycoses is affected by a number of factors:
the presence of the organisms in the environment, host
immunity, frequency and route of exposure and the use of
invasive or immunosuppressive medical technology
Mycoses - classification
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Superficial (including cutaneous)
Subcutaneous
Invasive (systemic, deep)
Endogenous
Exogenous
Fungal pathogens
a. true pathogens (dermatophytes, dimorphic fungi)
b. opportunists (Candida, Aspergillus)
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Superficial mycoses
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Infections limited to the outermost layers of the skin, the
nails and hair, and the mucous membranes
Dermatophytoses (ringworm) and superficial forms of
candidosis
Many of these infections are mild and readily diagnosed,
and respond well to treatment
Subcutaneous mycoses
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Infections involving the dermis, subcutaneous tissues and
bone
Infections are usually acquired as a result of the
traumatic implantation of organisms that grow as
saprobes in soil and decomposing vegetation
Most frequent in rural populations of the tropical and
subtropical regions, where individuals go barefoot and
wear minimum of clothing
Mycetoma – Madurella etc.
Invasive mycosis
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Infections that usually originate in the lungs, but may
spread to many other organs
Agents: the true pathogens and the opportunists
Invasive mycoses caused by true pathogens
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a.
b.
c.
d.
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Endemic mycoses
Fungi geographically restricted to specific geographic areas
Pathogens are living in soil, bird droppings and air
Agents:
Histoplasma capsulatum
Coccidioides immitis
Blastomyces dermatitidis
Paracoccidioides brasiliensis
They cause pneumonia and systemic disease in a previously
healthy persons
Invasive infections caused by opportunists
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a.
b.
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a.
b.
Endogenous - means that the fungus is a part of a
normal human flora
Candida
Pneumocystic jiroveci (previously known as P. carinii) most probably a part of normal flora of the lungs of
many mammals, including humans
Exogenous - means that the fungus does not normaly
live in/on human body, although it can transiently
contaminate human body surfaces (especially respiratory
tract)
Cryptococcus neoformans
Aspergillus
Opportunistic mycoses
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Occur in individuals who are debilitated or
immunosuppressed as a result of an underlying disease or
their treatment
In most cases, infection results in significant disease
Resolution of the infection does not confer protection,
and reinfection or reactivation may occur if host
resistance is again lowered
Many of the organisms involved are ubiquitous
saprobes, found in the soil, on plants and decomposing
organic matter and in the air
High risk patient – opportunistic mycoses
Neutropenia
 Immunosuppression
a. HIV, transplantation
Community acquired
b. premature
c. diabetic
Hospital acquired
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ICU
a. trauma, burn
b. septic shock
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Abdominal surgery
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Prolonged antibiotic tratment
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Hematology
Agent
Candida
Aspergillus
Mucorales, Fusarium, Scedosporium
Unknown
Cryptococcus
Dimorphic
Pneumocystis
Incidence
Decrease: 70 – 42%
13 – 29%
4-12%
6%
4%
3%
2%
Candidosis
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Although candidiasis is endogenous in most
cases, cross infections are described, especially
in intensive care unit patients
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Handwashing is the most important activity to
prevent spread of many hospital pathogens, and of
Candida too
Estimated annual cases of HIV-associated
cryptococcosis
Eastern Europe
Western &
Central Europe & Central Asia
North America
27,200
500
7,800
East Asia
Caribbean
North Africa
& Middle East
7,800
6,500
Latin America
54,400
Sub-Saharan
Africa
720,000
13,600
South
& South-East Asia
120,000
Oceania
100
Global total: 957,900 cases (range: 371,700 – 1,544,000)
Park et al. AIDS 2009; 23: 525-30
Aspergillosis
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Invasive aspergillosis in the ICU
High - risk category
Neutropenia (neutrophil count, <500 neutrophils/mm³)
Hematological malignancy
Allogenic bone marrow transplantation
Intermediate - risk category
Prolonged treatment with corticosteroids before admission to
the ICU
Autologous bone marrow transplantation
Chronic obstructive pulmonary disease
Low – risk category
Severe burns
Other solid-organ transplant recipients (heart, kidney, liver)
Sources of Aspergillus
 Environment
 Food
long list!
 sharing of salt and pepper pots
 Standing water
 Ice-making machines
 Fomites
 carpets/furniture/fabrics/soft toys
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Patients live in mouldy houses:
exposure to Aspergillus and more
Patients live in mouldy houses and are
exposed to Aspergillus
Prevention is better than cure !
Avoid exposure in the hospital and in
the home
The majority of IFIs
are identified post-mortem
Pre-mortem
Post-mortem
33%†
How can we better
identify patients
with
IFIs during life?
12.3%*
Only ¼
diagnosed premortem
*Incidence of moulds and yeasts in AML patients (7.9% due to moulds).
†Prevalence of invasive moulds and Candida (22% due to moulds).
1. Pagano L et al. Haematologica. 2006;91:1068-1075. 2. Chamilos G et al. Haematologica. 2006;91:986-989.
Opportunistic fungal infections are
difficult to diagnose
 difficult to treat
 difficult to prevent
 more and more frequent
(emerging diseases)
 a great challenge for a future work in all fields
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