Parasitology: Endoparasites Flashcards
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”
Commensalism:
Least intimate of relationships where one or both species may benefit
Transport, cleaning, protection e.g. micro-organisms that live on skin,
Mutualism:
An association where both partners benefit
Protozoa in hind gut of horses and fore stomach of ruminants
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
Host
Definitive host
Intermediate host
Paratenic host
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
Pathogenesis
Compete for nutrients
Damage gastrointestinal lining
Clinical Signs
Migrate through liver
Weight loss
Weight loss, diarrhoea, blood in feaces
Jaundice
Endoparasite Groups
Trematodes
Cestodes
Nematodes
Protozoa
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!
Cestodes
Indirect lifecycle
Hermaphrodites
Reliant on host – no free living stage
No mouth / anus – absorb pre-digested nutrients through tegument
Trematodes
Liver and stomach flukes
Indirect lifecycle - snails
Hermaphrodites
Paedogenesis - production of many new individuals from a single larval form
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)
Basic Nematode Lifecycle
egg -> L1 (free living) -> L2( free living) -> L3 (free living/ inefective) -> l4 (within host) -> l5 (within host) -> Adult -> repeate
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
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
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
Transmission
Faeco-oral Grazing, bedding, coat, Fungi Intermediate host Paratenic hosts
Pre-Patent Period
ppp
Time taken from ingestion of eggs/ larvae/ cysts to eggs being present in faeces
Migration in regards to endo parasites
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
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
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
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
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
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
