The Toxoplasma Gondii Oocyst From Cat Feces

Abstract

Toxoplasma infection is c o m m o n in m a n and animals, yet for 60 years the life cycle of Toxoplasma gondii remained unknown. R e c e n t l y a new form of Toxoplasma was found in the feces of cats that had eaten Toxoplasma-infected mice (for review of earlier work see [1]). This fecal form is biologically different from the known stages of Toxoplasma. While searching the feces of cats for a morphological equivalent of Toxoplasma, several candidate forms such as fungi, cysts of flagellates, and coccidian oocysts resembling those of Isospora fells, I. rivolta, and I. bigemina were found. Of these only oocysts resembling [. bigemina were constantly and q u a n t i t a t i v e l y associated with fecal Toxoplasma infectivity. W e will describe and characterize these oocysts and show b y a series of m u t u a l l y independent determinations that they should be regarded as oocysts of Toxoplasma got~dii. Some of these findings were briefly reported (2). DEFINITION O F TER3£STrophozoites refer to intracellular and free forms of Toxoplasma which are actively proliferating in the tissues of acutely infected animals (Fig. 1). Free trophozoites are quickly digested in solutions of pepsin at pH 1.3.Cyst refers to an accumulation of Toxoplasma (merozoites) characteristically occurring in the brain and muscle of chronically infected animals (Fig. 2). Cysts are surrounded by an elastic argyrophilic and periodic acid Schiff positive wall and contain much stored glycogen. The cyst wall is destroyed immediately on exposure to pepsin but the released merozoites survive in it for some time.

Mechanics of the Toxoplasma gondii oocyst wall

“…To evaluate the basic mechanics of the T. gondii oocyst wall, we limited the use of chemicals to avoid any modification of the wall structure because of handling or storage conditions. For this, oocysts were sporulated in water rather than in 2% (vol/vol) aqueous sulfuric acid solution, which is commonly used for oocyst sporulation and subsequent storage (11,22,48). After a 5-d sporulation process, the oocyst suspension contained 18.6 ± 2.7% of NS, 18.3 ± 6.4% of SB, and 63.0 ± 5.9% of SP oocysts (SI Appendix, Fig.…”

“…A few days postinfection, unsporulated (uninfective) spheroid oocysts (10 × 12 μm) are excreted in cat feces and become rapidly infective following aerobic sporulation (22). Sporulation results in different subpopulations of maturing oocysts during the first few days (22): unsporulated (NS), "sporoblast-staged" (SB), and fully sporulated (SP) oocysts (11,22).…”

Toxoplasma gondii: epidemiology, feline clinical aspects, and prevention

“…At the same time, it is only in the feline host that sexual multiplication of this parasite takes place, so cats serve as the only site wherein genetic recombination and re-assortment of this parasite can occur. For the past several decades, it has been considered that, in spite of sexual recombination, there is only minimal genetic diversity among different isolates of T. gondii from around the world, with isolates being placed mainly in one of three genetic strains, Type I, II, and III [28]. However, it has recently been shown that there is significantly more genetic diversity in isolates from Brazil [29].…”

“…No information yet exists to explain the drivers for this genetic diversity on St Kitts; additionally, no information exists to describe variability on other islands of the archipelago. We are only beginning to unravel the actual genetic relationship between virulence and the genetic makeup of the different strains of T. gondii present in the environment and in cases of human and animal disease [28]. Work on the genetics of virulence has indicated that some rhoptry proteins (held in the rhoptry organelles and released at the time of host cell penetration), for example ROP18, are linked to virulence in different genetic strains irrespective of their genetic strain assortment.…”

Infection by Toxoplasma gondii and Leishmania spp. in humans and dogs from rural settlements in Northern Paraná State, Brazil

“…Contact with cats, in general, was not epidemiologically important, but the presence of young cats was important (p = 0.031), probably because these animals are in age of greater risk of primo-infection by T. gondii and release oocysts into the environment (DUBEY, MILLER, FRENKEL, 1970). Souza et al (1987) studying a rural area, found that the presence of cats in the residences influenced on the parasite transmission, in the same way, in urban areas of Minas Gerais State, Camargo, Antunes and Chiari (1995) showed higher seroprevalence in humans who had contact with cats.…”