Parasitology 3 Flashcards
1
Q
What is the definitive host of Toxoplasma gondii?
A
Any member of Felidae
2
Q
What are the intermediate hosts of Toxoplasma gondii?
A
Any warm-blooded animal
3
Q
Describe the life cycle of Toxoplasma gondii
A
- Unsporulated oocyss passed in cat faeces
- Oocysts sporulate
- Contaminate food, ingested by intermediate host
- Asexual reproduction in muscles of intermediate hosts, can infect each other through tissue cysts
- Cat infected by ingestion of cysts in tissues of infected IH
- Sexual reproduction in gut epithelium of cat
4
Q
What are tachyzoites?
A
Proliferative form of Toxoplasma gondii in blood or CSF, can be acute or recurrent
5
Q
What is the prepatent period of tachyzoites?
A
> 13 days
6
Q
What are bradyzoites?
A
Life long “tissue cysts” of Toxoplasma gondii
7
Q
What is the prepatent period of bradyzoites?
A
3-10 days
8
Q
When do Toxoplasma gondii oocysts become infective?
A
After 48 hours or more environmental incubation
9
Q
Describe the survival of Toxoplasma gondii oocysts in the environment
A
- Survive months to years despite extreme conditions (freezing, heat, dehydration)
- Prepatent period >18 days
10
Q
Describe Toxoplasma oocyst shedding from the cat
A
- Thousands to millions shed per cat
- But only shed for 1-2 weeks
- Only ~1% of cats are shedding oocysts at a given time
11
Q
What factors trigger tachyzoite to bradyzoite switching?
A
- High pH
- Presence of nitric oxide
- Nitric oxide donor Sodium Nitroprusside
12
Q
What factors trigger bradyzoite to tachyzoite switching?
A
- Th2 cytokine bias
- Lack of IL-12
- Lack of IFN-y
- Lack of TNFalpha
- Lack of nitric oxide
13
Q
What is the purpose of bradyzoite switching?
A
- Protection and therefore persistence in the host
- May occur in response to treatment or immune response of host
- When immune weakness is indicated, switch back to tachyzoite
14
Q
List the most common signs of feline toxoplasmosis
A
- Anorexia
- Weight loss
- Lethargy
- Dyspnoea
- ocular signs
- Myositis
15
Q
List the less common signs of feline toxoplasmosis
A
- GI signs
- Neurological signs
- Jaundice
- Abortion
- Pneumonia
16
Q
How can toxoplasmosis be diagnosed?
A
- Detection of oocysts in felines difficult
- Serology better: IgG and IgM
17
Q
What treatment is used for toxoplasmosis in cats?
A
Clindamycin and pyrimethamine combination
18
Q
Why is oocyst detection in cat faeces difficult?
A
- Shedding occurs before clinical signs
- Only 10% of cats shed
- Intermittent shedding
19
Q
Outline the prevention of Toxoplasma infection in cats
A
- Do not allow cats to hunt rodents and birds
- Feed only cooked meat or processed food from commercial sources
- No vaccine available
20
Q
Outline toxoplasmosis in food production animals
A
- Pork greatest risk to humans and animals
- Can survive in pigs for over a year after infection
- Lamb second most common source of infection, then beef and chicken
- Wild game also high risk food source
21
Q
Outline the zoonotic potential of Toxoplasma
A
- Cats main reservoir for infection of other mammals
- Can spread to humans via contaminated food/water and soil
22
Q
Describe human toxoplasmosis in humans
A
- 40% chance of mother passing disease to foetus
- 10% have severe neurological and ocular disease
- 30-40% of people have antibodies suggesting exposure
- Linked to schizophrenia in humans
23
Q
How can toxoplasmosis in humans be prevented?
A
Ensure food is properly processed - freezing and boiling kills tissue cysts
24
Q
Describe human toxoplasmosis in immuno-competent individuals
A
- Typically no symptoms
- May be in-apparent or mild flu-like illness (lymphadenopathy, fever, malaise, psychiatric disease)
25
Describe human toxoplasmosis in immuno-compromised individuals
- Severe encephalitis
| - Recrudescent infection
26
Describe human toxoplasmosis in pregnant women
- Mainly affects foetus
- Foetal death
- Hydrocephalis
- Chroidoretinitis
- Mental retardation
- Blindness
- Epilepsy
- May not manifest in offspring for years
- May also be asymptomatic
27
Outline the diagnosis of congenital toxoplasmosis
- Serological tests to diagnose acute infection in pregnant women (frequent false positives)
- Sero-diagnosis confirmed at reference lab before treatment started
- PCR of amniotic fluid for test confirmation/exclusion
28
Describe the treatment of congenital toxoplasmosis
- Pyrimethamine and sulphonamide where PCR of amniotic fluid is positive
- Spiramycin where PCR of amniotic fluid is negative
29
Describe the treatment of acute toxoplasmosis in humans
- Generally not indicated for most people
- Pregnant or immunocompromised
- Diagnosis by IgM, IgG Ab titres
- Pyrimethamine +sulphadiazine or clindamycin
- Folinic acid to overcome thrombocytopaenia nad leukopaenia caused by damage to bone marrow from toxoplasmosis
30
Outline the treatment of toxoplasmosis in AIDs patietns
- In seropositive patietns with CD4+ lymphocyte count of <100/ul: prophylaxis against toxo ence[halitis, trimethoprim-sulphamethoxazole or Dapsone
- For toxo-encephalitis patients: pyrimethamine plus sulphadiazine or pyrimethamine + clindamycin
31
What are the consequences of infection with Neospora caninum in cattle?
- Abortion
| - Infertility
32
What are the consequences of infection with Neospora caninum in dogs?
Neuromuscular disorder
33
What is Neospora caninum?
Protozoan parasite
34
What is the key difference between Neospora caninum and Toxoplasma gondii?
- Neospora is disease of dogs (DH) and cattle (IH), with uncertain zoonotic risk to humans
- Toxoplasmosis mainly disease of humans, sheep and goats and cats are the only definitive hosts
35
Describe the life cycle of Neospora caninum
- Dog ingests tissue cysts
- Unsporulated oocysts shed in dog faeces
- Oocysts sporulate
- Contaminated food/water ingested by intermediate hosts or pregnant animal
- Form tissue cysts in intermediate hosts
- Tachyzoites transmitted through placenta to infect foetus in pregnant animal
36
What factors are related to infection risk with Neospora caninum?
- Age
- Presence of farm or wild canids
- Absence of cats
- Climate and season
- Farm-raised replacement heifers
- Proximity to town or village
37
How does age increase the risk of infection with Neospora caninum?
Increased potential for horizontal and vertical transmission and recrudescence
38
How does presence of farm dogs and absence of wild canids increase risk of infection with Neospora caninum?
- Farm dogs increase risk as are definitive host
- Wild canids decrease risk of infection as there is negative interaction between the presence of farm dogs which pose infection risk, and wild canids
39
How does the absence of cats suggest increased infection risk with Neospora caninum?
- Absence of cats related to presence of dogs which increase risk
- Cats would decrease the rat population which are intermediate hosts
40
How do farm-raised replacement heifers increase the risk of infection with Neospora caninum?
Increase risk as existing prevalence in a herd may persist
41
How does proximity to a town or village increase the risk of infection with Neospora caninum?
Associated with increased dog density
42
What are the 2 pathways of transplacental transmission of Neospora caninum?
Exogenous and endogenous
43
Explain exogenous transplacental transmission of Neospora caninum in cattle
- First time exposure
| - Cow infected while pregnant and infection straight to calf
44
Explain endogenous transplacental transmission of Neospora caninum in cattle
- Cow infected when not pregnant
- Becomes chronically infected and latent stage reactivated once pregnant
- Crosses placenta and infects calf
45
What factors increase the risk of infection with Neospora caninum associated with reproduction?
- Previous abortions
- High annual rate of cows returning to oestrus post-pregnancy
- Retained afterbirths
- USing calving pens to hospitalise sick animals
46
What factors decrease the risk of infection with Neospora caninum associated with reproduction?
- Use of beef-bull semen to inseminate dairy cattle
- Cross-breed pregnancies
- Attendance at cattle shows
47
What are the methods for controlling Neospora in cattle herds?
- Selective culling
- Farm biosecurity
- Reproductive management
- Chemotherapy
- Vaccination
48
Why is there no general strategy for the control of neosporosis?
- Regional differences in epidemiology of bovine neosporosis
| - Important to study regional epidemiology before starting control programme
49
Outline farm biosecruity measures used in the control of neosporosis in cattle
- Quarantine and testing of replacement and purchased cattle
- Prevention of transmission from dogs and other potential definitive hosts (test to ensure free from disease)
- Prevent waterborne transmission
- Rodent cotnrol
- Prevent putative factors for disease that may lead to recrudescence in congenitally infected cattle e.g. reduce stress (may lead to transformation from brady to tachyzoite)
50
Outline reproductive management measures in the control of neosporosis
- Embryo transfer
| - Artificial insemination of sero-positive dams with semen from beef bulls
51
Outline testing and culling in the control of neosporosis in cattle
- Expensive
- But minimises losses through infection or abortion
- Reduces level of infection in herd minimising losses
52
Outline chemotherapy in the control of neosporosis in cattle
- Hypothetical
| - Expensive
53
Outline vaccination in the control of neosporosis in cattle
- Can be effective but N. caninum is intracellular
- Immune response to N. caninum in dam may be incompatible with survival of the foetus
- There are diverse strain differences and 2 clinical forms of the disease
54
What drugs can be used to treat toxoplasmosis in sheep?
- Rumensin (monensin)
| - Decox (decoquinate)
55
Outline the control of toxoplasmosis in sheep
- Rumensin or decox to lessen effects of Toxoplasma
- Live vaccine Toxovac in use
- Isolate infected individuals and aborted foetuses
- Prevent dogs from eating foetal membranes and unprocessed meat
56
What are some limitations of using faecal egg counts for diagnosis of parasitic infection?
- Not all parasites can be found in faeces as eggs
- Intermittent shedding of eggs
- Single sex infections may mean no eggs are shed
57
Outline the agar larval development test
- Culture eggs until reach infective larval stage in different drug concentrations
- Development suggests resistant to the drug
- Theoretically can be used for benzimidazoles, levamisole, ivermectin
- Higher sensitivive cf faecal egg count reduction test
- Expensive and time consuming
- Interpretation is complex
58
What tests can be used to assess parasitic drug resistance?
- Faecal egg count reduction test
- Agar larval development test
- Molecular assay analysis
59
Describe molecular assay analysis to assess parasitic drug resistance
- PCR assays (also Strain fingerprinting assays)
- Expensive, time consuming, require expertise
- Cannot be done in house
- Allows comparison of identified parasite with database of known resistances in those parasites
60
Outline the process of genotyping worms
- Collect specimens of worms from affected animals
- Genotype worms from each attack in a reference lab
- Look for similarities/differences between worm populations
61
Compare the genotypes of worms found in a recurrent infection and a new infection
- Recurrent: same genotype
| - New: different genotypes
62
What is the significance of finding a recurrent parasitic infection?
- If treatment used previously then this suggests resistance
- Overstocking
- Bringing in of new stock
- Poor environmental management
- Inappropriate choice of anthelmintic
63
What is MAR?
Multiple anthelmintic resistance
64
Outline the action points regarding MAR
- Prompt isolation and treatment of symptomatic animals
- No treatment of asymptomatic animals that may act as a reservoir (undesirable and ineffective)
- Prevention by development of vaccine and immunisation
- Research into development of a "super-anthelmintic" against GI nematodes
- Better techniques and effective surveillance
65
What animals does the EU Pet Travel Scheme apply to?
- Cats
- Dogs
- Ferrets
66
What is the maximum number of all types of pet animals each person may bring into the EU from most non-EU listed countries?
- 5
- More than 5 if for competition/exhibition/sporting events/training for sporting events (require written evidence/registration, all animals over 6mo)
67
What are the requirements for pets travelling directly between UK and RoI?
Pet must have EU passport
68
What are the 5 main steps necessary for animals entering the UK from EU and listed non-EU countries (in chronological order)
- Microchipped
- Vaccination against rabies (after MC, min 12 weeks old)
- Rabies antibody test (non-EU only) (at least 30 days after date of vaccination, no less than 3 months before date of movement)
- Treatment against Echinococcus multilocularis (not more than 120 hrs and not less than 24 hours before the time of scheduled entry)
- Accompanied by a passport and declaration
69
List some exotic disease of concern in veterinary species
- Rabies
- Dirofiliaria immitis (heartworm)
- Leishmaniosis
- Babesiosis
- Ehrlichiosis
70
What is the likely effect of climate change on the prevalence of exotic diseases in the UK?
- Likely to increased
- Improved environment for the vectors with increasing temperatures
- increased range of movement of vectors
71
Outline the role of the vet in minimising the incidence of exotic diseases
- Vigilant for emerging diseases, consider as differential diagnoses
- Awareness of disease manifestations
- Confidence in confirmation of diagnosis
- report confirmed cases
- Advise clients regarding travel risks
72
What are the vectors of transmission for babesiosi?
- Ticks (Dermacentor reticulatus)
| - Contaminated instruments or needles
73
What is the vector for the transmission of leishmaniasis?
Phlebotomine sandflies
74
Describe the clinical signs of leishmaniasis
- Can be subclinical
- Lethargy, inappetance, weight loss, lymphadenomegally, splenomegaly, polyuria, polydipsia, V+D, non-pruritic exfoliative dermatitis +/- alopecia,erosive ulcerative dermatitis
- Nodular/papular dermatitis, pustular dermatiis, onnychogryphosis, keratoconjuncitivitis, blepharitis, anterior uveitis
- lameness, epistaxis, mucosal lesions, myositis, cutaneous and systemic vasculitis
75
What is the vector of transmission for ehrlichiosis?
Rhipicephalus sanguineus tick
76
What is the vector of transmission for dirofilariasis?
Mosquitoes
77
What are the clinical signs of acute phase ehrlichiosis?
- Weight loss
- Oculonasal discharge
- Lymphadenopathy
- Thrombocytopaenia
- Leukopaenia
- Low anaemia and hypergammaglobulinaemia
78
What are the clinical signs of chronic phase ehrlichiosis?
- Varying degrees of depression
- Fever, weight loss
- Combination of bleeding tendencies
- Pallor due to anaemia
- Abdominal tenderness
- Anterior uveitis
- Retinal haemorrhages
- Neurological signs
- bone marrow destruction
79
What is the main species of Leishmania that infect dogs?
Leishmania infantum
80
Outline the zoonotic potential of Leishmania infantum
- Can infect humans, particularly immunocompromised adults and children
- However dog to human transmission not reported
- Must be transmitted by Phlebotomine sandfly
81
What measures can be taken to prevent leishmaniasis in dogs?
- Vaccination
- Fly repellents
- Keep dogs indoors when flies are most active (7pm to 7am)
82
What measures can be taken to prevent heartworm?
- Mosquito repellent
- Monthly preventative treatment using Ivermectins
- In collies use milbemycin
83
What are the key clinical signs of heartworm?
Coughing, exercise intolerance, cachexia, anorexia, heart murmur, ascites
84
Outline the ideal features of an antiparasitic
- Selective
- Effective at removing adults and immature forms of parasites from the body
- Wide therapeutic index
- Easy to administer
- Inexpensive/economically justifiable
- No residue problems
- Specific advantages in terms of pharmacokinetics and/or metabolism
85
What are endoparasiticides?
Antiparasitics that kill parasites living inside the animal
| - includes anthelmintics and antiprotozoals
86
What are ectoparasiticides?
Antiparasitics that kill parasites living on the outside of the animal
- Including fleas, ticks, mites, lice
87
What are endectocide?
Parasiticides that act on ecto and endoparasites
88
What are the group 1 parasitices?
- Benzimidazoles
| - White drenches
89
What are the group 2 parasiticides?
- Levamisole
| - Yellow drench
90
What are the group 3 parasiticides?
- Macrocyclic lactones (avermectins and milbemycins)
| - Clear drenches
91
What are the group 4 parasiticides?
- Monepental
| - Orange drench
92
Why are parasiticides better than parasitistatics?
- Parasitisides remove pathogen entirely
| - With parasitistatics, infection can recur
93
What are the broad mechanisms of action of antiparasitics?
- Paralysis of parasites via mimicking the action of neurotransmitters
- Alteration of metabolic processes
- Alteration of parasite reproduction
94
Outline the paralysis of parasites via mimics of neurotransmitters
- Ach, GABA, glutamate, octpamine, serotonin can all be targets
- Can be present in more than one parasite category (nematode, cestode, trematode, arthropods)
- Affect homeostasis of depolarisation of NMJ
- Broad spectrum
95
Give examples of ways in which metabolic processes that can be altered by antiparasitics
- Inhibition of microtubule synthesis
- Uncoupling of oxidative phosphorylation
- Inhibition of folic acid synthesis/metabolism
- Inhibition of thiamine utilisation
- Inhibition of chitin formation (arthropods)
- Stimulation of insect juvenile hormones
- Ion gradients/membrane potential
- Inhibition of protein synthesis
- Inhibition of DNA synthesis
96
Give examples of ways in which antiparasitics can alter parasite reproduction
- Inhibition of egg production in nematodes
- Inhibition of multiplication of protozoa
- Note: this is not an anthelmintic action, but a consequence of an anthelmintic action
97
Explain the mode of action of benzimidazole
- Bind to beta-tubulin in molecules
- Leads to inhibition of polymerisation and disorders of intracellular homeostasis
- Tubulin structure altered, all body functions affected
98
Explain the mode of action of levamisole
- Affect nicotinic Ach receptors
- Mimic Ach action, change permeability of post-synaptic membrane
- Lead to depolarisation and spastic paralysis of worms
99
What "mode of action" group of anthelmintics does levamisole belong to and give examples of others in this group
- Cholinergic anthelmintics
- Pyrantel
- Morantel
100
What parasites are macrocyclic lactones effective against?
- Are endectocides
- Arthropods and nematodes
- Cestodes, tramtodes and adult heart worms are insensitive
101
What are the signs of macrocyclic lactone toxicity in dogs?
- Mydriasis
- tremor
- Ataxia
- Emesis
- Salivation
- Coma
102
Explain the mode of action of macrocyclic lactones
- Acts on membrane channels causing permanent depolarisation of membranes
- Leads to paralysis
- Affects pharynx, somatic muscle and uterus of nematode
103
What is the mechanism through which vertebrates (other than collies) are protected against the effects of macrocyclic lactones?
P-glycoprotein transmembrane transport pump (prevents entry of MLs in brain and CNS)
104
Explain the mechanism of action of monepantel
- Binds to, and irreversibly opens, MPTL-1 receptor in nervous system
- Prevents coordination of movement
105
Explain the mechanism of action of emodepside
- Acts on specific class of transmembrane G-protein coupled receotirs (depsiphilins)
- Latrophilin receptor class
- Ultimately leads to flaccid paralysis of pharynx
106
Explain the mechanism of action of praziquantel
- Binds to beta-subunit of voltage gated calcium channels
- Leads to spastic and tetanic muscle contractions
- May also have vacuolation/degradation of tegument
107
Against what parasites if praziquantel active?
- Cestodes (in particular used for Echinococcus)
| - Some helminths are not susceptible e.g. Fasciola spp.
108
Explain the mechanism of resistance against benzimidazoles
- Genetic changes in drug target
- Several single-nucleotide polymorphisms (SNPs) in drug's target molecule beta-tubulin isotype 1
- Can lead to amino acid substitution in drug target protein and so changes affinity of drug for target
109
What is the most common SNP in benzimidazole resistance?
Phenylalanine to tyrosine substitution at postion 200 in the gene (Phe200piyr)
110
What are the potential mechanisms of antiparasitic resistance?
- Point mutations (target alterations)
| - Increased efflux
111
Explain the mechanism of resistance against macrocyclic lactones
- Increased drug efflux into GI lumen
| - Reduces concentration in the cell leading to reduced effect
112
Outline the potential reasons for therapeutic failure
- Interactions with other drugs or health condition diminishing drug efficacy
- Failure to diagnose and treat present of miced infections
- Patient immunodeficiency
- Quick re-infection due to cotnaminated environment
- Failure to deliver or receive correct dosage (compliance, out of date drugs etc)
113
Outline the advice you would give to an owner in the case of Felicola infestation
- Treat with: fipronil + S-methoprene OR imidacloprid OR selamectin OR surolaner
- Wash cat
- Clean environment (basic hygiene should be sufficient)
- Treat any in contact animals
- Is not zoonotic
114
Outline the advice you would give to an owner in the case of finding a Rhipicephalus sanguineus tick
- Remove tick correctly and look for others
- Close monitoring, in particular for signs of Ehrlicha
- Rhipicephalus can carry babesia, ehrlicha, rickettsia, Anaplasma
- Recommend tick teatment if go abroad again e.g. pyrethroids, deltamethrin collars
- Treat with fipronil to kill ticks, and deltamethrin in order to repel
115
Outline the advice you would give to a farmer in the case of bovicola infestation
- Chewing louse
- Pour on synthetic pyrethroid e.g. deltamethrin
- 3-macrocyclic lactons clear 98% of chewing lice
- Treat in contact animals
- But treatment is generally rare
116
Outline the advice you would give to an owner in the case of Sarcoptic mange
- Treat using: advocate (imidaclorpid and moxidectin) OR amitraz OR selamectin OR sarolaner
- Advise owner of zoonotic risk
- Environmental cleaning required as can live in environment for several weeks
- Use household flea spray as this will be effective on mites
117
What drugs are effective againse mites?
- Pyrethroids
- Avermectins
- Amitraz
- Deltamethrin
118
What drugs can be used to prevent tick infestation?
- Isoxazolines e.g. flurolaner
- Pyrethroids e.g. deltamethrin collar
- Phenylpyrnazoles e.g. fipronil
