Introduction to Parasitology

Introduction to Parasitology

parasite definition An organism that lives off or in another

organism, obtaining nourishment and protection while offering no benefit in

return. Human parasites are often harmful to the body and can cause

diseases.

Note : The term parasite is often applied to a person who takes

advantage of other people and fails to offer anything in return.

Medical Parasitology

Parasites Parasitic diseases

Definition of Medical Parasitology

Mo

rph

olo

gy

Life

Cycle

Path

og

enesis

Diag

no

sis

Treatm

ent

Tran

smissio

n

Preven

tion

------ An association which is beneficial to

one partner and harmful to the other

partner. The former that is beneficial to

is called parasite, the latter that is

harmful to is called host.

Human / Hookworm

Parasitism

Parasite: It is an animal that is dependent

on another animal (host) for its

survival. Type of parasites

Protozoa

Nematodes

Parasites Helminths Trematodes Endo-

Cestodes

Arthropods ---------------- Ecto-

Parasite and the type of parasites


HelminthesCestodes (flatworms)Nematodes (roundworms)Trematodes (flukes)


Athropods Host Parasites

Insects

-mosquitoes, lice, and fleas Arachnids

- ticks and mites


3 major groups of parasites:

1. Protozoa- flagellates, amebas, malarial organisms

2. Helminths - parasitic worms such as the flukes, tapeworms, and roundworms

3. Arthropods - insects and arachnids that are ectoparasites and carriers (vectors) of diseases

Protozoa!

Arthropods!

Helminths

Worm classified as a parasite Contaminate food, water, air, feces, pets,

wild animals, toilet seats and door handles Prevention:

Frequent hand washing Frequent cleaning of bathrooms and kitchens Thorough cooking of beef, pork, sausage, and

bear meat.

---A parasite which lives in or on the

body of the host is called endoparasite

(protozoa and heminthes) or ectoparasite

(arthropods).

Endoparasite and ectoparasite

Nematodes (roundworms)

have long thin unsegmented tube-like bodies with anterior mouths and longitudinal digestive tracts.

They have a fluid-filled internal body cavity (pseudocoelum) which acts as a hydrostatic skeleton providing rigidity (so-called ‘tubes under pressure’).

Cestodes (tapeworms)

have long flat ribbon-like bodies with a single anterior holdfast organ (scolex) and numerous segments.

They do not have a gut and all nutrients are taken up through the tegument.

They do not have a body cavity (acoelomate) and are flattened to facilitate perfusion to all tissues.

Segments exhibit slow body flexion produced by longitudinal and transverse muscles. All tapeworms are hermaphroditic and each segment contains both male and female organs.

Trematodes (flukes)

have small flat leaf-like bodies with oral and ventral suckers and a blind sac-like gut.

They do not have a body cavity (acoelomate) and are dorsoventrally flattened with bilateral symmetry.

They exhibit elaborate gliding or creeping motion over substrates using compact 3-D arrays of muscles.

Most species are hermaphroditic (individuals with male and female reproductive systems) although some blood flukes form separate male and female adults.

Host : An organism that harbors the parasite usually larger than the parasite.

Intermediate host : The host harboring the larvae or asexual stage of parasite.

Final host : The host harboring adult or sexual stage of parasite.

Reservoir host : Animals harboring the same species of parasites as man. Potential sources of human infection.

Host and type of host

Life cycle : The whole process of parasite growing and developing.

The direct life-cycle : Only one host (no intermediate host).

The indirect life cycle : Life cycle with more than one host (intermediat host and final host).

Life cycle and type of life cycle

injure to

Parasites harbour in Host (animal or human)

to response immune produce

Effects of the host on the parasites

Relationship (Effect) between parasite and host

----The host can produce certain degree resistance to parasites in human body or re-infection. The resistance (Immunity) is not very strong. In general, It don’t wipe out parasites completely, but may limit the number of parasites and establish balance with parasites.

Innate immunity Acquired immunity

Effects of the host on the parasites

Barrier : Prevent parasites to invade in certain degree. Skin/Mucous membrance/Placenta.

Acid in skin or stomach can cause damage of the parasites.

Phagocytosis of phagocyte.

----Non-specific/effective against a wide range of parasitic infection/controlled by genetical factors. But not very strong!

Innate immunity

Mechanism : cellular and humoral immunity.

Sterilizing immunity : Wipe out the parasites completely, meanwhile get a long-term specific resistance to re-infection. Rare!

Non-sterilizing immunity : Wipe out most of the parasites, but not completely. Common! No parasite, no immunity!

Acquired immunity

Parasitic diseases Infectious diseases Transmission The source of the infection The routes of transmission The susceptible host

----The combined effect of those factors determine the dispensability and the prevalence of the parasites at a given time and place and regulate the incidence of the parasitic diseases in certain local population.

The basic factor of transmission of parasitic diseases

Patient : Persons who have parasites in their body and show clinical symptoms.

Carrier : Persons who have parasites in their body, not show symptoms.

Reservoir host : Animals that harbors the same species of parasites as man. Sometimes, the parasites in animals can transmit into human.

The source of the infection

Congenital transmission : From mother to infant. Toxoplasmosis

Contact transmission : Direct contact---Trichomonas vaginalis; Indirect contact---Ascaris lumbricoides

Food transmission : The infectious stage of parasites contaminated food / The meat of the intermediate hosts containing infectious stage of parasites.

The routes of transmission I

Water transmission : Drink or contact the water contaminated the infectious stage of parasites.

Soil transmission : Contamintion of the soil by feces containing the certain stage of parasites and this stage can develop into stage.

Arthropod transmission : Vectors of certain parasitic diseases.

The routes of transmission II

----In general, most people is the

susceptible host (Why?). The parasite

reaching a susceptible host must gain

entrance and set up a favorable residence

in order to complete its life cycle and

cause the transmission of parasitic

diseases.

The susceptible host

Digestive tract : Most common avenue of entrance. (Food/ Water transmission)

Skin : Infective larvae perforate skin and reach to body and establish infection. (soil/ water transmission)

Blood : Bloodsucking insects containing infective parasites bite the skin and inject parasites into human blood. (Arthropod transmission---malaria).

The avenues of invasion

Controlling the source of the infection. ----Treatment of the patients, carriers and reservoir

hosts.

Intervention at the routes of transmission ----Managing feces and water resource,controlling

or eliminating vectors and intermediate hosts.

Protecting the susceptible hosts.

----Paying attention to personal hygiene, changing bad eating habit, taking medicine.

The prevention measures of the parasitic diseases

Documents

Introduction to Parasitology