New Study Reveals Why Shelter Dogs Face Different Parasite Risks Across Portugal
A new scientific study from Portugal has identified important differences in the risk of intestinal worm infections among shelter dogs. Researchers found that the number of dogs sharing an enclosure, their age and their deworming arrangements all matter, but the surrounding environment also plays a significant role. The findings could help animal shelters develop more effective parasite-control programmes while protecting both canine and human health.
A Closer Look at Portugal’s Shelter Dogs
Animal shelters face a difficult challenge. They must provide safe accommodation for dogs arriving from different backgrounds, often with limited information about their medical histories. Preventing infectious diseases is an essential part of that responsibility, particularly when several animals share the same living space.
A team of Portuguese researchers has now investigated how shelter conditions and environmental factors influence the distribution of gastrointestinal nematodes, a group of parasitic roundworms that can infect dogs.The study, published in Preventive Veterinary Medicine, was conducted by Patrícia Lopes and five colleagues associated with Portuguese research institutions, including the University of Lisbon.
The researchers analysed 189 faecal samples collected from 19 shelters across mainland Portugal between November 2021 and October 2022. They combined laboratory testing with information about shelter management, animal characteristics, climate and the surrounding landscape.
Three Parasites, Different Risks
The investigation focused on three important groups of intestinal parasites: Toxocara canis, Trichuris vulpis and Ancylostoma species.Toxocara canis is a roundworm that commonly infects dogs, particularly puppies. Its eggs can contaminate the environment through infected faeces and may remain viable for long periods.
Trichuris vulpis, commonly known as the whipworm, lives in the large intestine. Hookworms, including Ancylostoma species, attach themselves to the intestinal lining and can cause health problems, particularly in vulnerable animals.
Although these parasites share some characteristics, the Portuguese researchers discovered that their environmental risk patterns were not identical.Their findings suggest that parasite prevention cannot always rely on a single approach applied equally to every shelter.
Crowding and Deworming Make a Difference
One of the study’s important findings concerned housing density: the number of dogs kept together in an enclosure.The researchers identified housing density, age group and deworming arrangements as relevant factors in parasite infection risk. Their importance varied according to the parasite involved.
This is particularly significant for shelters that accommodate large numbers of animals. Decisions about housing and veterinary care may influence the opportunities for parasites to spread.However, the study does not establish that crowding alone causes infection. The researchers examined several interacting factors, and their statistical models identified associations rather than proving a single cause.
Nevertheless, the findings support the importance of including parasite prevention in everyday shelter management rather than treating it as an occasional veterinary concern.
Geography Matters Too
Perhaps the most interesting discovery was the relationship between parasite risk and the environment.Using computer-based modelling, the researchers examined how climatic and geographical conditions might influence the distribution of different parasites.
For Toxocara canis, relevant environmental factors included solar radiation, temperature and soil characteristics.For Trichuris vulpis and Ancylostoma caninum, land cover and rainfall were particularly important.The resulting maps suggested that environmental conditions suitable for Toxocara canis and Trichuris vulpis occur across much of mainland Portugal. For Ancylostoma caninum, areas with greater predicted environmental suitability were concentrated mainly in southern Portugal.
These maps should not be interpreted as evidence of an outbreak or as proof that particular shelters are infected. They identify environmental conditions associated with potential parasite transmission, not confirmed infections at every mapped location.
Why Human Health Is Also Important
Intestinal parasites are not exclusively an animal-health concern. Some can infect humans, making effective prevention particularly important in places where animals and people interact closely. Toxocara canis is one example. Humans can become infected after accidentally swallowing infective eggs from contaminated soil or other environmental material.
According to the US Centers for Disease Control and Prevention, good hygiene, prompt disposal of animal waste and appropriate veterinary treatment are important preventive measures.
The eggs require time in the environment to become infective, which makes regular cleaning and waste removal especially valuable. The Portuguese study did not investigate human infections. Nevertheless, its findings provide additional information that could help veterinary professionals understand where environmental contamination may present greater risks.
What Can Animal Shelters Do?
The researchers conclude that parasite-control strategies should reflect local circumstances rather than relying entirely on uniform national recommendations. This could involve paying closer attention to the number of dogs housed together, their age, their treatment histories and the environmental conditions surrounding individual shelters.
Regular veterinary examinations and appropriate testing remain important tools for detecting infections. The European Scientific Counsel Companion Animal Parasites (ESCCAP) already provides evidence-based recommendations for worm control in dogs and cats. Its guidelines emphasise assessing individual risks and selecting suitable diagnostic and treatment programmes.
The Portuguese findings may help shelter veterinarians refine those decisions, particularly when resources must be directed towards animals or locations facing greater risks.
A Wider Lesson for Animal Welfare
Although the research was conducted in Portugal, the questions it raises are relevant to animal shelters elsewhere. Dogs do not live independently of their surroundings. Their health is influenced by housing conditions, veterinary care and the environments in which parasites survive and reproduce. The researchers used machine-learning techniques and ecological modelling to bring these different influences together.
Their approach offers a potential framework for further investigations in other countries, although local studies would be necessary before applying the Portuguese geographical predictions elsewhere.
The central message is encouraging: better information can help shelters make better decisions. Protecting dogs against intestinal parasites is not simply a matter of administering medication. It also requires understanding the conditions in which those animals live.
Primary Scientific Sources
Original peer-reviewed research
Lopes, P., Geraldes, M. A., Gomes, J., Louro, M., da Fonseca, I. P., & Cunha, M. V. (2026). Environmental and management drivers of gastrointestinal nematodes in shelter dogs across mainland Portugal revealed by ecological niche modelling. Preventive Veterinary Medicine, 255, 106962.
Original scientific paper — DOI
University of Lisbon research record
Additional authoritative sources
