34 terms


Case 1: 25 yr old woman returning from Rocky mountains, was traveling with a group of campers who had obtained water from a lake. On returning home, she suffered from profuse watery diarrhea, crampy epigastric pain, foul smelling flatulence. The same symptoms were reported by other campers. 3 stool specimen was neg for enteric bact pathogens and 2 were neg for parasites. A permanent trichrome stain revealed rare oval trophozoites measuring 9 - 20um length and 5-15 um in width. The str of this parasite gave the overall appearance of smiling face. Rare cysts with 4 nuclei and characteristic median bodies and longitudinal fibers were seen.
1. What is this parasite? 2. Which form is infectious?
Giardia lamblia (also known as G. intestinalis/ G. duodenalis)
The Cyst form is infectious
How is this parasite in Case 1 transmitted?
Fecal-oral route from ingestion of cysts in contaminated water. Food less likely to serve as vehicles of contamination. P2P through oral/anal sexual practices may occur
How is the infection in Case 1 prevented/controlled?
Prevented by drinking treated water. Also protection of water from reservoir hosts like beavers, muskrats.
How does the parasite in Case 1 attach to intestinal cell wall? Which condition might result as a consequence of this atatchment?
Ventral side is covered by a sucking disc. The firm attachment to the mucosa interferes with dislodgement during intestinal peristalsis,malabsorption or inhibition of mucosal enzymes leading to malabsorption syndrome.
Treatment of Case 1 infection
Metronidazole. Alternate choices include quinacrine, paromomycin, tinidazole or furazolidone. Recommend: treating asymp and symp pt because subclinical malabsorption may be occur and asymp pt may carry risk for spread of infection
Life cycle of Case 1 parasite
Cyst (infective) - ingested - passes thru stomach to small intestine - every 8h it multiples by binary fission - 2 trophozoites - attach to mucosa of duodenum - excystation occurs when trophs enter large intestine .

Trophs and cysts are diagnostic, may be found in feces. Predominant is cyst, since trophs are highly susceptible to envt conditions outside the body
Symptoms of Case 1 infection
Incubation period- 2/3 weeks
Mimics food poisoning, amebiasis or bacillary dysentery.
Include- nausea, explosive watery diarrhea, abdominal discomfort, flatulence and anorexia.
Pt often have rotten egg taste in mouth.
Lab detection of Case 1 parasite
O & P examination (can be easily missed)
Trichrome stain is valuable
As with amoeba, liquid/soft stools are more apt to contain actively motile trophs while cysts in formed stools.
Duodenal aspirates may also be tested, using the Entero-Test capsule.
Serology by AB detection: lack sensitivity; AG assays are better. Comibation kits with Crypto parvum are available (ICT)
Epidemiology of Case 1 parasite
Worldwide. Most common intestinal parasite in the US with the exception of Blastocystis hominis. Water sources; More prevalent in day care, nursery schools, also pt with gastrectomies (absence of gastric acidity) are more prone
Explain the str of trophozoites of Case 1 parasite
Has 2 nuclei or eyes. laterally located in the bilaterally symmetrical troph. Each nucleus has large central karyosome ( eyeball). An axostyle (nose) consisting of 2 axonemes divides the flagellate into 2 parts. 2 curved median/ parabasal bodies (mouth) cross the axoneme at an oblique angle.
Case 2: A 25 yr old American homosexual man was seen in the ER for bloody diarrhea, crampy abd pain of several weeks duration. Was treated and symptoms resolved. 6 months later, he presented to PCP with wt loss, malaise, fever, fatigue, abd pain in the right upper quadrant. Lab studies showed leukocystosis, mild anemia, elevated liver enzymes like Alk phosphatase and transaminases. Stool was neg for bact pathogens and parasites. CT scan of liver showed several hepatic lesions. This finding was confirmed by ELISA for serum AB. The cyst of the parasite causing the infection was 10 - 20um, contained 4 nuclei plus cigar shaped structures with rounded blunt ends.
The dx is liver abscess due to Entamoeba histolytica
Treatment for Case 2 infection
Metronidazole + one of the luminal drugs such as iodoquinol or diloxanide furoate
Which serological tests were probably ordered to confirm diagnosis of Case 2 infection?
ELISA, indirect hemagglutination and IFA
Lab diagnosis of Case 2 infection
Routine O & P- trophs/ cysts
Trophs: measure 12 - 60um, finely granular cytoplasm, evenly distributed peripheral nuclear chromatin and frequently ingested RBC.
Cysts are 10 - 20 um, 4 nuclei + cigar shaped str (chromatoid bodies) with smooth blunt ends. Routine O & P is neg in most amebic abscess.
Liver aspirates may be examined, however low yielding. The diagnosis is confirmed serologically. Lab cultivation is labor intensive, expensive and not clinically useful.
Where do the abscess of Case 2 occur?
Lungs, Liver, spleen, brain. Liver is most common
Lifecycle of Case 2 parasite
Begins with mature cyst (infective stage) - passes thru stomach to small intestine- The cyst develops into troph by binary fission - trophs multiply and may encyst in the lumen of large intestine - immature cysts (1/2 nuclei) are passed in the feces , although mature cysts w/4 nuclei are excreted mostly. Trophs, immature and mature cysts are found in feces. Trophs only in liquid feces.
Extraintestinal infection occurs when amebic trophs invade the wall of colon and enter blood circulation, spreading to other areas
Case 2 infection in homosexual men is known as
Gay bowel syndrome, especially in 1960s, sexual transmission of amebiasis occured mainly among urban homosexual men and E. histo was considered to be one of the most common pathogens included among sexually transmitted mo then.
Name the only ameba capable of causing extraintestinal infection
E. histo
Trophs invade the colon wall and enter circulation to spread to lungs, brain, spleen
# of specimens to be collected over 10 days for accurate diagnosis of amebiasis
3 specimens
How is E. histo differentiated from E. dispar?
E. dispar: trophs do not ingest RBC
PCR directly from feces
Treatment of E. histo
All pt should be treated with metronidazole and a luminal amebicide like iodoquinol.diloxanide furoate. Asympt cyst passage only requires a luminal drug
Epidemiology of E. histo
worldwide, but most prevalent in tropics and sub tropical; orphanages, prisons, mental institutions . In US - rural areas, south eastern and southwestern parts, lower socioeconomic grps
Case 3: A previously healthy 32 yr old woman with hx of several weeks of diarrhea alternating w/ constipation, abd discomfort, vomiting, anorexia, intense fatigue, myalgia, and other flu like symptoms. The pt had not traveled outside the US but her symptoms started after attending a june wedding in Florida. The other guests at the wedding also had similar symptoms. Stool was neg for enteric pathogens. Microscopic examination of stool w/ mod acid fast stain smear revealed 8 - 10 um spherical str, showing range of intensity between colorless to dark red. The spherical str showed fluorescence using UV scope.
What is the intestinal parasite?
Cyclospora cayetanensis.
The non-refractile wrinkled oocysts may not be seen on routine O & P. The modified acid-fast demonstrates light pink - dark str. UV epifluorescence: +1 - +2 green/blue fluorescence.
List other 2 protozoan parasites that might be confused with the Case 3 parasite. How do we differentiate them?
Crypto. parvum and Isospora belli as they also stain w/ mod acid fast. Differentiation based on size-
C. parvum: 4 - 6 um
I. belli - 25 - 30 um
C. parvum unlike C. cay and I . belli does not fluorescence under UV. I. belli is more ellipsoidal.
How does the Case 3 pt's travel hx correlate with dx?
Cases in the US usually associated with travel to developing countries but outbreaks seen in FL, IL, CA, NY. Also, higher chances in late spring and summer
Transmission of Case 3 parasite
Contaminated food, imported raspberries, strawberries. In this case, several guests developed similar GI symptoms suggestive of food associated infection.
Treatment of Case 3 parasite?
TMZ-SXT (unlike crypto which has no treatment)
Case 3 infection and AIDS pt?
Imm.compromised pt (AIDS) likely to suffer from long lasting cyclosporiasus, symptoms lasting weeks to months. Relapse is common. Biliary disease also seen.
Case 4: A 39 year old HIV infected pt presented w/ severe diarrhea of several months duration. He was not receiving antiviral therapy due to severe side effects of his drugs. His diarrhea was watery, profuse, w/ no blood. The pt had signs of dehydration. Non prescription antidiarrheal medications such as lmodium were unsuccessful. Stool specimens were neg for enteric pathogens and O & P. Modified acid fast stain revealed small round, pink str measuring 4 - 6 um.
Which parasite is causing these symptoms?
Crypto. parvum. Modified acid fast is used to diagnose this infection. The pink str are oocysts which stain pinkish by this procedure and are 4-6 um.
Lifecycle of the Case 4 parasite
After ingestion of oocysts- sporozoites are released in upper GI tract - sporozoites develop in the small intestine on the brush borders of intestinal epi cells - parasites develop intracellular extracytoplasmic location are are surrounded by host derived memb. Schizogony occurs with prod of merozoites - formation of zygotes after sexual reproduction - zygotes develop into thick walled oocysts which contain sporozoites - oocysts pass into feces and transmit to new hosts.
Oocysts are infectious stage, also cause autoinfection.
Sporozoites reinitiate new cycle as they parasitize new intestinal cells.
Lab diagnosis of Case 4 infection
IFA, ELISA - detection of AG.
Combination with Giardia kits are available.
Lab cultivation is labor intensive, difficult. Entero test may be used for diagnosis of crypto.
Treatment of Case 4 infection
No good treatment. In AIDS pt, disease becomes progressively worse and does not repsond to any treatment. Intractable infections are fatal. The presence of thick walled oocysts thought to be involved in autoinfection, may explain overwhelming infections. This pt is particularly at risk as he is unable to tolerate antiretroviral drugs. Other than GI, resp tract may also become infected.
Transmission of Case 4 parasite?
Cryptosporidiosis is zoonosis. Cattle are reservoirs. Contaminated food and water.
Other risk factors for Case 4 infection
children attending day care, nurseries, P2P, fecal-oral route.