Parasitology Flashcards
Outline the importance of parasites
- Significant production loss
- Welfare
- Death of animal
- Zoonoses
- Force change in management
- Substantial cost (treatment, pasture management, manure management, quarantine, diagnostic testing, biosecurity)
What does the method of treatment of endoparasites depend on?
The life cycle
What is the significance of finding worm eggs or larvae in faeces?
- Life cycle completed
- Adult present in animal and able to cause clinical signs
- Damage has occurred, dealing with an ill animal
- Parasite has reached patency stage
- Environmental contamination has occurred
- If animal has been treated, parasite must be resistant to the treatment
Describe the clinical signs associated with liver flukes
- Jaundice in some cases
- Loss of appetite, diarrhoea, emaciation
- Bottleneck may occur in some cases
Describe the clinical signs associated with lungworms
- Persistent cough
- Lowering of head and stretching of neck
- Mouth breathing
Describe the clinical signs associated with GI worms
- Weight loss, reduced appetite, diarrhoea, anaemia
- Bottleneck
Outline the laboratory findings associated with liver flukes
- y-glutamyl transpeptidase or transferase
- Function of liver affected
- Serological assays
Outline laboratory findings associated with lungworms
- Eosinophilia in blood and tracheal washes
- Serological assays
Outline laboratory findings associated with GI worms
Plasma pepsinogen or gastrin (less common) increased
Why is plasma pepsinogen increased with GI worms?
Pepsinogen cannot be converted to pepsin due to alteration in abomasal pH
Outline some risk factors that may increase chance of liver fluke infection
- Heavy rains
- Floods
- High number of snails present
Outline the typical epidemiology of lungworms
- Unpredictable
- Dependent on climate
- Fast development (5 days from first larval stage to infection)
- Typical signs within 1 week of ingestion of larval stage
Outline the typical epidemiology of GI worms
- Spring rise
- Acute death of lambs 2-3 weeks after turnout onto pasture
Give examples of changing patterns of sheep parasitism
- Haemonchosis: previously only SE England, now more widespread (Wales and Scotland)
- Nematodirosis: spring problem but now also in Autumn
- Trichostrongylosis: traditionally in autumn in store lambs, now earlier in summer, loss of younger lambs, or in mild winters so problems later than described
What is the purpose of NADIS regarding anthelmintic use?
- Allows prediction and therefore preventative action
- This minimises the use of anthelmintics and so reduces potential for resistance development
What is meant by parasitic load?
The amount of parasite infecting the host
How can parasitic load be assessed?
- Faecal egg count
- Number of parasites in tissue
Why might a parasitic infection be undetectable via faecal egg count?
- Parasite is in pre-patent stage and not yet shedding eggs/larvae
- Single sex infection (except cestodes and trematodes)
- Strong immune response from host preventing reproduction of parasites
What are the goals of helminth control?
- Prevention of clinical disease
- Immunisation
- Economic (increase/minimise loss of productivity)
What are the options for helminth control?
- Biological
- Vaccines
- Anthelmintics
- Pasture management
Outline an example of biological control of helminths
- Duddingtonia flagrans
- Aerobic fungus that reduces number of infective larvae on pastures to an economically acceptable level
- Broad spectrum, no residues, no withdrawal period, active against drug resistant worms
- Novel mode of action and failed to be commercialised as is impractical to administer to pastures daily
Outline the use of vaccines in helminth control
- Only 1-2 available
- Antigenes, native or recombinant/synthetic
- Targets include: intestinal protein, transporters, enzymes
- Can achieve high protection rate
- Problems in commercial large scale production
- Failure to commercialise
Outline the use of chemotherapy in helminth control
- Very high development costs
- Mainstay of parasite control
- Fears of anthelmintic resistance
- e.g. benzimidazoles, imidazothiazoles, macrocyclic lactones
How is anthelmintic resistance diagnosed?
- Faecal egg count comparison before and after treatment of the same animal
- Larval hatch test (in vitro culture of larvae in presence of anthelmintic compounds)
What is the mechanism for anthelmintic resistance?
- Point mutation leading to altered protein sequence and so anthelmintic is ineffective
- Established by selective pressure
Outline some treatment strategies to combat anthelmintic resistance
- Treatment frequency as low as possible to reduce selection pressure
- Grazing management
- New anthelmintic classes introduced
- Strict compliance with prescribed treatment regimes
- Change anthelmintic class annually
- Ensure are not underdosing
- no “dose and move”
- Quarantine infected animals
- Combination therapy
- Use plants with anthelmintic activity
- Avoid overstocking of animals
What is refugia?
Parasite finding refuge in tissue and so not exposed to anthelmintic
List the common abomasal helminth parasites of small ruminants
- Ostertagia ostertagi
- Haemonchus contortus
- Teladorsagia circumcincta
- Trichostrongylus axei
What is FAMACHA and how is it used?
- A scale to objectively assess the degree of anaemia due to abomasal worms
- Aids decision of whether to administer anthelmintic dose
Describe the classical post mortem signs of Haemochus contortus
- Severe gastroenteritis characterised by extensive submucosal hyperaemia and haemorrhage in the abomasum
- erosions adn ulcers as well as gross thickening of the abomasal wall
- Some degree of haemorrhages in parts of the small intestine
- Visible presence of worms
Why is faecal examination a good primary diagnostic tool for endoparasites?
- Eggs in faeces indicates GI worm
- Larvae in faeces indicates lungworm
- Non-invasive
How does an animal become infected with lungworm?
L3 larvae, either in intermediate host or free on pasture
What causes abdominal bleeding in an Angiostrongylus vasorum infection?
- Migration of larvae from stomach/intestine to lungs
- Secrete anticoagulants
- Parasite immune-mediated thrombocytopaenia, disseminated intravascular coagulation (DIC)
Describe the appearance of the heart and lungs of a dog infected with Angiostrongylus vasorum
- Alveolar infiltrates seen
- Interstitial patterning of lung
- Heart axis shifted to the left suggesting right ventricular enlargement
- Cardiac hypertrophy and pathological damages
How do sheep become infected with Haemonchus contortus?
Ingestion of L3 larval stage on damp grass
How is sudden death of lambs caused by Haemonchus contortus?
- Anaemia as a consequence of worms feeding
- Loss of appetite
List the parasitic worms that can be found in the intestine of pigs
- Hyostrongylus rubidus
- Trichuris suis
- Strongyloides ransomi
- Oesophagostamum spp
- Ascaris suum
- Isospora suis
- Trichinella spiralis (adult)
- Macracanthorhynchus hirudinaceus
How do pigs become infected with Trichuris suis?
Ingestion of eggs containing L1 larvae
What can be used to treat Trichuris ovis infection?
Common anthelmintics e.g. fenbendazole, benzimidazoles, levamisole
What is a proglottid?
A segment of cestode worms, containing an ovary and genital pore. It matures as it moves towards to last segment of the cestode, and is shed as the infective agent
What does tapeworm infection in dogs and cats indicate?
Presence of fleas
Describe the clinical signs of heartworm infection in dogs
- Exercise intolerance
- Hydrothorax
- Hydroperitoneum
- Chronic cough
- Dyspnoea
- Haemoptysis
- Eosinophillian lung
- Oedema in lung parenchyma
Outline the treatment for Dirofilaria immitis
- Kill adult parasite first with adulticide
- Then all circulating microfilariae with microfilaricide
- May require surgery if vena cava syndrome occurs
Outline control of Dirofilaria immitis
- Entirely preventable using medication
- Screening and prophylaxis
- Ensure patient if microfilaria and adult free, can start prophylaxis
Which 2 species of Taenia can cause human disease?
Taenia saginata, Taenia solium
Compare Taenia saginata and solium
- Solium has greater public health implications as it has the capacity to use humans as an intermediate host, develops multiple cysticerci in vital organs often with fatal consequences
- saginata does not do this
How is infection with Eimeria spp acquired?
Consumption of food/water contaminated with mature (sporulated) oocysts
What dog parasite forms hydatid cysts?
Echinococcus granulosus
What is the significance of Fasciola hepatic infections?
- Condemnation of livers
- Emaciation and reduced growth rate
- High mortality in sheep
Outline the control of liver flukes in ruminants
- Treat infected animals with flukicides
- Eliminate snails in environment
- Implement sound husbandry measures
What is a Baermannn apparatus used for?
Used to isolate and concentrate larvae of lungworms from faeces
Compare the appearance of sporulated oocysts of Eimeria, Isospora, Cryptosporidium
- Eimeria: 4 sporocysts, each with 2 sporozoites
- Isospora: 2 sporocysts, each with 4 sporozoites
- Cryptosporidium: no sporocysts, 4 sporozoites
Describe the generic life cycle of GI nematodes
- Eggs in faeces
- Hatch
- Moult to L1 to L2 and then L3
- L3 are infective, ingested on damp pasture by host
- free-livingn stages 2-12 weeks to complete
- Host stage 16-21 days to complete (unless L3 arrest in host over winter)
Describe the life cycle of Nematodirus
- L1-L3 development occurs in eggs
- L3 hatch
- L3-5 moults occur in the host
Describe the life cycle of liver flukes
- Eggs shed in faeces
- Miracidium
- Ingested by snail
- Develop to sporocyst
- Develop to redia
- Develop to cercaria
- Metacercaria shed by snail, ingested by sheep
- Hatch to adult in sheep
Describe the clinical signs and seasonality of Haemonchus contortus
- Spring, after rain
- Weight loss, anaemia
- Hypoproteinaemia
- Bottle jaw
- Does not usually cause diarrhoea
Describe the clinical signs and seasonality of Trichostrongylus spp
- Traditionally autumn, now also in late summer months
- Inappetance, diarrhoea, weigh loss, death, black scour
Describe the clinical signs and seasonality of Nematodirus battus
- Historically spring, now varying times of year
- Diarrhoea most prominent sign, dehydration
Describe the clinical signs and seasonality of acute Fasciola hepatic infection
- July to December
- Sudden death, anaemia, dullness, dyspnoea, ascites, abdominal pain
Describe the clinical signs and seasonality of sub-acute Fasciola hepatica infection
- October to January
- Rapid weight loss, anaemia, submandibular oedema, ascites in some cases
Describe the clinical signs and seasonality of chronic Fasciola hepatica infection
- January to April
- Progressive weight loss, anaemia, submandibular oedema, diarrhoea, ascites
What is the importance of ectoparasites?
- Animal welfare issue
- Economic impact (large animals)
- Zoonotic potential
List the direct effects of ectoparasites
- Pruritus and cutaneous lesions (secondary infection)
- Blood loss
- Myiasis
- Loss of production
- Downgrading of hide
- Allergy
- Zoonosis
List the indirect effects of ectoparasites
- Transmission of pathogens
- Transmission of zoonotic pathogens
- Accidental injury (cattle/horses bolting)
- Reduction in feeding due to discomfort
What is meant by eradication?
Elimination of a disease or pest without its return
Give an example of an ectoparasite that has been eradicated in the UK
Anopheles mosquito
- but reappeared in some countries such as India
Give reasons why eradication programmes may fail
- Insecticide resistance
- Socio-economic factors
- Poor surveillance
What is meant by ectoparasite control?
Reduction of population leading to reduced transmission, reduce to acceptable level
Give examples of ectoparasite control methods
- Chemical
- Physical
- Biological
- trapping
- Modelling and forecasting
What are some considerations when choosing chemical control methods?
- Mode of action of drug
- Spectrum of activity
- Mode of application
- Speed of action required
- Efficacy/duration/frequency of reapplication
- Resistance
- Species to be treated
- Withdrawal periods
- Age restrictions
- Contraindications/drug interactions
- Cost
- Environmental contamination/toxicity to non-target species
How might the life cycle of a parasite affect its control?
- Indirect life cycle more difficult to control as have to consider intermediate host
- Not all stages will be susceptible to the same chemical control methods for example
- Some stages may be persistent in the environment
List the groups of chemical control methods for ectoparasites
- Neurotoxins
- Insect growth regulators
- Repellants
- Dessicants
- Synergists
- Lime sulphur
List the mechanisms of action of neurotoxins for ectoparasite control
- Cholinesterase inhibitors
- Octopamine receptor stimulant
- GABA inhibitor
- Insect nicotininc Ach receptor stimulant (+/- GABA agonist)
- Na channel activator
- Na channel blocker
- Cl channel activators
- Cl and GABA channel inhibitors
List the groups of ectoparasite neurotoxins
- Organophosphates
- Carbamates
- Triazepentadienes
- Phenylpyrrazoles
- neonicatinoids
- Pyrethrins
- Pyrethroids
- Semicarbazones
- Macrocyclic lactones
- Isoxalines
- Spinosyns
What is the mechanism of action of organophosphates?
Cholinesterase inhibitors
Outline the use of organophosphates and give examples
- Used on animal/in environment
- Use reduced due to neurotoxicity concerns
- Fnethion, diazinon, dichlovos, malathion, proprtamphos, dimpylate
What is the mechanism of action of carbamates?
Cholinesterase inhibitors
Outline the use of carbamates and give examples
- Less toxic than organophosphates
- Propoxur, carbaryl, methiocarb, butocarb, fenoxycarb
What is the mechanism of action of triazepentadienes?
Octopamine receptor stimulant
Outline the use of triazepentadienes and give examples
- Broad action vs mites, ticks
- No effect on SA insects, but used for lice in cattle/pigs
- Dip/rinse, spot on
- Contraindicated in horses and cats
- e.g. Amitraz
What is the mechanism of action of phenylpyrrazoles?
GABA inhibitor
Outline the use of phenylpyrrazoles and give examples
- Action vs felas and ticks
- e.g. Fipronil and pyriprole
- Fipronil active vs Trichodectes canis but toxic to rabbits
What is the mechanism of action of neonicatinoids?
Insect nicotinic Ach receptor stimulant
Outline the use of neonicatinoids and give examples
- Action vs fleas
- e.g. Imidacloprid, Nitenpyram, dinotefuran
- Imidacloprid active against Trichodectes canis
- Nitenpyram fast acting but short lived effect
What is the mechanism of action of pyrethrins?
Na channel activator
Outline the use of pyrethrins and give examples
- Rapid knockdown vs insects/fleas
- Poor persistence
- Toxic to cats
- e.g. Dichlorvos, fenitrothion
What is the mechanism of action of pyrethroids?
Na channel activator
Outline the use of pyrethroids and give examples
- Active vs fleas, flies, keds, lice, ticks
- Repellant +/- knockdown
- Toxic to cats and fish
- e.g. permethrin, cypermethrin, deltamethrin, flumethrin
What is the mechanism of action of semicarbazones?
Na channel blocker
Outline the use of semicarbazones and give examples
- Active vs fleas
- e.g. Indoxacarb
- Indoxacarb is a pro-druc, activated by insect only and so has low mammalian toxicity
What is the mechanism of action of macrocyclic lactones?
Cl channel activators
Outline the use of macrocyclic lactones and give examples
- Action vs selected ecto and endoparasites
- Absorbed systemically so ectoparasite effect not affected by bathing
- Especially good for parasites with tissue stages e.g. warbles
- Care re neurotoxicity if MDR1 gene mutation (collies/herding breeds)
- Avermectins and milbemycins
Name the avermectins
- Ivermectin
- Selamectin
- Doramectin
Name the milbemycins
- Milbemycin oxime
- Moxidectin
What is the mechanism of action of isoxazolines?
GABA and Cl channel inhibitor
Outline the use of isoxazolines and give examples
- All licensed for fleas/ticks
- Unaffected by bathing
- Rapid onset - kill fleas before eggs laid
- e.g. Afoxolaner, flurolaner, sarolaner, lotilaner
- Serolaner also licensed for Sarcoptes, demodex, otodectes in dogs
What is the mechanism of action of spinosyns?
Nicotinic Ach receptor stimulant and GABA agonist
Outline the use of spinosyns and give an example
- Oral tablet for dogs/cats
- Unaffected by bathing, rapid effect
- May vomit after administration although effect usually short-lived
- e.g. Spinosad
What is the side effect of neonicatinoids of greatest concern?
May be causing the declining bee population
What are the 3 groups of Insect Growth Regulators?
- Juvenile growth hormone analogues
- Chitin synthesis inhibitors
- Triazine derivatives
