Pathologic Protozoa

CHARACTERISTICS OF PROTOZOA

1. Unicellular 2. Chemoheterotrophs (get their

energy by breaking down organic matter).

3. Most ingest their food; thus, they have special structures for this.

CHARACTERISTICS OF PROTOZOA

4. The vegetative form is the TROPHOZOA (tropho = movement; zoite = animal; they move like an animal). Trophozoa have special organelles for movement.

5. Capable of reproductionA. Asexual: fission, budding, or schizogony

(produces a large number of trophozoites)B. Sexual: conjugation

CHARACTERISTICS OF PROTOZOA 6. Some produce cysts. These are not tissue cysts like a human

gets under their skin; protozoa cysts are cellular.

They have a thick cell wall that allows for survival in harsh environments better than the trophozoite form.

PROTOZOA CYSTS Cysts are not as resistant as a bacterial

endospore. You can kill cysts by boiling them. They can live in the soil or water for

months. A cyst is no motile, so it is not trophozoic. A cyst does not procure its nutrients or

ingest food, but it can absorb nutrients. It has no organelles to ingest food.

ClassificationDomain: EukaryotesKingdom: Protista

Classification

Traditional classification of protozoa phylae was based on mode of locomotion. MASTIGOPHORA (flagella) CILIOPHORA (cilia) SARCODINA (amoebas) SPOROZOA (spore-formers)

Apicomplexa (attachment organ)

Modern Classification

Modern classification of protozoa is based on how they evolved and how closely related they are (phylogenetic taxonomy), as determined by their ribosomal RNA. The human pathogenic protozoa may be classified as follows:METAMONADA (multiple flagella with feeding grooves)AMOEBOZOA (amoebas)APICOMPLEXA (attachment organ)CILIOPHORA (cilia)EUGLENOZOA (flagella and disc-shaped cristae in mitochondria)

METAMONADA

Characteristics: no mitochondria, multiple flagella

Organisms Giardia lamblia

Disease: Ghiardosis Trichomonas vaginalis

Disease: Trichomoniasis

AMOEBOZOA (amoebas)

Characteristics: move by pseudopods to get food; consume red blood cells. In a fresh diarrheal specimen, you can see RBCs in the cytoplasm.

OrganismsEntamoeba histolyticaNaegleria fowleri

Disease: AMEBIASIS

APICOMPLEXA

Characteristics: has an organelle called an apical complex which allows the organism to attach to the host.Organisms

Plasmodium Disease: Malaria

Toxoplasma Disease: toxoplasmosis

Cryptosporidium Disease: Cryptosporidiosis

CILIOPHORA

CILIOPHORA: has cilia Organism

Balantidium coli Disease: Balantidiosis

EUGLENOZOA

EUGLENOZOA (older classification = Mastigophora): has flagella and its mitochondria have disc-shaped cristae

Organisms Trypanosoma

Disease: Trypanosomiasis Leishmania donovani

Disease: Leishmaniasis

TERMS

• Mastigote = flagella• Promastigote: has single flagella• Amastigote: has no flagella• Kinetoplast: round mass of circular DNA

Leishmania donovani

Domain: Eukaryota Kingdom: Protista Phylum: Euglenozoa Class: Kinetoplastida Order: Trypanosomatida Genus: Leishmania Species: donovani

Protozoa to study Giardia lambia (Giardosis) Trichomonas vaginalis (Trichomoniasis) Entamoeba histolytica (amoebiasis) Naegleria fowleri (amoebiasis) Plasmodium vivax (malaria; most common)

Plasmodium falciparum (malaria; most deadly) Cryptosporidium (Cryptosporidiosis) Toxplasmosis gondii (toxoplasmosis) Balantidium coli (Balantidiosis) Trypanosoma brucei gambiense (African Trypanosomiasis “African Sleeping

Sickness”) Trypanosoma brucei rhodesiense (African Trypanosomiasis “African Sleeping

Sickness”) Trypanosoma cruzi (American Trypanosomiasis “Chaga’s Disease”) Leishmania donovani (Leishmaniasis)

TERMS: Host Types The definitive host is the one in which

the parasite completes its sexual life cycle.

For instance, in Plasmodium, the definitive host is the tropical mosquito anopheles.

The intermediate host is the human.

TERMS: Host Types Its sexual life cycle also starts in the

human, so that can be confusing. What happens is the sporozoite form

enters the bloodstream when the mosquito bites the human.

First it begins its asexual reproduction, but if two mosquitoes inject one male and one female gametocyte into the human, there can be a sexual life cycle in the human as well.

TERMS Trophozoite: any stage in a

protozoa’s life cycle which can ingest food. In practice it refers to the motile form (pseudopods, cilia, flagella).

Cyst: Non-motile form, protected by a membrane. *infective stage*

Excystation: process of emergence of the trophozoite from the cyst.

Pseudopod: “false foot” temporary cytoplasmic process at the surface of the trophozoite.

ARCHAEZOA DISEASES

Ghiardosis Trichomoniasis

Ghiardosis Organism: Ghiardia lamblia Cysts are resistant forms and are

responsible for transmission of giardiasis. 

Both cysts and trophozoites can be found in the feces. 

Infection occurs by the ingestion of cysts in contaminated water, food (includes undercooked meat), or by the fecal-oral route. 

Ghiardia lamblia In the small intestine, excystation releases

trophozoites (each cyst produces two trophozoites). 

Trophozoites multiply, remaining in the lumen where they can be free or attached to the mucosa by a ventral sucking disk. 

Encystation occurs as the parasites transit toward the colon.  The cyst is the stage found most commonly in nondiarrheal feces. 

Because the cysts are infectious when passed in the stool or shortly afterward, person-to-person transmission is possible. 

Ghiardia lamblia Trophozoite form: piroform (pear or teardrop

shape), looks like a happy face. Discovered by Anton Van Leuwenhoek when he

examined his own feces when he had this infection.

You won’t see the flagella in lab because you need a special stain for that.

Cyst form: oval shaped. Nuclei looks like two eyes.

Geographic Distribution:Worldwide, more prevalent in warm climates, and in children.

Life Cycle of Giardia lamblia

Ghiardia lamblia

Trophozoite

Ghiardia lamblia

Trophozoites

Ghiardia lamblia

Trophozoites

Giardia lamblia trophozoite

Ghiardia lamblia

Cysts

Trichomoniasis Organism:Trichomonas vaginalis Trichomonas vaginalis resides in the female

lower genital tract and the male urethra and prostate. 

The parasite is a trophozoite only; it does not have a cyst form, and does not survive well in the external environment. 

Trichomonas vaginalis is transmitted among humans, its only known host, primarily by sexual intercourse.

Trichomonas vaginalis

Trichomonas vaginalis Trophozoite

Undulating membrane

Trichomonas vaginalis

Trichomonas vaginalis

RHIZOPODA DISEASE

Amebiasis Entamoeba histolytica Naegleria fowleri

Entamoeba histolytica

Disease: Amebiasis This is a global disease that any traveler can get.

As soon as you cross the border into Mexico, you are exposed to it.

Several protozoan species in the genus Entamoeba infect humans, but not all of them are associated with disease. 

Entamoeba histolytica is associated with intestinal and extraintestinal infections. 

The other species are important because they may be confused with E. histolytica in diagnostic investigations.

Geographic Distribution

Worldwide, with higher incidence of amebiasis in developing countries. 

In industrialized countries, risk groups include male homosexuals, travelers and recent immigrants, and institutionalized populations.

Entamoeba histolytica Life Cycle Cysts and trophozoites are passed in feces.  Infection occurs by ingestion fecally

contaminated food (including undercooked meat), water, or hands. 

Excystation occurs in the small intestine and trophozoites are released, which migrate to the large intestine. 

The trophozoites multiply by binary fission and produce cysts, and both stages are passed in the feces. 

Entamoeba histolytica Cysts can survive days to weeks in

the external environment and are responsible for transmission. 

Trophozoites passed in the stool are rapidly destroyed once outside the body, and if ingested would not survive exposure to the gastric environment. 

Entamoeba histolytica In many cases, the trophozoites remain

confined to the intestinal lumen (noninvasive infection) of individuals who are asymptomatic carriers, passing cysts in their stool. 

In some patients the trophozoites invade the intestinal mucosa (intestinal disease), with resultant pathologic manifestations. 

E. histolytica can be observed with ingested red blood cells. 

Entamoeba histolytica Diverse mammals such as dogs and cats

can become infected but usually do not shed cysts with their feces, thus do not contribute significantly to transmission.

The active (trophozoite) stage exists only in the host and in fresh feces; cysts survive outside the host in water and soils and on foods, especially under moist conditions on the latter. It is NOT caused by undercooked meat.

Entamoeba histolytica Entamoeba histolytica, as its name

suggests, can actually bore through the enteric walls (histolysis = destroying tissue) and reach the blood stream.

From there, it can reach different vital organs of the human body, like the liver, lungs, brain, eyes etc.

A typical effect is a liver abscess caused by such migrating Entamoeba histolytica, which can be fatal.

Entamoeba histolytica Entamoeba histolytica infection

can lead to amebiasis or amebic dysentery. Symptoms include dysentery, diarrhea, weight loss, fatigue, and abdominal pain.

It can be diagnosed by stool samples. Trophozoites should be seen in a fresh fecal smear and cysts in an ordinary stool sample.

Entamoeba histolytica

Treatment Metronidazole

Diagnostic Features Ingested RBC Bull’s eye Karyosome

Entamoeba histolyticaTrophozoites

Entamoeba histolytica

Trophozoites of Entamoeba histolytica with ingested erythrocytes

Entamoeba histolytica

Cysts

Entamoeba histolytica

Entamoeba histolytica

Naegleria fowleri Disease: Amebiasis; meningitis form

Acute, usually lethal, central nervous system (CNS) disease.

Three stages: Cysts Trophozoites Flagellated forms

Naegleria fowleri Naegleria fowleri is found in

fresh water, soil, heated swimming pools, hydrotherapy pools, aquariums, and sewage. 

Trophozoites infect humans or

animals by entering the olfactory epithelium and reaching the brain. 

Naegleria fowleri

Trophozoites

APICOMPLEXA All members of this phylum have an organelle called an apical

complex (located at the apex of the cell) which allows the organism to attach to the host. This is a type of adhesion complex.

 They all require a biological vector for transmission (to get into the blood of the host).

They have at least two hosts: the animal vector and the human host. That makes it a complex life cycle. Because it uses an animal host, there is an animal reservoir.

Definitive Host: where the parasite completes its sexual life cycle.

Intermediate Host: where the parasite goes through its asexual cycle.

APICOMPLEXA DISEASES

MalariaToxoplasmosisCryptosporidiosis

Malaria

Causal Agents: Plasmodium vivax (most common) Plasmodium falciparum (most deadly) P. ovale  P. malariae.

Plasmodium

Malaria

200-300 million infections a year 2-3 million deaths a year Affects mostly young people and

teenagers 2/3 of the cases are in Africa

Plasmodium The malaria parasite life cycle involves two hosts.  Sporogenic Stage

During a blood meal, a malaria-infected female Anopheles mosquito inoculates sporozoites into the human host. 

Hepatic Stage Sporozoites infect liver cells and mature into schizonts , which rupture

and release merozoites into the bloodstream.  Blood Stage

Merozoites infect red blood cells The parasites undergo asexual multiplication in the erythrocytes. The ring stage trophozoites mature into schizonts, which rupture

releasing merozoites. Some parasites differentiate into male and female gametocytes.  Blood stage parasites are responsible for the clinical manifestations of

the disease. 

Plasmodium The male and female gametocytes are ingested

by another Anopheles mosquito.  The parasites’ multiplication in the mosquito is

known as the sporogonic cycle, generating zygotes. 

The zygotes develop into oocysts.  The oocysts grow, rupture, and release

sporozoites, which make their way to the mosquito's salivary glands. 

Inoculation of the sporozoites into a new human host perpetuates the malaria life cycle. 

Malaria Symptoms

Fever, chills, sweating, headaches, muscle pains

Severe complications (cerebral malaria, anemia, kidney failure) can result in death.

Anopheles Mosquitoes Female mosquitoes need blood

meals to nourish their eggs.

Schizont: Hepatic Stage

Schizont: Hepatic Stage

Blood Phase: Rings

Blood Phase: Rings

Malaria

Merozoites being released from lysed RBC.

Gametocyte: Blood Stage

Gametocyte: Blood Stage

Toxoplasmosis

Organism: Toxplasmosis gondii Infects most species of warm blooded

animals, including humans.

Toxplasmosis gondii

Toxplasmosis Cats are the only known definitive hosts for

the sexual stages of T. gondii and thus are the main reservoirs of infection. 

Cats become infected by eating infected wild animals (e.g. birds)

Tissue cysts or oocysts are excreted in the feces.

Oocysts can survive in the environment for several months and are remarkably resistant to disinfectants.

Toxplasmosis

Human infection may be acquired in several ways: A) ingestion of undercooked infected

meat B) ingestion of the oocyst from fecally

contaminated hands or food C) organ transplantation or blood

transfusion D) transplacental transmission

ToxplasmosisGeographic Distribution:

Serologic prevalence data indicate that toxoplasmosis is one of the most common of humans infections throughout the world. 

Infection is more common in warm climates and at lower altitudes than in cold climates and mountainous regions. 

High prevalence of infection in France has been related to a preference for eating raw or undercooked meat

High prevalence in Central America has been related to the frequency of stray cats.

Toxplasmosis Cyst

Cyst in brain tissue

Toxplasmosis Tachyzoites Tachyzoites

Toxoplasmosis Trophozoites

Toxplasmosis

Oocyst

Toxoplasma tachizoites

Toxplasmosis

Ocular toxoplasmosis

Cryptosporidiosis

Organism: Cryptosporidium Spread through the fecal-oral route,

often through contaminated water Causes self-limiting diarrhea in

people with intact immune systems. In immunocompromised individuals

(such as AIDS patients), symptoms are severe and often fatal.

Cryptosporidium

CILIOPHORA DISEASE Disease: Balantidiosis Organism: Balentidium coli (The name tells

you it lives in the colon)

The animal reservoir is the pig. Its geographical distribution is world-wide, wherever humans and pigs live nearby each other.

This is the only ciliated protozoan that causes disease in humans.

Balantidiosis Causal Agent: Balantidium coli This is almost identical to Enamoeba

histolytica. The cyst form is infective. It has a thick wall to protect it from

stomach acid. It enters the human (and dogs) by

ingestion of fecal contaminants on food, water, and hands.

Balantidiosis Once in the colon, it undergoes

excystment (cyst transforms into trophozoite).

In the trophozoite form, they reproduce in the large intestine, invade the colon wall, and cause ulcerations in the colon.

Like Entamoeba, it leaves a flask-shaped ulcer.

Symptoms include diarrhea and GI discomfort.

Balantidiosis Cysts are the parasite stage

responsible for transmission.  The host acquires the cyst through

ingestion of contaminated food or water (NOT in undercooked meat). 

Common in pigs

Balantidium coli Following ingestion, excystation occurs in

the small intestine, and the trophozoites colonize the large intestine. 

The trophozoites reside in the lumen of the large intestine of humans and animals, where they replicate by binary fission, during which conjugation may occur. 

Trophozoites undergo encystation to produce infective cysts.

Mature cysts are passed with feces.

Balantidium coli

Balantidium coli Trophozoites characterized by:

Large size (40 µm to more than 70 µm). Presence of cilia on the cell surface A cytostome. A bean shaped macronucleus which is often

visible and a smaller, less conspicuous micronucleus.

Balantidium coli Trophozoites

Cytostome Cytostome

Balantidium coli

Trophozoites

Balantidium coli Trophozoite

Balantidium coli Cyst

Balantidium coli Cysts

MASTIGOPHORA DISEASES

Trypanosomiasis Leishmaniasis

Trypanosomiasis

African Trypanosomiasis (African Sleeping Sickness)

American Trypanosomiasis (Chaga’s Disease)

“African Sleeping Sickness”

Disease: African Tryptanosomiasis

Causal Agents: Trypanosoma brucei gambiense Trypanosoma brucei rhodesiense

Geographic Distribution

T. b. gambiense is found in foci in large areas of West and Central Africa.  Humans are the main reservoir for

Trypanosoma brucei gambiense, but this species can also be found in animals.

T. b. rhodesiense is found in East and Southeast Africa. Wild game animals are the main reservoir

of T. b. rhodesiense.

Trypanosomiasis

Trypanosomiasis has a biological vector, the tsetse (pronounced “set-see”) fly.

Wild animals may also be a reservoir (Zooinotic is when a disease is transmitted to animals as well as humans.)

Trypanosomiasis

The tsetse fly bites a human and injects the trypanomastigotes into the skin.

This causes a chanchre (pronounced “shanker”), which is an ulcer on the skin.

Then it enters the lymphatic system.

Trypanosomiasis

It is characterized by Winterbottom’s Sign: swelling of the cervical lymph nodes in the head and neck area.

CNS symptoms include a shuffling gait (like a stroke victim), slurred speech, and malaise (needing to sleep longer and longer each day).

They are also restless at night.

Trypanosomiasis CNS symptoms

Shuffling gait Slurred speech Malaise (sleeping all day)

Treatment Melarsoprol: which has dangerous side-effects like

chemostherapy. This drug requires administration with a substance called ethylene glycol, which will break down regular plastic tubing, so the drug must be administered with special plastic iv tubing.

Trypanosoma brucei Trypomastigote stages are the only

form found in patients. Posterior kinetoplast Centrally located nucleus Undulating membrane Anterior flagellum

Trypanosoma brucei

Trypanosoma brucei gambiense

trypomastigote

Trypanosoma

Trypanosoma brucei rhodesiense

Trypanosoma brucei

UM

Tsetse Fly

“Chaga’s Disease”

Disease: American TryptanosomiasisA zoonotic disease (can infect animals) that can be transmitted to humans by blood-sucking bugs. 

Causal Agent: Trypanosoma cruzi This organism is a little smaller than T.

bruceii and has a pronounced gametoplast.

“Chaga’s Disease” This disease is NOT found in Africa. This disease is also zoonotic; it can infect

animals as well as humans. The vector is a large bug called the “Kissing

Bug”. It is found in warm regions and crowded areas,

especially in the cracks of adobe huts. It comes out at night and crawls on a human

while they sleep.

“Chaga’s Disease” It prefers the lips because the blood supply is

close to the surface. It sucks the blood there, but they don’t

transmit the organism this way. When they suck the blood, they also defecate,

and the organism is in the feces.   When the human wakes up to scratch the itch,

feces get into the tiny wound. This is a fecal blood route.

“Chaga’s Disease” Symptoms include fever, anorexia, swollen

lymph nodes, hepatosplenomegally (enlarged liver and spleen), and myocarditis (inflammation of the heart), which usually causes death.

They also have megacolon (large colon) and megaesophagus (large esophagus).

Trypanosoma cruzi Insect vector is the “kissing” bug. It takes

a blood meal and releases trypomastigotes in its feces near the site of the bite wound. 

Trypomastigotes enter the host through the wound or through intact mucosal membranes, such as the conjunctiva. 

Trypanosoma cruzi can also be transmitted through blood transfusions, organ transplantation, transplacentally, and in laboratory accidents.

Trypanosoma cruzi Geographic Distribution:

The Americas from the southern United States to southern Argentina.  Mostly in poor, rural areas of Central and South America.  Chronic Chagas disease is a major health problem in many Latin American countries.  With increased population movements, the possibility of transmission by blood transfusion has become more substantial in the United States.

Trypanosoma cruzi

Trypanosoma cruzi

Trypanosoma cruzi

large kinetoplast

Trypanosoma cruzi

Triatomine bug, Trypanosoma cruzi vector, defecating on the wound after taking a blood meal.

Kissing Bug

Romana’s sign

Swollen eye, seen in Chagra’s disease.

TERMS Promastigote: has single flagella Amastigote: has no flagella Kinetoplast: round mass of circular DNA

Leishmania donovani

Domain: Eukaryota Kingdom: Protista Phylum: Mastigophora Class: Kinetoplastida Order: Trypanosomatida Genus: Leishmania Species: donovani

Leishmania donovani

Disease: Leishmaniasis Vector-borne disease transmitted

by sandflies.

Leishmania Life Cycle

Kinetoplast

It starts out as a spindle-shaped, single flagellated cell called a promastigote (mastigote means flagella).

You can also see the nucleus and a kinetoplast (mass of circular DNA).

Leishmania rosette

In prepared slides you can see promastigotes align their nose in a circle, called a rosette.

Leishmaniasis rosette

Leishmania Life Cycle It reproduces in the gut of a female

sandfly, and migrates to her proboscis (mouth part).

It is introduced into the human by her bite.

It then enters a macrophage and becomes intracellular.

Here, it loses its flagella and is now known as an amastigote.

Leishmaniasis These amastigotes multiply in various

organs including the spleen, liver, and lymph nodes.

Symptoms include hepatosplenomegaly, lymph adenopathy, fever, weight loss, and a decrease in all blood cells: WBC, RBC, and platelets.

The treatment is almost as bad as the disease because of the side effects. It is best to catch it early.

Leishmania Life Cycle The female sandflies inject the infective

stage, promastigotes, during blood meals. 

Macrophages phagocytize them and they transform into amastigotes. 

Other sandflies become infected during blood meals when they ingest infected macrophages.

In the sandfly's midgut, the parasites differentiate into promastigotes, which multiply and migrate to the proboscis.

Leishmaniasis Life Cycle

Leishmania donovani (Promastigote)Single flagellum found in sand flies

Leishmaniasis

Amastogotes

Amastogotes with nucleus and kinetoplast

Macrophage rupturing

Leishmania

Amastigotes

Sandfly This looks like

a mosquito, except its body is hairy and the wings are feathery.

Leishmaniasis Geographic Distribution:

More than 90 percent of the world's cases of visceral leishmaniasis are in India, Bangladesh, Nepal, Sudan, and Brazil.

Leishmaniasis is also found in Mexico, Central America, and South America, southern Europe, Asia, the Middle East, and Africa.

Leishmaniasis

There are three forms of Leishmaniasis: Cutaneous Mucocutaneus Visceral

Cutaneous Leishmaniasis The disease is only at the site of the bite. This form is seen in Texas, Mexico, Asia, and

the Middle East (our Iraq troops are coming down with this form).

It manifests as a large, wet sore with raised edges. It looks like a volcano with weepy serum coming out of the center.

The wound is not contagious, just the sandfly bite.

Dogs can get this disease, too.

Leishmaniasis (cutaneous)

Leishmaniasis (cutaneous)

Leishmaniasis (cutaneous)

Leishmaniasis (mucocunateous)

This is when the disease located in the mucous membranes of the nose and mouth.

The most gruesome photos are of this form.

Leishmaniasis (mucocunateous)

Leishmaniasis (visceral)

This is the most serious form. It occurs especially in immunocompromised people, especially HIV patients. The amastagotes reproduce inside

macrophages. Only T-cells can kill infected

macrophages, but HIV is a disease that infects T-cells.

This form is known as Kala Azar.

Kala Azar

Hepatosplenomegaly

Kala Azar (duodenum)