Parasitology Flashcards
What anatomical features can be used to determine taxonomic groups of nematodes?
- Structure of buccal capsule (teeth plates vs plates)
- Bursa
- Spicules
- Intestinal cells
- Features of eggs
Describe the common features of nematodes in the superfamily Trichuroidea
- Male posterior coiled
- Females longer
- Bioperculated eggs
What are the important genera found in the family Trichostrongylidae?
- Trichostrongylus
- Haemonchus
- Ostertagia
- Nematodirus
- Cooperia
- Hyostrongylus
- Teladorsagia
Describe the appearance of Nematodirus eggs
- Very large (175-75um)
- Obvious 2-8 cells (morula)
Describe the appearance of Strongyle eggs
- Similar to Nematodirus
- Thin shelled, conspicuous morula
- Know it isnt nematodirus as are only found in the horse
List the important families of the superfamily Strongyloidea
- Strongylidae (horses)
- Chabertiidae (sheep, pigs)
- Syngamidae (birds, pigs in tropics)
List the important genera of the family Strongylidae
- Strongylus
- Triodontophorus
- Cyathostomum
- Cylicocyclus
- Cylicodontophorus
- Cylicostephanus
What are the important genera of Charbertiidae?
- Charbertia
- Oesophagostomum
List the important families of the superfamily Ascaridoidea
- Ascaridiae
- Ascaridiidae
- Toxocaridae
- Hetrakidae
List the important genera of the family Ascarididae
- Ascaris
- Parascaris
- Toxascaris
Describe ascarid eggs
- Round
- Thick shelled
- Proteinaceous outer coating
- Very resistant
List the important abomasal worms of cattle
- Haemonchus placei
- Trichostrongylus axei
- OStertagia ostertagi
List the important small intestinal worms of cattle
- Cooperia oncophora
- Trichostrongylus colubriformis
- Nematodirus spathiger
- Chabertia
- Oesophagostomum
- Trichuris
Describe the general nematode life cycle
- Adult worms in GI tract (males and females)
- Strongyle-type egg in faeces
- Free-living L1 larval stage
- Free-living L2 larval stage
- Infective L3 in L2 sheath ingested with water droplets on herbage
- L4 migrating larvae wihin GI causing pathology
Describe the life cycle of Nematodirus
- Eggs in faeces
- Develop to L3 in egg
- L3 hatches
- Ingested with herbage
- Moult from L3 to L5 in host
Describe the life cycle of Ascarids
- Eggs in faeces
- L1 to L2 in eggs
- Eggs containing L2 ingested from contaminated pasture
- Hatch in intestine
- Migrate to HP vein and liver, L3 develops
- Migrate to heart and lungs (L4 develops)
- Coughed up and swallowed
- Adults develop in intestine
Describe the life cycle of Trichuris
- Eggs in faeces
- L1 in eggs
- Ingest eggs containg L1 from contaminated pasture
- Hatch in small intestine
- Migrate to LI
- Moult from L1 to L5 in host
Name the types of oesophagus present in nematodes
- Rhabditiform
- Filariform
- Bulb
- Double bulb
- Musculargalndular
- Trichuroid
Describe strongyle type eggs
- Elongated
- 75-95um x 40-50um
- Similar to hookworms, but larger
- Ends more pointed
- Lots of cells visible inside
Describe nematode respiration
- Gaseoues exchange across cuticle
- Aerobic and anaerobic phases
- TCA, glycolysis and alternative pathway
- Dependence on pathway varies with location and life cycle stage
- O2 in GIT low, free livign O2 high
- Glycolysis genetically wasteful, only 2 molecules of ATP vs 36-37 in TCA
- Glucose in abundance in intestine, wastefulness unimportant
- Glycogen is major energy reserve
- Some can use CO2 to benefit (few)
Describe the role of lipids in nematodes
- Important energy reserve in eggs adn free living larvae
- Used as energy source in aerobic conditions
- Cholesterol important sterol in cell membranes
- Sterols needed as hormon precursors
- Can also excrete/secrete lipids that influence host biology
Describe the role of tubulin and microtubules in the metazoan animals
- Similar to other eukaryotic organissm microtbules importat to the functioning of nematode cells
- alpha and beta-tubulin subunits form heterodimers
- Polymerised to form microtubules
- Meiosis, mitosis, cytokinesis and molecular transport utilise network of miccrotubules in nematodes
What are the muscle types found in nematodes?
- Longitudinal and radial
- NO circular!
Describe the muscles of nematodes
- Obliquely striated
- somatic muscles below cuticle used in locomotion
- Dense bodies rather than Z discs
- Each dense body and sarcomere attached directly to muscle cell membrane
- M line attaches filaments to each other and to the plasmalemma within each sarcomere
- Attached directly to motor neurones
Describe the locomotion of parasites
- Hydrostatic skeleton
- Force applied on off
- Forces opposed by hydrostatic pressure of coelom
- Dorso-ventral bending
- ACh = contraction = bends up, facilitated by GABA on top part = relaxation allowing bending
Describe the structure of the pharynx of nematodes
- Buccal capsule
- Procorpus
- Metacorpus
- Isthmus
- Terminal bulb
- Pharyngeal glands present
- pharyngeal muscles throughout pharynx
Describe the role of the pharynx
- Feeding
- Connects buccal capsule to intestine
- Secrete substances which may influence host biology
- Pumping action but also peristalsis
Describe the nematode nervous system
- Circumpharyngeal commissure (aka nerve brain)
- Around isthmus of pharynx
- System has a few hundred neurones (+ and -)
- Ventral dorsal nerve cords go back from nerve ring
- Connected by more commissures
- Pharyngeal nerves extend anterior from nerve ring
- Complex array of neurotransmitters and receptors
What are the important nematode neurotransmitters?
- ACh, GABA, glutamate, serotonin
- Dopamine, adrenaline, noradrenaline
What neurotransmitters of nematodes are teh best targets for therapeutics?
- ACh
- GABA
- Glutamate
- Serotonin
Describe the inhibitory neurotransmitters of nematode pharyngeal neurones
- Glutamate and GABA
- Bind to receptors in post-synaptic neuronal membranes
- Opens receptor, allows passage of Cl- but not cations
- Hyperpolarisation
- Inhibits muscle contraction
Describe the excitatory neurotransmitters of the pharyngeal nerves
- Serotonin induces rhythmic contractin of pharyngeal muscles (pumping)
- ACh controls rate of pharyngeal pumping
- Some FaRPS (not important)
Describe the action of ACh and GABA in locomotion
- ACh excitatory to contraction
- GABA inhibitory to contraction
- Antagonistic pair
- To generate upward flexion of body, ACh active on ventral side to generate contraction, GABA active on dorsal side to generate relaxation allowing flexion
Describe the role of GABA in nematode defaecation
- Excitatory for defaecation
- Need to defeacate when feeding otherwise will explode
What is the importance of nematode excretory/secretory produces?
- Make host environment beneficial to parasite
- Major source of nematode antigen
- Can inhibit contractino of host intestine preventing removal of parasite
What are some of the excreteory/secretory proteins produced by nematodes?
- AChE - function unknown
- Vasoactive intestinal peptide may secreted, may inhibit intestinal contraction
Describe some nematode lipids which influence host biology
- Polyunsaturated fats (arachidonic acid) react with cyclo-oxygenase to produce prostagalndins and leukotrienes
- Arachidonic acid can be used to produce unstable PG precursors, synthases produce series of PGs from these
- PGs inhibit immune response
Explain how benzimidazoles exert their action
- Inhibit beta-tubulin polymerisation
- No productino of microtubules
- Basic life processes not possible, no reproduction, eventually die
Explain how proton ionophores can be used as anthelmintics
- Alter H+ gradients
- No more synthesis of ATP
- Basic life processes cannot take place, unable to reproduce, die
Explain how diethylcarbamazine can be used in anthelmintics
- Blocks arachidonic acid synthesis
- No more production and secretion of PGs
- Unable to generate favourable host environment
- Immune system can tackle infection
Explain how GABA inhibitors can be used in anthelmintics
- GABA excitatoryto defaecation
- Need to defaecate when feeding or will explode
- Inhibitors e.g. ivermectin prevent this so wil die
What is meant by pseudocoelomate?
An invertebrate that has a fluid filled body cavity not lined with mesoderm tissue
What is meant by dioecious
Having male and female reproductive organs in separate organs
What is meant by cephalisation?
The concentration of sense organs, nervous control etc at the anterior end of the body forming head and brain both during evolution and during the course of the embryo’s development
What are nematodes, cestodes and trematodes?
- Nematodes: nemathelminths, roundworms
- Cestodes: platyhelminths, segmented flatworms
- Trematodes: platyhelminths, non-segmented flatworms
Describe gerenal features of nematodes
- Pseudocoelomate
- Bisymmetrical, non-segmented
- Dioecious
- Females larger than males
- 4 larval moults before becoming adults
- Usually L3 that are infectious
- Cephalisation
- Buccal capsule
- Oesophagus and digestive tract present
- Reproductive tract
- Complex nervous system with many different NTs
Give the main features of Monezia expansa
- SI of ruminant adults, cysticercoids in mites
- Long tape worms - 2m or more
- Suckers
- 2 sets of genital organs visible along lateral margin of each section
- Cestode
Describe factors that shows that parasitic infection is a dynamic balance between host and parasite
- More parasites during periods of reduced immune competency (spring rise)
- Parasite has effect on host immune system, reducing its effect
What is the succession of important GI nematodes on pasture?
- June: Nematodirus
- July: Teladorsagia
- Sept: Trichostrongylus
What is meant by succession of nematode species on pasture?
Genera peak at different times of year depending on favourable conditions
What is the importance of succession of nematode species on pasture?
- Animals constantly exposed to parasitic threat
- Over summer on pasture, will be infected with different nematodes at different times
- In some cases immuntiy will occur quickly while in other cases will take long time
Describe immunity to N battus in young lambs
- Immune response to this faster than to other nemaodes (occurs at less than 3 months, 6-7months for others)
- N. battus hatches early, very young lambs exposed
- With immature response will die so need to have an early response
How can immunity be measured?
- Reduced worm burden
- Increased larval arrest
- Low faecal egg count
Outline some of the innate host response mechanisms to parasitic infection
- N. battus coils around villi so villi are shed - clears infection
- Mast cells and eosinophils
- Serum IgM converts IgG as infection progresses - attract eosinophils
- IL-5 and IL-13 stimulate chemotaxis and degranulation
Outline some of the acquired immune response mechanisms to parasitic infection
- Th2 cells
- IL-4, B cell activator - promotes differentiation into plasma cell to produce different antibodies
Why does sterile immunity never occur in cattle infected by O. ostertagi?
- L4 and adults suppress T cell division
- DCs and macrophages presenting Ostertagia antigens may induce regulatory (suppressor) T cells
- Production of important cytokines reduced with Ostertagia
What are some mechanisms of immune evasion employed by parasites?
- Hypobiosis
- Evading host immune response
- Neonatal immunological unresponsiveness
- Concomitant immunity
- Polyclonal stimulation of immunoglobulin
Describe how some parasites are able to evade the host immune response
- Produce cuticular proteins not recognised by immune system
- e.g. Pinworms - little pathology or immune responsiveness
Describe how neonatal immunological unresponsiveness can aid parasitic infection
- Sometimes do not have vigorous enough immune response until exposed to reinfection
- Reduce immune response of foetus in situ
- When first born has to be exposed to pathogen
- Immune response working, but not seen disease before so gets disease before immuntiy built up
Describe concomitant immunity
- Immunity which protects from subsequent infections but unable to clear existing
- Parasites coated with host antigen, not recognised by immune response
- Immune response for other parasite and remove these
Describe polyclonal stimulation of immunglobulin
- Some nematode species stimulate polyclonal IgE
- Mast cell may be coated with IgE that does not recognise parasite antigen
- Mix of different antigens and Ig produced, not very effective
Explain how Ostertagia can suppress the immune response
- Produces GH-beta
- This suppresses Th1 and Th2 systems
- Activates suppressor T cells
- Reduces immune attack
Explain the importance of hypobiosis in clinical disease
- Arrested development/arrested larval development
- Some larvae of nematode stop developing in host
- Biological switching to ALD when unfavourable conditions
- Switch back on to growth when favourable conditions e.g. through stress such as pregnancy/birth or environmental conditions like weather
- Important in timing of treatment and pasture management
List GI nematodes in which hypobiosis is important
- Ostertagia ostertagi
- Cooperia spp.
- Haemoonchus contortus
- Teladorsagia circumcincta
Briegly outline the consequences of hypobiosis in O. ostertagi
- Arrested in gastric gland of host
- All develop at same time, destroys large numbers of gastric glands when reactivate
List important factors on hypobiosis
- Phenotype
- Temperature
- Moisture
- Stress
- State of host immune system
Describe how spring rise occurs
- Eggs and larvae overwintered on pasture
- Low immune competency just before lambing and after
- Arrested L4 develop into adults and produce eggs
- Eggs excreted by sheep from 2 weeks before and 4-6 weeks after birth
- L3 acquired from pasture
- Increased number of eggs and L3 on pasture at same time as new borns and susceptible ewes
- Increase of disease incidence in spring
Explain the disease management where peri-parturient rise is likely to occur
- Some anthelmintics kill arrested larvae, other do not
- Use anthelmintics just prior to lambing
- Rotation of pasture to avoid putting lambs and ewes on pasture with overwintered eggs and larve
- Need to know how long they can be viable in the environment in order for rotation to be effective
Describe the life cycle of Toxocara canis in pups
- Eggs containing L2 ingested
- L2 hatches
- Tracheal migration (L2 to L3)
- Swallowed
- L3 to L4 in stomach
- Adults in SI
Describe the life cycle of Toxocara canis with transmission to pup from dam
- Eggs containing L2 ingested
- L2 hatches and migrates to liver
- Somatic migration of L2
- Encyst in tissue
- In pregnant bitch can have transplancental migration of L2 to foetal liver then neonatal lung
- Can also go via mammary gland (L2-L3) and L3 ingested by suckling pups
Describe the life cycle of Toxocara canis via a paratenic host
- Dog ingests paratenic host (mouse)
- L2-adult in dog intestine
Outline the difference between Toxocara cati and Toxocara canis life cycle
- Similar
- cat infected by ingesting eggs or paratenic host
- Kittens infected transmammary
- No in utero infection in cats
Describe the life cycle of Oxyuris equi
- Horse ingests eggs containing L3
- L3 to L5 in intestine
- Adult inhabits caecum, colon, rectum
- Female migrates to anus to lay eggs
- Develop to L3 in egg
What are the pathological effects of Nematodirus battus?
- Many burrowing larvae ingested at once
- Can cause acute diarrhoea and death in lambs
- Larvae are cause of pathology
What are the pathological effects of Cooperia punctata?
- Adults burrow into SI and cause little pathology except in heavy infections
What are the pathological effects of Trichostrongylus axei?
- Adults penetrte lining of abomasum and sometimes SI
- Reduce appetite
- Cause diarrhoea
What are the pathological effects of Trichostrongylus colubriformis?
- Larvae and adults cause pathology
- Chronic diarrhoea in adults
- Acute diarrhoea in younger animals
- may cause bottle jaw
Describe the life cycle of Ancylostomatidea
- L3 ingested or penetrate the skin
- Eggs in faeces
- L1 hatch and develop to L3
Describe Ostertagia ostertagi
- Abomasal worm
- Cattle
- Trichostrongyle
- Nematode
- Brown stomach worm
- Bursate
- Square head
- 16 intestinal cells
- Generic nematode life cycle
Describe the effect of Ostertagia ostertagi on gastric glands
- L4 emerge from gastric glands causing pathology
- HCl not produced
- pH increases
- High pH prevents conversion pepsinogen to pepsin
- Reduced protein digestion
- Pepsinogen and gastrin increase in blood
- Blood proteins increase in abomasum abomasum (hypoalbuminaemia)
What are teh clinical signs of Ostertagiasis?
- Severe diarrhoea
- Rapid weight loss
- Cobblestone lesions as gastric glands are destroyed
- Sub-mandibular oedema (bottle jaw)
Describe immunity to O. ostertagia
- First immune response does not protect agains reinfection with L3
- Delays larval development, increases number of inhibited worms - immune induved hypobiosis
- Second immune response may take up to 2 years
- No sterile immunity
- Eosinophils and mast cells increase in intestine
- Th1 and Th2 cytokines present
What are the control measures for O. ostertagi?
- Ivermectin (kill hypobiotic L4)
- Frequent drenching around calving (prevent type II)
- Frequent drenching in first grazing season (prevent type I)
- Lower stocking density
- Rotate calves and adults
- Rotate onto fresh pasture
How can O. ostertagi be diagnosed?
- McMaster slides to count eggs
- Adults on necropsy
- Condition of abomasum (cobblestone)
Describe Haemonchus contortus
- Abomasal
- Sheep
- Trichostrongyle
- Barber’s pole worm
- Normal nematode life cycle
What happens in Haemonchus contortus infections?
- Anaemia due to feeding of worms
- May cause death
- Diarrhoea
- Loss of body condition
- Loss of wool quality
- May cauase bottle jaw
How is infection with Haemonchus contortus be diagnosed?
- Famacha scale (anaemia)
- McMaster technique
- Adults on necropsy (final diagnosis)
- Red haemorrhagic surface of abomasum
Describe type I Ostertagiasis
- Younger animals when enough L3 have been ingested
- Hypobiotic larvae activated in mother, more eggs released, increased risk of calf infection
- April/May
- Pasture grazed in previous years
- L3 overwinter so large numbers already present
- Peak is Aug/Sept
Describe type II Ostertagiasis
- Animals old enough to have arrested larvae from previous grazing seasons
- Already in animal
- Reactivated larvae, infect host
- In early autumn to late winter
- Or calves 9-12 months
What is the global significance of Haemonchus contortus in sheep and goat farming?
- Anthelmintic resistant
- Makes sheep farming non-sustainable in some areas
How can anthelmintic resistance be tested?
- Faecal egg coutn reduction
- Compare number of eggs before and after treatment
- Less than 60% reduction in number of eggs = resistance
Describe the McMaster technique
- Known mass of faeces
- Known vol of saline
- Add 10ml to faeces, shake to break
- Homogenous solution
- Strain, continue adding saline
- Use pipette o put final solution on McMaster slide
- View under LM
- Methodically count
- Calculate number of eggs per g of faeces
- (ml solution used x no. of eggs)/(vol of both sides of McMaster combined (usually 0.3)xmass of faeces used)
Describe the epidemiology of Nematodirus
- Trichostrongyle
- Common in temperate zones
- Scottish border, Northern England
- Small intestine of ruminants
List the common species of Nematodirus and their host species
- N. battus: Sheep (occasionally calves)
- N. fillicolis: sheep
- N. spathiger: sheep and cows
- N. helveticus: cattle
What stimulates N. battus hatching?
- Cold period followed by mean day/night temperature of around 10degreesC
- Is L3 that hatches
What is the importance of the N. battus egg?
- Extremely tough
- Resistant to freezing and drought
- Viable up to 2 years on pasture
- Hatching does not only occur in spring from eggs excreted in previous year
- Some eggs deposited in spring can hatch in autumn of same year
What are the clinical signs of infection with N. battus?
- Acute onset in young recently weaned lambs (6 weeks -4 months)
- Rapid weight loss
- Watery diarrhoea
- Dehydration
- Sudden death
What is the pathology of N. battus caused by?
- Developing larval stages and their migration
- Leads to damaged villi and erosions of mucosa
Describe the L3 larval appearance of N. battus
- 8 gut cells
- Head braod, rounded sheat
- Tail filamentous and exsheathed
- Tail notched or lobed
Compare N. battus eggs with other Nematodirus eggs
- N. battus brown
- Larger
- Straight sides
- Morula visible in both
Describe the climatic factors involved with nematodirus
- Warm March = early hatch
- Cool wet April/May increases larval survival on pasture
- Can forcast problems using weather
Describe the control/treatment of Nematodirus
- 3 treatments during May-June in years with predicted severe diseases, 2 in other years
- Ewes dosed prior to lambing
- Rotational grazing (swapping between sheep and cattle does not work for N. battus as cows can also be infeted by this)
Describe the immunity to N. battus
- Strong age related (after 3 months of age)
- Increased eosinophils and mast cells
- Nematode specific serum IgA and IgG
- Villus shedding (rejection mechanisms, organisms wrap around villi of SI)
Describe the epidemiology of Trichostrongylus species
- Alimentary tract of animals and birds
- Direct, non-migratory life cycle
- Typical life cycle
- Destroys villi
- Subclinical infection possible
Describe the general appearance of Trichostrongylus spp.
- Small
- Hair like worms
- Up to 0.7mm long
- Bursated
- Small buccal capsule
List some of the common Trichostrongylus spp. and their host species
- T. colubriformis: sheep, goats cattle
- T. capricola
- T. citrinus
- T. axei: sheep, goats cattle
- T. tenius: birds
Where is Trichostrongylus colubriformis found?
Small intestine of sheep, goats and cattle
Where is Trichostrongylus axei found?
Abomasum of sheep, goats and cattle
Describe the appearance of T. colubriformis
- 16 gut cells
- Head tapered
- Sheath forms short cone
- 560-796um lenght
- Male bursa with 2 spicules
- Lots of eggs visible in females
Describe the clinical signs of infection with Trichostrongylus spp.
- acute diarrhoea in young
- Chronic diarrhoea in older animals
- Intestine inflamed with hyperplasia
- May be blood spots
- Mesenteric lymph nodes enlarged
- May cause bottle jaw
Describe immune exclusion to trichostrongylus
- Exlusion of/barrier against L3
- Mucus from immune sheep prevents establishment of T. colubriformisn in naiive sheep intestine
- sIgA and mucus IgG recognises 3 different classes of L3 cuticular antigens
Describe the self cure fo Trichostrongylosis
- Expulsion of adults in intestine
- Mast cells, IgE, eosinophils (Th2 induced hypersensitivity response)
- IL-5 activates eosinophils, IL-13 stimulates eotaxin and eosinophil migration and class switching to IgE
- Self cure is T-cell induced
- Can be induced when naiive animals have T-cells from immune animals adoptively transferred to them
Describe subclinical infections of T. colubriformis
- Reduce weight gains by 35%
- Decrease wool growth by 10%
- Decrease milk production by 20%
Describe the epidemiology of T. tenius
- Hypobiosis and warm wet summers increase larval survival
- Chicks very susceptible if ingest enough L3
- When enough L3 on pasture, sudden death
- Fluctuation in grouse number due to T tenius
- In early spring food quality poor, high worm burden, adults more likely to die
- Normal nematode life cycle
Describe the control of T. tenius
- No self cure reported
- Fenbendazole used to cure infection
Discuss the veterinary importance of T. tenius in game birds
- Infects chickens, guinea fowl, pheasants, quail, many others
- Most notable impact on red grouse populations in North East and West england and Scotland
- Grouse shooting industry worth a lot of money
