The stakes are higher than the animals’ endearing reputation might suggest. Otters are apex predators in many freshwater and coastal systems, feeding at high trophic levels and accumulating contaminants and pathogens from the entire food web beneath them. That makes them ideal sentinel species, biological barometers whose health reflects the condition of the ecosystems they inhabit. Yet most of the thirteen otter species are now classified as threatened or near-threatened, beset by habitat loss, pollution, overhunting, climate change, disease emergence, and human disturbance. Conservation programs have scored local victories, but the editorial warns that these pressures are compounding, and their combined effects on individual animals and entire populations remain poorly understood.

A central theme running through the collection is how little we actually know about the parasites that afflict otters. Cotey and Reichard conducted a systematic review of helminths, protozoans, and ectoparasites reported in otters globally, and the results reveal a striking geographic imbalance. Most of the world’s parasite records come from just three otter species, while the remainder of the subfamily is essentially a blank slate. Opportunistic sampling concentrated near human development, insufficient spatial information, and methodological bias further distort the picture. The gap is widest in the biodiverse regions of the Global South, where logistical and financial constraints have long limited wildlife disease research precisely where parasite diversity is likely to be greatest.

Shanebeck and colleagues complemented that global review with a focused analysis of helminth parasites in the North American river otter and the American mink, two mustelids that share habitat, prey, and parasites. Alongside the literature synthesis, the team examined necropsy data from 259 animals in British Columbia and Alberta. The parasite communities they documented were distinct from those reported elsewhere in North America, suggesting strong regional structure in otter parasite ecology. Most notably, the study reports the first confirmed cases of the zoonotic parasite Alaria mustelae in river otters, including highly prevalent larval-stage infestations associated with clinical disease. That a zoonotic parasite had gone undetected in a well-studied North American carnivore until now underscores how much basic surveillance remains undone.

In Brazil, Perin and colleagues tackled the parasite communities of the giant otter and the neotropical otter, species whose remote habits and elusive behavior have historically limited such data. Necropsy and fecal analysis revealed diverse parasite assemblages spanning digeneans, cestodes, nematodes, and apicomplexans. The team also produced molecular characterizations of two parasite taxa, and the exercise exposed a critical technical bottleneck: the lack of reference sequence data for wildlife parasitology. Without genetic libraries to match sequences against, even well-equipped laboratories cannot confidently identify parasites from endangered species like the giant otter, leaving disease threats invisible until they become emergencies.

Regional context matters just as much as global synthesis. Wise and colleagues characterized parasite communities from the scats of river otters in Chesapeake Bay using metabarcoding, a technique that simultaneously recovers prey DNA and parasite sequences from fecal samples. Their analysis documented prey composition across estuarine and marine habitats alongside several parasite groups, with infestations dominated by strongylid nematodes. The authors suggest the strongylid dominance may reflect the contribution of marine fish in local diets, a reminder that parasite loads are shaped by local ecology, prey selection, and habitat, not by species-level averages. Effective wildlife health monitoring, they argue, must be grounded in regional ecological context.

The collection also confronts the spillover of pathogens from domestic animals into wild otter populations. Gonchoroski and colleagues studied neotropical otters within a protected conservation reserve in Brazil, combining serological, molecular, and camera-trapping techniques. Even inside a protected area, domestic carnivores influenced otter habitat use and exposed the animals to pathogens including Canine Distemper Virus and Toxoplasma gondii. Disease spillover from domestic dogs and cats is a significant and growing threat to vulnerable carnivores worldwide, and the findings make clear that managing domestic animals around conservation areas is not optional but essential when they may interact with at-risk species.

Human land use exerts its own pressure, independent of any pathogen. Moun and colleagues examined how land use and habitat quality shape the distributions of the smooth-coated otter and the Asian small-clawed otter in southern India, using self-organizing maps and random forest models. Both species avoided areas of intense human disturbance, particularly where water quality had been degraded by agricultural runoff. The results demonstrate how land use decisions directly determine habitat availability for species of conservation concern, and they highlight the importance of managing anthropogenic stressors, not merely protecting remaining habitat patches on paper.

Even harvest pressure responds to economics. Berg and Palmer used statistical population reconstruction to model how changing pelt prices affected North American river otter population dynamics in Kentucky between 2012 and 2023. Higher pelt prices drove increases in trapping effort, negatively impacting population health, and younger animals appeared more vulnerable to harvest pressure, which may carry long-term consequences for population growth and stability. The authors recommend that management agencies adjust harvest regulations in response to pelt prices, pre-empting population-level impacts rather than reacting after declines are underway, a technically straightforward but rarely implemented form of adaptive wildlife management.

The most haunting contribution may be the first documented cases of ocular disease in free-ranging giant otters in Brazil, reported by Soresini and colleagues. The authors propose several potential causes linked to anthropogenic change, including Toxoplasma gondii, canine adenovirus, and exposure to environmental contaminants such as organochlorine pesticides, though confirmation was not possible. The work highlights the barriers to assessing the health of elusive wildlife and the potential risks of accelerating anthropogenic change in the Pantanal, where giant otters, already endangered, may be losing their sight to diseases and toxins we cannot yet measure.

Taken together, the eight studies outline a diversity of threats and, just as importantly, the gaps in our understanding of them. Parasites are an understudied and serious threat, with many otter species lacking even basic survey data. Anthropogenic stressors, from habitat degradation and pathogen spillover to harvest pressure, further endanger populations. The reports also show how sampling limitations and regional bias shape what science knows, and how studying endangered wildlife in remote habitats imposes its own constraints. As human land use and climate change accelerate, these pressures are likely to intensify. The editorial’s authors argue that understanding and mitigating them will require closing regional knowledge gaps, long-term monitoring, and interdisciplinary approaches under a One Health framework, integrating infectious disease research, toxicology, social science, and landscape ecology. Improving our understanding of otter health, they conclude, is essential not only for the survival of these iconic species but for protecting the ecosystems they inhabit, and by extension, the health of the waters on which we all depend.

Subject of Research: Global threats to otter health: parasites, disease, and anthropogenic stressors

Article Title: Editorial: Global threats to otter health: parasites, disease, and anthropogenic stressors

Article References: Editorial: Global threats to otter health: parasites, disease, and anthropogenic stressors. (n.d.). https://doi.org/10.3389/fmamm.2026.1893131

Image Credits: AI Generated

DOI: 10.3389/fmamm.2026.1893131

Keywords: otters, wildlife health, parasites, conservation, One Health, Editorial, Global, threats, otter, health, disease, anthropogenic