Endoparasites - Nematodes, T. gondii, Fasciola spp. Flashcards
What is a parasite?
An organism which is metabolically dependent upon another where one benefits at the expense of another.
Describe the structure of a nematode.
- Cylindrical
- Radial symmetry
- Can be free-living and parasitic
- Dioecious
- Vary in size
What are the common names for nematode, trematode and cestode?
Round worm, fluke and tapeworm
What are the structural features of a trematode
Some free living and parasitic species
Dorso-ventrally flattened
Mainly hermaphrodite
What is a platyhelminth?
A flat worm
What is the average size of a cyathostomine?
1cm
Name the species of stronglyus we concentrate on.
S. VulgarisS. EdentatusS. Equinus
- How can you differentiate between strongylus species?
- Which species is shown here?
Head shape/ mouth piece
Vulgaris - Mickey Mouse mouth piece
Edentus and equinus - no teeth in mouth piece
What is meant by a direct parasitic lifecycle?
One where the parasite only infects a single host species
Name the order of the cyathostomine lifecycle.
Eggs – larval 1 – larval 2 – early larval 3 – late larval 3 – larval 4 – larval 5 – eggs
Which larval stage is considered the infective stage of development which can cause infection of the horse?
L3
How long does it take for cyathostomine eggs to develop into the infective stage?
2+ weeks
What are the defining features of cyathostomine eggs?
80 micronsOvalThin shelled Undifferentiated morula
What temperature must be exceeded for eggs for cyathostomines to develop?
10 degrees
Which larval phase of cyathostomine development matures and mates to form eggs? What is the fate of cyathostomine eggs?
L5They are expelled in the faecal pat
What is the average size of an infective L3 cyathostomine?
150 microns
What happens to the L3 cyathostomine when they are ingested by the horse?
They loose the L2 sheath which protected them on pasture
How long is the lifecycle of cyathostomine within the horse?
6-8 weeks
Hypobiosis
Parasite driven arrest in development within the host.
Which states of cyathostomine development undergo Hypobiosis?
EL3, LL3
What time of year would cyathostominosis occur usually?
Late winter/ spring
What is the 80:20 rule of cyathostomines?
Eighty percent of the burden in twenty percent of the population
What climatic features are required for parasitic development on pasture?
>10 degrees CelsiusHumidityRainfall which disperses the pat
What management protocol can be introduced to reduce cyathostomine present on pasture?
Removing faecesHarrowing, spread around and dry the faecesRotational grazing of the pastureBiological control - nematode trapping fungi
Which Anthelmintics are used in the control of cyathostomines?
IvermectinMoxidectinBenzimidazolesPyrantel
Which Anthelmintics has/ had the highest efficacy against nematodes?
Ivermectin
What characteristic features define Galba Truncatula?
Amphibious, fresh-water snail, feeds on algae, found at the edge of rivers and in puddles
What is meant by an indirect parasitic lifestyle?
One in which an immediate host is required before entering the definitive host
Which geographical areas are Fasciola Hepatic found?
EuropeAustraliaSouth AmericaHigh altitude tropics
Which geographical areas are Fasciola Gigantica found?
Hot, humid tropicsAsia
Where are juvenile Fasciola found within the body during a fluke infection?
Liver
Where are adult fluke found within the body during a fluke infection?
Bile ducts
Which structural component of Fasciola causes inflammation during fluke infections?
Spines on the outer surface
Multifocal necrotic/ haemorrhagic tracts in the liver are characteristic of which phase of fluke lifecycle?
Juvenile migration
Expulsion of cercaria causes _______ of the intermediate host.
Death
Which stage of the fasciola lifecycle is found on grass in the pasture and is considered the infective stage?
Metacercaria
How long does it take cercaria to locate substrate for development once they are expelled from the snail?
0-3 hours
How many cercaria are produced from one redia?
Hundreds
How many redia are produced from one sporocyst?
6-8
Name the stages of the Fasciola lifecycle, in order.
Eggs, embrionation, miracidium, sporocyst, redia, cercaria, Metacercaria, juvenile fluke, adult fluke
The encystment of Metacercaria is made from what?
Calcerous material
Which stages of the fluke lifecycle are found within the snail?
Sporocyst and redia
What is the appearance of Fasciola eggs?
Similar to cyathostomines but yellow due to absorbance of bile salts
How large are the eggs of Fasciola hepatica
150 micrometers
How does the miracidium of fluke hatch out of the embryonic shell?
Through the operlum, a type of lid
How long is the embryonic stage of fluke development?
2-4 weeks
Through October to January which type of Fasciola disease would be found and why?
Acute
Fluke mature on pasture over the late summer and autumn due to favorable climate and are ingested in large numbers. Migration of juvenile fluke through the liver causes clinical disease.
What post mortem features can be found in a sheep with acute Fasciola infection?
Anaemia - pancytopenia? Erythropenia?Necrotic and haemorrhagic tracts in the liverEnlarged liverLiver fibrosis
Metacercaria are ingested over a long time - fewer in number with both juvenile and adult fluke being found. This statement characterises which type of Fasciola disease?
Sub-acute
Hyperplasia of bile ducts, fibrosis, calcification and cholangitis are characteristic of which type of Fasciola infection?
Chronic
Bottle jaw describe which clinical symptom?
Sub-mandibular oedema
How many and where are suckers found on the fluke?
2 - oral and ventral
What are the function of the suckers found on Fasciola?
Sticking to bile duct wall and feeding on blood
A temperature of _____ and _____ time may cause death of eggs on pasture in the fluke.
<0 degrees CelsiusLong
How do Fasciola stages survive over winter on pasture?
- Fluke in snails during hibernation
- Metercercaria
- Eggs
- Carrier animals
Which temperature is vital for snail development?
7-10 degrees
Which Anthelmintic is used to treat all stages of the Fasciola lifecycle?
Triclabendazole
Closantel is active against which stage of the fluke lifecycle?
Mature and immature fluke
Name the three main groups of anthelmintic drugs.
Benzimidiazoles
Imidathiazoles/ tetrahydropyramidines
Macrocyclic lactones
Outline the mechanism of action of benzimidazoles.
They bind to beta-tubulin in the parasite and therefore inhibit microtubule mediated transport. Preventing transport and enzyme secretion - nutrition etc
Ovicidal
Causes death of eggs.
Outline the mechanism of action of 2LEV’s
Act upon nicotinic acetyl choline receptors affecting somatic muscle cells
LEV/PYR are mainly effective against which stages of nematode development?
Gut dwelling stages
Avermectins and Milbemycins are examples of which class of anthelmintics?`
Macrocyclic Lactones
Which class of anthelmintic drugs act upon GABA glutamate-gated chloride channels?
macrocyclic lactones
How do macrocyclic lactones affect GluCls?
They cause hyperpolarisation of parasitic cells by potentiating GluCl’s - keeping them open for longer.
Which stages of nematode development are ML’s used against?
Migrating larvae and hypobiosed larvae
Praziquantel is a potent drug against which type of helminth? At which life stage?
Cestode - adults
Name the three types of “new” anthelmintics.
Amino Acetonitrile
Spironidoles
Depsopeptide
What is meant by strategic dosing of anthelmintics?
Treating for the parasite when numbers are highest. This therefore disrupts the seasonal cycle of transmission.
“Treating at regular intervals based upon egg reappearance period”
This statment characterises which type of anthelimintic strategy?
Interval dosing
Which type of anthelmintic control strategy involves dosing for worms based on specific diagnostic parameters?
Targetted dosing
Ivermectin and selamectin are examples of which Macrocyclic lactone?
Avermectins
When using pyrantel to treat a cestode infection in the horse how much more would be given than when normally using this drug?
Twice normal dose
Which classes of anthelmintic drugs can be used to treat the hypobiosed larval stage of development?
Benzimidazoles
Macrocyclic lactones
Name a anthelmintic drug which has residual activity of 2 weeks
Ivermectin
Ivermectin can be toxic to which type of dog and is therefore contraindicated in breeds with this characteristic?
Long nosed dogs
eg Sight hounds
What is meant by drug resistance?
A specific drug at a specific dose no longer has its desired effect.
A heritable trait of parasites
Fasciola Hepatica have shown resistance to which drug which has been key to their control in the past?
Triclabendazole
Which class of anthelmintic has shown to have the most extensive resitance amongst helminths?
BZ’s
“Resistance is a reversible trait”
True or false?
False - Resistance is non-reversible
What is meant by the “in refugia” population of parasites?
Those which have not yet been exposed to the drug and have therefore not developed resistance.
How does anthelmintic resitance occur?
Overuse of anthelmintic drugs causes a selection pressure which favours those parasites with resistance genes. There numbers therefore increase until they are the majority strain
Draw and label a toxoplasma gondii tachyzoite.
Are T.gondii an example of an actively motile or non-motile endoparasite?
Non-motile, they glide around the body.
What is the function of the apical complex of T. gondii?
Attachment to and invasion of the host.
What are the names of the dense granules found in a T.gondii cell?
Micronemes, rhoptries
Outline the lifecycle of T.gondii.
Which lifecycle stage is infectious to the intermediate host?
In which phase can transplacental transmission occur?
Oocyst > sporulated oocyst > sporocyst > sporozoite > ingested sporozoites penetrate cells > tachzoite (rapidly divide in cells) > free tachyzoites > bradyzoite (cysts, slow developing)
Name the intermediate and definitive host of T.gondii.
Intermediate - Rat, mice (prey species), humans (warm-blooded mammels)
Definitive - cat
How do tachzoite and bradyzoite differ?
Tachyzoite - Intracellular, Rapidly dividing, Crescent shaped, 2x6um
Bradyzoite - Found within bradyzoite cyst in muscle or neural tissue, slow growing, persistent
How are T. gondii transmitted?
Ingestion of meat infected with tissue cysts. Transplacental trasnmission to the foestus during pregnancy.
What effect can T. gondii have on:
a) Immunocompromised patients
b) Pregnant women
c) Sheep ?
a) Toxoplasmic encephalitis (AIDs)
b) Foetal effects: hydrocephalus, retinochorioditis (2-3yrs blindness), convulsions, intracerebral calcification
c) Lambs: mummification in early gestation, abortion, still birth, strawberry lesions on the cotyledons, congenital infection. Ewe: barren, infertile
How can an infection of T.gondii be diagnosed in the ewe?
- Serology detects antibodies - dye test, IFAT, agglutination tests
- Histology of cotyledons or brain shows non-suppurative inflammation
How can T. gondii be controlled in sheep?
Since infection provides strong immunity any potential infection (eg by introduction of new stock) should occur well before tupping. Vaccination program (live, attenuated tachyzoite vaccine using S48 strain which doesn’t form cysts)
How is T. gondii controlled in humans?
Chemotherapy (using pyrimethamine and sulphonamides), reduing the risk of infection (washing vegetables, making sure meat is cooked properly)
Which type of cat is the main reservoir for T.gondii?
Farm and stray cats - those who do more hunting.
It is suspected that T. gondii has what effect on behaviour of prey species? How does this affect prevalence?
Individuals infected with T. gondii are less inhibited and fearful regarding preditors, they are therefore more likely to be caught by cats and therefore transmit the parasite.
It is predicted that a single cat can have an output of how many oocysts? How many are required to cause abortion in sheep?
10^8
10^3
How many sporocysts and sporozoites are contained within an oocyst?
Two sporocysts in each oocyst each containing four sporozoites each.
