Protozoa: Neospora caninum

Question 1

What hosts are involved in the life cycle of N. caninum?

Answer 1

IMH - mammals

FH - canines

Question 2

Describe the life cycle of N. caninum

Answer 2

1. Dogs release oocysts in faeces
2. Oocysts sporulate in the environment within several days
3. Cattle ingest sporulated oocysts
4. Oocysts rupture in stomach releasing sporozoites which invade the epithelium and form tachyzoites
5. Tachyzoites rapidly divide before being released form epithelial cell
6. Host (cow) triggers and immune response
7. Tachyzoites evade the immune response by transforming into slow dividing bradyzoites within a cyst wall
8. Bradyzoites reside within tissues (mainly neural)

Question 3

What occurs during ‘vertical transmission’?

Answer 3

N. caninum transmitted across placenta and infects the foetus.

1. During pregnancy dam immune response suppressed, triggers bradyzoites to rupture and tachyzoites to replicate
2. Tachyzoites cross placenta and infect developing foetus

Question 4

What occurs during ‘horizontal transmission’?

Answer 4

N. caninum transmitted from cow to dog

1. Dog eats tissue containing bradyzoites
2. Sexual phase of life cycle occurs in the dog
3. Oocysts formed and shed in faeces

Question 5

Describe the pathology of N. caninum in the pregnant cow

Answer 5

1st trimester - Limited immune response and tissue damage that results in abortion.
2nd trimester - foetal immune response but some damage to CNS causing neurological problems.
3rd trimester - strong foetal immune response causing tachyzoites to form bradyzoites in tissue.

Question 6

How is N. caninum diagnosed in cattle ?

Answer 6

1. ELISA - detect antibody in serum
2. IFAT/ELISA - aborted foetal fluid
3. Examination of neural tissue for lesoins (from aborted foetus)
4. Immunohistochemistry to detect bradyzoites and tachyzoites