Parasitology: Endoparasites

Question 1

Parasite – a definintion

Answer 1

An organism that lives for an appreciable part of it’s life on (ectoparasite) or in (endoparasite) another organism (the host), is dependent on the host and benefits from the association at the expense of the host”

Question 2

Commensalism:

Answer 2

Least intimate of relationships where one or both species may benefit
Transport, cleaning, protection e.g. micro-organisms that live on skin,

Question 3

Mutualism:

Answer 3

An association where both partners benefit

Protozoa in hind gut of horses and fore stomach of ruminants

Question 4

Why study parasitism?

Answer 4

Implications to human and animal health and welfare

Many millions of pounds spent annually on prevention and control

Ubiquitous nature of parasites means they will never be eradicated completely
Can only aim to minimise damage caused

Question 5

Host

Answer 5

Definitive host
Intermediate host
Paratenic host

Question 6

How do parasites affect the host?

Answer 6

Compete for nutrients
Depress appetite
Damage skin or internal organs
Diarrhoea
Liver failure
Respiratory problems
Increase chances of secondary infections
Stimulate immune system so that the animal is more susceptible to disease

Question 7

Pathogenesis

Answer 7

Compete for nutrients
Damage gastrointestinal lining

Clinical Signs

Migrate through liver

Weight loss
Weight loss, diarrhoea, blood in feaces

Jaundice

Question 8

Endoparasite Groups

Answer 8

Trematodes
Cestodes
Nematodes
Protozoa

Question 9

Nematodes

Answer 9

Among the most ubiquitous of all animals:
Antarctic, hot springs, soil, fresh and salt water
Where there is a living organism there will be several nematodes to parasitize it!

Question 10

Cestodes

Answer 10

Indirect lifecycle
Hermaphrodites

Reliant on host – no free living stage

No mouth / anus – absorb pre-digested nutrients through tegument

Question 11

Trematodes

Answer 11

Liver and stomach flukes
Indirect lifecycle - snails
Hermaphrodites
Paedogenesis - production of many new individuals from a single larval form

Question 12

Protozoa

Answer 12

Single celled organisms
50,000 known species
Only one fifth (10,000) of these are parasitic
Important groups in terms of animal health:
Eimeriidae (Eimeria spp. and Isospora spp.)
Cryptosporidium
Sarcocystidae (Toxoplasma, Neospora)
Babesiidae (Babesia)

Question 13

Basic Nematode Lifecycle

Answer 13

egg -> L1 (free living) -> L2( free living) -> L3 (free living/ inefective) -> l4 (within host) -> l5 (within host) -> Adult -> repeate

Question 14

Cestode Lifecycle

Answer 14

Adult (within definitive host) -> Gravid proglottids shed -> Embryophore
(in environment) ->Ingested by intermediate host -> Oncosphere
(within intermediate host) -> Breaks through gut wall of intermediate host and travels to site to form a …
-> Metacestode (cyst within intermediate host) -> Remains within intermediate host until it is ingested by definitive host -> repeate

Question 15

Trematode Lifecycle

Answer 15

Eggs-> Passed in faeces onto pasture ->Miracidium -> Miracidium hatches ->Within intermediate host -> Develop to sporocyst, rediae and cercariae -> Leave intermediate host ->Cercariae -> Metacercariae -> Ingested by grazing animals -> repeate

Question 16

Protozoa Eimeria Lifecycle (example)

Answer 16

Unsporolated oocyst
->Nucleus divides - sporocysts
->Sporolated oocyst
(infective)
->Ingested – liberation of sporocysts and sporozoites within them…
->Sporozoites
t ->Penetrate gut wall cells and reproduce asexually…
-> 1st generation merozoites
->Gut cells burst when full of 1st gen merozoites…
-> 2nd generation merozoites
-> Invade more gut cells…-> Gut cells burst when full of 2nd gen merozoites…-> Male / female
->Fuse = oocysts!
-> repeate

Question 17

Transmission

Answer 17

Faeco-oral
Grazing, bedding, coat,
Fungi
Intermediate host
Paratenic hosts

Question 18

Pre-Patent Period

ppp

Answer 18

Time taken from ingestion of eggs/ larvae/ cysts to eggs being present in faeces

Question 19

Migration in regards to endo parasites

Answer 19

Gastro-intestinal parasites may remain entirely within gut during development into adults

Or may migrate
e.g. Hepatotracheal = From gut > liver > heart > lungs > trachea > gut

Question 20

Migration - examples

Answer 20

Nematodes - Toxocara canis
Parascaris equoruum
Dictyocaulus viviparous

Cestodes- Within intermediate hosts to form cysts

Trematodes-Fasciola hepatica (within intermediate and definitive
Protozoa- Toxoplasma gondii (within intermediate host)

Question 21

Hypobiosis

Answer 21

Some parasite go through a period of arrested development
E.g. Teladorsagia circumcincta infection in sheep
L4 stage larvae burrow into abomasal gut mucosa
Remain dormant for several months
Inhibited development stage with mass emergence = longer PPP
No inhibited stage = shorter PPP
Environmental or external stimulus at free living stage?
Mass emergence
Examples:
Toxocara canis
Cyathostomins
Teladorsagia

Question 22

Effects of Nematodes on hosts

Answer 22

Gastrointestinal effects – next slide
Damage to other tissues / organs where reproduce or migrate through
Triggering of immune system – local effects and susceptibility to disease

Question 23

Gastrointestinal effects

Answer 23

Parasitic gastroenteritis (PGE)

Damaging gut / inflammation resulting in mal-absorption of nutrients (diarrhoea)
Increasing nutrient demands on host to repair damaged tissue (weight loss)
Placing high immunological demands on host (more susceptible to other diseases)
Blood sucking (anaemia)
Sheer loading of parasite burden (blockages)

Question 24

Effects of Cestodes on hosts

Definitive Host

Answer 24

Nutrient absorption - weight loss
Inflammation to intestinal lining - diarrhoea
Blockage of intestines - colic

Question 25

Intermediate Host

Answer 25

Cysts within organs – liver failure, neurological symptoms,

Question 26

Effects of Trematodes on hosts

Definitive Host

Answer 26

Larval migration through liver – liver damage, rupture, death
Adults within bile duct – liver failure

Question 27

Effects of Trematodes on hosts

Intermediate Host

Answer 27

Snails damaged possibly die as result

Question 28

Effects of Protozoa on hosts

Definitive Host

Answer 28

Damage to gastrointestinal cells – diarrhoea, bloody faeces, death

Question 29

Effects of Protozoa on hosts

Intermediate Host

Answer 29

Targeting rapidly reproducing cells – abortions, still births,

Question 30

Periparturient Rise

Answer 30

Temporary relaxation of female host’s immunity around time of parturition (4 wks before up to 8 wks after)

Decreased immunity to parasites:
Hormonal interactions
Stress
Nutritional stress in late pregnancy and early lactation

Question 31

Zoonotic implications of endo parasites

Answer 31

Humans as:
Definitive host – effects as discussed throughout session today
Intermediate host – Cysts (Cestodes)
Accidental host - Visceral larval migrans, cysts,

Question 32

Implications of parasite infections

Answer 32

Infected offspring
Colic
Intestinal blockage
Pulmonary damage
Nasal discharge
Coughing
Frothy
Abortions
Gastrointestinal lining damage
Weight loss / stunted growth
Diarrhoea
Death
Organ damage
Liver failure

Question 33

summary of endoparasites

Answer 33

Many different types of parasites resulting in many different forms of damage to hosts
Parasites are incredibly adaptable with different strategies to increase spread, infection, development within hosts
Understanding lifecycles is key to successful control strategies

Question 34

Eradication of parasites

Answer 34

Eradication???  Unrealistic!
Parasites very adaptable
Eradication prohibitively expensive
Treatment and control
Predominantly chemotherapy
Resistance 
Environmental concerns
Residues
Sustainable alternatives?

Question 35

Chemical treatments

Answer 35

Nematodes- Anthelmintics - various- Oral, pour-ons, spot-ons,

Cestodes- Oral praziquantel or double dose pyrantel- Oral

Trematodes-Triclabendazole,
Closantel, Nitroxynil,
Albendazole, Oxyclozanide-Oral

Protozoa- Sulphonamides- Oral
Used in 2 ways:
Against an existing infection

Prophylactically?

Question 36

Anthelmintics for endoparasites

Answer 36

Broad Spectrum
Effective against a range of parasite species
E.g. Ivermectin

Narrow spectrum
Effective against a limited range of parasites
E.g. Praziquantel

Benzimadazoles
Levamisoles
Macrocyclic Lactones 
Amino-acetonitrile derivative (AAD)
Spiroindoles

Question 37

Anthelmintic Resistance

Answer 37

No chemical treatment is ever 100% effective
Genetically resistant parasites

Excessive, frequent dosing
Under-dosing

Question 38

Avoiding Anthelmintic Resistance

Answer 38

Accurately assess weight -correct dose given
Dose for heaviest animal
Ensure full dose is administered
Drenching technique
Rotate chemical groups annually
Some drenches are more effective on empty gut – read the instructions!
Treat at right time of year
Treat all new animals on arrival
Do faecal egg counts

Question 39

Linking lifecycle knowledge to control

Answer 39

Knowing when to administer chemicals is essential
Key periods during parasite lifecycles where they are vulnerable
1) Gastrophilus
Which time of year should you treat horses and why?
Which part of the lifecycle are you targeting and where does it live?
2) Dipylidium caninum
What do we need to treat in order to eliminate this parasite in an infected dog and why?

3) Toxocara canis
Which dogs should we treat against this parasite and why?
Which age group of dogs in particular are at risk?
When should anthelmintics be given and why?

Question 40

Reducing incidence of parasitisim

Answer 40

No system should rely solely on anthelmintics
An integrated approach to parasite control is better
Breed for resistance
Graze on bioactive forages e.g. chicory, birdsfoot trefoil,
Stocking rates
Rotational grazing
Mixed species grazing, mixed age grazing

Dung lifting / removal / pick up poo
Harrowing
Monitor consumption of potential intermediate hosts
Prevent scavenging
Keep bedding and environment clean, dry, fresh
Treat new arrivals before mixing with other animals

Question 41

Determining parasite infection

Answer 41

Faecal examination or egg count
Post-mortem
Antibody tests 
Blood
Saliva

Question 42

Faecal Egg Counts

Answer 42

Test for what?
Level of infection
Low, medium or high
What treatment is needed

Question 43

Parasite Control

Answer 43

Chemical products
Treat what is present, various periods of activity
Endoparasite products such as anthelmintics used for treatment only
Some ectoparasite products can be active for months and form part of preventive measures but resistance also reported

Question 44

Creating a control plan

Answer 44

Need to know:
Which parasites are present, any resistance?
Perform faecal egg counts
Times of year those parasites cause problems
Best time to treat against them or use management to avoid them
e.g. Nematodirus, fluke, midges,
Which management strategies apply
Which chemicals are effective against the parasites that are present

Question 45

Summary of control of endo parasites

Answer 45

No chemical parasiticide is 100% effective nor 100% ideal
Where chemicals are used, they must be used correctly!!!
Resistance cannot be prevented but must be minimised / slowed down
Need to understand lifecycle of parasites to know when to treat and what non-chemical measures can be implemented
An integrated approach to control is essential