Parasitology: Endoparasites Flashcards by Beth Finlay

Parasite – a definintion

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”

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Commensalism:

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

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Mutualism:

An association where both partners benefit

Protozoa in hind gut of horses and fore stomach of ruminants

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Why study parasitism?

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

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Host

Definitive host
Intermediate host
Paratenic host

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How do parasites affect the host?

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

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Pathogenesis

Compete for nutrients
Damage gastrointestinal lining

Clinical Signs

Migrate through liver

Weight loss
Weight loss, diarrhoea, blood in feaces

Jaundice

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Endoparasite Groups

Trematodes
Cestodes
Nematodes
Protozoa

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Nematodes

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!

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Cestodes

Indirect lifecycle
Hermaphrodites

Reliant on host – no free living stage

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

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Trematodes

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

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Protozoa

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)

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Basic Nematode Lifecycle

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

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Cestode Lifecycle

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

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Trematode Lifecycle

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

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Protozoa Eimeria Lifecycle (example)

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

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Transmission

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

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Pre-Patent Period

ppp

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

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Migration in regards to endo parasites

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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

Migration - examples

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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)

Hypobiosis

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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

Effects of Nematodes on hosts

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

Gastrointestinal effects

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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)

Effects of Cestodes on hosts

Definitive Host

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

Intermediate Host

Cysts within organs – liver failure, neurological symptoms,

Effects of Trematodes on hosts | Definitive Host

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

Effects of Trematodes on hosts | Intermediate Host

Snails damaged possibly die as result

Effects of Protozoa on hosts | Definitive Host

Damage to gastrointestinal cells – diarrhoea, bloody faeces, death

Effects of Protozoa on hosts | Intermediate Host

Targeting rapidly reproducing cells – abortions, still births,

Periparturient Rise

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

Zoonotic implications of endo parasites

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

Implications of parasite infections

``` 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 ```

summary of endoparasites

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

Eradication of parasites

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

Chemical treatments

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?

Anthelmintics for endoparasites

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 ```

Anthelmintic Resistance

No chemical treatment is ever 100% effective Genetically resistant parasites Excessive, frequent dosing Under-dosing

Avoiding Anthelmintic Resistance

``` 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 ```

Linking lifecycle knowledge to control

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?

Reducing incidence of parasitisim

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

Determining parasite infection

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

Faecal Egg Counts

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

Parasite Control

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

Creating a control plan

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

Summary of control of endo parasites

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

Parasitology: Endoparasites Flashcards

(45 cards)