Metazoan Parasites Classification

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Metazoan Parasites - Classification

• Kingdom Animalia
• Subkingdom Metazoa
• Helminths parasitic worms
• Phylum Nematoda
• Nematodes - Roundworms
• Phylum Platyhelminthes
• Trematodes - Flukes
• Cestodes- Tapeworms

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Cestode - Characteristics

• Cestodes
• long flat ribbon-like intestinal worms consisting
  of many segments called proglottids each
  proglottid is highly developed for reproduction
• scolex - the end of the worm specialized for
  attachment to the intestinal epithelium
• Monoecious -each proglottid contains ovaries and
  testes and the worm is self fertilizing
• Ova - product of fertilization the survival form
  which is transmitted for one host to another

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Nematode - Characteristics

• Nematodes
• cyclindrical worms which range in size from a few
  millimeters to several centimeters thick
  protective cuticle, through which predigested
  nutrients are absorbed only well developed
  system is for reproduction
• Diecious both male and female worms (separate
  sexes)
• Ova fertile ova produced by female worm
  following mating
• Epidemiology Hosts
• Definitive Host host in which worm is sexually
  mature
• Intermediate Host host in which worm is
  sexually immature

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Trematode - Characteristics

• Trematodes
• flat, leaf-like worms with many different shapes
• attachment to tissue by specialized sucker
• often named for the tissue in which the mature
  worms infests
• Monoecious - both ovaries and testes in the same
  worm, but cross fertilization occurs
• Ova -product of cross fertilization is the stage
  that is transmitted and is the survival stage
  outside of the host

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Nematode Parasites of Humans/Animals

• Ascaris lumbricoides
• Enterobius vermicularis
• Necator americanus
• Ancyclostoma duodenale
• Trichnella spiralis
• Toxocara canis
• Wuchereria bancrofti
• Dracunculus medinensis

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Nematode Life Cycles - Principles

• Definitive Host -all nematodes have a definitive
  host this is the host in which the worms are
  sexually mature and produce fertilize ova or
  active larvae
• intestinal nematodes - nematodes that reside in
  the gastrointestinal tract of their definitive
  host. they derive all of their nutrients
  predigested from the host nematodes avoid being
  eliminated from their host either by continuous
  swimming movement by muscles in the body wall, or
  by burrowing deep into the intestinal crypts and
  escape of forces of peristalsis.
• blood and tissue nematodes - nematodes in which
  the adult worms live within the blood/tissues of
  the definitive host the female of their type of
  nematodes produces larvae called microfilariae
  microfilariae are ingested by blood feeding
  arthropods which serve as vectors the these
  filarial nematode worms
• Intermediate Host - most nematodes have a direct
  life cycle and do not possess an intermediate
  host Thus, the ova or larvae move from one host
  to another and do not go through a developmental
  phase in another host.

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Nematode Life Cycles - Principles

• Larval nematodes go through a series of
  developmental stages called molts there are
  generally four molts and the worms which emerge
  from the fourth molt grow and become sexually
  mature adult worm.
• Epidemiology the definitive hosts are the
  reservoirs of these worms
• their control centers around interruption of the
  life cycle
• by treating the affected host
• by interrupting the transmission of ova or
  larvae from one host to the next.

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Nematodes -Ascaris lumbricoides

• Large, diecious intestinal nematodes ( 8 - 12 in
  long x 1/8 in dia)
• after mating, the female worm produces 200,000
  ova per day for one year
• ova become infectious as embryo of larval worm
  develops
• no attachment structures worms maintain position
  by motion
• Clinical Disease ascariasis
• in most cases, only a few adult worms develop in
  the intestines and cause no symptoms the worms
  utilized predigested nutrients in the lumen.
• symptoms are often associated with the vascular
  phase of the worm cycle as they burrow out into
  the lungs causing pneumonitis and when the worms
  move in to other areas like the bile duct,
  gallbladder or liver
• Reservoir Hosts
• definitive hosts humans
• A similar species , Ascaris suum, in swine can
  also infect humans
• no intermediate host, so cycle is direct

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Ascaris lumbricoides Life Cycle

• Life Cycle
• embryonated ova are ingested larval worm emerges
  and moves through the duodenal wall into the
  blood the larval goes thru several developmental
  stages (molts) as in circulates in the blood to
  the heart where it is pumped into the pulmonary
  circulation in the lungs the larvae rupture the
  alveoli, are coughed up, and swallowed this take
  about three weeks in the intestine the fourth
  stage larva grows into an adult worms when male
  and female are present they mate the female
  becomes gravid and produces ova which are passed
  in the feces

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Nematodes - Ascaris lumbricoides

• Epidemiology
• Ascariasis is the most common helminth
  infestation in the world estimated one billion
  people infested
• parasite follows the fecal-oral mode of
  transmission with food and water the common
  sources of the ova the ova survive many months
  outside of the host in all kinds of harsh
  conditions
• Control
• interruption of the fecal-oral cycle by
  preventing fecal contamination of water and food
  human water in the agriculture setting account
  for most contamination of fresh vegetables/
  fruits
• Diagnosis fertilized and unfertilized ova in the
  feces X-rays of the visceria show worms in
  intestines and biliary system eosinophilia

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Enterobius vermicularis - Pinworm

• Characteristics
• very small white nematode worms about the size of
  a small straight pin human pinworm
• larvae hatch from embryonated eggs in the large
  intestine
• after mating the female worm deposits ova
  externally in the perinatal and / or vaginal
  folds a single female worm can produce gt 20,000
  in her life
• Clinical Disease
• when symptoms occur they begin as purititis of
  the perianal areas accompanied by irritability,
  loss of sleep, and fatigue
• most an infestation of children
• complications include allergic reaction to worm
  secretions and genitourinary inflammation in
  female children
• Parasite Enterobius vermicularis
• Host - human definitive host
• cycle is direct person-to-person, direct and
  indirect, fecal-oral
• Epidemiology - ova are passed via fecal-oral
  route via hands and fomites linens, towels,
  toys, etc
• Diagnosis ova in the perianal folds scotch
  tape test

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Nematodes - Toxocara canis/Toxocara cati

• Characteristics - a nematode worm similar to
  Ascaris lumbricoides, but smaller( 3 - 4 inches
  in length)
• Clinical Disease toxocariasis or visceral larval
  migrans
• cough, wheezing, fever, rash, anorexia, seizure,
  fatigue, abdominal discomforts due the movement
  of larva through the lungs, heart, kidneys,
  liver, skeletal muscle, and CNS. Causing
  esoinophilic granulomas and necrosis
• Life Cycle same as with Ascaris
• Reservoir Host intestine parasite of dogs and
  cats
• humans are an unnatural host thus the larva
  burrow into the visceral and do not mature in the
  intestines
• Epidemiology -ingestion of the ova form the worms
• Control - prevent the infestation in domestic
  pets
• Diagnosis- mostly history of contact with dogs
  and cats, and serological response to larval
  antigens

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Ancylostoma duodenale/ Necator americanus

• Characteristics
• nematode intestinal roundworms( approx 4 - 5 cm
  length)
• buccal cavity contains cutting plates ( Necator)
  for chewing/attachme
• or sharp teeth (Ancylostoma) for chewing and
  attachment
• Clinical Disease Hookworm Infestation
• symptoms vary from an allergic reaction to larval
  penetration to nausea, vomiting, diarrhea, and
  anemia daily blood loss is .15 - .25 ml/worm
• chronic infestations may be complicated by
  secondary bacterial infections
• Parasites New World Hookworm Necator americanus
• Old World Hookworm Ancylostoma duodenale

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Hookworm- Life Cycle

• Life Cycle
• adults worms reside in small intestine where
  absorb predigested nutrients and suck blood from
  injury tissue after mating the female becomes
  gravid and begins to produce ova(10 - 20,000 per
  day) which are released into the lumen and
  deposited in the feces the ova hatch in warm,
  moist soil and the larva molt to the filariform
  stage filariform larvae possess a buccal bulb
  which hydrolyzes cutaneous tissues and allow the
  larvae to penetrate through the skin and into the
  blood in the blood the larvae molt, burrow out
  through the lungs, are coughed up and swallowed
  then they develop into adult worms

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Ancylostoma duodenale/Necator americanus

• Epidemiology
• human reservoir
• person -to-person, mode of transmission via
  deposition of human feces on warm, moist, shady
  soil, where larvae filariform larvae develop and
  penetrate exposed skin most often feet
• incidence highest in tropical areas having poor
  sanitation
• 900 million cases world wide
• a few hundred cases in U.S
• Control - prevent fecal deposition to the soil
  and protect skin that is exposed to the soil
• Diagnosis symptoms of anemia and eosinophilia
• ova in the feces ova of the two human hook worms
  cannot be distinguished but if allowed to hatch
  in the laboratory, the larvae can be
  distinguished.

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Ancylostoma braziliense

• Characteristics canine filarial nematode
• Clinical Disease cutaneous larval migrans
• A non-specific response to larvae in humans
• Larvae cannot enter the blood, so they burrow
  into the skin forming inflamed channels
• Life Cycle same as all hookworms
• Parasite - dog and cat hookworm
• Ancylostoma braziliense
• Epidemiology filariform larvae to the skin of
  dogs, cats, and humans
• Control

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Trichinella spiralis - characteristics

• Small intestinal nematodes which derive their
  nutrients predigested in the definitive host
• female worm( does not produce ova ) deposits
  larvae into the intestinal mucous from which they
  burrow into the blood from the blood the larvae
  burrow into striated muscles where they encyst
• Clinical Disease - trichinosis or trichnellosis
• Parasite Trichinella spiralis
• Life Cycle
• humans and other animals serve as the definitive
  and intermediate host
• Epidemiology - the animal reservoir esp. swine
  are eaten by humans thus the encysted larvae
  are consumed the tissue is digested away in the
  intestine and releases the larvae to mature into
  adults
• Control prevent the cycle in animals if possible
• Cook the tissues of suspect animals to kill the
  encysted larvae
• Break the cycle in domestic swine

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Wuchereria bancrofti

• Characteristics nematode helminth producing
  microfilariae
• Clinical Disease elephantiasis
• Adult worms block the lymphatics which drain the
  lower extremities and genitalia
• Parasite Wuchereria bancrofti
• Life Cycle female worms releases larvae
  (microfilariae) into the lymph and blood of
  definitive host larvae are ingested by
  mosquitoes that feel on the definitive host
• Epidemiology person-to-person, indirect,
  arthropod-borne
• Anopheles and Culex Mosquitoes
• Control treat infected humans to reduce
  available microfilaria
• Mosquito control reduce available mosquito
  population
• Diagnosis microflilariae or their antigens in
  the blood

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Dirofilaria immitis

• Characteristics nematode helminth producing
  microfilariae
• Clinical Disease Canine Heartworm
• Does not causes infestation in humans
• Life Cycles adult worms develop and reside in
  the heart of their definitive host member of the
  canine family female worm releases larvae into
  the blood and mosquitoes ingest the larvae when
  they feed of the host
• Epidemiology animal-to-animal, indirect,
  arthropod-borne
• Diagnosis - observe mirofilariae in blood smears
  or detect larval antigen in the blood using
  monoclonal antibody

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Dracunculus medinensis

• Characteristics nematade helminth of the
  tissues
• Clinical Disease Dracunculasis
• cutaneous ulcer with pain progressing to abcess
  and allergic or inflammatory reaction sometimes
  secondary bacterial infection
• Parasite guinea worm fiery serpent
• Dracunculus medinensis
• Life Cycle after mating the female worms
  burrows through the tissues until she rest under
  the skin where she develops and becomes gravid
  when she senses moisture over the skin she
  extends her ovipositor through the skin and
  releases her larvae into water.
• Epidemiology larvae in drinking water are
  ingested by copedods
• ( water fleas) are ingested by humans when they
  drink the water
• Control
• Diagnosis

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Cestode Parasites of Humans/ Animals

• Taenia solium pork tapeworm
• Taenia saginata beef tapeworm
• Diphyllobothrium latum fish tape worm
• Hymenolepis nana dwarf tapeworm
• Hymenolepis diminuta rat tapeworm
• Dipylidium caninum dog tapeworm

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Cestode Life Cycles Principles

• Definitive Host the host in which the worm
  becomes sexually mature and produces fertile
  ova or active larvae
• Intermediate Host the host which habors the
  sexually immature stage of the worm often a
  specialized developmental stage
• Cestodes or tapeworms are intestinal parasites
  they derive all of their nutrients predigested by
  the host they have a special covering called a
  cuticle which protects them from being digested
  since they possess no muscles to counter the
  forces of peristalsis, they attach to the
  intestinal mucous by a special attachment
  structure called a scolex
• Epidemiology most cestode life cycles involve
  the transmission of ova in the feces of the
  definitive host thus, proper deposition of
  feces is an important step in the interruption
  of the cycle. The cycle can also be interrupted
  by killing the immature worms in their
  intermediated hosts.This is often accomplished by
  cooking.

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Taenia solium pork tapeworm

• Definitive Host humans with intestinal
  infestation
• the worm releases free fertile ova or proglottids
  containing fertile ova
• the fertile ova are ingested by the intermediate
  hosts
• the ova hatch in the intestines of the
  intermediate host and the larva(oncosphere)
  burrows through the intestinal mucosa into the
  blood
• the larvae circulate in the blood and emerge in
  striated muscles where they form a stage called a
  cysticercus in the interstitial connective
  tissue of striated muscles
• Intermediate Host swine, both domestic and wild,
  are the hosts which habors the cysticercii
  They are infested when they ingests the ova or
  proglottids in fecally contaminated soil or food
  the cysticercii are transmitted when pork is
  eaten raw or poorly cooked.
• Epidemiology
• Diagnosis ova or proglottids are observed in the
  feces of the human definitive host they cannot
  be distinguished from other Taenia

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Taenia saginata beet tapeworm

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology
• Diagnosis

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Diphyllobothrium latum fish tapeworm

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology
• Diagnosis

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Hymenolepis nana dwarf tapeworm

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology
• Diagnosis

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Hymenolepis diminuta rat tapeworm

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology
• Diagnosis

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Dipylidium caninum dog/cat tapeworm

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology
• Diagnosis

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Trematode Parasites of Humans/Animals

• Fasciolopsis buski intestinal fluke
• Fasciola hepatica sheep liver fluke
• Clonorchis sinensis human liver fluke
• Paragonimus westermani lung fluke
• Paragonimus mexicanii mexican lung fluke
• Schistosoma mansoni blood fluke
• Schistosoma haematobium blood fluke
• Schistosoma japonicum blood fluke
• Avian Schistomes avian blood flukes

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Trematode Life Cycle Principles

• Definitive Hosts
• Intermediate Host

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Fasciolopsis buski human intestinal fluke

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology
• Diagnosis

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Fasciola hepatica sheep liver fluke

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology
• Diagnosis

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Clonorchis(Opisthorchis) sinensis

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology
• Diagnosis

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Paragonimus westermani lung fluke

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology
• Diagnosis

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Paragonimus mexicanii mexican lung fluke

• Definitive Host
• Intermediate Host
• Symptoms
• Epidemiology
• Diagnosis

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Blood Flukes Schistosomes

• Definitive Hosts
• Intermediate Hosts
• Symptoms
• Epidemiology
• Diagnosis