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

Otters (subfamily Lutrinae) are semi-aquatic mustelids that play vital roles in aquatic ecosystems worldwide. Bridging aquatic and terrestrial ecosystems, they are exposed to diverse stressors, such as disease, environmental contaminants, and the effects of global change. Otters are also beloved globally, making them an ideal flagship species, both as sentinels of ecosystem health and as symbols for conservation awareness (Stevens et al., 2011). Yet, many otter species are in decline due to habitat loss, pollution, overhunting, climate change, disease emergence, and human disturbance, with most threatened or near-threatened (Duplaix and Savage, 2018; Garcês and Pires, 2024). Conservation efforts have had some local success, but pressures are increasing and may have compounding effects on individual and population health.

This Research Topic examines current threats to otter health, bringing together eight papers that span systematic literature reviews, case reports, statistical models, and field surveys, covering multiple species including the Asian small-clawed otter (Aonyx cinereus), smooth-coated otter (Lutrogale perspicillata), North American river otter (Lontra canadensis), neotropical otter (Lontra longicaudis), and giant otter (Pteronura brasiliensis). These contributions highlight both the diversity of approaches used to study otter health and substantial gaps in the literature that persist across regions and species.

A central theme is our limited understanding of otter parasites and emergent disease threats. Cotey and Reichard highlight this gap in their systematic review of helminths, protozoans, and ectoparasites in otters globally, which reveals a strong geographic imbalance in reporting. Most reports are derived from just three species. Geographic and methodological bias, insufficient spatial information, and opportunistic sampling, mostly near human development, further limits our knowledge. This is especially true in biodiverse regions of the Global South, where logistical and financial constraints limit research.

Shanebeck et al. offer a complementary systematic literature review of helminth parasites in the North American river otter and American mink (Neogale vison), species that share habitat, prey, and parasites. They present this alongside necropsy data from 259 animals in British Columbia and Alberta, revealing distinct parasite communities compared to other regions of North America. The authors report the first confirmed cases of the zoonotic parasite Alaria mustelae in river otter, including highly prevalent larval-stage infestations with associated clinical disease.

Perin et al. report on the parasites of giant otter and neotropical otter in Brazil, which previously had limited data due to the difficulties in studying remote and elusive species. Necropsy and fecal analysis revealed diverse communities including digeneans, cestodes, nematodes, and apicomplexans. Particularly valuable is their molecular characterization of two parasite taxa, which highlights the lack of reference sequence data available for wildlife parasitology, a critical gap for endangered species like the giant otter.

Wise et al. characterized parasite communities from the scats of river otter in the Chesapeake Bay. Their work emphasizes the importance of regional monitoring and ecological context, particularly local prey selection, in wildlife health research. Using metabarcoding, the authors provide information on prey composition across estuarine and marine habitats and the presence of several parasite groups. Infestations were dominated by strongylid nematodes, which may be due to the contribution of marine fish in local diets.

This Research Topic also highlighted the effect of stressors on both individual and populations. Gonchoroski et al. investigate neotropical otters in a protected conservation reserve in Brazil. Using serological, molecular, and camera trapping techniques, they show that even within protected areas, domestic carnivores can influence otter habitat and expose them to pathogens such as Canine Distemper Virus and Toxoplasma gondii. Disease spillover is a significant threat and may endanger vulnerable species. Managing domestic animals around conservation areas is critical, especially when they may interact with at risk species.

Moun et al. examine how land use and habitat quality shape the distribution of Smooth-coated otter and Asian small-clawed otter in southern India. Using self-organizing maps and random forest models, the authors report that both species avoid areas of intense human disturbance, especially with poor water quality due to agricultural runoff. Their findings highlight how land use impacts habitat availability for species of conservation concern, and the importance of managing anthropogenic stressors.

Berg and Palmer use statistical population reconstruction to model the effect of changing pelt prices on North American river otter population dynamics in Kentucky from 2012 to 2023. They find higher pelt prices drive increases in trapping effort, negatively impacting population health. Younger animals may also be more vulnerable to harvest pressure, which may have long-term effects on population growth and stability. The authors recommend that management agencies adjust harvest regulations in response to pelt prices to pre-empt population-level impacts.

Soresini et al. present the first documented cases of ocular disease in free-ranging giant otter in Brazil. The authors suggest several potential causes linked to anthropogenic change, including T. gondii, canine adenovirus, and exposure to environmental contaminants such as organochlorine pesticides, though confirmation was not possible. They highlight the barriers to assessing the health of elusive wildlife, such as the giant otter, and the potential risks of increasing anthropogenic changes in the Pantanal.

In summary, these articles outline the diversity of threats facing otters worldwide and significant gaps in our understanding. Parasites are an understudied, serious threat, with many species lacking even basic survey data. Anthropogenic stressors, such as habitat degradation, exposure to domestic animals, and harvesting pressure, further endanger populations. The reports highlight the difficulties of studying endangered wildlife in remote habitats and how sampling limitations and regional bias shape what we know. As human land use and climate change accelerate, these pressures are likely to intensify. Understanding and mitigating the effects of these stressors will require closing gaps in regional knowledge, long-term monitoring, and interdisciplinary approaches under a One Health framework, integrating infectious disease research, toxicology, social science, and landscape ecology. Ultimately, improving our understanding of otter health is essential for the conservation of these iconic species and protecting the ecosystems they inhabit.

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Footnotes

Edited and reviewed by: Nigel Bennett, University of Pretoria, South Africa