Major pathogens and disease states

What is a human infection caused by flukes called?

Distomiasis

Illustrated in the image shown is a 20 µm trophozoite of an amoeba as microscopically observed in a trichrome-stained mount of a stool specimen obtained from a patient with recurrent diarrhea. Based on the morphology of the trophozoite, presumptively identify the parasitic trophozoite.

Entamoeba histolytica

Which of the following organisms is considered to be pathogenic?

Entamoeba histolytica

Which obligate intracellular parasite may be transmitted to humans though accidental ingestion of infective oocysts from cat feces when gardening or changing a litterbox?

Toxoplasma gondii

Which of the following parasites can cross the placenta and cause serious infection to the fetus?

Toxoplasma gondii

Which parasite can be recovered from the eye?

Toxoplasma gondii

This suspicious form, found in stool, which measures 15 µm by 10 µm, is responsible for which of the following diseases?

Traveler's diarrhea

Which of the following helminths is a tissue nematode whose life cycle resides in a single host?

Trichinella spiralis

The image shows a scavenger that lives in the mouth and measures about 10 µm. What is the identification of the organism?

Trichomonas tenax trophozoite

All of the following parasites are correctly matched with its respective primary symptom, EXCEPT

Trichomonas vaginalis - diarrhea

A stool specimen has been left at room temperature overnight. The next day, many motile larvae with a short buccal cavity are seen upon microscopic exam, but there are no ova observed. What is the most likely identification and life stage of this parasite?

Strongyloides stercoralis - rhabditiform larvae

The image shown here is a thin blood smear stained with Giemsa. Identify the parasitic organism present in the blood smear, which is transmitted by the triatomid bug, or "kissing bug." (Image is courtesy of the CDC.)

Trypanosoma cruzi

A specimen suspected of containing which organism may be cultured by placing it on an agar plate with an overlay growth of Escherichia coli?

Acanthamoeba species

Dracunculus medinensis belongs to this category of parasites?

Nematode

In which of the following categories does the helminth Ascaris lumbricoides belong?

Nematode

Which of the following parasites has the longest undulating membrane?

Trichomonas hominis

Not all strains of Entamoeba histolytica appear to be pathogenic, and recent molecular studies indicated that there was a non-pathogenic variant of Entamoeba histolytica. What is this non-pathogenic variant?

Entamoeba dispar

A 21-year-old male presented in the emergency room with symptoms resembling a liver infection. The patient complained of abdominal pain, fever, cough, nausea, vomiting and constipation alternating with diarrhea. Further examination revealed the presence of a hepatic abscess. The form in the attached image was recovered following parasitic examination of a sample from the abscess and measures 20 µm. What condition is the patient most likely suffering from?

Extraintestinal amebiasis

A 20-year-old female was admitted into the hospital complaining of 10 to 15 bloody mucous stools per day, fever, gastrointestinal disturbances, abdominal pain, and nausea. The preliminary O & P report went out as "Probable Entamoeba histolytica trophozoites and cysts, confirmation pending." This patient is most likely suffering from:

Intestinal amebiasis

A 20-year-old female was admitted into the hospital complaining of 10 to 15 bloody mucous stools per day, fever, gastrointestinal disturbances, abdominal pain, and nausea. The preliminary O & P report went out as "Probable Entamoeba histolytica trophozoites and cysts, confirmation pending." What is this patient most likely suffering from?

Intestinal amebiasis

A 10-year-old male presented to the local Appalachian Mountain clinic complaining of vomiting, fever, and severe abdominal pain. Patient history revealed that the child lives in the area in substandard conditions and receives only one balanced meal per day. A stool was collected and submitted for parasite study. This suspicious form, measuring 50 µm by 35 µm was found. This patient is most likely infected with:

Large intestinal roundworm

Although not always the most practical, animal inoculation may be used to identify all but which of the following conditions?

Malaria

Beginning with human infection, which of the following is the first stage of the Wuchereria bancrofti life cycle?

Microfilariae in blood or skin of humans

Illustrated in the upper photograph is a 15-year-old native of Guatemala who presents with a 20 mm elevated skin nodule of the right forehead. A Giemsa-stained mount of aspirated fluid from within the nodule is shown in the lower image. From the appearance of the skin lesion and the microfilaria seen in the microscopic mount, select from the multiple choices the presumptive clinical and laboratory diagnosis.

Onchocerca volvulus

A 38-year-old male presented to the E.R. complaining of severe cough, chest pain, shortness of breath, and general fatigue. Parasitic examination of his bloody sputum revealed this suspicious form. The patient is most likely suffering from:

Paragonimus westermani

This organism is found endemically on the New England seacoast. When seen in peripheral blood smears, it resembles a parasite of the genus Plasmodium. When an organism resembling malarial parasites is found in the peripheral blood, it is most probably:

Babesia

What is the largest protozoan known to infect humans?

Balantidium coli

The optimum time to collect a urine sample to maximize recovery of the ovum illustrated in this iodine-stained mount of urine sediment is:

Between 10:00 A.M. and 2:00 P.M

The following is the vector for the transmission of Onchocerca volvulus:

Black Flies

The image shows an organism that measures 12 µm and is found in stool. What is the identification of this organism?

Blastocystis hominis

Illustrated in the photomicrograph is the tail portion of an adult worm of a filarial nematode in a peripheral blood smear. These worms measure up to 300 µm in length and commonly inhabit the lymphatics of the inguinal region resulting in swelling below the knee in what is known as "elephantiasis". What is this species pictured, which can be presumptively determined by the orientation of nuclei within the tail section (arrows)?

Brugia malayi

What is the anatomical feature of a tapeworm that possesses both male and female reproductive structures?

Proglottid

The adult worms of which of the following parasites resides in the human intestine?

Heterophyes heterophyes

Necator americanus is a parasite associated with which of the following conditions?

Hookworm infection

Which of the following would be considered the definitive host of a parasite?

Host in which parasites reproduce sexually

Trypanosoma cruzi is the etiologic agent of:

Chagas' disease

What term is defined as the presence of arthropods in or upon a human host:

Infestation

Which type of Plasmodium infection has a 72-hour cycle, tends to infect old cells, and will have normal sized red blood cells?

Plasmodium malariae

Adult Ascaris lumbricoides worms reside in the:

Small intestines

What is the recommended treatment if the patient is passing both cysts and trophozoites with an Entamoeba histolytica infection?

Tissue amebicide followed by a luminal amebicide

The parasitic form shown in the illustration may be found in the eye, as a cause of keratitis. It measures approximately 25 µm in diameter. What is the identity of this parasite?

Acanthamoeba species

Which of the following is the first stage in the life cycle of a hemoflagellate?

Amastigote

Binary fission is the means of reproduction for which of the following groups of parasites?

Amebae

This suspicious form, shown below at both low (10X) and high dry (40X) power, measures 90 mm by 42 mm. It was seen in a stool sample.

Ascaris lumbricoides egg

What is this form, measuring 45 µm and found in stool?

Ascaris lumbricoides egg

Human infection of the Schistosomes occurs following penetration of what morphologic form into the skin?

Cercariae

A 68-year-old female, who recently vacationed in Brazil, presented to her physician exhibiting overall weakness, fever, and enlarged lymph nodes. Blood was collected for culture and parasitic examination. The culture was negative. This suspicious form was recovered upon examining the Giemsa-stained preparation. This patient is most likely suffering from what condition/disease?

Chagas disease

Which of the following conditions is caused by Trypanosoma cruzi?

Chagas' Disease

Illustrated in the upper photograph is an adult trematode fluke that in human infections is most commonly found in the distant bile ducts of the liver. The fluke is relatively small, averaging 12 - 20 mm. The lower image is a close in view of this fluke to better illustrate its internal structures. Symptoms during infection may be minimal, but liver enlargement and jaundice may be experienced in heavy infections. Human infections are endemic in southern China. What is considered the appropriate identification?

Clonorchis sinensis

Humans serve as accidental hosts in the life cycles of which of these this parasites?

Echinococcus granulosus

What cestode, pictured here, resides in multiple tissues of the human body?

Echinococcus granulosus

A 7-year-old male presented to the local clinic experiencing mild, yet annoying, abdominal pain, diarrhea and nausea. Patient history revealed that the child lives in a shack where sanitation practices are marginal, at best. The dwelling is infested with rats and multiple insects. Stool was collected and submitted for an ova and parasites examination. Numerous suspicious forms, as depicted in the image to the right, measuring 60 µm by 75 µm were seen. This child is MOST likely infected with:

Hymenolepis diminuta

Which of the following amoebae has a flagellate form as part of its life cycle?

Naegleria fowleri

Which of these parasites can be contracted by swimming in infected water?

Naegleria fowleri

Which of the following can be found in cerebral spinal fluid (CSF) and measures approximately 15 µm?

Naegleria fowleri trophozoite

A 32-year-old male was seen in the emergency room with gastrointestinal discomfort. Upon questioning the patient it was learned that he first began feeling ill after spending a day at the park where he swam and played volleyball barefooted. He first noticed a lesion on his foot. Later, he developed vague respiratory symptoms. Now his largest complaint is severe abdominal pain along with occasional vomiting. This patient is most likely suffering from a parasitic infection with:

Necator americanus

The human infections related to the 60 X 40 µm ovum, as illustrated in the image, are reported by the World Health Organization to involve several million people worldwide. Symptoms vary from nausea and diarrhea in patients with light infection, to peripheral edema, anemia, dehydration, and congestive heart failure in those with heavy infections. Select the most likely genus/species identification.

Necator americanus

In the hookworm life cycle, which of the following is considered the noninfective larval form?:

Rhabditiform

Which of the following organisms is an obligate intracellular parasite?

Rickettsia

Cyclospora species are classified as:

Sporozoa

The class of protozoa with no apparent organelles for locomotion is known as:

Sporozoa

The specimen of choice for the recovery of Entamoeba hartmanni is:

Stool

Illustrated in the photomicrograph is a Giemsa-stained impression smear prepared from an aspirate of an enlarged cervical lymph node. Human infections are acquired through the ingestion of poorly cooked meat. Pregnant women in particular are advised to avoid handling of cats and the ingestion of under-cooked meat. Based on the morphology of the 8 µm long tachyzoites observed in the photomicrograph, select the name of the protozoan parasite as listed for making a presumptive identification.

Toxoplasma gondii

Which of the following is considered the technique of choice for isolating the oocysts of Isospora belli and Cryptosporidium parvum?

Zinc sulfate flotation

Each parasite listed below is correctly matched with its respective vector, EXCEPT:

Iodamoeba butschlii - pig

Illustrated in the photomicrograph is a relatively small pear-shaped trematode ovum, averaging 25 - 35 µm, as might be microscopically observed in a stool sample preparation. The shell is smooth and slightly thickened. Distinctive is the shouldered operculum at the cephalic end of the shell and a small knob at the posterior margin (arrows). Developing larvae at varying stages are observed internally. The adult flukes are most commonly found within the liver bile duct system and may cause obstruction and intermittent jaundice. What is the best presumptive identification?

Clonorchis sinensis

The patient was a 55-year-old male immigrant from Korea. His current symptom was severe jaundice. He had had intermittent less severe bouts of jaundice in the past. During surgery, his proximal bile duct appeared to be enlarged with a nodular area of inflammation. A surgical biopsy was done and a parasite was observed in a stained tissue section residing in the lumen. Further examination revealed a collection of ova within the ovary of this fluke as see in this image (arrow). Which of the organisms listed below is most likely?

Clonorchis sinensis

Which of these parasites are hermaphroditic in their adult phase?

Clonorchis sinensis

Parasites that belong to the category Sporozoa are also known as:

Coccidia

Protozoal parasites that typically do not produce disease in humans are referred to as being:

Commensal

A 27-year-old missionary returned from a three week visit to Panama. He presented to the emergency department with severe watery diarrhea, weight loss, abdominal pain, nausea and vomiting, a low grade fever, and fatigue. Fresh stool specimens were collected and submitted for ova and parasite examination. The images show a wet mount preparation of a cyst seen in the stool and a dry slide of the same cyst stained by modified acid-fast. Cysts are spherical and measure 8µm in diameter. What is the most likely identification of this parasite? Images courtesy of CDC DPDx.

Cyclospora cayetanensis

Which of the following groups correctly matches the parasite with its infective stage?

Dientamoeba fragilis : trophozoite

A 54-year-old Finnish male presented at the local clinic with abdominal pain, weight loss, overall weakness and digestive discomfort. Patient history revealed that the man's diet was rich in raw fish. A complete blood count (CBC) was performed and revealed macrocytic anemia. A stool for parasitic examination was ordered. This suspicious form was seen upon initial screening of the sample. It measures 70 µm by 48 µm. This patient is most likely suffering from an infection with:

Diphyllobothrium latum

The diagnostic stage for helminths is:

Egg

Which of the following symptoms is associated with infection of the parasite pictured?

Elephantiasis

A stool was received in the laboratory for parasitic examination on a 49-year-old female who just returned from missionary work in numerous developing countries around the world. The patient had been suffering from mild diarrhea over the previous two weeks. This suspicious form was seen. Notice in the image, five nuclei are visible. Upon focusing between two focal planes, a total of eight nuclei were observed. It measures 25 µm. What is the identification of this form?

Entamoeba coli

The 20 µm in diameter cyst illustrated in the photograph had been observed microscopically in a trichrome stained mount prepared from a stool specimen of a patient with low grade, intermittent diarrhea. What is the presumptive identification?

Entamoeba coli

The 6 µm in diameter cyst illustrated in the trichrome-stained photomicrograph was inadvertently observed a stool specimen that was being examined for reasons not clinically related to parasitic diseases. Further history revealed that the patient for whom the stool examination was being performed had only rare bouts of mild diarrhea. Based on the characteristics in the illustration and the patient information, the most likely identification is:

Entamoeba hartmanni

A 6-year-old female presented to the local clinic complaining of intense perianal itching and diarrhea. The doctor ordered a cellophane tape prep and stool for routine culture and parasitic examination. The cellophane tape prep revealed suspicious form on the left. The stool culture was negative. The form on the right was seen upon examination of the stool for parasites, which measures 10 µm. What are the two forms present in the image, from left to right?

Enterobius vermicularis and Dientamoeba fragilis

A 55-year-old female, who recently returned from an extensive trip to China, presented to her physician complaining of diarrhea and abdominal cramps. The doctor ordered a complete blood count (CBC), comprehensive metabolic panel (CMP), and stool for culture and parasite examination (O & P). The CBC revealed pronounced eosinophilia. The CMP and stool culture were unremarkable. The O & P revealed suspicious forms like the one below that each measured approximately 140 µm by 80 µm. This patient is most likely infected with:

Fasciola/Fasciolopsis eggs

Trichomonas, Giardia, and Chilomastix belong to the following parasitic group based on the type of motility:

Flagellates

Houseflies are a possible transport host for which of these categories of parasites?

Flagellates and amebae

A large number of antigen detection procedures and assays are available to diagnose clinically suspected parasitic diseases in the absence of finding ova or other forms of parasites in stool preparations or other body fluids. Illustrated in the photograph are antigen positive-staining green dots at sites where small drops of duodenal aspirated fluid had been applied to the test reagents. Trophozoites of this protozoan occupy the upper gastrointestinal tract and the excreted ova may not find the way down the long stretch of bowel to be excreted in stool specimens. From the list of multiple choice selections, indicate the genus/species in which antigen detection may be required to make a diagnosis.

Giardia duodenalis

The photograph demonstrates a microorganism detected in a stool sample submitted for ova and parasite examination. The organism measures 12 µm by 7 µm.

Giardia duodenalis cyst

A 40-year-old male recently completed a two-week hiking expedition in Russia. Upon his return to the United States, the man presented to his physician complaining of severe foul-smelling diarrhea and abdominal discomfort. The doctor immediately suspected a parasitic infection and ordered stool for examination. The sample was loaded with this suspicious form that averaged 13 µm in length. This patient is most likely suffering from:

Giardiasis

Fasciolopsis/Fasciola species

Illustrated in the photograph is a large trematode fluke averaging 3.0 - 7.0 cm. This fluke resides primarily in the small intestine. Characteristic is the rounded cephalic end, the convoluted uterus in the anterior half of the fluke, and a delicate branching testes in the posterior half. Humans become infected by ingesting metacercaria contaminated water vegetables. Select the presumptive identification.

This suspicious form measures 18 µm and was seen in ova and parasite exam from a stool specimen. The most likely identification is:

Iodamoeba b?tschlii

A 27-year-old female graduate student recently returned from South America, where she completed a nature study of the rainforest. She spent months "living off the land." The woman went to her physician seeking treatment for a sinus infection, which she thought was responsible for several recent bouts of diarrhea. Upon questioning the patient, the doctor decided to collect stool for culture and parasitic examination. The stool culture was reported as "no enteric pathogens isolated." This suspicious form was seen on both wet preparations and on a permanent stain. It measures 17 µm. The identity of this form is most likely:

Iodamoeba butschlii

Each of the following parasites, whose common names are listed, is associated with intestinal infections, EXCEPT:

Malayan filarial worm

Multiple ring forms in one red blood cell are most frequently seen in which Plasmodium species infections?

P. falciparum

Which Plasmodium species tends to infect any red blood cell, regardless of the age of the cell?

Plasmodium falciparum

Which malaria pathogen is associated with massive hemolysis, blackwater fever, and blockage of capillaries?

Plasmodium falciparum

Patients with a diagnosis of malaria who have fever spikes less frequently, spanning three or four days, are said to have "quartan malaria". Illustrated in the high power upper photomicrograph is a stained peripheral blood smear. Note the infected red blood cell that contains a developing trophozoite that distinctively "bridge" between the opposite erythrocyte membranes. The lower photomicrograph illustrates the schizont stage of development in which segments are arranged as a rosette around a central aggregate of malarial pigment. Which of the Plasmodium species is represented in this scenario?

Plasmodium malariae

Consider the following matches of parasites with their common names. Each is a correct match EXCEPT:

Pork tapeworm =Taenia saginata

Illustrated in the upper image is a cercaria that is capable of penetrating the skin of a human who might be swimming in contaminated water. These cercaria in turn enter the circulation, and mature in the portal vascular system where they develop into adult flukes. Distinctively the female flukes occupy the gynecophoral canal of the male fluke, as illustrated in the lower image. From the list of trematode genera, select the genus that represents the parts of the life cycle as described.

Schistosoma

The ovum as illustrated in the high-power photomicrograph, averages 140 µm. These ova are most commonly observed in a urine sediment from a patient complaining of frequent urination, dysuria, hematuria and recurrent urinary tract infections. Note the characteristic delicate, sharply pointed terminal spine (blue arrow) extruding from the anterior margin of the shell. From the multiple choices listed below, select the presumptive identification of this ovum.

Schistosoma haematobium

Illustrated in the high power photomicrograph is a large 140 µm ovum as it would appear in a stool specimen preparation. The adult flukes reside in the portal veins of the large intestine where ova are discharged into the lumen and into the feces. Low grade diarrhea may be experienced. From the multiple choices select the species of fluke related to this ovum.

Schistosoma mansoni

The following parasite is transmitted through the ingestion of contaminated pork:

Taenia solium

The 40 µm in diameter ovum illustrated in the photograph may be observed in the stool specimens of individuals presenting with minimal abdominal discomfort and low grade diarrhea. Pairs of hooklets are observed internally in the absence of an internal membrane. Select from the multiple choice answers the presumptive identification of this cestode ovum.

Taenia spp.

A blood specimen collected in EDTA was submitted to the laboratory from a patient that recently returned from a missionary trip to West Africa. The patient presented with fever and lymphadenopathy. The physician requested that the laboratory examine a blood smear for parasitic infection. The image shows the parasite in the specimen. Identify this parasite.

Trypanosoma brucei