EUKARYOTIC PATHOGENS (WEEK 3)

What are the eukaryotic pathogens?

• fungi

• algae

• protozoa (single celled)

• helminths (worms)

What are the characteristics of fungi?

• multi or unicellular forms

• chemoheterotrophic

• aerobic or facultatively anaerobic

• cell wall containing chitin; cell membrane containing ergosterol

• asexual and sexual reproduction

What two forms of fungi exist?

• yeasts that exist as single cells that are round to oval

• molds that exist as hyphae

• most pathogenic fungi are dimorphic (yeast or mold)

What are hyphae?

• long threadlike structures of cells

What are yeasts?

• can grow on agar plates

• colonies resemble bacterial colonies (bigger with colour)

• reproduce asexually thru budding

What are molds?

• made of hyphae that give fuzzy appearance

• reproduce thru spore formation and fragmentation

What is mycelium?

• a tangled mass of hyphae

What is fragmentation?

• asexual reproduction

• a piece of a hypha breaks off and begins new growth

What is spore production?

• aerial hyphae cells form spores

• asexual or sexual

• the spores are released and allow fungi dispersal over long distances

What are the different fungal infections / mycoses?

• systemic mycoses

• subcutaneous mycoses

• cutaneous mycoses

• superficial mycoses

• opportunistic mycoses

What is systemic mycoses?

• deep within the body

• eg. cryptococcosis

What is subcutaneous mucoses?

• exist beneath the skin

What is cutaneous mycoses?

• affects hair, epidermis, and nails by digesting keratin

• caused by dermatophytes

• transmitted via skin contact with humans / animals

• eg. tinea pedis / athlete’s foot

What is superficial mycoses?

• on hair and skin without the digestion of keratin

What is opportunistic mycoses?

• caused by normal microbiota or environmental fungi in immunosuppressed individuals

• eg. thrush / candida albicans

What is candida?

• is part of a normal microbiota which flourishes in the mouth, vagina, or skin of immunocompromised individuals

What happens with cryptococcosis from systemic and opportunistic mycosis?

• cause lung infection or meningitis

• caused by yeast (cryptococcus neoformans and C. gattii)

• found in soail of urban environments and may become airborne

• cells have a gelatinous capsule for evasion of phagocytosis

• big problem for immunosuppressed individuals

What is ergot toxin?

• produced by claviceps purpurea

• causes ergotism

• a derivative used to prevent post partum hemorrhage

• natural LSD source

What is ergotism?

• leads to seizures and hallucinations

• gangrene via vasoconstriction

What is alfatoxin?

• produced by aspergillus flavus

• grows on diverse foods including peanuts and corn

• carcinogenic meaning associated with development of liver cancer

What are the characteristics of algae?

• unicellular or multicellular

• photoautotrophs meaning they have chloroplasts

• have cell walls

• reproduce sexually and asexually

• doesnt cause infection but produce toxins and cause intoxications

What are diatoms?

• unicellular

• called demoic acid, a neurotoxin

• causes amnesiac shellfish poisoning

• symptoms are diarrhea and memory loss

What are dinoflagellates?

• unicellular

• called saxitoxins, a neurotoxin

• causes paralytic shellfish poisoning

• symptoms are numb lips, dizziness, and difficulty of breathing

What are the characteristics of a protozoa?

• unicellular eukaryotes; no cell wall and may have a covering called a pellicle

• chemoheterotrophic

• mainly asexual reproduction via binary fission or budding

• complex life cycles with multiple stages

• may form cysts

What is a cyst?

• protective structure that enables survival in poor conditions

• similar to an endospore

What is the lifecycle of a parasitic protozoa?

1. transmission to human host

2. multiplication in host

3. microbe leave host and re enters new host

What is a definitive host?

• the organism taht hosts the sexual reproductive stage of a parasite

What is an intermediate host?

• the organism that hosts the asexual reproductive stage of a parasite

• eg. plasmodium vivax, toxoplasma gondii

What is amoebic dysentry?

• caused by entamoeba histolytica

• causes dysentry which is bloody diarrhea, cramping, nausea, vomiting, fever

• transmitted through fecal oral transmission where human ingests a cyst

• only one host; humans

What is the disease course of amoebic dysentry?

1. cysts germinate into amoeba to multiple in large intestine

2. amoeba form new cysts which shed in feces to infect other hosts

3. invasive disease may occur where active amoeba lyse and feed on intestinal epithelial cells causing ulcer and bleeding

4. may penetrate other organs to cause abcesses

What is malaria?

• caused by plasmodium species

• symptoms are cycles of fever and chills, anemia, joint pain

• two host life cycle: human as intermedaite, mosquito as definitive

What is the malaria transmission life cycle?

1. transmits to human by infected female mosquito to human, passing on plasmodium / sporozoite

2. plasmodium infect human liver cells, mature and reproduce asexually inside; escapes by cell lysis

3. plasmodium infect and consume human RBC, reproduces asexually inside; escape by lysis which causes anemia, fever, and chills

4. some plasmodium form gametocytes in RBC

5. infected human is bitten by another female mosquito which picks up plasmodium gametocytes

6. gametocytes are fertilized sexually in mosquito intestine and mature into sporozoites

7. sporozoites move to salivary glands

What is toxoplasmosis?

• caused by toxoplasma gondii

• cysts are shed in cat feces and picked up by humans

• no significant infection in healthy people from cysts

• cysts lead to congenital infections in pregnant women or grow in immunocompromised individuals

What is the toxoplasmosis host life cycle?

• definitive host are cats

• intermediate hosts are humans

What are the characteristics of helminths?

• multicellular

• no cell wall

• chemoheterotrophs

• reproduce sexually]

• has free living and parasitic / pathogenic species

What are the two main groups of helminths?

• platyhelminths / flat worms

• nematodes / round worms

What are the characteristics of parasitic / pathogenic helminths?

• reproductive organs are most edveloepd which caused reduces digestive, nervous, and motor systems

• monoeicious OR dioecious

• Life cycle: egg > larva > adult worm

• intermediate host for larval development

• definitive host for adult helminth

What does monoecious mean?

• hermaphroditic

• male and female reproductive systems in one

What does diecious mean?

• separate male and female animals

What are the pathogenic platyhelminthes?

• schistosoma

• taenia solium

What are the pathogenic nematodes?

• enterobius vermicularis

• ascaris lumbricoides

What are flukes?

• platyhelminthes

• aka trematodes

• non segmented worm with oral sucker

• eg. schistosoma spp. (blood flukes)

What is schistosoma?

• blood fluke

• cause tropical disease schistosomiasis

• definitive host is human

• intermediate host is water snail

What is the schistosoma life cycle?

1. eggs from infected human in feces or urine

2. eggs hatch in fresh water (miracidia)

3. imature larvae / miracidia infect water snails

4. mature larvae / cercariae are sehd and invade skin of human bathers

5. larvae enter blood vessels to mature

6. adults move to intestine or bladder to mate

7. fertilized eggs are shed or can enter different organs to cause damage

What are tapeworms?

• also known as cestodes

• segmented worm with suckers or hooks at the head (scolex)

• parasites of small intestine

What are examples of tapeworms?

• taenia solium / pork tapeworm

• taenia saginata / beef tapeworm

• echinococcus granulosus / dog tapeworm

What is the body structure of a tapeworm?

• head / scolex has suckers and hooks to attach to intestinal wall of definitive host; continually produces segments / proglottids

• segments closest to head contain male and female reproductive organs (hermaphrodite / monoecious)

• segments at end of worm are sacs of fertilized eggs (sexual reproduction) which detach and shed in feces

What is the life cycle of a tapeworm?

• intermediate host consumes egg which hatch into larave as oncosphere and burrow into tissue to form cysticerci (asexual reproduction)

• definitive host consmes cysticerci and develop into adult tapeworms in small intestine (sexual reproduction)

What is taenia solium?

• humans are definitive host, pigs are intermediate host

• infection occurs if human ingests undercooked larvae infested meat

• scolex of larvae latch onto small intestine, grows segments, eggs self fertilize and shed in feces

• causes taeniasis which is abdominal discomfort, weight loss, fatigue

• grows 2-10 m

What is the lifecycle of taenia solium?

1. adult tapeworm grows in human small intestine

2. fertilized eggs pass out in feces

3. pigs eat grass contaminated with eggs

4. eggs hatch into larvae and burrow into muscle to develop into cysticerci

5. human eats infected undercooked meat

6. digest all but the head / scolex

7. head attaches to intestinal wall of human

How can humans be the intermediate and definitive host of taenia solium?

• human to human transmission; if human ingests tapeworm eggs, human is the intermediate

• eggs hatch in intestine, larvae burrow into body tissues like the eyes and brain then develop into cysticerci

• causes cysticercosis

What is the tapeworm lifecycle when the human is the intermediate host?

1. adult tapeworm grows in human small intestine

2. eggs passed out in feces

3. another human consumes the eggs thru poor hygeine

4. eggs hatch and larvae burrow into organs like brain and develop into cysticerci

5. causes cysticercosis

What is enterobius vermicularis / pinworm?

• human is only host

• infection eggs are ingested thru oral or fecal contamination of fomites and hatch into larvae to mature in large intestine

• is dioecious and female migrates to anus to deposit eggs at night

• symptoms are itchy anus and some abdominal discomfort

• often occurs in families and more frequently in younger children

What is the lifecycle of enterobius vermicularis?

1. adult female deposits fertilized eggs at anus

2. eggs passed out in feces or under fingernails due to itching

3. human consumes eggs thru poor hygiene

4. larvae hatch in large intestine

5. adult male and female worms mate

6. adult female migrates to anus

What is ascaris lumbricoides / roundworm?

• human is only host;

• causes tropical disease ascariasis

• symptoms are shortness of breath, cough, diarrhea, abdominal pain, weight loss, fatigue

• treated by drugs or surgery

What is the lifecycle of ascaris lumbricoides?.

1. adult female lay eggs in intestine

2. eggs passed out in feces

3. human consumes eggs and hatch in intestine

4. immature worms burrow into circulatory system

5. worms migrate to lungs

6. worms migrate to pharynx and are swallowed

7. adult worms migrate to mate in small intestine