Zoonosis and prevention at home

When intestinal parasites affect the whole family

When we talk about intestinal parasites, there is one idea that we should keep in mind: some do not stay “only” in dogs or cats, but can have an impact on the whole family, especially children, the elderly, immunocompromised individuals and, in the case of Toxoplasma, during pregnancy. Most infections are spread through the same chain: faeces → soil/water → hands/mouth and, in some cases, fleas. Therefore, knowing the protagonists helps, but the key is learning how to break the cycle.

Zoonoses: which parasites can affect the family

Helminths, highly harmful macroparasites

Toxocara spp. – the great public health classic

Toxocara is relevant because its eggs can contaminate soil, gardens and sandpits and remain a “silent” risk. In fact, a meta-analysis on environmental contamination in public spaces estimated a global pooled prevalence of 21% of soil positive for Toxocara eggs in places such as parks, beaches and public areas.

When we look at local data, a study in parks in Valencia found 10.9% of soil samples to be positive (with higher positivity in dog areas).

CURIOSITY – “Viable egg” ≠ “egg present”: time also plays a role

In parks/play areas in Lisbon, soil with 53% positivity was reported, along with a disturbing fact: some of the eggs recovered were viable and infectious after incubation. Translation: it is not enough that “there are few”; what matters is whether the environment allows them to mature and persist. 

Source: https://www.sciencedirect.com/science/article/pii/S187603411730134X

In humans, the most significant risk is not “seeing worms,” but rather cases of visceral or ocular larva migrans, especially in children if there is repeated exposure to contaminated soil. In practice, the message is clear: the problem usually lies in the environment, and prevention is based on removing faeces and reinforcing hand hygiene.

Ancylostoma spp. – the one that can enter through the skin

Ancylostoma adds a key nuance: its larvae can penetrate the skin after contact with contaminated soil or sand, causing cutaneous larva migrans in humans, with winding paths and intense itching. This is described very directly by the health authorities (CDC) on “zoonotic hookworm“.

Therefore, in addition to deworming, it is very important to avoid exposure: damp soil, sand, areas frequented by dogs/cats, and direct skin contact (especially barefoot or sitting/lying on “questionable” sand).

Dipylidium caninum – the “flea parasite”

Dipylidium is transmitted by ingesting an infected flea, so when Dipylidium appears, the real problem is almost always a failure in flea control. The route is explained literally in CDC – DPDx Dipylidium, also indicating that in humans, cases are mainly seen in children through close contact with flea-infested pets.

The practical lesson to take home is clear: no fleas, no Dipylidium, so the correct plan is always twofold: animal + home.

Trichuris vulpis – the one that turns the garden into a reservoir

Trichuris is not considered here as a “major” zoonosis in everyday life, but it is a serious domestic enemy because of its ability to perpetuate itself in the environment. Its eggs are resistant and, under suitable conditions, can remain viable for up to 5 years, according to the MSD Veterinary Manual.

This explains why some gardens ‘have a memory’: if faeces are not removed consistently and the environment is not managed, the dog can become reinfected again and again even if the treatment is correct.

Protozoa, persistent microparasites

Giardia duodenalis – the queen of “repeat outbreaks”

Giardia can cause persistent problems because its cysts survive well in humid environments and are transmitted via the faecal-oral route. To make this less abstract, there are some very illustrative figures: the European DOGWALKS study (Parasites & Vectors, 2022) found that 22.8% of dogs sampled in parks tested positive for some intestinal parasite, and that Giardia was the most common finding: 17.3% of dogs, also present in 83.5% of parks sampled.

And when we look at age groups, the pattern repeats itself: in a 2025 study, Giardia cysts were detected in 11.3% of dogs and 7.1% of cats, rising to 16.9% in dogs <1 year old and 19.8% in cats <1 year old.

Therefore, with Giardia, the motto is not “one syrup and that’s it”: treatment must be accompanied by sustained environmental hygiene, control of risky water, and a “reinfection prevention” strategy (otherwise, the system will start up again).

Toxoplasma gondii – important during pregnancy, but not from petting cats

Here it is worth correcting a myth: you cannot catch it by petting a cat. The relevant domestic risk is associated with faeces and litter trays if they are not handled hygienically, and there is a crucial biological detail: oocysts need 1 to 5 days in the environment to become infectious, and cats usually shed oocysts for 1–3 weeks when they eliminate them.

Hence, one measure that really changes the risk: daily cleaning of the litter tray. The CDC brochure for cat owners also summarises this in a practical way: change the litter tray daily because it “takes more than a day” to become infectious.

Coccidia – common in young animals, but not a typical zoonosis

Coccidia can cause diarrhoea (especially in puppies and kittens) and thrive in communities or when there is environmental contamination. In family public health, the key point is: dog and cat Cystoisospora are not considered zoonotic under normal conditions; this is summarised by the fact that humans are not susceptible to canine Cystoisospora (and in general, dog/cat coccidia are very host-specific).

Note: this does not mean “it doesn’t matter”; it means that the focus is on preventing transmission between animals and preventing a puppy from spending weeks with diarrhoea due to environmental contamination.

Real zoonosis at home: Cryptosporidium leaves a molecular ‘footprint’

In a family study, Cryptosporidium infection in children was strongly associated with having a dog with the same parasite; a very high odds ratio (129.75) and evidence of transmission within the home were reported.

Reminder: diarrhoea at home + pet = hygiene and diagnosis with care, but seriously.

Source (URL):https://pubmed.ncbi.nlm.nih.gov/36898625/

Key preventive measures

Prevention begins with a simple and powerful gesture: always pick up faeces during walks and remove them frequently from patios or gardens, because cutting environmental contamination reduces reinfection and lowers the risk to the family.

Hand hygiene works better than any “trick”: washing your hands thoroughly after handling your pet, its toys, its food bowl or its faeces directly reduces exposure, especially in households with children.

Prevention is based on consistency, so it is useful to establish routines: frequently cleaning the areas where the animal sleeps and eats, and keeping those spaces dry and tidy, reduces the survival of many agents and decreases the environmental burden.

If Giardia is suspected or diagnosed, hygiene must be stricter and more consistent, because cysts can perpetuate the problem. so it is important to wash textiles and utensils at 60 °C or higher, clean surfaces consistently, and prevent the dog from drinking from puddles, ditches, or shared water bowls during treatment (if the animal is reinfected every day, treatment becomes a futile endeavour).

Flea control is not an “extra”, but a central part of family health when it comes to Dipylidium, because without fleas there is no cycle; therefore, the correct approach is to maintain a continuous flea control protocol for the animal and accompany it with domestic measures such as frequent vacuuming of carpets and upholstery and washing blankets and beds.

Prevention against Ancylostoma improves when contact with damp and potentially contaminated soil is reduced; therefore, it is advisable to prevent the dog from lying down for long periods of time in wet or very dirty areas, and it is useful to clean its paws when returning home if it has been in heavily trafficked damp soil.

Prevention in homes with cats should include the fact that the strategy against Toxoplasma changes: as oocysts need 1–5 days to become infectious, cleaning the litter tray daily significantly reduces the risk.

During pregnancy, prevention becomes even simpler and clearer: it is recommended that someone else take care of the litter tray if possible, or that it be done with gloves and rigorous hygiene, and it is advisable to avoid gardening without gloves on soil where cats may have defecated, as stated in public health recommendations.

Prevention in gardens against Trichuris requires discipline, because the environment has a “memory”; that is why it is important to remove faeces from the garden frequently and prevent dogs from having unsupervised access to the same areas where they have previously defecated, especially knowing that the eggs can remain viable for up to 5 years under the right conditions.

Your vet advises – Children’s sandpits

The AAP, American Academy of Paediatrics (Red Book) includes a very specific recommendation against toxocariasis: cover sandboxes when not in use to prevent animal faeces and contamination of children’s play areas. A small gesture, a big reduction in risk.

Prevention also involves avoiding habits that feed parasitic cycles; therefore, it is advisable to prevent animals from eating faeces, food scraps on the street or hunted prey, and it is prudent not to offer raw meat or offal of dubious origin.

Finally, prevention works best when it is adapted to each family’s actual lifestyle; that is why at Eurovet Veterinary Clinic (Peñíscola) we propose internal and external deworming plans tailored to each household’s routine and reinforced with periodic reminders so that no doses are missed.

When the individual risk cannot be properly assessed, your own text provides a practical reference: the ESCCAP 2025 guidelines recommend deworming or performing coproparasitological checks at least four times a year as a baseline, and increasing the frequency in high-risk animals; they also point out that 1–3 deworming treatments per year do not offer sufficient protection.

Prevention that works: how to turn it into a system

Good prevention is not measured by ‘not seeing worms’, but by much more useful signs: it is measured by the regularity of the plan, by control of the environment and by the ability to react quickly to persistent digestive signs.

Warning signs that warrant action (even if you don’t see anything)

When a pet has recurrent diarrhoea, soft stools that come and go, mucus, intermittent vomiting, weight loss, dull coat, or anal itching, the most sensible thing to do is not to normalise it and seek veterinary evaluation, because many parasitic infections can run their course discreetly while continuing to contaminate the environment.

When there are several pets in the home, prevention necessarily becomes a ‘group’ effort, because if one animal sheds infectious forms, the rest can become reinfected and keep the problem going without anyone noticing.

The “anti-rebound protocol”: treat well + stop reinfection + clean thoroughly

A typical reinfection occurs when the animal is treated, but the source is not addressed: garden with old faeces, contaminated textiles, damp floors, persistent fleas or risky habits. Effective prevention combines three simultaneous approaches: correct treatment, realistic environmental hygiene and cutting off exposure during the critical period.

In Giardia, this is especially important because data show that the parasite is present in significant proportions in canine environments: for example, in DOGWALKS it was the most frequent finding and appeared in 83.5% of parks sampled.

In Dipylidium, internal treatment without consistent flea control is often a short-lived victory, because the vector is key to the cycle, as emphasised by reference sources in medical and veterinary parasitology.

What controls really help

Solid prevention is based on a plan, but also on diagnosis when there are doubts or recurrences. A well-indicated coproparasitological test allows the type of problem to be identified and blind treatments to be avoided. In intermittent cases, it is worth remembering that some parasites may not be detected consistently, so the vet may suggest repeating samples or using complementary techniques (e.g. antigens/coproantigens in selected cases).

Your family ‘dashboard’: a minimum that keeps the risk low

Prevention becomes easy when it becomes routine. A family is usually on the right track when these conditions are met on a consistent basis:

• Faeces are always removed and the garden does not become a reservoir.
• Real hand hygiene is maintained, especially before eating and after handling the animal’s belongings.
• Fleas are controlled continuously when appropriate for the animal’s lifestyle.
• Risky water is avoided and hygiene is reinforced if there is persistent diarrhoea.
• The cat’s litter tray is cleaned daily and simple precautions are taken during pregnancy (gloves, hygiene and, if possible, another person).
• Review the preventive plan when lifestyle changes occur (new puppy, moving to a house with a garden, daycare, hunting, multiple pets, etc.).

Your vet advises you – Travel: the “mandatory” worming treatment that many forget

If you are travelling with your dog to countries that seek to remain free of E. multilocularis, praziquantel may be required 1–5 days before entry (regulations vary by country). It is one of those things that should be added to your checklist along with your passport. ESCCAP

The ultimate goal is simple: for families to live happily and peacefully with their pets, but with realistic and constant prevention. At Eurovet, we sum it up in a phrase that never fails: to care is to love… and to love means to prevent 🧡.

Scientific sources and recommended reading

Fakhri, Y., Gasser, R. B., Rostami, A., Fan, C. K., Ghasemi, S. M., Javanian, M., Bayani, M., Armoon, B., Moradi, B., & Pouriran, R. (2018) – Toxocara eggs in public places worldwide: A systematic review and meta-analysis – Environmental Pollution – Global meta-analysis estimating a pooled prevalence of 21% of soil contamination with Toxocara eggs in public spaces – https://www.sciencedirect.com/science/article/abs/pii/S0269749118326708

Köchle, B. R., (authors according to document) (year not verified here) – Prevalence of Toxocara Eggs in Public Parks… (Valencia) – (Source not verified here) – Study in parks in Valencia that found 10.9% of soil samples positive for Toxocara eggs, with higher positivity in dog areas – https://repositorioinstitucional.ceu.es/bitstreams/e4284393-ca01-442e-884c-c64b36098675/download

Drake, J., (co-authors according to article) (2022) – Detection of gastrointestinal parasites in dogs visiting urban parks in Western Europe: the DOGWALKS study – Parasites & Vectors – Multicentre study in European parks: 22.8% of dogs tested positive for an intestinal parasite; Giardia was the most common finding (17.3%) and was detected in 83.5% of parks sampled – https://link.springer.com/article/10.1186/s13071-022-05440-2

Jańczak, D., (co-authors according to article) (2025) – Prevalence of Giardia duodenalis genetic assemblages in dogs and cats… – (Journal according to article in PMC) – Study that detected Giardia cysts in 11.3% of dogs and 7.1% of cats, with higher prevalence in <1 year (16.9% dogs; 19.8% cats) – https://pmc.ncbi.nlm.nih.gov/articles/PMC12503213/

Centres for Disease Control and Prevention (CDC) (n.d./updated on website) – DPDx – Toxoplasmosis – CDC DPDx – Official resource describing the cycle: oocyst shedding for 1–3 weeks and requiring 1–5 days in the environment to become infectious – https://www.cdc.gov/dpdx/toxoplasmosis/index.html

Centres for Disease Control and Prevention (CDC) (n.d.) – Toxoplasmosis: An Important Message for Cat Owners (PDF) – CDC (educational PDF) – Official brochure recommending daily cleaning/changing of the litter tray and detailing precautions during pregnancy and for immunocompromised individuals – https://www.cdc.gov/parasites/toxoplasmosis/resources/printresources/catowners.pdf

Centres for Disease Control and Prevention (CDC) (n.d.) – Zoonotic Hookworm: Clinical features – CDC – Official clinical page describing skin penetration and typical presentation of cutaneous larva migrans caused by zoonotic hookworms – https://www.cdc.gov/zoonotic-hookworm/hcp/clinical-features/index.html

Centres for Disease Control and Prevention (CDC) (n.d.) – DPDx – Dipylidium caninum – CDC DPDx – Official resource explaining transmission through ingestion of infected fleas and that human cases are mainly seen in children – https://www.cdc.gov/dpdx/dipylidium/index.html

MSD Veterinary Manual (n.d.) – Whipworms in Small Animals (Trichuris vulpis) – MSD Veterinary Manual – Veterinary review indicating that eggs can remain viable in the environment for up to 5 years (depending on conditions) – https://www.msdvetmanual.com/digestive-system/gastrointestinal-parasites-of-small-animals/whipworms-in-small-animals

European Scientific Counsel Companion Animal Parasites (ESCCAP) (2025) – Worm Control in Dogs and Cats (Guideline 01, PDF) – ESCCAP (European guideline, PDF) – Guideline recommending, when the risk cannot be individualised, deworming or coproparasitological control at least 4 times a year, and points out that 1–3 dewormings per year do not offer sufficient protection – https://www.esccap.org/uploads/docs/biu0jhej_0778_ESCCAP_GL1__English_2025_v21_1p.pdf

Companion Animal Parasite Council (CAPC) (n.d./updated on website) – Coccidia (Cystoisospora) – CAPC Guidelines – Guidelines indicating that humans are not susceptible to Cystoisospora from dogs/cats and it is not considered a typical zoonosis – https://capcvet.org/guidelines/coccidia/