Unit 1 Introductory Concepts of Parasitology

MT 639 LECTURE

Symbiosis

living together of unlike organisms

association of two species for food and shelter

Commensalism

“eating at the same table” in Latin

one species benefits from the relationship without harming or benefiting from the other

Commensalism

What type of symbiosis?

*Entamoeba coli* living in intestinal lumen and does not harm

Mutualism

a symbiosis where two organisms benefit from each other

“give and take”

Mutualism

What type of symbiosis?

Termites and flagellates, where flagellates have enzymes (Lignin & cellulose) to digest wood

Parasitism

symbiosis where an organism lives in or on another for its survival and usually at the expense of the host

Parasitism

What type of symbiosis?

Entamoeba histolytica gets nutrition from human host and causes amebic dysentery (blood in stool)

ONE HEALTH - GIDA

Geographically Isolated and Disadvantaged Areas

public health initiative wherein we should also take care of other organisms and the environment for parasites not to circulate in the community

Endoparasite

Ectoparasite

Erratic

3 types of parasite acc. to habitat

Endoparasite

**= INFECTION**

parasite inside the host’s body

located in organs and circulates around the body

EX. *Ascaris lumbricoides*

* giant intestinal roundworm / nematode


* also **erratic parasite**

Ectoparasite

**= INFESTATION**

parasite on the surface of the body

EX. Lice

* head, body, and pubic lice
* humans as their only host
* sucks blood, skin gets itchy

Erratic

a parasite in an organ which is **not its usual habitat**

Obligate

Temporary

Intermittent

Facultative

Accidental / incidental

Permanent

Spurious

Types of parasites acc. to relationship between host and parasite

Obligate parasite

type of parasite that requires host otherwise **it dies**

* cannot survive in any other manner in the absence of its host

ex. Soil transmitted helminths

Temporary parasite

parasite that lives on host for short amount of time

* obligatory at one or more stages of their life cycle but free living at others

Intermittent parasite

parasites that visit their host during feeding time for nourishment

* mosquitoes

Facultative parasite

parasite that may exist in free-living state or as a commensal and become parasitic when they need to

can survive w/o host

ex. hot springs in Laguna

Accidental or Incidental parasite

parasite that establishes itself in a host in which it does not usually live

ex. a parasite of the pig but human ingested the feces

Permanent parasite

parasite that remains on / in the body of host for its entire life

Spurious parasite

parasite that is free-living

passes thru the digestive tract w/o infecting the host

Commensal / Non-pathogenic

Disease-causing / Pathogenic

Types of parasite acc. to pathogenicity

Definitive or Final

Intermediate

Paratenic

Reservoir

Vectors

Types of Host

Definitive or Final Host

type of host that has the **adult or sexually mature stage** of parasite

ex. human - host for lymphatic filarial worms - elephantiasis

Intermediate Host

type of host that has the __**larval stages or asexual stage**__ of parasite and will leave the host eventually

First Intermediate Host

type of IH that has **early larval stage**

ex. snail

Second Intermediate Host

type of IH that has **infective larval stage**

ex. snail, fish, vegetable, crabs, ants

Paratenic or Transport Host

type of host that has **undeveloped or arrested state of development parasite**

* parasite __**does not develop to later stages**__ but remains alive and can infect other hosts
* ex. *Paragonimus westermani*
* **wild boar** - ingested a parasite but it doesn’t develop further

Reservoir Host

type of host that can hold the parasite and can spread disease

it allows the parasite’s life cycle to continue

alternative host of a parasite

Zoonosis

an infectious disease that has jumped from a non-human animal to humans. 

Preadaptation (evolutionary changes)

parasite undergoes this change due to increased resistance to enzymes of the host

Vectors

responsible for transmission

spreads the parasite

ex. blood feeding arthropods

Biologic Vector

a vector that is an intermediate host

ex. mosquitoes - blood meal

Mechanical or Phoretic Vector

type of vector that does not bite

serve as bridge that transfers infection

ex. flies, lice, cockroaches

* on their feet, transfers cysts from feces to food/drink that humans eat

Oral

Skin penetration

Arthropod bites (vector borne)

Congenital

* Transmammary

Diff. modes of transmission

Oral

most common MOT

contaminated food and water - most common source of infection

**portal of exit: anus** (fecal-oral route)

ex. tapeworms

* scolex (head) should be killed in deworming

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ex. *E. histolytica, Giardia duodenalis, Clonorchis, Opisthorchis, Haplorchis*

*Taenia solium*

pig tapeworm

*Taenia saginata*

cow tapeworm

*Dibothriocephalus latus*

fish tapeworm

Skin penetration

MOT examples:

Hookworms, Strongyloides - Filariform larvae (Infective stage)

Schistosoma sp. enter skin via water - Cercariae (Infective stage)

Arthropod bites (vector borne)

MOT thru mosquito, fly, ticks, bugs

Mosquito

Anopheles:

* Malaria - unicellular, protozoans
* Filariasis - microscopic worms
* Litoralis - found in brackish water

Aedes aegypti

* dengue
* zika virus
* yellow fever

Anopheles mosquito

mosquito that lives in rural or forest

wants clean streams of water

Aedes mosquito

mosquito that lives in urban or cities

wants decaying matter

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African trypanosomiasis

“african sleeping sickness”

disease caused by *Trypanosoma brucei*

**tsetse fly** - bites humans

Fly

what causes:

Onchocerciasis

Loiasis

Leishmaniasis - South America

Tick

Babesiosis

Bug (Reduviid)

**Chagas’ disease**

* at night, “kissing bug” likes to bite near the mouth, suck blood then poop

Congenital Transmission

MOT where a mother gets infected while pregnant and is passed to the baby

ex. *Toxoplasma gondii* - in cat feces; cats as their host

Transmammary

The transfer of infective larval stages of helminths via the mammary glands.

ex. Ancylostoma and Strongyloides

* travel to the lymphatics

Autoinfection

transfer of a life cycle stage of the parasite from one site to another inside the same host / “getting infected again”

ex. *E. vermicularis -* inhalation of airborne eggs

* pinworm
* inhaling hands after itching (pruritus) the butt with layed eggs

Trichomonas vaginalis

* acquired thru sex
* “ping pong disease”
* males are asymptomatic

Signs:

* offensive frothy discharge
* +/- vulvitis or vaginitis
* **strawberry cervix** - the parasite bites the cervix

Epidemiology

* the study of distribution, and occurrence of disease
* How what when why
* Movement of disease across a population

Incidence

number of new cases or infections

Prevalence

number of old and new cases or infections

total population

Intensity of Infection

refers to burden of infection, which is related to the **number of worms per infected person**

* counts the worms through the eggs and get proximate number
* fecal analysis technique

Worm Burden

* checked thru eggs
* count eggs to approximate number of adult worms
* this serves as guide for deworming
* higher values means difficult to deworm (ascaris)

Morbidity

number of people with disease - population

how worse the disease - individual

Mortality

number of people that died - population

risk of an individual to die - individual

Deworming

the use of anthelmintic drugs in an individual or a public health program

Paralyzes the muscles of the parasite

Disease eradication

permanent reduction to zero of worldwide incidence of infection caused by specific agent as a result of deliberate efforts

ex. smallpox

the world wala na itong certain disease

Disease elimination

reduction to zero of incidence of disease in a defined or small geographic area as a result of deliberate efforts

Sporadic

disease that occurs infrequently and irregularly

* every once in a while, appears occassionally

Endemic

constant presence and/or prevalence of a disease or infectious agent within a geographic area, steady, moderate level

stays in the place where the host is

ex. Malaria in Palawan; Dengue in tropical countries

Epidemic

increase in the incidence, often sudden in the number of cases of a disease often above what is normally expected in the population of an area

Pandemic

epidemic that spread over countries or continents = GLOBAL

Prevention (quarantine)

done before a disease

suspected to have a disease but not yet confirmed

Control (isolation)

confirmed to have disease and should be isolated to gain **control** over the development of the infection and provide treatment

Creation of enzymes

Invasion and destruction of host tissue

Depriving the host of essential nutrients and substances

3 Mechanisms by which parasites cause injury

HOOKWORM

this parasite sucks blood because it needs iron

FISH TAPEWORM

parasite that sucks blood for Vitamin B12 (humans need it for formation of RBCs)

*Fasciolopsis buski* (giant intestinal fluke)

may produce severe local damage to the intestinal wall by means of its powerful suckers

E. histolytica

parasite that erodes the intestinal wall

has proteolytic enzyme for destroying tissues

Plasmodium falciparum (malarial parasite)

parasite that invades and multiplies in RBCs which get destroyed in the process

Ascaris lumbricoides

parasite that may perforate the bowel wall, cause intestinal obstruction if present in large numbers, and ectopically may invade the appendix, bile duct, or other organs

Genetic make-up of host - **Duffy antigen** helps protect against malaria

Nutritional status of host

Immunity of the host

Factors that affect outcome of Infection in the host

Parasite fails to become established in host.

It becomes established and host eliminates infection.

It becomes established, host begins to overcome infection but not totally successful. -- remnants of parasite and may regrow

It becomes established, host tries to eliminate it but damages itself.

It becomes established and kills the host.

Possible outcomes of parasite to host interactions

Physical barriers

the 1st line of defense against pathogens

* skin
* mucous membranes
* components of bodily fluids
* physiologic functions of the body

Innate immune response

this immune response where the body detects and eliminates pathogens through **non-specific mechanisms**

ex. Phagocytosis - macrophage & dendritic cells

Acquired immune response

the host is exposed to parasite antigens which stimulate the immune response

ex. T & B cells

Resistance to infection

this permits survival of parasites upon entering blood and tissues

ex. cuticle and skin resist macrophage

Immune suppression

parasites reduce the immune function of the macrophages, hence defective processing of antigen

Antigenic variation

Changes in the antigenic molecules of parasite exposed to the immune system over the course of an infection.

ex. Trypanosoma brucei infection - variant surface glycoproteins

Plasmodium - antigenic diversity

Host mimicry

Parasites that are molecular mimics express proteins which resemble host proteins

a structural similarity between parasite and host components kaya hindi namumukaan ng body

ex. Echinococcus granulosus - larval stages carry P blood group antigens

Schistosoma sp. - can acquire antigenic molecules from host, the body cannot differentiate self from non-self

Intracellular sequestration

process of binding or confining in an intracellular area such that they are separated from other components of a biological system

ex. Leishmania & Plasmodium

Type 1

immediate type hypersensitivity

allergies

eosinophils involved

\
what type of immune reaction?

Type 2

immune complex formation

requires antibodies

\
**what type of immune reaction?**

Type 3

cytotoxic reactions of antibody

T cells

\
what type of immune reaction?

Type 4

delayed hypersensitivity

ex. eczema (chronic)

\
what type of immune reaction?

Protozoans

unicellular eukaryotic organisms

Phylum Sarcomastigophora

what phylum?

* amoeba
* atrial flagellates
* hemoflagellates

Phylum Ciliophora

what phylum?

* ciliates
* Balantidum coli

Phylum Apicomplexa

what phylum?

* plasmodium
* babesia
* intestinal coccidians
* tissue coccidians

Encystation

from trophozoite to cyst

Excystation

from cyst to trophozoite

TROPHOZOITE

* motile stage
* feeding stage
* vulnerable
* has locomotor apparatus
* pesudopod - false feet
* flagellum
* cilia

CYST

* non-motile stage
* non-feeding stage
* no locomotor apparatus
* **C**ircular
* **Stable, Stronger, Stationary**
* infective stage of protozoan

METAZOANS (HELMINTHS)

* the worms

Nematodes

* roundworms
* elongated and cylindrical
* Ascaris lumbricoides

Trematodes

* flukes
* leaf-like shape
* Fasciola hepatica

Cestodes

* tapeworms
* ribbon-like segmented
* Taenia solium