Protozoa - Cyst forming coccidia Flashcards
Toxoplasma gondii sporulated oocyst configuration
1 oocyst: 2 sporocysts: 4 sporozoites
Significance of Toxoplasmosis
Economic losses
Zoonosis
Abortions in humans and small ruminants
Systemic disease - involves CNS
Toxoplasma gondii
DH
IH
PPP
How long is patency?
DH = felid
IH = any warm blooded animal
PPP = 1 week
Patent for 1 month
Transmission of Toxoplasma gondii
Oral -> ingestion of oocysts.
Oocysts resistant in environment for up to 18 months
Ingestion of tissue cysts (raw / undercooked meat / unpasteurised milk)
transplacental and transmammary to foetus
Toxoplasma gondii site sexual replication
only in feline intestines
Where can asexual replication of T. gondii occur?
- feline intestinal epithelium
- In any nucleated cell in IH
What is a tachyzoite?
Rapidly dividing (schizogony) parasite that is moving around te body, penetrating tissues and causing damage
What is a bradyzoite?
Dormant stage in IH brain, heart or skeletal muscle, long lived cysts. Cysts develop as the host immunity increases.
Can differentiate into a sporozoite -> transmit infection when it is eaten.
T. gondii lifecycle
Oocyst excreted from cat -> sporulation ->
ingestion by IH -> schizogony and tachyzoite formation -> bradyzoite formation as host immunity increases -> ingestion by felid.
OR
-> transmammary/tranplacental infection of kittens -> large amounts of oocyst secretion (20 million in 10-21 days) - kitten develops immunity and reinfection is rare
What happens if a previously immune animal with bradyzoites becomes immunocompromised (HIV, FeLV, FIV)?
Bradyzoites -> tachyzoites -> disease
Won’t get shedding of oocysts as the tachzoite will not go back into the intestines
Pathogenesis of T. gondii
- acute infection in naive host
- re activation of latent infection of immunocompromised animal
- > tachyzoites multiply and destroy tissue. Muscle will regenerate but nerves may not.
- can cause abortion, stillborn or congenital abnormalities if T. gondii is acquired durring pregnancy
- if she is infected prior to pregnancy the immunity is passed on to the foetus
Toxoplasmosis in cats
Intestinal - self limiting diarrhoea
- systemic disease
- pyrexia and multi systemic disease
- CNS, hepatic necrosis -> jaundice, uvetitis, interstitial pneumonia
Toxoplasmosis in dogs
- neurological
- gastrointestinal
- respiratory signs
+- ocular signs
Public health significance
majority asymptomatic
- 1/3 exposed
- mild flu like symptoms - fever, sore throat, weakness
High infectious dose in outbreak -> chorioretinitis
HIV-AIDS / organ transplant patients -> 10-30% fatality from latent or newly aquired infection. Encephalitis, pneumonia, ocular disease
Pregnant women risks
- Life-long immunity once exposed -> protect against vertical transplacental transmission unless immunocompromised
- if infection contracted during pregnancy -> may be transmitted to foetus
Diagnosis of T. gondii
Detection of T. gondii antibodies - IgM or rising IgG. Acute infection indicated by 4-16 fold increase in antibodies over a 2 week period.
Dection of tachyzoites
- biopsy, (necropsy placenta, amniotic fluid, foetus), cytology and PCR
- CBC and biochem with consistant finding of organ specific disease
Treatment of T. gondii
Chemotherapy as this targets rapridly dividing tachyzoites (can’t get bradyzoites easily).
- Pyrimethamine +
- clindamycin, sulphonamides or azithromycin
Clinical improvement usually noticed after 24-48 hours unless permanent organ damage.
Control of T. gondii
- Hygiene!
- prevent ingestion of oocysts; gloves when gardening/ empty kitty litter
- Thorough cooking or freezing of meat
- washing potentially contaminated food stuff
- vaccine (toxovax) for sheep
Neopspora caninum
DH
IH
Transmission
Oocyte configuration
DH = dog
IH - range of mammals
Transmitted orally/transplacental
Configuration 1:2:4
Sites of Neospora caninum
Cysts in various tissues; brain, spinal cord and muscles.
Lifecycle of Neospora caninum
- Transplacental transmission can occur in dogs but poorly understood.
- dogs become infected with tissue cysts and subsequently excrete oocysts. Poorly understood
Significant of N. caninum
Cattle:
- abortions - 5-7 months
- congenitally abnormal calves
- asymptomatic carrier -> persistent infection
Dogs:
- paralysis in pups
- multi systemic in older immunocompromised animals
- NOT ZOONOTIC
Neosporosis in dogs
- polyradiculo - neuritis
- myositis
- degenerative
weakness in legs -> loss of propriocetion
Diagnosis of N. caninum
Parasites detected in histological section of necropsy/biopsy material by immunolabelling
