Eukaryote take two Flashcards
1
Q
Amebic dysentery
A
-
Cause:
- Caused by the protozoan Entamoeba histolytica
- Spread via ingestion of cysts in contaminated food or water (fecal-oral route)
-
Life Cycle Summary:
- Cysts survive stomach acid → reach small intestine
- Excystation releases trophozoites
- Trophozoites migrate to colon, multiply, and form ulcers
- Some trophozoites encyst and are shed in feces; others may enter bloodstream → liver → liver abscess
- As a protozoan parasite, E. histolytica reproduces asexually through binary fission.
-
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)
2
Q
Animal
A
Animals are multicellular eukaryotic organisms that lack cell walls, are heterotrophic, and typically have complex organ systems and mobility at some life stage. Have cholesterol in their cell wall.
3
Q
Antimicrobial resistance
A
Antimicrobial resistance is the ability of microbes (bacteria, fungi, parasites) to resist drugs, making treatments less effective and leading to persistent infections.
4
Q
Ascariasis
A
Ascariasis is an intestinal infection caused by the roundworm Ascaris lumbricoides. Infection occurs by ingesting eggs in contaminated food or water. It can cause malnutrition and intestinal blockage.
a large intestinal roundworm that resembles an earthworm in size and shape.
roundworm = nematode
5
Q
Ascaris lumbricoides
A
Ascaris lumbricoides is a large parasitic roundworm that infects the intestines of humans. Adults live in the intestine; eggs are passed in feces and become infective in soil.
- Reproduction: Adults lay eggs that are passed in feces; eggs become infective in soil.
- Transmission: Fecal-oral route; no intermediate host.
6
Q
Budding
A
Budding is an asexual reproductive process where a new organism forms from a small projection on the parent and detaches when mature. Leaves a bud scar. Common in yeasts.
7
Q
Candidiasis
A
-
Definition:
- A fungal infection caused by Candida species most commonly Candida albicans
- Often occurs when the normal balance of microbes in the body is disrupted
-
Causes:
- Overgrowth of Candida, which is a normal part of the human microbiota (mouth, gut, skin, vagina)
- Triggered by factors like antibiotic use, immunosuppression, diabetes, or hormonal changes
-
Common Forms:
- Oral candidiasis (thrush): white patches on tongue, cheeks, or throat
- Vaginal candidiasis: itching, discharge, inflammation
- Cutaneous candidiasis: moist skin folds (e.g., under breasts or in groin)
- Invasive candidiasis (candidemia): Candida enters bloodstream → serious systemic infection (seen in hospitalized or immunocompromised patients)
-
Morphology:
- Candida can switch between yeast form (budding cells) and hyphal form
- This dimorphism helps with tissue invasion and immune evasion
8
Q
Cholesterol
A
Cholesterol is a lipid molecule found in animal and protozoa cell membranes. It maintains membrane fluidity and serves as a precursor for steroid hormones and vitamin D.
fungi -> ergosterol
9
Q
Cilia
A
Cilia are short, hair-like projections on the surface of some eukaryotic cells used for locomotion or moving fluid and particles across cell surfaces.
Cilia are found in certain Animal cells and in many protozoa. Not found in molds and yeast cells.
10
Q
Coccidioidomycosis
A
Valley Fever
-
Cause:
- Caused by inhalation of arthroconidia (spores) from the dimorphic fungus Coccidioides immitis
-
Type:
- Dimorphic fungus
- Transitions from mold in soil to spherules in host tissue (not yeast)
-
Transmission & Development:
- Mold in arid soil produces spores
- Spores become airborne when soil is disturbed
- Inhaled spores lodge in lungs and transform into spherules, which release endospores that spread the infection
-
Disease:
- Ranges from mild flu-like illness to chronic pneumonia or disseminated disease
- Can infect healthy individuals but is more severe in immunocompromised hosts
-
Key Features:
- No yeast phase: spherules are unique to Coccidioides
- No human-to-human transmission
- Classified as a primary pathogen
11
Q
Cryptococcosis
A
Cryptococcosis is a fungal disease caused by Cryptococcus neoformans, often affecting immunocompromised individuals. It can cause pneumonia or spread to the brain (meningitis).
Cryptococcus neoformans
- Type: Dimorphic fungus
- Transmission: Inhalation of spores from soil contaminated with bird droppings.
- Disease: Causes cryptococcosis, which may begin as a lung infection and can spread to the central nervous system, causing cryptococcal meningitis, especially in immunocompromised individuals (e.g., AIDS patients).
- Key Features: Has a thick polysaccharide capsule that helps it evade the immune system; detected with India ink staining.
- primary pathogen
12
Q
Cryptosporidiosis
A
cryptosporidium parvum
-
Transmission:
- Ingestion of oocysts from contaminated water, food, or surfaces
- Oocysts are immediately infectious and highly resistant to chlorine
-
Disease:
- Causes cryptosporidiosis, a diarrheal illness
- Self-limiting in immunocompetent individuals
- Can be severe, chronic, or life-threatening in immunocompromised hosts
-
Life Cycle Summary:
Thick-walled oocyst is ingested
Found in contaminated water, food, or recreational water
Oocyst reaches small intestine
Releases sporozoites, which invade intestinal epithelial cells
3a. Asexual reproduction (merogony)
Sporozoites replicate as merozoites
Some reinfect nearby cells → auto-infection, maintains infection in host
3b. Sexual reproduction (gametogony)
Merozoites differentiate into male and female gametes
Fuse to form a zygote
Zygote develops into thick and thing wall oocysts
Thick-walled oocysts: excreted in feces → transmission to new hosts
Thin-walled oocysts: remain in host -> burst within the same host and release sporozoites -> cause auto-infection
Asexual reproduction
results in reinfection - Infection persists in current host through auto-infection
Sexual reproduction
- results in transmission - new host become infected by ingesting thick walled oocysts
- results in reinfection - thin walled oocysts burst releasing sporozoites which infect nearby cells*
-
Key Features:
- Autoinfection may occur: reinfection from new oocysts in the same host
- No fully effective treatment; prevention and water safety are essential
13
Q
Cyst - protozoa
A
- A dormant, environmentally resistant stage formed by certain protozoa to survive outside the host and enable transmission
-
Function:
- Allows survival under harsh conditions (e.g., desiccation, stomach acid, disinfectants)
- Enables fecal-oral transmission by remaining viable in the environment
- After ingestion, cysts undergo excystation in the host to release trophozoites
-
Key Features:
- Thick outer wall
- Non-replicative while encysted
- Highly resistant to environmental stressors
- Common in intestinal protozoa such as Entamoeba histolytica and Giardia duodenalis
-
Reproduction:
- Cysts do not reproduce; active forms (trophozoites) replicate after excystation
-
Transmission:
- Typically shed in feces and ingested by a new host via water, food, or surfaces
-
Side Note (Helminths):
- Some helminths form cystic larvae (e.g., cysticerci in Taenia solium)
- These are multicellular larval forms, not protozoan cysts, and occur within host tissues, not the environment
14
Q
Cysticerci
A
-
Definition:
- Cysticerci are the encysted larval stage of the tapeworm Taenia solium
- Singular: cysticercus
-
Structure:
- Fluid-filled cyst containing an immature scolex
- Found in tissues of the intermediate host (e.g., pigs or humans)
-
Infection in Humans:
- Humans can ingest T. solium eggs (e.g., via fecal-oral route)
- Larvae hatch, penetrate the intestinal wall, and migrate to tissues (muscle, brain, eye)
- Develop into cysticerci → leads to cysticercosis
- In the brain: neurocysticercosis, which can cause seizures
-
Key Points:
- Not environmentally resistant like protozoan cysts
- Not the same as ingestion of cysts in undercooked pork, which leads to adult tapeworm (taeniasis)
- In cysticercosis, humans act as an accidental intermediate host
15
Q
Cysticercosis
A
Cysticercosis is a tissue infection caused by ingestion of Taenia solium eggs, leading to cysticerci formation in muscles, eyes, or brain neurocysticercosis.
16
Q
Cysticercus
A
- A fluid-filled, encysted larval stage of the pork tapeworm Taenia solium
- Plural: cysticerci
-
Structure:
- Contains an invaginated scolex within a cyst
- Resides in host tissue / intermediate host tissue such as muscle, brain, or eye
-
Formation:
- Develops when a human or pig ingests T. solium eggs
- Oncospheres hatch in the intestine, penetrate the wall, and travel via the bloodstream to tissues
- There, they encyst and develop into cysticerci
-
Clinical Relevance:
- In pigs: intermediate stage leading to taeniasis in humans
- In humans (accidental intermediate host): causes cysticercosis
- If cysticerci lodge in the brain → neurocysticercosis → seizures, neurological symptoms
17
Q
Dermatitis
A
Dermatitis is inflammation of the skin, often due to infection, allergens, or irritants. Symptoms include redness, itching, and swelling.
18
Q
Dimorphic fungus
A
- 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
19
Q
Dioecious
A
Dioecious organisms have distinct male and female individuals, each producing one type of gamete. Seen in some parasitic worms.
20
Q
Dysbiosis
A
Dysbiosis is an imbalance in the microbial communities of the body (e.g., gut), often linked to disease or antibiotic use.
21
Q
Ergosterol
A
Ergosterol is a sterol component of fungal cell membranes, serving a role similar to cholesterol in animal cells. Target of many antifungal drugs.
22
Q
Flagella
A
Flagella are long, whip-like appendages used by certain protozoa and bacteria for motility.
23
Q
Fungal vaginitis
A
Fungal vaginitis is a vaginal infection caused by Candida species, resulting in itching, discharge, and discomfort.
24
Q
Fungemia
A
Fungemia is the presence of fungi (usually Candida) in the bloodstream, a serious condition often seen in hospitalized or immunocompromised patients.
25
Fungi
*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**
2. Normally **saprophytic**
3. Use **Aerobic respiration** and/or **fermentation** to produce ATP
4. Are **hapload** for the majority of life-cycle
5. Most fungi can reproduce both sexually and asexually. Asexual is generally more common.
- 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
- Sexual reproduction: Two haploid cells of different mating types fuse -> diploid cell -> meiosis -> produce haploid spore.
```
Saprophytic organisms obtain nutrients by decomposing dead or decaying organic matter.
saprophytic fungi a key role in nutrient recycling, breaking down complex organic material and returning elements like carbon and nitrogen to the ecosystem.
```
26
Giardiasis
Giardiasis is a diarrheal illness caused by the protozoan *Giardia duodenalis*.
- Spread via contaminated water, it involves both cyst and trophozoite stages.
27
Histoplasmosis
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**.
28
Hooks
Hooks are structures found in the scolex tapeworms, used for attachment to the host's intestinal wall.
29
Hookworm
Hookworm refers to parasitic nematodes that attach to the intestinal lining and feed on blood, causing anemia and fatigue. 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.
**Necator americanus**
- *Type:* Parasitic nematode (roundworm); one of the two main species of human hookworm.
- *Transmission:* Infective larvae in soil penetrate the skin (often through bare feet), enter the bloodstream, migrate to the lungs, ascend the trachea, are swallowed, and mature in the small intestine.
- *Disease:* Causes **hookworm infection**, leading to symptoms like abdominal pain, diarrhea, fatigue, and **iron-deficiency anemia** due to blood feeding.
- *Key Features:* Has cutting plates in its mouth for attachment; prevalent in tropical and subtropical regions.
30
Hyphae
Hyphae are long, branching filaments of fungi made up of connected cells.
These cells are typically separated by septa (cross-walls), but even when septa are present:
They often have pores that allow cytoplasm, organelles, and sometimes nuclei to move between cells.
- Yeasts do **not** form hyphae, distinguishing them from **molds**
31
Malaria
Malaria is a protozoan disease caused by *Plasmodium* species, transmitted by *Anopheles mosquitoes*. It infects liver and red blood cells.
32
Monoecious
Monoecious organisms have both male and female reproductive organs in one individual. Seen in many flatworms.
33
Mycelium
Mycelium is the mass of hyphae forming the vegetative part of a mold, often growing in or on the substrate.
34
Mycosis
Mycosis refers to any disease caused by fungal infection, ranging from superficial (e.g., ringworm) to systemic (e.g., cryptococcosis).
35
Neurocysticercosis
Neurocysticercosis is a severe form of cysticercosis where larval cysts of *Taenia solium* develop in the brain, causing seizures and neurological symptoms.
36
Nosocomial infection
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
37
Onychomycosis
- *Definition:* Fungal infection of the nails (toenails or fingernails).
- *Dermatophyte-caused:*
- Most common cause (~80–90% of cases).
- Caused by fungi like **Trichophyton rubrum**.
- Affects **toenails more commonly**.
- Invade keratinized tissue (skin, nails, hair).
- *Candida-caused:*
- Less common; a type of **yeast infection**.
- More often affects **fingernails**, especially in those with frequent hand immersion or immunosuppression.
- Caused by *Candida species* (e.g., *Candida albicans*).
- *Note:* Both types require antifungal treatment, but identification helps guide appropriate therapy.
38
Opportunistic pathogen
An opportunistic pathogen causes disease primarily in immunocompromised individuals. Example: *Candida albicans*
39
Oral thrush
Oral thrush is a fungal infection of the mouth caused by *Candida albicans*; it appears as white plaques on the tongue and mucosa.
40
Pinworm
Pinworm is a common intestinal nematode *Enterobius vermicularis* that causes perianal itching, especially in children.
41
Protozoa
- 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 host
42
Pseudopod
Pseudopods are temporary extensions of cytoplasm used by amoeboid protozoa for movement and feeding.
43
Ringworm
**Ringworm (Tinea) – Fungal Infection**
- *Type:* Superficial **fungal infection** of the skin, not a worm.
- *Cause:* Caused by **dermatophyte fungi**, primarily:
- **Trichophyton rubrum**
- **Microsporum** species
- **Epidermophyton** species
- *Transmission:* Spread by **direct contact** with infected skin, animals, surfaces, or soil.
- *Appearance:* Red, scaly, **ring-shaped rash** with a clear center and raised, itchy edges.
- *Types by Location:*
- **Tinea corporis** – body
- **Tinea capitis** – scalp
- **Tinea pedis** – feet (athlete’s foot)
- **Tinea cruris** – groin (jock itch)
- **Tinea unguium** – nails (onychomycosis)
- *Treatment:* Topical or oral **antifungal medications**.
44
Saprophyte
A saprophyte is an organism, usually a fungus or bacterium, that feeds on and decomposes dead organic matter.
45
Suckers
Suckers are attachment structures found on parasitic worms like flukes and tapeworms, used to anchor to host tissue.
46
*Taeniasis*
Taeniasis is the intestinal infection with adult *Taenia* tapeworms acquired by eating undercooked pork or beef containing cysticerci.
*taenia solium*
*cestode*
47
Tapeworm
Tapeworms are flat, segmented parasitic worms (cestodes) that absorb nutrients through their skin and attach to the intestine via a scolex.
*Physical Characteristics*
**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
48
Tinea cruris
**Tinea cruris (Jock Itch)**
- *Definition:* A **fungal infection of the groin**, inner thighs, and buttocks.
- *Cause:* Caused by **dermatophyte fungi**, most commonly: **Trichophyton rubrum**
- *Transmission:* Spread through direct contact with infected skin, clothing, towels, or surfaces; thrives in warm, moist environments.
- *Symptoms:* Red, itchy, scaly rash with well-defined edges; may form a ring-like shape.
- *Treatment:* Topical or oral **antifungal medications** (e.g., terbinafine, clotrimazole).
49
Tinea pedis
**Tinea pedis (Athlete’s Foot)**
- *Definition:* A **fungal infection of the feet**, especially between the toes.
- *Cause:* Caused by **dermatophyte fungi**, primarily:
- **Trichophyton rubrum**
- *Transmission:* Spread through direct contact with contaminated surfaces (e.g., locker rooms, showers, footwear); thrives in moist, warm environments.
- *Symptoms:* Itching, burning, scaling, and cracking of the skin between the toes or on the soles; may also involve blisters or thickened skin.
- *Treatment:* Topical or oral **antifungal medications** (e.g., terbinafine, miconazole).
50
Toxoplasmosis
**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
51
Trichomoniasis
**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
52
Trophozoite
A trophozoite is the active, feeding stage of a protozoan, typically found in host tissues or fluids.
*cyst is the dormant state, not found in all protozoa*
53
Valley fever
Valley fever is another name for coccidioidomycosis, a fungal respiratory infection caused by inhaling *Coccidioides* spores.
54
Front
Back
55
Compare and contrast the major components of eukaryotic and prokaryotic cells.
Eukaryotic cells have a nucleus, membrane-bound organelles, larger size, and linear DNA; prokaryotes lack a nucleus and organelles, have circular DNA, and are typically smaller.
56
Compare and contrast Animals, Fungi, and Protists
**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 but can use ergosterol
- 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
**Common characteristics**
- True nucleus
- membrane bound organelles
- 80s ribosome
57
Compare and contrast parasitic worms: Nematodes vs. Cestodes
- *Body Shape:*
- **Nematodes (roundworms):** Cylindrical, unsegmented, tapered at both ends
- **Cestodes (tapeworms):** Flat, ribbon-like, segmented body
- *Digestive System:*
- **Nematodes:** Complete digestive tract (mouth and anus)
- **Cestodes:** **Lack a digestive system**; absorb nutrients through their tegument
- *Body Parts (Cestodes):*
- **Scolex:** Head with suckers and/or hooks for attachment
- **Neck:** Narrow region behind scolex; site of segment generation
- **Proglottids:** Repeated reproductive segments that make up the strobila
- **Strobila:** Entire chain of proglottids forming the body
- *Reproductive System:*
- **Nematodes:** Usually **dioecious** (separate sexes)
- **Cestodes:** Usually **monoecious** (each proglottid contains both male and female organs)
- *Transmission:*
- **Nematodes:** Often by ingestion of eggs or skin penetration by larvae
- **Cestodes:** Usually by ingestion of **larval cysts** in undercooked meat
- *Intermediate Hosts:*
- **Nematodes:** Not always required
- **Cestodes:** Typically **require intermediate hosts** (e.g., pigs or cows)
- *Examples:*
- **Nematodes:** *Ascaris lumbricoides*, *Necator americanus*, *Enterobius vermicularis*
- **Cestodes:** *Taenia solium*, *Taenia saginata*, *Diphyllobothrium latum*
58
Describe *Enterobius vermicularis*
- *Type:* Parasitic **nematode (roundworm)**
- *Transmission:* **Fecal-oral route**; humans ingest embryonated eggs from contaminated hands, surfaces, or food
- *Life Cycle:*
- Eggs hatch in the **small intestine**
- Larvae migrate to the **colon**, mature into adults
- At night, **females migrate to the perianal region** to lay eggs
- *Symptoms:*
- **Perianal itching**, especially at night
- Irritability, disrupted sleep; may cause secondary bacterial infection from scratching
- *Host:* **Humans are the only host**; no intermediate host involved
59
Describe Necator americanus
- *Type:* Parasitic **nematode (roundworm)**
- *Transmission:* **Skin penetration** by larvae in contaminated soil (e.g., walking barefoot)
- *Life Cycle:*
- Larvae enter through skin, migrate via bloodstream to lungs
- Ascend respiratory tract, are swallowed
- Mature into adults in the **small intestine** and attach to the intestinal wall
- *Feeding:* Feeds on **host blood**, causing **iron-deficiency anemia** and fatigue
- *Symptoms:*
- Ground itch at entry site
- Cough during lung migration
- GI discomfort, anemia, weakness
- *Host:* **Humans are the definitive host**; no intermediate host required
60
Describe Taenia solium
- *Type:* Parasitic **cestode (tapeworm)**
- *Physical Characteristics:*
- **Scolex** with **hooks and suckers** for intestinal attachment
- *strobila** made of **proglottids** (reproductive segments)
- No digestive system—absorbs nutrients through its surface.
- *DISEASES*:
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
61
Define oncosphere
Oncosphere is the embryo inside the egg of a tapeworm; it hatches in the intermediate host and penetrates tissue.
62
Define proglottid
**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.
63
Define scolex
**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
64
Define strobila
**strobila**
- body of tapeworm
- Long, flat, ribbon-like structure
- Can grow to meters in length
65
Describe the life cycle of Taenia solium
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 *oncosphere*s 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
```
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Why does Taenia solium cause two diseases in humans?
Ingesting eggs (not larvae) causes cysticercosis—larvae migrate to tissues including brain (neurocysticercosis); ingesting larvae causes intestinal taeniasis.
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General characteristics of protozoa
- 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
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Life Stages of protozoa
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
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Types of motility in protozoa
- *Amoeboid movement*
- Protozoa extend **pseudopodia** ("false feet")
- Example: *Entamoeba histolytica*
- Used for crawling and engulfing food
- *Flagellar movement*
- Use one or more **flagella** (long whip-like structures)
- Example: *Giardia duodenalis*, *Trypanosoma*
- Enables swimming in a directed manner
- *Ciliary movement*
- Covered in rows of **cilia** (short hair-like structures) that beat in coordinated waves
- Example: *Balantidium coli*
- Allows fast, flexible movement
- *Gliding movement*
- No visible organelles; uses **cytoskeletal machinery** to slide along surfaces
- Example: *Plasmodium falciparum*, *Toxoplasma gondii*
- Often seen in **Apicomplexans**, associated with invasion of host cells
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Compare Excavata, Apicomplexans, and Amoebozoa
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
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Describe Entamoeba histolytica
**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
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Describe Giardia duodenalis
**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
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Describe Naegleria fowleri
**Naegleria fowleri**
- *Type:* **Free-living amoeboid protozoan** in the group Excavata
- *Transmission:* Enters the body when **contaminated warm freshwater** (lakes, hot springs, poorly chlorinated pools) enters the **nose** during swimming or diving
- *Life Cycle:*
- Exists in **three forms**: cyst, trophozoite (infectious stage), and flagellated form
- **Trophozoites** migrate along the olfactory nerve to the brain
- *Disease:*
- Causes **Primary Amebic Meningoencephalitis (PAM)**
- Rapidly progressive and often fatal brain infection
- Symptoms include headache, fever, stiff neck, confusion, and seizures
- Disease progresses quickly, usually within days.
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Describe Plasmodium falciparum
**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
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Why is dimorphism adaptive for fungal pathogens?
- *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**, **Blastomyces dermatitidis**
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Describe characteristics of *Candida albicans*
- *Opportunistic pathogen*
- transitions between **yeast** and **hyphal** forms
- Causes **candidiasis**, ranging from superficial to systemic infections
- 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
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Define beta-glucans
**Beta-glucans**
- *Definition:* **Polysaccharides** made of glucose monomers linked by β-glycosidic bonds
- *Location:* Found in the **cell walls of fungi**, including **Candida albicans**
- *Function:*
- Provide **structural strength** to the fungal cell wall
- Recognized by the host **innate immune system** (e.g., via Dectin-1 receptors), triggering immune responses
- *Clinical relevance:*
- Targeted by some **antifungal drugs** (e.g., echinocandins inhibit β-glucan synthesis)
- Presence in bloodstream can be used as a **biomarker for invasive fungal infections**
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Define pseudohyphae
Pseudohyphae are chains of elongated yeast cells resembling hyphae, seen in *Candida* species during tissue invasion.
