Protozoa: Structure and Life Cycle

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Questions and Answers

What is a characteristic of primary fungal pathogens?

Always display severe symptoms in healthy individuals

Only cause infections in individuals with a weakened immune system

Require large quantities to cause infection in healthy individuals

Can cause disease in anyone, regardless of health status (correct)

Which type of mycoses infects only the outer layers of skin or hair?

Deep mycoses

Systemic mycoses

Cutaneous mycoses

Superficial mycoses (correct)

What is a common feature of cutaneous fungal infections?

They invade deeper tissues like organs

They grow within the dermis at the body surface (correct)

They are always associated with severe inflammation

They are caused by viruses

What type of agents are typically used to treat pityriasis versicolor?

Keratinolytic agents and topical imidazoles Signup and view all the answers

Which genera of fungi are responsible for cutaneous mycoses?

Microsporum, Trichophyton, and Epidermophyton Signup and view all the answers

What is the primary reason cutaneous mycoses are considered contagious?

They can spread through shared clothing Signup and view all the answers

What does the term 'tinea' refer to in fungal infections?

Dermatophyte infections with specific names for different body areas Signup and view all the answers

Which of the following does NOT describe opportunistic fungal pathogens?

They can cause severe infections in healthy individuals Signup and view all the answers

What is the primary mode of transmission for Entamoeba histolytica?

Fecal/oral route Signup and view all the answers

What form does Trichomonas vaginalis exist in?

Trophozoite form Signup and view all the answers

Which of the following characteristics is true for the cyst form of protozoa?

It is non-motile and provides protection. Signup and view all the answers

What is the leading cause of diarrhea outbreaks linked to water in the United States?

Cryptosporidium species Signup and view all the answers

What type of nutritional requirements do protozoa have?

Assimilation of organic nutrients Signup and view all the answers

When do many protozoa transition to a cyst form?

Under adverse conditions Signup and view all the answers

What is meant by excystation in the context of protozoa?

The emergence of trophozoites from cysts. Signup and view all the answers

Which of the following statements about protozoa's immuno-evasive mechanisms is true?

They consistently change their surface antigens. Signup and view all the answers

What is the primary treatment for tinea pedis?

Topical antifungals for 2-4 weeks Signup and view all the answers

What characterizes sporotrichosis?

Multiple lesions develop along lymphatic tracts Signup and view all the answers

Which of the following statements is true about systemic mycoses?

They can cause disease in healthy hosts. Signup and view all the answers

Which fungus is associated with coccidioidomycosis?

Coccidioides immitis Signup and view all the answers

What is a common characteristic of blastomycosis?

It mimics conditions like tuberculosis or lung cancer. Signup and view all the answers

Which of the following is NOT a common characteristic of histoplasmosis?

It causes immediate systemic illness in healthy individuals Signup and view all the answers

What is the typical duration for treating sporotrichosis?

3-6 months Signup and view all the answers

Which symptom is most commonly associated with tinea pedis?

Fluid-filled lesions that dry and peel Signup and view all the answers

What is essential for managing C. auris infections in hospitalized patients?

To quickly identify C. auris for proper infection control measures Signup and view all the answers

What characteristic of Candida biofilms makes them particularly difficult to eradicate?

They produce an extracellular matrix that provides protection Signup and view all the answers

Which factor contributes to the increasing antifungal drug resistance observed today?

The limited number of antifungal drug targets causing host toxicity Signup and view all the answers

What is a key reason why the removal of infected medical devices is necessary for curing Candida biofilm infections?

Biofilms are resistant to common drug therapies, requiring device removal Signup and view all the answers

What is a common complication of untreated Candida biofilm infections?

Progression to bloodstream infections and high mortality risks Signup and view all the answers

Which symptom is most characteristic of cryptococcosis?

Severe headaches and confusion Signup and view all the answers

What condition is Paracoccidioidomycosis primarily associated with?

Individuals living in Central and South America Signup and view all the answers

Which opportunistic fungi primarily affect immunocompromised individuals?

Aspergillus species Signup and view all the answers

How does cryptococcosis typically progress in infected individuals?

It begins as a mild lung infection Signup and view all the answers

What treatment method is suggested for serious Aspergillosis infections?

IV amphotericin B Signup and view all the answers

What is a common source of Cryptococcus neoformans?

Bird droppings Signup and view all the answers

What is a hallmark of infection with Cryptococcus neoformans in AIDS patients?

Chronic meningitis Signup and view all the answers

In managing severe cases of cryptococcosis, what is the approximate cure rate with proper treatment?

80-90% Signup and view all the answers

Study Notes

Protozoa

Adult Sporozoa are not motile, examples include Plasmodium and Cryptosporidium
Protozoa can infect the lumen (intestinal and urogenital) or tissues (blood and tissue)
Protozoa have simple nutritional requirements and assimilate organic nutrients
Protozoa exist in a trophozoite form (motile) or a cyst form (non-motile) when under adverse conditions
Protozoa use elaborate immuno-evasive mechanisms to avoid host immune system attack
Trophozoite is any stage in a protozoan life cycle that can ingest food
Cyst is the non-motile form protected by a distinct membrane that facilitates host-to-host transmission
Excystation is the process where the trophozoite emerges from the cyst
Intestinal Protozoa:
- Entamoeba histolytica, found worldwide (Sarcodina)
  - Transmitted via fecal-oral route, ingested cysts disintegrate in the small bowel, amebas go to the colon and live on red blood cells and bacteria
  - Causes necrosis, ulceration (bloody diarrhea), flatulence and cramping, lasting for years
  - Treatment includes metronidazole, iodoquinol, and paromomycin
  - Found in most mammals, especially bovine, cattle, cats, and dogs
- Giardia lambia, found worldwide (flagellate)
- Cryptosporidium species, found worldwide (Sporozoa)
  - Leading cause of water-linked outbreaks of diarrhea
  - Third leading cause of diarrhea associated with animal contact in the US
  - Causes include contaminated water in pools or playgrounds, infected cattle, and contact with infected individuals in child care settings
Urogenital Protozoa:
- Trichomonas vaginalis, found worldwide (flagellate)
  - Exists in trophozoite form only
  - Transmitted via intimate sexual contact
  - 10 to 25% of adult women become infected, 2 to 10% of adult men

Fungal Pathogens

Primary fungal pathogens can cause disease in any individual, regardless of health status
Opportunistic fungal pathogens are not pathogenic enough to cause disease in healthy individuals, but can infect individuals with weakened immune systems
Opportunistic fungi can cause infection in healthy individuals if enough is inhaled
Fungal Pathogenesis:
- Adhesion to mucosal surfaces
- Invasion of host tissues
- Production of extracellular products
- Evasion of the immune system

Classification of Mycoses

Mycoses are classified by the tissues they infect:
- Superficial: outside layers of skin or hair only
  - Example: pityriasis versicolor
    - Chronic, superficial infection of the outer skin caused by Malassezia furfur
    - Causes hypo- or hyperpigmented scaly lesions
    - Limited inflammation, primarily a cosmetic problem
    - Treatment includes keratinolytic agents (salicylic acid) and topical imidazoles (miconazole)
- Cutaneous: invade skin, hair, and nails (dermatophytes)
  - Caused by three genera: Microsporum sp., Trichophyton sp., and Epidermophyton sp.
  - Features:
    - Grow only in the dermis at the body surface
    - Produce enzymes to break down keratin, elastin, and collagen in skin, hair, and nails
    - Mostly troublesome, not serious
    - Millions of dollars spent annually to treat them
  - Also called tineas or ringworms:
    - Tinea corporis – non-hairy body parts
    - Tinea capitis – scalp
    - Tinea pedis – athlete’s foot
    - Tinea barbae – beard
    - Tinea cruris – jock itch
    - Tinea unguium – nails
  - The only truly contagious fungal infections
  - Examples:
    - Tinea corporis: typical “ringworm” lesions with clearing, scaly center with raised red edges
    - Tinea pedis (athlete’s foot): the most prevalent dermatophytosis in the US
      - Uncommon in children, primarily affects adults who wear shoes
      - Chronic infection of toe webs and soles
      - Fluid-filled lesions dry to itchy, crack, and peel
      - Treatment includes keeping areas dry and topical or oral antifungals (terbinafine, azoles)
- Subcutaneous: localized, enter by trauma
  - Example: sporotrichosis
    - Generally introduced by trauma
    - Caused by Sporothrix schenckii, found in soil and decaying vegetation
    - Most common in agricultural workers and gardeners
    - Also called “rose-handler’s” disease
    - Initial lesion usually on extremities
    - Multiple lesions develop along lymphatic tracts
    - Usually few systemic signs of illness
    - Treatment includes newer azole, e.g. itraconazole for 3-6 months
- Systemic: affects multiple organs/tissues or whole body
  - Often initially an infection of the lungs, spreads to other parts of the body
  - More virulent, can cause disease in healthy hosts
  - Dimorphic Systemic Mycoses:
    - Involves virulent fungi capable of causing infection in healthy people
    - Fungi overcome host defenses by changing form (mold to yeast form)
    - Primary site of infection: pulmonary following inhalation but can disseminate to other (systemic) sites
    - Geographically restricted
    - Examples:
      - Histoplasmosis: caused by Histoplasma capsulatum, endemic in the Ohio and Mississippi River valleys
        
        Most infections are asymptomatic and self limiting, immunocompromised patients can experience problems
        
        Forms localized granuloma, can disseminate, and can mimic tuberculosis
      - Blastomycosis: caused by Blastomyces dermatitidis, endemic in the Ohio and Mississippi River valleys and Missouri and Arkansas River basins
        
        Disease is also seen in horses and dogs
        
        Similar to histoplasmosis and can mimic tuberculosis or lung cancer
        
        Symptomatic infection is common
      - Coccidioidomycosis: caused by Coccidioides immitis, endemic in the southwest US, Mexico, and South America
        
        Infection is usually asymptomatic but mortality of untreated disseminated disease is ~ 50%
      - Paracoccidioidomycosis: caused by Paracoccidioides brasiliensis, restricted to Central and South America
        
        Asymptomatic infections are common
        
        General symptoms are similar to histoplasmosis and blastomycosis
        
        Disseminated disease is rare, usually oral, nasal and facial nodular ulcerative lesions and lymphadenopathy
  - Opportunistic and Systemic Fungal Infections:
    - Increasing due to:
      - Increase in immunocompromised individuals due to transplants, chemotherapy, etc.
      - Emergence of HIV/AIDS
      - Medical advances, including longer lifespans, increased survival of premature neonates, use of artificial heart valves and indwelling catheters
    - Important issue is the emergence of opportunistic pathogenic fungi previously thought to be non-pathogenic
    - More immunosuppressed hosts are more susceptible to infection from obscure fungi
    - Examples:
      - Aspergillosis:
        
        Caused by over 150 species of Aspergillus
        
        Ubiquitous in soil and plants worldwide
        
        Infection requires profound immunosuppression
        
        Generally due to inhalation of spores
        
        Patients: gardeners and farmers with underlying disease; cancer and transplant patients (90% have had chemotherapy or steroids); people with low neutrophil counts
        
        Not particularly common in AIDS patients
        
        In immunocompromised hosts, spores germinate and hyphae invade tissues
        
        Cutaneous infections usually occur at catheter sites and wounds
        
        Disseminated infections invade tissues and fill them with hyphae
        
        Treatment is IV amphotericin B, posaconazole, or echinocandin
        
        Rarely successful unless immunosuppression is reversed
      - Cryptococcosis:
        
        Most common species is Cryptococcus neoformans
        
        Not dimorphic – always a yeast
        
        Encapsulated yeast
        
        Forms titan cells that have undergone huge ploidy increase
        
        Isolated from soil (bird droppings)
        
        Hallmark infection of AIDS patients
        
        Mild infection begins in the lungs
        
        May go systemic with a predilection for the CNS
        
        Slowly-developing meningitis that may mimic brain tumor, abscess, or multiple sclerosis
        
        Symptoms include headaches, dizziness, irritability, and confusion that increase in intensity over time
        
        Treatment:
        
        Mortality rate if untreated is ~100%
        
        80-90% cure rate with treatment
        
        Amphotericin B IV ± 5-flucytosine
        
        Sometimes can switch to oral azole
      - Important to quickly identify C.auris in a hospitalized patient for appropriate infection control measures
      - Black fungus (Mucor) infections in COVID patients (India):
        
        Recognition of diagnostic gaps for laboratory diagnosis of fungal diseases
      - Fungal biofilms:
        
        Candida commonly adheres to implanted medical devices, forming a resilient biofilm resistant to high antifungal concentrations
        
        A variety of biomaterials support Candida biofilm formation (e.g. catheters and dentures)
        
        Biofilms produce extracellular matrix, promoting adherence and protecting cells from insults
        
        Matrix retains nutrients, water, and enzymes
        
        Common drug therapies do not eradicate Candida biofilms, device removal is usually necessary to cure infection
        
        If untreated, Candida biofilm infections can progress to bloodstream infections and invasive fungal infections with high mortality risks

Antifungal Drugs

Limited number of antifungal drug targets without causing host toxicity
Antifungal drug resistance, including multidrug resistance, is increasing

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Description

This quiz covers the classification, structure, and life cycle of protozoa, with a focus on sporozoa like Plasmodium and Cryptosporidium. Learn about their motility, nutritional requirements, and mechanisms to evade host immunity. Additionally, explore the differences between trophozoite and cyst forms.