title: Experimental Toxoplasmosis in Rats Induced Orally with Eleven Strains of Toxoplasma gondii of Seven Genotypes: Tissue Tropism, Tissue Cyst Size, Neural Lesions, Tissue Cyst Rupture without Reactivation, and Ocular Lesions.
abstract: BACKGROUND
  The protozoan parasite Toxoplasma gondii is one of the most widely distributed and successful parasites. Toxoplasma gondii alters rodent behavior such that infected rodents reverse their fear of cat odor, and indeed are attracted rather than repelled by feline urine. The location of the parasite encysted in the brain may influence this behavior. However, most studies are based on the highly susceptible rodent, the mouse.
  
  
  RESULTS
  Latent toxoplasmosis was induced in rats (10 rats per T. gondii strains) of the same age, strain, and sex, after oral inoculation with oocysts (natural route and natural stage of infection) of 11 T. gondii strains of seven genotypes. Rats were euthanized at two months post inoculation (p.i.) to investigate whether the parasite genotype affects the distribution, location, tissue cyst size, or lesions. Tissue cysts were enumerated in different regions of the brains, both in histological sections as well in saline homogenates. Tissue cysts were found in all regions of the brain. The tissue cyst density in different brain regions varied extensively between rats with many regions highly infected in some animals. Overall, the colliculus was most highly infected although there was a large amount of variability. The cerebral cortex, thalamus, and cerebellum had higher tissue cyst densities and two strains exhibited tropism for the colliculus and olfactory bulb. Histologically, lesions were confined to the brain and eyes. Tissue cyst rupture was frequent with no clear evidence for reactivation of tachyzoites. Ocular lesions were found in 23 (25%) of 92 rat eyes at two months p.i. The predominant lesion was focal inflammation in the retina. Tissue cysts were seen in the sclera of one and in the optic nerve of two rats. The choroid was not affected. Only tissue cysts, not active tachyzoite infections, were detected. Tissue cysts were seen in histological sections of tongue of 20 rats but not in myocardium and leg muscle.
  
  
  CONCLUSIONS
  This study reevaluated in depth the rat model of toxoplasmosis visualizing cyst rupture and clarified many aspects of the biology of the parasite useful for future investigations.
authors.affiliation: United States Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Animal Parasitic Diseases Laboratory, Beltsville, Maryland, United States of America.
authors.forename: Jitender P
authors.initials: JP
authors.lastname: Dubey
authors.affiliation: United States Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Animal Parasitic Diseases Laboratory, Beltsville, Maryland, United States of America.
authors.forename: Leandra R
authors.initials: LR
authors.lastname: Ferreira
authors.affiliation: Faculty of Biological Sciences, University of Leeds, Miall Building, Clarendon Way, Leeds, United Kingdom.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Alsaad
authors.affiliation: United States Department of Agriculture, Agricultural Research Service, Beltsville Agricultural Research Center, Animal Parasitic Diseases Laboratory, Beltsville, Maryland, United States of America.
authors.forename: Shiv K
authors.initials: SK
authors.lastname: Verma
authors.affiliation: Veterinary Pathology Services Joint Pathology Center, 606 Stephen Sitter Ave. Silver Spring, Maryland, United States of America.
authors.forename: Derron A
authors.initials: DA
authors.lastname: Alves
authors.affiliation: Ocular Inflammatory Disease Center, University of California at Los Angles Stein Eye Institute and Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, United States of America.
authors.forename: Gary N
authors.initials: GN
authors.lastname: Holland
authors.affiliation: Faculty of Biological Sciences, University of Leeds, Miall Building, Clarendon Way, Leeds, United Kingdom.
authors.forename: Glenn A
authors.initials: GA
authors.lastname: McConkey
mesh_terms: D000818:Animals; D001921:Brain / Q000469:parasitology* / Q000473:pathology; D005128:Eye Diseases / Q000469:parasitology* / Q000473:pathology; D005260:Female; D005838:Genotype; D033661:Oocysts / Q000469:parasitology* / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014122:Toxoplasma / Q000166:cytology* / Q000235:genetics*; D014124:Toxoplasmosis, Animal / Q000469:parasitology* / Q000473:pathology