Protozoa including Giardia Flashcards
Name some examples of protozoan infections
- Toxoplasma gondii (cats)
- Neospora caninum (dogs)
- Sarcocystis (cats and dogs)
- Cystoisospora (cats and dogs)
- Giardia
- Leishmania infantum
- Babesia canis
Describe the main features of phylum apicomplexa
- Large group of protozoa
- Mostly intracellular
- Locomotion by gliding
- Undergo sexual and asexual reproduction
- Involved in host cell invasion
How is Toxoplasma gondii linked to sheep?
Second most important cause of abortion in sheep in Britain
What spp is the definitive host of Toxoplasma gondii?
Cats
What are the 3 life cycle stages of the Toxoplasma gondii parasite?
- Tachyzoite
- Bradyzoite
- Oocyst
Describe a tachyzoite
- Intracellular
- Rapidly dividing
- Crescent shaped - 2x6um
Describe a bradyzoite
- Within a bradyzoite cyst
- Neural or muscle tissue
- Slow growing
- Persistent
Describe an oocyst
- Unsporulated oocyst passed in faeces
- Sporulated oocyst contains two sporocysts and four sporozoites
- 12um
Describe the life cycle of Toxoplasma gondii within the definitive host
- Sexual reproduction part of the life cycle
- Ingestion of prey containing bradyzoite cysts
- Cyst wall is digested in the GIT, liberating bradyzoites
- Bradyzoites invade the intestinal epithelial cells
- Bradyzoites divide by schizogony giving rise to merozoites
- Differentiate into male and female gametocytes - microgametes and macrogametes.
- Fertilization gives rise to an unsporulated oocyst shed with cat faeces
- Sporulation occurs and generates two sporocysts with four sporozoites each.
What is schizogony?
Asexual reproduction
Describe the life cycle of Toxoplasma gondii inside the intermediate host
- Following ingestion sporozoites are released and they cross the gut wall
- Develop into tachyzoites which replicate rapidly
- They then differentiate into bradyzoites which form cysts
Describe toxoplasma gondii disease in cats
- No disease
- No clinical signs
- Restricted to the sexual cycle in the gut
- Produce oocysts
Can Toxoplasma gondii be controlled in cats?
- Drugs are not a realistic, practical option
- No vaccines
How is Toxoplasmosis transmitted to humans?
- Tissue cysts in undercooked meat
- Ingesting oocysts contaminating food
Describe vertical transmission of Toxoplasma in humans
- Infected mother prior to pregnancy, foetus is protected by mothers immunity
- Primary infection during pregnancy can have severe effects on the foetus
What are the effects of Toxoplasma on a foetus?
- Miscarriage, still born
- Hydrocephalus
- Convulsions
- Intracerebral calcification
- Retinochoroiditis
Which people are most at risk of Toxoplasma?
Immunocompromised
How can toxoplasma be controlled in humans?
- Chemotherapy: pyrimethamine and sulphonamides used to treat acute infections in humans
- Reduce risk of infection, especially pregnant women: oocysts in soil (gardening, unwashed vegetables), cook meat to kill bradyzoite cysts
Which spp are the definitive and intermediate hosts of Neospora caninum
Definitive = dog Intermediate = dog and cattle
How does the seroprevalence of Toxoplasma compare to Neospora
Lower number of Neospora oocysts produced by an infected dog compared to Toxoplasma oocysts produced by an infected cat
Describe the life cycle of Neospora caninum in the definitive host
- Ingestion of bradyzoites from bovine tissues, released into the dogs duodenum where they undergo merogony
- Transient appearance of oocysts in faeces – sexual phase
- No disease
- Antibody response may or may not be present
Describe the life cycle of Neospora caninum in the intermediate host
- Transplacental transmission following ingestion
- Cysts in the muscle of intermediate host
- No oocysts in faeces as this is the asexual phase
- Positive antibody response
Describe the disease of Neospora caninum in dogs vs cattle
- Disease in dogs – neonatal paresis
* Disease in cattle – abortion
What are the clinical signs of Neospora caninum in young dogs?
- Ataxia, hindlimb paresis, loss of reflexes
- Ascending paralysis, dysphagia
- Hyperextension of hindlimb(s)
What are the clinical signs of Neospora caninum in older dogs?
- CNS disturbances
- Abnormal behaviour
- Vision defects, seizures
- Myocarditis, dermatitis
- Pancreatitis
How can Neospora caninum be diagnosed?
- Clinical signs
- Serology by IFAT
- Creatine kinase elevation
- Muscle biopsy and tissue aspirates - PCR or immunocytochemistry to identify the parasites
How can Neospora caninum be treated?
- Clindamycin (same as Toxoplasma)
- Initiate treatment as soon as possible after clinical signs develop
- Prognosis variable as it doesn’t act on the bradyzoite cysts
- Doesn’t stop vertical transmission so don’t breed from an Ab + mother
What are the main features of the life cycle of Sarcocystis spp?
Two host life cycle – prey-predator:
- Prey: asexual reproduction & muscle cyst development (sacrocyst)
- Final predator host: intestinal sexual reproduction & production of mature oocysts
What are the two predator-prey relationships for Sarcocystis spp?
Sheep - Dog
Cattle - cat
Describe the sporulated oocyst of Sarcocystis spp
- In faeces of dog/cat (two sporocysts each containing four sporozoites) – ready to infect
- Classical 2 sporocyst appearance with a very light surrounding membrane encasing them which disintegrates easily
Cattle infected with Sarcocystis at which point in pregnancy may abort?
Third trimester
What are the main features of the Cystiospora spp life cycle?
- Direct life cycle – no asexual part of the cycle
- Infection by faeco-oral transmission
- Oocysts passed in faeces (20-40µm)
- Sporulated oocysts - 2 sporocysts, 4 sporozoites
What is the clinical signs of Cystiospora spp infection?
Diarrhoea in puppies and kittens
How is Cystiospora spp diagnosed?
- History and clinical signs
- Oocysts sometimes differentiated on size
- The more oocysts there are, the more likely disease is as a result of coccidia
How is Cystiospora spp controlled?
Good sanitation and treat with sulphonamides
Which protozoa is the cause of travellers diarrhoea in humans?
Giardia
How does Giardia affect puppies?
Important cause of Diarrhoea
What are the two morphological stages of Giardia?
Trophozoite
Cyst
Describe the trophozoite stage of Giardia and its appearance
- Diving stage
- Adhesive disc attaches it to the intestinal mucosa
- Pear shaped (12-15um x 5-9um)
- Bi-nucleated
- 4 pairs of flagellae (8 total)
Describe the cyst stage of Giardia and its appearance
- Found in the intestinal lumen and faeces
- Transmitted among hosts
- Oval/ellipsoid, smooth cyst wall
- 8x12um
- Each cyst contains two trophozoites with 4 nuclei total
Describe the life cycle of Giardia
- Infective cysts from the environment are ingested by host
- Excyst in small intestine: each cyst releases 2 actively moving trophozoites
- Trophozoites attach to the intestinal epithelium and multiply asexually by longitudinal binary fission
- Secrete cyst forming protein and transform into multi-nucleated resistant cysts excreted in the faeces
How long is the PPP of Giardia?
1-2 weeks
What are the clinical signs of Giardia?
- Puppies
- Trophozoites erode mucosa and villi
- Malabsorptive diarrhoea
- Dehydration
- Steatorrhoea (greasy stools)
How is Giardia controlled and treated?
- Control based on good hygiene
- Clean drinking water
- Treatment with metronidazole
- Fenbendazole licensed for use in puppies
- Zoonotic: important to warn owners
Tritrichomonas foetus is an obligate parasite of which two spp?
- Bovine reproductive tract
- Feline gastrointestinal tract
Tritrichomonas foetus is a commensal parasite of which spp?
Pigs - nasal cavities, intestines, and stomachs
How does Tritrichomonas disease affect cattle?
Cause of abortion and infertility in cows
How does Tritrichomonas disease affect cats?
Diarrhoea, colitis (large bowel)
Young cats
How is Tritrichomonas diagnosed in cats and differentiated from Giardia?
- Faecal smears: differentiate from Giardia
- Culture from faecal sample (In Pouch system)
- Giardia = slow moving
- Tritrichomonas = jerky, rapid movements
How is Tritrichomonas foetus treated?
Treatment with ronidazole (related to metronidazole) – not licensed in the UK
Diarrhoea is a typical clinical sign for which 4 protozoan infections?
- Sarcocystis spp.
- Cystoisospora (Isospora)
- Giardia spp.
- Tritrichomonas foetus
