Parasite-Host Relationships

Parasite-Host Relationship

• Obligatory parasites cannot survive outside a host.
• Facultative parasites can exist independently of a host.
• Endoparasites are established inside a host.
• Ectoparasites are established on the exterior surface of a host.

Host Types

• Accidental or incidental: A host that is not the normal one for a parasite.
• Definitive: The host in which the adult sexual phase of a parasite occurs.
• Intermediate: The host in which the larval asexual phase of a parasite occurs.
• Reservoir: A host harboring parasites that are parasitic for humans and from which humans may become infected.
• Transport: A host responsible for transferring a parasite from one location to another.
• Carrier: A host harboring a parasite, not exhibiting clinical symptoms, but can infect others.

Parasite-Host Relationship Terms

• Symbiosis: Living together; association of two living organisms, each of a different species
• Commensalism: Association of two different species of organisms that is beneficial to one and neutral to the other.
• Mutualism: Association of two different species of organisms that is beneficial to both.
• Parasitism: Association of two different species of organisms that is beneficial to one at the other's expense.
• Commensal: Benefits one organism, has a neutral effect on another.
• Pathogenic: Parasite that can cause disease.

Parasite Life Cycle

• Mode of transmission.
• Infective stage: The form that invades humans.
• Diagnostic stage: The form that can be detected via lab methods.

Disease and Symptoms

• Major body areas associated with parasitic processes include gastrointestinal, urogenital tracts, blood, tissue, liver, lung, and other organs such as cerebrospinal fluid, eye, skin, and extremities
• Common symptoms are diarrhea, fever, chills, abdominal pain, and cramping.

Specimen Collection and Handling

• Standard stool collection: 3 specimens, 1 every other day over 10 days
• For amebiasis: 6 specimens in 14 days is acceptable.
• Stool samples from patients treated with barium, bismuth, or mineral oil should be collected either before therapy, or 5-7 days after completion
• Stool samples following antibiotics or antimalarials should be delayed for 2 weeks.
• Use clean, watertight containers with tight lids.
• Collect 2 to 5 g of stool (walnut-size).
• Liquid stool sample should be examined within 30 minutes.
• Semiformed stools should be examined within 1 hour.
• Formed stool should be examined within 24 hours.
• Urine, toilet bowl water, and toilet paper should not contaminate stool specimens.
• Ratio of stool to fixative should be 3:1
• Allow 30 minutes of fixation before processing.

Formalin

• Used for recovery of protozoa and helminths.
• Two concentrations 5% (protozoan cysts) and 10% (helminth eggs and larvae).
• Good for direct examinations and concentration procedures, but not permanent smears.
• Easy to prepare and preserves specimens for years.
• May not adequately preserve parasite morphology for permanent smears.

Polyvinyl Alcohol (PVA)

• A plastic powder adhesive for preparing slides for staining, often combined with Schaudinn solution.
• Used in a two-vial system: formalin for concentration, PVA for stained slides.
• Can detect trophozoites, cysts, and helminth eggs.
• Used for permanent smears
• Long shelf life.
• Potential health hazard due to mercury in Schaudinn's solution.

Sodium Acetate Formalin (SAF)

• An alternative to PVA and Schaudinn fixative, used to prepare smears for staining coccidian oocysts with modified acid-fast stain.
• Only requires a single vial, is mercury-free, and has a long shelf life.
• Adhesive properties aren't as good, and protozoa morphology isn't as clear as with mercury-containing preservatives.

Processing

• Perform macroscopic and microscopic examination.
• Macroscopic: note stool consistency, color, and gross abnormalities
• Microscopic: examination of fresh specimens or those in fixative
• Direct wet preparation: mixing stool with saline or iodine for detection of protozoan trophozoites, cysts, oocysts, helminth eggs, and larvae.

Concentrated Wet Preparations

• 2nd procedure in O&P exam
• Useful for detecting low # of parasites
• Can be performed on fresh or preserved stool
• Allows detection of protozoan cysts, oocysts, helminth eggs, and larvae
• Protozoan trophozoites do not usually survive the procedure.

Formalin-Ethyl Acetate Sedimentation

• Widely used concentration method based on specific gravity.
• Ethyl acetate is added to formalin-fixed sample
• Parasites settle in sediment; fecal debris rises.
• Provides good parasite recovery but contains more fecal debris than flotation.

Zinc Sulfate Flotation

• Based on specific gravity; parasites float toward the top.
• Zinc sulfate is added and centrifuged.
• Yields a cleaner preparation but may miss some dense helminth eggs.

Sheather's Sugar Flotation

• For recovery of coccidian oocysts (Cryptosporidium, Cyclospora, Isospora).
• A boiled sugar solution is used, preserved with phenol.

Permanently Stained Smear

• The final procedure in the O&P exam, providing fixed sample for detailed protozoa observation.
• Identification is tentative until the smear confirms.
• Not ideal for helminth eggs or larvae identification, which are better detected with concentration.
• Sample of choice: PVA-preserved sample.

Slides under OIO

• (100×), 300 fields are reviewed before the slide can be negative
• Wheatley Trichrome and Iron Hematoxylin are the two most common stains used:

Modified Acid-Fast Stain (CIC)

• Staining procedure for detection of oocysts of Cryptosporidium, Isospora, and Cyclospora.
• The modified iron hematoxylin incorporates carbol fuchsin for detecting acid-fast parasites, using SAF-preserved samples.
• Modified Trichrome is used for enhanced detection of microsporidia.

Intestinal Specimens

• Duodenal material and Enterotest are other intestinal specimen types.
• Duodenal Material: collected by nasogastric intubation
• Enterotest: The patient swallows a gelatin capsule

Sigmoidoscopy Material

• Helpful for detecting E. histolytica.
• Coccidian parasites and microsporidia may also be recovered

Cellophane Tape Preparation

• Is most effective for detecting Enterobius vermicularis (pinworm) eggs.
• Specimen should be collected early in the morning before washing or defecating.
• Also used for Taenia spp. recovery.

Techniques For Blood Specimen

• Blood smears (Thick and Thin Smears), buffy coat slides and cultures
• Knott Technique concentrate microfilariae in blood
• Specialized stains for specific organisms

Blood Smears

• Prepared with or without anticoagulant (EDTA).
• If malaria is suspected, prepare within 1-hour collection.
• Thick Smear: serves for screening ,used when parasites are few or when thin smears are negative and is Dehemoglobinized/laked
• Thin Smear: Recommended for species identification
• Permanent Stains contain Wright's stain and Giemsa stain

Spinal Fluid Testing

• Analysis of CSF and other sterile fluids is used for detecting various parasites, for example, Naegleria Fowleri
• If suspecting either Naegleria or acanthamoeba species, samples can be cultured on non-nutrient agar seeded with E. coli

Tissue and Biopsy specimens

• Tissues and biopsy specimens are recommended for organisms like Leishmania species.
• Other parasites that can be detected: free-living ameba and Trypanosoma

Sputum Testing

• Commonly analyzed to check for lung fluke Paragonimus westermani infections.
• May also include: microsporidia and E. histolytica

Urine and Genital Secretions

• Testing in this manner can identify Schistosoma haematobium eggs in urine.
• Additionally may yield a test result of Trichomonas Vaginalis

Eye and Mouth Specimens

• Eye specimen testing works to diagnose Acanthamoeba Keratitis
• Mouth scrapings works to detect E. gingivalis and Trichonomas tenax

Diagnostic Analysis (Parasites)

• Leishmania, Trypansoma, and Toxoplasma can be ID'd through animal inoculation.
• Furthermore: Xeno diagnosis works to identify Chagas' disease

Amebas (General Information)

• These infectious agents are equipped with pseudopods: this allows them to move within an environment
• The mode of transmission is through the ingestion of cysts from contaminated food sources
• 2 Morphological forms: cyst and trophozoites

Trophozoite

• Feeding stage
• undergoes replication with binary fission
• This feeds/multiplies and possesses a pseudopod

Cyst

• Non-feeding
• Has a thick protective cell wall
• Able to survive more harsh outside contaminants/environments

Entamoeba histiolytica (Facts)

• The only known pathogenic intestinal ameba that leads to carriers
• In symptomatic circumstances; this ameba causes colitis's
• Furthermore the agent can lead to amebic dysentery within stool

Nagleria Fowleri (facts)

• The agent is known for causing Primary Amebic Meningoencephalitis: it does this by invading tissue and causing rapid destruction
• Humans are primarily infected because of the agent contaminating sources of drinking water

Acanthamoeba (facts)

• This bacteria can cause a number of complications stemming from granlomatous amebic ecephalitus as well as keratitis
• These complications are caused by lesions, which can cause vision impairment and severe ocular pain

Flagellates (Motility and Location)

• The are noted for Flagella: a whiplike structure that enables movement
• Major components of flagellates, primarily found in the duodenum, small and large intestine
• G. Intestialis lives in the duodenum

Axostyle (key information and facts)

• Nuclear components are helpful in determining differences between flagellates
• This is primarily used as a rod linke support structure

Giardia Intestialis (key components and morphology)

• Giardiasis
• Transmitted from contaminated water

Cysts (giardia intestinalis morphology)

• Contains an ovoid shape: also known to entail karyosomes in shape

"Chilomastic Mestinil" Cysts

• One singular nucleus is present with this agent (with a eccentric singular karysome)

Dientamoeba Fragilis (facts and notes)

• Does not have a cyst component with the agent
• However the agent is able to transmitted via eggs

Trichomonas Tenax (transmission and facts)

• Noted that trichomonas agents and the like can transmit through sexual intercourse

Trichonomas vaginalis (Transmission/Morphology)

• Sexual and mother-child transfer are the main modes of transmission with this agent
• Notably affects the growth state of morphology
• Most often is asymptomatic

"Hemoflagellates" (Description)

• A name used to describe a flagellate inhabiting bodily tissues of the blood

Wuchereria bancrofile (Transmission)

• With most cases; transmissions is facilitated by anthropoid carriers
• This agent is noted by its ability to contain and create sheaths

Trypanosomes (Facts)

• These agents can create serious conditions if not tended to; and can affect both blood streams and major organs
• These are primarily transmitted from reduviid bug carriers

Ciliates (Information)

• Characterized as parasites that have a similar parasitic presence; most often transmitted from consuming contaminated food

Balantidium COli Ciliate

• Very difficult to contain
• In general the infection will be localized to both the large and small intestines

Ciliate Cysts

• Ciliate Cysts form to create a outer protection wall
• They often include an inner structure of macronucleus

Sporozoans and Microsporidia Classification

• Sporozoans : No means of motility
• Plasmodium species : most common
• Vector : Anopheles bites
• Some merozoites differentiate into gametocyte Clinically significant infections :
• Cerebral malaria
• Blackwater fever

Plasmodium species

• P.vivax : Amoeboid, Schuffner's dots V-Shape every 48 hours ( OV-)
• P.malariae : Band/bar Shape , Ziemann's dots Z-shape every 72 hours (M -)
• P. Falciparum Crescent, Maurer Cuneiform dots (FM) Every 36

Plasmodium Blood examination

Blood should be smeared and stained and thicked :

• Thick smear use for screening & remove hemoglobin
• Thin smear use for Differentiate stages, fixed with methanol

"Babesia" Transmission and Effects

• Transmitted via Irodes ticks
• Can result in hemoglobinuria

"Entamoeba" Transmission and Effects

• In all known circumstances this can cause serious damages if untreated