Magnitude and distribution of canine fecal contamination and helminth eggs in two areas of different urban structure, Greater Buenos Aires, Argentina

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1 Veterinary Parasitology 133 (2005) Magnitude and distribution of canine fecal contamination and helminth eggs in two areas of different urban structure, Greater Buenos Aires, Argentina D. Rubel *, C. Wisnivesky Unidad Ecología de Reservorios y Vectores de Parásitos, Fac. Cs. Exactas y Naturales, Universidad de Buenos Aires. Ciudad Universitaria, Pabellón II, 48 piso, C1428EHA, Buenos Aires, Argentina Received 8 March 2005; received in revised form 18 May 2005; accepted 2 June 2005 Abstract The canine fecal contamination and the potential transmission of parasites to human and canine populations represent a public health problem of cosmopolitan importance. The objectives of this work were to evaluate the magnitude of fecal and parasite contamination in two suburban areas of different characteristics, and to investigate their distribution in various urban microenvironments such as yards, green spaces and sidewalks. The areas were referred to as middle-income neighbourhood (MIN) and low-income neighbourhood (LIN). To evaluate fecal contamination and its distribution, feces were counted and areas surveyed were calculated. The parasite contamination was evaluated from the prevalence of helminthosis found in a randomly selected fecal sample of the canine population in each of the study areas. The respective median fecal densities in MIN and LIN were 0.11 and 0.12 feces/m 2 for green spaces, 0.10 and 0.19 feces/m 2 for sidewalks (Mann Whitney test, p < 0.05), and 0.04 and 0.07 feces/m 2 for households. In all the surveyed environments, dogs were free-ranging animals and preferred to defecate on grass surfaces rather than on bare soil, tile or sand. In MIN and LIN the respective prevalences were 40% and 70% for helminths in general (Chi square = 15.17, p < 0.01), 14 and 53% for Ancylostoma (Chi square = 23.99, p < 0.01), 9 and 17% for Toxocara ( p > 0.05), and 26 and 38% for Trichuris ( p > 0.05). Sidewalks were the most contaminated environments in LIN. The level of infected feces in sidewalks and yards was higher in LIN than in MIN (Mann Whitney test, p < 0.05). This study includes a discussion of the influence of variables such as canine population density, sidewalk structure and amount of available green spaces on the distribution of fecal contamination, and results obtained are compared with those previously recorded for Buenos Aires City. An increasing gradient of contamination by canine feces and parasites was observed as socioeconomic status decreased, the canine population increased and the sanitation condition decrease. # 2005 Elsevier B.V. All rights reserved. Keywords: Canine fecal contamination; Urban environments; Dog-transmitted helminthiases; Toxocarosis * Corresponding author. Tel.: /09x364; fax: address: dianaru@bg.fcen.uba.ar (D. Rubel) /$ see front matter # 2005 Elsevier B.V. All rights reserved. doi: /j.vetpar

2 340 D. Rubel, C. Wisnivesky / Veterinary Parasitology 133 (2005) Introduction Canine helminthic infections transmissible to humans such as toxocarosis, ancylostomosis or uncinarosis have a cosmopolitan distribution. Studies performed in the green spaces in various cities show highly variable prevalences of different parasite species in samples from dog feces and/or soil (Surgan et al., 1980; Smith et al., 1984; Conde García et al., 1989; Ludlam and Platt, 1989; Minvielle et al., 1993; Alvares Santarém et al., 1998; Martínez- Barbabosa et al., 1998; Alonso et al., 2001; Ruiz de Ybáñez et al., 2001; among others). Variations in prevalences have also been documented in studies conducted within the same city (Pereira et al., 1991; Minvielle et al., 1993; Sommerfelt et al., 1994; Petersen, ). This variability could be explained by the characteristics of human populations (socioeconomic, ethnic and occupational features), as well as by environmental conditions (climate), taking into account that both have an influence on the epidemiological pattern (Conde García et al., 1989). In addition, variables related to the type of urbanization (number of green spaces, type of sidewalks, etc) and to the canine population (density, proportion of dogs with or without owner, sex and age structure), can also be considered as relevant for the transmission of canine parasites and risk of infection in humans. Fecal contamination can be an important indicator of a potential transmission status, since this, together with prevalence, determine the amount and distribution of infective eggs on the soil in different environments (Uga, 1993). Urban environments offer different microenvironment types for defecation of dogs, and the control of fecal contamination is regarded as a difficult problem (Beck, 1973). Both the magnitude and distribution of fecal contamination should be considered for planning a sustainable control strategy. The influence of urban structure on the distribution pattern of feces has been scarcely studied. For example, some authors have proposed that a nonplanned urbanization with the reduction of green areas would account for a decline in transmission by decreasing the surface favourable for parasite development (Martínez-Barbabosa et al., 1998). The general objective of this study was to provide base information leading to design control programs of parasitic diseases of dogs in urban areas with different characteristics. The contamination level and distribution of dog feces was investigated in different microenvironments of two neighbourhoods with distinctive urban characteristics. Parasite prevalences-proportion of infected dogs-were also determined to evaluate the relative importance of each environment in parasite transmission. In addition, a preliminary estimation of the intensity of use of green spaces by the canine population and its daily variation was investigated. 2. Materials and methods 2.1. Study area The study area comprised two demographic units of approximately 1000 inhabitants each, as defined by the National Institute of Statistics and Census (INDEC), located in the Partido de San Martín, Greater Buenos Aires, Argentina ( S; W). San Martín is bounded on the southeast by Buenos Aires City, covers an area of 56.4 km 2 that includes 348,000 m 2 of green spaces and has a population of 470,000 inhabitants (INDEC, 1991/ 2001). The demographic units were a middle-income neighbourhood (MIN, 10 blocks including one block of green space, about 950 residents), and a low-income neighbourhood (LIN, 12 blocks including one block of green space or park, about 1500 residents). Both units were selected according to their socioeconomic status and contrasting urban characteristics such as: all streets paved in MIN and 20% in LIN; 6% of precarious households, unfinished or built entirely or partially with other materials than concrete, brick or woods, e.g. metal plates, in MIN and 67% in LIN; 87% of households with water supply services in MIN and 0% in LIN (Rubel et al., 2003) Canine population On the basis of a census performed in households, the estimated densities of domiciled dogs/km 2 were 2114 and 3575 for MIN and LIN, respectively, and the mean number of inhabitants per domiciled dog were

3 D. Rubel, C. Wisnivesky / Veterinary Parasitology 133 (2005) and 4.3 for MIN and LIN, respectively (Rubel et al., 2003). Because both domiciled and unowned dogs were free-ranging animals, the category unowned dogs could not be evaluated. The female proportion was 64% in MIN and 37% in LIN. The age structure showed that the median age was 4 years in MIN (first-third quartiles = 2 8) and 3 years in LIN (first-third quartiles = 1 5) ( p < 0.01). The percentage of puppies less than 1 year old was higher in LIN than in MIN: 11.6% in MIN and 26.2% in LIN ( p < 0.01) (Rubel et al., 2003) Data collection Estimation of fecal contamination During August 1999, a census of dog feces which included to draw a detailed map (scale 10 cm) and to calculate all areas drawed was performed from the two opposite sidewalks, to left and right from street-of six and four block segments selected at random in MIN and LIN, respectively. The term block segment means the linear stretch of the street between the curblines of the cross streets that intersect such block. The term sidewalk means each one of the areas that runs along a street that is set aside for pedestrians, limits with a street or an house, and is approximately 100 m long. In both study areas, the sidewalks include concrete, bare dirt, grass, sand, garbage and shrubs or trees in different proportions. One of the 12 sidewalks sampled in MIN was not included in the analysis because it was adjacent to the railway track and could not be used by people. All dog feces in yards, housing premises, from 10 (MIN) and 31 (LIN) randomly selected households were counted. The green spaces or parks, defined as areas with no building used for recreation (one in each neighbourhood), covered an area of 2610 m 2 in MIN and 8500 m 2 in LIN. Despite the neglected of the green space in LIN presence of garbage, water-it will be referred to as park because of its recreational purpose. The park in MIN showed six sectors delimited by paved roads. All sectors showed trees, shrubs, grass and bare ground, and only one sector included a playground. The whole observed canine feces were located in these six sectors. The four sidewalks surrounding the park were also surveyed, and they were analysed separately from the rest of the sidewalks and park. The park in LIN lacked paved roads and surrounding sidewalks. In this park, three fringes were sampled in each of the following heterogeneous areas: area with accumulation of garbage and water (693 m 2 ), playground area (723 m 2 ), and area comprising a soccer field (1868 m 2 ). In addition, an unused and unoccupied ground-containing bare ground, grass, wastes and debris-was also surveyed in LIN. It covered part of the inner central space of one block. To evaluate the use of parks by dogs in each neighbourhood, green spaces were surveyed between 9 AM and 6:30 PM during one day in August All animals entering the park were counted and the time of arrival was registered, as well as whether dogs defecated or urinated during their stay at the park. In LIN, the time spent in the park was also recorded Estimation of parasite prevalence A cross-sectional survey was carried out during August 1999 to estimate the prevalences of different parasites in the canine population. Fecal samples from all dogs present at the time of the study were taken on a randomly selected sample of households (MIN: 65 dogs in 53 households; LIN: 77 dogs in 52 households). Fecal samples were fixed in 5% formaldehyde and transported to the laboratory Diagnostic techniques Fecal samples were processed using a modified version of Teleman s concentration-sedimentation formalin/ether method (Shore García and Ash, 1973). Microscopic examination of dog feces for the presence of parasite eggs was carried out in 16 slides containing the sediment obtained from each sample (one slide had one 20 mm 20 mm coverslip). This procedure resulted in a sensitivity of 95% for the detection of the less frequently found eggs, according to a previous study on the sensitivity of the diagnostic technique mentioned above (Zunino et al., 1999) Data analysis Differences between proportions were analysed using the chi-square test and differences between medians by the Mann Whitney test.

4 342 D. Rubel, C. Wisnivesky / Veterinary Parasitology 133 (2005) Table 1 Amount and distribution of faeces per environment in the middleincome neighbourhood and the low-income neighbourhood, San Martín, Greater Buenos Aires, 1999 Environment MIN n LIN n Sidewalks Households Parks a 309 c d 1 Unoccupied ground b Total faeces a Areas with no building used for recreation. b Area unoccupied and unused containing bare ground, grass, wastes and debris. c 177 in all six sectors of bare ground or vegetation delimited by paved roads and 132 in the four surrounding sidewalks. d 83 in the area with accumulation of garbage and water, and 126 in the soccer field area. 3. Results The total number of observed feces was 847 in MIN and 1570 in LIN. The general distribution of observed feces is shown in Table 1 and the density of feces in each environment is shown in Table 2. With respect to fecal contamination in parks, in LIN the playground area and the area with accumulation of garbage and water had a higher contamination level than the soccer field and the unoccupied ground (15 and 12 feces /100 m 2 versus 7 and 6 feces/100 m 2, respectively. In MIN, the park showed two sectors with low fecal density (1/100 m 2 ), one of which included the playground, and four sectors with higher densities (between 9 and 17 feces/100 m 2 ). Feces concentrated on grass surfaces in all the surveyed environments (Table 3). Parasites found in feces belonged to genera Ancylostoma, Trichuris, Toxocara and Dipylidium. The percents of parasitized dogs, tools with helminth eggs, were 40 and 70% in MIN and LIN, respectively (26/65 and 54/77, x 2 = 15.17, p < 0.01). The respective prevalences in MIN and LIN were as follows: 14 and 53% for Ancylostoma (9/65 and 41/77, x 2 = 23.99, p < 0.01), 9 and 17% for Toxocara (6/65 and 13/77, p > 0.05), 26, and 38% for Trichuris (17/65 and 29/77, p > 0.05). Dipylidium was detected in a single sample from MIN (1.5%). Table 2 Contamination of households, sidewalks and parks by dog faeces in both studied neighbourhoods, expressed as the number of faeces and density per environment and density, San Martín, Greater Buenos Aires, 1999 Households Parks Sidewalks b MIN LIN MIN LIN MIN LIN n a Faeces b Total area surveyed (m 2 ) Median number of faeces Quartiles (Q 1 Q 3 ) Median density (faeces/m 2 ) c 0.19 c Quartiles (Q 1 Q 3 ) a MIN: all six sectors of bare ground or vegetation delimited by paved roads were surveyed. LIN: three sectors of the park (8500 m 2 ) were surveyed. Data from the unoccupied ground are not shown in the table: 163 faeces were counted in m 2, density: 0.06 faeces/m 2. b Data from sidewalks surrounding the park in MIN are not included. c Significant differences between the sidewalks of the two studied neighbourhoods (Mann Whitney test p < 0.05). Table 3 Percentages of censused faeces in each type of substratum and environment in the middle-income neighbourhood and the low-income neighbourhood, San Martín, Greater Buenos Aires, 1999 Concrete Bare ground Grass (variable cover) Other (sand, garbage) Sidewalks-LIN 3% (22/727) 9% (66/727) 86% (625/727) 2% (14/727) Park-LIN 0% (0/315) 3% (10/315) 96% (302/315) 1% (3/315) Sidewalks-MIN 4% (19/470) 3% (14/470) 93% (437/470) 0% (0/470) Park-MIN 0% (0/177) 9% (16/177) 91% (161/177) 0% (0/177)

5 D. Rubel, C. Wisnivesky / Veterinary Parasitology 133 (2005) On the basis of the calculated fecal densities and infection prevalences, the density of infected feces/m 2 was estimated for each of the studied environments. The comparison of fecal and parasite contamination between the different environments in both neighbourhoods is shown in Fig. 1. In LIN, fecal density in sidewalks was higher than in the park and households (Mann Whitney test, p < 0.05). In MIN, fecal density in sidewalks was higher than in households ( p < 0.01), and this was the only statistically significant contrast between environments. Sidewalks surrounding the park (n =4; median feces density = 0.21; q 1 q 3 = ) showed higher levels of fecal contamination than the rest of the sidewalks surveyed, but differences were non-significant (n = 11; median feces density = 0.10; q 1 q 3 = ). Sidewalks and housing premises in LIN had a higher density of infected feces than those in MIN (Mann Whitney test, p < 0.05). The evaluation in the use of parks by the canine population is shown in Table 4, and the temporal pattern of use is shown in Fig. 2. The mean number of entries per hour was 14 in LIN and 5 in MIN. All dogs visiting the parks in both studied neighbourhoods were unleashed. Fig. 1. Density of faeces, infected faeces and faeces positive for Ancylostoma, Toxocara and Trichuris in the different environments in both areas, San Martín, Greater Buenos Aires, SdLIN: sidewalks of LIN, SdPkMIN: sidewalks of MIN park, SdMIN: sidewalks of MIN, ParkLIN: park of LIN, ParkMIN: park of MIN, PrLIN: premises of LIN, PrMIN: premises of MIN. A, B, C: significant differences by Mann Whitney Test between box with equal type ( p < 0.05).

6 344 D. Rubel, C. Wisnivesky / Veterinary Parasitology 133 (2005) Fig. 2. Canine visits into parks in the middle-income neighbourhood (MIN) and the low-income neighbourhood (LIN), according to the hours of the day (n MIN = 49 and n LIN = 139), San Martín, Greater Buenos Aires, Discussion The school age children, aged lower than 12 years, in different Argentine cities are highly exposed to eggs of parasites transmitted by canine feces. Antibodies against Toxocara canis, have been detected in 37% of 206 children tested from Resistencia City (Northeastern Argentina) (Alonso et al., 2000), 39% of 156 patients of different sex and age from La Plata City (Radman et al., 2000) and 12.8% of children attended at Mi Pueblo Hospital in the Locality of Florencio Varela (Greater Buenos Aires, Faggiano, 2000). Currently, one case of ocular toxocarosis is diagnosed every week at the Ophthalmology Unit of the Prof. Dr. J.P. Garrahan Paediatric Hospital, which serves patients from Buenos Aires City and Greater Buenos Aires (Draghi, 2003). A clinic studies carried out in Buenos Aires showed that 44.4% from 54 children seropositive to Toxocara were asymptomatic, 16.7% showed pneumonitis, 11.1% hepatomegaly, 9.3% uveitis, 9.3% strabismus, 7.4% leukocoria and 5.6% fever (Altcheh et al., 2003). Other study carried out in 38 patients with asthma from La Plata City (distant 60 km from Buenos Aires City), proved that 68.42% of this patients suffered a covert toxocarosis (Minvielle et al., 1999). Consequently with this epidemiologic view and the high prevalences of helminthiases in the canine population, solid baseline information is needed to design effective and sustainable control programmes. The urban characteristics of Buenos Aires suburbs (Greater Buenos Aires) differ from those of Buenos Aires City. For example, the availability of green spaces (parks) per inhabitant is lower in Greater Table 4 Canine census in the parks located in each of the studied neighbourhoods (9 AM 6:30 PM), San Martín, Greater Buenos Aires, 1999 MIN LIN Number of canine visits Number dogs Number entries/dog Percentage transitory entries a 36.7% 70% Percentage unowned entries b 62% (30/48) 86% (118/137) Time of permanence nd 1 min (Q1 = 0, Q3 = 5) c a Transitory entries: the dog did not defecate or urinate during its stay at the park. b Unowned entries: unowned dogs wandering about the park. c Median is provided, and first and third quartiles are within brackets. The minimum time of permanence was 0 (less than 1 min) and the maximum time of permanence was 45 min (based on 135 observations). Buenos Aires than in Buenos Aires City (0.9 and 2 m 2, respectively), but the distribution of green spaces varies in different sectors of the City (GCBA, 2003). In the studied Partido de San Martín, the available of green space per inhabitant was 0.74 m 2. In contrast to Buenos Aires City, the sidewalks in Greater Buenos Aires have a higher surface area covered with grass, hence a greater dilution of fecal contamination is expected, accounting for the greater availability of suitable surfaces and the preference of dogs for defecating on grass surfaces. On the contrary, the paved sidewalks of Buenos Aires City, show a very low proportion of bare ground, usually less than 1 m around trees, where the feces concentrate (Rossi et al., 2001). This hypothesis have been previously suggested by other authors (Alonso et al., 2001). This effect of dilution of fecal contamination was not verified when the available information for Buenos Aires City was compared with our results in suburban areas, such as MIN and LIN (see Table 5). Data from this Table may indicate an increasing contamination gradient from the area with a better urban infrastructure (Buenos Aires City) to the less urbanized area. This apparent gradient coincided with the gradient of density of the canine population, which increased in the same direction. Available data indicate that in Buenos Aires City there is one dog per 7.4 inhabitants (Anderson et al., 1996), while in the Partido de San Martín we recorded one dog per four (MIN) and two (LIN) inhabitants.

7 D. Rubel, C. Wisnivesky / Veterinary Parasitology 133 (2005) Table 5 Comparison between data reported for Buenos Aires City and results from both study areas MIN (middle-income neighbourhood) and LIN (low-income neighbourhood), Partido de San Martín, 1999 Buenos MIN LIN Aires Parks a n =15 parks n =6 sectors n =3 sectors Number faeces/100 m Number infected faeces/100 m Sidewalks a,b n = 154 n =11 n =8 Number faeces/100 m Number infected faeces/100 m a Data of parks and parasite prevalences taken from Petersen et al. (1995). b Data of sidewalks taken from Rossi et al. (2001). These results were in general agreement with a survey conducted in different municipalities of Greater Buenos Aires, where densities ranged between 2.5 and 4.6 people/dog (González and Manchini, 1998). With respect to parasite contamination, the importance of sidewalks and other spaces in comparison with public parks (as the so-called camellones in México D.F.: green areas in the middle of wide avenues) has already been suggested by various authors for other cities (Martínez-Barbabosa et al., 1998; Alonso et al., 2001; Duménigo B, personal communication). In suburbs, sidewalks are usually used as playgrounds by children, partially because of the limited availability of green spaces. On this basis, and considering that according to our results sidewalks were the most contaminated environments, these should be regarded as priority sites targets for prevention programmes of parasites transmitted by dogs. Yards or housing premises may also play an important role in the transmission of parasites because they show a high fecal contamination and are frequently used by children, as previously proposed by other authors (Smith et al., 1984; Alonso et al., 2001). Therefore, yards should also be taken into account in control programmes. The problem posed by green spaces deserves special attention because of their intensive use as recreational places by children and adults, and the widespread habit of Buenos Aires citizens of sunbathing with bathing suits in the parks. According to data on canine density and availability of green spaces, in Buenos Aires there would be approximately 0.05 dogs/m 2 of available green space. In contrast, in Greater Buenos Aires the value is from 7 to 11 times higher: 0.34 and 0.58 dogs/m 2 of green space for MIN and LIN, respectively [based on the canine densities estimated from both study areas, the area of Partido de San Martín and the area of green spaces available in the Partido (Agostini et al., 1986; Anderson et al., 1996)]. However, the pressure of using green spaces by dogs may be lower in Greater Buenos Aires because in such area dogs tend to be free-ranging animals not accompanied by their owners (personal observations; Ministerio de Salud de la Pcia. de Bs As, 1994), and almost all sidewalks are provided with grass surfaces. The comparison between the numbers of dogs per day visiting parks in MIN and LIN and available data from Buenos Aires City shows that parks in the latter area are used by a higher number of dogs. The median of canine visits per day estimated from 10 parks was 175, q 1 q 3 = (De Francesco et al., 1998 and De Francesco, personal communication). Despite this higher pressure of use, green spaces in the City are less contaminated than those in suburban areas, probably due to the implementation of cleaning policies in public spaces, an activity that is almost lacking in Greater Buenos Aires. The temporal pattern of use of green spaces by dogs was uniform in both studied area, and if preliminary observations are confirmed, the results could be used to select the most appropriate time-period for park cleaning. It is also important to mention that fecal contamination in the green spaces of Buenos Aires City and in the suburbs is not concentrated in sandpits, thus confirming previous studies conducted in the same urban system (Sommerfelt et al., 1994). This is in contrast with the situation in other countries, where fecal density was found to range between 9 and 63 feces/m 2 of sandpit (Uga, 1993). Both in parks of Buenos Aires City and suburbs, feces concentrate in bare soil or grass surfaces, which are frequently used by children to play soccer, particularly in Buenos Aires City. In addition, such surfaces are chosen to plant trees, thus providing a shady environment suitable for egg survival, as demonstrated in a study showing that the prevalence of Toxocara and the

8 346 D. Rubel, C. Wisnivesky / Veterinary Parasitology 133 (2005) proportion of viable eggs were higher in samples taken from shady sectors than in samples from sunny sectors (Ruiz de Ybáñez et al., 2001). As a consequence, it would be highly recommendable to provide separate public sectors for people and for dogs. In regards to the differences observed between the two study areas in Greater Buenos Aires, canine density in LIN would be double that canine density in MIN when considering the higher proportion of unowned dogs in the former. This is likely to account for the fecal density in sidewalks and households, since median fecal density in LIN were almost twice those in MIN. Although canine visits per day to the park in LIN also were more than twice those in MIN, the median densities of feces in both green spaces were similar. This fact may suggest the presence of behavioural patterns involving the selection of defecation sites that are still not understood, and therefore more detailed studies on the defecating behaviour of dogs may be needed for the rational design of effective control programmes. The temporal fluctuations in the number of canine visits into parks in both study areas could be related to behavioural patterns. Our results agree with other behavioural studies on the patterns of daily activity in feral dog populations (Macdonald and Carr, 1995). Parasite prevalences seem to be higher in the suburbs (MIN and LIN) than in Buenos Aires City. In parks of the city mean maximum and minimum percentages of parasitized feces were 9 and 33% for three parks surveyed over 5 years (Petersen, ), while in this study the parasite prevalences were 40 and 70% for MIN and LIN, respectively. In part, this would be associated with different levels of veterinary care in both areas, since the percentage of owned dogs that never received anthelminthic treatment was 53% in LIN and 22% in MIN (Rubel et al., 2003, no evaluations available for Buenos Aires City). Thus, the proportion of veterinary cared dogs seems increased with the socioeconomic status. On the other hand, higher dog densities and pet ownership habits (such as allowing dogs to roam the neighbourhood unsupervised) could result in higher infection frequencies. On the contrary, a high proportion of dogs in Buenos Aires City are leashed and under the control of the owner. Although no significant differences were detected between the prevalences of some of the parasites (Trichuris and Toxocara) in stool samples from the two studied areas, fecal contamination levels differed significantly. Therefore, the contrast of the density of feces infected with these parasites between areas was significant, and areas were different in contamination and transmission levels, particularly in sidewalks and yards or housing premises. Finally, all facts mentioned above support the need for further studies regarding the Buenos Aires Metropolitan Area (Buenos Aires City and Greater Buenos Aires) as a single system, in view that the canine density, fecal contamination and prevalences appeared to follow an increasing gradient to the less urbanized areas, which in turn coincided with population nuclei of lower socioeconomic level and lowest levels of sanitation. At the same time, the canine fecal contamination of available public spaces seem to vary in areas with different urban structures and ownership habits: sidewalks more contaminated in the suburban area, and green spaces or parks more contaminated in the more urbanized area. Acknowledgements This study was supported by the National Agency for Scientific and Technological Promotion (ANPCyT, Argentina). We would like to thank Dr. Peter Schantz (CDC, Atlanta) by his useful comments on the manuscript. We are indebted to Dr. Dora Kurchin and the personnel of Public Health Local Center, to Dr. Eyerabide from Head Office of Preventive Medicine of San Martín and to the neighbours. Thanks are due to Gabriela Zunino, Laura Abramowicz, Manuela Chomnalez, Sebastián Torrella and Pablo Salomon for field assistance and to Alfredo Mendoza of FCEyN for providing a vehicle for field work. References Agostini, A., Franco, A., Sommerfelt, I., Arando de Lema, J., Kistermann, J.C., Aspectos de la demografía canina y felina en el Partido de General San Martín. Buenos Aires. Rev. Med. Vet. (Bs. As.) 67, Alonso, J.M., Bojanich, M.V., Chamorro, M.C., Gorodner, J.O., Toxocara seroprevalence in children from a subtropical city in Argentina. Rev. Inst. Med. Trop. S. Paulo 42,

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