Clinical parasitology (Yr 4) Flashcards
what would resistance to an anthelmintic be defined as?
<95% drug efficacy
what are the main nematodes causing disease in sheep?
Nematodirus battus
Teladorsagia circumcincta
Trichostrongylus spp.
Haemonchus contorts
Dictyocaulus filaria
what age is Nematodirus battus seen in sheep?
6-12 week old lambs in late spring
what is the main clinical sign of Nematodirus battus?
acute severe diarrhoea
what age is type 1 Teladorsagia infection seen?
first season grazing lambs from mid summer onwards
what the is type 2 Teladorsagia seen?
yearling in winter months (due to emergence of hypobiotic larvae
what age is Trichostrongylus seen?
lambs/replacements in late summer to autumn
what is the main clinical sign of Trichostrongylus infection?
black scour
what is the main clinical sign of Haemonchus contortus?
acute regenerative anaemia
what nematodes have a typical trichostrongyle lifecycle?
Telodorsagia circumcinta
Trichostrongylus spp.
Haemonchus spp.
what is the typical trichostrongyle lifecycle?
L3 (infective) is ingested
mature into L4 and adults
eggs passed in faeces
moult to L1, L2 and L3
L3 are eaten or overwinter
what is the pre-patent period of nematodes with a typical trichostrongyle lifecycle?
3 weeks
why does egg output from ewes rise around lambing?
peri-parturient rise (drop in immunity around lambing)
where does most of the eggs come from for Haemonchus infections?
from the ewes (doesn’t overwinter very well)
when do Trichostrongylus infections peak?
late summer
what is the main way Haemonchus survive over winter?
hypobiosis
how do lambs become infected with Nematodirus battus?
eggs shed by lambs previous year remain on pasture and will infect the next crop of lambs
what causes hatching of Nematodirus battus?
prolonged period of chill followed by increased temperature cause mass hatching on master (this coincides with lambs being turned out)
do sheep develop resistance to nematodes?
yes - if they have been exposed they will develop resistance at about 6 months old
what are the classes of anthelmintics?
- benzimadazoles (white)
- levamisole (yellow)
- macrocytic lactones (clear)
- amino-acetonitrile (orange)
- spiroindoles (purple)
how do benzimadazoles work?
prevent glucose uptake (ovicidal)
how does levamisole work?
causes paralysis of parasites (ovoidal)
how do macrocyclic lactones work?
block GABA channels to cause paralysis
what endoparasites will benzimidazoles kill?
nematodes
tapeworms
fluke (albendazole)
Nematodirus battus (little resistance)
what parasites will macrocyclic lactones kill?
nematodes and mites (injectables)
how can you test for resistance to anthelmintics?
faecal egg count reduction (compare faecal egg count before and after dosing, a reducing of <95% means that there is resistance)
drench test (FEC after dosing)
what are the SCOPS principles?
always make sure treatment is effective
reduce dependance on anthelmintics through management
avoid bringing in resistant worms through biosecurity
minimise selection for resistant worms when treating
what nematode do sheep not gain resistance to?
Haemonchus spp.
if treating at lambing time for nematodes, should you treat all the ewes?
no, treat the ones that will have the highest worm output during their peri-parturient rise such as triplets, thin ewes, ewe lambs…
what nematode is there a vaccine against?
Haemonchus (barbervax)
what clinical sign can be used as a guide for dosing Hameonchus?
pallor of eye MM (anaemia) - this is called the FAMANCHA test
how often should you sample lambs for FEC?
2-4 weeks
what nematode can FEC not be used for a diagnosis tool to guide dosing?
Nematodirus battus
why can’t FEC be used as an accurate way of deciding to dose Nematodirus?
the larval stages cause disease, so FEC won’t determine how many larva are present only adults
how should quarantined sheep be treated for nematodes?
dose with class 4 or 5 and hold inside for 2 days then place on contaminated pasture so they pick up the infections of the farm
how can selection for anthelmintic resistance be minimised?
worm when majority of worms are in the sheep and not on pasture (eg. don’t dose at lambing)
don’t dose and move (leave on contaminated pasture for a few days)
only treat thin, young or immunocompromised sheep
avoid long acting products
when do we want to dose sheep in relation to the amount of parasites on pasture?
when lowest number are on pasture, as this is a massive selection pressure
which cestode is zoonotic?
Echinococcus granulosus
what is the primary host for the majority of cestode infections?
dog
what is the clinical significance of Taenia hydatigena?
cysts in liver causing condemnation
what is the clinical significance of Taenia ovis?
cysts cause muscle damage and condemnation
what is the clinical significance of Taenia muliticeps?
cysts cause neurological disease in sheep
what is the clinical significance of Echinococcus granulosus?
cysts in liver/lungs cause condemnation
zoonotic
what is the control strategy for Monezia expansa?
worm sheep with benzimadzoles
how are Taenia spp. and Echniocccus controlled?
treating dogs with praziquantel to kill adults
no dogs faeces on pasture or scavenging of carcasses
