PARASITOLOGY LECTURE 9 – Cestode Infections Notes from W.U. DeLeon, J.A. Solon
USTMED ’07 Sec C – AsM
HYMENOLEPIS NANA (dwarf tapeworm)
•
smallest tapeworm infecting man•
only human tapeworm which can complete its entire life cycle in a single host• does not require an obligatory intermediate host • man can harbor both adult and larval stages of parasite DISTRIBUTION
• worldwide among children DISEASES
• hymenolepiasis MORPHOLOGY
1. Adult Worm - found in the ileum
- delicate strobila that measures 25 to 45 mm x 1 mm (lw) - Scolex o Subglobular o 4 cup-shaped suckers o retractable rostellum with a single row of 20 to 30 y-shaped hooklets - Neck
o long and slender - Proglottids o Anterior = short o Posterior = broader o Measures 0.15 to 0.3 mm x 0.8 to 1.0 mm (lw) o Mature proglottids :
contain 3 ovoid testes and one ovary
o Gravid proglottids :
testes and ovary disappear
uterus hollows out and becomes filled with eggs
segments are separated from the strobila and disintegrate as they pass out of the intestines, releasing eggs in stool
- Segments
o 175 to 220 segments
o genital pores found along the side of segments 2. Eggs
-
Shape : spherical or subspherical - Measures 30 to 47 um in diameter - Oncosphereo thin outer membrane
o thick inner membrane with conspicuous bipolar thickenings
4 to 8 hair-like polar filaments arise filaments are embedded in the inner
membrane H. nana cysticercoid
LIFE CYCLE
- Dual pathway 1. Direct
• host ingests eggs which hatch in the duodenum • liberated embryos penetrate mucosal villi
•
develop into infective cysticercoid larvae• larvae break out of villi and attaches to intestinal mucosa 4 to 5 days later
• develop into adults 2. Indirect
•
infection is usually via accidental ingestion of infected arthropod intermediate hosts like rice and flour beetles (Tenebrio sp.)• cysticercoid larvae are released and will eventually develop into adult tapeworms in the intestines of the host
- takes 20 to 30 days from time of ingestion for eggs to appear in the feces
- eggs are viable immediately after discharge from bowel - autoinfection can occur through the fecal-oral route or
w/in the small bowel
- oncospheres from eggs are released and they invade the host villi to start new generation
PATHOGENESIS AND CLINICAL MANIFESTATION
• symptoms are produced because of patient’s immunological response to the presence of the parasite • asymptomatic – light worm burden
• clinical manifestations: o headache o dizziness o anorexia
o pruritus of nose and anus o diarrhea o abdominal pain o pallor • infected children o restless o irritable
o exhibit sleep disturbances o convulsions (rare) • Heavy infections
o Enteritis due to necrosis and desquamation of the intestinal epithelial cells
• Regulatory immunity
o
(time) clears H. nana spontaneously. DIAGNOSIS• specific diagnosis = demonstration of characteristic eggs in stool
• light infections = need to concentrate stool specimens • proglottids are not recovered because they undergo
degeneration prior to passage with stools TREATMENT
• *Praziquantel = 25mg/kg single dose
o causes vacuolization and disruption of tegument in the neck region
o dosage for hymenolepiasis is higher than for taeniasis because of relative resistant cysticercoids in the intestinal tissue
• examine stool after 2 weeks
o repeat treatment to cover for the worms emerging from remaining viable cysticercoids EPIDEMIOLOGY
• found in warm countries o Southern USA o Latin America o Mediterranean o East Asia o Philippines
• Transmission : poor sanitation, overcrowding, poor personal hygiene
• Direct contact plays an important role because eggs cannot survive long outside host
• Familial and institutional infection • Found in mice and rats
PREVENTION AND CONTROL
• involves a single host and transmission is direct • personal hygiene and environmental sanitation • rodent control
• prevent food from infections by grain beetles
HYMENOLEPIS DIMINUTA (rat tapeworm)
• cosmopolitan parasite primarily of rats
•
differs from H. nana in that it requires an intermediate hostDISEASE
• Hymenolepiasis – due to accidental human infections MORPHOLOGY
1. Adult
-
larger than H. nana - Measures : 60 cm in length-
Scolex :o
Has a rudimentary unarmed rostellum - Proglottids :o Broader than long
o
Arrangement of sexual organs is similar toH.nana
o
Larger than H. nana may reach 7.5mm x 3.5 mm (lw)o Unilateral genital pores o Gravid proglottids:
@ contains a sac-like uterus filled with eggs. 2. Eggs - Shape : circular - Measures 60 to 80 um - Bile-stained - Oncosphere o Enclosed in an inner membrane
o Has bipolar thickenings o Lacks bipolar filaments - Hooklets have a fan-like arrangements
LIFE CYCLE
•
Gravid proglottids separate from the main body of worm disintegrates release eggs in feces• Eggs are ingested by a wide range of adult and larval insects
o Fleas, beetles, cockroaches, mealworms and earwigs
• Once ingested, they develop into cysticercoid larvae
• When infected insects are ingested by rats or man, larva is released
• Develops into adult worm in ~ 3 weeks
PATHOGENESIS AND CLINICAL MANIFESTATIONS
• worm burden in rodents is relatively low • in man, the highest number recorded is 19 worms • manifestations are minimal and non-specific DIAGNOSIS
• based on identification of eggs from stool
•
H. diminuta eggs are more circular, larger and lackbipolar filaments
• At times the whole worm is expelled and the scolex may be used in diagnosis
TREATMENT
•
similar to H. nana = Praziquantel 25mg/kg single dose EPIDEMIOLOGY• human infections occur worldwide but more common among children
• in poor countries with rat infestations
• occurs by accidental ingestion of grain beetles infesting dried grains, dried fruits, flour and cereals
• prevalence in Phil in rats is 8% PREVENTION AND CONTROL
• rodent control
• elimination of insect intermediate hosts • protection of food
• sanitary disposal of waste DIPYLIDIUM CANINUM (double pored tapeworm)
• very common intestinal parasite of dogs and cats DISEASE
• Dipylidiasis in humans is accidental MORPHOLOGY
1. Adult worm - Color : pale reddish - Measures 10 to 70 cm in length
-
Scolex : o Small o Globular o 4 deeply cupped suckers o protrusible rostellum o 1-7 rows of rosethorn-shaped hooklets - Proglottids: o Narrowo 2 sets of male and female reproductive organs
o bilateral genital pores (hence double pored tapeworm) o Gravid proglottids Shape : pumpkin seed Filled with capsules or packets of 8 to 15 eggs enclosed in an embryonic membrane 2. Eggs - Shape : spherical - Thin-shelled - Hexacanth embryo LIFE CYCLE
•
when gravid segments are detached, they either: o migrate out of the anuso passed out with feces • ova are released by:
o contraction of the proglottid or o disintegration outside the host • egg capsules may remain in the fur of the host
o larval fleas feed on epidermal debris
• Intermediate hosts
o
Ctenocephalides canis (dog flea)o
Ctenocephalides felis (cat flea)o
Pulex irritans (human flea)o
Trichodectes canis (dog louse)• In the arthropod host, the hexacanth embryo develops into cysticercoid larvae
o Able to survive flea’s development
o When ingested, the cysticercoid is liberated and becomes an adult in 3 to 4 weeks
PATHOGENESIS AND CLINICAL MANIFESTATIONS • infection rarely multiple • symptoms are minimal
o slight intestinal discomfort o epigastric pain
o diarrhea o anal pruritus o allergic reactions • some are asymptomatic DIAGNOSIS
• recovery of gravid proglottids passed out single or in chains
•
proglottids may crawl out of anus or passed out involuntarily• proglottids should be pressed or flatted between 2 glass slides for examination
• Stool examination is not recommended since gravid proglottids do not disintegrate in intestines but in the environment
• Egg capsules are rarely recovered TREATMENT
• Praziquantel = 5 to 10 mg/kg single dose EPIDEMIOLOGY
• human infections rare but reported in: o Europe o USA o Argentina o Rhodesia o China o Philippines
• Infants and young children usually infected
• Observe actively motile proglottids in feces or underwear
• Adults are not commonly infected because of age tolerance against the parasite
PREVENTION AND CONTROL
• periodic deworming of pet cats and dogs • insecticide dusting of dogs and cats against fleas DIPHYLLOBOTHRIUM LATUM (fish tapeworm or broad tapeworm)
• belongs to order Pseudophyllidea • one of 13 species that infects humans DISEASE
worm MORPHOLOGY 1. Adult - Measures 3 to 10 m length - Up to 4000 proglottids
-
Scolex : o Shape: spatulate o Measures 2 to 3 mm x 1 mm (ld)o Has 2 bothria or sucking grooves located dorsally and ventrally
- Neck :
o Long and attenuated - Proglottids:
o Immature o Mature
Longer width than length
Measures 2 to 4 mm x 10 to 12 mm (lw)
Contains one set of reproductive organs
Testes
• Located at dorsolateral part of proglottid
•
Vas efferens converge to form a vas deferens enlarge into seminal vesicle terminates in muscular cirrus (at midventral genital pore) Ovary• Symmetrical • Bilobed
• Present at posterior third immediately above Mehlis’ gland o Gravid Uterus • Dark • Rosette-like • Coiled • Located at middle
• Extends from ootyle and opens through uterine pore behind common genital pore
Proglottids disintegrate only when the segment has completed its reproductive function
2. Eggs
- Color: yellowish brown - Moderately thick shell - Inconspicuous operculum
- Opposite operculum is a knob-like thickening - Measures 66 x 44 um
LIFE CYCLE
• with disintegration of uterus, the uterine pore is relaxed and unembryonated ova are discharged
• approx. 1,000,000 may be released daily • ova complete development in water
• release free-swimming coracidium (a ciliated embryo)
•
ingested by copepods of genera Cyclops and Diaptomus • a procercoid larva develops in copepodso still retains 3 hooklets in the cercomer (a caudal attachment organ)
• copepod ingested by fish
• procercoid larva migrates to tissues and develops into plerocercoid larva in muscles and viscera
• plerocercoid larva appears glistening, opaque, white and unsegmented
• fish is ingested raw by definitive host :man, dog, cat, other mammals
• Paratenic hosts : carnivorous fish
•
2nd Intermediate hosts (fish)=perch, trout, salmon & pike• The plerocercoid attaches to the intestinal wall and reaches maturity in 3 weeks within the definitive host
PATHOGENESIS AND CLINICAL MANIFESTATIONS • usually limited to one worm
• infected individuals may be asymptomatic • symptoms o nervous disturbances o digestive disorders o abdominal discomfort o weight loss o weakness o anemia
• symptoms may be due to absorbed toxins or byproducts of degenerating proglottids or due to mucosal irritation • infection results in
o hyperchromic, megaloblastic anemia with thrombocytopenia and leucopenia
o
anemia seen is typically similar to that seen in Vit B12 deficiency•
worms in jejunum compete effectively with the host for Vit B12• if worms are pushed down the intestines with treatment, anemia is relieved
•
Vit B12 content of D. latum is 50 x of T. saginata DIAGNOSIS- suggestive:
• residence or travel to endemic area • raw fish diet
• pernicious type of anemia - definite diagnosis:
o finding characteristic operculated eggs o or proglottids in stools
o direct fecal smear
o Kato technique to demonstrate eggs
- differential diagnosis (anemia due to diphyllobothriasis from pernicious anemia)
o examination of gastric juice for presence of free hydrocholoric acid
o pernicious anemia is associated with achlorhydria
TREATMENT
• Praziquantel – 5 to 10 mg/kg single dose
• Criterior : recovery of scolex in feces after treatment • If scolex is not recovered, repeat stool examination
after 3 months to be certain that patient is no longer infected
EPIDEMIOLOGY
• human infection is dependent on:
1. presence of human or animal definitive hosts 2. presence of suitable intermediate hosts 3. dietary habits
4. amount of pollution of fresh waters 5. preference for eating raw fish 6. lack of sanitary toilet facilities • Reservoir hosts
o Dogs o Cats o Bears
• prevalent in temperate zones
• Baltic countries: Switzerland, Romania, Danube basin • Asia : Russia, Turkistan, Israel, Manchuria, Japan • Americas: Chile, Argentina, N. American states, Canada
•
Philippines – 7 casesSPARGANOSIS
•
larval infection with plerocercoid larvae (aka spargana of pseudophyllidean tapeworms under GenusSpirometra)
• involved in human sparganosis o Spirometra mansoni
o Spirometra erinacei
o Spirometra ranarum
MORHOPHOLOGY
• Adults are intestinal parasites of cats, dogs, and other carnivores
•
Adults are usually mistaken for D. latum• Spargana showed typical solid body with worm-like appearance
• Pseudosegmentation with a slit-like invagination at the head end
• Larvae
o Opaque, glistening, white o Found in any part of the body
o Most commonly found in the eye, subcutaneous tissue, muscular tissues of thorax, abdomen, thighs, inguinal region and in viscera
proglottid scolex
S. mansoni eggs
LIFE CYCLE
• Human infected through
1.
drinking water containing Cyclops or copepods infected with procercoid larvae2.
eating infected 2nd intermediate hosts like frogs,toads or snakes containing plerocercoird larvae
3.
applying plerocercoid infected flesh of frogs andsnakes as poultices in sores in the eye, vagina, and skin penetration into cutaneous tissues
4. consumption of infected flesh of pratenic hosts (wild pigs)
PATHOGENESIS AND CLINICAL MANIFESTATION - Symptoms
o
Complain of painful edema due to migrating larvaeo Local indurations o Periodic giant urticaria
o Edema
o Erythema with chills, fever o High eosinophilia
DIAGNOSIS
• Finding white larvae in the lesion
• Species identification done by experimental infection of animals
TREATMENT
- Surgical removal of plerocercoid
-
In cases reported, spargana were motile upon excision of the massPREVENTION AND CONTROL
- Drinking boiled or filtered water - Proper cooking
- Avoid applying flesh of frogs to inflamed areas
-fin-auds
