Eukaryote

Question 1

Bacteria v. Eukarya

Answer 1

1. absence (prokaryote) or presence (eukaryote) of a nucleus is the defining characteristic
2. Cell wall is always composed of carbohydrates, in bacteria peptidoglycan, in plants cellulose, Fungi chitin
3. Having organelles is a defining features of eukarya, rare in bacteria

Question 2

Defining characteristics of Animals v., Protozoa v., Fungi

Answer 2

Animals

• Cellularity: Multicellular
• Reproduction: Sexual or Asexual
• Membrane Sterol: Cholesterol
• Cell Wall: No
• Organ Systems: Yes -> defining characteristic

Protozoa
- Cellularity: Unicellular
- Reproduction: Asexual or Sexual
- Membrane Sterol: cholesterol is the dominant sterol
- Cell Wall: No
- Organ Systems: No

Fungi
- Cellularity: Unicellular or Multicellular. Unicellular fungi → Yeast. Multicellular fungi → Mold
- Reproduction: Asexual or Sexual
- Membrane Sterol: Ergosterol (targeted by antifungal drugs)
- Cell Wall: Yes
- Organ Systems: No

Question 3

Example Animal Microorganisms

Answer 3

All Helminths (worms)
la lombriz

1. Ascaris lumbricoides
   - Type: Nematode (roundworm)
   - Disease: Ascariasis (intestinal obstruction)
2. Enterobius vermicularis
   - Type: Nematode (pinworm)
   - Disease: Pinworm infection / Enterobiasis (perianal itching, especially in children)
3. Necator americanus
   - el anquilostoma
   - Type: Nematode (hookworm)
   - Disease: Hookworm infection / Necatoriasis (anemia, fatigue)
4. Taenia solium
   - la solitaria / la tenia
   - Type: Cestode (tapeworm)
   - Disease: Taeniasis (intestinal), Cysticercosis (brain/organ infection from larvae)

Trichophyton rubrum -> mold -> ringworm

Question 4

Characteristics of Helminths

Answer 4

Las lombriz
- Posses multiple organ systems, but not all species have all systems, somes species are missing some systems or have a very simplified system -> can be a distinguishing characteristic between species
- Life cycles vary between simple to complex
- Less common and less problematic in temperate regions

Reproductions
Sexual reproduction common:
Dioecious: Male and female organs in separate individuals -> the species has a male and female sex
Monoecious: Male and female organs in the same individual -> tapeworm

Some organisms can undergo asexual reproduction during certain lifestages

Question 5

Asexual vs Sexual reproduction

Answer 5

Sexual Reproduction:
- involves two gametes: sperm and egg
- Offspring are genetically diverse
- Requires fertilization
- Occurs in both dioecious and monoecious organisms

Asexual Reproduction
- Offspring are genetically identical (clones) of parent
- No gametes or fertilization involved

Question 6

Characteristics of Roundworms

Answer 6

Nematodes
1. Fully intact digestive system -> mouth to anus
2. Dioecious -> separate male and female worms

Examples
1. Ascaris lumbricoides → Ascariasis
2. Enterobius vermicularis → Pinworm, Enterobiasis (most common in U.S.)
3. Necator americanus → Hookworm, Necatoriasis -> endemic to the SE US. Can make you lethargic, may have contributed to our stereotypes of southerners. Infect barefoot individuals by biting and entering through foot.

Question 7

General Characteristics of Tapeworms

Answer 7

Cestodes
1. Lack digestive system
2. Monoecious

Example
1. Taenia solium -> pork tapeworm -> pork intermediate species
- Common in: Areas where undercooked pork is eaten
- Disease: Taeniasis (intestinal tapeworm)
- Cysticercosis (larvae can invade human tissues — can be severe, especially in the brain)

2. Taenia saginata -> beef tapeworm -> beef intermediate species
   - More common than T. solium in many regions
   - Disease: Only causes taeniasis (intestinal infection, generally milder)
   - No cysticercosis risk (does not form larval cysts in humans)

Question 8

Physical characteristic of tapeworm

Answer 8

strobila
- body of tapeworm
- Long, flat, ribbon-like structure
- Can grow to meters in length

proglottids
- repeating segments that constitute body
- Older proglottids are larger and located at the tail end
- New segments are added at the scolex end
- Each mature proglottid contains both male and female reproductive organs → tapeworms are monoecious.
- Once fertilized, proglottids become gravid (filled with eggs), break off, and exit via the host’s feces to continue the cycle.

Scolex
- Specialized attachment structure at one end
- Has hooks (made of hardened chitin-like material) and suckers (muscular structures for attachment)
- Function: Attaches to intestinal wall and resists peristalsis
- Marks the youngest part of the tapeworm

Question 9

Describe Taenia solium / Taenia saginata lifecycle

Answer 9

1. Eggs released
   Humans (definitive host) pass eggs or gravid proglottids in feces.
   Contaminate the environment (soil, water, vegetation).
2. Intermediate host ingests eggs
   Pigs / cows (intermediate host) eat contaminated food or water.
   Eggs hatch into oncospheres inside the pig’s / cow’s intestine.
3. Larvae migrate
   Oncospheres penetrate the intestinal wall.
   Travel via blood to muscles, where they develop into cysticerci (larval cysts).
4. Humans ingest cysticerci
   Eating undercooked or raw pork with cysticerci infects humans.
   Larvae evaginate in the small intestine.
5. Scolex attaches
   The scolex (head) of the tapeworm attaches to the intestinal wall.
   Matures into an adult worm.
6. Adult worm develops
   Grows in the small intestine, producing proglottids that generate new eggs.
   Cycle continues when eggs are excreted again.

Humans = Definitive host (host adult worm)

Pigs = Intermediate host  for Taenia solium -> risk of cysticercosis 

Cows = Intermediate hosts for Taenia saginata -> no risk of cysticercosis

oncospheres are the early larval stage, cysticercus the latter. Cysticercus is a fluid-filled cyst with an invaginated scolex. Oncospheres develop in intestine, cysticercus found in host tissue

Question 10

Diseases of Taenia solium

Answer 10

1. Taeniasis - most common
   - Humans are the definitive host
   - caused by ingestion of tapeworm larva (cysticerci) in muscle tissue of food animal
   - the mature tapeworm lives in the gut
   - Symptoms: Often mild or asymptomatic; may include abdominal discomfort, nausea, or visible proglottids in stool.
   - easily treatable
2. Cysticercosis
   - Humans as accidental intermediate host
   - Caused by ingestion of tapeworm eggs
   - Cysticerci live in human tissue
   - Symptoms: Depends on location; may involve muscle nodules, pain, or skin lumps.
   - treatable
   - Long-term effects: May cause scarring or calcified cysts in tissue.
3. Neurocysticercosis
   - Cysticercosis of the brain
   - symptoms: Seizures, headaches, neurological deficits
   - seizures may persist long-term, brain scarring or damage can be permanent

Question 11

Protozoa

Answer 11

• unicellular
• non-photosynthetic
• motile - Flagella, cilia, or pseudopodia -> the majority of protozoa are mobile during trophozoite stage. Cysts are typically non-motile. Historically motility was used to classify (ex/ flagellates -> flagella, ciliates -> cilia, amoeboids -> pseudopodia, apicomplexans -> gliding (non-motile forms)
• Organelles may be unique, modified, or missing (diverse adaptations)
• Reproduction: Can be asexual, sexual, or both, Some species have separate sexual and asexual life cycles
• Lifecycles may be complex with asexual and sexual reproductive steps and multiple hosts

Question 12

Life stages of Protozoa

Answer 12

1. Trophozoite
   - stage that occurs in ALL protozoa
   - Vegetative form: organisms are metabolically and reproductively active, are motile. During this stage they feed, grow, and reproduce
2. Cyst
   - Not found in all protozoa
   - a dormant state
   - cysts have a higher (outside the host) resistance compared to trophozoite

In many intestinal protozoa like Entamoeba histolytica or Giardia lamblia, the cyst is the infective stage 

BUT

in some protozoa, like Trichomonas vaginalis, do not form cysts — transmission occurs via trophozoite during direct contact 

Question 13

Motility types protozoa

Answer 13

1. Cilia
   - Structure: Many short, hair-like projections covering the cell
   - Movement: Coordinated beating of cilia propels the organism through liquid. Movement is fast and smooth
2. Pseudopodia
   - Structure: Extensions of cytoplasm called pseudopods (“false feet”)
   - Movement: Crawling motion by flowing cytoplasm (amoeboid movement). Movement is flexible, slow, shape-shifting
3. Flagella
   - Structure: One or a few long, whip-like appendages
   - Movement: Rotational or whip-like motion of the flagellum pulls the cell forward

Motility is closely linked to life cycle stage and function -> trophozoites are usually the motile form

Question 14

Example groups of protozoa

Answer 14

1. Amoebozoa
   A group of protozoa that move and feed using pseudopodia (temporary projections of cytoplasm).
   
   • Protozoa that move and feed using pseudopodia
   • Often free-living, but some are parasitic
   • Example species: Entamoeba histolytica → amebic dysentery
2. Apicomplexa
   A group of obligate intracellular parasitic protozoa characterized by an apical complex used to invade host cells.
   
   • Non-motile in adult form. It lacks flagella and cilia but exhibits gliding motility, a unique form of movement using its actin-myosin cytoskeleton and secretory organelles (micronemes and rhoptries). functionally motile, but structurally non-motile (i.e., they don’t have classic motility structures).
   • All possess an apicoplast (organelle from secondary endosymbiosis)
   • Complex life cycles with sexual and asexual stages
   • Example species:
     
     1. Plasmodium falciparum → malaria
     2. Cryptosporidium parvum → cryptosporidiosis
     3. Toxoplasma gondii → toxoplasmosis
3. Excavata
   A diverse group of protozoa, many of which have a feeding groove (“excavated”) and use flagella for movement.
   
   • Often anaerobic or have modified mitochondria
   • Many are intestinal parasites or live in other low-oxygen environments
   • Example species:
     
     1. Giardia duodenalis → giardiasis
     2. Trichomonas vaginalis → trichomoniasis (STD)
     3. Naegleria fowleri → primary amebic encephalitis

Question 15

Lifecycle toxoplasma gondii

Answer 15

• Oocyst → Cyst stage
  
  • Formed by sexual reproduction in cats
  • Shed in feces; survives in environment
  • Infective to intermediate hosts (e.g., humans, rodents)
  • Contains sporozoites
• Sporozoite → Trophozoite stage
  
  • Released from oocyst after ingestion
  • Invades host intestinal epithelium
  • Initiates tissue infection and conversion to tachyzoite
• Tachyzoite → Trophozoite stage
  
  • Rapidly dividing, active stage
  • Disseminates through blood/lymph
  • Responsible for acute infection
  • Converts to bradyzoite in chronic phase
• Bradyzoite → Trophozoite stage
  
  • Slowly dividing, semi-dormant
  • Found within tissue cysts
  • Dominates chronic infection phase
  • Reactivates to tachyzoite in immunosuppressed hosts
• Tissue cyst → Cyst stage
  
  • Contains bradyzoites
  • Found in brain, muscle, and retina
  • Infective to cats when consumed in prey

Question 16

Lifecycle Cryptosporidium parvum

state disease caused

Answer 16

Cryptosporidiosis –Apicomplexa

1. Ingestion of thick-walled oocyst
   
   • Found in contaminated water, food, or recreational water
   • Oocyst = cyst stage (infective, environmental form)
2. Excystation in small intestine
   
   • Oocyst releases sporozoites (trophozoite stage)
   • Sporozoites invade intestinal epithelial cells

3a. Asexual reproduction (merogony)
- Sporozoites develop into trophozoites
- Trophozoites undergo multiple rounds of asexual replication → produce merozoites (trophozoite stage)
- Merozoites infect new epithelial cells → may cause auto-infection

3b. Sexual reproduction (gametogony)
- Some merozoites differentiate into male and female gametes
- Gametes fuse → form zygote
- Zygote develops into two oocyst types:
- Thick-walled oocyst: cyst stage; excreted in feces → infects new hosts
- Thin-walled oocyst: cyst stage; remains in host → bursts internally → releases sporozoites → auto-infection

Summary of Reproduction Outcomes:

• Asexual reproduction
  
  • Maintains infection within the same host
  • Involves trophozoite stages (sporozoites, trophozoites, merozoites)
• Sexual reproduction
  
  • Produces oocysts (cyst stage)
  • Thick-walled oocysts: lead to transmission to new hosts
  • Thin-walled oocysts: lead to auto-infection in the current host

Question 17

Describe Giardia duodenalis

Answer 17

Giardiasis – Giardia duodenalis
Flagellated protozoan – Excavata group

Life Stages:
1. Cyst stage (infective, diagnostic)
- Formed by encystment in the large intestine
- Released in feces along with trophozoites
- Trophozoites perish outside the host; cysts survive
- Cysts persist in cool, moist, rainy environments
- Ingested via contaminated water, food, or fecal-oral contact
- Excystment occurs after stomach, in the small intestine

2. Trophozoite stage (active, symptomatic)
   
   • Arises after excystment; remains inside host only
   • Reproduces asexually by via mitosis
   • Attaches to intestinal mucosa using a ventral adhesive disc
   • Causes malabsorption, greasy diarrhea, flatulence

Clinical Notes:
- Most common intestinal protozoan in the U.S.
- Fecal-oral transmission (esp. untreated water)
- Common in campers, daycare centers, travelers

Structure and Features:
- 4 pairs of flagella → motility + attachment
- Adhesive disc → attaches to intestinal epithelium
- The disc + flagellar motion help create a negative pressure (“vacuum”) that keeps the organism anchored to the intestinal wall.
- 2 nuclei, symmetrically placed
- No true mitochondria → has mitosomes
- Strict anaerobe – relies on anaerobic metabolism

Question 18

Lifecycle Giardia duodenalis

Answer 18

1. Encystment occurs in the large intestine of host
   Trophozoites form protective cysts before being passed in stool
2. Cysts and trophozoites are released in feces
   Only cysts survive outside the host
   Trophozoites perish quickly in the environment
3. Cysts persist in the environment
   Especially in cool, moist, rainy conditions (e.g., soil, water, surfaces)
   Can survive for long periods
4. Cyst is ingested by a new host
   Often via contaminated water, food, hands, or surfaces
5. Excystment occurs after cyst passes through the stomach -> Releases trophozoites, which attach to intestinal lining and reproduce

Have adhesive disk on ventral surface.
Motile via flagella. Flagella also create a vaccume between ventral surface and host.
No mitochondria - have mitosome
Two nuclei

Question 19

Name of Fungal diseases

Answer 19

Mycosis refers to any disease caused by fungal infection, ranging from superficial (e.g., ringworm) to systemic (e.g., cryptococcosis).

mycoses -> plural

mycosis -> singular

Question 20

Describe Yeast Morphology

Answer 20

• unicellular
• Cells are typically oval to round
• Yeasts do not form hyphae, distinguishing them from molds
• Yeasts most commonly reproduce asexually in a process called budding. - produces spores

Question 21

Describe Mold Morphology

Answer 21

• multicellular
• long tubular filaments of interconnected cells called hyphae (hypha singular). Hyphae often give mold its “fuzzy” appearance.
• Mass of hyphae is called a mycelium

Question 22

Dimorphic Fungi

Answer 22

• can grow as either mold or yeast, depending on environmental temperature
• Grow as mold outside human host (cooler temps)
• Convert to yeasthen inside the human host (at 37°C)
• Yeast form is associated with invasion and dissemination in the body
• Dimorphism is a COMMON trait of primary (true) pathogens — fungi that can cause disease in healthy individuals
• Not typical of opportunistic pathogens, which require a compromised immune system

Question 23

Describe Coccidioides immitis

Answer 23

• Primary pathogen
• Dimorphic: mold in environment, spherule in host
• Causes coccidioidomycosis (Valley Fever)
• Found in dry soils, especially in Arizona and southern California
• Transmitted by inhalation of spores carried in dust
• Can cause pulmonary infection or disseminated disease
• Key Features:
  
  • No yeast phase: spherules are unique to Coccidioides
  • No human-to-human transmission
  • Classified as a primary pathogen

Question 24

Cryptococcus neoformans

Answer 24

Cryptococcosis is a fungal disease caused by Cryptococcus neoformans

• Type: Dimorphic fungus
• Pathogenicity: Primary pathogen (can infect immunocompetent hosts, but more severe in immunocompromised)
• Transmission: Inhalation of spores from soil contaminated with bird droppings
• Virulence factor: Thick polysaccharide capsule — protects against phagocytosis and promotes survival in macrophages. Survive and replicate within the phagolysosome.
• Diagnosis: India ink stain reveals capsule as a clear halo around yeast
• Disease: Causes cryptococcosis, often presenting as pneumonia and potentially spreading to the central nervous system, leading to cryptococcal meningitis

Question 25

**Trichophyton rubrum** - name diseases

Answer 25

- *Opportunistic pathogen* - **Mold (filamentous fungus)** - Reproduces **asexually via conidia (spores)** - Causes **tinea (ringworm) infections** - Spread by **direct contact** or **fomites** (*contaminated objects like towels, shoes, floors*) - Thrives in **moist, warm environments** - **Tinea pedis** → *Athlete’s foot* - **Tinea cruris** → *Jock itch* - **Tinea corporis** → *Ringworm of the body* - **Tinea capitis** → *Scalp ringworm* - **Tinea unguium** (aka **onychomycosis**) → *Nail fungus*

Question 26

**Candida auris**

Answer 26

- *Opportunistic pathogen* - Causes **invasive infections**, especially in healthcare settings -> **Nosocomial** - Notably **multidrug-resistant**, complicating treatment - Can **persist on surfaces**, leading to nosocomial outbreaks - Requires **specialized laboratory methods** for accurate identification - contain β-glucans but are tightly masked by mannan-rich outer layer so do not trigger strong immune response.

Question 27

**Candida albicans**

Answer 27

- *Opportunistic pathogen* - contains β-glucans in cell wall. β-glucans exposed especially under stress or during "hyphal" growth -> elicit immune response - transitions between **yeast** and **hyphal** forms - Causes **candidiasis** -> fungal vaginitis, oral thrush, dermatitis, fungemia, onychomycosis - Part of normal **human microbiota**, but can overgrow when host defenses are compromised (dysbiosis) - **Hyphal form** is associated with tissue invasion and virulence - Typically **susceptible** to antifungals, but resistance can develop

Question 28

Amebic dysentery

Answer 28

- *Cause:* - Caused by the protozoan *Entamoeba histolytica* - Spread via ingestion of **cysts** in contaminated food or water (fecal-oral route) - *Life Cycle Summary:* 1. **Cysts** survive stomach acid → reach small intestine 2. Excystation releases **trophozoites** 3. Trophozoites migrate to **colon**, multiply, and form **ulcers** 4. Some trophozoites **encyst** and are shed in feces; others may enter bloodstream → liver → **liver abscess** 5. As a protozoan parasite, *E. histolytica* reproduces asexually through **mitosis**. - *Symptoms:* - **Bloody, mucus-filled diarrhea** - Abdominal cramping and pain - Possible fever and **liver tenderness** if extraintestinal spread occurs - *Name Breakdown:* - **Entamoeba** = “internal amoeba” (*enta* = within, *amoeba* = shape-shifting cell) - **Histolytica** = “tissue-destroying” (*histo* = tissue, *lytica* = lysis)

Question 29

Fungemia

Answer 29

Fungemia is the presence of fungi (usually *Candida*) in the bloodstream, a serious condition often seen in hospitalized or immunocompromised patients.

Question 30

Fungal vaginitis

Answer 30

**Fungal Vaginitis (Yeast Infection)** - Vaginal infection caused **primarily by *Candida albicans*** - **~85–90% of cases** - forms pseudohyphae in tissue - Overgrowth of normal vaginal flora - **Symptoms**: - Vaginal **itching**, **burning**, **thick white discharge**, **discomfort** - **Risk factors**: - Antibiotics, diabetes, pregnancy, immunosuppression, hormonal changes ``` C. albicans It exists in yeast form (round/oval single cells) and can form pseudohyphae and true hyphae under certain conditions. This is sometimes called "pleomorphic" or "polymorphic", rather than classic dimorphism (like Histoplasma, which has distinct mold vs yeast phases depending on temperature). ```

Question 31

Giardiasis

Answer 31

Giardiasis is a diarrheal illness caused by the protozoan *Giardia duodenalis*. - Spread via contaminated water, it involves both cyst and trophozoite stages.

Question 32

Histoplasmosis

Answer 32

Histoplasmosis is a fungal infection caused by *Histoplasma capsulatum*. Transmitted by inhalation of spores from bird or bat droppings. **Histoplasma capsulatum** - *Type:* Dimorphic fungus (mold in environment, yeast in tissue). - *Transmission:* Inhalation of microconidia from soil contaminated with bird or bat droppings, especially in river valleys (e.g., Ohio & Mississippi River). - *Disease:* Causes **histoplasmosis**, a respiratory infection that may resemble flu or pneumonia; can become disseminated in immunocompromised individuals. - *Key Features:* Converts to yeast form at body temperature; survives and multiplies inside **macrophages**.

Question 33

Malaria

Answer 33

**Protozoan Disease** - Caused by the protozoan *Plasmodium falciparum*. Belongs to phylum **Apicomplexa** -> obligate intracellular parasites / non-motile - Infects **liver cells** first, then **red blood cells** - Transmitted by environmental exposure to infected blood (e.g., via mosquitoes

Question 34

Nosocomial infection

Answer 34

A nosocomial infection is acquired in a hospital setting, often caused by resistant pathogens like MRSA or *Candida auris*. hospital conditions allow opportunistic pathogens — microbes that don't usually cause disease in healthy individuals — to cause serious infection

Question 35

Onychomycosis

Answer 35

- *Definition:* Fungal infection of the nails (toenails or fingernails). 1. **Caused by *Trichophyton rubrum*** - Most common cause of onychomycosis (~80–90% of cases) - Affects **toenails more often** than fingernails - Invades **keratinized nail tissue** - Classified as a **dermatophyte** (mold-like fungus that infects skin, nails, and hair) 2. **Caused by *Candida albicans*** - Less common overall, but more often affects **fingernails** - Associated with **frequent water exposure**, hand immersion, or **immunosuppression** - *C. albicans* is a **yeast**, not a dermatophyte - *Note:* Both forms require antifungal treatment, but correct identification is important for choosing therapy

Question 36

Oral thrush

Answer 36

Oral thrush is a fungal infection of the mouth caused by *Candida albicans*; it appears as white plaques on the tongue and mucosa.

Question 37

Saprophyte

Answer 37

A saprophyte is an organism, usually a fungus or bacterium, that feeds on and decomposes dead organic matter.

Question 38

Toxoplasmosis

Answer 38

**Toxoplasmosis** - *Cause:* Caused by the protozoan parasite *Toxoplasma gondii*. - *Transmission:* - Ingestion of oocysts from **cat feces** (litter boxes, soil) - Ingestion of tissue cysts in **undercooked meat** - **Congenital transmission** (mother to fetus) - Rarely through organ transplant or blood transfusion - *Disease:* - Often **asymptomatic** in healthy individuals - Can cause **flu-like symptoms** (fever, lymphadenopathy, fatigue) - In **immunocompromised patients** (e.g., AIDS), it can cause **severe encephalitis** - In **pregnancy**, may lead to **congenital toxoplasmosis** (brain and eye damage in fetus) - *Key Features:* - Forms **tissue cysts** in brain, muscle, and other organs - Diagnosed via **serology** or PCR; visible on imaging in CNS infections - *Treatment:* - **Pyrimethamine + sulfadiazine + folinic acid** for active disease - No treatment needed for asymptomatic, immunocompetent individuals

Question 39

Trichomoniasis

Answer 39

**Trichomoniasis** - *Cause:* Caused by **Trichomonas vaginalis**, a flagellated protozoan parasite. - *Transmission:* **Sexually transmitted**; no cyst stage—transmitted as trophozoites. - *Disease:* - In **females**: Vaginal itching, frothy yellow-green discharge, burning, and discomfort during urination or intercourse. - In **males**: Often asymptomatic, but may cause urethritis or prostatitis. - *Key Features:* - Motile **trophozoite** stage visible in wet mount microscopy - Lacks a cyst stage - Confined to the **urogenital tract** - *Diagnosis:* Microscopy, antigen tests, or nucleic acid amplification (NAAT) - *Treatment:* **Metronidazole** or **tinidazole** (single dose), treat both partners to prevent reinfection

Question 40

Describe Naegleria fowleri

Answer 40

- *Type:* **Free-living amoeboid protozoan** in the group Excavata - *Transmission:* trophozoite Enters via the **nose** when swimming in **warm freshwater** (lakes, hot springs, poorly chlorinated pools) - *Life Cycle:* - Exists in **three forms**: - **Cyst** – dormant; forms only in harsh conditions - **Trophozoite** – **infectious and replicative** form; **not flagellated** - **Flagellated form** – temporary, non-replicative; found in water - **Trophozoites** migrate along the **olfactory nerve** to the brain - Reproduces **asexually via mitosis** (binary fission) - Primarily **aerobic**, but can tolerate **low-oxygen environments** - *Disease:* - Causes **Primary Amebic Meningoencephalitis (PAM)** - Rapidly progressive and often fatal **brain infection** - Symptoms: headache, fever, stiff neck, confusion, seizures - Death usually occurs within days if untreated

Question 41

Describe Entamoeba histolytica

Answer 41

**Entamoeba histolytica** - *Type:* **Protozoan parasite** in the group Amoebozoa - *Transmission:* **Fecal-oral route** via ingestion of mature cysts in contaminated food or water - *Life Cycle:* - Ingested **cysts** pass through the stomach and release **trophozoites** in the intestine - Trophozoites multiply and may invade the intestinal wall or spread via blood to the liver - Some trophozoites encyst and are passed in feces - *Disease:* - Causes **amebic dysentery** (bloody diarrhea, abdominal pain) - Can lead to **liver abscesses** and extraintestinal disease in severe cases

Question 42

Describe Giardia duodenalis

Answer 42

**Giardia duodenalis (also known as G. lamblia or G. intestinalis)** - *Type:* **Flagellated protozoan parasite** in the group Excavata - *Transmission:* **Fecal-oral route**, commonly through ingestion of cysts in contaminated water or food - *Life Cycle:* - Ingested **cysts** pass through the stomach and release **trophozoites** in the small intestine - Trophozoites attach to the intestinal wall with a ventral adhesive disc - Some trophozoites encyst before being passed in feces - Both **cysts** (infectious) and **trophozoites** (non-infectious) may be excreted - *Disease:* - Causes **giardiasis**, marked by **watery diarrhea**, gas, abdominal cramps, and **foul-smelling stools** - Does **not invade tissue**; symptoms result from malabsorption and inflammation of the intestinal lining

Question 43

Why is dimorphism adaptive for fungal pathogens?

Answer 43

- *Definition:* Dimorphic fungi can switch between **mold (mycelial) form in the environment** and **yeast form in host tissues** - *Adaptation Benefits:* - **Survival in diverse environments**: Mold form thrives at lower temperatures (soil), yeast form thrives at body temperature - **Tissue invasion:** Yeast form is better suited for spreading within host tissues - **Immune evasion:** Yeast form may avoid immune detection or resist phagocytosis - **Efficient transmission:** Mold form produces spores for dispersal in the environment - *Examples:* **Histoplasma capsulatum**, **Coccidioides immitis**, **crytosporium neoformans**

Question 44

Describe Plasmodium falciparum

Answer 44

**Plasmodium falciparum** - *Type:* **Apicomplexan protozoan parasite** - *Transmission:* Transmitted by the bite of an infected **female Anopheles mosquito** - *Life Cycle:* - **Sporozoites** enter bloodstream, travel to liver, and infect hepatocytes - Multiply to form **merozoites**, which are released into the blood - Merozoites infect **red blood cells**, multiply, and cause RBC lysis - Some develop into **gametocytes**, which are taken up by a mosquito to continue the cycle - *Disease:* - Causes the **most severe form of malaria** - Symptoms include **cyclical fever**, chills, anemia, fatigue, and **cerebral malaria** in severe cases - Destroys red blood cells and can obstruct capillaries, especially in the brain, kidneys, and lungs

Question 45

Compare Excavata, Apicomplexans, and Amoebozoa

Answer 45

1. **Amoebozoa** A group of protozoa that move and feed using pseudopodia (temporary projections of cytoplasm). - protozoa that move and feed using pseudopodia - Often free-living, but some are parasitic - Example species: *Entamoeba histolytica* -> amebic dysentery 2. **Apicomplexa** A group of obligate intracellular parasitic protozoa characterized by an apical complex used to invade host cells. - Non-motile in adult form - All possess an apicoplast (organelle from secondary endosymbiosis) - Complex life cycles with sexual and asexual stages - Example species: *plasmodium falciparum* -> malaria, *cryptosporidium parvum* -> cryptosporidiosis, *toxoplasma gondii* -> toxoplasmosis 3. **Excavata** A diverse group of protozoa, many of which have a feeding groove ("excavated") and use flagella for movement. - Often anaerobic or have modified mitochondria - Many are intestinal parasites or live in other low-oxygen environments - Example species: *giardia duodenalis* -> giardiasis, *Trichomonas vaginalis* -> trichomoniasis (STD), *Naegleria fowleri* -> primary amebic encephalitis

Question 46

Fungi

Answer 46

*Eukaryotic organisms that may be unicellular (yeasts) or multicellular (molds)* Distinguishing features: 1. Cell wall primarily composed of **chitin**. May contain other carbohydrates such as **β-glucans**. **Ergosterol** in cell membrane 2. Normally **saprophytic** 3. Use **Aerobic respiration** and/or **fermentation** to produce ATP 4. Are **haploid** for the majority of life-cycle 5. Most fungi can reproduce both sexually and asexually. Asexual is generally more common. 6. Asexual Reproduction: **Budding** small daughter cell forms from the parent, enlarges, and detaches releasing a spore. This leaves a **bud scar** on the parent cell 7. Sexual reproduction: Two haploid cells of different mating types fuse -> diploid cell -> meiosis -> produce haploid spore. ``` Fungal spores are the reproductive units of fungi, analogous to seeds in plants. They are microscopic, single-celled structures that can be produced asexually or sexually. These spores are adapted for dispersal and survival, allowing fungi to spread to new areas and survive unfavorable conditions. ```

Question 47

Fungal Dermatitis

Answer 47

- *Definition:* Superficial fungal infection of the skin (cutaneous mycosis) - *Caused by:* 1. **Dermatophytes** (e.g., *Trichophyton rubrum*) - Infect **keratinized skin**, hair, and nails - Common forms: - **Tinea corporis** (body) - **Tinea pedis** (feet) - **Tinea cruris** (groin) - **Tinea capitis** (scalp) - Lesions: scaly, ring-shaped, itchy 2. **Candida species** (especially *Candida albicans*) - Infect **moist skin folds** (e.g., armpits, groin, under breasts) - Common in infants (diaper rash) and immunocompromised - Lesions: red, moist plaques with **satellite pustules** - *Note:* Tinea infections = dermatophyte dermatitis Candidiasis = yeast dermatitis