Prevalence of anti-T. canis antibodies in stray dogs in Mexico City Ignacio Martı ´nez-Barbabosa a, * , Manuel Gutie ´rrez Quiroz b , Leticia Araceli Ruiz Gonza ´lez b , Elena Marcia Gutie ´rrez Ca ´rdenas a , Arturo Alpizar Sosa Edubiel a , Jose Luis Valencia Jua ´rez b , Enrique Gaona c a Departamento de Atencio ´n a la Salud, A ´ rea de Ciencias Ba ´sicas Edif, H-102, Universidad Auto ´noma Metropolitana-Xochimilco, Calzada del Hueso 1100, Colonia Villa Quietud, Delegacio ´n Coyoacan, C.P. 04960 Me ´xico, DF, Mexico b Departamento de Microbiologı ´a y Parasitologı ´a, Facultad de Medicina, Universidad Nacional Auto ´noma de Me ´xico, Me ´xico, Mexico c Departamento El Hombre y su Ambiente. Universidad Auto ´noma Metropolitana-Xochimilco, Me ´xico, Mexico Received 5 September 2006; received in revised form 1 February 2008; accepted 9 February 2008 Abstract Toxocara canis is a common intestinal helminth found in dogs. In humans, it is a cause of Visceral Larva Migrans (VLM), a zoonosis rarely studied in Mexico. The aim of this study is to examine, by means of the indirect haemaglutination test (IHAT), the prevalence of antibodies of T. canis in the serum of stray dogs in Mexico City. Methods and materials: 141 stray dog serum samples from three different districts of the city were analyzed: Iztacalco (49), Iztapalapa (49) and Coyoacan (43). In each location three study groups were formed. Group I with 35 dogs (less than a year old), Group II with 91 dogs (ages 1  n < 6) and Group III with 15 dogs (ages 6 and over). An extract of raw adult T. canis worms was used as an antigen. Finally, a modified version of Boyden’s IHA serological test was carried out. Results: Out of the 141 sera, 94 (40 males and 54 females) proved positive (dilution titres of from 1:32 to 1:4096) with a global infection prevalence of 66.7%. The frequency of infected dogs in Iztacalco was 61.2%, 51% in Iztapalapa and 90.7% in Coyoacan. The largest seroreactivity was found in Group II (ages 1–6) with 61 positive tests and a total frequency of 43.3%. Conclusions: The high seroprevalence of anti-T. canis antibodies found in the dogs of the study population is an indicator of the contact which exists between these animals and the parasite. This is the result of the high degree of contamination of the soil of Mexico City with the parasite’s eggs. Paradoxically, Coyoacan, with more green areas, is also the most polluted municipality. Statistical analysis confirms this. Dogs seek green areas to defecate. There exists a serious risk for the population of being infected with Visceral larva migrans. # 2008 Published by Elsevier B.V. Keywords: T. canis; Toxocariasis; Serology; Visceral larva migrans 1. Introduction Toxocara canis is the etiological agent for Toxocar- iasis, an intestinal parasitosis that affects dogs and other canines (Beaver, 1956; Schantz, 1989; Glickman et al., 1978; Fisher, 2003). Antibodies produced in dogs as a response to infection by T. canis can be detected from 1 to 2 months after birth (Matsumura et al., 1984). This is due to the fact that the puppies are born with parasites because the foetus is infected in the uterus. What happens is that the larvae, previously encapsulated in the mother’s tissues, www.elsevier.com/locate/vetpar Available online at www.sciencedirect.com Veterinary Parasitology 153 (2008) 270–276 * Corresponding author. E-mail address: imarti@correo.xoc.uam.mx (M.-B. Ignacio). 0304-4017/$ – see front matter # 2008 Published by Elsevier B.V. doi:10.1016/j.vetpar.2008.02.011