Dogs surveyed
For the present study 101 dogs (Canis familiaris) that were in the animal shelter of the Medellín municipality in Veracruz State, Mexico from February to May 2013 were studied. The animal shelter holds stray dogs and unwanted pet dogs abandoned by the owners for adoption. The Medellín municipality is located in the Sotavento region (19°03’N 96°09 W) which has an altitude of 52 meters above sea level, a warm-humid climate, a mean annual rainfall of 1,417.8 mm, and a mean annual temperature of 25.3°C. Dogs are kept outdoors during the day in a yard with soil flooring, and indoors at nights. Most (88.1%) dogs had received deworming medication and some (32.7%) dogs had been vaccinated against rabies. A minority of dogs had had contact with cats (11.9%). Age in dogs ranged from 0.5 to > 4 years. Thirty seven (36.6%) dogs were males and 64 (63.4%) were females. A questionnaire was used to record the general characteristics of the dogs including age, sex, and breed (pure or mixed).
Ethical aspects
This study was approved by the Bioethics and Animal Welfare Commission of the Facultad de Medicina Veterinaria y Zootecnia of Universidad Veracruzana, and consent was obtained from the owner of the animal shelter.
Laboratory tests
Sera of dogs were obtained and stored at −20°C until assayed. Dog sera were tested for T. gondii IgG antibodies using 2-fold serial dilutions from 1:25 to 1:3,200 with the modified agglutination test (MAT) as described by Dubey and Desmonts [11]. A titer of 1:25 was used as cut off for seropositivity in MAT.
Statistical analysis
Results were analyzed with the aid of the software Epi Info version 7 (Centers for Disease Control and Prevention: http://wwwn.cdc.gov/epiinfo/ and SPSS version 15.0 (SPSS Inc. Chicago, Illinois). For comparison of the frequencies among the groups, the Pearson’s chi-squared test, and when indicated the Fisher exact test, were used. Multivariable analysis (logistic regression analysis with the Enter method) was used to assess the association between the dogs’ characteristics and T. gondii seropositivity. The dependent variable was seropositivity by MAT for an individual animal. Independent variables included in the multivariable analysis were age, sex, breed, and history of deworming, rabies vaccination, and contact with cats. The Hosmer-Lemeshow goodness of fit test was used to assess the fitness of the regression model. Statistical significance was set at a P value of < 0.05.