Parasitology Test 2

Helminths

• some are free-living organisms in aquatic and terrestrial environments

• others are parasites in most animals and some plants

• most species have worms in them somewhere

• general term meaning “worm”

• multicellular eukaryotic invertebrates

• tube-like or flattened bodies

• bilateral symmetry

• triploblastic

  • with endo-, meso-, and ecto-dermal tissues

play-helminths

• “flat worms”

  • acoelomate

  • do not have body cavities

nemat-helminths

• round worms

  • pseudocoelomate

  • body cavities not enclosed by mesoderm

segmented annelids

• earthworms

  • coelomate

  • with body cavities enclosed by mesoderm

Platyhelminthes

• flatworms

• acoelomate

  • dorsoventrally flattened

• bilaterally symmetric

• organ systems

  • digestive

    • closed in trematodes

    • none in cestodes

• reproductive— most are monoecious

  • excretory

  • neuromuscular

Trematodes

• flukes

• monogenea

  • flatworms ordinarily living as ectoparasites on single host throughout entire life cycle

• mostly parasites of fish

  • direct lifecycles

• digenea

  • alternation of sexual reproduction as internal parasite of vertebrate with asexual reproduction in mollusk

    • parasites of many types of animals

• indirect lifecycles

  • mostly monoecious

• cestodes— tapeworms

Trematodes— Monogeneans

• may or may not have a weakly developed oral sucker

• posterior end has larger posterior adhesive disk— opisthaptor

  • usually has hooks

• anterior and dorsal excretory pores paired

• simple life cycle

  • mainly found in the epithelial layers

Trematodes— Digeneans

• organ systems

  • tegument

    • surficial covering of a multicellular organism

  • neuromuscular

  • digestive

  • reproductive

• indirect life cycle

  • definitive host

  • first intermediate host

  • second intermediate host

Digeneans— Life Stages

• vertebrate (definitive host)

  • adult

• environment

  • egg

  • miracidia (infect 1st intermediate host)

• snail (1st intermediate host)

  • sporocyst

  • redia

• environment

  • cercaria

  • mesocercariae

  • metacercariae (in 2nd intermediate host)

    • infect definitive host

Digenetic Trematodes— Organ Systems

• tegument— may have spines

• neuromuscular

• digestive

  • closed— mouth, gut, — no anus

  • feed on blood, mucus, tissue with mouth and pharynx

• reproductive

  • monoecious

  • hermaphroditic

Digenetic Trematodes life cycle

• indirect life cycle

• definitive host

  • various vertebrates

• 1st intermediate host

  • almost always a mollusk

• 2nd intermediate host

  • various vertebrates

Metacercariae of adult Digenetic Trematodes

• a tailless encysted late larva of a digenetic trematode

• usually the form which is infective for the definitive host

Cercariae of Adults Digenetic Trematodes

• a free-swimming larval stage

• passes from an intermediate host (typically a snail) to another intermediate host or to the final vertebrate host

Eggs of Digenetic Trematodes

• embryo encased in a capsule

• most have an operculum— groove around one end of it

  • will open to release miracidium

• variety of sizes, shapes, thickness, coloration

  • contain fully developed miracidia or only a few cells

• most eggs hatch in environment

  • require water

  • also require certain O₂ levels, temperatures, etc.

Miracidia of Digenetic Trematodes

• free-swimming larval stage

• tiny, ciliated organism

  • has penetration glands and apical glands

  • have germ cells in posterior region—will become sporocysts

• usually hatch in water

  • must swim rapidly— survive only a few hours

  • must find a mulluscan host

  • attracted to mullusc by mucus → attaches with apical papilla, penetrates snail in about 30 mins

Sporocysts of Digenetic Trematodes within 1st Intermediate Host

• result from metamorphosis of miracidia in snail host

• NO digestive system

• functions only to nurture developing embryos

  • next stage may be daughter sporocysts, redia, or cercariae

Redia of Digenetic Trematodes within first intermediate host

• burst out of sporocyst or leave via terminal birth pore

• migrate through host

  • feed on host tissue and other sporocysts

• function to nurture developing embryos

  • next stage may be daughter redia or cercariae

Trematodes— Cercariae

• juvenile stage released from first intermediate host

• free swimming

  • most have tails for swimming

  • have a mouth, oral sucker, penetration glands, digestive and excretory systems

• find new host (usually second intermediate host) by chance

  • respond to stimuli

  • some penetrate definitive host

  • usually migrate in host for a period of time

Termatodes— Metacercariae

• encyst— either in an intermediate host or on vegetation

• lose their tails and undergo development

  • encyst on vegetation— little development, infective within hours

• do not encyst in intermediate host, need several days of development

  • encyst in intermediate host— need weeks for development

• after development— enter resting stage, infective to definitive host

  • allows for survival during unfavorable times

  • transports parasite from intermediate host to definitive host

Alaria americana

• definitive host: canids

• 1st IH: aquatic snail (helisomid)

• 2nd IH: tadpoles

• paratenic hosts

  • water snakes

• have a mesocercariae

  • unencysted intermediate between cercariae and metacercarie (only one we talk about)

  • develop in 2 weeks

  • accumulate in 2nd intermediate host

  • eaten by paratenic host or definitive host

Alaria americana life cycle

• adults in definitive host small intestine

• miracidia penetrate snail (1st intermediate host)

• cercariae penetrate tadpoles (2nd intermediate host)

• tadpole/frog infected with mesocercariae can be eaten by either definitive host or paratenic host

• paratenic host may accumulate many mesocercariae

• definitive host eats paratenic host or 2nd intermediate host

• humans can be infected by eating undercooked frog legs

  • human acts as paratenic host

Alaraia americana Pathogenesis

• definitive host is canids

  • adults cause severe enteritis

  • death

• 2nd intermediate host— tadpole

  • mesocercariae, in high numbers, can cause disease

• humans—rare

  • nearly every organ infected

  • hemorrhage, tissue damage, death

What is the most likely intermediate host for digenetic trematodes?

snails

What is the juvenile stage of trematode released from the first intermediate host?

cercariae

What is the definitive host for Alaria americana?

canids

Which species of Schistosoma is most likely to cause a UTI?

S. haetmatobium

Schistosoma spp.

• unique among trematodes

  • causes schistosomiasis (snail fever)

• major disease in tropics

  • 200 million people infected

• dioecious

  • sexual dimorphism

    • females— long and slender

    • males— short and stout

  • mate in blood circulation

• non-operculated eggs

Schistosoma spp. — pathology

• eggs

  • cause major pathology

  • migrate through tissue

    • pass through veins to get to lumen of bladder or intestine

    • mechanism unknown

• granuloma formation

  • immune response: WBCs “wall off” eggs

  • granulomas trapped in vessels

  • may occlude vessels

Schistosoma spp. — Distribution

• about 85% of world’s cases in Africa

  • prevalence rates can exceed 50% in local populations

• schistosoma mansoni and S. haematobium distributed throughout Africa

• Schistosoma haematobium

  • throughout Africa

  • only S. haematobium in areas of middle East

• Schistosoma japonicum

  • Indonesia

  • parts of China and Southeast Asia

Schistosoma spp.— Life cycle

Schistosoma mansoni

• distribution

  • throughout Africa

  • not in US— do not have snail host

• definitive host is humans

• first intermediate host is aquatic snails

• eggs— large lateral (subterminal) spine

• adults— reside in veins of large intestine

Schistosoma mansoni pathology

• penetration of skin by cercariae

• dermatitis (1-4 days)

  • swelling, itching, allergic reaction

• migration (3-4 weeks)

  • through lungs

    • fever, cough, difficulty breathing

  • through liver

    • hepatitis

• acute stage (egg production)

  • chills, fever, malaise, abdominal pain and tenderness, diarrhea, bloody stool

• chronic stage

  • granuloma formation— hallmark symptom of Schistomiasis

• hepatosplenic schistosomiasis

• intestinal schistosomiasis

• Katayama syndrome

• Clay Pipestem Fibrosis

Hepatosplenic schistosomiasis

• liver and spleen enlargement

• granulomas in liver

• jaundice

Intestinal schistosomiasis

colitis, abdominal cramps, granulomas

Katayama Syndrome

• severe reaction to eggs

• fever, chills, abdominal pain, cough

• not seen in every case

Clay Pipestem Fibrosis

• portal vein surrounded by granulomas

  • portal vein major blood supply for liver

• often fatal

Schistosoma japonicum

• distribution

  • indonesia, parts of china and southeast asia

• humans and mammals are definitive host

• aquatic snail is intermediate host

• domestic animals are reservoir host

• eggs are in the small lateral spine

• adults reside in veins of small intestine

Schistosoma japonicum pathology

• same as S. mansoni

• Katayama Syndrome— more common

• cerebral schistosomiasis

• diagnosed by eggs in feces

• treated with praziquantel

Cerebral schistosomiasis

• eggs enter brain (smaller spine)

• granulomas in brain

• neurological signs

  • lethargy, seizures, vision problems

  • speech impairment

Schistosoma haematobium

• distributed throughout Africa, areas of Middle East

• humans is definitive host

• aquatic snail is intermediate host

• chimpanzees and baboons are the reservoir hosts

• eggs have terminal spines

• adults reside in veins of urinary bladder

  • can be in uterus, prostate, etc.

Schistosoma haematobium

• same as S. mansoni but less severe

• urinary schistosomiasis

• major cause of bladder cancer in Nile region

• hepatosplenomegaly— children

• pulmonary

  • rapid breathing, cough, cyanosis (bluish skin, low oxygen in blood)

Urinary Schistosomiasis

• hematuria (blood in urine)

• frequent urination

• bacteria in urine

Schistosoma spp. epidemiology

• main source of infection

  • human waste, urine, in water with intermediate host

  • people at risk:

    • low economic and education levels related to sanitation

    • more common in 10-20 years old

    • males are more infected than females

Schistosome Cercarial Dermatitis (Swimmer’s Itch)

• caused by avian schistosomes

  • humans are a dead-end host

• cercariae penetrate skin; unable to complete migration

• immune system kills cercariae

• cercariae release antigens

• causes inflammatory response

  • purulent-filled lesion

  • severe itching

  • not serious health problem

  • more common in Great Lakes region

Fasciola hepatica— sheep liver fluke

• known for 100s of years

  • first trematode life cycle described

• one of the largest trematodes

  • 30 mm long by 13 mm wide

• DH— ruminants, humans

• IH0— aquatic snail

• RH— sheep, cattle, rabbits

• human cases in europe, africa, south america

  • few cases in US

  • parasite common in areas of south and west

Fasciola hepatica— in humans

• maturation

  • metacercariae to adult flukes ~ 3-4 months

• adult flukes are large

• reside in large biliary ducts of mammalian host

• eggs passed out of bile ducts with bile

  • enter intestines and exit with feces

Fasciola hepatica— pathology

• liver migration (metacercariae)

  • feed on liver cells and blood

  • necrosis

• parasites in bile ducts (adults)

  • inflammation, edema, anemia

  • stimulate growth of fibrous tissue in duct walls

    • cirrhosis

    • jaundice

• heavy infections

  • gallbladder damage

  • anemia

  • erosion of bile ducts

  • large liver abscesses

  • death

• migrate juveniles

  • ulcers in ectopic locations

    • eyes, brain, skin, lungs

Fascioloides magna

• large

• DH— cervids (deer, elk, etc.), cattle, sheep

• IH— snail

• degree of pathogenicity depends on host

  • sheep

    • extensive damage

    • migration leads to hemorrhage and peritonitis

    • no capsule around fluke

  • cervids

    • less damage, limited migration

    • form capsule around fluke

Fasciolopsis buski

• DH— swine and humans

• IH— aquatic snail

• life cycle similar to F. hepatica

• common in Asia

• infects small intestine

  • pathology seen in small intestine

  • inflammation and mucous secretion at attachment site

  • blockage, ulcers, hemorrhage, abscesses, chronic diarrhea, death

• prevention

  • boil vegetables

  • cease use of nightsoil as fertilizer

Ribeiroia ondatrae

• DH— carnivorous birds and mammals

  • hawks, eagles, falcons

• 1 IH— aquatic snail

• 2 IH— fish and amphibians

• cause of recent frog deformities

  • cercariae attracted to limb bud region in tadpoles

  • cause limb deformities as tadpoles metamorphose

Dicrocoelium dendriticum

• DH— sheep, cattle, goats, pigs, cervids

  • localizes to the bile ducts

• 1 IH— land snail

• 2 IH— ants

• life cycle does not require water

  • ex of parasite manipulating host behavior to enhance transmission

• distributed throughout Europe, Asia, North America, Australia

Paragonimus westermani

• DH— mammals

  • felids, canids, mustelids, viverrids, humans, swine

  • mustelidae— otters, ferrets, badgers, and weasels

  • viverridae— civets, oyans, genets

• 1 IH— aquatic snail

• 2 IH— crabs, crayfish

• PH— various mammals and birds

• distributed throughout Asia, Africa, South and Central America

Paragonimus westermani pathology— pulmonary infections

• rarely fatal

• inflammatory response leading to granuloma formation

• difficulty breathing, chronic cough, sputum streaked red (blood) or brown (eggs)

Nanophyetus salmincola

• dog salmon poisoning disease

• example of hyperparasitism

• zoonotic

• DH— mammals (dogs, humans, others)

• 1 IH— aquatic snails

• 2 IH— fish (salmon!) and crustaceans

• distributed throughout Pacific Northwest US and Siberia

Dog Salmon Poisoning

• caused by rickettsial organism

• affects canids

• rapid and severe disease

• fever, swelling of face, eye discharge

• depression, anorexia, thirst

• vomiting, diarrhea

• enlarged and hemorrhaging lymph nodes

• death 10-14 days after first signs— 90% mortality without treatment

Chlonorchis sinesis

• Chinese Liver Fluke

• DH— humans, other mammals

• 1 IH— aquatic snail

• 2 IH— fish, crustaceans

• RH— dogs, cats

• distributed throughout Asia and other countries where people consider raw fish a delicacy

Clonorchis sinesis pathology

• erosion of epithelial lining of bile ducts

• mucous production, inflammation

• necrosis of liver cells

• occlusion of bile ducts

• eggs can cause granulomas and gallstones

• cancer of bile ducts

liver

Where in the body are immature Fasciola hepatica released?

inappropriate; change to triclabendazole

a 20 year old college student is diagnosed with Fasciola hepatica. They are prescribed praziquantel. Which is true about their treatment?

lungs

Where in the host does Paragonimus westermani develop into adults?

eating raw fish

Which of the following is most likely to result in Chlonorchis sinesis?

Cestodes

• dorso-ventrally flattened

• segmented

• no digestive system

• monoecious

• live in intestines of most vertebrates

Structures of Cestodes

• Scolex- head

  • may have attachment organ

    • suckers

    • hooks

  • simple or missing

• neck

  • undifferentiated area

  • produces new segments

• stroblia

  • sum of proglottids

• proglottid

  • “segment”

  • contains male and female organs

Cestode Reproduction

• occurs through genital pore

• exchanges spermatozoa

  • fertilizes other proglottids in the strobila

• can also fertilize proglottids in other worms

• fertilization of the same proglottid segment is rare

• strobilation

• new proglottids move toward posterior end

  • maturing as they descend

  • as they reach posterior end of stobila → reproduction and egg formation have taken place

    • result is gravid proglottid

Cestode Egg Release

• may pass gravid proglottids with eggs

  • results in proglottids in feces

• proglottid may disintegrate and release eggs

  • results in eggs in feces

Pseudophyllidean

• procercoid

  • crustacean ingests ciliated coracidium

  • procercoid develops in body cavity of crusteacean

• plerocercoid

  • develops from procercoid in 2nd IH that ingested infected crustacean

Cyclophyllidean

• cysticercus

• coenurus

• cysticercoid

• hydatid cyst

  • unilocular

  • multilocular

• one or other will occur in IH; which one depends on cyclophyllidean species

Cysticerus

fluid filled body; one scolex, grossly visible, invaginated ex. Tania sp

Coenurus

fluid filled body; many scolices, invaginated, up to a baseball size

Cysticercoid

solid bodied, 1 scolex, invaginated

Hydatid cyst

fluid filled; many scolices, invaginated, up to a basketball size

Unilocular

internal budding to produce internal daughter cysts (also contain scolices)

Mulitlocular

external budding to produce external daughter cysts (also contain scolices)— can metatasize

Diphyllobothrum latum Fish Tapeworm

• DH— fish-eating mammals and humans

  • canine, felines, mustelids, pinnipeds, bears, humans

• 1st IH— copepods (crustacean)

• 2nd IH— fish

• up to 10 m

• shed up to 1 mil eggs/day

• scolex has bothria (two longitudinal grooves used in attachment to intestinal wall)

• distributed throughout Scandinavia, Baltic States, Western Russia, United States, Great Lakes Area

• Pacific Northwest

Diphyllobothriasis Pathology

• DH

  • asymptomatic

  • vague symptoms

    • abdominal pain, diarrhea, nausea, weakness

  • anemia

    • Finnish people

    • parasite absorbs vitamin B12

    • treatment of parasite usually resolves anemia

• Diagnosis

  • eggs in stool

• Treatment

  • Niclosamide and Praziquantel

Diphyllobothriasis

• control of D. lactum

  • humans infected by eating raw or undercooked fish

    • cook fish thoroughly (especially imported fish)

• At risk:

  • communities that dispose of sewage in lakes, rivers— leads to higher prevalence in fish

  • use of human waste as fertilizer

Spirometra mansonoides

• human acts as accidental 2nd IH

• transmission to humans from accidental ingestion of copepods infected with procercoids

  • migrate from intestine, become plerocercoids

• ingestion of raw/undercooked amphibians, reptiles, birds, or mammals infected with plerocercoids

  • use of poultices made from frogs/snakes on open skin wounds, mucous membranes

    • plerocercoid migrates into human

Sparganosis

• rarely, spargana can proliferate

  • split longitudionally or bud

  • results in 1000s of worms and honeycombed organs

• North America

  • Spirometra mansonoides

  • DH— cats

    • may live up to 10 years

• Treatment

  • surgical removal

  • praziquantel

Taenia saginata

• beef tapeworm

• length: 3-5 m, up to 20 m

• scolex has 4 suckers, no hooks

• DH— humans

• IH— cattle

Taenia saginata Pathology

• most are asymptomatic or have vauge symptoms

  • abdominal pain, diarrhea, nausea

  • dizziness, headache

• sometimes..

  • intestinal obstruction

  • delirium

• loss of appetite

• psychological issues

Taenia saginata Diagnosis and Treatment

• cannot diagnose based on eggs

• need scolex and proglottid morphology

• PCR—RFLP

• ELISA

• treatment

  • Niclosamide and praziquantel

Taenia solium

• pork tapeworm

• DH- humans

• IH- swine

• length 2-3 m, up to 10 m

• scolex— rostellum with 4 suckers and 2 rows of hooks

• distributed throughout Mexico, Central and South America, Africa, India, China, Eastern Asia

Taenia solium pathology

• most are asymptomatic or have vague symptoms:

  • Ab pain, diarrhea, nausea

  • dizziness, headache

• sometimes have:

  • intestinal obstruction

  • delirium

• loss of appetite

• psychological issues

Taenia solium Cysticercosis Pathology

• signs depend on infection site

• skeletal muscle, skin, liver

Taenia solium Cysticercosis Pathology

• signs depend on infection site

• skeletal muscle, skin, liver

  • few signs

• eye

  • damage to retina, etc

  • vision loss

• CNS

  • epilpsy (most common)

  • necrosis, blindness, paralysis, hydrocephalus, etc

Taenia solium Diagnosis and Treatment

• diagnosis in DH

  • presence of eggs/proglottids in feces, antibody tests

• diagnoses in IH

  • signs, imaging, antibody tests

• treatment with praziquantel

  • not for CNS or eye cysticerci

    • worm death → severe inflammatory response → death of host

  • surgery

Taenia solium Prevention/Control

• early detection and treatment of infection with adults T. solium

• personal hygiene

  • prevent spread of eggs within household

• prevent contamination of food and water

• do not use human sewage as fertilizer

Echinococcus granulosus

• adults very small

• DH— mainly canids

• IH— many, exp. herbivores

• cystic echinococcosis in humans

• areas where herbivores are raised with our near carnivores

• transmitted in definitive host when dogs feed on organs of butchered animals

• transmitted in intermediate host when herbivores ingesting eggs in feces from infected dogs

Echinococcus granulosus pathology

• IH (including humans)

  • may not see signs for months to years

  • crowds and disrupts function of organs

  • extent of pathology depends on location of cyst

  • accidental rupture of hydatid cyst

Echinococcus granulosus diagnoses

• DH— detect eggs in feces

• IH— detect hydatid

Treatment of Echinococcus granulosus

• drugs for inoperable cysts; Albendazole, Prazinquantel

• surgery

Echinococcus multilocularis

• small, morphology like E. granulosus

• DH— mainly canids (foxes)

• IH— rodents

  • smaller DH/IH host range than E. granulosus

  • tend to cycle in wild populations

• alveolar echinococcosis in humans

Echinococus multilocularis distrubution

• Boreal (sub-artic)

• Europe

• Asia

• North America

Echinococcus multilocularis Transmission

• life cycle similar to E. granulosus

• DH

  • ingestion of infected rodent IH

• IH

  • rodents ingest eggs shed in DH feces

  • humans— accidental ingestion of eggs

Echinococcus multilocularis Pathology

• multilocular hydatid cyst

  • thin outer wall

  • grows and infiltrates host tissues

    • faster growing than unilocular cyst

Echinococcus multilocularis epidemiology

• diagnosis

  • DH— detect eggs in feces

  • IH— detect alveolar hydatids

• treatment

  • albendazole

  • surgery— often inoperable

• control

  • avoid dog feces in endemic areas; thorough washing of fruits/veggies; regular deworming of dogs; education

Dipylidium caninum

• “cucumber tapeworm”

• worldwide, common

• DH— dogs, cats, humans

• IH— fleas

• adults ~ 18 inches long

Dipylidium caninum epidemiology

• pathology

  • signs and symptoms rare

• diagnosis

  • characteristic proglottids or egg packets in feces

• treatment

  • praziquantel

Hymenolepis nana

• dwarf tapeworm

• worldwide

• very common cestode in humans

  • especially children

• DH— rodents and humans

• IH— fleas and beetles

• rostellum with one row of hooks

• adults ~ 40 mm long

Rostellum

fleshy protuberance of the scolex of a tapeworm, which may or may not bear hooks