Define: Parasite

A symbiotic relationship between 2 organism whereparasite lives in/on host, and derives nutrition and/or protection from the host (at some point in its life), but the parasite provides no benefit and may harm host

Define: Symbiosis

Any association, temporary or permanent, between at least 2 living organisms of different species

Types of symbiosis

• Predator-prey: extremely short relationship where one organism benefits at the expense of the other
  
• Phoresis: smaller symbiont is mechanically carried by larger symbiont
  
• Mutualism: when both parties involved benefits
  
• Commensalism: one benefits; one totally unaffected
  
• Parasitism: parasite lives in/on host, and derives nutrition and/or protection from the host (at some point in its life), but the parasite provides no benefit and may harm host

Define: Ectoparasite

Parasite living ON the exterior of the host body

Define: Endoparasite

Parasite living within the host's body

Define: Aberrant (erratic) parasite

Moves from its usual site of infection into a location it ordinarily does not live

Define: Incidental parasite

Parasite occurs in host in which it does not usually live

Define: Facultative parasites

Normally non-parasitic but can become parasitic under certain circumstances

Define: Obligatory parasites

Must lead a parasitic existance, though may be free living at some parts of its life cycle.

Define: Periodic parasite

Doesn't live on/in host but makes frequent visits

(e.g. mosquitos)

Define: Pseudoparasite

Organisms that are not parasitic but

often mistaken for one

Define: Direct life cycle

Involve definitive hosts only.

No intermediate host is required

Define: Definitive host

The host that harbors the adult/sexual

stages of parasites

Define: Indirect life cycle

Has a definitive and intermediate host

(obligatory indirect life cycle),

or a paratenic host

(facultative indirect life cycle)

Define: Paratenic host

Host that harbors pre-adult/asexual stages.

Little/no dev't occurs in host and is

NOT required for completion of life cycle.

Define: Intermediate host

Host that harbors pre-adult/asexual stages

(parasite development occurs within host).

Required for completion of life cycle

Define: Reservoire host

Hosts in which parasite occurs in nature

and is source of infection for humans and

domesticated animals. All parasites have one.

Classification: Phylum Platyhelminthes

• Class Trematoda: Flukes
  • Subclass Digenea
• Class cestoda: Tapeworms
  • Order: cyclophyllidea
  • Order: pseudophyllidea

Classification:

Phylum Nemathelminthes

• Nematodes!
  • Class adenophorea
  • Class secernentea

Classification: Phylum Acanthocephala

Thorny headed worms

Define: Coelem

True body cavity lined with mesoderm derived peritoneum that holds organs in place

Define: Pseudocoelom

A body cavity that is fluid filled but not

entirely lined by mesoderm

Define: Acoelomate

Does not have a body cavity, so organs

are in direct contact with epithelium.

Define: Monoecious

One organism has both male and

female reproductive organs

Define: Dioecious

One organism has either female or male

reproductive parts, but not both

Characteristics of Trematodes

Phylum Platyhelminthes - Flukes

• Dorso-ventrally flattened
• Leaf shaped, unsegmented
• Acoelomate
• Incomplete digestive tract (mouth, esophagus, intestine)
• Monoecious with exceptions

Characteristics of cestodes

Phylum Platyhelminthes - Tapeworm

• Dorso-ventrally flattened
• Long, segmented
• Acoelomate
• Lack digestive tract
• Monoecious

Characteristics of Nematodes

• Long, round worms
• Unsegmented
• Pseudocoel
• Complete digestive system (mouth, esophagus, intestine, anus)
• Dioecious

Characteristics of Acanthocephalans

Thorny headed worms

• Long, round
• Anterior spiny proboscis
• Unsegmented (though looks segmented)
• Pseudocoel
• Lack digestive system
• Dioecious

Characterisitcs of Parasite Phyla

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Life Cycle of Acanthocephalans

• All have indirect life cycle, where IH = arthropods
• Paratenic hosts may exist: wide range of vertebrate hosts including mammals
• Egg contains fully developed larva (acanthor) when passed by female)
• Egg ingested by suitable IH, then develops to acanthella stage then to cystacanth (encysted) stage
• Cystacanth is the stage infective to the DH

Examples of Acanthocephalans

Macracanthorhynchus hirudinaceus

Intermediate hosts of

Macracanthorhynchus hirudinaceus

Beeltes, particularly dung beetles, water beetles

Define: Acanthor

Fully developed larva of

Macracanthorhynchus hirudinaceus

Prepatent period of

Macracanthorhynchus hirudinaceus

2-3 months

What determines the severity of clinical signs in

Macracanthorhynchus hirudinaceus?

How deeply the proboscis is embedded into the intestinal wall. (The parasite uses the proboscis to attach to the intestinal wall by penetrating into wall with it)

• Granulomatous inflammation around attachment site
• If penetrated all the way, can cause fatal peritonitis
• Heavy infections may induce catarrhal enteritis (mucoid inflammation of intestines)

Clinical signs of

Macracanthorhynchus hirudinaceus

• May show no outward clinical signs
• May have diarrhea and emaciation with evidence of acute abdominal pain (occasionally, parasite may penetrate teh small intestine, migrating into the abdomen where it becomes entangled in the mesenteries)

Detection of

Macracanthorhynchus hirudinaceus

• Ante-mortem: can find eggs on fecal flotation
• Post-mortem: Parasites are readily visualized at necropsy
  • Males are ~10 cm
  • Females are as long as 35 cm

Public Health concerns for

Macracanthorhyncus hirudinaceus

Humans can become infected though rarely

develop to patency (rarely shed eggs)

Define: Prepatent period

The period between infection of the host

and the earliest time at eggs or larvae can be

recovered from feces, urine or blood.

Examples of Trematodes

Fasciola hepatica

Fascioloides magna

Dicrocoelium dendriticum

Paragonimus kellicotti

Nanophyetus salmincola

Neorickettsia risticii

General life cycles of trematodes

• Eggs are passed through the feces into the environment, where it hatches into a Miracidium (ciliated larva) which swims around in water
• The miracidium penetrates into or is eaten by a snail/slug (1st IH), where it undergoes lots of asexual reproduction to produce many cercariae
• Cercarie develop into an encysted metacercaria either after penetrating into a 2nd IH or just sitting on vegetation in the environment. (Cercariae can penetrate the definitive host in schistosomes (blood flukes)
• DH infected by ingesting plants or IH with metacercaria. Juvenile fluke migration can be extensive so adults live in a variety of organs
  

Life stages of trematodes

Operculated egg

Ciliated embryo (miracidium)

asexual reproductive stages

cercaria

metacercaria

adult

Common name for

Fasciola hepatica

Liver fluke

Definitive hosts of

Fasciola hepatica

ruminants, pigs, horses, occasionally in humans

Intermediate hosts of

Fasciola hepatica

lymnaeid (aquatic) snails

2 groups of Cestodes

Cyclophyllidea

Pseudophyllidea

Characteristics of Pseudophyllidea

• Indirect life cycle
• Requires 2 IH during Metacestode Stages
  • Procercoids (1st IH)
  • Plerocercoid (2nd IH
• Depends on Water

Characteristics of Cyclophyllidea

• Indirect life cycle
• Requires 1 IH
• Does not depend on water
• Metacestode is one of the following:
  • Cysticercoid
  • Cysticercus
  • Strobilocercus
  • Coenurus
  • Hydatid Cyst

Genearl Pseudophyllidean Life Cycle

• Proglottids are pooped out
• Operculated egg released from proglottid
• Coracidium develops in egg, hatches in water, and infects 1st IH, where it develops into Procercoid (metacestode) at an extraintestinal site
• 2nd IH eats first IH, where it develops into 2nd metacestode - Plerocercoid.
• Infects definitive host, where it stays within SI and matures.

Examples of Pseudophyllideans

Diphyllobothrium latum

Spirometra mansonoides; Spirometra proliferum

Metacestode Types in Cyclophyllidea

Cysticercoid

Cysticercus

Strobilocercus

Coenurus

Hydatid syst

Cysticercoid

• Metacestode of Cyclophyllidea
• thin walled, solid vesicle containing a single invaginated scolex
• for every one cysticercoid ingested, only one tapeworm develops

Cysticercus

• Metacestode of Cyclophyllidea

• Thin walled, fluid filled vesicle containing single invaginated scolex
• For every cysticercus ingested by DH, one tapeworm develops

Strobilocercus

• Metacestode of Cyclophyllidea
• Variation of cysticercus that has evaginated.
• Consists of scolex attached ot long neck to the fluid-filled bladder
• For every strobilocercus ingested by DH, one tapeform develops

Coenurus

• Metacestode of Cyclophyllidea
• Single, large fluid-filled bladder containing numerous scolices attached to the inner wall
• For every coenurus ingested by the definitive host, several tapeworms can develop

Hydatid cyst

• Metacestode of Cyclophyllidea
• Single large fluid-filled bladder contining numerous "daughter" cysts within which are numerous protoscolices attached to the inner wall.
• For every hydatid cyst ingested by definitive host, several tapeworms can develop.

General life cycle of cyclophyllideans

• Eggs pooped out in feces
• Egg in environment where hexacanth embryo developed and hatched
• Hexacanth ingested by one of the many types of metacestodes
• Metacestode ingested by the DH and develop in SI