Review of Parasitology

Dr. Sana ArshadStudent of Doctor of Medical Laboratory Sciences

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The science dealing with the study of parasites & their pathogenicity is called parasitology.

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A living organism that has adopted itself to exist in other animal-HOST is called parasite.• Definitive Host (Sexual Life Cycle)• Intermediate Host (Asexual Life Cycle)

Direct Life Cycle (ONLY ONE HOST)Indirect Life Cycle (TWO OR MORE HOSTS)

Parasites3

Classification4

Unicellular Simple OrganismsSarcodina (Amoeba)Ciliata (Paramecium)Sporozoa (Plasmodia)Mastigophora (Trichomonas, Giardia lamblia)

Protozoa5

Sarcodina--Amoeba (Entamoeba histolytica)

Disease:Amebic Dysentery & liver abscesses

Transmission & Epidemiology:

Fecal-oral route of cyst. Humans are definitive host. Most common in tropical countries.

Characteristics:Intestinal protozoan; Trophozoite(motile form, 1 nucleus karyosomal point, several RBCs);

Cyst (Coin shaped, 2-4 nuclei, chromatin bodies).

Pathogenesis:Trophozoite invade colon epithelium & produce flask shaped ulcers. Can spread to liver and cause amebic abscess.

Lab Diagnosis:Trophozoite and cysts visible on stool sample. Serological and Molecular tests give positive result.

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Sarcodina--Amoeba (Entamoeba histolytica)

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Life Cycle

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Mastigophora--Flagellates (Trichromonas)

Disease:Trichomoniasis

Transmission & Epidemiology: Transmitted sexually. Human are their definitive host. Occurs worldwide.

Characteristics:Urogenital protozoan; Trophozoite only (Pear shaped, flagellated)

Pathogenesis:Trophozoite attach to wall of vagina & cause inflammation & greenish-watery discharge

Lab Diagnosis:Trophozoites are visible in HVS. No serological test.

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Mastigophora--Flagellates (Trichromonas)10

Life Cycle

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Mastigophora--Flagellates (Giardia lamblia)

Disease:Giardiasis (diarrhea)

Transmission & Epidemiology:

Fecal-oral route of cysts; Human are their definitive host; occurs worldwide

Characteristics: Intestinal protozoan; trophozoite ( pear shaped, 2 nuclei, flagellated); cyst (oval shaped, 4 nuclei)

Pathogenesis:

Trophozoites attach to intestinal wall but do not invade. Causes malabsorption of proteins & fats. Severe chronic diarrhea with no fever.

Lab Diagnosis:Trophozoite and cysts are visible in stool or duodenal aspirate.

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Mastigophora--Flagellates (Giardia lamblia)13

Life Cycle

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Sporozoa--Protozoans (Plasmodium)

Disease:Malaria

SpeciesP.vivax, P.falciparum (Common), P.malariae, P.ovale.

Transmission & Epidemiology:

Transmitted by female Anopheles mosquitoes (definitive host) to humans (intermediated host). Occurs in tropical areas.

Characteristics:

Two phases of life cycle (Sporogony or schizogony)

Pathogenesis:Merozoites destroy RBCs causing Anemia, hepatomegaly, splenomegaly, Blackwater fever, fever cycle, Cerebral malaria

Lab Diagnosis:Protozoans are visible in blood smears, serological tests are available to detect malaria antigen.

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Sporozoa--Protozoans (Plasmodium)16

Mal

aria

Quartan(78hrs)

P. malariae Infect Mature RBCS

Tertian(48hrs)

Others

Benign

P. vivax Infect reticulocytes

P. ovale

Malignant P. falciparum Infect all Stages of RBCs

Life Cycle

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Multicellular Complex OrganismsNemathelminthesPlatyhelminthes

TrematodesCestodes

Metazoa18

Nematodes--Roundworms19

Nematodes

Intestinal worms

Entrobius

Trichuris

Ascaris

Necator

Ancylostoma

Tissue worms

Loa

Wuchereria

Onchocerca

Guinea worm Dracunculus

Nematodes--Roundworms (Ascaris lumbricoides)

Disease:Ascariasis

Transmission & Epidemiology:

Transmitted by food contaminated with soil containing eggs. Humans are their Definitive host.

Characteristics:Intestinal Nematode; fertilized egg (yellow brown-oval shaped or thick shell); infertile eggs (darken color-elongated shape or thin shell); pinkish worm, male is thinner and smaller than female

and tail is curved. Pathogenesis:

Larvae in lungs cause pneumonia. Heavy worm burden may cause intestinal obstruction and malabsorption.

Lab Diagnosis:Eggs are visible in stool samples; Eosinophilia occur.

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Nematodes--Roundworms (Ascaris lumbricoides)

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Schistosoma (blood flukes)• S. mansoni

• S. japonicum

• S. hematobium

• S. intercalatum

• S. mekongi

Clonorchis sinesis (liver flukes)Paragonium westermani (lungs flukes)

Trematodes--Flukes23

GIT

Urinary Tract

Trematodes—Flukes (Schistosoma)

Disease:Schistosomiasis

Transmission: Transmitted by penetration of skin by cercariae. Human are definitive host, snails are intermediate host.

Characteristics:Trematodes blood flukes; adult exists as two separate sexes attaches to each other; eggs of S. mansoni (prominent lateral spine), S. japonicum (rudimentary spine) or S. hematobium (Terminal spine).

Pathogenesis:

Eggs in tissue induce inflammation, granulomas, fibrosis & obstructions in liver, spleen & urinary bladder; S. mansoni & S. japonicum damages the GIT or S. hematobium damages the Urinary bladder

Lab Diagnosis:Eggs visible in stool or urine sample.

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Trematodes—Flukes (Schistosoma)25

S. japonicumS. hematobiumS. mansoni

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Taenia soliumTaenia saginataDiphyllobothrium latumEchinococcus granulosus

Cetodes/Tapeworms27

Cestodes--Tapeworms (Echniococcus granulosus)

Disease:Hydatid Cyst Disease

Transmission: Transmitted by ingestion of eggs in food contaminated with pets (dogs). Dogs are definitive host, sheepsare intermediate host while humansare dead end host.

Characteristics:Dog tapeworm; scolex has 4 suckers & pair of hooks, adult worms has only 3 proglottids (Immature, Mature, Gravid); eggs( 3 pairs of hoocklets); hydatid cyst( fibrous wall of host, fluid fill cavity,

brood capsule contains scolices); protoscolex (invaginated or evaginated)

Pathogenesis:Hydatid cyst is a space occupying lesions, if rupture causing anaphylaxis. Also cause diseases of lungs, bones & liver.

Lab Diagnosis:Serological test (+ve serum hem-agglutination test). Pathological examination of cyst.

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Cestodes--Tapeworms (Echniococcus granulosus)29

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THANK YOUAny question?????

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