Helminths Flashcards
Important direct and indirect dis causes as cause
Prod limit
Compromise welfare
Can be fatal and zoonotic
Helminths living in brain
Tapeworm larvae
Blood helminth
Flukes
Skin helminths
Filarial worms
Small intestine helminths
Adult tapeworm
Large intestine helminth
Nematodes
Muscle helminths
Trichinella larvae
Liver helminths
Fasciola adults
Adomasum helmiths
Nematodes
Lung helminths
Lungworms
Feeding
Passive eg tapeworm
Browsers eg ascarids
Solid tissue feeders eg strongyle
Blood feeders eg haemonchus
Guts and digestion
Nematodes have nouth and anus
Trematodes have mouth that food passes in and out of
Cestodss have no gut absorb nutrients through cuticle
Repro
All sexual dioecious (nematodes) monoeicious (trem and cest)
Some can also repro asex
Adults sexually mature found only in defin host
Larvae sex immature and found in int def transport and paratenic host
Eggs usually passed in faeces
Def host
Where adult parasite stages dec
Int host
Where immature stages dev in case of indirect lifecycle
Transport host
Immature stages taken up but not retained and no dev
Not essential for lifecycle
Paratenic host
Inmature stages retained in host tissue but no dev
Not essential for lifecycle
Evolution
From free living organisms in O2 starved benthic deposits
Nor highly complex with v pleomorphic genome si can overcome any eradication strategy
Become parasitic as hosts coevolved
Nematode morphology
Cylinderical tapering at both ends
Body has ridges rings and pther structures
Distinctive head
Epiderm covered by collagenous cuticle
M cells under epiderm projections run towards n cords
M layer around a fluid filled body cavity
Gut at centre of body
Nematode feeding
Compete with host for nutrients
Either mouth like struct to browse mainly close to muc surf of GIT or specialised cuticular struct eg buccal capsule and stylets to feed directly on host tissue or blood
Have true gut and excretory orifice
Rel inefficient feeders only a small proportion of ingested nutrients used by parasite
Nematode repro
Dioecious
Spec anatom adaptation to mating
Most adopt r strategy to allow rapid expansion in favourable conditions and residual level maintainance in unfavourable
Nutrients req for high egg no provided by host and esp with digestive inefficiency explains why small no canhave large impact on host
GI trichostrongyle nematodes
Direct lifecycle
Adults in prediliction site in GIT of final host
Eggs shed in faeces and dev L1 L2 and L3 free living larvae
L1 and 2 feed on bact in faeces
Outer cuticular layer of L2 retained and form protective sheath when moult to L3
L3 cant feed but migrate out of faeces into herbage to be ingested by another defin host (L3 are the infective form) once ingested L3 exsheath and moult to L4 in rumen (abomasal parasites) or abomasum (intestinal parasites)
L4 reach predeliction site and moult to L5 and become adults
Prepatent period
L3/infective stage to mature adult time
Time taken from infection to adult presence
Determine treatment interval in programmes to suppress faecal output
Angiostrongylus vasorum canine heartworm nematodes hists
Canid final host to adult (in CV syste)
Terrestrial mollisc int host (key to lifecycle but only larval stages in them)
Amphibian paratenic host
Free living nematode enviro conditions
Most teichostrong eggs survive best at 18-26 degrees at higher temp dev is faster but energy rate more quickly depleted so incr mortality rate
Eghs dont hatch or larvae dev at temp below 10
Larval dev only when humidity over 80% and optimal at 100 survival low at below 80 in herbage
Humidity in grass and faeces allows dev when dry
Dessication kills L3
Nematode survival stretegy
Thick walled enviro res eggs (ascarid) Retention of L2 cuticle sheath on L3 assist harsh enviro survival (trichostrongyle) Arrested dev/hypobiosis Critical egg hatching req Periparturient rise in egg prod
Arrested dev hypobiosis
Temporary pause in dev in host as evolutionary strategy to survive adverse enviro conditions
Physiological- toxocara canis - larvae enter hypobiosis in tissues and are react 3 wk pre parturition and migrate to and infect foetus
Seasonal - ostergaia ostertagi - larvae ingested in autumn and overwinter in abomasal gastric glands larval dev resume in spring
Crit egg hatching req
Larvae overwinter in eggs
Hatch onto pasture in spring after receiving enviro trigger usually temp
Allow mass emergence in spring when many suscept hosts around
Periparturient ruse
Incr faecal egg count of ewes and goats around parturition
Competition between host imm stst and pro req of pregnancy and lactation so arrested larvae mature incr new infect establishment incre female egg output
Platy helminthes
Cestodes and trematodes Dorso ventr flattened No bidy cavity Organs embedded in solid matrix Monoecious Both sex and asex repro Some trematodes are triploid
Trematodes - flukes
Unsegmented leaf like
One or two suckers for host attachment
Blind gut with single opening
Indirect lifecyvle with one or two int hosts one of which is always a mollisc
Cestodes - tapeworms
Segmented
Very ling sometimed
Usually have a distinct scolex/head with hooks and or duckers for hist attachment
Identical proglotids (segments) continually prod form neck of scolex
Proglottids flat white and rectamgles in tape form known as strobila
Mature into self cont hermaphroditic egg prod units
No gut-nutrients diffuse through cuticle
Indirect lifecycle with vert and invert int host
helminth host balance
Upset by domestication and intensive farming dev creating enviros that:
Suited to dev and survival of free living stages with enganced exposure to infective forms
Inadvertantly alter host imm or inn resp
Enable exposure to prev unrecog species and strains
Can upset sustainable equilibrium between parasote and host
Can guve competetive advantage to some allowing them to presominate and be more patjogenic
Control
Evasion : low stocking densities on variety of herbage and co grazing or browsing with other animals that are hosts to same parasites
Grazing rotation
Seldom conducive to economic prod
Strategic use of anthelmintics aim to suppress infective larval pop, due to highly pleomorphic genome they will become res
Most farms and pet owners etc have become athlemintic dep to maintain productivity and good welfarr
Used to strike balance between level of challenge that impairs an animal and that needed to enable protective imm dev
Anthelmintic problems
Effect of climatic variation on livestock and helminths
Freq stockpvement and quarantine impracticality
Sub efficacy of some drug usage
Innapripriate timing of administration
Effect of concurrent dis or managment on anthelmintic action
Important public health concerns
Hook worms and cutaneous larva migrans
Ascarid and visceral nematodes
Human fasciolosis
Exhinococcus tapeworm
