Article

Toxoplasma gondii: from animal to humans

Institut für Parasitologie, Tierärztliche Hochschule Hannover, Bünteweg 17, D-30559, Hannover, Germany.
International Journal for Parasitology (Impact Factor: 3.4). 11/2000; 30(12-13):1217-58. DOI: 10.1016/S0020-7519(00)00124-7
Source: PubMed

ABSTRACT Toxoplasmosis is one of the more common parasitic zoonoses world-wide. Its causative agent, Toxoplasma gondii, is a facultatively heteroxenous, polyxenous protozoon that has developed several potential routes of transmission within and between different host species. If first contracted during pregnancy, T. gondii may be transmitted vertically by tachyzoites that are passed to the foetus via the placenta. Horizontal transmission of T. gondii may involve three life-cycle stages, i.e. ingesting infectious oocysts from the environment or ingesting tissue cysts or tachyzoites which are contained in meat or primary offal (viscera) of many different animals. Transmission may also occur via tachyzoites contained in blood products, tissue transplants, or unpasteurised milk. However, it is not known which of these routes is more important epidemiologically. In the past, the consumption of raw or undercooked meat, in particular of pigs and sheep, has been regarded as a major route of transmission to humans. However, recent studies showed that the prevalence of T. gondii in meat-producing animals decreased considerably over the past 20 years in areas with intensive farm management. For example, in several countries of the European Union prevalences of T. gondii in fattening pigs are now <1%. Considering these data it is unlikely that pork is still a major source of infection for humans in these countries. However, it is likely that the major routes of transmission are different in human populations with differences in culture and eating habits. In the Americas, recent outbreaks of acute toxoplasmosis in humans have been associated with oocyst contamination of the environment. Therefore, future epidemiological studies on T. gondii infections should consider the role of oocysts as potential sources of infection for humans, and methods to monitor these are currently being developed. This review presents recent epidemiological data on T. gondii, hypotheses on the major routes of transmission to humans in different populations, and preventive measures that may reduce the risk of contracting a primary infection during pregnancy.

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    • "More than 5000 species have been described to date, and over 1 million apicomplexan species are estimated to exist (Adl et al., 2007; Pawlowski et al., 2012). Clinically and economically important apicomplexan pathogens, for example, Babesia, Cryptosporidium, Eimeria, Neospora, Theileria, Toxoplasma (Tenter et al., 2000), and the malaria-causing parasite Plasmodium wreak profound negative impacts on animal and human welfare. Despite their diverse host tropism (Roos, 2005) and life cycle strategies, apicomplexans possess several unifying molecular and cellular features, including the abundance of specific classes of nucleic acid-binding eLife digest Single-celled parasites cause many severe diseases in humans and animals. "
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    ABSTRACT: The eukaryotic phylum Apicomplexa encompasses thousands of obligate intracellular parasites of humans and animals with immense socio-economic and health impacts. We sequenced nuclear genomes of Chromera velia and Vitrella brassicaformis, free-living non-parasitic photosynthetic algae closely related to apicomplexans. Proteins from key metabolic pathways and from the endomembrane trafficking systems associated with a free-living lifestyle have been progressively and non-randomly lost during adaptation to parasitism. The free-living ancestor contained a broad repertoire of genes many of which were repurposed for parasitic processes, such as extracellular proteins, components of a motility apparatus, and DNA- and RNA-binding protein families. Based on transcriptome analyses across 36 environmental conditions, Chromera orthologs of apicomplexan invasion-related motility genes were co-regulated with genes encoding the flagellar apparatus, supporting the functional contribution of flagella to the evolution of invasion machinery. This study provides insights into how obligate parasites with diverse life strategies arose from a once free-living phototrophic marine alga.
    eLife Sciences 07/2015; 4. DOI:10.7554/eLife.06974.001 · 8.52 Impact Factor
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    • "More than 5000 species have been described to date, and over 1 million apicomplexan species are estimated to exist (Adl et al., 2007; Pawlowski et al., 2012). Clinically and economically important apicomplexan pathogens, for example, Babesia, Cryptosporidium, Eimeria, Neospora, Theileria, Toxoplasma (Tenter et al., 2000), and the malaria-causing parasite Plasmodium wreak profound negative impacts on animal and human welfare. Despite their diverse host tropism (Roos, 2005) and life cycle strategies, apicomplexans possess several unifying molecular and cellular features, including the abundance of specific classes of nucleic acid-binding eLife digest Single-celled parasites cause many severe diseases in humans and animals. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The eukaryotic phylum Apicomplexa encompasses thousands of obligate intracellular parasites of humans and animals with immense socio- economic and health impacts. We sequenced nuclear genomes of Chromera velia and Vitrella brassicaformis, free-living non-parasitic photosynthetic algae closely related to apicomplexans. Proteins from key metabolic pathways and from the endomembrane trafficking systems associated with a free-living lifestyle have been progressively and non-randomly lost during adaptation to parasitism. The free- living ancestor contained a broad repertoire of genes many of which were repurposed for parasitic processes, such as extracellular proteins, components of a motility apparatus, and DNA- and RNA-binding protein families. Based on transcriptome analyses across 36 environmental conditions, Chromera orthologs of apicomplexan invasion-related motility genes were co-regulated with genes encoding the flagellar apparatus, supporting the functional contribution of flagella to the evolution of invasion machinery. This study provides insights into how obligate parasites with diverse life strategies arose from a once free-living phototrophic marine alga.
    eLife Sciences 06/2015; · 8.52 Impact Factor
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    • "Toxoplasma gondii is an obligate intracellular protozoan parasite that infects large variety of domestic and wild animals including birds and human beings. It is well established that this intracellular protozoan is one of the few organisms to cause congenital infection in humans and many species of domestic animals that can lead to abortions and other neonatal consequences (Petersen and Dubey, 2001; Tenter et al., 2000). The ability of the parasite to multiply virtually in all the www.elsevier.com/locate/vetpar "
    Dataset: VETPAR4338
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