Parasites 2 Flashcards

Question

Trematodes and Cestodes

Answer 1

``` • Trematodes – General aspects – Schistosomes – Other flukes • Cestodes – Taenia infections – Diphyllobothrium latum – Other tapeworms • 173 species isolated from humans ```

Answer 2

• Flatworms without a true gut • All have a snail in the life cycle somewhere • "Some molluscs (not many) can have children merely by sitting around and thinking about it... others are like us, dioecious, possessed of only one sexual nature but thankful for small favors." -James Thurber, Is Sex Necessary?

Answer 3

``` • Schistosoma mansoni – Africa, the Middle East, South America, and the Caribbean – Roughly 83 million cases – Some animal reservoirs ```

Answer 4

``` • Schistosoma japonicum and mekongi – Found in Southeast Asia, China, and the Philippines – Roughly 1.5 million cases of S. japonicum, 900,000 S. mekongi – Many animal reservoirs; cattle, horses, pigs, dogs, cats, rodents, and deer ```

Answer 5

• Schistosoma haematobium – Large areas of Africa and the Middle East – Roughly 114 million human cases

Answer 6

``` • Direct contact with water harboring infected snails – Infective cerceriae penetrate skin – migrate to venules • Gi tract (mansoni, japonicum, mekongi) • bladder and ureters (hematobium) • larvae mature in venues ```

Answer 7

``` • Adults reside in the bloodstream of the patient – relatively little morbidity – ova laid, most pass out in stool or urine • Prepatent period is 5-8 weeks • Ova hatch in water and infect snail vector ```

Answer 8

``` • Swimmer’s itch • Systemic disease 4-8 weeks after exposure – fever, malaise, aches – lymphadenopathy and hepatomegaly – abdominal pain & diarrhea – eosinophilia – specific syndromes related to ectopic worms ```

Answer 9

``` • Disease related to the ova • Each female releases ~300 (S. mansoni) or 3000 (S. japonicum) eggs/day – some migrate through the intestinal mucosa to be excreted in the feces – others swept up in portal blood and carried to liver – induce a granulomatous periportal response ```

Answer 10

``` – heavily infected individuals -- periportal fibrosis (Symmer's fibrosis) – synthetic and detoxification function is initially wellpreserved • portal hypertension • variceal bleeding • hypersplenism • hepatic failure • cor pulmonale, glomerulonephritis from immune complex shunting ```

Answer 11

``` • Initially – hematuria and dysuria – an intense inflammatory response around entrapped eggs – urinary obstruction – bladder or ureters -- mass lesion and ulceration are seen ```

Answer 12

``` • Later manifestations – host response changes • fibrosis increased, less inflammation – fibrotic lesions may calcify – relatively few patients go on to chronic obstruction and renal failure. – eggs passing into the pulmonary circulation may induce pulmonary hypertension – increase in Salmonella UTIs and prolonged carriage – squamous cell carcinoma of the bladder ```

Answer 13

``` • Ova identified from stool or urine • S. mansoni – 118-180 um – Prominent lateral spine ``` • S. hematobium – 112-170 um – Terminal spine • S. japonicum – Smaller (70-100 um) and rounder than the others – Small or absent lateral spine

Answer 14

• In chronic disease, particularly with severe fibrosis, excretion of eggs may decline or stop – Rectal/ bladder biopsy in these patients. • Serology useful (90% sensitivity) where eggs cannot be found – positive in both active and cured infections • Treat with praziquantel

Answer 15

``` • Prevalent in Japan, Korea, China, Taiwan, and Vietnam • Clonorchis sinensis infects more than 7 million people. • Related flukes of the Opisthorchis group are clinically similar – affect persons in Siberia as well as the Far East – 10 million affected ```

Answer 16

``` • Adults reside in the biliary tree and shed eggs – Eggs must be ingested by a freshwater snail – Cercariae released by the snail penetrate fish and encyst – Fish eaten uncooked, larvae released in duodenum – Migrate into the bile ducts, where they mature in about a month • Dogs, rats, pigs, and cats serve as reservoir hosts. ```

Answer 17

``` • Light infections usually asymptomatic • 500+ flukes can cause fever, chills, jaundice, and eosinophilia • Biliary fibrosis and recurrent suppurative cholangitis – obstruction by dead flukes – increased Salmonella typhi carriage with gallstones – long-standing infections -- cholangiocarcinoma. • Acute pancreatitis ```

Answer 18

``` • Adult flukes produce up to 4000 eggs per day • Detect ova in stool – The prepatent period is about 1 month – The ova are 26-30 um long by 15-17 um wide. There is a wide, prominent operculum • Treat with praziquantel ```

Answer 19

• Worldwide, nearly anywhere sheep are raised – 2.4 million infected • Adult worms dwell in the bile ducts, live up to 11 years • Acquired by eating larvae with edible water plants • Chronic biliary fibrosis and obstruction • Late invasion of liver parenchyma and ectopic migration

Answer 20

• Found in China, Thailand, and elsewhere in the Far East • A disease of pigs with humans serving as a less important reservoir. • Acquired by eating any of a number of water plants (including the water chestnut) • It probably infects over 210,000 persons • Adult worms dwell in the small intestine, attached to the mucosa – usually asymptomatic unless very heavy (500 flukes). – Diarrhea with excess mucous, abdominal pain, hemorrhage, and obstruction

Answer 21

``` • Hermaphrodite worms • Morphologically similar ova • 130-159 um long • Small operculum, may pop open when cover slip pressed ```

Answer 22

``` • The lung fluke – Several species in various parts of the world – Far East, the East Indies, Pacific islands, western Africa, Latin America • Acquired from poorly cooked shellfish • Adults encysted in the lungs • Chronic bronchitis and sputum production with hemoptysis – Radiographically, diffuse infiltrates replaced by nodules which may cavitate • Ectopic adults ```

Answer 23

``` • adult flukes overall resemble coffee beans, may live 10-20 years • Eggs found in feces or sputum – Prominent operculum – 68-118 um long ```

Answer 24

``` • Tapeworms • GI worms with segmented bodies • Tissue cysts in intermediate hosts • "Peckish is not the word. I felt like a homeless tapeworm" -P.G. Wodehouse ```

Answer 25

• The fish tapeworm • Most common in areas with cold freshwater lakes – Scandinavia, northern Europe, Russia, northern Japan, and northern North America • 9 million cases worldwide

Answer 26

``` • Adult worms can be more than 10m – live for up to 20 years – may release up to a million eggs per day • Egg hatches and infects freshwater crustacean – Crustacean eaten by a fish. • Tapeworm acquired by eating undercooked fish ```

Answer 27

``` • Like most tapeworm infections, symptoms usually slight – Rarely, more severe pain – diarrhea or constipation – vomiting, and weight loss. • Tapeworm pernicious anemia, mostly in Finland – The worm successfully competes for B12 with the host, absorbing 80-100% of a labeled dose – Attachment to proximal jejunum ```

Answer 28

• Eggs are 60-75 um in length and 40-50 um wide – Operculum, sometimes difficult to visualize – Small knob on the abopercular end, may or may not be evident; sometimes only a roughening or thickening of the egg wall

Answer 29

• Beef tapeworm -- T. saginata – sub-Saharan Africa, the Balkans and Middle East, Latin America, and Russia – 77 million infected • Pork tapeworm -- T. solium – Latin America (especially Mexico), Africa, southeast Asia, and eastern Europe – 10 million infected

Answer 30

``` • Adults live in human GI tract – eggs passed in the stool of patients eaten by cattle or pig – eggs hatch, and larva migrates to muscle and encysts • Encysted form -- cysticercus – human ingests cysticercus in undercooked meat – larva is activated in response to bile salts – prepatent 2-12 weeks ```

Answer 31

``` • Most patients have few symptoms – mild abdominal pain, nausea – mild hunger sensations and loss of appetite is also common. – syndrome of dizziness, abdominal pain, headache, hyperesthesia, and rarely delirium thought to be a toxic reaction in heavy infections. • The adult worm may live for up to 25 years and is typically 5-10m long. ```

Answer 32

• Proglottids: often the presenting symptom of tapeworm infection – typically pass intact out the anus and crawl actively about * T. solium: 7-13 uterine branches * T. saginata: 15-30 branches

Answer 33

• Detection of proglottids • Detection of ova in stool or Scotch tape prep – 30-45 um in diameter • Recovery of scolex provides proof of cure • Treat with praziquantel

Answer 34

``` • Ova (from an infected human) ingested – fecal-oral route – reverse peristalsis & autoinfection – larvae migrate to tissues and encyst • Endemic in rural Mexico, and elsewhere ```

Answer 35

• Cysticerci – most in subcutaneous connective tissue, then eye, brain, muscles, heart, and liver – 1-2 cm in diameter surrounded by a fibrous capsule of host origin. – inflammatory response to the live larva becomes severe when it dies or is killed.

Answer 36

``` Seizures: the most common cause of adult-onset seizures in endemic areas. • Obstructive hydrocephalus • Meningoencephalitis – massive infestations – patients inadvertently treated in the course of therapy for other parasitic infestations • Ocular disease ```

Answer 37

``` • Diagnosis requires a high degree of suspicion – nodules on head imaging, or in soft tissues. • Serology helpful -- new CDC immunoblot test • Treat with albendazole/ praziquantel +/- steroids – Don’t treat asymptomatic calcified nodules – supportive and symptomatic care ```

Answer 38

• Humans incidental participants in the canine/herbivore life cycle of E. granulosus or E. multilocularis • E. granulosus -- 2.7 million infected – places where sheep and cattle are tended with the help of dogs – Middle East, Australia, New Zealand, east and south Africa, South America, and central Europe • E. multilocularis – a rare infection, mainly of northern temperate zones.

Answer 39

• Usually acquired by ingestion of infective eggs from the feces of dogs which carry the adult worm • Larval stage typically develops within the liver or lung, though it may be found anywhere

Answer 40

• The E. granulosus hydatid forms a slowly growing cyst containing numerous larval forms – liver & lung 80% – other assorted organs • E. multilocularis forms an invasive, infiltrating growth in the liver which may be mistaken for a malignancy

Answer 41

``` • Typically radiographic for E. granulosus – serology may be helpful if positive • Clinical manifestations vary depending on the site of the cyst and upon whether it ruptures – anaphylaxis to ruptured cyst contents • Therapy -- albendazole + drainage ```

Answer 42

``` • The dwarf tapeworm – the most common both worldwide and in the US – spread by the direct fecal-oral route or by internal autoinfection • Usually asymptomatic – cramping and diarrhea observed – Rarely, dizziness and seizures in children attributed to a neurotoxin ```

Answer 43

``` • Adults 15-40 mm long • Diagnosis – Ova in stool – 40-60 x 30-40 um – Oval with polar filaments ```

Answer 44

``` • The rat tapeworm • Rare in humans – Acquired by ingesting infected insects – Mostly asymptomatic • Ova – 70 - 86 um X 60 - 80 um – Striated outer wall, could be confused with Taenia but is larger, with a space between embryo and striations ```