TrendsinParasitology TrendsinParasitology
Trends in Parasitology | Parasite of the Month
Toxoplasma gondii
Sebastian Lourido1,2,
*
1
Whitehead Institute for Biomedical Research, Cambridge, MA, USA
2
Biology Department, Massachusetts Institute of Technology, Cambridge, MA, USA
TrendsinParasitology
KEY FACTS:
Broad host range, infecting warm-blooded
animals from birds to humans, with sexual
recombination restricted to felines.
Following infection of the intestine from
consumption of oocysts or tissue cysts,
parasites disseminate systemically to
replicate in a variety of nucleated cell types.
Slow-replicating chronic stages may
persist life-long as tissue cysts within
neurons and muscle cells.
Three genomes in the nucleus (66 Mb
encoding ~8320 genes), mitochondrion,
and apicoplast.
Continuous asexual culture and
extensive genetic approaches enable the
study of physiology, cell biology, and
host–parasite interactions.
DISEASE FACTS:
Most infections are asymptomatic,
although ocular lesions can occur in
immunocompetent individuals and are
frequently associated with recrudescence.
Parasites can enter immunologically
privileged sites by crossing biologically
restrictive barriers like the blood–brain
and placental barriers.
Reactivation of chronic infection in
immunocompromised individuals can
cause life-threatening infections of the
central nervous system.
Congenital transmission can occur during
an untreated primary infection of the
mother, commonly resulting in
chorioretinitis and hydrocephalus in the
newborn.
Chemotherapy is effective against the acute
disease but fails to clear chronic stages.
TAXONOMY AND CLASSIFICATION:
PHYLUM: Apicomplexa
CLASS: Conoidasida
ORDER: Eucoccidiorida
FAMILY: Sarcocystidae
GENUS: Toxoplasma
SPECIES: T. gondii
*Correspondence:
lourido@wi.mit.edu
Toxoplasma gondii is an obligate intracellular eukaryotic parasite from the phylum Apicomplexa that infects up to
one-third of the global population. Although most infections are asymptomatic, some cause retinal lesions and,
in immunocompromised individuals or when contracted congenitally, can lead to life-threatening disseminated
infections involving the central nervous system. Parasites can enter a chronic state, resistant to current therapies,
which can be a reservoir for recrudescence. Felines are the strict definitive hosts for T. gondii, in which the parasite
can sexually develop, forming highly infectious, environmentally resistant oocysts. Virtually all warm-blooded animals
can act as intermediate hosts, acquiring the infection from consuming oocysts or tissues of chronically infected
animals. A variety of specialized organelles release proteins that mediate motility and invasion and modulate host
pathways. Extensive genetic tools make T. gondii a tractable model to dissect the biology of the phylum.
944	 Trends in Parasitology, November 2019, Vol. 35, No. 11    © 2019 Elsevier Ltd. All rights reserved.       https://doi.org/10.1016/j.pt.2019.07.001
Trends in Parasitology | Parasite of the Month
Acknowledgments
Jeroen Saeij, Vern Carruthers, and members of the Lourido laboratory provided helpful discussions and comments. Wandy Beatty at the Washington University Molecular Microbiology
Imaging Facility performed the electron microscopy. This work was supported by the National Institutes of Health (NIH) Director’s Early Independence Award (1DP5OD017892) and a
grant from the Mathers Foundation (1706-00164) to S.L.
Resources
www.toxodb.org
www.cdc.gov/parasites/toxoplasmosis/
www.llamp.net
Literature
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Trends in Parasitology, November 2019, Vol. 35, No. 11    © 2019 Elsevier Ltd. All rights reserved.       https://doi.org/10.1016/j.pt.2019.07.001       945