Parasitology Midterm 2

Diarrhea - Presumptive Diagnosis

-Returning travelers

-Known outbreaks

-Acut food poisoning

Diarrhea - Laboratory-Based Diagnosis

-Stool culture

-O&P (Ova & Parasites)

-PCR Panels

-Fecal fat analysis

Stool O&P

-Stool tests

• Wet mount (if fresh)

• Concentration smear

• Permanent stain

• Antigen testing possible

• PCR panel testing typically reserved

-Looks for ova (eggs - shed by adult worms in the GI tract or elsewhere) and parasites

Typical Fecal-Oral Life Cycle

-Cyst → Excystation → Trophozoite → Encystment → Cyst

-Trophozoite phase only

Entamoeba histolytica

-Several protozoan species in the genus colonize humans

• Not all associated with disease, must differentiate

-Intestinal and extraintestinal infections

-E. dispar is morphologically indistinguishable but not generally not considered pathogenic

• Diagnosis confusion unless erythrophagocytosis

Entamoeba histolytica Lifecycle

-Mature cysts are ingested → Excystation → Trophozoites → Produces both more trophozoites and cysts → Cysts and trophozoites are passed in feces

-Cysts are what causes infection

-Both can be used to help with diagnosis

Entamoeba Symptoms

-Asymptomatic infection - luminal

-Invasive intestinal

• Dysentery and ulcerous colitis

• Appendicitis

• Toxic megacolon

-Invasive extraintestinal

• Liver abscess and peritonitis

• Pleuropulmonary abscess

• Cutaneous and genital lesions

• Brain hemorrhages

Entamoeba Diagnosis - If You Can See Them

-Rule out with 3x stool exam

-Fresh stool wet mounts and permanent stains

-Concentration techniques esp. for cysts

• Not for EIA/Ag-based tests due to Ag loss

-Biopsy can show trophs

-Liver scan, CT scan, ultrasound

Microscopic Features of E.histo/dispar

-Trophozoite (usually in diarrheal stool)

• 15-20 um (10-60 um range), elongated +/-

• Single nucleus with central karyosome and peripheral chromatin

• Eryhtrophagocytosis

• Ground glass cytoplasm

-Cyst (usually in formed stool)

• Four nuclei and chromatoida body (nucleic acid)

• 1 cyst gives 4 trophozoites

• Size of a monocyte

Entamoeba Diagnosis - If You Can’t See Them

-Use immuno- or molecular assays

-Fecal antigen EIA as microscopy adjunct

-Multiplex PCR

-Serology (antibody EIA) can be useful in extraintestinal disease

• Highly specific

• Cannot differentiate between new and past infections

E. dispar vs. E. histolytica

-Frequency

• E. dispar is 10x more frequent than E. histolytica

-E. dispar = non-invasive

-E. histo/dispar can be distinguished by immunologic or molecular assays

Dientamoeba fragilis

-Not ameba but a flagellate

-Trophozoites only (no cyst stage)

-Symptomatic and asymptomatic infections

Dientamoeba fragilis Lifecycle

-Trophozoites ingested → binary fission → trophozoites in lumen of colon → Trophozoites in feces → Transmission via fecal-oral route

-2 nuclei inclusions possible

Entamoeba Prevention

-Common for all intestinal parasites

-Handwashing

-Washing fruits/vegetables

-Role as a STI

-Water treatment

• Boiling water works

• Iodination works

• Chlorination does not work

Entamoeba Treatment

-If asymptomatic, eradicate cysts

• Iodoquinol or paromomycin

-If symptomatic, eradicate trophozoites

• Metronidazole, immediately followed by above treatment

Balantidium coli

-Parasite of pigs (reservoir)

-Ciliated parasite

-Not common in humans; (sub)tropics

-Similar clinical picutre to dysenteric form of E. histolytica, extremely rare to form abscesses

-Responds to tetracycline (unlike E. histo)

-Cyst ←→ trophozoite back and forth

-Fecal-oral transmission

Balantidium coli Lifecycle

-Enters host as a cyst → Invades the body → Excreted out of the host as either a cyst or a trophozoite → Repeats cycle

-The cyst is the infectious stage and is acquired by the host through ingestion of contaminated food or water

Giardia duodenalis

-Intestinal flagellate

-750,000 cases in US anually

-Overwhelming (and mostly undiagnosed) burden in tropics

-Synonyms: lamblia/intestinalis

-Worldwide distribution

• Human reservoir crucial

• Importance of animal reservoirs unclear

-Contains ventral suction disk

Giardia duodenalis Lifecycle

-Enters host as a cyst through contaminated water, food, or hands/fomites → Becomes trophozoites → Longitudinal binary fission → Cysts → Cysts are passed in stool (trophozoites are also passed in stool but they do not survive in the environment)

-1 cyst → 2 trophozoites

-Cysts can survive months in cold water

-Cysts infectious shortly after passage (person-to-person transmission is possible)

Giardia duodenalis Clinical Disease and Pathology

-Non-invasive inflammation of the jejunum

-Asymptomatic cyst carriers (reservoir)

-Acute = water stools/floating/fatty

-Chronic = fat malabsorption syndrome → loss of fat soluble vitamins (ADEK) → rickets, stunted growth

-Treatment: metronidazole

Giardia duodenalis Diagnosis

-Demonstrate cysts/trophs in feces

• Up to 3 stool exams to rule out “low excreters”

• Direct exam possible but concentration techniques useful

-Antigen assay EIA or RDT kits (useful)

• Do not use concentrates

-Direct fluorescent antigen test kits

-Duodenal fluid/biopsy, jejunal biopsy for trophs

-Multiplex PCR panels (e.g. Biofire GI FilmArray)

Giardia DFA

-Commercial kits available

-Cannot be archived

-More sensitive for low cyst concentrations

Giardia Prevention

-Same approaches as for amebiasis

• Chlorination doesn’t work well

• Iodination is method of choice

• Clean water, clean hands, clean food

Trichomonas vaginalis

-Flagellated protozoan

-Sexually transmitted

-Males = more asymptomatic (less symptoms)

-Females = more symptomatic (more prolonged symptoms + more symptoms)

-No cyst stage

-Most common pathogenic protozoan infection in developed countries

-Most cmmon non-viral STI

Trichomonas vaginalis Lifecycle

-Trophozoite in vaginal and prostatic secretions and urine → Multiplies by longitudinal binary fission → Trophozoite in vagina or orifice or urethra

-Resides in female lower genital tract and in male urethra/prostate

-No cyst form

-Replicates by binary fission

-Human only

-Sexually transmitted

Trichomonas vaginalis Symptoms

-Women

• More frequently symptomatic, persists

• Main symptom: vaginitis with purulent discharge

  • Occasionally vulvar/cervical lesions, abdominal pain, dysuria and dyspareunia

• Incubation period: 5-28 days

-Men

• More frequently asymptomatic, resolves

• More rarely urethritis, epididymitis and prostatitis

-Neonates

• Congenital transmission, rare involvement of lung

Trichomonas Complications

-Women

• Preterm delivery, low birth weight, increased risk of HIV infection and cervical cancer

-Men

• Possible increased risk of prostate cancer, especially for extraprostatic disease, bony mets, or prostate cancer-specific death

Trichomonas Diagnosis

-Wet mounts: actively motile organisms only

• Rapid but poor sensitivity (about 67%)

• Must be done ASAP - organism will die in transit

-DFA stain: sensitive (80-90%) but complex

-Gold standard: anaerobic culture (sensitivity > 95%)

• Slow (3-7 days until results) and labor intensive

-PCR is preferred method (next slide)

• Ideal balance of sensitivity, speed

-Vaginal/urethral secretions (women) or anterior urethral or prostatic secretions (men)

-Look-alikes: epithelial cells

Trichomonas Prevention and Treatment

-Safe sex/latex condoms

-Treat under medical supervision

• Include all sexual partners of the infected person(s)

• Metronidazole and tinidazole (usually works)

• Strains of Trichomonas vaginalis resistant to both drugs have been reported

• “Relapse” usually due to untreated partner

The Class Cestoda

-Parasitic flatworms (aka tapeworms)

-Reside in GI tracts of vertebrates as adults

-Often reside in tissues of animals as juveniles

->1000 named species

-All vertebrates have at least one species of tapeworm

Taenia Lifecycle

-Oncospheres develop into cysticerci in muscle → Humans consume infected meat →Scolex attaches to intestine → Adults in small intestine →Eggs or gravid proglottids in feces and passed into environment →Cattle and pigs become infected by ingesting vegetation contaminated by eggs or gravid proglottids → Oncospheres hatch, penetrate intestinal wall, and circlate to musculature

-Pig version can cause cysticercosis if you ingest the ova instead of the cystericerci

Taenia Comparison

-Solium has hooks while Saginata doesn’t

-Saginata has more branches (>14) in the proglottid than Solium does (7-13)

Taenia Stool O&P

-Eggs indistinguishable between species

-Take extreme care in processing the specimens

-Ingestion of solium eggs can result in cystericercosis

-Hooks in the eggs = tapeworm egg

Taenia solium

-Lifecycle: Egg → larvae (cystericeri) → worm → egg

-Adult worm: Eat bad pork → larvae in cysticeri become worm → shed eggs in stool

-Cysticercosis → Eat eggs (fecal-oral contaminant) → larvae form cysts in humans

• Peri-anal itching facilitates fecal-oral transfer

• Also regurgitation of intestinal content

Neurocysticercosis

-T. solium - Yes

• Propensity to make cysticeri in the brain

-T. saginata - No

• No cysticerci in humans

• Cysticerci in beef muscles

Tapeworm Prevention

-Post-mortem inspection of swine carcasses by USDA

-Cook food thoroughly

-Stop coprophagia

-Prevent pig direct access to human toilets

-Praziquantel for humans

Human Echinococcus

-Hydatidosis or hydatid disease

-Caused by larval stages of Echinococcus cestodes (tapeworms)

• Cystic - E. granulosus

  • Most frequent agent

• Alveolar - E. multiocularis

• Polycystic (exclusively new world)

  • E. vogeli

  • E. oligarthrus (extremely rare)

Echinococcus Lifecycle

-Embryonated egg in feces → egg enters human (dead end host)

-Embryonated egg in feces → Oncosphere hatches; penetrates intestinal wall → Hydatid cyst in liver, lungs, etc. → Protoscolex from cyst → Scolex attaches to intestine → adult in small intestine

-Ingestion of eggs (in feces) → Intermediate host (sheep, goats, swine, etc.) → Ingestion of cysts (in organs) → Definitive host (dogs and other canidae)

Echinococcus Hosts

-Definitive (carnivores) → dogs and canidae

-Intermediate

• E. granulosus: sheep, goats, swine, other wild herbivores

• E. multilocularis: rodents

• E. volgeli: rodents

• E. oligarthus: rodents

• Humans are dead-end intermediate host for all

-Tapeworm is in definitive host → not in humans

Echinococcus Pathology

-Often clinically silent (up to 50 years)

-Enlarging cysts → symptoms in affected organs

• Liver: abdominal pain/mass/biliary duct obstruction

• Lungs: chest pain/cough/hemoptysis

-Cyst rupture: fever, urticaria, eosinophilia, anaphylactic shock, cyst dissemination

-Other organs more rarely: brain, bone, heart

Echinoccus Diagnosis

-Ultrasonography, MRI, CT scan

-Serology

• ELISA or IHA = screening

• Immunoblot = confirmation

• Sens/spec depending on cyst location

  • Good in liver, poor in lung

-Microscopy

-If imaging suggestive but serology negative

• Ultrasound guided fine needle biopsy for path

• Avoid leakage of hydatid fluid to prevent severe allergic reactions and secondary recurrence

Echinococcus Prevention and Treatment

-Surgical removal of hydatid cysts

-Albendazole (or mebendazole)

-PAIR: puncture, aspirate, inject medication, re-aspirate

-Avoid feeding raw offal to dogs

-Deworm dogs

-Enforce meat inspection procedures

-Good hygiene

Fish Tapeworm - Diphyllobothriid Worms

-30+ feet long

-Definitive host: fish-eating mammals

-Intermediate hosts:

• 1st: crustacean

• 2nd: freshwater fish

-Absorbs huge quantities of Vitamin B12

• Leads to deficiency → anemia

Fish Tapeworm Lifecycle

-Definitive host ingests plerocercoids in infected fish → Unembyonated eggs passed in feces of definitive host → Eggs embryonate in water → Coraidia hatch from eggs and are ingested by the first intermediate → Procercoid larvae develop in body cavity of crustaceans → Infects second intermediate host

Hymenolepis nana - Dwarf Tapeworm

-Grain beetles = intermediate host (cysticerci)

-House mouse = definitive host (scolex/proglottids/eggs)

-Only tapeworm transmitted human-to-human

-Two routes of entry

• Cysticercoid larvae-infected grain beetle consumed → tapeworm develops in gut → asymptomatic

• Feces contaminated food is consumed → eggs hatch and larvae penetrate intestinal villi → cysticeri ruptures villus → adult develops in gut → autoinfection (cramping abdominal pain for years is possible)

Dipylidium caninum

-Cat or dog tapeworm

-10-70 cm

-”Cucumber seed” when wet or “dried grain of rice”

-May stick to the skin around the anal area

-Commnly found in children

Dipylidium Morphology

-Armed rostellum

-Four suckers

-Tends to form egg packets

• Round

• Thin shelled

• Oncosphere with six hooklets

Enterobius vermicularis - Pinworm

-Small nematode

-Reside in the cecum

-Egg deposition leads to peri-anal itching

-Secondary infections may occur

-Eggs inective within a few hours

-Wash linens, treat family, trim fingernails