Toxoplasma gondii

phylum

apicomplexa

genus

toxoplasma

species

gondii

distribution

worldwide

step 1

ingestion of oocysts from soil, water, plant material

step 2

oocysts release sporozoites

step 3

sporozoites develop into tachyzoites

step 4

tachyzoites invade muscle and neural tissue/any cell with a nucleus

step 5

tachyzoites asexually reproduce inside cells

step 6

intracellular tachyzoites release more tachyzoites that invade more cells

step 7

some tachyzoites develop into tissue cyst bradyzoites

step 8

cats ingest tissue cyst bradyzoites when they eat prey

or

cats ingest oocysts with sporozoites from poop of other felines

step 9

bradyzoites or sporozoites released in stomach

step 10

bradyzoites or sporozoites invade intestinal epithelial cells

step 11

bradyzoites and sporozoites develop into schizonts

step 12

schizonts produce merozoites

step 13

intestinal epithelial cells rupture and release merozoites

step 14

merozoites invade new cells and repeat cycle

step 15

some merozoites differentiate into gametes

step 16

microgametes fertilize macrogametes to produce immature oocysts

step 17

immature oocysts passed in cat poop

not immediately infectious

step 18

oocysts sporulate in environment

can survive for months

step 19

sporulated oocysts produce 2 sporocysts

step 20

sporocysts produce 4 sporozoites

step 21

human ingests oocysts or tissue cysts/tachyzoites/bradyzoites

step 22

oocysts release sporozoites in human that develop into tachyzoites

step 23

tachyzoites invade human muscle, brain, or eyes and develop into tissue cysts

cysts may persist for lifetime

transmission

eating tissue cysts in undercooked meat or shellfish

ingesting tachyzoites in unpasteurized dairy products

handling cat poop

from parent to offspring during pregnancy

blood transfusion (rare)

organ transplant

intermediate host

mammals, birds

sometimes humans

definitive host

cats

deadend intermediate host

humans

incubation period

5-23 days

symptoms

asymptomatic

swollen lymph nodes in neck

flu-like symptoms

severe cases: ocular infections, vision loss

immunocompromised patients: central nervous system disease, eye lesions, lung inflammation, encephalitis, intracerebral mass lesions, relapse can occur in AIDS patients, fatal if left untreated (rare)

congenital infection: asymptomatic until 2-3 decades later, eye lesions, some infants have eye or brain damage at birth

treatment

no treatment for asymptomatic unless pregnant

target tachyzoite stage not cysts

drugs to combat side effects of disease treatment

different plans for ocular symptoms, pregnant people, infants

diagnosis

detection for antibodies (serology), dye test, indirect fluorescent antibody test, enzyme immunoassays, agglutination test, avidity test

PCR

microscopy of tissue sections or CSF

eye exam

prevention

be clean

avoid cat poop