Introduction

Ecoepidemiology has emerged to explain how biotic, environmental and even social factors influence the dynamics of infectious diseases1. However, few studies have been carried out on this topic in neglected sectors of Ecuador, as well as in some territories of the Americas.

Ecuador is located in northwestern South America; it is crossed by the equatorial line (hence its name) and has four geographic regions: coastal, Andes, Amazon and insular. The coastal region is characterized by a warm and humid climate; it is influenced by the warm El Niño current and the cold Humboldt current and has abundant fauna and flora2.

In these territories, various zoonotic parasitic infections can proliferate, especially due to the synergism between the infectious agent, host (animal or human) and the environment. When there is an imbalance, epidemic or epizootic outbreaks may occur2.

Likewise, inadequate hygiene, poor health systems and facilities, social indifference, inadequate sanitation, lack of access to medical care, low levels of education and the presence of infested domestic and stray dogs make impoverished people particularly susceptible to zoonotic intestinal parasitic infections. Furthermore, it is important to highlight that in Ecuador, there are no epidemiological records of the prevalence of intestinal helminths in domestic dogs from neglected areas3.

Neglected parasitosis (NP) belongs to neglected tropical diseases (NTDs) and are very prevalent in the tropical and subtropical regions of low- and middle-income countries, especially among marginal and rural populations that face poverty, representing a public health problem. Soil-transmitted protozoa and helminths are the two main etiologies of NP in humans3,4. It is estimated that more than 3.5 billion people worldwide harbor at least one species of intestinal parasite at some time, causing more than 450 million serious protozoan infections5 and some 300 million people suffering from severe morbidity due to intestinal helminths, of which between 10,000 and 135,000 deaths occur per year6.

Intestinal parasites affect human productivity by causing a variety of medical complications, such as abdominal pain, anemia, diarrhea, growth retardation, malnutrition, reduced physical activity, and impaired cognitive development, especially in schoolchildren5,6.

Among the most common protozoa in humans are Entamoeba (E) coli, E. histolytica, Giardia lamblia, and Cystoisospora spp., among others5. The most prevalent helminths are Toxocara canis, Ascaris lumbricoides, Trichuris trichiura, Enterobius vermicularis, Hookworm species, Echinococcus (E) granulosus, Hymenolepis (H) nana and H. diminuta6.

On the other hand, in domestic dogs, the most prevalent zoonotic protozoa are Entamoeba spp., Giardia spp., and Cystoisospora spp. Among zoonotic helminths, the following are mentioned: Ancylostoma spp., Uncinaria spp., Strongyloides stercoralis, Toxocara spp., Trichuris spp., Dipylidium caninum, Capillaria spp., and Spirometra mansoni, among others. Enteroparasites in canines result in developmental delay, anorexia, diarrhea, vomiting, abdominal distention, constipation, anemia, cough, runny nose, and intestinal and biliary obstruction; sometimes, they cause the death of the animal7.

The main route of infection in dogs and humans is the fecal‒oral route, which involves the ingestion of water or food contaminated with infectious forms; however, zoonotic transmission may also be possible through close contact between animals and humans8.

Likewise, it is important to highlight that dogs with intra- and peridomiciliary habitats play important roles in the transmission of parasitic diseases7,8.

The objective of this study was to identify enteroparasites of dogs and humans to calculate the prevalence of infection by intestinal parasites in 500 domestic dogs and 160 people and their zoonotic relationships in neglected sectors of the Ecuadorian coast. The environmental variables, social determinants and epidemiological health indicators were analyzed between April and October 2024. This research is the final result of Project approved and financed by the University of Guayaquil from Ecuador, which is titled “Ecoepidemiology of neglected intestinal helminthiasis in marginal urban and rural areas of the province of Guayas”.

Materials and methods

Ethics statement

 The present study was approved by the Research Council of the Faculty of Veterinary Medicine and Zootechnics (FMVZ) of the University of Guayaquil, the Research Department of the University of Guayaquil (DIUG), and the Ethics Committee of the Hospital “Luis Vernaza” of Guayaquil (approval code: 03EICEISHHLV-2023). All field and laboratory procedures performed were reviewed and approved by these institutional and ethical review boards. All methods were carried out in accordance with the relevant national and international guidelines and regulations, including ethical standards for research involving human participants and animals. Written informed consent was obtained from the owners of all dogs, all human participants and from the legal guardians of minors prior to their inclusion in the study.

Sampling areas

Fecal samples of domestic dogs were collected through convenience sampling (not probabilistic) in two rural sectors (Loma Larga belonging to the city of Nobol and Santa Rosa to the city of Daule) and two urban-marginal sectors of Guayaquil (Balerio Estacio and La Ladrillera), located on the Ecuadorian coast in the province of Guayas. The temperature ranges between 20 °C and 37 °C, with a tropical savanna climate (Fig. 1).

Fig. 1
figure 1

The red dots indicate two marginal urban areas (Balerio Estacio and Ladrillera) in the city of Guayaquil, and two rural areas: Loma Larga in the city of Nobol and Santa Rosa in the city of Daule. All are located in the province of Guayas, Ecuador.

Full size image

Sampling protocol

The populations of the four zones are as follows: Loma Larga, 1,000 inhabitants; Santa Rosa, 1,450; La Ladrillera, 3,607; and Balerio Estacio, 32,000. A total of 38,057 inhabitants resided in 7,212 dwellings/homes. Using the WinEpi program, the sample size was calculated with a sampling error of 2%, a confidence level of 98%, a population size of 38,057 inhabitants and a minimum expected prevalence of 3%9. According to the calculations, 129 households would be sampled; however, in this study, a total of 160 families were analyzed, where convenience sampling was used, taking into account the inclusion criteria: (1) Owners of pet dogs living in homes with poor sanitary infrastructure; (2) Owners with two or more pet dogs (Pre-survey observation showed that most dog-owning homes kept more than one dog, so limiting enrollment to these households maximized sample yield under finite resources.); (3) Persons who have the most contact with the pet dog in the home with poor sanitary infrastructure; (4) Sampling of people and their pet dogs of all ages.

Recognition of areas, informed consent, surveys

The areas were surveyed, and the importance of the study and the risk of acquiring zoonotic parasites were discussed. In addition, the methods used to collect and identify samples from people10 and their pets11 were explained.

Additionally, with prior informed consent, a survey was conducted with people who owned more than two domestic dogs, which included epidemiological indicators (prevalence, morbidity and mortality); social variables (number of family members and ages, occupation, barefootness, household infrastructure, presence of sewerage and type of water supply, water and food consumption of dogs, disposal of excrement, health system, economic level and education, knowledge of parasitic diseases, deworming of dogs, housing of animals, habitat of dogs and veterinary care); and environmental parameters (temperature, humidity, precipitation, solar radiation, soil texture, type of vegetation, pH, deforestation and fauna).

Estimation of epidemiological indicators and social determinants

The estimation of the epidemiological indicators was carried out using the results of the diagnoses obtained and based on the surveys. In the case of social determinants, the results of the surveys were taken into account.

Characterization of the environmental variables

The environmental variables were obtained from Meteored12, AccuWeather13, and meteorological bulletins of the National Institute of Meteorology and Hydrology (INAMHI)14. Similarly, an observation of the studied sites was carried out, and studies described in described in the Development and Territorial Planning plans of the National Planning Secretariat were used. It is important to mention that all daily results of the environmental variables obtained from the sectors studied from April 1 to October 31, 2024, were finally averaged15.

Collection, transport and analysis of samples from domestic dogs

To obtain fecal samples from people and their domestic dogs (from April to October 2024), sterile jars were used, and the address, telephone number and other useful information were recorded. Study participants were instructed to handle their samples and their animals with sterile gloves. The pet owner was instructed to keep the dog in the yard (separated from other dogs) for sampling purposes to avoid confusion. The dogs were not sampled freely; they were properly identified by the owner. Dog habits, such as defecation time (6:00 AM to 12:00 PM), were also taken into account. The dogs’ defecation monitoring was conducted by the researchers and the dog owners. In cases where the owner of an animal could not collect a sample of the pet, a technical team collected the sample following the procedures of Dubie et al.16.

The human stool samples were transported in refrigerated coolers between 4 and 8 °C to the Pazmiño Clinical and Microbiological Laboratory in the city of Milagro10. The faeces of the dogs were transported in Styrofoam refrigerator refrigerated at 4 °C to the laboratory of Microbiology Laboratory of the Faculty of Veterinary Medicine and Zootechnics of the University of Guayaquil (Ecuador)11. All samples were immediately analyzed by coproparasitological techniques/methods: direct, flotation, sedimentation with centrifugation with saline solution and modified Baermann. They were then stained with Lugol’s solution and finally observed by optical microscopy at 10X and 40X. The samples that tested positive by the aforementioned methods were processed with DNA/RNA Shield, and then stored at −20 °C for further molecular study10,17.

With regard to the morbidity of symptomatic animals, the following stool analyses were performed: viral (antigen for parvovirus and canine distemper), fungal (AFB and lactophenol staining), and bacterial (culture and Gram staining) analyses.

Notably, all the participants were aware of the procedure, and guardians signed the consent form on the behalf of their children prior to their participation in the study. The sampling protocol used for the domestic dogs was analyzed and approved by the Institutional Committee for the Care and Use of Animals of the FMVZ of the UG.

Sampling of synanthropic rodents

The rodents were captured between June 14 to July 11, 2024, in the “La Ladrillera” sector by using 30 Tomahawk and 10 Sherman traps. Nontoxic bait was used (100 g of oats with a quantity of 20 g of peanuts and 5 ml of vanilla, tuna, meat, fish, or fried chicken skin). The traps were strategically placed in landfills, drains, market peripheries, and other places that presented evidence of rodents. Once the live animals were captured, they were sprayed with “Fipronil” insecticide. In the laboratory, the rodents were euthanized by an overdose of 10% ketamine. Subsequently, each rodent was dissected, and its digestive tract was removed. The stool was placed in a Petri dish with physiological solution8.

The intestinal contents of the animals were analyzed by applying the following coproparasitic methods: direct, flotation and sedimentation-centrifugation with saline solution. Then, the samples were analyzed via optical microscopy using the 10× and 40× objectives8.

Diagnostic criteria

For the identification of intestinal parasitic forms, the criteria described by Bowman17, Romero Cabello18 and Botero and Restrepo19 were considered. For the identification of eggs or cysts, parasitic methods, namely, direct, flotation and sedimentation with centrifugation using saline solution, were used, and for the identification of larvae, the modified Baermann method was used. Finally, to confirm the identities of the parasites, the morphometric method was used. To develop the morphometric procedures, the Better Scientific BS200D 2.0 Mpx LCD 7” LED Digital Biological Microscope was used.

Morphometry of the parasitic forms

All samples that were positive (from humans and domestic dogs) according to the indicated parasitic methods were confirmed by morphometry following the criteria of Bowman17, Romero Cabello18 and Botero and Restrepo19.

Identification of parasitic diseases of zoonotic origin in people

The presence of parasitic pathologies of zoonotic origin was determined by clinical examination (anamnesis, physical verification, hospital clinical tracing) and laboratory examination of each patient.

Statistical analysis

Previously, the prevalence of intestinal parasites in humans and domestic dogs was quantified as a percentage, together with their specific identification, morbidity, zoonotic parasitic pathologies and social determinants. In addition, Pearson’s chi-square statistic was used for the comparative evaluation between sectors populated in different sociodemographic aspects and to relate human parasitosis grouped into taxa (protozoa, nematodes and flatworms). An adjustment of logistic regression models (with robust standard errors clustered at the household level to account for intra-household correlation) was proposed to estimate which socioenvironmental variables best explained the probability that an individual would contract parasites according to the proposed taxa. Parameter estimates were based on the maximum likelihood method, and Akaike’s information criterion (AIC) was used to select the model that presented the lowest AIC value among the other options by McCullagh & Nelder20 and Zuur et al.21. Because only 5% of households had nematode infections, all three taxon-specific models were refitted with penalised Firth logistic regression (R package logistf), which reduces small-sample bias; unpenalised and penalised estimates were nearly identical for protozoa (22% positives) and platyhelminths (7% positives). Before modeling, all candidate covariates were screened for multicollinearity (variance-inflation factor and tolerance); every variable showed VIF < 3, so none were removed. It was analyzed: odds ratios (OR), standard errors, 95% confidence intervals and model fit. In addition, possible associations between this parasitosis and social and environmental variables were measured. For all the analyses, 2024 INFOSTAT software (Di Renzo et al.22 and the R 4.3.223 were used.

Results

Epidemiological indicators

The total prevalence of enteroparasites in the 4 areas studied in humans was 31.87% (51/160) (CI 95% − 24.65%, 39.1%), with 9 parasite taxa being observed; in domestic dogs, the prevalence was 78% (390/500) (CI 95% − 74.37%, 81.63%), with 19 parasite taxa being observed. The most common human parasite was Entamoeba coli (18.13%, 29/160). Representative samples of parasitic forms identified in human feces are shown in Fig. 2. Additionally, the following species were identified: Entamoeba histolytica, 10% (16/160); Hymenolepis nana, 3.75% (6/160); Taenia spp., 3.13% (5/160); Ascaris lumbricoides, 1.88% (3/160); Enterobius vermicularis, 1.88% (3/160); Ancilostoma duodenalis, 1.25% (2/160); Cystoisospora belli, 1 25% (2/160); and Strongyloides stercoralis, 0.63% (1/160) (Table 1.). On the other hand, in canines, Ancylostoma caninum presented the highest prevalence at 53.6% (268/500). Figure 3 presents representative samples of the parasitic forms found in the feces of domestic dogs. Additionally, Taenia spp. (E. granulosus) had a prevalence of 15.2% (76/500); Toxocara canis, 12.4% (62/500); Cystoisospora spp., 11.4% (57/500); Spirometra mansoni, 9.4% (47/500); Strongyloides stercoralis, 6.2% (31/500); Uncinaria stenocephala, 6.2% (31/500); Ancylostoma spp., 4.4% (22/500); Entamoeba spp., 2.2% (11/500); Capillaria spp., 1.2% (6/500); Trichuris vulpis, 1% (5/500); Dipilidium caninum, 0.8% (4/500); Diphyllobrothrium spp., 0.6% (3/550); Giardia spp., 0.4% (2/500); Hymenolepis nana, 0.4% (2/500); Heterobilharzia americana, 0.4% (2/500); and Dicrocoelium dendriticum 0.2% (1/500) (Table 2).

Fig. 2
figure 2

Parasitic forms identified in human feces: (A) Entamoeba histolytica cyst, (B) Entamoeba coli cyst, (C) Cystoisospora belli cyst, (D) Ascaris lumbricoides cyst, (E) Enterobius vermicularis egg, (F) Ancylostoma duodenalis egg, (G)Hymenolepis nana egg, (H) Taenia spp. egg, (I) Strongyloides stercoralis larva with a genital primordium. Scale A, C = 5 um; Scale B, D-H = 10 um; Scale I = 30 um.

Full size image
Table 1. Prevalence of intestinal parasites in humans and IC values.
Full size table
Fig. 3
figure 3

Parasitic forms identified in the feces of domestic dogs: (A) Entamoeba spp. Cyst., (B) Cysts of Giardia spp., (C) Cystoisospora spp. cyst, (D) Ancylostoma caninum egg, (E) Ancylostoma spp. egg, (F) Toxocara canis egg, (G) Spirometra mansoni egg, (H) Taenia spp. (Echinococcus granulosus) egg, (I) Strongyloides stercoralis larva with genital primordium, (J) Uncinaria stenocephala egg, (k) Capillaria spp. egg, (L) Trichuris vulpis egg, (M) Dipylidium caninum egg, (N) Diphyllobothrium spp. Egg, (O) Hymenolepis nana egg, (P) Heterobilharzia americana egg, (Q) Dicrocoelium spp. Scale A, C, G, H y Q = 5 μm; Scale B, D-F, I-L, N-P = 10 μm, Scale M = 30 μm.

Full size image
Table 2 Prevalence of intestinal parasites in dogs and IC values.
Full size table
Table 3 Prevalence of intestinal parasites in dogs and IC values.
Full size table

Fifteen people presented diarrheal symptoms, and one presented pain in the right epichondrium derived from Echinococcosis, resulting in 10% morbidity; there was no mortality. The diarrheal cases were associated with parasites such as: Entamoeba coli, Entamoeba histolytica, Hymenolepis nana, Ascaris lumbricoides and Enterobius vermicularis. No individuals with symptoms tested positive for viruses (rotavirus and HIV), fungi (lactophenol staining and AFB) or bacteria (Gram staining and culture).

The canine morbidity rate was 7.8% (38/500), and the patients presented diarrhea, vomiting, decay, dehydration, pale mucous membranes and weakness. The mortality rate was 1.4% (7/500). Both morbidity and mortality in domestic dogs were associated with cases of Ancylostoma caninum, Toxocara canis, and Spirometra mansoni; this was supported by clinical, epidemiological, and laboratory evidence. Domestic dogs also did not test positive for any type of bacteria (Gram stain and culture), fungus (lactophenol staining and AFB) or virus (antigen for canine distemper and parvovirus).

In this study, monoparasitism was more common (57%) than was polyparasitism (43%).

Social determinants

160 people were surveyed (40 people from each area were sampled). With an average of five to six people per household, with ages ranging from two to 85 years and various occupations being represented (36.88% informal trade, agriculture 33.12% and formal trade 30%). On the other hand, 55% of people reported not wearing shoes outside or inside the house. A total of 56.87% of the households studied had houses with mixed infrastructure, 32.50% were made from cane and 10.63% were made from wood. Various water supplies were observed (54.37% drinking water, 26.25% purchased from tankers, 10.63% obtained from deep wells and 8.75% from rivers). Excreta was disposed of through septic tanks (56.25%), latrines (37.50%), and open air pits (6.25%). The areas studied did not have a sewer system. Finally, 90% did not have access to a healthcare system, whereas 10% did (4.4% social security and 5.6% public insurance for farmers). The standard of living is low (78.13%) and intermediate (21.87%), with complete primary education (40%), incomplete primary education (33.13%) and incomplete secondary education (26.87%). 96% of people were unaware of zoonotic parasites.

With respect to dogs, 97% of food and drinking water was untreated, and 90% was not dewormed. All the families analyzed had an average of five to six domestic dogs, with intra- and peridomiciliary (53.75%), peridomiciliary (36.88%) and intradomestic (9.37%) habitats; 97% did not receive veterinary care.

Parasitic pathologies of zoonotic origin in people

Among the cases of zoonotic parasitic pathologies detected are the following: in Balerio Estacio, 1 case of hydatidosis and one case of strongyloidiasis and in the “La Ladrillera” sector, 1 case of Cutaneous Larva Migrans. A representative clinical image of Cutaneous Larva Migrans (CLM) in a child is shown in Fig. 4. In addition, in the latter, there were 6 cases of hymenolepiasis related to homes with infected rodents.

Fig. 4
figure 4

A 13-year-old boy with a palpable serpiginous lesion on his right foot, compatible with a diagnosis of cutaneous larva migrans (CLM).

Full size image

Environmental parameters

In the urban-marginal sectors (Balerio Estacio and Ladrillera), the average temperature is 21.60–31.66 °C, the humidity is 73.96%, the rainfall in April (10–130) to October (10–100 mm). The climate is tropical savanna and the solar radiation every month is 12 h and 4 min; the soil texture is soft clayey and clayey‒sandy, with a pH between 6.5 (Balerio Estacio) and 6.7 (Ladrillera). Similarly, a great diversity of animals (cats, dogs, birds, opossums and rodents) and deforestation due to the growth of the community were observed.

In rural areas (Santa Rosa and Loma Larga), the temperatures ranged between 21.49 °C and 32.03 °C, with a humidity of 73.84%. The precipitation in April and May is 50–200, and of June to October, it is 10–100 mm. The climate is tropical savanna and the solar radiation every month is 12 h and 4 min, with a clay soil texture with sandy areas and pH values of 6 (Santa Rosa) and 6.4 (Loma Larga). These sites are forested with native trees and cropped with rice, corn and grass for livestock. In addition, there are a great variety of wild and domestic animals (cats, dogs, pigs, cows, birds, horses, fish, opossums, squirrels, monkeys, snakes and rodents); However, there are deforested areas that are used for agricultural and livestock purposes.

With respect to the social aspects of the four areas studied, significant differences were detected in the proportions of incomplete secondary education among residents (Santa Rosa, 45%; Loma Larga, 86%), informal work (Ladrillera, 40%; Santa Rosa, 91%) and low economic level (Ladrillera, 52%; Loma Larga, 95%).

The four areas presented high levels of deforestation and peridomiciliary vegetation without adequate sanitation or cleaning and without sewerage. A significant difference in drinking water consumption was detected (Loma Larga, 0%; Balerio Estacio, 98%).

In the case of parasites caused by protozoa, statistical significance was detected in people who consumed water from tankers and who used septic tanks, regardless of their neighborhood. With respect to parasites produced by flatworms, higher percentages of positive samples were detected among people who consumed water from tankers and walked barefoot. Owing to the low percentage of positive cases with nematode parasites (5%), it was not possible to fit a logistic model or any other model. In addition, parasites in domestic dogs were associated with factors such as morbidity, the presence of a septic tank, sandy-clay soil and a peridomiciliary habitat. Similarly, the probability of a dog contracting the A. caninum parasite increases in these environments; if the dog shows any sign of morbidity, if it is infested with another parasite. In addition, if the dog lives in the Loma Larga sector, where there are sandy-clay soils compared to the Barrio Balerio sector (reference sector), and if the dog lives in a peridomiciliary habitat in sandy-clay soils independent of the area where it lives, it will have a greater probability of contracting parasites.

Due to the low percentage of positive cases (5%) for nematode parasitosis in families, the penalized Firth logistic regression method was used (R package: logistf). This method penalizes the likelihood function to reduce bias in coefficient estimates, particularly in rare cases24. Because the unpenalized estimates in sufficiently large sample sizes are almost equal to the penalized estimates, the same method was used to evaluate protozoan (22%) and platyhelminthe (7%) parasitosis.

The models that best fit the probabilities of contracting different parasitic infections in families are presented, which were related according to clusters and some household environmental variables. With respect to protozoan parasitic infections, the model indicates that the odds of contracting the parasitic infection decreases by 99.8% if they live in Loma Larga than in Balerio. And, if there is a latrine, the possibility of this parasitic infection decreases by 92.7% (AIC = 85.214, Table 3.). If the family lives in Barrio Ladrillera compared to Balerio the odds of contracting flatworm parasitic infections increases by 399%; and by 725% in homes with a septic tank (AIC = 31.401, Table 4.). But, the possibility of contracting nematode parasitic infections decreases by 98.9% if the family lives in Barrio Ladrillera compared to Balerio, and water through pipelines by 97.2%. While contracting this parasitosis increases by 383.40% if the family has a sandy clay soil compared to another soil (AIC = 26.870, Table 5.).

Table 4. Factors that influence the probability that the household presents platelmint parasitosis.
Full size table
Table 5. Factors that influence the probability that the household presents nematoda parasitosis.
Full size table
Table 6 Treatment of intestinal parasites in humans.
Full size table

Finally, it is important to mention that the people and their domestic dogs that participated in the study received the results of their diagnoses, received medical treatment and an explanation of measures to control and prevent parasitosis (Tables 6 and 7)17,25.

Table 7 Treatment of intestinal parasites in domestic dogs.
Full size table

Discussions

This is the first study research carried out in Ecuador on the ecoepidemiology of intestinal parasites among humans and their domestic dogs in 4 overlooked sectors26.

The prevalence of NP varies from country to country, particularly in sub-Saharan Africa, Asia, Latin America and the Caribbean. In some sub-Saharan African regions, more than 50% of the population has an neglected parasitic infection. According to the World Health Organization (WHO), 1,500 million people, that is, 24% of the world’s population, have enteroparasites, mainly soil-transmitted helminths. Among the most common species are Ascaris lumbricoides, Trichuris trichiura, Ancylostoma duodenale and Necator americanus. Among the most common intestinal protozoal infections in developing countries are Giardia lamblia, E. histolytica, and Cryptosporidium27.

Likewise, the prevalence observed in this research (31.87%) is very similar to that reported in Ecuador (33.33%)28, but it is lower than that reported in Brazil (46%)29, Venezuela (49.3%)30, Bolivia (82.2%)31 and Peru (100%)32. However, the prevalence is higher than that reported in Colombia (14.5%)33, Argentina (22.6%)34 and Chile (28.3%)35. Importantly, the intestinal parasites identified in this study coincide with those reported by Durán et al.28, except for Cystoisospora belli, which is rarely reported in Ecuador.

On the other hand, in domestic dogs, a prevalence of 78% was obtained. In dogs, this value fluctuates greatly depending on the continent. Worldwide, the prevalence ranges from 20.5%7 to 100%32,36; in Europe, it ranges from 26% − 81%37; in Asia, it ranges from 5.87%38 − 95.7%39; in Africa, it ranges from 4% − 97.8%40; and in the Americas, it ranges from 12.5% − 77.3%41 and 100%32. Some enteroparasites detected in domestic dogs are similar to those described by Calvopina et al.9 and Coello et al.10. In this work, the following parasites were observed for the first time in domestic dogs from Ecuador: Spirometra mansoni and Uncinaria stenocephala.

According to the results, human morbidity due to intestinal parasites was 10%, which is lower than that reported by Elmonir et al.19,42 and Rajoo et al.43 [36–48%]. The positive result of this research is that the mortality rate was 0%; however, it has been reported that up to 33% of the population worldwide has intestinal parasites42. In domestic dogs, the morbidity rate was 7.8%, and the mortality rate was 1.4%. Similar values are mentioned by Coello et al.8, who reported morbidity of 9–24% and mortality of 1–14%.

The high prevalence of enteroparasites at the studied sites reveals the presence of poor environmental conditions and hygienic conditions in the sector.

The zoonotic parasites reported, such as hydatidosis, cutaneous larva migrans and hymenolepiasis, are consistent with those previously reported by Coello et al.8,10,44. The case of strongyloidiasis reported here is similar to that mentioned by Romero Cabello18 and Botero and Restrepo19.

It is important to note that social determinants and environmental variables influence the prevalence, transmission and nature of parasitic diseases. In addition, infections caused by enteroparasites are commonly associated with hygiene habits, age and nutritional or immunological conditions of people8.

In this study, significant associations obtained were found between parasitic infections and social factors such as water source (non-potable water and water from trucks), sanitary infrastructure (septic tank), barefoot walking, and the dogs’ peridomiciliary habitat, these are similar to those of the studies described by Souza et al.7 and Cociancic et al.45 and differ from those of Wickramasinghe et al.46. Intestinal parasites are associated with neglected sectors of underdeveloped tropical countries with low socioeconomic and educational levels43,44. It’s important to mention that untreated, non-potable truck water is associated with the presence of Amebiasis, Cystoisosporiasis, and others28,45; wet soils with Ancylostoma spp. support this biological plausibility8.

The environmental parameters observed in this research are different from those described in previous years by Coello et al.8 since there was a drought between June and October, which was more intense than that in the previous year47. Regarding deforestation in the studied sectors, it remains the same and the environmental parameters obtained differ from those reported by Coello et al.8. Such ecological change influences the emergence and re-emergence of intestinal parasites48.

With respect to the environmental and ecological conditions of the transmission of endoparasites to animal and human hosts, the optimum temperature for transmission is between 20 and 37 °C49,50, with a higher prevalence in winter, when humidities are between 60 and 90%48,49, rainfall is abundant, the climate is temperate, the soil is loose, moist and fertile8,48,50, solar radiation is lower8, deforestation is decreased48, and fauna and vegetation are abundant8. All these parameters influence parasite persistence48 and are similar to what was reported in our research. In all the areas studied (neglected), there were differences in fauna, vegetation and deforestation, and cases of endoparasites in humans and their domestic dogs were also observed.

The prevalence of intestinal parasites varied statistically between humans and their domestic dogs relative to social and environmental variables, and these results differed from those reported by Coello et al.8 and Wickramasinghe et al.46 but are similar to those reported by Souza et al.7 and Cociancic et al.45. Therefore, there is a potential risk of enteroparasites in neglected areas where there are infested domestic and stray dogs for those who walk barefoot and have poor or no hygiene habits and for those who have the habit of ingesting water or food contaminated with infected feces8.

Heavy rains increase the frequency of parasites, especially when the rain becomes wastewater and then enters the waterway without treatment and with parasites; this problem is exacerbated in island nations that are easily flooded during extreme weather events48. In Ecuador, Coello et al.8,43,44 reported zoonotic cases of MCL, hydatidosis and hymenolepidiasis at the same sites in 2023 and 2024.

This research and other studies have confirmed that vigorous vegetation, clear and humid soils, high temperatures and fertile and sandy soils with a pH between 5.7 and 6.7 are strongly associated with the prevalence of zoonotic intestinal parasites. The presence of abundant vegetation also favors the act of defecating in the open air, as the plants provide privacy to individuals and to domestic dogs, leading to the release of parasite eggs within the feces, which later transform into infective larvae8,50.

It should be noted that in parasitic research, biases in results may occur due to the heterogeneity of canine behavior (access to the street, diet, movement), environmental factors, the local density of stray dogs, the microbiological and parasitological quality of the water, and the presence of infective forms of parasites in the soil. However, in these commonly neglected areas, there is a potential risk of transmission of various parasitic infections that affect animal health and zoonoses that affect public health51.

It is important to note that the presence of infected people, domestic dogs, and the different climatic conditions in the country are risk factors for the appearance of outbreaks, epizootics and epidemics.

This research contributes to the epidemiological surveillance of animals and neglected intestinal parasites and their effects on public health, which benefits the Ecuadorian society.

Limitations of the study

Research should be conducted in other underserved sectors. Furthermore, future studies should consider other domestic animals. However, this study demonstrated the need to measure new sociocultural variables and their contribution to the results, as well as the need to educate the population to prevent parasitic transmission. Furthermore, PCR techniques could be included in future studies for better parasite identification.

Conclusions

Endoparasitosis is a zoonotic infection with high prevalence in developing countries and affects susceptible populations in endemic areas. In this study, the prevalence of intestinal parasites in the inhabitants of the four areas studied was 31.87%, while in their dogs it was 78%. Similarly, the following zoonotic relationships between humans and domestic dogs were observed: cutaneous larva migrans, hydatidosis and strongyloidiasis. For the identification of parasite eggs (screening), coproparasitic methods were used: direct, flotation and sedimentation with centrifugation using saline solution; for the identification of larvae, a modified Baermann method was performed using optical microscopy and the presence of these parasites was confirmed by morphometry.

Social variables that influence the high prevalence of parasites in residents and their pets were identified through surveys; as well as environmental parameters through online environmental programs, INAMHI meteorological bulletins, observation and land use plans of the National Planning Secretariat. According to the results obtained, the presence of more than one taxon of parasites in zoonoses can be inferred; however, further studies are required to confirm this finding.

Significant associations were found between parasitic infections and factors such as water source, sanitation infrastructure, barefoot walking, and the dogs’ peridomiciliary habitat. Finally, the population should be educated about sanitary measures and the need to periodically deworm their pets to prevent the transmission of enteroparasites.