Lecture 10 Flashcards
Parasitic disease is an
endemic only
ectoparasite - a parasite that lives ON another organ- TICK
Endoparasite - a parasite that lives IN another organism - Guinea worm
Symbiosis
Close relationship between two species - can be parasitic, commensal or mutualistic
Parasitic relationship
Relationship where one species of organism lives on or within another at the expense of or causing harm to the host
Obligate parasites
Must spend part or all, of their life cycle within a host to survive
Facultative parasites
Are free living but can become parasitic if accidentally ingested or enters a wound or other body opening
Host Parasite
Reservoir host
Vector
Intermediate/Secondary host
Definitive/true host
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)
Parasite Classifications
Protozoa - what is it
What are the 4 main groups of protozoa - classified by their method of movement
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
Forms Protozoa Exist In 2 forms:
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
Excystation to Trophozoite Form
cyst to trophozoite and Trophozoite to Cyst
- 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
Microscopic Identifying Features of Protozoan Parasites
- 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
Amoebiasis - Pathogenic Amoeba
how can the illness manifest
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
Example of a Pathogenic Flagellate:
Trichomonas vaginalis
symptoms in men and women
- 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
Example of a Pathogenic Ciliate:
Balantidium coli
-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
Example of a Pathogenic Sporazoa:
Toxoplasma gondii
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
Parasite Classification – Helminths with subdivisions & Ectoparasites
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
PATHOGENIC Helminth TREMATODE - Schistosoma
types of Flukes - classification
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
Schistosomiasis species
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
Helminth Nematodes
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
Example of a Pathogenic Helminth
Nematode: Enterobius vermicularis
- 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
Example of a Pathogenic Helminth
Nematode: Strongyloides stercoralis and diagnosis
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
Types of Strongyloides Infections
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
Example of a Pathogenic Helminth Cestode: Taenia
- 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
- Scolex (head): anchor that attaches to intestinal mucosa
- Neck: unsegmented region with
regenerative capacity - 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
O&P Stool Specimen Collection Guidelines
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
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
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
