Parasitology II

Helminths worms are divided into two groups

1. Platyhelminthes (flat worms)
2. Nemathelminthes (round worms)

The Platyhelminthes (flat worms) are divided into two groups

1. Cestoda (tapeworms)
2. Trematoda (flukes)

Cestodes bodies are characterized by 3 principle features

1.Scolex (head) with attachment organs (hooks/suckers), 2. neck (immature) region that gives rise to 3. strobila

What is strobilation?

Neck forms the segments (proglottids) of the strobila

What is ribbon shaped body composed of multiple segments, each an independent reproductive unit.

Strobila

The segments of strobila (proglottids) do what?

They are mature sexual reproductive units

What is the outer covering of the worm called?

Tegument

How is nutrition absorbed in worms?

Directly through the outer covering (tegument)

Infection of adult worms is acquired by what?

Ingestion of raw/improperly cooked flesh of intermediate host.

What are three tapeworms (Cestodes) that are intestinal tapeworms?

1. Diphyllobothrium latum (fish)
2. Taenia solium (pork)
3. Taenia saginata (beef)

What is infective agent of Diphyllobothrium latum?

Pleurocercoid

What is the definitive host in Diphyllobothrium latum?

Humans

What are intermediate hosts in Diphyllobothrium latum?

Copepod and freshwater fish

Minor digestive upset, abdominal discomfort, weight loss, weakness, pernicious anemia (B12 uptake)

Diphyllobothrium latum

Jewish Housewife Disease

Diphyllobothrium latum

Endemic in lake regions of colder climates

Diphyllobothrium latum

Largest tapeworm of humans (13-33 ft), scolex with lateral sucking grooves, gravid prolotiids broader than long, eggs operculate (little trap door)

Diphyllobothrium latum

What is the diagnosis for Diphyllobothrium latum?

Proglottids or eggs in stool

What is the life cycle of Taenia worms?

1. adult worms live in small intestine of humans
2. gravid proglottids break from tapeworm and rupture, releasing eggs which are passed in stools.
3. Eggs or proglottids are ingested by cows or pigs
4. Oncosphere (six hooks) hatches from egg and carried i

What is the infective form of Taenia?

Cysticercus

Internal autoinfection of Taenia occurs in what patient population?

Immunocompromised

Which form of Taenia can humans serve as intermediate hosts by ingesting eggs? (anus-finger-mouth) What is this condition called?

Taenia solium (pork)
Cysticercosis

Cysts from Taenia solium ingested by humans can grow where?

Anywhere with muscle being preferred site. Bad when it goes to brain or eyes

USA - in recent immigrants can carry what types of tapeworm?

T. solium

Which Taenia has scolex with 4 suckers, no hooks, gravid proglottids >12 uterine branches?

T. saginata

Which Taenia has scolex with 4 suckers, double row of hooks, gravid proglottids <12 uterine branches

T. solium

Can you distinguish the difference between eggs of Taenia species?

No. It has thick shell with radial striations containing hexacanth embryo.

Infective form of Taenia

Cysticerus and/or eggs (in the case of T. solium)

What is the diagnosis of Taenia?

Detection of egg or proglottid in stool
Cysticerocosis can be picked up on x-ray, CT scans, and MRI.

What is a tissue tapeworm?

Echinococcus granulosus

What causes hydatid cyst disease?

Echinococcus granulosus

What is the life cycle of Echinococcus granulosus?

1. adult worm lives in intestine of dogs/wolves
2. eggs are passed in feces and eaten by sheep, cattle, moose
3. eggs hatch and oncosphere penetrates the intestinal wall, develops into hydatid form (larval form)
4. Dogs/wolves infected by ingestion of hyd

What is the infective form of Echinococcus granulosus?

Hydatid cysts (containing numerous protoscolices that attaches to small intestine)

How do humans get Echinococcus granulosus? What are some clinical symptoms?

Humans get infected by ingestion of eggs shed in feces of infected dogs. Majority of cysts occur in the liver (liver dysfunction, palplable abdominal mass) and lung

Sheep and cattle

Echinococcus granulosus

Flat leaf shaped organisms

Trematodes

Embryonated eggs from flukes are shed in feces and must reach what to survive?

Water

What is the general life cycle of flukes?

Eggs -> miricidium (infects 1st intermediate) -> cercariae (infects 2nd intermediate) -> metacercaria (infects definitive host)

Infecting flukes are found principally in four sites

Intestine, liver, lung, and blood

What is the liver fluke?

Fasciola hepatica

What are the 1st intermediate, 2nd intermediate, and definitive host for Fasciola hepatica?

1st intermediate: Stream and pasture snails
2nd intermediate: Watercress, aquatic vegetation, grass
Definitive host: Sheep, cattle, goats, and humans

What is the infective agent in Fasciola hepatica?

Ingestion of plants with encysted metacercariae

What is clinical disease of Fasciola hepatica?

Migration to liver causing necrosis, fever and pain in right upper quadrant. Metacercariae larvae migrated to bile ducts and matured to adults where they produce damage due to mechanical irritation and obstruction. Hepatomegaly, eosinophilia

What is the detection of Fasciola hepatica?

Large operculate eggs in stool

What is the lung fluke?

Paragonimus westermani

What are 1st, 2nd, and definitive host for Paragonimus westermani?

1st intermediate: Snails
2nd intermediate: freshwater crabs or crayfish
Definitive host: man, mammals

What is the general life cycle of Paragonimus westermani?

Human eats metacercaria -> worms in lungs -> eggs to fresh water via sputum and feces -> miracidium develops from eggs in water -> Miracidium hatches and penetrates snail -> cercaria from snails -> crustacean eats cercaria -> becomes metacercaria crustace

Infection is by ingestion of raw/improperly cooked infected crab/crawfish.

Paragonimus westermani

What is the infective agent in Paragonimus westermani?

Metacercaria

Where is Paragonimus westermani found?

Far east, Southeast Asia

What is the diagnosis of Paragonimus westermani?

Detection of eggs in sputum or stool

What are the blood flukes?

Schistosoma hematobium, S. mansoni, S. japonicum

Which blood flukes are found in vessels in urinary bladder wall and which ones are found in vessels of intestine?

S. hematobium in urinary bladder wall
S. mansoni/japonicum in vessels of intestine

What is the infective agent in Schistosoma?

Cercariae

Describe the general life cycle of Schistosoma.

Adult in blood vessels -> eggs in feces -> miracidia from eggs penetrate snail and becomes cercariae -> cercariae infects bare skin -> migrates and transforms to schistosomula in the lungs then migrates to liver and mate then migrate against hepatic porta

Mate for life

Schistosoma

Which Schistosoma is from Egypt, India, and Portugal?

S. hematobium

Which Schistosoma is from Africa, S. America, Caribbean islands?

S. mansoni

Which Schistosoma is from China, Japan, Philippines, Indonesia?

S. japonicum

Which egg has oblong, terminal spine?

S. hematobium

Which egg are oblong, lateral spine

S. mansoni

Which egg are short, elliptical, lateral spine?

S. japonicum

In Schistosoma species, which causes more damage, the eggs or the worms? Why?

Eggs. They are highly antigenic

Separate sexes, tubes within tubes, different stage larvae (L1 is rhabditiform, L3 is filariform - infective).

Nematodes (roundworms)

Home made pork sausage

Trichinella spiralis

Describe the general life cycle of Trichinella spiralis.

When eaten, larva excysts in small intestine and develops into adults, Larva from adults deposited in intestinal tissue and carried by blood to striated muscle where it gets encysts in muscle cell.
Larvae encysted in striated muscle of pigs and eaten by h

What are the clinical symptoms of Trichinella spiralis?

Intestinal discomfort then when larvae penetrates muscle you get muscle damage, facial edema, muscle pain

How is Trichinella spiralis diagnosed?

Muscle biopsy

Strongyloides stercoralis occurs in what types of patients?

Immunocompromised patients

Barefoot in grass

Strongyloides stercoralis

What is the infectious form of Strongyloides stercoralis?

Filariform larva

Rhabditiform larva to filariform larva requires how many molts?

Two

Describe the life cycle of Strongyloids stercoralis.

Filariform larva penetrates skin, enters blood, to right heart to lungs to esophagus, eggs deposited in intestine and rhabditiform hatches. Rhabditiform can pass into feces or autoinfection (HIV) to blood stream. Ones passed into soil from feces can go on

What is the diagnosis of Strongyloides stercoralis?

Rhabditiform larvae in stool, sputum, or filariform in stool too

What is the hookworm of the new world?

Necator americanus

What is the hookworm of the old world?

Ancylostoma duodenale

What is the general life cycle of hookworms?

Adults live attached in intestine and lay eggs. Eggs pass in feces and develop from rhabditiform to filariform larvae in soil. Filariform enters skin to heart and lungs. Larvae break into alveoli, migrate to trachae and are swallowed. Larvae matures to ad

What is the infectious form of hookworm?

Filariform larvae

What are some clinical symptoms of hookworms?

Ground itch - cutaneous phase, pneumonitis - pulmonary phase, and anemia of iron - intestinal infection

How is hookworms diagnosed?

Eggs (thin walled oval eggs) in stool

What is the world's most common parasite, affects mostly children?

Enterobium vermicularis (pinworm)

What is the life cycle of Enterobium vermicularis?

Adults in intestines, female migrates to anus and deposits eggs on perianal skin, eggs are ingested on fecaled fingers, and eggs hatch and develop in duodenum.

Which type occurs in 30-40% of world population, unsegmented?

Ascaris lumbricoides

Describe the life cycle of Ascaris lumbricoides.

Adult worms in intestine, eggs pass in feces, larvae develop within the egg, ingest egg and larvae penetrate gut and migrate through blood to liver, lung, trachea, to esophagus to adults in intestine.

What are the clinical disease of Ascaris lumbricoides?

Pneumonitis when larvae migrate through lung tissue, bowel obstruction if large number is present, abnormal migration causes inflammation (appendix)

Which has bumpy oval eggs?

Ascaris lumbricoides

How is Ascaris lumbricoides diagnosed?

Detection of knobby eggs in stool, or could be in sputum

Name three types of Filariasis.

1. Wuchereria bancrofti
2. Onchocerca volvulus
3. Loa loa

Elephantiasis (lymph vessel blockage)

Wuchereria bancrofti

What is the vector for Wuchereria bancrofti?

Mosquito

How is Wuchereria bancrofti diagnosed?

Microfilaria in blood

River blindness, suicide from itching,

Onchocerca volvulus

What is the vector for ONchocerca volvulus?

Black fly in fast moving rivers

Calabar swelling, eye worm

Loa loa

What is the vector for Loa loa?

Deer fly, mango fly

Fiery serpent of biblical Israelites

Dracunculus medinensis

What is the life cycle of Dracunculus medinensis?

Adult worms in the body. Gravid females migrate to subcutaneous tissues at ankles or wrists and secrete products which cause formation of ulcer. On contact with water, blister erupts and uterus of female worm prolapses releasing rhabditiform larvae into t

What is the diagnosis of Dracunculus medinensis?

Ulcerated blisters with protruding worms