05- Parasitology (Exam # 5) Flashcards
Define the following term.
Parasite
Organism that lives in or on and takes its nourishment from another organism.
Define the following term.
Obligate parasite
Microorganism or virus unable to live independently outside a living cell.
Define the following term.
Definitive host
Individual in which a parasite has its adult and/ or sexual reproductive stage.
Define the following term.
Intermediate host
Individual in which a parasite has its larval and or asexual reproductive stage.
Define the following term.
Accidental host
An organism that generally does not allow transmission to the definitive host, thereby preventing the parasite from completing its development.
Define the following term.
Reservoir host
Host who harbors a parasite that is also infective for humans
Define the following term.
Ectoparasite
Organisms that live on, rather than in, the human body; include fleas, lice, ticks, and mites.
Define the following term.
Endoparasite
A parasite, such as a tapeworm, that lives inside its host.
Define the following term.
Vector
Organism responsible for transmitting parasite from infected host to noninfected host.
Define the following term.
Periodicity
Recurring at a regular time period
Define the following term.
Nocturnal
Primary expression of the periodicity during the night
Define the following term.
Diurnal
Primary expression of the periodicity during daylight hours
Stool
Macroscopic examination of stools
- Consistency (liquid, soft, formed)
- The color of the stool specimen (brown, red, black, mucus)
- Intact worms or proglottids (tapeworm segments)
Stool
Microscopic examination of stools
1.Direct wet mount examination (stained with iodine and unstained) of fresh stool specimens. Unstained could show motility.
2.Concentration procedures on stools with wet mount examination of the concentrate
3.Preparation of permanently stained smears
Stool
List preservatives used for specimen stabilization
Stool
Describe the purpose of adding a fixative to the preservative
Trophozoites, the motile and reproductive form of some amebae, or eggs of some helminths may disintegrate if not preserved or examined within a short time.
What is the ratio of preservative to feces for optimal fixation?
3 parts preservative to 1 part feces
Stool
Discuss the number of and timing of specimen collection for optimal detection of intestinal parasites.
- Because many intestinal organisms are shed into the stool irregularly, a single stool specimen may be insufficient to detect an intestinal parasite.
- 58% to 72% of protozoa are detected with a single specimen.
- For optimal detection of intestinal parasites, a series of three stool specimens collected a day or two apart, within a 10-day period, has been recommended.
Stool
Discuss specimen rejection criteria
- Stool specimens should never be collected from bedpans or toilet bowls; such practice might contaminate the specimen with urine or water, resulting in the destruction of trophozoites or introduction of free-living protozoa.
- Stool specimens for parasites should be collected before a barium enema, certain procedures using dyes, or the start of antimicrobial therapy. Antimicrobials can reduce the number of organisms present.
- If the patient has undergone a barium enema, stool examination should be delayed for 7 to 10 days because barium obscures organisms when specimens are examined microscopically, even after concentration procedures.
- If a purged specimen is to be collected, it is recommended that a saline or phosphosoda purgative be used because mineral oil droplets interfere with identification of parasites, especially protozoan cysts, an infective dormant form resistant to environmental stress. The second or third specimen after the purge is more likely to contain trophozoites that inhabit the cecum.
Stool
Discuss the purpose of performing concentration techniques designed to enhance recovery of parasites
- Concentration techniques are designed to concentrate the parasites present into a small volume of fluid and remove as much debris as possible. Fresh or formalin-preserved stool specimens may be used. The concentrate sediment may then be examined unstained or stained with iodine.
- Protozoan cysts, helminth larvae, and helminth eggs can be detected using this method.
What protozoan stage does not survive the concentration procedure?
Protozoan trophozoites do not survive the procedure.
Name the 2 types of concentration techniques?
- Sedimentation and Flotation methods
- Both are based on the difference in specific gravity between the parasites and concentrating solution and are used to concentrate parasites into a small volume for easier detection.
Describe
Sedimentation method
- The organisms are concentrated in sediment at the bottom of the centrifuge tube.
- The sediment is used for wet mounts.
- The formalin– ethyl acetate sedimentation (FES) method is the standard sedimentation method.
Stool
Flotation method
- The organisms are suspended at the top of a high-density fluid.
- The fluid is extracted from the top for wet mounts.
- The zinc sulfate method is the usual flotation procedure.
Stool
Contrast the flotation method versus the sedimentation method for enhancing the detection of parasites.
Although the zinc sulfate flotation method yields less fecal debris in the finished preparation compared with the FES sedinentation method, the zinc sulfate causes operculated eggs to open or collapse. It also tends to distort protozoan cysts. When used, this procedure may miss infertile Ascaris lumbricoides eggs and Schistosoma spp. eggs. Because of their high density, these eggs sink to the bottom of the test tube. Overall, sedimentation methods concentrate a greater diversity of organisms, including cysts, larvae, and eggs.
What is included in an ova and parasite examination?
Discuss risk factors for acquiring a parasitic infection.
- Immunocompromised patients
- Travel to countries that have less than ideal sanitation and a large number of endemic parasite
- Ongoing climate change might affect the movement of insect vectors into new geographic areas, thus expanding the range of some diseases normally associated with tropical climates.
Discuss the rationale for identifying and reporting both presumed pathogenic and non-pathogenic parasites.
In the case of intestinal protozoa, it could indicate exposure to fecally contaminted food or water.
Urine, Vaginal, and Urethral Specimens
Describe the wet mount preparation for vaginal specimens
- Place one drop of saline-diluted fluid onto microscope slide. Coverslip and remove
excess fluid from the edges (if necessary) by gently blotting on edge against a paper
towel. Examine under 40x magnification with reduced light. - The trophozoites of Trichomonas, if present, move with a nervous, jerky motion.
They possess an undulating membrane, which extends only half the length of the
organism
Describe the collection of duodenal aspirates for parasite evaluation.
* For the detection of duodenal infections such as Giardia intestinalis or Strongyloides stercoralis.
- Collected using direct aspiration during endoscopy or with the “Beale String” technique AKA the duodenal capsule Entero-Test
- Performed in cases of suspected giardiasis or strongyloidiasis when clinical symptoms are suggestive of infection but repeated routine stool examination results are negative.
- In the Entero-Test, the patient swallows a gelatin capsule containing a weighted string. One end of the string is taped to the side of the patient’s mouth; the weighted end is carried into the upper small intestine. After about 4 hours, the string is brought up, and part of the mucus adhering to the surface is stripped off and examined on a wet mount for motile trophozoites. The remainder of the specimen is placed in a fixative for a permanently stained smear. Eggs of Fasciola hepatica and Clonorchis sinensis, as well as oocysts of Cryptosporidium and Cystoisospora belli, can also be recovered.
Discuss the importance of noting the macroscopic examination of unpreserved fecal specimens.
- Consistency may help determine the type of preservative to be used, indicate the forms of parasites expected to be present, or dictate the immediacy of examination.
- Fig. 28.1 shows the relationship between stool consistency and protozoan stage. Cysts (infective stage) are most likely to be found in formed stools and sometimes in soft stools, whereas liquid stools will most likely contain the trophozoite stage.
Discuss the purpose of wet mount preparations
- The direct wet mount of unpreserved fecal material is primarily used to detect the presence of motile protozoan trophozoites in a fresh liquid stool or from sigmoidoscopy material.
- Specimens should be examined within 1 hour and direct wet mount performed using saline & iodine solutions (note: iodine will kill trophozoites)
Explain the microscopy procedure for concentrated specimens
10x & entire slide
40x & at least 50% of slide
Discuss the purpose of preparing permanently stained smears
- Permanently stained smear preparations of all stool specimens should be made to detect and identify protozoan trophozoites and cysts.
- The characteristics needed for identification of the protozoa, including nuclear detail, size, and internal structures, are visible in a well-made and properly stained smear.
**In a well-stained trichrome smear, the cytoplasm of protozoan cysts and trophozoites stains blue-green, although Entamoeba coli often stains purple. Nuclear peripheral chromatin (deoxyribonucleic acid [DNA] and proteins on the edge of the nucleus), karyosome (mass of chromatin in the nucleus), chromatoidal bars (dark-staining cytoplasmic inclusions of chromatin), and RBCs stain dark red to purple. Eggs and larvae stain red; however, they are often distorted or destroyed in the staining process. Background debris and yeasts stain green. With an iron hematoxylin stain, the parasites stain gray to black, nuclear material stains black, and background material stains light blue to gray.
What are the most commonly used permanent stains?
- Iron hematoxylin and trichrome
- The stain of choice in most laboratories is the trichrome stain because results are somewhat less dependent on the technique and the procedure is less time-consuming.
How to calibrate an ocular micrometer
What is the size of the egg in um?
Contrast the use of enzyme immunoassays and microscopic exam for the detection of parasites.
Immunoassys are more sensitive and specific
What parasitic antigens can be detected by EIA?
Giardia, Cryptosporidium, Entamoeba histolytica
DFA (direct flourescent antibody) can be used for detecting which parasites?
Cryptosporidium and Giardia
Describe the purpose of performing an analysis for occult blood, white blood cells, lactoferrin and fecal fat
- Lactoferrin is a marker for fecal leukocytes (wbcs) and an indicator of intestinal inflammation.
- Leukocytes are found in stools in the presence of infection with bacteria that invade the colonic mucosa (i.e. Salmonella, Shigella, Yersinia and invasive E. coli).
- Other disorders that may be associated with fecal leukocytes are ulcerative colitis, Crohns disease and antibiotic associated colitis.
* Fecal leukocytes are usually absent in diarrhea secondary to parasites or viruses. - Useful for diagnosing fat malabsorption due to pancreatic or intestinal disorders
Recall appropriate therapy for the following parasites.
Giardia duodenalis (lamblia)
Metronidazole
Recall appropriate therapy for the following parasites.
Cryptosporidium parvum
Generally self limiting. Drink plenty of fluids to stay hydrated
Recall appropriate therapy for the following parasites.
Trichomonas vaginalis
Metronidazole
Recall appropriate therapy for the following parasites.
Enterobius vermicularis
Mebendazole
Explain the picture
- The Metro (metronidazole) runs over Entamoeba histolytica, Giardia lamblia, Trichomonas vaginalis, and the anaerobic organisms including Bacteroides fragilis, Clostridioides difficile and Gardnerella vaginalis.
- This drug is also called Flagyl (it’s trade name) because it kills the flagellated bugs, Giardia and Trichomonas
PROTOZOA
What are the general characteristics of Amoebas?
- Single celled
- Move by pseudopodia
- Trophozoite and cyst stages
- Asexual reproduction
Protozoa
Describe the intenstinal ameba life cycle.
The life cycle of amebae is relatively simple, with direct fecal-oral transmission in food or water via the cyst stage and no intermediate hosts. Humans ingest the infective cysts, which excyst in the intestinal tract, and the emerged trophozoites multiply by binary fission. Trophozoites colonize the cecal area.
Cyst
Infective form of a protozoan; characterized by the formation of a thick protective wall that is resistant to environmental factors.
Trophozoite
The motile and reproductive form of some protozoa
Karyosome
Spherical chromatin mass within the nucleus of protozoa.
Chromatoid body (bars)
RNA that has been condensed into a barlike structure within the cyst of some protozoan organisms.
Kinetoplast
Structure found in some blood and tissue protozoans composed of the granule, from which the flagellum or undulating membrane arises, and a mitochondrion.
Protozoa
Name the 2 intestinal pathogenic amoebas?
- Entamoeba histolytica
- Blastocystis hominis
What stage in the life cycle of intestinal amoeba is infective?
Cyst
What three intestinal amoeba have a centrally located karysome with even peripheral chromatin?
- Entamoeba histolytica/dispar
- Entamoeba hartmanni
Protozoa
Which form E. histolytica/E. dispar is depicted in the picture?
Trophozoites
Protozoa
These mature cysts have 4 nuclei that characteristically have centrally-located karyosomes and fine, uniformly distributed peripheral chromatin. Cysts usually measure 12 to 15 µm.
Entamoeba histolytica/Entamoeba dispar
Cyst of E. histolytica/E. dispar stained with trichrome. Three nuclei are visible in the focal plane (black arrows), and the cyst contains a chromatoid body with typically blunted ends (red arrow). The chromatoid body in this image is particularly well demonstrated.
Protozoa
Erythrophagocytosis (ingestion of red blood cells by the parasite) is classically associated with what organism?
Trophozoite with ingested erythrocytes stained with trichrome. The ingested erythrocytes appear as dark inclusions. The parasite above shows nuclei that have the typical small, centrally located karyosome, and thin, uniform peripheral chromatin.
E. histolytica
What host is the primary reservoir for E. histolytica?
Humans
Describe the clinical infections associated with E. histolytica.
- 90% are asyptomatic
- Most experience vague abdominal symptoms
- Severe infections develop liver or lung abscesses
Protozoa
This intestinal Amoeba is pathogenic
Blastocystis hominis
Protozoa
Identify this non-pathogenic intestinal Amoeba in its cyst form
Entamoeba hartmanni
Protozoa
Identify this non-pathogenic intestinal Amoeba in its cyst form
Entamoeba coli
What two intestinal amoeba lack peripheral chromatin?
- Endolimax nana
- Iodamoeba butschlii
Protozoa
Identify this non-pathogenic intestinal Amoeba in its cyst form
Endolimax nana
Protozoa
Identify this non-pathogenic intestinal Amoeba in its cyst form
Iodamoeba buetschlii
Protozoa
Name 3 Nonintestinal (free living) amoeba?
- Acanthamoeba spp
- Naegleria fowleri
- Balamuthia mandrillaris
What stage in the life cycle of free-living pathogenic amoeba is infective?
Trophozoite
Protozoa
Identify the cyst form of this nonintestinal (free living) pathogenic amoeba
Acanthamoeba spp
Protozoa
Describe the life cycle of Acanthamoeba
Route of infection is direct inoculation
Acanthamoeba spp. have been found in soil; fresh, brackish, and sea water; sewage; swimming pools; contact lens equipment; medicinal pools; dental treatment units; dialysis machines; heating, ventilating, and air conditioning systems; mammalian cell cultures; vegetables; human nostrils and throats; and human and animal brain, skin, and lung tissues. Unlike N. fowleri, Acanthamoeba has only two stages, cysts (1) and trophozoites (2), in its life cycle. No flagellated stage exists as part of the life cycle. The trophozoites replicate by mitosis (nuclear membrane does not remain intact) (3). The trophozoites are the infective forms, although both cysts and trophozoites gain entry into the body (4) through various means. Entry can occur through the eye (5), the nasal passages to the lower respiratory tract (6), or ulcerated or broken skin (7). When Acanthamoeba spp. enters the eye it can cause severe keratitis in otherwise healthy individuals, particularly contact lens users (8). When it enters the respiratory system or through the skin, it can invade the central nervous system by hematogenous dissemination causing granulomatous amebic encephalitis (GAE) (9) or disseminated disease (10), or skin lesions (11) in individuals with compromised immune systems. Acanthamoeba spp. cysts and trophozoites are found in tissue.
Protozoa
Identify the cyst form of this nonintestinal (free living) pathogenic amoeba
Balamuthia mandrillaris
Protozoa
Describe the life cycle of Balamuthia mandrillaris
Balamuthia mandrillaris has only recently been isolated from the environment and has also been isolated from autopsy specimens of infected humans and animals. B. mandrillaris has only two stages, cysts (1) and trophozoites (2), in its life cycle. No flagellated stage exists as part of the life cycle. The trophozoites replicate by mitosis (3). The trophozoites are the infective forms, although both cysts and trophozoites gain entry into the body (4) through various means. Entry can occur through the nasal passages to the lower respiratory tract (5), or ulcerated or broken skin (6). When B. mandrillaris enters the respiratory system or through the skin, it can invade the central nervous system by hematogenous dissemination causing granulomatous amebic encephalitis (GAE) (7), or disseminated disease (8), or skin lesions (9) in individuals who are immune competent as well as those with compromised immune systems. B. mandrillaris cysts and trophozoites are found in tissue.
Protozoa
Identify this nonintestinal (free living) pathogenic amoeba
Naegleria fowleri
Describe the causative parasitic agent and the disease syndrome.
Primary amebic meningoencephalitis (PAM)
Naegleria fowleri
- The trophozoite enters the nasal cavity through inhalation of contaminated water or soil. The amebic form colonizes the nasal cavity, invades the nasal mucosa, attaches to olfactory nerves, penetrates the cribriform plate, moves along the olfactory nerve to the olfactory bulb, and moves into the arachnoid space. From there, it is free to spread throughout the CNS.
- Clinically, the disease cannot be distinguished from bacterial meningitis.
- The organism multiplies in brain tissue, and within 2 to 4 days, the patient can experience drowsiness, confusion, and seizures, and progress to coma. The disease usually is fatal within 1 week of the appearance of clinical symptoms.
Protozoa
Which free living amoeba causes GAE (granulomatous amebic encephalitis)?
Both Acanthamoeba & Balamuthia mandrillaris
Protozoa
Amebic keratitis in contact lens wearers is caused by which free living amoeba?
Acanthamoeba spp
Ussually due to contaminated lens care solution
Protozoa
Cultures can be performed on a lawn of bacteria (E. coli) for which two free living amoebas?
Both Acanthamoeba & Balamuthia mandrillaris
SPOROZOA
Protozoa
What class of protozoa reproduce both sexually and assexually in thier life cycle and are nonmotile?
Sporozoa
What stain is used to identify coccidia?
Modified Acid-fast
Stains the oocyst
What 3 organisms make up the coccidia?
- Cryptosporidium parvum
- Cystoisospora belli
- Cyclospora cayetanensis
Oocyst
The encysted form of the fertilized macrogamete, or zygote, in coccidian Sporozoea in which sporogonic multiplication occurs; results in the formation of sporozoites, infectious agents for the next stage of the sporozoan life cycle.
Coccidian parasite
Identify the oocysts of this pathogenic intestinal sporozoa
Cryptosporidium (“Crypto”)
While this parasite can be spread in several different ways, water (drinking water and recreational water) is the most common way to spread the parasite. Cryptosporidium is a leading cause of waterborne disease among humans in the United States.
Coccidian parasite
Describe the life cycle of Cryptosporidium
Sporulated oocysts, containing 4 sporozoites, are excreted by the infected host through feces and possibly other routes such as respiratory secretions (1). Transmission of Cryptosporidium parvum and C. hominis occurs mainly through contact with contaminated water (e.g., drinking or recreational water). Occasionally food sources, such as chicken salad, may serve as vehicles for transmission. Many outbreaks in the United States have occurred in waterparks, community swimming pools, and day care centers. Zoonotic and anthroponotic transmission of C. parvum and anthroponotic transmission of C. hominis occur through exposure to infected animals or exposure to water contaminated by feces of infected animals (2). Following ingestion (and possibly inhalation) by a suitable host (3), excystation (a) occurs. The sporozoites are released and parasitize epithelial cells (b, c) of the gastrointestinal tract or other tissues such as the respiratory tract. In these cells, the parasites undergo asexual multiplication (schizogony or merogony) (d, e, f) and then sexual multiplication (gametogony) producing microgamonts (male) (g) and macrogamonts (female) (h). Upon fertilization of the macrogamonts by the microgametes (i), oocysts (j, k) develop that sporulate in the infected host. Two different types of oocysts are produced, the thick-walled, which is commonly excreted from the host (j), and the thin-walled oocyst (k), which is primarily involved in autoinfection. Oocysts are infective upon excretion, thus permitting direct and immediate fecal-oral transmission.
Coccidian parasite
Identify the oocysts of this pathogenic intestinal sporozoa
Cyclospora cayetanensis
Associated with contaminated raspberries
Coccidian parasite
Describe the life cycle of Cyclospora
When freshly passed in stools, the oocyst is not infective (thus, direct fecal-oral transmission cannot occur; this differentiates Cyclospora from another important coccidian parasite, Cryptosporidium). In the environment , sporulation occurs after days or weeks at temperatures between 22°C to 32°C, resulting in division of the sporont into two sporocysts, each containing two elongate sporozoites. The sporulated oocysts can contaminate fresh produce and water, which are then ingested. The oocysts excyst in the gastrointestinal tract, freeing the sporozoites, which invade the epithelial cells of the small intestine. Inside the cells, they undergo asexual multiplication into type I and type II meronts. Merozoites from type I meronts likely remain in the asexual cycle, while merozoites from type II meronts undergo sexual development into macrogametocytes and microgametocytes upon invasion of another host cell. Fertilization occurs, and the zygote develops to an oocyst which is released from the host cell and shed in the stool. Several aspects of intracellular replication and development are still unknown, and the potential mechanisms of contamination of food and water are still under investigation.
Coccidian parasite
Identify the oocysts of this pathogenic intestinal sporozoa
Cystoisospora belli
How is malaria spread?
- All malarial species are spread by the female Anopheles mosquito
- Sporozoites injected into the host go to the liver and proliferate (exoerythrocytic schizogony)
- Schizonts rupture and release merozoites into the bloodstream
- These infected red cells initiate schizogony
Merozoite
Parasitic form produced during schizogony. In malaria, these structures are released from a ruptured erythrocyte and invade other erythrocytes at the end of an asexual reproductive cycle. Some merozoites differentiate into gametocytes.
Gametocyte
The sexual cell of sporozoans; the female (macrogametocyte) and male (microgametocyte) that develop into gametes.
Schizont
Parasitic form producing merozoites during schizogony. In malaria, it is part of the erythrocytic asexual life cycle.
Describe the thick and thin processing of specimens for evaluation of blood parasites.
- A thick film is best for the detection of parasites (high sensitivity) because of the larger volume of blood and the fact that organisms are concentrated in a relatively small area.
- In a thick film, the organisms may be difficult to identify, and there is no way to compare the size of infected and noninfected erythrocytes. Therefore species identification should be made from a thin film because the characteristics of the parasite and the RBCs can be seen.
- The thin film is made in the same way as that for a differential cell count. It should be fixed in methanol for 1 minute and air-dried before staining with Giemsa stain. The entire smear should be scanned at × 100 magnification for detection of large organisms, such as microfilariae; then at least 100 oil immersion fields (× 1000) must be examined for the presence of some organisms, such as Trypanosoma, or for intracellular organisms, such as Plasmodium or Babesia.
Identify the parasite.
P. falciparum
- Ring forms may have double chromatin dots “headphone forms”
- Multiple ring forms commonly found in a single erythrocyte
- Maurer clefts may be seen (round to comma-shaped red cytoplasmic dots)
- Gametocytes are banana shaped
Applique forms
- Plasmodium falciparum parasites at the edge of the RBC
- Multiple ring forms in a single RBC are common.
Maurer dots
Coarse granulations present in red blood cells invaded by the **P. falciparum **malaria parasite.
Identify the parasite.
P. malariae
- Normocytic
- No Schuffner dots
- Schizonts have 6-12 merozoites
- Trophozoites tend to have a band form
Identify the parasite.
P. ovale
- Macrocytic
- Schuffner dots (stippling) may be present
- Schizonts have 6-14 merozoites
- Infected RBCs are slightly enlarged and have an oval shape, with tufted ends
Schuffner’s stippling
Malarial pigment characterized as tiny red staining dots in infected red blood cells infected with Plasmodium vivax or P. ovale.
Identify the parasite.
P. vivax
- Macrocytic
- Throphozoites are ameboid in shape
- Schizonts have 12-24 merozoites present
Identify the parasite.
Babesia spp
- Trophozoites often multiple in red cells; may form diads or tetrads (Maltese cross); light blue ring forms with red chromatin dots
- Extraerythrocytic ring forms often present
- No pigment or nonring forms seen
Maltese cross
Ring trophozoites of Babesia species usually lie in pairs at an acute angle. Occasionaly, they lie as a tetrad.
Identify the parasite.
How is Babesia transmitted?
The vector is the Ixodes tick
Not spread by mosquitos! The resevoirs are the white-footed mouse and white-tailed deer
Which organism is represented by both tachyzoite and bradyzoite forms?
Toxoplasmosis gondii
Tachyzoite
Motile, replicating intracellular stage of Toxoplasma gondii.
How does Toxoplasmosis present in a pregnancy?
- In the 1st trimester, there is risk of fetal loss
- In late pregnancy there is risk of fetal CNS infection
Congenital transmission occurs when the tachyzoites, the motile, rapidly dividing forms in maternal circulation, cross the placenta and enter fetal circulation and tissues. Children who acquire T. gondii in this way may have a range of serious complications, including mental retardation, microcephaly, seizures, hydrocephalus, retinochoroiditis, and blindness.
How does Toxoplasmosis present in immunosuppressed patients?
- Immunosuppressed patients, particularly those with leukemia or lymphoma and those undergoing chemotherapy, may experience a serious primary infection or reactivation of a latent infection that can manifest itself as a fulminating encephalitis and result in rapid death.
- Up to 10% of the deaths of patients with AIDS are caused by reactivation of latent toxoplasmosis, resulting in encephalitis.
- Computed tomography (CT) may demonstrate lesions in the brain that represent Toxoplasma spp. cysts.
- Pulmonary toxoplasmosis may be present in conjunction with CNS infections or can be the presenting condition; however, the organism can spread to any organ of the body.
Describe the life cycle of Toxoplasmosis gondii.
Coccidian parasite
Describe the life cycle of Cystoisospora belli
At the time of excretion in stool, the oocyst is immature and usually contains just one sporoblast (sometimes, two). 1. During further maturation after excretion, the sporoblast divides in two (the oocyst now contains two sporoblasts); the sporoblasts secrete a cyst wall, thus becoming sporocysts; and the sporocysts divide twice, resulting in four sporozoites per each of two sporocysts. 2. Infection occurs by ingestion of mature (fully sporulated) oocysts: the sporocysts excyst in the small intestine and release their sporozoites, which invade the epithelial cells and initiate schizogony. 3. Upon rupture of the schizonts, merozoites are released, which invade epithelial cells and continue the cycle of asexual multiplication. 4. Trophozoites develop into schizonts, which contain multiple merozoites. After a minimum of one week, the sexual stage begins, with the development of male and female gametocytes. 5. Fertilization results in the development of oocysts, which are excreted in the stool. 1.
Protozoa: Flagellates
Identify the cysts of this intestinal flagellates
Giardia duodenalis
When viewed from top, kite shaped with axoneme; 2 nuclei, 1 on either side of centrally located axostyle, 2 parabasal bodies located by axostyle; 2 sucking disks
Protozoa: Flagellates
What is the specimen of choice for Giardia?
Duodenal aspirate
Protozoa: Flagellates
Describe the life cycle of Giardia
- Giardia cysts can contaminate food, water, and surfaces, and they can cause giardiasis when swallowed in this infective stage of their life cycle. Infection occurs when a person swallows Giardia cysts from contaminated water, food, hands, surfaces, or objects.
- When Giardia cysts are swallowed, they pass through the mouth, esophagus, and stomach into the small intestine where each cyst releases two trophozoites through a process called excystation. The Giardia trophozoites then feed off and absorb nutrients from the infected person.
- Giardia trophozoites multiply by splitting in two in a process called longitudinal binary fission, remaining in the small intestine where they can be free or attached to the inside lining of the small intestine.
- The Giardia trophozoites then move toward the colon and transform back into cyst form through a process called encystation. The Giardia cyst is the stage found most commonly in stool.
- Both Giardia cysts and trophozoites can be found in the stool of someone who has giardiasis and may be observed microscopically to diagnose giardiasis. Giardia cysts are immediately infectious when passed in the stool or shortly afterward, and the cysts can survive several months in cold water or soil.
Protozoa: Flagellates
Identify the trophozoites of this intestinal flagellate
Dientamoeba fragilis
Protozoa: Flagellates
Which nonintestinal flagellate is transmitted sexually?
Trichomonas vaginalis
In women the infection is primarily localized to the vagina, resulting in itching and the production of a frothy, creamy, mucopurulent vaginal discharge, as well as dysuria. About one third of infected women, however, are asymptomatic. Men infected with T. vaginalis are usually asymptomatic and serve as carriers.
Protozoa: Flagellates
Describe the trophozoite of Trichomonas vaginalis
- Pear shaped with large nucleus at the anterior end of central axostyle
- Undulating membrane that extends about halfway down the organism
- 4 flagella
- Characteristic jerky nondirectional motility
Axostyle
The axial rod functioning as support in flagellates
Undulating membrane
A protoplasmic membrane with a flagellar rim extending out like a fin along the outer edge of the body of certain protozoa; it moves in a wavelike pattern.
Protozoa: Flagellates
Identify the cysts of this nonpathogenic flagellate.
Chilomastix mesnili
Protozoa: Flagellates
Which nonpathogenic flagellate has an undulating membrane that runs the full length of its body ?
(Penta)trichomonas hominis
Cilliate
Identify the trophopozoite of this intestinal cilliate
Balantidium coli
Describe the different morphologic states of the blood-borne flagellates.
Leishmania and Trypanosoma are transmitted by the bite of a blood-sucking insect. Although they cause different diseases, they pass through similar morphologic states in the human and insect host. They can exist as:
Rounded cells without flagella, called amistigotes
Or as flagellated motile forms called promastigotes, epimastigotes, and trypomastogotes.
These are named according to the insertion site of their singular flageelum. All these organisms cause an initial skin ulcer at the site of the insect bite, followed by systemic invasion. These parasites can also be transmitted via blood transfusion.
Identify the trypomastigote
Blood concentration methods are often needed because of the small number of organisms present. The organism can also be detected in lymphatic fluid and CSF. In infected individuals, CSF will often show increased numbers of WBCs (primarily lymphocytes) and elevated protein levels. The trypomastigote is 15 to 20 µm long, with a single large nucleus and a posterior kinetoplast to which is attached the flagellum of the undulating membrane
Trypanosoma spp
Describe the causative parasitic agent and the disease syndrome.
Chagas Disease
Trypanosoma cruzi
The American trypanosome. To remember that T. cruzi causes megacolon, electrical arrythmias, and dialation of the heart, and is transmitted by the feces of the kissing bug, picture Tom** Cruise** ( the American actor)
Identify the hemoflaggelate:
Leishmania spp.
Leishmania presents in 3 clinical forms of disease:
1. Cutaneous
2. Mucocutaneous
3. Visceral
Which is the most severe and what disease does it cause?
Visceral, AKA “kala-azar”
Caused by Leishmania donovani
Identify the eggs of this large intestinal nematode (roundworm).
Ascaris lumbricoides
- Largest nematode parasitizing the human intestine
- Infection results from ingestion of eggs (usually contaminated food), which hatch to produce larvae
- Larvae penetrate mucosa, enter bloodstream, and are carried to lungs
- Expectorated & swallowed, mature into adults which infect duodenum
Mammillated
Albuminous covering of Ascaris eggs
Decorticated
Ascaris eggs that have lost the albuminous covering
Identify the eggs of this intestinal round worm.
Trichuris trichiura AKA “whipworm”
- Infection asymptomatic to dysenterylike
- Rectal prolapse in young children
Identify the eggs of this intestinal round worm.
Enterobius vermicularis (pinworm)
- Most common helminthic infection in American children
- Infection is aquired from ingestion of eggs
- Mature females inhabit cecum & appendix; nocturnally lay eggs in perianal region
Pinworm
Describe the cellophane tape preparation (Sticky Paddle) method for pinworm analysis
The life cycle of the pinworm Enterobius vermicularis includes migration of the female from the anus at night to lay eggs in the perianal area. Therefore a fecal specimen is not the optimal specimen for diagnosis of infection with this organism. Instead, the cellophane tape preparation is routinely used for detection of suspected pinworm infections. This procedure involves swabbing the person’s perianal area with a tongue blade covered with cellophane tape (sticky side out). The collection should take place first thing in the morning before the individual uses the bathroom or has bathed. After the sample has been taken, the sticky side of the tape is placed on a microscope slide and scanned at low- and high-power magnification for the characteristically shaped eggs.
Nematodes: Intestinal Free-living Worms
Describe the life cycle of hookworms
- Infection results from penetration of skin by filariform larvae, usually skin of feet
- Larvae pass through lungs (Loeffler syndrome) are expectorated and swallowed
- Adults infest small bowell; may produce iron-deficiency anemia
Nematodes: Intestinal Free-living Worms
Which hookworm egg is depicted, Necator americanus or Ancylostoma duodenale?
Hookworm eggs are indestistinguishable from one another.
Nematodes: Intestinal Free-living Worms
This hookworm has a distinctive mouth part called cutting plates.
Necator americanus
Nematodes: Intestinal Free-living Worms
This hookworm has a distinctive mouth part called teeth.
Ancylostoma duodenale
Sheath
A thin, translucent eggshell remnant covering the body of microfilaria and extending past the head and tail
Describe the causative parasitic agent and the disease syndrome.
Filariasis
Brugia malayi & Wuchereria bancrofti
(Filarial worms)
- Aquired through mosquito bites
- Adults infect the lymphatics (elephantitis)
- Shed into blood primarily at night (nocturnal periodicity)
Nematodes: Intestinal Free-living Worms
Filariform larvae
- Nematodes have 2 larval forms:
- Filariform larval stage is the infective or pathogenic form for the definitive host.
Nematodes: Intestinal Free-living Worms
Rhabditiform larvae
- Nematodes have 2 larval forms:
- Rhabitiforme is the feeding but noninfective larval stage; this stage hatches from the egg.
The rhabditiform larva of hookworms must be differentiated from that of S. stercoralis because treatment is different. How is the distinction made?
- Hookworm larvae are characterized by a long buccal cavity and a small inconspicuous genital primordium
- Strongyloides has a short buccal capsule and prominent genital primordium (short & sexy)
Describe the causative parasitic agent and the disease syndrome.
Cutaneous larva migrans
Dog or Cat hookworm (Ancylostoma caninum)
The larva penetrates skin through a hair follicle, a break in skin, or unbroken skin. Once inside the body, it does not enter the circulation but wanders through the subcutaneous tissue, creating long, winding tunnels. Secretions from the larva create a severe allergic reaction, with intensely itchy skin lesions that are vesicular and erythematous. Secondary bacterial infections can result from scratching. The infection resolves within several weeks when the larva dies. Diagnosis is based primarily on history and clinical symptoms.
Describe
Scolex
The anterior headlike segment of a tapeworm. Can have suckers and, in some species, hooklets as a means of attachment to the intestinal mucosa.
Which parasite is transmitted by ingesting fresh water, migrates to the skin and grows up to 30 inches forming a blister?
Dracunculus medinesis
(Guinea worm)
Worm is removed by slowly pulling it around a stick (1 inch/day)
Which adult worm can often be seen as it migrates across the surface of the eye?
Loa loa
Proglottid
Tapeworm segments. Contains both sex organs and produces eggs.
Gravid proglottid
Tapeworm segments with eggs.
Strobila
Body of a tapeworm (all the proglottids)
Rostellum
The fleshy, anterior protuberance of the scolex of some tapeworms (species specific); may bear a cirucular row (or rows) of hooks; may be retractable.
Cestodes: (Tapeworms)
Identify the egg of this intestinal tapeworm
Hymenolepis nana AKA “dwarf tapeworm”
Cestodes: (Tapeworms)
Identify the egg of this intestinal tapeworm
The absence of polar thickening and the 6 hooklets are clearly illustrated (arrow)
Hymenolepsis diminuta AKA “Rat tapeworm”
Cysticercus
Larval stage of Taenia spp.; fluid-filled sac that contains the scolex of the tapeworm.
Describe the causative parasitic agent and the disease syndrome.
Cysticercosis
- Scolex has 4 suckers and tiny hooklets (armed rostellem)
- Less than 13 lateral uterine branches in the proglottids
Taenia solium (pork tape worm)
- Intestinal infection results from ingestion of encysted organisms (cystercerci) in undercooked pork
- Cysticercosis results from ingestion of eggs shed in feces of person with intestinal infection: pork ingestion not required
Name the beef tape worm.
- Scolex has 4 suckers and a smooth surface (unarmed rostellum)
* Greater than 13 lateral uterine branches
Taenia saginata
Describe the causative parasitic agent and the disease syndrome.
Trichinosis
Trichinella spiralis
- Consumption of undercooked meat, especially pork and wild game
- Infection of skelatal muscle by encysted larvae, producing myositis and weakness
- Can be seen on histologic sections of infected skelatal muscle
Cestodes: (Tapeworms)
Identify the eggs
Taenia spp.
Operculum
The lidlike or caplike cover on certain flatworm eggs.
Cestodes: (Tapeworms)
Identify this egg
Diphyllobothrium latum (fish tapeworm)
“broad tapeworm”
- Scolex has 2 sucking grooves
- Proglottids wider than it is long
- Coiled uterus in the shape of rosettes
Cestodes: (Tapeworms)
Identify this egg
Dipylidium caninum (dog tapeworm)
- Infects cats & dogs
- May infect humans after accidental ingestion of fleas
Hydatid cyst
A vesicular structure formed by Echinococcus granulosus larva in the intermediate host; contains fluid, brood capsules, and daughter cysts in which the scolices of potential tapeworms are formed. Grows slowly and can get quite large.
Miracidium
Ciliated first-stage, free-swimming larva of flukes, which emerges from the egg and must penetrate the appropiate species of snail to continue its life cycle.
Cercaria
Tailed stage in the life cycle of flukes that is produced from rediae that develop in snail tissue. This stage is released into the water.
Coracidium
A ciliated hexacanth embryo; D. latum eggs develop to this stage and then can hatch in fresh water.
This organism’s 2nd host is freshwater plants (watercress) and is commonly associated with sheep. AKA the sheep liver luke
Fasciola hepatica
Infection of the bile duct. Can lead to fibrosis/cirrhosis
This organism’s eggs are identical to F. hepatica. The snail is the 1st host but is aquired by ingesting the 2nd host: water chestnuts. It infects the duodenem.
Fasciolopsis buski (intestinal fluke)
Identify this egg. Also known as a liver fluke. It’s 1st intermediate host is a snail. The 2nd is fresh water fish.
Clonorchis sinensis
Identify this egg. 1st intermediate host is snail. The 2nd intermediate host is crustaceans (crabs or crayfish). Causes lung infection w/ pneumonitis. Eggs can be found in stool or sputum.
Paragonimus westermani (oriental lung fluke)
This Schistosoma spp. is found in the Far East (Asia); affects the liver, leading to cirrhosis.
Schistosoma japonicum
This Schistosoma spp. migrates through the blood stream and infects mesenteric vessels. Eggs can be found in rectal biopsies.
Schistosoma mansoni
This Schistosoma spp., found in Africa & Middle East, affects the bladder, leading to hematuria and irritative bladder symptoms.
Schistosoma haematobium
