Epidemiological Analysis of Intestinal Parasites in Canine Faecal Samples from Public Green Places: Spatial, Socioeconomic, and Environmental Associations

Abstract

Dogs harbour a wide range of endoparasites, many of which pose a significant risk to public health globally due to their zoonotic potential. Addressing the dynamics of zoonotic parasites comprehensively requires epidemiological studies under the One Health paradigm, incorporating multidisciplinary methodologies to explore the complex interactions among humans, animals and the environment. The present study aimed to investigate the presence of canine parasites in public green places (PGPs) in Tandil, Argentina, using epidemiological and geographical tools to enhance efforts towards the prevention and control of canine parasitic diseases impacting public health. Between August 2024 and January 2025, 893 canine faecal samples were collected through a randomised two-stage sampling process from 92 public green places. The overall prevalence of intestinal parasites was 29.9% and the identified parasites were Trichuris vulpis, Ancylostoma caninum, Eucoleus spp., Uncinaria stenocephala, Toxascaris leonina, and Cystoisospora sp. Risk factors identified included the presence of playgrounds and a higher dog density, while protective factors comprised sampling during spring vs. winter and presence of areas of bare soil on the public green places. Spatial analysis revealed clusters of high prevalence in areas with lower socioeconomic status, and clusters of low prevalence in higher socioeconomic areas. These findings emphasise the need for targeted preventive measures, including responsible pet ownership policies. Moreover, the methodological approach adopted could be replicated in other regions to enhance public health protection and mitigate the risks associated with zoonotic parasitic diseases.

1. Introduction

Dogs are hosts to a wide range of endoparasites, many of which pose a global public health threat as zoonotic species capable of causing diseases in humans [1]. Humans can become infected through direct contact with parasitised dogs or their faeces, or indirectly through contaminated water, soil, or raw food. Some of these parasitoses can have severe health consequences, such as cystic echinococcosis [2], while other less known ones, e.g., visceral or ocular larva migrans, are also causes of concern [3]. The most vulnerable groups include children, pregnant women, and immunosuppressed individuals. Propagation of these canine parasitoses is a worldwide problem. Amongst people affected are individuals who have never been pet owners; this has led to recognising environmental contamination with faeces from parasitised dogs as a problem, especially in public places [4,5]. This situation is exacerbated by factors such as high concentrations of parasitic infective stages in the environment [6], environmental conditions favourable to their survival, large populations of street dogs or dogs without responsible owners [7,8], and human habits that facilitate individual exposure to the source of infection [9].

Several parasitological surveys have been conducted in different locations in Argentina; their results show the presence of parasite eggs in diverse environments, such as streets, sidewalks, public squares, etc., and places ranging from affordable touristic cities to precarious neighbourhoods [10,11,12,13,14,15,16,17,18,19,20,21,22,23]. The prevalence of parasitic forms in these studies ranged from 36% to 55%, thus indicating a clear risk of exposure and infection for the local inhabitants as well as other dogs accessing such places.

While previous studies in Argentina have focused on urban environments such as streets and sidewalks, this is the first study to investigate zoonotic dog parasites specifically in PGPs using both epidemiological and geographical tools, which provide novel insights into the interactions between humans, animals, and the environment. Given the need to comprehensively address the understanding of zoonotic parasite dynamics, it is necessary to perform epidemiological studies under the One Health approach by incorporating multidisciplinary methodologies to unravel the complex interactions between humans, animals, and the environment. Thus, the objective of the present study was to determine the situation of dog parasites in public green places in Tandil, Argentina, and use epidemiological and geographical tools to obtain information conducive to strengthening all efforts towards prevention and control of canine parasitic diseases affecting public health.

2. Materials and Methods

2.1. Study Location and Its Socioeconomic Stratifications

The study was conducted in Tandil (37°19′ S, 59°08′ W), central-east of Argentina. The city, surrounded by the Tandilia Hills System (175 m.a.s.l.), covers an area of 52.34 km² and has a population of over 140,000 inhabitants [24]. The mean annual temperature is 13.4 °C and the annual range is 14.5 °C. The precipitation is concentrated between spring and summer (October to March), with an annual amount of 893 mm [25].

Three urban socioeconomic regions (low, medium, high) were generated based on the following socioeconomic and housing variables obtained from the INDEC 2022 Census: household educational climate, ownership of a computer or tablet, unsatisfied basic needs, health coverage, economic activity status, occupational category, home ownership, overcrowding, housing type, and quality of materials. The K-means method was used within the clustering tools in ArcGIS v.10.5, allowing for the identification of three regions based on these variables. This method works by initially assigning each census unit to a group and then iteratively adjusting the assignments to minimise the internal variability of each cluster. For each iteration, it recalculates the centroids and reassigns the census units to the nearest cluster until the assignment stabilises.

2.2. Sampling

A random 2-stage sampling was conducted in 92 public green places (PGPs), aiming to collect 920 samples of dog faeces, i.e., 10 samples per PGP. The sampling size was determined considering the following factors: the total number of existing local PGPs (114) [26], excluding those places categorised as stadium or lookouts; an expected prevalence of 44% of parasitic forms in dog faeces, according to previous reports [10,11,27]; a relative error of 0.2 and a confidence level of 95%.

Each PGP was georeferenced, and the following data were collected for each sampling: date and time; type of ground observed (grass, gravel, bare soil, concrete, hill rocks); presence of playgrounds; number of dog faeces observed; and number of dogs observed. The data were collected while systematically walking two perpendicular transects that initiated and ended at the opposed endpoints of the PGP and computing the total length (m) covered. The study did not aim to work with freshly voided faeces but with faeces found on the ground at the time of each sampling, i.e., some samples were a few hours old, while others had been on the ground for several days or weeks.

2.3. Parasitological Procedures

Dog faecal samples were collected from the ground and placed in plastic bags, sealed, and identified. The samples were transported to the Laboratory of Clinical and Experimental Parasitology, Faculty of Veterinary Sciences, National University of Central Buenos Aires Province (LPCE, FCV, UNCPBA) in Tandil, and kept at 4 °C until being processed 24–48 h after collection.

Each sample was processed following a modification of the sedimentation–flotation centrifugation technique previously described [28,29] using a salt–sucrose solution (specific gravity 1.3). The modifications consisted of mixing 4 g of faeces with 20 mL of water; the tubes were filled leaving a 1 cm margin from the top and, after the second centrifugation, a few drops of solution were added to each tube until a meniscus without bubbles was formed at the top; then, a 22 × 22 mm coverslip was gently placed on the top. After 5 min, the coverslip was removed and placed on a microscope slide, which was observed under an optical microscope. Parasite eggs were measured and identified by their morphological features and size based on published keys [30].

2.4. Data Handling and Statistical Analysis

A database was created with the parasitological and epidemiological data. Overall parasite prevalence and individual genera prevalence were estimated with a 95% CI. The association between different parasite genera was evaluated using the chi square test or Fisher’s exact test. The percentage of samples with one or more than one parasitic genus was also determined. The variable distribution was explored using a multiple correspondence analysis (MCA). The association between the presence of positive samples in the PGP and the different studied variables was analysed by Poisson regression. Different regressions were established considering the total number of positive samples as a dependent variable and the total number of analysed samples as offset; the independent variables were those mentioned as data collected above (see Sampling). The variables dog density and faeces density were created quantitatively and qualitatively considering the number of dogs/100 m and number of faecal depositions/m, and transforming them into categorical variables with the median as the cut-point. These variables were graphically added to a human population density map of the city. The georeferencing (latitude and longitude) of each sampling site was used for the spatial analysis. The existence of spatial clusters with a high/low frequency of positive samples was analysed using a Poisson model. The factors associated with the PGPs in those spatial clusters were evaluated. Bivariate associations were determined using the chi square test or the Fisher’s exact test, as appropriate, for qualitative variables, and the Wilcoxon test for quantitative variables. To identify possible confusion factors, the association between variables was assessed by the chi square test. In addition, the interaction among variables was also evaluated in a logistic regression model. The significance level for all statistical analyses was established at 0.05. A 95% confidence interval odds ratio (OR) was estimated for those variables associated with positive samples or with the spatial clusters. The software used for all the above analyses were InfoStat v2018P, R Core Team v2020, Epidat v4.1, and SatScan v9.6.1.

Ethical approval for this study was not required as it was not an interventional study involving either animals or humans.

3. Results

A total of 893 samples of dog faeces were collected from 92 PGPs between 17 August 2024 and 2 January 2025. Although the aim was to collect 10 samples/PGP, this was not possible in a few of them. The average (and standard deviation) faeces density was 0.05 (0.07) faeces/m; these numbers for dog density were 0.89 (1.93; min: 0, max: 16.67) dogs/100 m for all the PGPs sampled. The spatial location of the PGPs and the two mentioned variables are shown in Figure 1, which also shows the density of human population.

Positive diagnosis of at least one endoparasite genus was made in 84.8% (79/92) of the surveyed PGPs. Figure 2 shows the proportion of positive samples in each of the PGPs.

The coprological analysis showed that 267/893 samples were positive for one or more parasite genera. The overall prevalence was 29.9% (95% lower confidence interval limit (LCL): 26.84 and 95% upper confidence interval limit (UCL): 32.96) The prevalence (%, 95% LCL and 95% UCL) for each parasite found was as follows: Trichuris vulpis (Froelich, 1789), 16.91% (14.4 and 19.42); Ancylostoma caninum (Ercolani, 1859), 8.85% (6.30 and 10.76); Eucoleus spp. (Dujardin, 1845), 8.01 (6.22 and 9.9); Uncinaria stenocephala (Railliet, 1884), 6.27 (4.62 and 7.92); Toxocara canis (Werner, 1782), 4.70% (3.26 and 6.15); Toxascaris leonina (Gmelin, 1790), 0.11% (0.003 and 1.57); Cystoisospora spp. (Frenken, 1977), 0.90 (0.22 and 1.57). See Supplementary Material for photographs of most of the parasite eggs identified.

A total of 63% (169/267) of the samples harboured only one parasite genus. The most frequently identified parasites from these samples were T. vulpis (49%), followed by Eucoleus spp. (18%), A. caninum (17%), U. stenocephala (8%), T. canis (5%), T. leonina (1%), and Cystoisosospora spp. (1%). While 37% (98/267) of the samples contained combinations of two or more genera (

Table 1. Relative frequency of multiple parasite combinations (2 to 6 species) found in 98 canine faeces samples taken from 92 public green places (PGPs).

Parasite Combinations	Frequency (%)
T. vulpis + A. caninum	17.304
T. vulpis + U. stenocephala	12.24
T. vulpis + Eucoleus spp.	10.20
T. vulpis + T. canis	7.14
A. caninum + U. stenocephala	6.12
U. stenocephala + Eucoleus spp.	6.12
T. vulpis + A. caninum + Eucoleus spp.	5.10
Eucoleus spp. + T. canis	4.08
T. vulpis + U. stenocephala + A. caninum	4.08
T. vulpis + U. stenocephala + T. canis	3.06
T. vulpis + A. caninum + T. canis	3.06
T. vulpis + U. stenocephala + A. caninum + Eucoleus spp.	3.06
U. stenocephala + A. caninum + Eucoleus spp.	2.04
U. stenocephala + T. canis	2.04
A. caninum + T. canis	2.04
Eucoleus spp. + Cystoisospora spp.	2.04
A. caninum + Eucoleus spp.	1.02
Cystoisospora spp. + A. caninum	1.02
T. canis + Cystoisospora spp.	1.02
T. vulpis + U. stenocephala + Eucoleus spp.	1.02
T. vulpis + T. canis + T. Leonina	1.02
T. vulpis + T. canis + Cystoisospora spp.	1.02
U. stenocephala + A. caninum + T. canis + U. stenocephala	1.02
A. caninum + Eucoleus spp. + T. canis + Cystoisospora spp.	1.02
A. caninum + U. stenocephala + Eucoleus spp. + T. canis	1.02
T. vulpis + A. caninum + U. stenocephala + Eucoleus spp. + T. canis + T. leonina	1.02

).

Significant associations were found between the presence of T. canis and Eucoleus spp. (p = 0.0017), T. canis and Cystosispora spp. (p < 0.0001), A. caninum and T. vulpis (p = 0.0001), and A. caninum and U. stenocephala (p = 0.0001).

The exploratory approach using MCA indicated that the variables associated with the overall presence of parasites in the PGPs were the presence of playgrounds as well as the absence of gravel and hill rocks (see graph in Supplementary Material). The identified risk factors were the presence of playgrounds (p = 0.0434; OR 1.3364, 95% LCL 1.01572, 95% UCL 1.75839) and dog density (p = 0.0014; OR 1.0942, 95% LCL 1.03169, 95% UCL 1.16044). The protective factors identified were spring sampling (p < 0.0001; OR 0.5599, 95% LCL 0.42554, 95% UCL 0.73668) and the presence of bare soil in the PGP (p < 0.0001; OR 0.4868, 95% LCL 0.35572, 95% UCL 0.66604). See Supplementary Material for complete details of the Poisson regression model output.

Three spatial clusters of high rates of positive samples were detected in the north of the city (2.2–2.59 times higher than in those PGPs outside the clusters), coinciding with residential areas of low–middle socioeconomic status. Also, three clusters of low rates of positive samples (up to 3.125 times lower than in the PGPs outside the clusters) were found in the south of the city, which coincides with residential areas of high socioeconomic status (Figure 3). The complete details of the spatial analysis output are shown in the Supplementary Material.

The analysis of the variables associated with the PGPs in clusters of high rates of positive samples revealed that fewer of those sites were sampled in spring (p = 0.0243; OR 0.0963, 95% LCL 0.01031, 95% UCL 0.89978) and fewer were covered by bare soil (p = 0.0405; OR 0.492, 95% LCL 0.359, 95% UCL 0.672) when compared to the PGPs outside the clusters. The analysis of the variables associated with the PGPs in clusters of low rates of positive samples showed that there was more soil cover in those PGPs compared to the PGPs outside the clusters (p = 0.0386; OR 2.6645, 95% LCL 1.060, 95% UCL 6.694). See Supplementary Data for complete details of the logistic regression model output.

4. Discussion

The findings of the present study reveal the presence of intestinal parasites of dogs with zoonotic potential in most public green places of Tandil, Argentina. This translates into a risk of parasite infections for the people using these areas, either recreationally or for work. The study presents, as well, the first account of the prevalence and diversity of canine intestinal parasite species in public green spaces in this area. By incorporating epidemiological and geographical tools, the spatial, socioeconomic, and environmental variables were analysed to provide a comprehensive perspective on the factors influencing the distribution and prevalence of the zoonotic parasites involved. The overall parasite prevalence is in agreement with that communicated for other cities in Argentina [10,11,16,31,32], and other countries such as Brazil [33], Romania [34], Serbia [35], and Spain [36], amongst others.

Six parasite genera/species were found in this study, three of them known for their zoonotic potential (A. caninum, U. stenocephala, and T. canis). Although T. vulpis has been sporadically reported in human faeces, sometimes even associated with signs of gastrointestinal disease, its zoonotic potential is still debatable [37]. The parasitic species found are consistent with those reported previously in Argentina [14,15,19,21,23] and other countries [35,36], emphasising the notion that the problem of urban environments contaminated with dog parasites—zoonotic or non-zoonotic—is indeed cosmopolitan. The most prevalent species in the present study were T. vulpis and A. caninum, and their combination was the most identified in the samples with more than one parasite species and the most associated statistically. Together with T. canis, these species are those that most commonly infect dogs—both females and males—of all ages worldwide [37]. The association between T. canis and Cystoisospora spp. could probably mean that the samples from which they were jointly identified were from very young animals. These two parasites are very frequently present in puppies, the former because of its transplacental transmission [38], and the latter because immunity to these protozoa is still not developed in very young animals [39]. An association between T. canis and Eucoleus spp. in faecal samples was observed in the present study, suggesting that co-infection with T. canis could predispose animals to respiratory infections caused by Eucoleus spp. A previous study reported that co-infection with T. canis increased the prevalence of cardiorespiratory nematodes such as E. boehmi and E. aerophilus in dogs [40]. This finding suggests that the presence of T. canis may facilitate infection by Eucoleus spp., possibly due to partial immunosuppression in the affected animals. The association between T. vulpis and A. caninum could likely be influenced by environmental factors that promote the persistence of their infective forms. The resistance of T. vulpis eggs and A. caninum larvae in the environment is a key factor in understanding their association and co-infection in dogs. The persistence of these infective forms in soils and contaminated areas, combined with the high exposure of puppies to these environments, facilitates simultaneous infection by both parasites. The eggs of T. vulpis can survive in the environment for several months, increasing the likelihood of infection in dogs, while A. caninum infective larvae can also remain viable in the soil for a significant period [1]. Moreover, the prolonged survival of these parasites in the environment increases the parasitic load and the probability of co-infection, highlighting the importance of controlling hygiene and environmental management to reduce parasite transmission [41]. The association between A. caninum and U. stenocephala may be explained by their similar biological and ecological characteristics, particularly their environmental resistance and modes of transmission. Both are nematodes of the Ancylostomatidae family, and their infective larvae develop in the environment under comparable conditions—moist, warm, and shaded soils—which allow them to survive and remain infective for extended periods. Studies have shown that these environmental conditions favour the survival and dissemination of hookworm larvae. For example, the presence of Ancylostoma spp. and Uncinaria spp. in dogs from public parks was highlighted in Mérida, Yucatán [42], emphasising that the tropical climate and the presence of organic matter in soil are conducive to larval development and persistence. These findings indicate that when one of these parasites is able to establish and thrive in a given environment, the other likely benefits from the same conditions, increasing the chances of co-infection. Moreover, both parasites can infect their hosts through skin penetration or ingestion of infective larvae. This overlap in transmission routes, especially in young or immunocompromised animals frequently exposed to contaminated environments, contributes to the likelihood of simultaneous infection. The absence of cross-protective immunity between Ancylostoma and Uncinaria also means that an infection with one genus does not prevent the establishment of the other, further facilitating co-infection [43]. These overlapping environmental requirements and infection pathways underscore the importance of implementing control measures focused on environmental hygiene and regular deworming protocols, particularly in areas where canine populations are in close contact with contaminated soil.

The PGPs in the present study featuring children’s playgrounds and larger dog densities were associated with dog faeces positive to parasites. Similarly, a higher prevalence of hookworms and hookworms + T. vulpis in canine faeces close to playgrounds was found in Belgrade, Serbia [34], and Málaga, Spain [36]. In the latter study, a high prevalence of parasites with zoonotic potential such as T. canis, A. caninum, Giardia duodenalis, and Dipylidium caninum was recorded in samples from soil and canine faeces around playgrounds. This could be explained by the common fact of families with young children using the playgrounds in public areas while walking their dogs. Added to this could be the natural sociable and docile behaviour of either pets or stray dogs, which tend to come close to people, seeking food or refuge. In any case, high numbers of people attending certain public areas (recreational, touristic, etc.) would be associated with an increased density of dogs in such places [11].

The present study also revealed that those PGPs sampled in spring (vs. winter) and that featured areas of bare soil had less dog faeces positive to parasites. A possible explanation could be that a warmer climate could generate a drier microenvironment in those PGPs with bare soil, thus negatively influencing the survival and infectivity of some parasites [44]; hookworm larvae, for example, do not develop when they are exposed to direct sunlight and desiccation [1]. Another explanation could be the preference of dogs to defecate on grassy areas rather than bare soil, tiles, or sand [41]; however, no association was found between the density of faeces and the presence of positive samples; in fact, the distribution of dog faeces was found to be uniformly spread, without any pattern of differential spatial distribution.

The high proportions of both PGPs and faeces positive to parasites recorded in the present study suggest a low level of routine antiparasitic treatment for dogs, which seems to be more evident in those areas of low-to-medium socioeconomic status. This is a similar finding to others previously reported in Argentina [45,46]. The three spatial clusters with high rates of positive samples identified in the present study were located in the north part of the city, while the three spatial clusters with low rates of positive samples were located in the south, which coincides with residential areas of low–medium and high socioeconomic status, respectively. These results are in agreement with those reported previously [16], where the authors identified a higher risk of infection with certain parasite genera in neighbourhoods of low-and-medium quality-of-life indexes (QLIs) compared to those areas with high QLIs. Likewise, the number of veterinary medical centres was higher in neighbourhoods with better QLIs. The variables to generate the QLI indicator used in that paper [16] are comparable to the ones used in the present study, with the exception that the QLI involves an environmental variable that was not taken into account to generate the socioeconomic status for the present study.

The canine faeces had been in the PGPs for some time before sampling (from a few hours or days to several days or weeks) and most of the sampling of this transversal study occurred during spring and summer; this means that infective larvae of some genera could have developed and migrated out of the faeces by the time the samples were collected. Therefore, the overall and individual parasite prevalence reported in this study should be taken as base numbers as they could be lower than the actual ones.

The results reported here highlight the need to conduct additional studies to determine whether other environmental or urban variables not used in this study can influence the overall and individual prevalence of parasites in either fresh or considerably aged canine faeces in different urban green spaces.

5. Conclusions

The present study revealed a high overall prevalence of canine intestinal parasites with zoonotic potential in public green spaces of Tandil, Argentina, thus posing a risk of parasitic infections for people using these spaces for recreational or occupational activities. Given that limited financial resources are allocated to combating neglected diseases such as geohelminthiasis, preventive measures should be prioritised in the high-risk areas identified in this study and those with characteristics associated with an increased risk of infection. These measures could include policies promoting responsible pet ownership and responsible use of public spaces by pets, ultimately helping to reduce the risks of zoonotic diseases in humans.