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      High prevalence of Toxoplasma gondii oocyst shedding in stray and pet cats ( Felis catus) in Virginia, United States

      research-article
      1 , , 1
      Parasites & Vectors
      BioMed Central
      Cat, Fecal, Felis catus, Molecular detection, Oocyst, Parasite, PCR, Prevalence, Toxoplasma gondii

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          Abstract

          Background

          The protozoan Toxoplasma gondii is the causative agent of toxoplasmosis, with complications varying from mental disease to death. While human infection can occur via ingestion of tissue cysts from infected meat, most human infection comes from oocysts. Cats are the only definitive host, and thus shedding of oocysts by cats provides the ultimate source of toxoplasmosis.

          Methods

          While most studies in the area use seroprevalence to monitor Toxoplasma incidence in cat populations, this provides only a history of infection. This study used PCR detection of oocysts from cat feces to more accurately estimate the numbers of cats producing oocysts and thus posing an active health risk. DNA sequencing was use to confirm the identity of the PCR products.

          Results

          Of the 49 cats tested, 9 yielded PCR products of the expected size. Six of the nine were determined by sequence analysis to be false positives, while three products were true positives. Overall, 6% of cats examined were found to be actively shedding oocysts.

          Conclusions

          The incidence of oocyst shedding in the cat population studied was significantly higher than expected and higher than found in most cat populations world-wide. Of equal importance, the primers tested were shown to produce PCR products of multiple sizes and non-target products of expected size. We detected false positives at a higher rate than true positives, emphasizing the need for confirmatory analysis. Further research may produce better protocols for Toxoplasma detection from cat fecal samples.

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          Most cited references28

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          Identification of a 200- to 300-fold repetitive 529 bp DNA fragment in Toxoplasma gondii, and its use for diagnostic and quantitative PCR.

          We have identified a novel 529bp fragment that is repeated 200- to 300-fold in the genome of Toxoplasma gondii. This 529bp fragment was utilised for the development of a very sensitive and specific PCR for diagnostic purposes, and a quantitative competitive-PCR for the evaluation of cyst numbers in the brains of chronically infected mice. The 529bp fragment was found in all 60 strains of T. gondii tested, and it discriminates DNA of T. gondii from that of other parasites. Toxoplasma gondii DNA was detected in amniotic fluid of patients, as well as in various tissues from infected mice. Polymerase chain reaction with the 529bp fragment was more sensitive than with the 35-copy B1 gene. For the quantitative competitive-PCR, a 410-bp competitor molecule was co-amplified with similar efficiency as the 529bp fragment. Quantitative competitive-PCR produced a linear relationship between the relative amounts of PCR product and the number of tachyzoites in the range of 10(2)-10(4) tachyzoites and 100-3000 tissue cysts. A highly significant correlation between visual counting of brain cysts and quantitative competitive-PCR was obtained in mice chronically infected with Toxoplasma. Thus, quantitative competitive-PCR with the 529bp fragment can be used as an alternative for the tedious visual counting of brain cysts in experimental animals. With the quantitative competitive-PCR, furthermore, we could confirm the copy number of the 529bp fragment in tachyzoites and estimate the number of bradyzoites per cyst.
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            Risk factors for Toxoplasma gondii infection in the United States.

            Toxoplasmosis can cause severe ocular and neurological disease. We sought to determine risk factors for Toxoplasma gondii infection in the United States. We conducted a case-control study of adults recently infected with T. gondii. Case patients were selected from the Palo Alto Medical Foundation Toxoplasma Serology Laboratory from August 2002 through May 2007; control patients were randomly selected from among T. gondii-seronegative persons. Data were obtained from serological testing and patient questionnaires. We evaluated 148 case patients with recent T. gondii infection and 413 control patients. In multivariate analysis, an elevated risk of recent T. gondii infection was associated with the following factors: eating raw ground beef (adjusted odds ratio [aOR], 6.67; 95% confidence limits [CLs], 2.09, 21.24; attributable risk [AR], 7%); eating rare lamb (aOR, 8.39; 95% CLs, 3.68, 19.16; AR, 20%); eating locally produced cured, dried, or smoked meat (aOR, 1.97; 95% CLs, 1.18, 3.28; AR, 22%); working with meat (aOR, 3.15; 95% CLs, 1.09, 9.10; AR, 5%); drinking unpasteurized goat's milk (aOR, 5.09; 95% CLs, 1.45, 17.80; AR, 4%); and having 3 or more kittens (aOR, 27.89; 95% CLs, 5.72, 135.86; AR, 10%). Eating raw oysters, clams, or mussels (aOR, 2.22; 95% CLs, 1.07, 4.61; AR, 16%) was significant in a separate model among persons asked this question. Subgroup results are also provided for women and for pregnant women. In the United States, exposure to certain raw or undercooked foods and exposure to kittens are risk factors for T. gondii infection. Knowledge of these risk factors will help to target prevention efforts.
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              Waterborne toxoplasmosis--recent developments.

              Humans become infected with Toxoplasma gondii mainly by ingesting uncooked meat containing viable tissue cysts or by ingesting food or water contaminated with oocysts from the feces of infected cats. Circumstantial evidence suggests that oocyst-induced infections in humans are clinically more severe than tissue cyst-acquired infections. Until recently, waterborne transmission of T. gondii was considered uncommon, but a large human outbreak linked to contamination of a municipal water reservoir in Canada by wild felids and the widespread infection of marine mammals in the USA provided reasons to question this view. The present paper examines the possible importance of T. gondii transmission by water. Published by Elsevier Inc.
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                Author and article information

                Contributors
                Journal
                Parasit Vectors
                Parasit Vectors
                Parasites & Vectors
                BioMed Central
                1756-3305
                2013
                17 September 2013
                : 6
                : 266
                Affiliations
                [1 ]Biology Department, Virginia Military Institute, Lexington, VA 24450, USA
                Article
                1756-3305-6-266
                10.1186/1756-3305-6-266
                3849917
                24330950
                2b5e5521-6929-456d-a74f-b50b3df91474
                Copyright © 2013 Lilly and Wortham; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 28 May 2013
                : 14 August 2013
                Categories
                Research

                Parasitology
                cat,fecal,felis catus,molecular detection,oocyst,parasite,pcr,prevalence,toxoplasma gondii
                Parasitology
                cat, fecal, felis catus, molecular detection, oocyst, parasite, pcr, prevalence, toxoplasma gondii

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