Protozoa, Slime Molds & HelminthsChapter 5 & 23

Talaro

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Protozoa• 65,000 species

• Heterotrophic

• Eukaryotic

• Most are unicellular, colonies are rare

• Most have locomotive structures – flagella, cilia, or pseudopods

• Vary in shape

• Typically inhabit water or soil

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Protozoa• Trophozoite

– Motile feeding stage

• Cyst – A dormant resistant stage

• Asexual and sexual reproduction– Most propagate by simple asexual

cell division of the trophozoite– Many undergo formation of a cyst– Others have a complex life cycle that

includes asexual & sexual phases

• Majority are NOT pathogens• Some are animal parasites & can

be spread by insect vectors

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ZoonosisAn infectious disease in animals that can be transmitted to people. The natural reservoir for the infectious agent is an animal.

The apical complex include structures that allow the parasite to enter other cells.

Anterior vesicles that secrete digestive enzymes.

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Flagellated Protozoa

• Motility by flagella alone or by both flagella & amoeboid motion

• Several parasites– Giardia– Trichomonas– Trypanosoma– Leishmania

attachment

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Trichomonas• Small, pear-shaped cells• 4 anterior flagella & an undulating

membrane• Exists only in trophozoite form• 3 species infect humans

– T. vaginalis– T. tenax– T. hominis

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Trichomonas vaginalis• Causes an STD called trichomoniasis• Reservoir is human urogenital tract• 50% of infected are asymptomatic• Strict parasite, cannot survive long outside of host• 3 million cases/year• Female symptoms

– Foul-smelling, green-to-yellow discharge– Vulvitis– Cervicitis– Urinary frequency & pain

• Male symptoms – Urethritis, thin, milky discharge, occasionally prostate infection

Flagyl (Metronidazole)Interferes with DNA synthesis

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Giardia lamblia• Unique symmetrical heart shaped

cells• Cysts are small, compact, and

multinucleate• Cysts can survive for 2 months in

environment• Cysts enter duodenum, geminate, &

travel to jejunum to feed & multiply• Spread through contaiminated water

& food– Fecal oral contamination

• Giardiasis – Diarrhea, abdominal pain

• Diagnosis is difficult because organism is shed in feces intermittently

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Hemoflagellates• Live in blood & tissues of human host• Obligate parasites• Incite life-threatening and debilitating zoonoses• Spread by blood-sucking insects that serve as

intermediate hosts• Acquired in specific tropical regions• Have complicated life cycles & undergo morphological

changes• Trypanosoma T. brucei (causes sleeping sickness)- T. cruzi (causes Chagas disease)• Leishmania (causes Leishmaniasis)

10Trypanosoma cruzi

no flagella

anterior flagellumundulating membrane

large fully formed stage

Diagnostic

Infective

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Trypanosoma brucei• Causes African Sleeping Sickness• Spread by tsetse flies• Harbored by reservoir mammals• Biting of fly inoculates skin with

trypanosome, which multiplies in blood & damages spleen, lymph nodes & brain

• Chronic disease symptoms are sleep disturbances, tremors, paralysis & coma

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Trypanosoma cruzi• Chagas disease• Kissing bug is the vector

– Reduviid / Assassin Bugsre·du·vi·id (family Reduvidae, subfamilyTriatominae (Triatomine Bugs))

• Infection occurs when bug feces are inoculated into a cutaneous portal

• Local lesion, fever, & swelling of lymph nodes, spleen, & liver

• Heart muscle & large intestine harbor masses of amastigotes– Divide by binary fission

• Chronic inflammation occurs in the organs – Especially heart & brain

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Chagas Disease

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Leishmania• Leishmaniasis is a zoonosis

transmitted among mammalian hosts by female sand flies that require a blood meal to produce eggs

• Infected macrophages carry the pathogen into the skin & bloodstream, giving rise to fever, enlarged organs & anemia

• Kala azar is the most severe & fatal form

Viscera or the internal organs, particularly the liver, spleen, bone marrow & lymph nodes

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Amoeboid Protozoa

• Amoeba– Pseudopods

• Radiolarian– Shelled ameba

• Entamoeba histolytica– Incites dysentery, abdominal pain, fever, diarrhea

& weight loss– Carried by 10% of world population– Asymptomatic in 90% of patients

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Entamoeba histolytica• Alternates between a large trophozoite, motile by

means of pseudopods & a smaller nonmotile cyst• Humans are the primary hosts• Ingested• Cysts are swallowed & enter the small intestine;

alkaline pH & digestive juices stimulate cyst to release 4 trophozoites

• Trophozoites attach, multiply, actively move about & feed

• Ameba may secrete enzymes that dissolve tissues & penetrate deeper layers of the mucosa

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Amebic DysenteryEntamoeba histolytica

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Entamoeba histolytica

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Ciliated Protozoa• Trophozoites have cilia• Majority are

nonpathogens• Balantidium coli

– An occupant of the intestines of domestic animals such as pigs & cattle

– Acquired by ingesting cyst-containing food or water

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Balantidium coli

• Trophozoite erodes intestine & elicits intestinal symptoms

• Healthy humans are resistant

• Rarely penetrates intestine or enters blood

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Apicomplexan Protozoa• Non-motile in mature stage

– Male gametes are motile• Alternate between sexual & asexual phases & between

different animal hosts• All members are parasitic• Most form specialized infective bodies that are

transmitted by arthropod vectors, food, water, or other means– Plasmodium– Toxoplasma – Cryptosporidium

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Plasmodium• Causes malaria• Female Anopheles mosquito

is the vector• Obligate intracellular

sporozoan• 4 species: P. malariae, P.

vivax, P. falciparum & P. ovale

• 300-500 million new cases each year

• 2 million deaths each year

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Plasmodium• Infective forms for humans (sporozoites) enter blood

with mosquito saliva, penetrate liver cells, multiply, and form hundreds of merozoites, which multiply in & lyse RBCs.

• Symptoms include episodes of chills-fever-sweating, anemia, and organ enlargement.

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Toxoplasma gondii• Causes toxoplasmosis• Obligate parasite with

extensive distribution• Lives naturally in cats that

harbor oocysts in the GI tract

• Acquired by ingesting raw meats or substances contaminated by cat feces

• Most cases of toxoplasmosis go unnoticed except in the fetus & AIDS patients which can suffer brain & heart damage

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Cryptosporidium• An intestinal pathogen• Infects a variety of animals• Exists in tissue & oocyst

phases• 1990s – 370,000 cases in

Milwaukee, WI due to contaminated water

• Causes enteric symptoms• AIDS patients may suffer

chronic persistent diarrhea

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Slime Molds

• Two classifications - cellular and plasmodial • Motile• Not pathogens• Ingest food by endocytosis• Form spores on erect fruiting bodies

• Cellular slime molds only undergo asexual reproduction

• Plasmodial slime molds undergo both sexual and asexual reproduction

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Cellular Slime Molds - Asexual• Unusual life cycle - both amebal and fungal-like characteristics

• Favorable conditions allow amebal growth

• Unfavorable conditions cause some cells to generate cAMP

• Cells migrate toward cAMP and aggregate – form a pseudoplasmodium

• ‘Slug’ moves toward light - differentiates

• Spores generate in cap

• Released to germinate as amoebal form under favorable conditions

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Cellular Slime Mold

Amebas congregatetoward cAMP

migrates

Amebas disseminatedas spores

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Plasmodial (acellular) Slime Molds• Large cell with many nuclei - PLASMODIUM

• Moves as giant amoeba engulfing organic matter and bacteria

• Distributes nutrients through cytoplasmic streaming

• Form stalks and reproductive structures under starvation conditions

• Sporangium with spores

• Nuclei undergo meiosis, spores released under favorable conditions

• Fuse to form diploid cells, cells fuse to make plasmodium

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Plasmodial Slime Molds

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Parasitic Helminths• Multicellular parasitic animals• Adult worms mate & produce fertilized eggs that hatch into larvae

that mature in several stages to adults• The sexes may separate or hermaphroditic• Adults live in the definitive host• Eggs & larvae may develop in the same host, external environment or

an intermediate host• A transport host experiences no parasitic development• Have mouthparts for attachment to or digestion of host tissues• Most have well-developed sex organs that produce eggs and sperm• 50 species parasitize humans • Acquired though ingestion of larvae or eggs in food; from soil or

water; some are carried by insect vectors• Afflict billions of humans

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Major Groups of Helminths1. Roundworms (nematodes) - cylindrical, a

complete digestive tract, a protective surface cuticle, spines & hooks on mouth; excretory & nervous systems poorly developed

2. Flatworms – flat, no definite body cavity; digestive tract a blind pouch; simple excretory & nervous systems• Cestodes (tapeworms)• Trematodes or flukes, are flattened , nonsegmented

worms with sucking mouthparts

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Roundworms

• Filamentous with protective cuticles, circular muscles, a complete digestive tract, & separate sexes

• Ascaris lumbricoides• Trichuris trichiura• Enterobius vermicularis –pinworm• Hookworms• Strongyloides stercoralis• Trichinella spiralis – raw pork…• Filarial worms

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Ascaris lumbricoides• A large (up to 30 mm long) intestinal roundworm• 1 billion cases worldwide• Most cases in the US occur in the southeastern states• Indigenous to humans• Ascaris spends its larval & adult stages in humans &

releases embryonic eggs in feces, which are spread to other humans

• Ingested eggs hatch into larvae & burrow through the intestine into circulation & travel to the lungs & pharynx & are swallowed

• Adult worms complete cycle in intestines

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Ascaris

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Hookworms

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Ascaris lumbricoides

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Ascaris lumbricoides

• Worms retain motility, do not attach

• Severe inflammatory reactions mark the migratory route

• Allergic reactions can occur

• Heavy worm loads can retard physical & mental development

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Tapeworms• Flatworms• Long, very thin, ribbonlike bodies composed of sacs

(proglottids) & a scolex (head) that grips the intestine• Each proglottid is an independent unit adapted to

absorbing food & making & releasing eggs• Taenia saginata• Taenia solium

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Taenia saginata

• Beef tapeworm• Very large, up to 2,000 proglottids• Humans are the definitive host• Animals are infected by grazing on land contaminated

with human feces• Infection occurs from eating raw beef in which the

larval form has encysted• Larva attaches to the small intestine & becomes an

adult• Causes few symptoms – sometimes weight loss

despite good appetite

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Taenia solium

• Pork tapeworm• Infects humans through ingesting cysts or eggs• Eggs hatch in intestine, releasing tapeworm

larva that migrate to all tissues & encyst• Most damaging if they lodge in heart muscle,

eye, or brain• May cause seizures, psychiatric disturbances

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Taeniasolium