Introduction to helminth parasites

Question 1

What type of damage might Ascaris suum induce?

Answer 1

Mechanical damage - intestinal occlusions

Question 2

What type of damage might Ancylostoma induce?

Answer 2

Hook work

Traumatic damage

Attaches to intestinal mucosa with buccal capsule

Question 3

What intestinal issues are Giardia associated with?

Answer 3

Malabsorption

Increases intestinal permeability and causes loss of epithelial barrier function

Question 4

Which parasites are typically associated with malnutrition of the host?

Answer 4

Helminths

Use hosts nutrients for their own growth, development, and repro

Question 5

Which parasite can cause pressure atrophy?

Answer 5

Echinocooccus granulosus larvae

Large fluid filled cysts in liver, brain, or body cavities

Question 6

Definitive host

Answer 6

Adult or sexual stages of the parasite develop

For protozoa it is just the vertebrate host

Question 7

Intermediate hosts

Answer 7

An intermediate/immature/larval stage of a parasite undergoes development to a different stage and/or multiplies asexually

Question 8

Terminal hosts

Answer 8

An intermediate host that does not allow transmission to definitive host

Question 9

Paratenic host (transport host)

Answer 9

Parasite is simply carried or transported to next host without multiplication/development

Question 10

Biological vector

Answer 10

Essential to lifecycle of parasite so also an intermediate host

E.g. tick

Question 11

Mechanical host

Answer 11

Can only carry the parasite passively

Question 12

Life cycle definition

Answer 12

The set of all phases of parasite development that culminate through sexual and/or asexual reproduction, with the production of a new generation of infective parasites.

Any life cycle may include two or more morphocytes (morphologically different types) of the same parasite

Question 13

Direct lifecycle

Answer 13

Can be complted in only a single host, may partly develop in environment

Transmitted directly from definitive host to definitive host

Question 14

Indirect life cycle

Answer 14

Two or more hosts are used for its completion

Question 15

Protozoa

Answer 15

Single eukaryotic cells

Genetic material carried on chromosomes and contained in nuclear membrane

Question 16

Helminths (metazoans)

Answer 16

Worms

Include:

Flat worms
- Trematodes
- Cestodes

Round worms
- Nematodes

Question 17

Trematodes

Answer 17

Tend to be bilaterally symmetrical and leaf like

No body cavity

Question 18

Cestodes

Answer 18

Usually extremely elongate and segmented as adults

No body cavity

Question 19

Nematodes

Answer 19

Elongate

Usually circular in cross section, tapered at both ends

Have a body cavity

Question 20

Arthropoda (metazoans)

Answer 20

Insects
Ticks
Mites

Jointed limbs
Exoskeleton of chitin

Usually metamerically segmented

Question 21

Morphology of nematodes

Answer 21

Cylindrical, tapered at both ends

Covered in translucent layer - cuticle

Muscle cells arranged longitudinally between the hypodermis and body cavity (pseudocoelom)

Alimentary tract is tubular and complete (various oesophageal forms)

Male repro tract is filamentous tubes - single continuous testis, vas deferens, spicules (inserted)

Female repro tract is a vulval opening, uterus, oviduct, ovary

Question 22

Basic lifecycle of nematodes

Answer 22

Direct -

Egg -> larval L1 -> Larval L2 -> Larval L3 infective into definitive host -> Larval L4 -> Adult -> excreted

Indirect
Egg into intermediate host -> Larval L2 -> Larval L3 (infective) excreted -> ingested by definitive host -> Larval L4 -> Adult

Question 23

What are the two most important factors affecting development and survival of nematode larvae in environment?

Answer 23

Temperature and humidity

Question 24

Optimal temperatures for nematode larval development in environment

Answer 24

18-26 degrees

So in UK almost no development in winter, slow in march/april, faster in July, Aug, Sept, ceasing about end of sept

Question 25

Optimal humidity for nematode larval development in environment

Answer 25

100% Some development occurs down to 80% But microclimate in faeces/soil may be higher than recorded humidity

Question 26

Hypobiosis

Answer 26

Temporary cessation in development of a nematode - arrested larval development

Question 27

Periparturient rise

Answer 27

An increase in numbers of nematode eggs in faeces of animals around parturition More marked in ewes, goats, and sows Hypotheses: - maturation of arrest larvae due to host immunity - increased establishment of infection - increased fecundity of existing adult worm popn

Question 28

Morphology of trematodes

Answer 28

Digestive - oral sucker - oesophagus - ventral sucker (movement) - yolk gland - 2 branched intestinal caeca) Skin - tegument - absorptive and covered in spines Nervous - pair of longitudinal trunks connecting anteriorly Reproductive - hermaphrodites - cross- and self-fertilisation

Question 29

Basic lifecycle of trematodes

Answer 29

One egg can develop into hundreds of adults - asexual repro (parthenogony) in mollusc intermediate host Adult -> eggs (within a ciliated larva develops - miracidium) -> miracidium finds mollusc intermediate host -> sporocyst (contain germinal cells that develop to rediae) -> rediae migrate to hepato-pancreas of snail -> cercariae (young flukes with long tails) produced indefinitely -> swim, shed tails, encyst to become metacercariae -> ingested by definitive host -> outer cyst wall removed by chewing -> inner cyst ruptures in intestine -> juveline fluke migrates to predilection site -> becomes adult after several weeks

Question 30

Morphology of cestodes

Answer 30

Consists of head/scolex, short unsegmented neck, chain of segments (strobila made of proglottids) Scolex - armed: has hooks - unarmed: no hooks - penetrates mucosa (hooks for anchorage) Proglottid - Each is a sexual, reproductive unit - new from the neck - immature -> mature -> gravid (full of eggs) -> last one detatches and is excreted with faeces

Question 31

Basic lifecycle of cestodes

Answer 31

Typically indirect Adult tapeworm in SI of final host All larval stages in intermediate host (dont all have the same stages) - cysticercus (fluid filled cyst, one invaginated scolex) - coenurus (similar but several invaginated scolices) - strobilocercus (scolex evaginated and connected to cyst by chain of asexual proglottids) - hydatid (fluid filled cyst with germinal epithelium which produces invaginated scolices) - cysticercoid (single evaginated scolex embedded in small solid cyst)