Toxoplasmosis: Protozoa Flashcards
Characteristics of protozoa
- single cell eukaryotes
- small (5-20um)
Trophozoite
any stage in protozoan’s life cycle which can ingest food (motile form)
Cyst
Non-motile form protected by distinct membrane or cyst wall (infective stage)
Excystation
process of emergence of trophozoite from cyst
Reproduction of protozoa
Asexual reproduction then sexual reproduction
Encystment of protoza
- cysts forms
- resting stage w protective covering
Conditions for encystment
- loss of food source
- dessication
- increase in salt
- change in O2 conc
- change in pH
- temp change OR
- change in terminal stage of a life cycle
Process of encysting
- food is stored
- locomoter organelles absorbed
- nuclear division occurs
- cyst wall secreted
4 major groups of protozoa
- Amoeba
- Flagellae
- Cilia
- Apicomplexa
Neonate porcine coccidiosis
- pale, watery diarrhoea
- decreased growth
- 5-15 day old piglets
- high morbidity & low mortality
2-host life cycle of cyst forming coccidia (Neospora, Toxoplasma)
- Definitive host (predator) produces oocysts shed in env and picked up by intermediate host (prey)
- Asexual multiplication in intermediate host –> development of dormant cysts packed w infectious dose for definitive host
- these parasites can infect new intermediate host (omnivore) and skip definitive host route
- During acute phase of asexual multiplication the infection can spread throughout the host. If pregnant, infection will be transmitted to offspring–> abortion, stillbirth, congenital infection
Horizontal transmission
transmission of infection between hosts (not parent-child relo)
Vertical transmission
mother-child transmission during perinatal period
Foetal immunity vs Neospora caninum
Abortion incidence decreases w subsequent pregnancies–> maternal immunity matures after first pregnancy and influences outcome of subsequent pregnancies
Toxoplasmosis
- congenital infection
- ingestion of infected meat followed by poor hygiene
Toxoplasma gondii
- zoonotic
- heteroxenous, 2 host life cycle
Definitive host of Toxoplasma gondii
- cat (sexual reproduction in intestine)
- oocysts shed by cat are environmentally resistant
Intermediate host of Toxoplasma gondii
all types of mammals and some birds
Immunity against toxoplasma gondii
- antibodies found in 30% of human population > 18yrs
- antibody-mediated lysis of tachyzoites clears infection
- recovery yields complete immunity
- immunity can be boosted by tissue cyst breakdown
Toxoplasma gondii: Epidemiology
- reservoir is bradyzoite (cyst) in many animals and birds
- cat only host w sexual stage; sheds from intestinal tract (main transmitters)
- modes of transmission: fecal oral from cat, oral/raw meat, transplacental during acute infection
Toxoplasma gondii epidemiology cont.
- sandpits –> litterboxes–> infect children
- oocysts must sporulate before becoming infectious
- infectious cysts in meat can be killed by freezing
Toxoplasma gondii can remain infectious for up to
2 years in suitable env (sandpit)
Pathogenesis of Toxaoplasma gondii
- Acute infection
- Subacute infection
- Chronic infections
- Congenital toxoplasmosis
Acute infection: toxoplasma gondii
- often asymptomatic in cats but can kill kittens
- humans have flu-like symptoms but immunity develops
- Sheep & goats have abortion
Subacute infection: toxoplasma gondii
hosts humoral immunity develops slowly.
Tachyzoites produce lesions in lung, liver, heart, brain, eyes
Chronic infections
-Ab immune response depresses tachyzoites but cysts from bradyzoites cause intense inflammation, encephalitis, retinal degeneration, myocarditis
Congenital toxoplasmosis
- infection during preg can infect foetus, cause still birth, abortion, birth defects
- hydrocephaly, microcephaly, blindness
