 Pseudallescheria / Scedosporium:
emerging
therapy-refractory opportunists in humans
Need and relevance
Co-operation between academic, health organizations and industry is promoted
by the European Confederation of Medical Mycology, covering the mycological
societies of 19 European countries. One of the key activities of this platform
is the implementation of Surveillance Working Groups. These are extremely useful
to acquire an overview of the clinical significance of major mycoses and of
changing epidemiological trends and promote awareness of the emergence of resistance
against antifungal drugs.
 An ECMM
Working Group was founded at the ECMM congress in Budapest, August
2002 as a continuation of an existing informal international network, to focus
European attention on the much overlooked but important, potentially life-threatening
systemic and disseminated infections by Pseudallescheria and Scedosporium.
Due to the therapy-refractory character of these fungi, morbidity and mortality
by such infections is high. There is a high degree of genetic diversity within
both species, which diminishes the predictive value of standard antifungal
susceptibility data. Consequently the infectious diseases united under the
umbrella term Pseudallescheriasis provide a potent model for
the development of new strategies for control of therapy-refractory emerging
opportunists. The consortium will obtain insight into the occurrence and genetic
variability of these fungi, and provide data on possible sources of contamination
and infection routes. A multidisciplinary approach in health
care of the immunocompromised patient population is necessary to understand
the emergence of new fungal diseases. Improved diagnostics, at the generic
level and down to the (sub)specific level, can be developed and disseminated
to the European clinician, which is expected to greatly stimulate awareness
of Pseudallescheria, Scedosporium and other fungal infections.
This synergistic approach of the pan-European network will lead to an expertise
centre with public data bank containing information on strains and
their genetic make-up, clinical cases, and antifungal susceptibilities, and
will contribute to diagnostic protocols and guidelines for therapy. A
genomic approach will be implemented to select key-genes involved in the resistance
to antimycotics, providing a basis for the development of novel and dedicated
antifungals by pharmaceutical companies, and to efficient treatment
protocols.
Infections
by Pseudallescheria / Scedosporium have a relatively high degree of
virulence. This intrinsic virulence can be deduced from the extremely infrequent
occurrence of the species in air but the high prevalence in the lungs of susceptible
patients: P. boydii is with a frequency of 8.6% the second most common
filamentous fungus in the lungs of CF patients. In Europe around 18,000 patients
will be diagnosed with acute leukemia alone and around 13,000 die of this disease
each year. 99,000 patients will be treated for a hematologic malignancy and
around 18,800 will be bone-marrow or organ transplanted. About 5-24% of the
patients undergoing lung or allogenic bone-marrow transplantation and of the
patients with acute leukemia will develop invasive mycoses. Roughly estimated,
5-6000 cases concern filamentous fungi, which will in the vast majority be
the cause of death. Many of these are unnecessary deaths because the underlying
disease can be cured or temporarily stabilized. Important is the present lack
of sufficient early diagnostics, including the identification of the infectious
agent. Due to significant differences in the susceptibility of fungi to antimycotic
agents, an universal recommendation for an antifungal therapy without knowledge
about the individual fungal isolate is not possible. For Pseudallescheria
/ Scedosporium there are major problems to be solved: (1) the agents
of disease are often not or inappropriately recognized, and (2) if
recognized, current therapeutic regimens are inadequate, and
(3) knowledge on the biology, clinical potential, virulence,
and routes of transmission and infection is lacking. Investigation of the scattered
data on this species complex is hardly possible without (4) an extended data
bank.
All members of the Network are kindly requested to put the following footnote
on their publications:
*Communication of the ECMM Working Group on Pseudallescheria and Scedosporium
(www.Scedosporium-ECMM.com).
OVERVIEW OF ACTIVITIES
(1) Clinical surveillance, epidemiology and isolation
A preliminary inquiry of a number of strictly comparable university hospitals
revealed that the frequency of Pseudallescheria and Scedosporium infections
was very different. This is possibly explained by two major problem areas:
isolation, and diagnosis.
Presence
of the fungus in non-sterile body sites is often concealed by rapidly growing
colonizers such as Aspergillus and Candida. Selective protocols
and guidelines of incubations times and conditions are therefore necessary.
It is noted in CF lungs A. fumigatus may appear first, and subsequently
the therapy-refractory Pseudallescheria appears after administration
of antifungals against Aspergillus. This suggests that Pseudallescheria was
present but overlooked.
The histopathology
of Scedosporium is identical to that of aspergillosis and therefore
the species are frequently misidentified as such. With serology, cross-reactivity
is noted with phylogenetically remote fungi like Cryptococcus neoformans.
In culture the species may be highly polymorphic. This has led to the frequent
redescription of the fungus as a new species and even new genus, the last of
which was Polycytella, in 1987. In members of our consortium with
increased awareness their frequency currently is estimated to be fatal in about
1-3:106 patients per year, and increasing. It is expected that upon re-evaluation
of archival autopsy specimens, numerous cases ascribed to Aspergillus will
turn out to have been caused by a Pseudallescheria or Scedosporium species.
Aims: Obtain a balanced picture of the clinical presentation
of Pseudallescheria / Scedosporium, including colonization and invasion,
and routes of dissemination within the patient.
Expected practical outcome: Isolation / detection protocols;
collection of strains for research; epidemiology and frequency.
Specific tasks:
(1) Define the real occurrence of the different forms of pseudallescheriasis
(with a particular emphasis in CF patients),
(2) Define guidelines for mycological examination of clinical samples (with
an emphasis on sputum samples from CF patients),
(3) Improve isolation protocols from any clinical sample,
(4) Improve the serological diagnosis of scedosporiosis and analyis of the
antigenic equipment of the fungus,
(4) Identify specific antigens allowing the development of a western-blot procedure
or of an ELISA test using a monoclonal antibody directed towards one of these
specific antigens,
(5) Improve the histopathological examination of biopsies and necropsies with
a MAb-based kit or using a molecular biological approach,
(6) Describe routes of dissemination within the patient,
(7) Establish numbers of genotypes within the patient,
(8) Preserve strains for later research.
Steering committee: Jean-Philippe Bouchara, Gerhard Haase,
Sevtap Arikan.
(2) Virulence, animal models, antifungals and therapy
Their variable but always remarkably high tolerance to antimycotics makes
the species a severe threat for the hospitalised population. In these patients,
immediate and adequate antimycotic therapy is mandatory. However, this is hampered
by the bewildering genetic diversity of the Pseudallescheria. Published
MIC values have limited predictive value for effective treatment of the patient
at hand. Thus there is a severe gap in our knowledge on these organisms, with
the unnecessary loss of patients as a probable consequence. The proposed concerted
action will provide a major leap forward towards the development of reliable
treatment protocols. The increasing frequency, the high case fatality rate
in immunocompromised patients, and the recent availability of genomic techniques
to solve many of the problems, warrant concerted action to diminish the mortality
caused by this disease.
Aims: Obtain insight into the virulence factors of Pseudallescheria
/ Scedosporium, including colonization and invasion, and routes of dissemination
in the patient; development of adequate antifungal therapy.
Expected practical outcome: Insight in virulence factors;
animal models; therapeutic guidelines.
Specific tasks:
(1) Prepare a genomic bank for S. apiospermum which will be use for
the identification and characterization of some putative virulence factors
of the fungus (e.g. adhesins, anti-oxidant systems, proteases, etc.),
(2) Elaborate and develop vertebrate and non-vertebrate animal models for invasive
disease, and perhaps also for ingestion,
(3) Establish correlation of in vitro MIC and in vivo outcome
in animal model,
(4) Develop effective antifungal (combination) therapy for P. boydii and S.
prolificans.
(5) Develop phagocytose assays for P. boydii.
Steering committee: Paul Verweij, Josep Guarro, Aristea Velegraki,
Bernard Cimon.
(3) Biology, diagnostics and transmission
 Why particular fungal species are emerging? Pseudallescheria is normally
associated with heavily polluted environments, such as sewage, mud of geese-inhabited
village ponds, manure and agricultural soil. Its frequency in the environment
is strongly enhanced by the behaviour of mankind in rural and urban settings,
where nitrogenic compounds are ubiquitous pollutants. In the unpolluted environment
the species is very rare; there are only occasional reports of the fungus recovered
from the intestinal tract of amphibians. Despite their occurrence in soil and
water in temperate climates, the species are consistently thermotolerant and
have the ability to survive at very low oxygen pressures. This may indicate
a natural ecological niche involving the use of a warm-blooded animal as a
vector of dissemination.
The jump of the fungus from the unknown natural niche to the man-dominated
environment may be accompanied by selection of virulent genotypes and thus
by an evolution towards higher average degrees of virulence. The possibility
of such events is suggested by the presence of genetic entities within the
species with different ecology, such as predominantly clinical vs. environmental.
The dung-polluted rural environment has created an enormous window of opportunity
for the species. Therefore the fungus species may develop towards higher virulence
without jeopardizing its own existence. Apparently it is best for the species
to propagate with large numbers, regardless if this interferes with mobilization
of eventual hosts. More rapidly growing genotypes thus have an increased probability
of transmission and thus have a higher evolutionary fitness. If this hypothesis
is correct, it is likely that genotypes with higher virulence and micro-aerophily
are selected and that the fungus indeed becomes more virulent in the course
of its evolution. From our own data it is apparent that several genotypes with
marked differences in growth rate occur next to each other in the same ecosystem,
which suggests that the slower genotypes have not yet been outcompeted by the
virulent ones. It is probable that new genotypes are continuously brought in.
The human creation of new environments which enhance the eutrophic opportunistic
pathogen Pseudallescheria leads to the prediction that more virulent
and more resistant genotypes will be selected in the course of short-term evolution.
This would mean that the current problems with infection of the immunocompromised
patient by Pseudallescheria and Scedosporium will aggravate.
The problem of resistance to antifungal therapy facing a growing population
of susceptible patients increases concomitantly. Using Pseudallescheria as
a model, our research will provide insight into the question why only some
of opportunists, out of the 100,000 species known, are emerging. This is a
fundamental question in any research on virulence of opportunistic fungi such
as Candida or Aspergillus.
Aims: Obtain insight into the environmental ecology of Pseudallescheria
/ Scedosporium, including routes of  transmission, and evolutionary events
during adaptation to the man-dominated environment.
Expected practical outcome: Hygienic guidelines.
Specific tasks:
(1) Description of phylogenetic structure of P. boydii and related
species,
(2) Description of intraspecific variability using independent markers,
(3) Revealing processes of selection and of speciation by competition experiments,
(4) Description of genetic processes of breeding, compatibility and clonality,
(5) Refined diagnostic protocols using culture- and nonculture-methods,
(6) Revealing natural ecological niche of the species,
(7) Experimental set-up of routes of airborne transmission including hijack
with Aspergillus conidia,
(8) Exploring possibilities of development of P. boydii as a biomarker
for environmental pollution.
Steering committee: Sybren de Hoog, Johannes Rainer, Juan
Rodriguez-Tudela.
(4) Data bank
In order to obtain materials for study covering variability of the species,
a pan-European surveillance system is mandatory. A web-based data base will
be built up and made accessible for all participants for streamlining formatted
data management and safeguarding of strains through central collections. The
collection will be largely virtual: all data on strains will be stored centrally,
but the strains do not need to be stored centrally. Central storage is recommended
for strains that are at risk to be lost, such as those isolated during patient
surveillance in hospitals, where the infrastructure for long-term preservation
may be absent. Francoise Symoens (IHEM, Brussels) is prepared to store all
threatened strains and smaller collections, and to make working collections
available to all participants of the network. All participants will share their
strains with any other participant freely.
With any
research in the network, we will take sets of reference strains into account,
as strains may have a different status. The nomenclatural type
strains (i.e. first strains on which species descriptions were
based) are available at CBS. We will select sets of methodical
reference strains, in order to enhance comparability of research
outcome. It is recommended to include these strains in any study. The set will
be selected on (a) genetic diversity, and (b) strains that were used in laborious
experiments, such as animal experiments or phagocytosis assays.
Aims: Building a central, web-accessible information centre
aupporting workers in themes (1-3) above.
Expected practical outcome: General purpose data bank.
Specific tasks:
(1) Establishment of a webdatabase accessible for all the participants.
(2) Distribution of reference strains for research purposes and long term preservation
of the clinical isolates no preserved in hospital centres,
(3) Preparation of a form enhancing deposition of strains in data base and
one of the culture reference centres.
Steering committee: Vincent Robert, Francoise Symoens, Regine
Horré.
Sybren de Hoog
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