Medically important Protozoa, Helminths and Arthropods

LEARNING OBJECTIVESBy the end of the lecture, student should be able:

• To classify medically important protozoa and helminths by:

• To classify medically important arthropods.

LECTURE’S OUTLINES

• protozoa and

• helminths by:

• arthropods.

Parasitic Diseases

• Protozoan and helminthic parasites exist worldwide

• Occur among people in rural, undeveloped, or overcrowded places

• Emerging as serious threats in developed nations

• Parasitic infections often involve several hosts

– Definitive host

– Intermediate host

• Parasites can infect humans in one of three ways

Routes by which humans acquire parasitic infections

THE PROTOZOANS

(SARCODINA – AMEOBA [move by pseudopodia] & MASTIGOPHORA - FLAGELLETTES)

- CILIA

or – COMPLEX LIFE CYCLE & NO LOCOMOTIVE STRUCTURE

– PRODUCE SPORE

Taxonomic classification of protozoa

Sub

kingdom

Phylum Sub-phylum Genus-

examples

Species-

examples

Protozoa Sarcomastig-

ophorafurther divided into

Sarcodina-- -move by

pseudopodia

Entamoeba E. histolytica

Mastigophoramove by flagella

Giardia G. lamblia

Apicomplexano organelle of

locomotion

Plasmodium P. falciparum,

P. vivax,

P. malariae,

P. ovale

Ciliophoramove by cillia

Balantidium B. coli

MicrosporaSpore-forming

Enterocyto-

zoa

E. bienusi

Basic Properties of Protozoa

• Cellular properties– Eukaryotic microorganisms having animal-like

cells

– No cell walls

– Most have heterotrophic metabolisms

– A few protozoa (eg Euglena) are photosynthetic

– Many are free-living in soil or aquatic environments; a few are parasitic

– Single-celled or simple colonial organization

– Classification based predominately on the mechanism of motility

Basic Properties of Protozoa

• “Trophozoite” and “Cyst”

– Some protozoa go through different stages in their life cycle.

– This is especially true of certain parasitic protozoa.

– Trophozoite: Actively growing and reproducing stage

– Cyst: A dormant stage, enclosed in a resistant cyst coat

Protozoan Diseases

A. Basic Properties of Protozoa

B. Amebiasis

C. Primary Amebic Meningoencephalitis

D. Giardiasis

E. Trichomoniasis

F. Balantidiasis

G. Toxoplasmosis

H. Malaria

I. Cryptosporidiosis

J. Pneumocystosis

SARCOMASTIGOPHORASARCODINA –

PSEUDOPODIA / AMEOBA

1. ENTAMEOBA HISTOLYTICA

1. NAEGLERIA FOWLERI

VIII. A. Basic Properties of Protozoa

• Classification– Class Sarcodina

• Motile by pseudopodia & amoeboid movement

• Amebas, radiolaria, and foraminifera

• Examples:

–Amoeba

–Entamoeba histolytica

–Naegleria fowleri

VIII. A. Basic Properties of Protozoa

• Classification (cont.)

– Class Mastigophora

• Motile by flagella

• Examples:

–Euglena

–Giardia lamblia

–Trichomonas vaginalis

VIII. A. Basic Properties of Protozoa

• Classification (cont.)

– Class Ciliophora

• Motile by cilia

• Examples:

–Paramecium

–Balantidium coli

VIII. A. Basic Properties of Protozoa

• Classification (cont.)– Class Sporozoa

• A class of parasitic protozoa

• Most have complex life cycles with both sexual & asexual stages

• Adult forms are nonmotile

• Examples:

–Plasmodium

–Toxoplasma gondii

VIII. B. Amebiasis

• Cause: Entamoeba histolytica

– A parasitic ameba; class Sarcodina

– Transmitted via contaminated food & water

– Cysts are shed in the feces

– When ingested: Excystation occurs in the intestine

– Trophozoites grow & reproduce in the intestinal tract

VIII. B. Amebiasis

• Symptoms

– Abdominal pain

– Little diarrhea but often blood in the stool (“amebic dysentery”)

– Possibly of intestinal ulceration; perforation; infection of internal organs such as liver & lungs

VIII. C. Primary Amebic Meningoencephalitis

• Cause: Naegleria fowleri– A fresh water, free living ameba

– No cyst stage

– Several cases of infections in swimmers

• Transmission and Symptoms:– Transmission through the nasal & sinus

passages

– Infection of the brain & meninges

– Headaches; delirium; seizures

VIII. D. Giardiasis

• Cause: Giardia lamblia

– A flagellate of class Mastigophora

– The trophozoite has four pairs of flagella & two nuclei; giving it a face-like appearance

– Grows in the intestinal tract

– Cysts are shed in the feces

VIII. D. Giardiasis

• Transmission and Symptoms

– Transmitted via contaminated water & food

– Foul-smelling profuse diarrhea

– Sometimes chronic

– Often misdiagnosed

– Diagnosis via microscopic examination

– Enterotest capsule

VIII. E. Trichomoniasis

• Cause: Trichomonas vaginalis– Flagellate of the class Mastigophora

– No cyst stage

• Transmission & Symptoms– Transmitted via sexual contact

– Genital itching

– Painful urination with a white, mucoid discharge

– Occasional reduction of sperm count or erosion of the cervix

VIII. F. Balantidiasis

• Cause: Balantidium coli– Ciliated, in Class Ciliophora

– Trophozoites grow in the intestinal tract

– Cysts are shed in the feces and may remain embedded in intestinal walls, causing chronic infections

• Transmission & Symptoms– Contaminated water & food

– Ulceration in intestines

– Profuse diarrhea

VIII. G. Toxoplasmosis

• Cause: Toxoplasma gondii

– In Class Sporozoa

– Both asexual & sexual stages

– Invasion of several areas of the body, including internal organs & muscle tissue

– Possibly the most prevalent protozoan parasite of humans

VIII. G. Toxoplasmosis

• Transmission & Symptoms

– Transmitted via eating contaminated meat

– Cysts are found in the meat, especially of grazing animals such as cattle

– Cats can transmit the disease through their feces

– Lymph node swelling; flu-like symptoms

VIII. G. Toxoplasmosis

• Transmission & Symptoms (cont.)

– Generally mild in non-immunosuppressed persons

– Severe infections in immunosuppressed persons

– Pregnant women are in danger of fetal damage or miscarriage

VIII. H. Malaria

• Cause: Plasmodium species

– In Class Sporozoa

– Complex life cycle requiring two hosts: a mammal (human) and the mosquito Anopheles

VIII. H. Malaria • Transmission and Symptoms

– The asexual merozoite stage infects human blood from the bite of a mosquito

– The parasite invades erythrocytes & reproduces

– Erythrocytes break open & release the parasite; this causes the characteristic fever, chills, anemia, weakness, hemorrhaging

– Intense fever & chills about 48 - 72 hr after exposure, due to the simultaneous rupture of so many erythrocytes

VIII. H. Malaria

• Transmission and Symptoms (cont.)

– The sexual stage of Plasmodium develops in the human host and is picked up by a mosquito

– The sexual stage is completed in the salivary gland of the mosquito to complete the cycle

– Treatment by quinine & other antimalarial drugs

VIII. I. Cryptosporidiosis

• Cause: Cryptosporidium species– In class Sporozoa

– A common protozoan parasite in humans

• Transmission and Symptoms– Contaminated water

– Mild diarrhea in non-immunosuppressed persons

– Severe diarrhea in immunosuppressed persons

VIII. J. Pneumocystosis • Cause: Pneumocystis carinii

– Usually classified as a protozoan of class Sporozoa, but recent evidence suggests that it may be a fungus

• Transmission and Symptoms– Transmitted by airborne contact– Usually asymptomatic or with mild respiratory

symptoms– Causes severe pneumonia in

immunocompromised persons– A major secondary infection & cause of death

in AIDS patients

Taxonomic classification of helminths

Sub

kingdom

Phylum Class Genus –

examples

Metazoa Nematodes

Round worms; appear round

in cross section, they have

body cavities, a straight

alimentary canal and an

anus

Ascaris (roundworm)

Trichuris (whipworm)

Ancylostoma (hookworm)

Necator (hookworm)

Enterobius (pinworm or

threadworm)

Strongyloides

Platyhelminthes

Flat worms; dorsoventrally

flattened, no body cavity

and, if present, the

alimentary canal is blind

ending

CestodesAdult tapeworms are found in

the intestine of their host

They have a head (scolex) with

sucking organs, a segmented

body but no alimentary canal

Each body segment is

hermaphrodite

Taenia (tapeworm)

TrematodesNon-segmented, usually leaf-

shaped, with two suckers but

no distinct head

They have an alimentary canal

and are usually hermaphrodite

and leaf shaped

Schistosomes are the

exception. They are thread-

like, and have separate sexes

Fasciolopsis (liver fluke)

Schistosoma (not leaf

shaped!)

Comparison of Body Organization of Flatworms, Roundworms, and Earthworms

Flatworm

Earthworm

Roundworm