Pathogenic Fungi Flashcards
Fungi
– Fungi can be single-celled yeasts or hyphae-forming
mold.
▪ hyphae eventually intertwine to form visible
masses called mycelia.
Dimorphic
Some pathogenic fungi are dimorphic, meaning they
can be either molds or yeasts (Candida albicans for
example)
▪ typically dictated by environmental factors, such
as temperature and moisture level.
No. of fungal species that cause disease
50
Mechanisms in which fungi can cause disease
– inappropriate immune responses
▪ produce potent allergens, triggering asthma attacks or other hypersensitivity reactions e.g. aspergillus, cladosporium and penicillium.
– mycotoxins (e.g.. Aflatoxins, Ergot Alkaloids made by Claviceps sp.)
– infections (mycoses)
▪ superficial
▪ subcutaneous
▪ systemic
Superficial mycoses
Caused by dermatophytes
▪ Fungi that colonize the hair, skin, or nails and infect only the
surface layers
E.Superficial mycoses
Trichophyton cause infections of the feet (athlete’s
foot) and other moist skin surfaces and are quite common
Subcutaneous mycoses
Fungi colonize deeper layers of skin
-Tend to be more serious than superficial fungal infections
E. Subcutaneous
▪ Sporothrix
▪ Fonsecaea
▪ Cladosporium
Systemic mycoses
Fungal growth in internal organs of the body
E. Systemic mycoses
histoplasmosis caused by Histoplasma capsulatum
cryptococcosis caused by Cryptococcus neoformans
Pre-desposing conditions for fungal infections
Systemic:
-Impaired immune system (AIDS) or taking immunosuppressive drugs
All fungal infections:
-Pregnancy and very young and old individuals as they all have a weakened immune response
-Antibiotis- Disrupt the normal microbiota which leads to fungal overgrowth
E. antibiotics causing fungal infection
Mucosal
vaginal yeast (Candida) infections are common with
antibiotic use.
Fungal infections of alveoli
-histoplasmosis, H. capsulatum microconidia
found in soil, and guano (bird or bat droppings) are inhaled and
reach the alveoli.
-In alveoli, they are digested by macrophages and survive inside the phagolysosome
-They are thermally dimorphic and transform into yeat that then grows and multiplies within the phagolysosome
-The macrophages then travel in lymph and spread disease to different organs and this spread is associated with immune disfunction
Fungal infection that causes pneumonia
Cryptococcus neoformans
-Causes pneumonia or meningitis or encephalitis in immunocompromised and AIDS patients
Entamoeba histolytica description
-a pathogenic protist transmitted to humans primarily through contaminated water and sometimes food
-anaerboic and produces resistant cysts
-causes thousands of deaths
-responsible for diarrhea and dysentry or could be asymptomatic
Entamoeba histolytica disease effects
▪ intestinal inflammation, fever, and the passage of intestinal blood and mucus, which often leads to anemia.
▪ It may become invasive; cells can invade the liver and occasionally the lungs and brain
▪ can be treated with amoebicidal drugs (e.g
nitroimidazole
Entamoeba histolytica infection mechanism
- Infection begins by ingestion of cysts
-These germinate in large intestine into active trophozites which multiplly by division within intestinal crypts
-Many conditions can alter dynamic and lead to virulence: - Trophoziites migrate through intestinal mucus and bind to epithelial cells and release proteases, lipases, and pore-forming cytolysins which kill epithelial cells
*Parasite engulfs dead cells and releases nutrients which results in intestinal ulcers and bloody diarrhoea
*Invasive strains migrate through ulcerated intestinal tissue into blood where the trophozites invade lung, skin, liver or brain
Asymptomatic carriers of E.histolytica vs individuals with dysentry
Asymptomatic shed high numbers of cysts while dysnety individuals dont
Naegleria fowleri
Known as brain eating amoeba
– A free-living amoeba found in soil and water runoff; exists in a trophozoite, flagellated and cyst form.
– Infections usually result from swimming in warm, soil contaminated natural water sources (e.g., hot springs or
lakes)
-Causes primary amebic meningoenceohalitis
how is primary amebic meningoencephalitis caused
– Enters the human body through the nose and travels along olfactory axons to the brain and feeds on astrocytes and neurons causing extensive hemorrhage and brain damage.
-drug treatment is effective only with early diagnosis
Giardia intestinalis
– flagellated anaerobic parasite
– produces highly resistant cysts (resistant to chlorination)
▪ cause of giardiasis, a common waterborne disease
Giardiasis symptoms + infectious mechanism
– explosive, foul-smelling diarrhea, intestinal
cramps, nausea, weight loss, and malaise
– many individuals exhibit no symptoms and can act as carriers
- Does not lyse cells but feeds on mucus and prevents nutrient absorbtion in small intestine and damage to intestinal microvilli
Sexually transmitted infections (STIs)
– Also called sexually transmitted diseases (STDs)
– Caused by a variety of bacteria, viruses, protists, and even fungi
– Pathogens are generally only found in body fluids from the genitourinary tract that are exchanged during sexual activity
Gonorrhea and syphillis trend
Upward trend for both disease and immergence of multi drug resistant N.gonorrhea strains
- Gonorrhea + mechanism of infection
– caused by Neisseria gonorrhoeae
– In 2016, the WHO estimated that there were 86.9 among 100? adults 15–49 years of age
- N. Gonorrhoeae is a fastidious organism that only grows well within the host, using a variety of highly evolved mechanisms for attachment, immune evasion and iron uptake
Gonorrhea symptoms in females
– symptoms in females
▪ characterized by a mild vaginitis that often goes unnoticed
▪ untreated gonorrhea can lead to pelvic inflammatory disease (an infection of the fallopian tubes, uterus, ovaries, which can lead to chronic pain, infertility, ectopic pregnancies and other complications
Gonorrhea – symptoms in males
▪ characterized by a painful infection of the urethral canal
Gonorrhea pathogenesis
-caused by the release of bacterial cell wall
fragments which are toxic to epithelial cells and activate immune cells.
-Immune activation causes tissue damage and scarring.
Syphilis
– caused by Treponema pallidum
– often transmitted at the same time as gonorrhea
– can be transmitted to the fetus during pregnancy (congenital syphilis)
– three stages: primary, secondary, and tertiary
– penicillin highly effective for primary and secondary stages.
– Before the advent of antibiotics, in the 1940’s syphilis was incurable.
Past Syphillis treatment
Paul Ehrlich and Sahachiro Hata discovered arsenic based compound called Arsephenamine which was marketed as Salvarsan
- first example of drug with a specific therepeutic effect to be created based off theoretical considerations
- Most widely prescribed drug and most effective in treating syphillis until penicillin was developed in 1940
Primary syphilis
-appears 10 to 90 days after exposure to the infection
-comprises a painless, indurated ulcer (chancre) at the site of inoculation with
the T. pallidum.
-These lesions resolve without treatment in 3-6 weeks.
-Regional lymph node swelling is common and consists of rubbery lymph nodes.
Secondary syphilis
-appears 2 to 8 weeks after the disappearance of the chancre
-has multiple systemic manifestations including rashes and flu-like symptoms.
- Individuals are highly contagious at this point.
-Untreated primary or secondary syphilis is followed by an early latent phase
(one year or less later on) or late latent phase (over one year) and is characterized by positive serologic tests but negative clinical manifestations.
Tertiary syphilis
-late symptomatic syphilis that can manifest months or years after the initial infection
-cardiovascular syphilis, neurosyphilis, or
gummatous syphilis (infiltration of any organ and its subsequent destruction).
Chlamydia trachomatis
-Total infection significantly outnumber gonorrhea making it most prevelant STI in world
-Often asymptomatic but causes pelvic inflammatory syndrome in women
-Obligate intracellular parasites that form elementary bodies and reticulate bodies
Types of chlamydia infections
– nongonococcal urethritis (NGU)
– lymphogranuloma venereum (LGV)
Trichomonas vaginalis
-Eu parasite
– flagellated anaerobic parasite, which feeds on leukocytes and bacteria within the vagina
– has hydrogenosomes in place of mitochondria
– transmitted person-to-person by sexual intercourse
– can survive on moist surfaces like and can be transmitted by toilet seats, sauna benches and towels
-Infects over 100 million people anually
T. Vaginalis in males
– asymptomatic in males, although it can cause prostatitis and urethritis
T.Vaginalis in females
– vaginal discharge, itching, and burning in women
T. Vaginalis treatment
antiprotozoal drug metronidazole used in treatment
Pathogenicity of T.vaginalis
-Virulence factors that facilitate adhesion to vaginal epithelial cells: AP65, AP51, AP33 and AP23
-Cysteine proteases facilitate both adhesion and damage ECM which leads to inflammation, intense itching and thick white or green discharge
-Inflammation can increase susceptibility to HIV-1 infection
-Also effects pregnancy by causing complications like preterm delivery, low birth weight and increased feotal mortality
