Lecture 10

Question 1

Parasitic disease is an

Answer 1

endemic only

ectoparasite - a parasite that lives ON another organ- TICK

Endoparasite - a parasite that lives IN another organism - Guinea worm

Question 2

Symbiosis

Answer 2

Close relationship between two species - can be parasitic, commensal or mutualistic

Question 3

Parasitic relationship

Answer 3

Relationship where one species of organism lives on or within another at the expense of or causing harm to the host

Question 4

Obligate parasites

Answer 4

Must spend part or all, of their life cycle within a host to survive

Question 5

Facultative parasites

Answer 5

Are free living but can become parasitic if accidentally ingested or enters a wound or other body opening

Question 6

Host Parasite

Reservoir host

Vector

Intermediate/Secondary host

Definitive/true host

Answer 6

Reservoir host: Primary host of the parasite that can maintain the organism indefinitely without any ill effects
* Sustains the parasite when it is not infecting its true host
* Acts as the source of infection

Vector : Living organism that transmits the parasite to another living organism
* Often also the intermediate host, but not always

Intermediate/Secondary host: The in between host where the parasite develops into its sexually immature form (like a larvae)

Definitive/true host : final organism where the parasite develops into its sexually mature form (like an adult worm)

Question 7

Parasite Classifications

Protozoa - what is it

What are the 4 main groups of protozoa - classified by their method of movement

Answer 7

3 main classifications: protozoa , helminths and ectoparasites

Protozoa: unicellular organisms, subdivided by how they move

Amoeba→ move by pseudopods
Example: Entamoeba histolytica

Flagellates→ move by flagella
Examples: Trichomonas vaginalis

Ciliata→ move by cilia all over the org Example: Balantinium coli

Sporozoan→ nonmotile spore formation
Example: Toxoplasma gondi

Question 8

Forms Protozoa Exist In 2 forms:

Answer 8

Cyst form: exist outside the host
* Small round with a thick protective shell ( not an egg)
* Non-feeding, reproducing or moving
* 1-4 nuclei (some have more)
* infective stage

Trophozoite form: Can’t survive outside the host
* Larger fragile form, amorphous oval shape
* Actively feeding, reproducing & moving form
* 1 -2 nuclei
* causes symptoms & disease

Question 9

Excystation to Trophozoite Form

cyst to trophozoite and Trophozoite to Cyst

Answer 9

• Person ingests the cyst
• Cyst wall gets dissolved by the acid juices of the Ilium
• Nucleus inside divides again to form 8 daughter nuclei - binary fission
• Cytoplasm surrounds each of the nuclei to form 8 trophozoites
• They move from small intestine into the caecum and colon of the hosts large intestine and begin feeding
• As they move further down the intestine, they must undergo encystation to survive

Pre- Cyst Stage-between the
trophozoite and the cystic forms
 Trophozoite reduces in size and becomes ovoid
 Has a single blunt pseudopod
 Trophozoite stops feeding at this time
 A single nucleus present

Mature Cyst Stage: “infective stage”
* Becomes round with a refractile wall
* The one nucleus inside cyst divide by binary fission to binucleate, then quadrinucleate form. If this happens outside of the body it can infect another host but the trophs are fragile and will die outside the small intestine

Question 10

Microscopic Identifying Features of Protozoan Parasites

Answer 10

• Size and shape of trophozoite
• Size and shape of mature cyst
• Number of nuclei in the trophozoite or mature cyst
• Type of karyosome (dot in the middle can be large or small) and peripheral chromatin (fine or rough)
• Cytoplasm characteristic & inclusions
  -Chromatoid bar
  -Ingested red cells
  -Vacuoles

Question 11

Amoebiasis - Pathogenic Amoeba

how can the illness manifest

Answer 11

example: Entamoeba histolytica
-caused by poor sanitation, Transmitted by ingesting contaminated water, unwashed food or sexually men to men
-finding trophozoite or cyst in stool, by staining fluid, biopsy of infected tissue, immuno or molecular techniques
-mature cyst will have 4 nuclei . no vegetative cyst so not motile

Asymptomatic colonization -hosts are carriers & can spread to others

Amebic dysentery- either acute or chronic colitis with severe bloody diarrhea & pain –lesions of intestinal lining

Extra-intestinal amebiasis-Organism erodes the intestinal lining and spreads via circulation to liver & lungs

Question 12

Example of a Pathogenic Flagellate:
Trichomonas vaginalis

symptoms in men and women

Answer 12

• Transmission by sexual intercourse (STI)
• Trophozoite is the diagnostic and infective stage- it it oval shaped and motile (may see the flagella or may not) with one nuclei
  *central axostyle like a thick line in the middle
  *frothy cytoplasm
• No cyst stage

Symptoms In Females
* vaginal inflammation
* Yellowish, frothy, foul-smelling discharge
* Burning on urination
* Itching and irritation in the vaginal area

Symptoms In Males
* Asymptomatic – but can still spread disease

Diagnostic Tests
-wet prep with swab
* Culture in growth broth like Diamond media or In Pouch System
* Gram or other stain of vaginal or urethral swab
* PCR
* Rapid antigen tests

Question 13

Example of a Pathogenic Ciliate:
Balantidium coli

Answer 13

-Only ciliated parasite that is a
human pathogen
* Largest of the protozoa - Have cilia
all over the trophozoite for movement
* Transmitted by the fecal-oral route in
contaminated food and water
* Reservoir host is pigs (pig farmers at
increased risk)
* Infection is mostly asymptomatic in
humans
* People with other serious illnesses
can have persistent diarrhea, pain,
and sometimes a perforated colon

Question 14

Example of a Pathogenic Sporazoa:
Toxoplasma gondii

Answer 14

 host is the cat, intermediate hosts are small animals - humans are accidental host
 complex- exists in 3 possible forms
 Tachyzoite (motile feeding form), Bradyzoite (form contained within a cyst in tissue), oocysts (immature infective eggs that develop only in the cat) & sporocyst (mature infective egg that develops in the environment)

Humans infected by:
* Eating undercooked meat with tachyzoite or bradyzoite
 Ingesting oocysts or sporocyst from litter or sand boxes
 Congenitally, mother to fetus or organ transplant

Most human infections are asymptomatic - immune system protects
but parasite stays in tissues in the body in an inactive state forever
Immunocompromised can have severe consequences
pregnant woman -may cause a miscarriage, or infant born with abnormal enlargement or smallness of the head
Infant may show no symptoms at birth but may develop them later in life: potential vision loss, mental disability,
and seizures

Diagnosis: Serology, Molecular testing, Tissue biopsy or CSF to look for bradyzoites or tachyzoites

Question 15

Parasite Classification – Helminths with subdivisions & Ectoparasites

Answer 15

Helminths: : different reproductive stages, eggs (unicellular), larvae & adult worms (multicellular). further subdivided by the shape of the worm

Trematodes→ flat leaf-shaped worms, (flukes) Schistosoma species

Nematodes→ roundworm
Strongyloides

Cestodes→ Long flat worms made up of segments- tapeworms Taenia

Ectoparasites/Arthropods: small organisms with hard exoskeleton and jointed appendages. ticks, mites, fleas

Question 16

PATHOGENIC Helminth TREMATODE - Schistosoma
types of Flukes - classification

Answer 16

Tissue flukes: unsegmented flat leaf shaped bodies, with oral &
ventral suckers. Worm has both male & female genitalia hermaphrodites . Infect tissue –lung or liver

Blood flukes: cylinder type body, have oral and ventral suckers. Separate male & female worms NOT hermaphroditic. Immature worms infect veins around liver, mature worms infect mesenteric or bladder veins

Schistosoma are blood flukes -the second most prevalent tropical infectious disease
* People contaminate the freshwater source with eggs in their feces
* New person becomes infected when larval forms of the parasite – released by freshwater snails (intermediate host) – penetrate the person’s skin during contact with infested water

Question 17

Schistosomiasis species

Answer 17

Schistosoma haematobium -Africa and Middle East -inhabits veins of urinary tract/ around bladder
-can cause scarring with squamous cell carcinoma of the bladder
-found as egg in urine with terminal spine (down or up)

Schistosoma mansoni -Africa and South America - inhabits veins around liver & intestine
-found as egg with lateral spine (on the side)

Schistosoma japonicum (China & Philippines) inhabits veins around liver & intestine
-found as egg with small spike

 Some infections are asymptomatic - symptoms happen due to body’s reaction to the eggs, like itchy rash where larvae enter the skin
 Some can get acute infection with fever, cough, diarrhea, hepatosplenomegaly
 Chronic infection - get granulomas in affected organ

Diagnosis is by finding egg in stool or urine or by serology

Question 18

Helminth Nematodes

Answer 18

 non-segmented round worms
male or a female worm
Have mouths and digestive tracts
 larvae and adult worm -produce eggs
can be pathogenic
Infect humans either through ingestion of eggs via oral fecal or thru food or water, or larvae can penetrate skin

Examples of pathogenic Nematodes:
Enterobius vermicularis & Strongyloides stercoralis

Question 19

Example of a Pathogenic Helminth
Nematode: Enterobius vermicularis

Answer 19

• pinworm
• Humans only host
• Most common in children and those who care for them
• adults who are institutionalized
• Person-to-person transmission - handling of contaminated clothes or bed linens, carpets with eggs
• Small number eggs airborne are inhaled or swallowed
• Autoinfection by larvae penetrating anal skin

Symptoms: perianal, perineal, vaginal irritation or itchiness
* Insomnia & irritability in children

Diagnosis:
* Recovery of eggs or worm from perianal region
* Specimen taken with Scotch tape prep or under nails
* Looked at under the microscope:
Egg: oval, elongated with one side flattened, larva may or may not be visible

Adult female worms: small white
roundworm. Longer than
male

Question 20

Example of a Pathogenic Helminth
Nematode: Strongyloides stercoralis and diagnosis

Answer 20

 Worm can be free living -infective filiform larval form found in soil – burrows thru host skin
 Enter bloodstream & migrate to lungs where they are coughed up and
swallowed
 Go to submucosa of the small intestine to develop into adult female worms that lay eggs with rhabditiform larvae (diagnostic)
 Rhabditiform larvae transform into filiform larvae that penetrate intestinal wall or anus to cause autoinfection – results in chronic infections
 Rhabditiform larvae can become free living worms outside the host

DIAGNOSIS
 Find larval forms microscopically, in
stool is gold standard – can take many sample (3 or 7)
 Duodenal fluid or biopsy better but
invasive procedure
 Serological tests also done but can cross react with other parasites
 Usually combination of stool sample & serology
 Gram or agar from sputum may show
migrating larvae

chronic is autoinfection when they infect themselves

Question 21

Types of Strongyloides Infections

Answer 21

Acute infection: limited to GI & lungs
* Asymptomatic or mild symptoms like skin rash & cough from larvae migrating to lungs – Diarrhea
-eventually get better

Chronic infection: limited to GI & lungs
* Same as acute - constant rash due to
autoinfection, intestinal obstruction -asthma & arthritis
-chronic rash- autoinfection

Hyper infection/Dissemination: all over the body many organs
* overload of larvae that spread through the body by cortisol shots for another condition steroids keep the infection down until it cant
* Rash, cough, respiratory, organ failure, obstruction, death
 worse prognosis in those with HTLV-1 (T cell lymph) or immunocompromised

Question 22

Example of a Pathogenic Helminth Cestode: Taenia

Answer 22

• Multisegmented flat worms- tapeworms
• No digestive tract - absorb nutrients directly from the host’s intestine. Each segment of the worm has both male &
  female reproductive organs. Hermaphrodite

Taenia spp.: Taenia saginata (cow), Taenia solium (pig). The species differs based on the host type
* Cows & pigs are reservoir & intermediate host
* Humans are the reservoir & definitive host
* Eggs in soil are eaten by cow or pig, hatch in intestine – larvae travel to tissue to cause cysts
* Humans eat undercooked meat with cyst larvae – develop into adult worm in their intestine – eggs released with stool
* For T. solium only human can reinfect themselves with eggs in own stool or accidently eat eggs on unwashed fruit or vegetables grown in pig manure. usually you have to eat the larvae but in this species you eat the eggs. The head has hooklets

Diagnosis of
Tapeworms have 3 main body sections

1. Scolex (head): anchor that attaches to intestinal mucosa
2. Neck: unsegmented region with
   regenerative capacity
3. Proglottids (segments): develops
   hermaphroditic sex organs. Distal
   proglottids are gravid and contain eggs
   in a uterus.
   * Scolex and proglottid are used to
   diagnose & help identify which species
   of Taenia is causing infection. eggs for all taenia species look the same

Question 23

O&P Stool Specimen Collection Guidelines

Answer 23

Physician would ask for O&P testing - exposure to raw meat, travel history, bloody stool , eosinophilia and consistency of the stool
 3 stool collected 1-2 days apart within a 10 day period - stages of cyst, egg or larvae development are shown
 Use clean, sterile, tightly lidded container

 Do not collect from bed pan or toilet water
 Collect before barium enema or procedures where dyes are used or before anti-parasitic drugs are started
 O&P exam include 3 containers. 1 without any additives (unpreserved - culture for bacteria - salmonella, shigella) a 2nd with 10% formalin or SAF and a 3rd container with PVA (polyvinyl acetate fixative)
 1 part stool to 3 parts preservative to preserve the stages they were in the body
 time that stool is passed and time added to preservative containers must be written on the containers

Question 24

what can detect from:

Stools (preserved/unpreserved)

Scotch tape preparation (anal
folds)

Blood

Body Fluids: CSF

Urines

Vaginal and Urethral

Organs and Tissues biopsy

Sputum

Answer 24

Stools (preserved/unpreserved) - intestinal parasites eggs, worms

Scotch tape preparation (anal
folds) - Enterobius vermicularis

Blood -malaria

Body Fluids: CSF - Toxoplasma

Urines -Schistosoma

Vaginal and Urethral-Trichomonas vaginalis

Organs and Tissues biopsy-Toxoplasma, Strongyloides, Entamoeba histolytica

Sputum -Strongyloides stercoralis larvae, Entamoeba histolytica

Question 25

what can Unpreserved Stool be for

Answer 25

Used for bacterial culture -preservative kill bacteria
Used for direct wet mounts to look for motile trophozoites
Trophozoites will still be moving if done early enough –are fragile and disintegrate if too long
Trophozoites in loose or soft stools
Cysts in formed
If black indicates bleeding in upper GI
If bright red indicates bleeding in lower GI
Look for worms or tapeworm segments on surface of stool

Question 26

10% Formalin

Advantages Disadvantage

Answer 26

Advantages
* All purpose fixative
* good for Formalin ethyl acetate, concentration procedures, UV fluorescence & acid-fast stains
* Compatible with immunoassay kits

Disadvantage
* Can’t use for PCR

Question 27

PVA (polyvinyl-alcohol)

Advantages Disadvantage

Answer 27

Advantages
* great for permanent stained smears
* Great for PCR

Disadvantage
* Has mercuric chloride - difficult and expensive to dispose of
* Not suitable for concentration procedures, immunoassay kits or acid fast stains

Question 28

SAF
(sodium acetateacetic acidformalin)

Advantages Disadvantage

Answer 28

Advantages
*Suitable for concentration and permanent stained smears

Disadvantages
* Can’t use for PCR

Question 29

disease caused by tinea

Answer 29

Ingestion of tissue cyst larvae in undercooked meat causes infection with minimal symptoms
* May cause abdominal discomfort, diarrhea, and weight loss; vitamin
B12 deficiency and anemia.
* May see tapeworm segments (proglottids) in stool
* Segments can get stuck in appendix or bile ducts to cause serious problems
* But with T. solium only where human infected with eggs can cause human cysticercosis
* Eggs hatch in their intestine & larvae migrate to brain, liver, lungs, eyes, muscles and form tissue cysts
* Can cause seizures and severe tissue damage

Question 30

why is consistency importantt

Answer 30

stool that are more formed will contain more cysts
while watery stool will have cyst and troph because they have been taken out of the body too quick