- Commensalism - Mutualism - Parasitism

1. Definitive/Final Host 2. Intermediate Host 3. Paratenic Host 4. Reservoir Host

1 - INTRODUCTION TO MEDICAL PARASITOLOGY Flashcards by Erika Verde

Branch of biology focused on the animal parasites of human and their significance to public health
From the Greek word, “parasitos” meaning food at the expense of others

Medical Parasitology

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Living together for food and shelter

Symbiosis

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Types of Symbiosis

Commensalism
Mutualism
Parasitism

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1 benefits while the other is unharmed

Commensalism

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both organisms benefit for each other

Mutualism

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1 benefits while the other is harmed

Parasitism

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Organism that provides physical protection and nourishment to the parasite

Host

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Types of Host

Definitive/Final Host
Intermediate Host
Paratenic Host
Reservoir Host

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harbors the adult or sexually mature stage of parasite

Definitive/Final Host

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harbors the larval stage or asexual/immature forms of the parasite

Intermediate Host

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early larval stage

1st Intermediate Host

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infective/more mature larval stage; does not reach adult stage

2nd Intermediate Host

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harbors underdeveloped stage / arrested stage of development

Paratenic Host

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alternative host to a parasite that is harbored normally by humans

Reservoir Host

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Caused by Filarial worms
Intermediate Host: insect
Final Host: human

Filariasis

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Class of parasite
All infect snails as first intermediate host
Intermediate Host: snail

Trematodes (zombie snail)

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Caused by Paragonimus westermani
2nd Intermediate Host: snail, crab, human
Paratenic Host: wild boar
Continues life cycle through ingestion

Paragonimiasis

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Reservoir Host: pigs

Balantidium coli

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Organism that depends on the host for survival

Parasite

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a vector (arthropod) that serves as a vehicle to transfer a parasite to a host but is not essential in its life cycle

Mechanical Vector

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arthropod that is essential to the life cycle

Biological Vector

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Types of Parasites According to Relationship

Obligate
Facultative
Temporary
Intermittent

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Obligate

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free-living/commensal but have the tendency to become parasitic

Facultative

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obligatory to 1 stage cycle but free-living in another

Temporary

visits the host only during feeding time

Intermittent

Types of Parasites According to Habitat

1. Endoparasite 2. Ectoparasite 3. Erratic 4. Coprophilic 5. Hematozoic 6. Cytozoic 7. Coelozoic 8. Enterozoic

within the host = infection (ex. Helminthic worms)

Endoparasite

outside the host = infestation (ex. ticks, fleas)

Ectoparasite

unusual place or habitat

Erratic

usually protozoans, able to multiple in fecal matter outside of the human body

Coprophilic

lives inside red blood cells

Hematozoic

lives in cells/tissues

Cytozoic

lives in body cavities

Coelozoic

parasite residing in intestines

Enterozoic

Adaptations to Parasitism

1. Physiologic Adaptation 2. Morphologic Adaptation 3. Biochemical Changes

loss of enzymes

Physiologic Adaptation

Morphologic Adaptation

alteration of metabolic pathways and development of specialized mechanisms

Biochemical Changes

Effects of Parasites on Host (Mechanisms of Parasite Infection)

1. Damage and obstruction to intestinal wall 2. Destruction of tissues in intestinal wall 3. Destruction of RBC, causing ischemia 4. Perforation of bowel wall and invasion of nearby organs 5. Competition against essential nutrients

Damage and obstruction to intestinal wall

Fasciolopsis buski (suckers)

Destruction of tissues in intestinal wall

Entamoeba histolytica (proteolytic enzymes)

Destruction of RBC, causing ischemia

Plasmodium falciparum

Perforation of bowel wall and invasion of nearby organs

Ascaris lumbricoides

Competition against essential nutrients

* Human hookworms (N. americanus and A. duodanale) * Dibothriocephalus latus (deprives nutrients)

Human hookworms (N. americanus and A. duodanale)

Iron: Microcytic hypochromic anemia

Vit B12: Megaloblastic anemia

Dibothriocephalus latus (deprives nutrients)

Effects of Host on the Parasite

1. Genetic Constitution 2. Nutritional Status 3. Immune Mechanisms

Genetic Constitution

* Duffy null phenotype * Sickle cell trait

resistant to P. vivax

Duffy null phenotype

resistant to P. falciparum

Sickle cell trait

Nutritional Status

* High-protein diet * Low-protein diet * Rich-carbohydrate diet

High-protein diet

unfavorable for development of intestinal protozoa

Low-protein diet

appearance of amoebiasis symptoms

Rich-carbohydrate diet

favors development of tapeworms

Immune Mechanisms

may be natural or acquired

* Exist as motile trophozoite stage and the nonmotile infective cyst * Locomotor apparatus serves as one of the bases of classification

Protozoan

* Sarcodina: amoebae: equipped with pseudopods or false feet * Mastigophora: flagellates: equipped with flagellum, a whip-like structure

Phylum Sarcomastigophora

* Ciliata: ciliates: equipped with cilia, hair-like structures * Some ciliates are multinucleate, while others contain but two nuclei, a large macronucleus, and a small micronucleus

Phylum Ciliophora

only ciliate parasite of humans

Balantidium coli

* Parasites that are not equipped with definite locomotor apparatus * Demonstrates 2 cycles: * Schizogony – asexual cycle * Sporogony – sexual cycle * Contains apical complex that is composed of the ff: micronemes, subpellicular tubules, polar rings, conoids, rhoptries

Phylum Apicomplexa

causative agent of malaria

Plasmodium spp.

causative agent of Nantucket fever

Babesia microti

causative agent of Toxoplasmosis

Toxoplasma gondii

* Flatworms * Characterized by a flat, bilaterally symmetrical body * Most are hermaphroditic; having both male and female reproductive organs in the same individual * Except schistosomes * Adults may be less than 1 mm long or they may reach a length of many meters * Most are parasites, living on or in the body of their hosts

Phylum Platyhelminthes

* Mostly existing as free-living forms inhabiting terrestrial, freshwater, and marine environments * Ciliated epithelium envelops the body of the adult worm * With or without suckers * Direct development without metamorphosis * Commensals or parasites of invertebrates especially of echinoderms and molluscs

Class Turbellaria

* “Flukes” * Leaf-shaped or elongated, slender organisms * Possess attachment organs in the form of cup-shaped muscular depressions called suckers * An incomplete digestive tract is present * Of the three orders of the * Trematoda, the order Digenea contains all the species that are parasitic in humans * Members of this order have complex life histories, with at least one intermediate molluscan host * Included in the digenetic trematodes of humans are forms that inhabit: small intestine, liver, lungs, pancreas, and blood vessels

Class Trematoda

* Elongated, ribbon-like, segmented body that bears a specialized anterior attachment organ called the scolex * A digestive tract is absent * Adult cestodes or tapeworms inhabit the small intestine * Cestode larvae require an intermediate host for development * Hymenolepis nana or the dwarf tapeworm may or may not require an intermediate host; autoinfection is also observed in its life cycle * Humans may be host to either adult or larval stages depending on the species of cestode

Class Cestoda

* Nematodes or roundworms * Elongated, cylindrical worms frequently attenuated at both ends * They possess a stiff cuticle which may be smooth or may be extended to form a variety of structures, particularly at the anterior and posterior ends * The sexes are separate * Males are frequently smaller than the female and possess copulatory structures like spicule or bursa * A complete digestive tract is present * A large number of species are parasitic * Intermediate hosts are necessary for the larval development of some forms * Parasites of humans include intestinal and tissue-inhabiting species

Phylum Nemathelminthes

* Formerly classified with the Sporozoa * Minute intracellular parasites of many kinds of vertebrates and invertebrates * Differ significantly in structure from the Apicomplexa * Rarely cause disease in immunocompetent persons, but may do so with greater frequency in immunosuppressed persons * Fungi-related microorganisms * Most human infections are caused by the ff genera: Enterocytozoon and Encephalitozoon

Phylum Microsporidia

Life Cycle

1. Mode of Transmission 2. Infective Stage 3. Diagnostic Stage

means whereby a parasite gains entry into an unsuspecting host

Mode of Transmission

morphologic forms which invades humans

Infective Stage

forms that can be detected in laboratory retrieval methods (nag-iiba based on lab test)

Diagnostic Stage

Multicellular

aMetazoan

Unicellular

Protozoan

Life Stages of a Protozoan Parasite

1. Cyst 2. Trophozoite

nonmotile, resting/nonfeeding form

Cyst

motile, active/feeding form

Trophozoite

transformation from trophozoite to cyst stage

Encystation

transformation from cyst to trophozoite stage

Excystation

Life Stages of a Metazoan Parasite

1. Ova/Egg 2. Larva 3. Adult

Modes of Reproduction

1. Sexual 2. Asexual

release unembryonated/immature eggs; is not infective right away

Oviparous

release embryonated eggs; already infective (autoinfection)

Ovoviviparous

release larva directly/immediately

Larviparous

like mitosis

Binary Fission

Parasite Transmission Based on Transmission

1. Soil-transmitted 2. Vector-transmitted 3. Food-borne 4. Water-borne 5. Direct Contact

Through ingestion

Ascaris lumbricoides Trichuris trichiura

Through skin penetration

Hookworm Strongyloides stercoralis

Unholy Three

* Most common parasites * Can be present simultaneously * Ascaris lumbricoides * Trichuris trichiura * Strongyloides stercoralis

Any agent which carries and transmits an infectious organism into another living organism

Vector-transmitted

such as mosquitoes and ticks may carry pathogens that can multiply within their bodies and be delivered to new hosts, usually by biting

Biological Vector

such as flies can pick up infectious agents on the outside of their bodies and transmit them through physical contact

Mechanical Vector

Examples of Vectors

* mosquito * tsetse fly * reduviid bug * sand-fly * ticks * snails * black fly * fruitfly

causative agent of malaria

Plasmodium spp.

causative agent of filariasis

Wuchereria bancrofti

causative agent of sleeping sickness

Trypanosoma brucei

causative agent of chagas disease

Trypanosoma cruzi

causative agent of leishmaniasis

Leishmania spp

causative agent of babesiosis

Babesia microti

Snails

Schistosoma spp

Black Fly

Onchocerca volvulus

Fruit Fly

Loa loa

Copepods

Dracunculus medinensis

From raw pork meat

Taenia solium Trichinella spiralis Toxoplasma gondii

From raw beef

Taenia saginata (beef tapeworm)

From raw fish

Heterophyes heterophyes Clonorchis sinensis Opistorchis spp

From crabs/crustaceans

Paragonimus westermani

From vegetables

Fasciola spp Fasciolopsis buski

Water-borne protozoans

Intestinal Amoeba Intestinal Flagellates Intestinal Coccidian

Direct Contact

Trichomonas vaginalis Enterobius vermiculari

Portals of Entry

1. mouth 2. skin 3. intranasal 4. transmamary 5. sexual

Embryonated egg

Ascaris, Trichuris

Cyst

Entamoeba histolytica

Metacercaria

Fasciola spp

Trophozoite

Entamoeba gingivalis

Filariform Larvae

Hookworm & Strongyloides stercoralis

Cercaria

Schistosoma japonicum

Sporozoites

Plasmodium spp

Trypomastigotes

Trypanosoma spp

Intranasal

Naegleria fowleri trophozoite

Transmammary

Ancylostoma duodenale (hookworm)

Sexual

Trichomonas vaginalis

Infected individual becomes his own direct source of infection

Autoinfection

* Already infected individual is further infected with the same species leading to massive infection with the parasite * Also known as hyperinfection

Superinfection

Portals of Exit

1. Stool 2. Blood 3. Sputum 4. Urine

Stool

Ascaris lumbricoides Trichuris Hookworm Taenia Entamoeba

Blood

Plasmodium spp Wuchereria Trypanosoma

Sputum

Paragonimus Ascaris

Urine

Schistosoma haematobium Trichomonas vaginalis

Study of occurrence and distribution of disease in human population and communities

Epidemiology

No. of cases of a disease that are present in the population at a given time

Prevalence

No. of new cases that developed

Incidence

The act of occurring again

Recurrence

Clinical consequences of infections or diseases

Morbidity

No. of deaths within a particular society and period of time

Mortality

No. of worms per infected persons

Intensity of Infection

When a disease in a population maintains a relatively steady, moderate level

Endemic

When an outbreak of considerable intensity/sharp rise occur

Epidemic

If the prevalence of a disease is high

Hyperendemic

If it appears only occasionally in one or few members of the community

Sporadic

The disease covers extensive area of the world

Pandemic

1 - INTRODUCTION TO MEDICAL PARASITOLOGY Flashcards

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