2. Opportunistic Mycoses
• affect the immunocompromised but are rare in normal individuals
• Etiology: Omnipresent, yeasts or moulds
• Opportunistic organisms become pathogenic only when the host's
immune defenses are altered,
– Organ transplantation,
– post chemotherapy for cancer, immunosuppressive therapy,
– immunodeficient due to AIDS and congenital
immunodeficiency states
– in a chronic disease, such as diabetes mellitus, or
– during steroid or antibacterial therapy that upsets the balance
of bacterial flora in the body.
• Important cause of morbidity & mortality in hospitalized
patients.
3. Common Opportunistic Fungus
• We find the highest frequency of opportunistic fungal
infections come in the following order:
1. Candidiasis
2. Aspergillosis
3. Cryptococcosis
4. Pneumocystosis
5. Zygomycosis
4. Candidosis
• Also called Candidiasis
• Caused by C. albicans
• Habitat: normal human flora
• Normal flora : Exist in Mouth,
Gastrointestinal tract, Vagina, skin in 20
% of normal Individuals.
• Can infect Skin, Mucosa, or Internal
Organs
• Called as Yeast Like fungus
• Pathogenesis:
– colonized areas: overgrowth
– noncolonized areas: invasion
5. Systemic Candidosis
• Occurs in Patients who carry more
yeasts in Mouth, Gastrointestinal
system,
• The following predisposes a person
to systemic infection by Candida
albicans :
A) severe burns
B) broad spectrum antibiotics
C) post-operative status
D) corticosteroids
6. C. albicans
• Virulence: ability to adhere to vaginal epithelium
• Protease production: Increased Invasiveness
• Germ tube formation: Increased adherence
Clinical pictures
• C. albicans causes vaginitis - inflammation and invasion of the
vaginal mucosa, --usually acquired by sexual contact
• Usually localized in skin, mouth, nails, vagina, vulva, bronchi or
lungs but may invade the blood stream
• Most candidal infections are mucocutaneous
7. Oral Thrush produced by Candia albicans
Many cases of AIDS are suspected by observation of Oral
Cavity
9. Lab diagnosis
• Typical appearance of discharge.
• To be differentiated from other
vaginal infections- bacterial
vaginosis and trichomoniasis.
• Microscopy
– Gram staining – A rapid method
– KoH preparation
• Culture
• Germ tube test identifies
C.albicans from other
Candida species.
• Molecular Methods
– PCR
10. CRYPTOCOCCOSIS
• Fungal disease caused by an encapsulated yeast
Cryptococcus neoformans,
• 2nd most common fungal infection after candidiasis in
HIV - infected individuals.
• Isolated from pigeon nests, droppings, old buildings &
nitrogenous soil - Creatine favour the growth.
12. Pathogenesis
• Infection occurs by inhalation, but sometimes through skin or
mucosa.
• Weakening of immune system leads to reactivation & dissemination
to CNS and other sites.
• Seen in HIV +ve patients when CD4+ count falls below 200 cells /
mm3
• Extra pulmonary cryptococcosis is one of the AIDS – defining
disease.
• Clinical types :
1. Pulmonary
2. Extrapulmonary – CNS, viscera, bones & skin
Cryptococcal meningitis is the most serious type of infection,
resembles TB and is often seen in AIDS pts.
13. Laboratory Diagnosis
• Specimen – Serum, CSF, body fluids
• Direct examination
• Wet mount:
– India ink - budding yeast cells
– Gram’s stain - Gram +ve budding yeast
cells
• Culture
– SDA - highly mucoid, cream to buff
colored.
– Birdseed (Niger seed) agar – selective
media . Brown colored colonies due to
melanin production.
• Serology
– Crypto LA test – Ag detection in
Serum, CSF & Urine
14. Aspergillosis
• Caused by aspergillus spps
• Since Aspergillus species are many and are widespread in soil, air,
and decaying vegetable matter many person are heavily exposed
to inhalation of spores.
• Imp. species –
• 1 A.fumigatus
• 2 A.niger
• 3 A.flavus
• Infection occurs by
- Inhalation of conidia
- Direct entry through wounds or during surgery.
16. Pathogenesis - varied clinical presentations
• The spectrum of human disease caused by Asperagillus ranges from
allergy to disseminated infection.
• may develop IgE. against Aspergillus and present with allergic
condition. Example, asthma
• Non-invasive colonization:- Aspergillus can colonize a pre-existing
lung cavity e.g., tuberculosis, forming fungus ball or aspergilloma.
• Invasive aspergillosis
– may occur in severely immunocompromised patients, organ transplant
recipients,.
– Patients under corticosteroid therapy and patients with leukaemia.
• Toxin production
– e.g. aflatoxin of Aspergillus flavus is carcinogenic; cause liver cancer
and necrosis.
18. What is a Mycotoxin?
• Secondary metabolites (chemicals) of a fungus that produce
toxic results in another organism.
• Mycotoxin is a toxin produced by a fungus under special
conditions of moisture and temperature.
• are toxic substances produced by fungi (molds) growing on
crops/grains in the field or in storage.
• Cytotoxic: disrupt cell structures such as membranes, and
processes such as protein, DNA, and RNA synthesis.
19. Mycotoxicoses
• Some fungi produce toxic substances that poison a person
who ingest them.
• Present major problems for clinicians.
• Diseases produced by mycotoxins are difficult to diagnose.
• They are bizarre molecules with molecular weight 50 - >500.
• Such small molecules induce no response in human immune
system !
• Major danger of mycotoxin in diet is our inability to detect
them biologically.
20. Mycotoxicosis
Three major genera of molds;
– Aspergillus,
– Penicillium,
– Fusarium
• Mold contamination can occur in the field as well as during
harvest, processing, transportation and storage.
• Toxigenic molds are major problems in agriculture products such as
grains, cereals, nuts and fruits.
• Mycotoxins are highly stable and are difficult to destroy by
traditional food processing conditions
22. Mycotoxicosis
Three general mechanisms of mycotoxin action are described
Mutagenic, teratogenic, carcinogenic
Mutagenic action,
toxin binds to DNA, especially the liver mitochondrial DNA
resulting in point mutation , addition or substitution in DNA and
affect liver function (hence hepatotoxic).
Teratogenic action leads to birth defects
The carcinogenic effect cause irreversible defects in cell
physiology resulting in abnormal cell growth and metastasis.
In recent years, the importance of mycotoxins has been highlighted for
their potential use as weapon for bioterrorism.
23. Aflatoxicosis
Aflatoxicosis is primarily
a hepatic disease.
Aflatoxin B1 and Tumor
Induction
•Aflatoxin (Aspergillus flavus toxin) is produced by
•Aspergillus flavus and A. parasiticus
