Intestinal Parasites in Dogs: Zoonotic Risks and Management

Introduction

Intestinal parasites in dogs represent a significant concern for veterinary medicine and public health, given the close proximity of dogs to humans and the shared environment of many communities [1, 2]. Dogs can serve as definitive hosts, reservoir hosts, or accidental hosts for a wide array of helminths, protozoa, and occasionally ectoparasites that colonize the gastrointestinal tract [3, 4]. The global prevalence of these infections is substantial, with rates frequently exceeding 50% in stray or shelter populations [5, 6]. The question "are dog intestinal parasites contagious to humans" underscores the zoonotic potential that makes this topic critical for veterinary professionals and dog owners alike. This article reviews the etiology, epidemiology, clinical signs, diagnostic methods, treatment strategies, and control measures for intestinal parasites in dogs, with a focus on their zoonotic risks.

Etiology and Classification

Canine intestinal parasites encompass two major groups: helminths and protozoa [7, 8]. Helminths include nematodes (roundworms, hookworms, whipworms), cestodes (tapeworms), and trematodes (flukes) [9, 10]. Protozoa include organisms such as Giardia duodenalis, Cryptosporidium spp., Cystoisospora spp., and Entamoeba spp. [1, 11]. The most frequently reported helminths in dogs are Toxocara canis (roundworm), Ancylostoma caninum (hookworm), Trichuris vulpis (whipworm), and Dipylidium caninum (tapeworm) [5, 12, 13]. Among protozoa, Giardia duodenalis and Cryptosporidium spp. are commonly identified [2, 11]. Many of these organisms have direct life cycles, relying on fecal-oral transmission, while others require intermediate hosts (e.g., cestodes require fleas or mammals) [14, 15]. The life cycle complexity influences both prevalence and control strategies [8, 16].

Epidemiology

The prevalence of intestinal parasites in dogs varies widely by geographic region, management system, and dog population studied [1, 3]. In a high-altitude region of Nepal, overall parasitism reached 75.49%, with 17 species identified in free-ranging dogs [1]. Similarly, a study in Ecuador reported 78% prevalence in domestic dogs, with Ancylostoma caninum being the most common (53.6%) [5]. In Morocco, 58% of sampled dogs were positive, with Ancylostoma/Uncinaria spp. (31.9%) and Toxocara canis (27.1%) prevalent [6]. In Serbia, shelter dogs showed 58.3% positivity, with younger dogs (<1 year) having significantly higher infection rates (78.1%) than adults (53.1%) [9]. A study from Romania found 74.63% of shelter dogs infected, with hookworms (55.97%) and Cystoisospora sp. (31.91%) most frequent [10]. In Moscow, Russia, Giardia spp. was detected in 10.2% of dogs, Cryptosporidium in 2.7%, and T. canis in 2% [11]. In Canada (Ontario), prevalence was lower; Giardia and hookworms were common [12]. In Spain, 65.8% of dogs were infected, with Giardia duodenalis (35.4%) and Ancylostomatidae (27.0%) predominating [13]. In Mexico (Lalitpur, Nepal), 95.7% of street dogs were positive, with 23 species identified [16]. In Mississippi, USA, soil-transmitted helminths were found in 62.7% of shelter dogs, hookworms in 50.0% and Toxocara in 24.2% [17]. These data highlight that intestinal parasitism remains a global challenge, particularly in regions with limited veterinary care and poor sanitation [18, 19, 20].

Table 1 summarizes representative prevalence data from recent studies.

Clinical Signs and Pathology

Clinical manifestations of intestinal parasitism in dogs range from subclinical to severe, depending on parasite load, species involved, host age, nutritional status, and immune competence [4, 15]. Common signs include diarrhea (sometimes hemorrhagic), weight loss, poor coat condition, vomiting, anorexia, and abdominal distension [3, 9]. Puppies are particularly susceptible to heavy burdens of Toxocara canis and hookworms, which can cause growth retardation, anemia, and even death [4, 21]. Ancylostoma caninum is a blood-feeding hookworm that can induce microcytic hypochromic anemia, especially in young dogs [4, 21]. In a study of dogs with canine visceral leishmaniasis, coinfection with Ancylostoma sp. was associated with more severe clinical staging and anemia [4]. Trichuris vulpis infection often presents with mucoid diarrhea and weight loss [9, 22]. Protozoan infections such as Giardia duodenalis typically cause acute or chronic diarrhea with foul-smelling stools [8, 11]. Cryptosporidium may cause self-limiting diarrhea in immunocompetent dogs but persistent infections in immunocompromised individuals [23]. Histopathological changes in the intestine include villous atrophy, crypt hyperplasia, and inflammatory cell infiltration [14]. For example, Toxocara canis larvae can distort villous architecture and induce granulomatous inflammation [14]. Polyparasitism is common, with mixed infections occurring frequently [1, 9].

Diagnostics

Accurate diagnosis relies on coproparasitological techniques and molecular methods [6, 12]. Common flotation methods (e.g., Sheather's sugar, zinc sulfate centrifugal flotation) are effective for detecting helminth eggs and protozoan cysts [6, 9]. Sedimentation techniques (e.g., formalin-ethyl acetate) are useful for trematode eggs and larger structures [17, 22]. Direct wet mounts allow detection of motile protozoan trophozoites. Acid-fast staining is employed for Cryptosporidium oocysts [1]. Modern diagnostics also include immunofluorescence assays (IFA) for Giardia and Cryptosporidium [8, 20], and real-time PCR for species identification and genotyping [17, 24]. Multiplex qPCR panels can simultaneously detect hookworms, Toxocara, and Strongyloides [17]. In a study comparing diagnostic techniques, centrifugal flotation showed high sensitivity for Ancylostoma and Toxocara [33]. The diagnostic workflow often involves multiple methods to maximize sensitivity.

graph TD
    A[Fecal sample], > B{Clinical history & risk factors?}
    B, > C[Direct wet mount / Iodine stain]
    C, > D{Protozoan trophozoites?}
    D, >|Yes| E[Report positive]
    D, >|No| F[Flotation method (ZnSO4 or Sheather's)]
    F, > G{Helminth eggs or protozoan cysts?}
    G, >|Yes| H[Identify species & quantify]
    G, >|No| I[Sedimentation (formalin-ethyl acetate)]
    I, > J{Helminth eggs?}
    J, >|Yes| K[Identify species]
    J, >|No| L[Acid-fast stain (Cryptosporidium)]
    L, > M[IFA for Giardia/Cryptosporidium if needed]
    M, > N[PCR/genotyping for zoonotic assessment]
    N, > O[Final diagnosis]

Figure 1. Diagnostic decision tree for canine intestinal parasites.

Treatment and Control

Anthelmintic therapy forms the cornerstone of treatment [6, 9]. For nematodes, benzimidazoles (fenbendazole), macrocyclic lactones (ivermectin, milbemycin oxime), and tetrahydropyrimidines (pyrantel pamoate) are commonly used [21]. Cestodes require praziquantel [9]. Protozoan infections are more challenging; metronidazole or fenbendazole are used for Giardia, while Cryptosporidium often requires supportive care and nitazoxanide [11, 23]. Control strategies emphasize regular deworming (especially in puppies), environmental hygiene (prompt removal of feces), and preventing access to intermediate hosts (e.g., fleas for Dipylidium) [16, 21]. Integration of diagnostics before treatment is critical to avoid indiscriminate use of anthelmintics and to address parasites outside typical spectrum (e.g., Cryptosporidium) [23].

Zoonotic Risks: Are dog intestinal parasites contagious to humans?

The zoonotic potential of canine intestinal parasites is well-documented [5, 7, 25]. Several species are capable of infecting humans through direct contact, ingestion of eggs, or penetration of skin by larvae [2, 26]. The question "are dog intestinal parasites contagious to humans" can be answered affirmatively for multiple common parasites. Toxocara canis causes visceral and ocular larva migrans in humans, particularly in children who ingest embryonated eggs from contaminated soil [1, 6]. Ancylostoma caninum and Uncinaria stenocephala cause cutaneous larva migrans (creeping eruption) when third-stage larvae penetrate human skin [5, 26]. Strongyloides stercoralis can also cause cutaneous and intestinal infections [11, 25]. Giardia duodenalis (particularly assemblages A and B) is zoonotic [20, 24]. Cryptosporidium spp. (especially C. parvum) can infect humans [11, 23]. Tapeworms such as Dipylidium caninum can infect children who accidentally ingest fleas [9, 14]. Moreover, Echinococcus granulosus (hydatid tapeworm) is a major zoonotic threat in endemic areas, causing cystic echinococcosis in humans [5, 15]. In a One Health study from Colombia, lack of deworming in dogs was significantly associated with human parasitism (OR 3.80) [7]. Similarly, in a Cuban study, dogs infected with Giardia and other parasites posed transmission risk to children [2]. Environmental contamination with canine feces is a key risk factor [25, 27]. Thus, from a veterinary public health perspective, dogs serve as important reservoirs for several zoonotic parasites.

Management Strategies

Management of intestinal parasites in dogs requires a multi-pronged approach integrating veterinary care, owner education, and environmental control [3, 6]. Routine fecal screening (at least annually) is recommended for owned dogs [12]. Deworming protocols should target common parasites; for puppies, treatment every 2 weeks until 8 weeks old, then monthly until 6 months, is standard [21]. Adult dogs in high-risk environments (shelters, kennels) should be dewormed more frequently [9]. Strategic use of antiparasitic drugs based on local epidemiology improves efficacy and reduces resistance selection [8, 28]. Owners should be educated on zoonotic risks, proper disposal of feces, and preventing coprophagy [6, 25]. In public parks, contamination can be reduced by enforcing leash laws and providing bag dispensers [20]. In shelter settings, quarantine and treatment upon intake, followed by re-testing before adoption, reduces parasite burden [21]. A study in Texas showed that sedimentation increased detection rates for T. vulpis and Ancylostoma [22]. Integrated control programs that include environmental sanitation (e.g., removing feces daily, using lime or ammonia on concrete surfaces) can break the life cycle [16, 18].

Conclusion

Intestinal parasites in dogs remain a significant veterinary and zoonotic problem globally, with prevalence rates commonly exceeding 50% in many populations [1, 5, 9]. The diversity of parasites, including nematodes, cestodes, and protozoa, demands robust diagnostic approaches that combine microscopy, flotation, sedimentation, and molecular methods [6, 17]. Effective management requires regular anthelmintic treatment tailored to local epidemiology, environmental hygiene, and education of dog owners about zoonotic risks [3, 28]. Veterinary professionals are key to implementing One Health strategies that protect both animal and human health from these ubiquitous parasites [6, 7].

References

[1] Acharya D, Lama RP, Ghimire TR. Prevalence of Intestinal Parasites in Dogs (Canis familiaris Linnaeus, 1758) and Dzos (Bos grunniens Linnaeus, 1766) in Upper Humla, Nepal. Iranian Journal of Veterinary Medicine. 2025. URL: https://www.semanticscholar.org/paper/29cd751e70817bd42b1ee540beed35be4a13d928

[2] Jerez Puebla LE, La Rosa Osoria E, Núñez Fernández FN, et al. Are intestinal parasites in dogs an infection risk to children in the same household? An investigation in Cuba. Transactions of the Royal Society of Tropical Medicine and Hygiene. 2025. URL: https://www.semanticscholar.org/paper/4ba7286fcb6e503361666a2d684536815bdf7133

[3] Morelli S, di Cesare A, Traversa D, et al. Occurrence of Cystoisospora spp. and other intestinal parasites in dogs and cats with diarrhea. Veterinary parasitology. 2025. URL: https://www.semanticscholar.org/paper/f2bf974b209358cda1487801c4e2ae2c5d8e1e47

[4] Severino AJM, Gomes DS, Costa AT, et al. Intestinal parasites in dogs and their association with clinical manifestations of canine visceral leishmaniasis. Veterinary parasitology. 2025. URL: https://www.semanticscholar.org/paper/71b77ce7ef175695f21cbcc323c01d4ac6becfe6

[5] Coello-Peralta R, Vinueza R, Pazmiño Gómez BJ, et al. Ecoepidemiology and zoonotic risk of intestinal parasites in humans and domestic dogs in marginalized coastal communities of Ecuador. Scientific Reports. 2025. URL: https://www.semanticscholar.org/paper/4b903a8017ac4b0c68aad9f43bd9bc3c2c053599

[6] Idrissi H, Khatat SE, Duchateau L, et al. Prevalence, risk factors and zoonotic potential of intestinal parasites in dogs from four locations in Morocco. Veterinary Parasitology: Regional Studies and Reports. 2022. URL: https://www.semanticscholar.org/paper/f6fbf6af1278c0ac6b6eec3d74ae935eddfe3d51

[7] Fontalvo Rivera DM, Tirado Ballestas I, Morales Aleans M, et al. One Health assessment of zoonotic intestinal parasites in humans, dogs, and soil of coastal Cartagena, Colombia. Veterinary World. 2025. URL: https://www.semanticscholar.org/paper/aef7e9d3dd2ac9b8646ea3e0f5f170a785a24bca

[8] Faraguna S, Vlahek I, Miočić K, et al. Prevalence of Intestinal Parasites in Dogs and Cats from the Kvarner Region in Croatia. Acta Veterinaria. 2023. URL: https://www.semanticscholar.org/paper/1801b975c468709a7412d3202cdc18857c2e9a4f

[9] Ilić T, Nišavić U, Gajić B, et al. Prevalence of intestinal parasites in dogs from public shelters in Serbia. Comparative Immunology, Microbiology & Infectious Diseases. 2021. URL: https://www.semanticscholar.org/paper/000d0249ce9d4721536a12a3b974d1ea93eac124

[10] Hermina RA, Larisa I, Gabriela M, et al. The prevalence of intestinal parasites in dogs from shelters in Constanța County-Romania. Scientific Papers Journal VETERINARY SERIES. 2023. URL: https://www.semanticscholar.org/paper/5567aec9584d20696744dbaea5f26d6870900988

[11] Kurnosova O, Panova O, Arisov M. The prevalence of potentially zoonotic intestinal parasites in dogs and cats in Moscow, Russia. Helminthologia. 2023. URL: https://www.semanticscholar.org/paper/937233bf07653115542bbb6387622b855f5505af

[12] Kotwa JD, French SK, Greer T, et al. Prevalence of intestinal parasites in dogs in southern Ontario, Canada, based on fecal samples tested using sucrose double centrifugation and Fecal Dx® tests. Veterinary Parasitology: Regional Studies and Reports. 2021. URL: https://www.semanticscholar.org/paper/217fd608e5da6ed2be4346fdd2383868c1a45c7d

[13] Sánchez-Thevenet P, Carmena D, Adell-Aledón M, et al. High Prevalence and Diversity of Zoonotic and Other Intestinal Parasites in Dogs from Eastern Spain. Vector Borne and Zoonotic Diseases. 2019. URL: https://www.semanticscholar.org/paper/b5b0d6f75012f616b298952a344c2e7d5204e91f

[14] Mahmoud AJ. Study the percentage of infection with intestinal parasites in dogs in salahaldin prevence. Tikrit Journal of Pure Science. 2023. URL: https://www.semanticscholar.org/paper/3a61d04d51f15f0571ad378a8cc1c7fae0e57cca

[15] Chapkunovska B, Rashikj L, Shikoska I, et al. Prevalence, Risk Factors, and Zoonotic Potential of Intestinal Parasites in Shelter Dogs in North Macedonia: A Cross-Sectional Study. Macedonian Veterinary Review. 2026. URL: https://www.semanticscholar.org/paper/f95d7251a96f0e6fd76911b364791f77b78e8fbb

[16] Adhikari R, Dhakal MA, Ghimire T. Prevalence of intestinal parasites in street dogs (Canis lupus familiaris) with highlights on zoonosis in Lalitpur, Nepal. Veterinary Medicine and Science. 2023. URL: https://www.semanticscholar.org/paper/40fa4594b21363fb2f798b86283d84fe03b17b45

[17] Zhao H, Zendejas-Heredia PA, Colella V, et al. Surveillance of soil-transmitted helminths and other intestinal parasites in shelter dogs, Mississippi, USA. One Health. 2024. URL: https://www.semanticscholar.org/paper/037be6f55a212b3ba84cca79a6765d98cd4d1c1d

[18] Ramirez-Barrios R, Barboza-Mena G, Muñoz J, et al. Prevalence of intestinal parasites in dogs under veterinary care in Maracaibo, Venezuela. Veterinary parasitology. 2004. URL: https://www.semanticscholar.org/paper/5db0681617fc479c5035991370412bb26921f909

[19] Oliveira-Sequeira T, Amarante A, Ferrari TB, et al. Prevalence of intestinal parasites in dogs from São Paulo State, Brazil. Veterinary parasitology. 2002. URL: https://www.semanticscholar.org/paper/4faf6f94b29b957fd22c0ace983b403f8cdab419

[20] Utaaker KS, Tysnes K, Krosness MM, et al. Not just a walk in the park: Occurrence of intestinal parasites in dogs roaming recreational parks in Chandigarh, Northern India. Veterinary Parasitology: Regional Studies and Reports. 2018. URL: https://www.semanticscholar.org/paper/5e2cadd6aa5d2c26b1f9dac03ca0327004a9b1ad

[21] Campanale DN, Walden H, Garcia LN, et al. Zoonotic and non-zoonotic intestinal parasites in shelter dogs at admission and before discharge. Journal of Shelter Medicine and Community Animal Health. 2023. URL: https://www.semanticscholar.org/paper/a1dafc349494d57e6f16e635f6c98a121b2f597f

[22] Rodriguez JY, Cummings K, Hodo CL, et al. A repeated cross-sectional study of intestinal parasites in Texas shelter dogs using fecal flotation and saline sedimentation. Parasitology Research. 2022. URL: https://www.semanticscholar.org/paper/d4dea23174ec2e1a4613e0d4d4add262c08ac208

[23] Gonzalez-Saldívar DS, Trasviña-Muñoz E, López-Valencia G, et al. Frequency and risk factors of intestinal parasites in pet dogs from Mexicali, Mexico. Austral journal of veterinary sciences. 2023. URL: https://www.semanticscholar.org/paper/301ed4ae0d42e6825f40c9ca02fbc4a2f31e8401

[24] De Silva TK, Rajakaruna R, Mohotti K, et al. First Molecular Identification of Ancylostoma Species in Dogs in a Rural Tea Estate Community in Sri Lanka and the Detection of Other Zoonotic Gastro-intestinal Parasites. Acta Parasitologica. 2022. URL: https://

[25] Mulugeta Y, Yohannes M, Wolde D, et al. Intestinal Parasites in Dogs and Humans, Environmental Egg Contamination and Risk of Human Infection with Zoonotic Helminth Parasites from Dog in Hosanna Town. International Journal of Biomedical Materials Research. 2019. URL: https://www.semanticscholar.org/paper/283e7009b213f7dd6c181e88fb8e746702ffcd34

[26] Martínez-Sotelo J, Sánchez-Jasso J, Ibarra-Zimbrón S, et al. Zoonotic intestinal parasites in free-ranging dogs (Canis lupus familiaris): a risk to public health in a Mexican Protected Area. Nature Conservation Research. 2022. URL: https://www.semanticscholar.org/paper/2c6a080d14cae82dcba7d851849967accd82c325

[27] Puebla LJ, Núñez F, Rivero L, et al. Prevalence of Intestinal Parasites in Dogs from Municipality La Lisa, Havana, Cuba. 2015. URL: https://www.semanticscholar.org/paper/98bb8c7d4fd0fba52af86d583d4766052c3ca9d2

[28] Rajpoot P, Singh M, Shakya M, et al. Percent positivity and risk analysis of zoonotic intestinal parasites (helminths) in dogs population- a participatory epidemiological study. Veterinary Parasitology: Regional Studies and Reports. 2026. URL: https://www.semanticscholar.org/paper/11aa3df5673c30c4ecf1b7c9622e12c4ad7d3457

[29] Dubná S, Langrová I, Nápravník J, et al. The prevalence of intestinal parasites in dogs from Prague, rural areas, and shelters of the Czech Republic. Veterinary parasitology. 2007. URL: https://www.semanticscholar.org/paper/43ae05804577d52fec4e2bfb70148b315e199b43

[30] Joffe D, Van Niekerk D, Gagné F, et al. The prevalence of intestinal parasites in dogs and cats in Calgary, Alberta. The Canadian veterinary journal. 2011. URL: https://www.semanticscholar.org/paper/269bb29edc743b87d67b5579195427a533fb090b

[31] Fok E, Szatmári V, Busak K, et al. Prevalence of intestinal parasites in dogs in some urban and rural areas of Hungary. Veterinary Quarterly. 2001. URL: https://www.semanticscholar.org/paper/a9574ae8faa9664ab853f5740d23268d9567586f

[32] Arruda IF, Ramos RCF, Barbosa A, et al. Intestinal parasites and risk factors in dogs and cats from Rio de Janeiro, Brazil. Veterinary Parasitology: Regional Studies and Reports. 2021. URL: https://www.semanticscholar.org/paper/b9d24cd3d82207a8ea3791f3d8585e5b62fee69f