Parasitology Final

Ideal parasite

move from a parasitic relationship to a commensal relationship

Example of an ideal parasite

*T. saginata*

What is parasitism?

a symbiotic relationship between two different species, where one, the parasite, benefits at the expense of the other, the host.

What can be considered as an extreme environment?

the host

Parasite habitats

vertebrate alimentary canal and lumens; tissues

What are the three basic types of adaptations?

behavioral, physiological (LC), and structural (morphological)

list of morphological adaptations

size, shape, attachment, body surface, reproductive system

size

larger to house reproductive system

list of shape adaptations

* long and thin: dense connective tissue (*D. medinensis*)
* flat and broad: cling to host tissue (*F. buski and T.solium*)
* round: lumen dwelling (*W. bancrofti*)

list of attachment adaptations

* suckers/acetabula
* biological holdfast
* hooks
* teeth

parasites with suckers/acetabula

Cestodes and Trematodes

parasites with biological holdfast

Protozoa and Giardia

parasites with hooks

Cestodes and Acanthocephalans

list of body surface adaptations

* cuticle (resistance to host natural & specific immunity)
* absorptive surface (absorb nutrients via tegument)

parasites with cuticle

Nematodes

parasites with absorptive surface

tapeworms

methods of absorptive surface

* active transport
* facilitated diffusion
* simple diffusion

example of dioecious reproductive system (2 separate sexes)

nematodes; *A. lumbricoides*

examples of a hermaphroditic parasite

* Cestodes; *T. saginata*
* Trematodes

parasite with reproductive cyst

*E. histolytica*

complex life cycle

allow sexual and asexual reproduction

parasites with complex life cycles

Schistosomes and Plasmodium

parasites with bioaccumulation

*D. latum*

parasite with a parasitic and free living life cycle

*Strongyloides stercoralis*

what is nonspecific immunity?

differentiates self from non self

aspects of nonspecific immunity

phagocytosis and inflammation

what is inflammation?

movement and actions of WBCs at the site of injury/infection

steps of inflammation?

* margination (adhesion)
* diapedesis (migration of cells through the walls of blood capillaries into the tissue spaces)
* chemotaxis (movement)
* ingestion
* digestion
* granuloma formation

specific immunity mediated by

T-cells and B-cells

humoral (immunoglobulin or antibody) = ?

B-cells

cell mediated immunity = ?

T-cells

maturation of T-cells location

thymus

maturation of B-cells location in mammals

bone marrow

maturation of B-cells location in birds

bursa

parasitic infection can result in

disease

results of disease

* chronic infection
* recovery
* death

chronic infection

immunity to trickle infections

recovery

immunity to reinfection

list of intestinal nematodes

* *Ascaris lumbricoide*s (giant round worm)
* *Necator americanus* (hookworm)
* *Trichinella spiralis* (pork worm)

list of blood and tissue parasites

* *Schistosoma mansoni* (Bilharzia)
* *Trypanosoma gambiense* (African sleeping sickness)

blood and tissue parasites have

greater pathology

Immune response to *Ascaris*

avoids the immune system by living in the small intestines (feeds on what we eat, not us)

Immune response to hookworms (*Necator*)

some inflammation due to partial tissue invader

Immune response to *Trichinella*

tissue invader; good immune response, but leave larvae behind

*Ascaris lumbricoides* location

* larvae in lungs
* adults in small intestines

*Ascaris* pathology

blockage of small intestine, bile duct, mouth and nose, appendix

*Trichinella spiralis* adults cause

severe intestinal inflammation - self-cure - worms expelled in 14 days

*Trichinenella spiralis* larvae travel to and are sequestered in

muscle cells

Who lives in the most extreme environment?

*Trichinella* - deep in the mucosa of the small intestine

what type of immunity is most important in *Trichinella* expulsion?

cell mediated immunity (T-cells)

which T-cell is most important in *Trichinella* expulsion?

Th1 cell

*Trichinella spiralis* immune response mechanism:

1. worm antigens
2. Cell stimulation (Th2, Antibody in lymph node, Th1)
3. antibody and Th1 cell locate antigens
4. Th1 secrete lymphokines (attracts immune response; stimulatory, chemotactic, and arming)
5. Inflammatory cells activated (monocytes-macrophages target antigens)
6. worms move down the S.I. until expulsion
7. larvae left behind

Primary immune response of *Trichinella spiralis* (initial exposure)

small numbers of Th1/Th2/B-cells that recognize T.spiralis = expulsion in 14 days

Secondary immune response of *Trichinella spiralis* (secondary exposure)

MEMORY Th1/ Th2/ B-cells that recognize T.spiralis = expulsion in 7 days

*Trichinella* moves to new tissue…

inflammation follows

which experiment proves molecular mimicry by worm transplants between host?

Smithers’ Experiment

molecular mimicry

antigen masking

immunity against schistosomes

antibody and WBCs most effective

Smithers’ experiment conclusion

* worms survive by using molecular mimicry by acquiring blood group antigens on their outer surface
* surface of schistosomes is comprised of novel glycans

Smithers’ experiment transfer outcomes:

* infected monkey → normal monkey = worms survive
* infected monkey → anti-mouse monkey = worms survive
* infected mouse → normal monkey = worms survive but egg laying was interrupted
* infected mouse → anti-mouse monkey = worms killed

*Trypanosoma gambiensis* pathology

* African sleeping sickness
* gains access to the CNS → perivascular cuffing
* confusion → inactivity → coma → death

why does *Trypanosome* parasitemia fluctuate?

* specific antibody against glycoprotein coat and changing glycoprotein coat
* alternate expression of genes controlling variant specific surface glycoproteins (VSG coat)

Is *Trypanosoma* manipulating the immune system?

yes

What benefit is it to the parasite to manipulate the immune system?

population control

which parasites have **immuno-avoidance**?

*Ascaris* & hookworm

which parasite is dependent on **life cycle development**?

*Trichinella*

which parasite use **molecular mimicry**?

Schistosomes

which parasite have **antigenic variation**?

Trypanosomes