Introduction

Dogs are associated with at least 60 zoonotic diseases; statistically, intestinal parasites stand out, specifically helminthiasis. In underdeveloped countries, like the ones in Sub-Saharan Africa, Latin America and Asia, helminthiasis are a public health issue (^{Hotez et al., 2007}; ^{Rinaldi et al., 2006}). Studies carried out in different cities reported the presence of gastrointestinal (GI) parasites in dog feces, mainly in public parks and median strips. In Leon, Mexico, these places have not been evaluated. These are common recreational places in which humans and dogs meet, so attending places are considered a risk factor to acquire parasites, for both dogs and humans (^{Smith, Semeniuk, Kutz & Massolo, 2014}). Children have an increased risk due to geophagy (^{Elliot, Tolle, Goldberg & Miller, 1985}).

Zoonotic GI parasites can be classified in nematodes, tapeworms and protozoans. Toxocara canis, Acylostoma spp., Strongyloides stercolaris and Trichuris vulpis stand out in the group of nematodes for being part of the group of tropical neglected diseases (^{Hotez et al., 2007}). It is also worth mentioning Uncinaria stenocephala and Toxascaris leonina due to their zoonotic potential.

Previous research in Mexico reported parasitosis rates between 6.2% and 47.48% for T. canis (^{Rodríguez-Vivas et al., 2011}; ^{Vélez-Hernández et al., 2014}), 17.88% to 88.1% for A. caninum (^{Alvarado-Esquivel et al., 2015}; ^{Vélez-Hernández et al., 2014}), and 42% to 51% for G. intestinalis (^{Ponce-Macotela, Peralta-Abarca & Martínez-Gordillo, 2005}). One study in Leon reported a rate of 8% for T. canis (^{Méndez, Arreguín-Nava, Aguilar-Orozco & Álvarez, 2012}). The objective of this study was to document the rates of fecal contamination in public parks and GI parasites found in dog feces in Leon, Mexico.

Methods

A descriptive, transversal and observational study was developed in the summer between June and August of 2015 in Leon, Mexico (21°12′27″N-101°67′72″O). Leon city is in the center of Mexico, 1800 meters (5905 ft) above sea level. Its population is 1.4 million people (Instituto Nacional de Estadística y Geografía ^{[INEGI], 2010}) and around 200 000 dogs of which 10% are stray dogs (^{Unidad Municipal de Acceso a la Información Pública, 2014}). The weather in Leon is warm with a subtropical temperate variation, with summer rains with annual precipitation ranging from 378 mm to 840 mm and an average temperature of 18.1 °C (64.58 °F) and 27.3 °C (81.14 °F) (Sistema Meteorológico Nacional ^{[SMN], n.d.}).

The city was divided in six sections. Sixty public parks and four median streets were selected randomly. All the parks were located at residential or commercial areas, and some had schools nearby. The total of collected fecal samples was 443. Each spot was visited once, and the samples were collected in polyethylene bags that contained phenol, alcohol and formaldehyde (PAF) for its preservation and transportation at room temperature. The samples were stored in the Laboratory of Microbiology of the University of Guanajuato for its future analysis. The maximum time between preservation and observation was four months. The samples that lost air tightness were discarded.

The samples were analyzed by the formalin-ether sedimentation technique (^{Salazar-Schettino, 2011}). The sediment was stained with iodine solution for parasitology. Samples were observed under a light microscope at 10X and 40X objective lenses, up to three times. All the observations were done by qualified staff from the laboratory. The identification of parasites was made according to their morphologic characteristics. The qualitative variable results were expressed as frequencies and rates with its confident interval of 95% (CI 95%). The results of the quantitative variables were expressed as the median, and its range was expressed as Q1 to Q3, not to show a normal distribution according to the Kolmogorov-Smirnov analysis.

Results

Of the 64 studied areas (Figure 1), 46 showed fecal contamination (71.88%; 95% IC: 59.87% to 81.41%) and, from these 46, at least one parasite was found in five areas (10.87%; 95% IC 4.07% to 24.36%). A total of 443 samples were collected, and the median was 6 (Q1 to Q3: 2 a 12) samples by park. Four samples lost air tightness and were discarded. From the 439 remaining samples, five (1.14%; 95% IC: 0.4% to 2.8%) were positive for one parasite and one (0.23%; 95% IC: 0.01% to 1.47%) for two. The general prevalence was 1.4%. The most common parasite was Ancylostoma sp. in 3/439 (0.68%; 95% IC:0.18% to 2.15%) samples, followed by T. canis (eggs) 1/439 (0.23%; 95% IC: 0.01% to 1.47%), Strongyloides sp. 1/439 (0.23%; 95% IC: 0.01% to 1.47%), and G. intestinalis (cysts) 1/439 (0.23%; 95% IC: 0.01% to 1.47%); the positive sample for two parasites contained Strongyloides sp. and Ancylostoma sp. (Figure 2).

Source: Map of the City of León, Guanajuato. Courtesy of Architect Jorge Mauricio Hernández Hidalgo.

Figure 1: Map of Leon, Mexico, which shows the 64 studied areas. Circles are negative for parasitic forms by formalin-ether sedimentation technique and diamonds are positive. 

Source: Author´s own elaboration.

Figure 2: Photomicrograph of parasitic forms found in the study, stained with iodine solution for parasitology. A Toxocara canis egg B Strongyloides sp. larvae C Ancylostoma sp. larvae. 

Discussion

A general prevalence of parasites of 1.4% was found, this differs with studies made in other cities of Mexico which report rates from 37% to 98% (^{Alvarado-Esquivel et al., 2015}; ^{Martínez-Barbabosa, Gutiérrez-Cárdenas, Alpízar-Sosa & Pimienta-Lastra, 2008}). The sample collection was carried out only in summer, when parasite rates are higher (^{Ponce-Macotela et al., 2005}). A possible explanation to these results is that the rainy season in Leon occurs during summer. The samples might have been washed out, because an accumulated precipitation of 125 mm in July 2015 was reported (^{SMN, 2015}). Also, it is not possible to discard that most of the samples came from house dogs, treated regularly with antiparasitic drugs.

Canine health depends on their owner’s care, including administration of antiparasitic drugs and fecal recollection from public places. The rate of public parks contaminated with feces and the number of fecal samples collected show a poor interest of dog owners in collecting their dog’s feces. The education of the owners should be promoted in several ways in which dog breeders, veterinarians, physicians, and other owners should be involved. This education can take place during vaccination and sterilization campaigns, dog-related events, veterinary attention and social networks.

In Leon, there are city programs to encourage an appropriate dog care and feces disposition, these programs include conferences in elementary schools. During 2015, the Animal Control Center of Leon gave nine conferences and in 2016 at least 106. The public health system of Mexico has a zoonosis prevention program that offers free antiparasitic drugs and vaccines. These programs function all year round and were implemented in 2015 (Non-published data from the Animal Control Center of Leon 2016). In the same year, 1253 dogs were dewormed. Until October 2016, at least 2445 dogs were dewormed. In Leon, there are many civil organizations offering antiparasitic drugs at a low cost, this allows more accessibility to deworming treatments (Non-published data from the Animal Control Center of Leon 2016). This could explain that in a previous work done in Leon, the rate of parasites found in collected dog feces was higher (18%) (^{Méndez et al., 2012}).

The formalin-ether sedimentation technique is used to detect helminth eggs, larvae and protozoan cysts (^{Uga, Tanaka & Iwamoto, 2010}). In addition, the preservation of the samples was done with PAF which preserves trophozoites, cysts, eggs, and larvae. Other studies based on the same technique reported T. leonina, T. vulpis, D. caninum, E. granulosus, and Cryptosporidium spp.; however, none of the aforementioned was found and Cryptosporidium spp. was not searched intentionally.

This study has some limitations. The feces were collected from public parks and it is unsure which belongs to stray dogs or housedogs. There is no gold standard for intestinal parasite detection; however, the formalin-ether sedimentation technique is more suitable for the detection of larvae and eggs than the direct exam and flotation techniques (^{Salazar-Schettino, 2011}; ^{Yimer, Hailu, Mulu & Abera, 2015}). The microscopic feces exam depends on the skill of the laboratory technician and allows to detect between 20% and 90% of eggs and parasites (^{McHardy, Wu, Shimizu-Cohen, Couturier & Humphries, 2014}). Another limitation is that the fecal analysis was made with one sample and the evidence shows that the probability of detecting any parasitic form with a single fecal sample is 83% compared to 95% obtained with two samples (^{Thomson, Haas & Thompson, 1984}). More studies are needed to evaluate the efficacy of local antiparasitic programs, the percentage of owners who dewormed their dogs as well as the frequency, the most commonly used anti-parasite schemes by veterinarians, and the intentional search for gastrointestinal parasites in stray dogs.

Despite the low parasitic index found in dog feces in the city of Leon, Mexico, 1.14% 95% IC: 0.4% to 2.8% compared to other studies, the percentage of parks with fecal contamination was high 71.88%; 95% IC: 59.87% to 81.41%. Educating dog owners is crucial in reducing the risk of transmission of gastrointestinal parasites to other dogs and to humans. Apparently, free deworming campaigns reduced the rate of parasitosis in domestic dogs, so it is necessary to continue with education programs and sanitary measures to reduce both fecal contamination in parks and the number of parasitized dogs.