Parasitic Infections II - Helminths Flashcards
Helminths
platyhelminths (flatworms) - include termatodes (flukes) and cestodes (tapeworms)
nematodes (roundworms)
annelids (segmented roundworms) - leeches are the only ones of medical importance
trematodes (flukes)
leaf-shaped flatworms of various size
two anterior (oral) suckers, one ventral sucker
most are hermaphroditic (schistosomes are not)
all trematode life cycles include molluscan hosts
blood flukes - Schistosoma mansomi, Schistosoma japonicum, Schistosoma haematobium
liver flukes
intestinal flukes
lung flukes
cestodes
intestinal tapeworms:
- Diphyllobothrium latum*
- Taenia saginata*
- Taenia solium*
extraintestinal tapeworms (Echinococcus granulosus)
Schistosomiasis
250,000,000 people are infected annually, 1,000,000 die
three species infect humans:
- Schistosoma mansoni*
- Schistosoma japnicum*
- Schistosoma haematobium*
Intravascular locations of adult Schistosomes
- S. mansoni* - inferior mesenteric venules
- S. japonicum* - superior mesenteric venules
- S. haematobium* - cystic (bladder) venules
immunology of scistosome infection
immune responses to schistosomeulae and adults are not generated because these forms of the parasite adsorbe human antigens
hundreds to thousands of eggs are produced daily, of these, half are released into feces or urine and half remain in the body, those that remain may elicit inflammatory responses including delayed-type hypersensitivity and granuloma formation
Schistosome eggs
thousands produced daily, half released in feces or urine, other half remains in the body
round or oval with an appendage that is:
spiny with lateral location in S mansoni
small and round with a lateral location in S. japonicum
spiny with a terminal location in S. haematobium
disease properties of Schistosomiasis
cercarial dermatitis - from cercareiae that don’t completely penetrate skin, die
acute schistosomiasis (katayama fever)
- occurs 4- weeks after heavy primar yinfections
- due to release of egg antigen and antigen-antibody complexes
- resembles serum sickenss
- disease lasts for weeks
- significant mortality
chronic schistosomiasis
- granulomatous reaction to eggs deposited in various tissues
- gastrointestinal schistosomiasis - mild mucohemorrhagic diarrhea initially
- later granulomatous hepatosplenomegaly, periportal fibrosis
- even later protal hypertension, intractable ascites, esophageal varicies, intestinal polyposis
- finally protein-losing enteropathy
- urinary tract schistosomiasis - dysuria, terminal hematuria initially
- obstructive uropathy with pyelonephritis, gram negative rod bacteremia
- leads to renal failure, chronic bacteriuria, bladder cancer
- other sequalae causes pulmonary fibrosis, CNS problems, and secondary infections
diagnosis made by detection of eggs in urine and feces
Cestodes (tapeworms)
- largest and most disgusting of the intestinal parasites
- long-ribbonlike helmonths with no body cavity
- adult divided into scolex (head), neck, and strobila (segmented body)
-
Scolex
- attachment organ with sucking discs and hooklets
-
Strobila
- composed of proglottids (generated at neck)
- self-contained, hermaphroditic reproductive units
- as new proglottids are added at the neck, the older proglottids proceed posteriorly
- during the progression, the male and female gonads mature and effect fertilization
- gravid proglottid ruptures or disintegrates, releasing eggs
Taeniasis saginata (Beef Tapeworm Infection)
- caused by the cestode Taenia saginata
- worldwide distribution
- human is the only definitive host
- intermediate host is cow
Disease Properties
- dull, colicky abdominal pain
- symptoms usually mild
Diagnosis
- detection of eggs and/or proglottids in feces
Taeniasis solium (Pork Tapeworm Infection)
- caused by cestode Taenia solium
- found in Mexico, Latin America, Africa, Asia
- human may be both definitive host and intermediate host
- life cycle same as that of Taenia saginata, except that pig is usual intermediate host
Cysticercosis
- usually proglottids and eggs passed in feces
- if eggs (eaten by human or carried to stomach by reverse peristalsis) mature and hatch, human may serve as intermeidate host
- larvae carried into tissues develop into cysticerci
- cysts may develop in a variety of body tissues
Disease Properties
- tapeworm infection, same as for T. saginata infection
- central nervous sistem disease
- seizures, focal deficits, hydrocephalus (ventricular cysts)
- ocular disease
Diagonosis
- detection of eggs and/or proglottids in feces
- eggs of T. solium and T. saginata are indistingushable
- proglottids differ
general properties of nematodes
elongate, cylindrical worms, primarily bilaterally symmetrical
digestive-excretory, nervous and reproductive systems
no circulatory system, but fluid in body cavity fulfills functions of blood
separates sexes
over 80,000 species parasitize vertebrates
range in size from 2mm (strongyloides) to ove ra meter (dracunculus)
parasitic nematodes
intestinal nematodes
blood, lymphatic and subcutaneous tissue nematodes
nematodes the larvae of which cause pathology in human tissues
intestinal nematodes
- Enterobius vermicularis* (pinworm)
- Trichuris trichiura* (whipworm)
- Ascaris lumbricoides* (large roundworm)
- Ancylostoma duodenale *(Old World hookworm)
- Necator americanus* (New World hookworm)
- Strongyloides stercoralis*
- Trichinella spiralis*
bood, lymphatic and subcutaneous tissue nematodes
- Wuchereria bancrofti*
- Brugia malayi*
- Loa loa*
- Onchocerca volvulus*
nematodes the larvae of which cause pathology in human tissues
- Trichinella spiralis*
- Toxocarea* spp.
- Ancylostoma braziliense*
Enterobiasis (pinworm infection)
caused by Enterobius vermicularis
Morphology
- adult worms 8-13mm (female)
- 2-5mm (male)
- egg flattened on one side
Epidemiology
- fecal-oral transmission
- most common helminth
- world-wide distribution
- family members of infected are at risk
Disease Properties
- symptoms of infection uncommon
- pruritus ani
Diagnosis
- scotch tape test
- demonstration of eggs
Trichuriasis (Whipworm infection)
caused by Trichuris trichiura
Morphology
- adult worm 35-50mm (female)
- egg barrel-shaped with mucoid plug
- 50 um long
Epidemiology
- fecal-oral transmission
- mostly in young children
- Asia, Africa, Latin America
Disease Properties
- symptoms of infection uncommon
- heavy infection
- preotin calorie malnutrition
- rectal prolapse
- inflammatory diarrhea
Diagnosis
- demonstration of eggs in feces
Ascariasis (Large Roundworm Infection)
caused by Ascaris lumbricoides
Morphology
- largest intestinal nematode (arond 30cm)
- mammilated egg
Epidemiology
- fecal-oral transmission
- tropics, subtropics
- transmission from by consumption of vegetables if nightsoil used for fertilization
Disease Properties
- usually no symptoms of infection
- Loeffler’s syndrome - transient infiltration of lungs, cough, fever, dyspnea, eosinophilia
- adults may migrate from intestine and can cause serious complications
- heavy infections - malnutrition
Diagnosis
- demonstration of eggs in feces
- eosinophilia during tissue phases
Hookworm Infection
caused by Ancylostoma duodenale (Old World hookworm) and Necator americanus (New World hookworm)
Morphology
- rhabditiform (rod-like) larvae feed on organic debris and grow from 275um to 600um over five days
- molt to become slender, nonfeeding filariform (thread-like) larvae
Epidemiology
- A. duodenale infects over 500,000,000 individuals per year, wich a widespread distribution (mostly tropical, subtropical regions)
- N. americanus found in southeast United States, South America, Indonesia, Philippines
Diseaes Properties
- larval penetration causes severe itching and leads to production of maculopapules and localized erythema
- symptoms uncommon during chronic infection
- heavy infection
- protein calorie malnutrition
- anemia due to consumption of blood (up to 0.2 mL/worm/day)
Diagnosis
- demonstration of eggs in feces
- A. duodenale and N. americanus eggs are indistinguishable
Filariasis
Properties of Filarial Worms
- adults reside in skin or lymphatics
- microfiliariae
- immature larvae in blood or skin
- circulate in the blood corresponding to insect vector’s feeding habits
Morphology
- adult worms are 20 to 70 mm in length
- sheathed microfilariae are 0.2 to 0.3 mm in length
Epidemiology
- found in Africa, India, Far East Indochina
- human is only reservoir
- worms do not multiply in human host
Disease Properties
- Bancroftian filariasis
- Malayan Filariasis
- Loiasis
- River Blindness
Diagnosis
- made by demonstration of microfilariae in blood or biopsy of skin nodule (O. volvulus)
Bancroftian Filariasis
caused by Wuchereria bancrofti
microfilariae in bloodstream have nocturnal or diurnal periodicity
adults reside in lymphatic vessels and nodes, especially inguinal, epitrochlear, axillary, testicular, epididymal
Acute Disease
- filarial fever (microfilariae)
- filarial adenolymphantitis
- orchitis (adults)
Chronic Disease
- lymphatic obstruction -> elephantiasis, especially inguinal, epitrochlear, axillary
- tropical pulmonary eosinophilia
Malayan Filariasis
caused by Brugia malayi
lymphatic obstruction occurs in extremities more often (especially lower), genial area less often, than bancroftian filariasis
Loiasis
- caused by Loa loa
- adults migrate through subcutaneous tissue, conjunctivae
-
calabar swellings
- subcutaneous edematous areas
- up to several centimeters in diameter
- appear suddenly in different locations
- last for several days
- may be accompanied by fever, pruritus, and urticaria
River Blindness
- caused by Onchocerca volvulus
- found in tropical and subtropical Africa
- adults reside in nodules in subcutaneous tissues, microfilariae in skin
Symptoms of Infection
- subcutaneous nodules
- dermatitis
- regional lymphoma
- ocular manifestations
- microfilariae trapped in the eye
- harbor endosymbiotic Wolbachia bacteria
- innate immune response to bacterial LPS causes ocular inflammation and blindness
Trichinosis
caused by Trichinella spiralis
Morphology
- encysted larvae
Epidemiology
- widespread in wild mammals, wild and domestic pigs
Acquisition
- consumption of meat containing trichinella cysts
Disease Properties
- variable, due to larvae in striated muscles and organs
- dependent on the parasite load
- 50-500, moderate symptoms
- >1000, severe symtpms
- common symptoms
- orbital edema
- muscle pain, respiratory distress, headache and generalized weakness
- myocardial and central nervous system involvement also produces signs and symptoms
Diagnosis
- primarily clinical
- history of ingestion of poorly cooked meat (especially pork)
- serologic tests are useful
- demonstration of larvae in muscle biopsy confirmatory
Larva Migrans
Agent
- Ancylostoma braziliense, the cat and dog hookworm
- acquired by direct skin penetration
Disease
- serpiginous line of creeping eruption
- reflects movement of larva beneath skin
- parasites persist for weeks to months
Diagnosis
- identification of larvae in skin
