Parasitology Flashcards

1
Q

What is a parasite?

A

An organism which lives briefly/permanently, on or with the host.

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2
Q

Parasite classification

A

Ecto – live on the outer surface of host
Endo – Reside inside body
Obligate – totally dependent on their host during a certain stage
Zoonotic – Primarily infects animals and also is transmissible to humans
Facultative – display both parasitic and non-parasitic modes of existence
Accidental – attacks an unnatural host and survives
Erratic – wanders into an organ in which it is not usually found

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3
Q

Classification by parasite role in lifecycle

A

Definitive host - habours sexually mature stages of the parasite
Intermediate - harbours larval and sexually immature stages of the parasite
Reservoir host - carries same species and same stages of parasite as human, maintains the life cycle of parasite in nature and is a reservoir source of infection for man
Paratenic/transport - does not undergo development but remains alive and infective to another host
Vector - arthropod that transmits parasites from one host to another

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4
Q

Host-Microbe relationship

A

When two organisms interact together - known as symbiosis - 3types
Mutualism - generally obligatory relationship, both partners benefit.
Commensalism - one partner benfits from the association but host is neither helped nor harmed.
Parasitism - one organisms either harms or lives at expense of host

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5
Q

Modse of transmission

A

Fecal-oral transmission - egg/cysts contaminate food and consumed by host
Trophic - Parasite makes use of established predator-prey relationship that is present between definitive and intermediate host
Vertical - Transmission from mother to offspring, either via placenta or breast milk
Direct penetration
Vector transmission -
Parasites move between vector and host as vector takes blood meal

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6
Q

Vector competence and capacity

A

Not all blood feeding arthropods can act as vectors: Parasite must be able to penetrate vector gut wall, reproduce/develop/migrate to salivary glands/resist selective pressure of immune system and achieve transmission

Vector Competence - ability of particular type to become infected with a specific pathogen

Capacity linked to extrinsic factors - population size, feeding freq and time, life span, dispersal ability

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7
Q

Site specificity

A

Originates from fact that different parasites prefer to survive in different environmental conditions

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8
Q

Parasitics strategies to maintain position on/within host

A

Endo-parasites need to resist intestinal peristalsis – must cope with blood surge
Ecto-parasites – wind, rain and grooming to contend with

Methods to maintain their position –
invasion of intestinal tissue by Toxoplasma gondii
Adhesive disks – Giardia lamblia
Scolex – tapeworms
P. Faliciparum – erythrocyte membrane protein 1 – protrudes from membrane of infected cells and forms nobs

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9
Q

Parasite environmental response

A

Constant surveillance of environmental signals by parasites
Change in transcritptome and proteome – genes differentially expressed in a stage of specific manner are required for nutrient acquisition, calc signalling, lipid metab, and host immune system escape

Plasmoidum species alter production of transmissible gameteocytes in response to host stress hormones.
Trypanosoma brucei – changes morphology from long slender form to shorter form by detecting its density in the blood

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10
Q

Prevention Methods

A

General improved sanitation
Vector control
Mass screening and drug admin programmes

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11
Q

Food Safety

A

Many parasites consumed from raw/undercooked meat - beef Tapeworm, lung fluke from crabs

Food safety practices - toxoplasma gondii reduced due to increased consumption of frozen meat
Prevention through modern farming practices

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12
Q

Proper sanitation

A

Hygenic disposal of human/animal waste, provision of uncontaminated food and water cuts transmission cycle of parasites relying on fecal-oral transmission

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13
Q

Chemical prevention

A

DDT - opens sodium ion channels in neurones lading to unregulated neuron firing, spasms and death

DDT resistance - upregulation of P450 genes results in enzymatic oxidiation of certain molecules including DDT in certain insects

Organophosphates - malathion - inhibits acetylcholinesterase
Carbamate - bendiocarb - toxic to mammals
Pyrethoids - deltametrin - disrupts sodium ion channel proteins on neurons - toxic to aquatic life

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14
Q

Biological Control

A

Biological control – purposeful introduction of a biological agents to control or eradicate a pest
Preys upon/competes against pest
Cheap, environ friendly + resis development is less likely

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15
Q

Transgenic vectors

A

Transgenic vectors – reduced vector capacity
Reduction strategy – relies on vector introduction with lower fitness – mating does not lead to progeny
Replacement – Introduction of a vector resistance to disease agent – replaces wild type.
Sterile-male technique

Limitations - transgenic vectors less competitive/fit than their wild type counterparts

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16
Q

Helminths

A

Multicellular, billateraly symmetrical parasites

Cestode - tape worms
Trematode -flukes
Nematode - round worms

17
Q

Trematodes (Flukes)

A

Vetabrate parasites – require one or more intermediate hosts
Eggs pass through environment and larva hatch and swim away to infect intermediate host (a species of mollusk)
Larva known as cercariae are produced
Infiltrate via skin and develop into adults which enter an intermediate host and wait to be ingested – metacercariae
Attach to vegetation, secrete a resistant cyst wall and wait to be eaten

18
Q

Shistosamiasis - Bilharzia

A

Human infection takes place by direct penetration of cercariae

Exposure to freshwater contaminated with eggs
Symptoms include rash/itchy skin, fever, chills, cough, muscle eggs
Symptoms cause by bodies reaction to eggs produced by worms not the worms themselves
Definitive diagnosis by identifying the schistosome
Praziquantel used for therapy

19
Q

Cestodes

A

Cestodes – adult worms found in small intestine
Larval tapeworms – extraintestinal tissues and produce systemic infections with clinical effects related to the size, number and location of cysts

Eggs hatch in gut releasing onchosphere that migrates through gut wall and blood vessels to encysts in muscle – forms cysticerci (scolex containing cysts)

20
Q

Cestode examples

A

Intestinal - Tapeworms
Taenia saginata - worldwide, uncooked contaminated beef, common infection causing minimal symptoms
Taenia solium - worldwide, uncooked pork containing cysticerci, less common causes cysticercosis

Systemic - Echniococcus granulosus (dog tapeworm) and Echinicoccus multicocularis (rodent tapeworm) -
hydatid disease occurs when larval stages of these organisms are ingested
Larvae develop in human host and cause space-occupying lesions in several organs

21
Q

Taenia solium/saginata (tapeworm) lifecycle

A

Eggs passes in faeces (in solium ingestion or release of eggs in upper intestines can cause cysticercosis)

Cattle (saginata) and pigs (solium) infected from ingesting eggs/proglottids

Eggs hatch releasing onchosphere which migrates through gut wall and blood vessels to encyst in striated muscle, forms cysticerci (cysts containing scolex).

Raw/undercooked meat ingested

22
Q

Ascaris lumbricoides - life cycle

A

Adult worms in small intestine lay large numbers of eggs
Eggs passed with faeces and contaminate veg
Larvae develop inside eggs, swallowed in undercooked food
Eggs enter small intestine where larvae hatch
Larvae penertrate gut mucosa – carried via hepatic circulation to heart and lungs
Develop and escape into alveoli
Re-enter stomach via trachea/oesophagus – pass into small intestine and grow to adulthood

23
Q

Toxocara canis/cati

A

Eggs from dogs/cats passed in faeces and mature in soil
Eggs ingested and hatch in small intestine
Larvae penertrate intestinal mucosa, enter bloodstream and carried to tissues
In humans – larvae become arrested in tissues – gives visceral larva migrans/ocular larva migrans