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Archived Comments for: Toxoplasma gondii exposure in patients suffering from mental and behavioral disorders due to psychoactive substance use

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  1. A critical view 

    Ana Flisser, Facultad de Medicina, UNAM. Mexico

    17 December 2015

    I am a professor of students that are undertaking their bachelor in sciences in the Faculty of Sciences of the National University of Mexico (UNAM) in a course that has as its main objective, to teach how to understand, analyze and criticize original research articles. For this purpose students read recent articles on immunoparasitology prior to class that allows them acquiring knowledge and, during class, we discuss thoroughly the information that allows them getting a critical vision. Although it is gratifying to find an article published by a Mexican author in an international indexed journal (1), we found important mistakes, so we decided to comment this article because it generated a lot of questioning and criticism in class, such as: 

    1. The paper is based on a previous descriptive study by the same author regarding psychiatric patients, and states that they "found that 4 of 26 patients with mental and behavioral disorders due to psychoactive substance use had T. gondii antibodies". In the present study the authors discuss that "mental and behavioral disorders due to psychoactive substance use are not associated with infection with T. gondii" nevertheless they conclude “further studies to elucidate the role of T. gondii infection in suicidal ideation and behavior are needed to develop optimal strategies for the prevention of infection with T. gondii”. Therefore this article (1) has no congruency.

    2. In the section on methods the authors indicate that they used Excel for statistical analysis; this is not necessary since the authors also state that they used SPSS. In the same section the authors indicate that “written consent was obtained from each participant”, this may result improper considering that participants have mental disorders, added to the fact that it is not mentioned whether the degree or type of mental disorders indeed allowed the patients to be able to give their consent (1).

    3. The frequency of IgG directed to this parasite in the world population is around 23% (2) but in this study the authors indicate that  "anti-T. gondii  IgG antibodies were present in 10.1% of 149 cases and in 9.4% of 149 controls", being low in all individuals. Furthermore other authors that have performed epidemiological studies of T. gondii in Mexico during the last years reported that the seroprevalence ranges from 15 to 50% among the general population (3,4) and that arid regions of the country (such as the state of Durango), have the lowest prevalence (13%). The diagnosis kit used in the referred study (ELISA) (Diagnostic Automation Inc., Calabasas, CA, USA) has, according to the manufacturer, 100% sensitivity for IgG and IgM, and specificity values of 95% and 100% respectively, further supporting that the population studied has a very low exposure to toxoplasmosis, thus the number of cases used is insufficient for epidemiological studies of toxoplasmosis, such as the present one (1) and others (not cited here) that the corresponding author has published. This may explain the lack of correlation in most of the variables analyzed in the paper by Alvarado-Esquivel et al.

    4. Meat sources listed along the article (pork, beef, venison, lamb, goat, chicken, boar, pigeon, duck, armadillo squirrel, turkey, pigeon, iguana and opossum) are more or less common in several parts of the country, including Durango, but it is very doubtful if participants knew what meat they consumed because it is well known that psychiatric patients have loss of memory (5-8). 

    5. Comparison of serology in animals used for human consumption resulting from different studies is difficult due to variation in serological techniques and choice of threshold for positive cut-off; also differences in farming and husbandry methods (both within and between countries) and climatic conditions will also introduce biases into the results. However, despite all this, when studies from various countries are looked at in an overall pattern, a median seroprevalence emerges; based on review of the literature it may give some indication as to the relative importance of each species in human infections: 30% sheep, 24% pork, 13% cattle, and 7% equine (9). The variable seroprevalence in animals and the low human seroprevalence in Durango may be the reason why no statistical significance between types of meat and toxoplasmosis were found, except for opossum and armadillo. Therefore the only result that would have been worthwhile publishing, but as a letter to the editor without all the long tables of this paper, is the association of opossum and armadillo with toxoplasmosis.

    I hope this comment in BMC Infectious Diseases will thrive authors towards publication of reliable and worthwhile information and students to select BMC as source of useful reading.

    References

    1. Alvarado-Esquivel C, Carrillo-Oropeza D, Pacheco-Vega SJ, Hernandez-Tinoco J, Salcedo-Jaquez I. Sanchez-Anguiano LF, Ortiz-Jurado MN, Alarcon-Alvarado Y, Liesenfeld O, Beristain-Garcia I. Toxoplasma gondii exposure in patients suffering from mental and behavioral disorders due to psychoactive substance use. BMC Infect Dis 2015, 15:172

     2.Flegr J, Prandota J, Sovickova M, Isralli ZH. Toxoplasmosis--a global threat. Correlation of latent toxoplasmosis with specific disease burden in a set of 88 countries. PLoS One 2014;9:e90203. doi: 10.1371/journal.pone.0090203.

    3. Caballero-Ortega H, Uribe-Salas FJ, Conde-Gonzalez CJ, Cedillo-Pelaez C, Vargas-Villavicencio JA, Luna-Pasten H, Cañedo-Solares I, Ortiz-Alegria LB and Correa A. Seroprevalence and national distribution of human toxoplasmosis in Mexico: analysis of the 2000 and 2006 National Health Surveys. Trans Royal Soc Trop Med Hyg 2012;106:653-659

    4. Hernández-Cortazar I, Acosta-Viana KY, Ortega-Pacheco A, Guzman-Marin ES, Aguilar-Caballero AJ, Jiménez-Coello M. Toxoplasmosis in Mexico: epidemiological situation In humans and animals. Rev Inst Med Trop Sao Paulo 2015;57:93-103

    5. Fein G, Di Sclafani, V. Cerebral reserve capacity: implications for alcohol and drug abuse. Alcohol 2004;32, 63-67

    6. Hyman SE. Addiction: a disease of learning and memory. Am J Psychiatry 2005;162:1414-22

    7. Lundqvist, T. Cognitive consequences of cannabis use: comparison with abuse of stimulants and heroin with regard to attention, memory and executive functions. Pharmacol Biochem Behavior 2005;81,319-330

    8. Roth T, Hartse KM, Saab PG, Piccione PM, Kramer M. The effects of flurazepam, lorazepam, and triazolam on sleep and memory. Psychopharmacology 1980;70, 231-237

    9. Guo M, Dubey JP, Hill D, Buchanan RL, Gamble HR. Jones JL, Pradhan AK.  Prevalence and risk factors for Toxoplasma gondii infection in meat animals and meat products destined for human consumption. J Food Protect 2015;78,457-476

    Authors: Dr. Ana Flisser (professor), My students: Alina Marisa Mendez-Vega Gil (107006305), Coral Itzel Huidobro-Hernández (311174067), Gloria Marcela Capula-León (310127259), Karen Itzel Rueda-Martínez (311194283), Karla Daniela Rodríguez-Basurto (311013247), Karla Fernanda Martinez-Rea (307197687), Kelly Pamela Velazquez-Espinoza (311133697), Luis Daniel Almaguer-Rivera (309242240), Mariana Dinazar Chávez-Vargas (310030524), Roberto Velasco-González (310135117), Suemy Andrea Vega-Garcia (311204393). UNAM ID numbers are in parenthesis.

    Competing interests

    I don't have any competeing interest

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