ISKNV, a megalocytivirus, produced the largest testing base and the highest cumulative positivity of the extensively sampled agents: 23.3% across 30,917 tests. Lactococcus spp. reached 18.4% across 8,589 tests, while Streptococcus spp. reached 15.2% across 12,629 tests. The network covered 280 companies operating at 154 culture sites in 16 states. Most samples came from the Southeast, which contributed 75.6% of all diagnostic records, compared with 13.3% from the Northeast and 11.1% from the Central-West. The Southeast consequently remained the principal production core for detection, while expanding foci in the Northeast provided the clearest evidence of geographic change.

Several patterns in the Northeast were compatible with genuine northward expansion rather than simply more intensive testing. ISKNV positivity rose from 0.2% in 2023, based on 1,484 tests, to 14.6% in 2024 and 17.8% in 2025. Streptococcus spp. detection increased from zero in 2023 to 14.8% in 2024 and 15.5% in 2025, while Lactococcus spp. rose from zero to 1.3% and then 5.9%. Georeferenced records showed the number and northern reach of positive localities increasing for these three agents between 2023 and 2025. By contrast, Edwardsiella spp. remained largely anchored to the Southeast, and Francisella orientalis was absent from the Northeast in all three years. Because regional sampling also expanded, the authors treated the Northeast signal as an inference requiring prospective confirmation rather than a demonstrated causal pathway.

Time-series analysis provided a more qualified view of endemicity and change. Augmented Dickey-Fuller tests classified the series for Aeromonas spp., Edwardsiella spp., F. orientalis, ISKNV and Lactococcus spp. as stationary, a property compatible with broadly stable circulation but not proof that a pathogen was endemic. Streptococcus spp. was non-stationary, with an ADF p-value of 0.267, and its positivity rose steadily from 10.7% in 2023 to 13.5% in 2024 and 18.6% in 2025 while the testing base expanded. This combination was interpreted cautiously as consistent with directional geographic expansion. Flavobacterium spp. was also non-stationary, but its abrupt changes occurred against very small period-specific denominators, making sampling instability a more plausible explanation than sustained epidemiological change.

Quarterly aggregation produced the lowest prediction error for every pathogen among the monthly, four-monthly, weekly and quarterly intervals evaluated, with mean absolute errors ranging from 0.068 for Edwardsiella spp. to 0.181 for Lactococcus spp. The result identifies quarterly sampling as a reasonable candidate for surveillance design, rather than a formally optimized standard that has already been validated prospectively. Residual distributions were non-normal for most pathogens and frequencies, indicating that uncertainty intervals derived from these models require caution. The surveillance data also showed that host developmental stage had heterogeneous effects on pathogen detection. Stage improved pathogen-specific model fit for Aeromonas spp., Streptococcus spp. and Lactococcus spp., but not for the other four agents; across the pooled pathogen assemblage, its influence was weak.

Mixed-effects models accounted for clustering of records within culture sites, epidemiological weeks and individual observations. A model with all three random effects was best supported by information criteria, and fixed-effect estimates remained directionally consistent with the simpler generalized linear models, indicating that farm-level clustering did not create the principal patterns. Between-site variation was substantial for every pathogen. Developmental stage was especially influential in models for Lactococcus spp. and ISKNV, while year was significant for most agents and macro-region generally was not after site was included. These results show why simple national averages can conceal the local variation that matters in farm health surveillance, while also indicating that estimates for sparsely sampled regions and production stages remain less precise.

Pathogens were usually detected independently rather than in strong combinations. Pairwise correlations ranged from −0.02 to 0.12. The only multi-pathogen network module linked ISKNV, Streptococcus spp. and Lactococcus spp., the three most widely detected agents, through weak associations. These values are compatible with shared environmental and production pressures but do not demonstrate direct biological interaction, pathogen facilitation or a stable co-infection syndrome. The cross-sectional presence-or-absence design also could not establish which agent appeared first. The signal is therefore hypothesis-generating and supports longitudinal work designed to order viral and bacterial detections in time rather than treating the network module as evidence of a causal pathway.

Antimicrobial susceptibility testing showed that resistance patterns were structured by pathogen, antibiotic and their interaction, with developmental stage also affecting minimum inhibitory concentrations (MICs). The analysis included 4,318 isolates across Aeromonas, Edwardsiella, Flavobacterium, Lactococcus and Streptococcus. A Gamma generalized linear model fitted to 160 median-MIC combinations found higher MICs in fry than adults, while juveniles did not differ significantly from adults. Aeromonas spp. had the highest baseline MICs relative to the other modeled genera. Resistant isolates also had significantly higher MICs than susceptible isolates, supporting internal consistency between categorical antibiograms and quantitative measurements.

Pathogen-by-antibiotic interactions showed why susceptibility cannot be generalized across bacterial agents. Edwardsiella spp. and Lactococcus spp. had elevated MICs in combination with enrofloxacin and florfenicol relative to the model’s reference structure, while Streptococcus spp. also showed elevated MICs with enrofloxacin. These are combination-level associations because the model was fitted to median values rather than individual isolates and did not directly model farm-level clustering of isolates. Moreover, aquatic-animal breakpoints were unavailable for some pathogen-drug pairings, so the study reported those MICs numerically without assigning susceptible, intermediate or resistant categories. The results do not establish clinical treatment outcomes, but they show that antimicrobial susceptibility data need to be interpreted separately for each pathogen and compound.

Taken together, the surveillance data challenge a historically Streptococcus-centered view of Brazilian tilapia health and provide a baseline for a more pathogen-specific national system. The clearest priorities include resolving infections to species, serotype and lineage, maintaining surveillance for S. agalactiae serotype Ia, balancing production-stage sampling, and improving coverage outside the Southeast. No serotype Ia was detected by serotype-specific qPCR during the three years, although absence from a non-probabilistic sample cannot establish national absence. Future studies would also need probabilistic recruitment, correction for diagnostic performance, standardized observation units and prospective validation of alert thresholds. Until those steps are completed, the results are most useful as a descriptive map of pathogen circulation, temporal variability and antimicrobial susceptibility in the farms that submitted samples.

Subject of Research: Multi-pathogen epidemiological surveillance of Brazilian Nile tilapia aquaculture

Article Title: Epidemiological surveillance reveals major pathogen dynamics in Brazilian Nile tilapia aquaculture from 2023 to 2025

Article References: Cardoso-Guimarães, M., Fernandez-Alarcon, M. F., Correa, R., Miyoko-Natori, M., Galetti, R., Brito de Souza, A., Squizatto, A. C., Silva, R., Araújo de Almeida, L., Mota Sátiro, T., Ildefonso, R., & Rozas-Serri, M. (2026). Epidemiological surveillance reveals major pathogen dynamics in Brazilian Nile tilapia aquaculture from 2023 to 2025. Frontiers in Veterinary Science, 13, Article 1944605. https://doi.org/10.3389/fvets.2026.1944605

Image Credits: AI Generated

DOI: 10.3389/fvets.2026.1944605

Keywords: Nile tilapia, Brazilian aquaculture, ISKNV, Lactococcus, Streptococcus, epidemiological surveillance, antimicrobial susceptibility, pathogen co-detection, disease ecology, Epidemiological, surveillance, reveals

The research, published in Frontiers in Bird Science, followed individually color-ringed greenfinches (Chloris chloris) across winters from 2019 to 2021 at feeding sites in the Krāslava countryside. The team, led by Indrikis A. Krams of the University of Latvia together with colleagues from Latvia, Estonia, and the United States, captured birds with mist nets, measured body mass to the nearest 0.1 gram and wing length to the nearest millimeter, and recorded each bird’s flock identity, sex, and social rank. In total, 894 marked individuals with complete data on dominance rank, body condition, flock size, epidemic status, and overwinter survival entered the final analyses, drawn from 52 flocks whose sizes ranged from just 6 to as many as 360 birds.

The study’s central methodological insight concerns how body reserves are measured. Rather than relying on raw body mass alone, the researchers calculated a body mass index by dividing mass by wing length cubed, producing a size-corrected proxy of energetic condition. The logic is subtle but important: a large bird naturally weighs more than a small one, so raw mass conflates structural size with actual reserves. The analyses revealed that this size-adjusted BMI responded far more strongly to dominance and epidemic context than total body mass did, indicating that size-corrected condition is a more sensitive indicator of the short-term energetic strategies birds deploy under disease pressure.

Dominance itself was quantified rigorously. Trained observers spent hours each day at the feeding sites recording displacement events, in which one bird supplanted another from access to food. Only these unambiguous displacements were used to build dominance hierarchies, since minor agonistic behaviors such as wing flicks are less repeatable. In small flocks of about ten birds, every individual was captured and ranked directly. In larger flocks, each marked bird was assigned a relative rank on a percentage scale, from 0 to 10 percent for the most subordinate individuals to 90 to 100 percent for consistent victors. Rank was then treated as a continuous predictor, standardized so that coefficients represent the effect of a 10 percent change in social standing.

The epidemic context emerged naturally during the third winter. In 2019 and 2020, no clinical cases of trichomonosis appeared at the feeding sites, and those winters were classified as non-epidemic. Winter 2021 was different: multiple dead birds suddenly appeared at the sites, mortality escalated over subsequent days and weeks, and oral-crop swabs examined under light microscopes repeatedly revealed motile Trichomonas gallinae trophozoites, identified by their characteristic rapid, non-directional movement and flagellated morphology, with the undulating membrane visible at higher magnification. Birds suffering from this protozoan parasite experience dysphagia, lethargy, anorexia, and dehydration, and infection typically impairs feeding, causing rapid loss of body condition.

The results on body reserves were strikingly context-dependent. Averaged across all social settings, dominance rank alone did not predict BMI. Instead, a significant interaction between rank and flock size showed that rank-related differences in body condition emerged only in particular social environments. In medium-sized flocks of 55 to 88 birds and in very large flocks of 125 to 330 individuals, higher-ranking birds maintained significantly higher BMI than subordinates. In small flocks of 10 to 38 birds, no clear rank-related differences in BMI were detected at all. The researchers interpret this through the lens of social ecology: in small flocks, hierarchies are stable and food access is predictable, so even dominant birds can meet their energetic needs without carrying bulky reserves, and selection for agility may favor lean phenotypes. In larger flocks, where competition is fiercer and feeding opportunities are less predictable, dominants appear to accrue greater reserves.

Disease then reshaped these social gradients in a flock-size-specific way. The three-way interaction between dominance rank, flock size, and epidemic status was statistically significant, and it was driven primarily by medium-sized flocks, where the positive association between rank and BMI observed in non-epidemic winters was significantly reduced during the epidemic. In the largest flocks, a similar attenuation was suggested but fell just short of conventional significance. Meanwhile, the epidemic had an overall negative effect on BMI, indicating that birds carried reduced reserves during the outbreak winter. Total body mass, by contrast, was comparatively insensitive to disease-driven change, consistent with the idea that mass integrates both fat and lean tissue and therefore reflects a more stable energetic state than the more responsive BMI.

The survival findings represent the most dramatic reversal in the study. During the trichomonosis epidemic, higher BMI was associated with a substantially increased probability of surviving until spring, with a strong positive interaction between BMI and epidemic status. Individuals entering the epidemic with greater relative adiposity retained a markedly greater likelihood of reaching spring, presumably because fat stores buffer the prolonged periods of reduced food intake that the parasite induces. Outside epidemic conditions, the pattern flipped: BMI showed a weak but statistically significant negative association with survival, exactly as mass-dependent predation models predict when the cost of carrying extra weight, through reduced escape performance, slightly outweighs its benefit under benign conditions. In other words, the same body condition that was a slight liability in ordinary winters became a powerful lifeline when disease struck.

Dominance, meanwhile, did not guarantee survival under disease pressure. Higher-ranking individuals did show higher survival probabilities on average, but once individual body condition was accounted for during the epidemic, the survival advantage of rank was substantially reduced. The authors suggest that infectious disease may act as a conditional equalizer within social groups, weakening the fitness disparity between dominant and subordinate individuals when survival depends primarily on physiological resilience rather than competitive ability. Social rank may also shape disease outcomes through immunological pathways, since prior work across taxa links dominance to altered inflammatory profiles and pathogen resistance, although immune parameters were not directly measured in this study.

An extended model that jointly considered BMI and size-independent body mass, derived as residuals from the relationship between log-transformed mass and wing length, added a further layer of physiological nuance. Individuals heavier than expected for their structural size showed higher overwinter survival overall, suggesting that total somatic reserves, potentially including metabolically accessible lean tissue such as muscle protein, contribute to winter survival more generally. Yet size-independent mass conferred no additional epidemic-specific advantage beyond that provided by BMI, implying that relative adiposity is the dominant energetic buffer during the acute phases of disease-induced anorexia. The authors propose a sequential model of reserve use: fat supports short-term tolerance to reduced intake, while lean tissue extends endurance once fat stores are exhausted. The findings also carry a caveat about predators, since Eurasian sparrowhawks can acquire the parasite from infected prey, raising the possibility that predator activity itself shifts during epidemics. As emerging pathogens become increasingly prevalent in wildlife, the study argues that the fitness value of body reserves cannot be inferred from simple main effects; it emerges only from the interaction of social structure, group size, and disease context, and predicting survival in a changing world will require integrating disease ecology into traditional frameworks of winter behavior.

Subject of Research: Disease ecology and winter survival in European greenfinches

Article Title: Disease-driven variation in body reserves links social rank, flock size, and overwinter survival in European greenfinches

Article References: Krams, I. A., Krams, R., Popovs, S., Adams, C. B., Freeberg, T. M., & Krama, T. (2026). Disease-driven variation in body reserves links social rank, flock size, and overwinter survival in European greenfinches. Frontiers in Bird Science, 5, Article 1779032. https://doi.org/10.3389/fbirs.2026.1779032

Image Credits: AI Generated

DOI: 10.3389/fbirs.2026.1779032

Keywords: greenfinches, trichomonosis, body condition, social dominance, flock size, overwinter survival, disease ecology, Latvia, Disease-driven, variation, body, reserves

The research, published in the Journal for Nature Conservation, builds on a deceptively simple ecological insight. Just as human influenza surges in winter and recedes in summer, chytrid severity fluctuates with temperature and humidity. The fungus thrives in cool, moist conditions and falters when environments become too hot or too dry for its zoospores to survive and infect amphibian skin. By combining previously developed models that tracked where the disease occurs and when it reaches peak intensity, the research team constructed new chytrid suitability maps for Panama. These maps identify climatic refugia, places that are environmentally hostile to the pathogen yet perfectly hospitable to the frogs themselves. In effect, the scientists have produced a ranking system for potential release sites, allowing conservationists to direct scarce reintroduction resources toward locations where the odds of survival are highest.

The urgency of this work is rooted in painful experience. Conservationists have previously released captive-bred harlequin toads back into Panamanian forests, only to watch many of the animals succumb to the chytrid fungus that persists in soils, waterways and the skin of resistant carrier species. Brian Gratwicke, a conservation biologist at the Smithsonian’s National Zoo and Conservation Biology Institute and senior author of the study, explained that these repeated losses underscored the need for a smarter siting strategy. By mapping climatic refuges, he noted, the team finally has a practical tool to rank candidate release sites and select places where released animals have the best chance of persisting. The approach transforms what has largely been a gamble into a data-driven decision, grounded in the seasonal dynamics of a pathogen that can be modeled with the same rigor applied to crop pests or human disease vectors.

The analytical core of the study lies in comparing where harlequin toads still survive against the modeled intensity of chytrid infection across seasons. The results were striking. Most Atelopus species in Panama were found to persist only at sites where more than 80 percent of the seasons were unsuitable for medium and high-intensity infections. In other words, surviving populations cling to the very few corners of the landscape where the fungus cannot reliably build to lethal levels. This pattern provides strong indirect evidence that the disease, rather than habitat loss alone, is the dominant filter determining where these amphibians can endure. It also validates the underlying models: if the suitability maps were meaningless, surviving populations should be distributed randomly with respect to predicted disease pressure, and they are not.

One species stands out as a remarkable exception. The variable harlequin toad, Atelopus varius, was the only species found at sites classified as suitable for the disease. Scientists interpret this as consistent with growing evidence that the species may have evolved some degree of resistance to chytrid. Such evolutionary responses have been documented elsewhere in the amphibian world, where populations that survived initial epizootics sometimes carry genetic variants that blunt the fungus’s effects. If A. varius truly possesses enhanced tolerance, it could serve as both a biological benchmark for understanding resistance and a candidate for reintroduction programs that do not require the strictest disease-free conditions. For the many Atelopus species that lack this advantage, however, the refugia maps remain the most promising blueprint.

Beyond guiding reintroductions, the maps serve a second, equally valuable purpose: locating wild populations that may have quietly persisted in places scientists have not yet searched. Carrie Lewis, a doctoral candidate at George Mason University and lead author of the publication, emphasized that the ability to identify climate refugia is critical for finding populations that might have disappeared from most of their former range. These surviving pockets could act as genetic reservoirs, supplying founders to bolster assurance colonies under human care and providing stock to augment dwindling wild populations. In conservation genetics, maintaining diversity is paramount; small, isolated refugial populations risk inbreeding, and infusing new genes from rediscovered survivors could mean the difference between a population that limps along and one that recovers robustly.

The study also confronts an uncomfortable complication: climate change is redrawing the map in real time. The models forecast areas that, while currently suitable for the fungus, may become unsuitable in the coming years as temperatures rise and rainfall patterns shift. These emerging refuges could expand the portfolio of potential release sites, offering new opportunities that did not exist a decade ago. Yet the same climatic forces carry a threat. Many harlequin toads are adapted to cool, mountainous habitats, and warming may render those high-elevation refuges inhospitable to the frogs even as they become inhospitable to the fungus. The interplay between pathogen suitability and amphibian habitat suitability is therefore not a simple overlap but a moving target that conservation planners must track continuously, updating models as conditions change.

The research is already moving from theory to practice. Roberto Ibáñez, a staff scientist at the Smithsonian Tropical Research Institute and co-author of the study, reported that guided by the climate refugia and habitat-suitability maps, the team has begun surveying potential sites for habitat quality and preparing for release trials. These field experiments will allow scientists to test the climate refugia hypothesis directly, comparing survival rates of released frogs at sites predicted to be disease refuges against those at more chytrid-suitable locations. Such experimental validation is essential; models are hypotheses, and only on-the-ground outcomes with tagged, monitored animals can confirm that the mapped refuges deliver the protection they promise. Success would establish a template transferable to other chytrid-affected landscapes across the neotropics.

The institutional machinery behind this effort reflects decades of investment. The Panama Amphibian Rescue and Conservation Project, founded in 2009, unites Zoo New England, Cheyenne Mountain Zoo, the Smithsonian’s National Zoo and Conservation Biology Institute and the Smithsonian Tropical Research Institute in a coordinated mission to build captive populations of species at risk, develop methods to reduce the impact of chytrid, and return imperiled species to the wild. The new research was supported in part by the Bezos Earth Fund, signaling growing philanthropic recognition that amphibian conservation requires both ex situ insurance colonies and in situ solutions. The modeling study itself employed computational simulation, a method well suited to integrating climate data, disease dynamics and species distributions across complex tropical terrain.

For a genus that has become an emblem of the global amphibian crisis, the Panama maps represent something rare: actionable hope. Harlequin toads, with their jewel-like colors and their dependence on clean, flowing streams, are sentinels of ecosystem health, and their decline has rippled through the food webs of montane forests. If release trials in the mapped refuges succeed, captive-bred frogs descended from rescued founders could once again patrol Panamanian streams, and the framework could be extended to other countries and other pathogens. The study does not promise a cure for chytrid, which remains ubiquitous across the region. What it offers instead is precision, the knowledge of exactly where the odds tilt in the frogs’ favor, and a disciplined strategy for spending that advantage before it disappears in a warming, shifting world.

Subject of Research: Mapping climatic refugia of the chytrid fungus to guide reintroduction of harlequin toads in Panama

Article Title: Climate refuges may be key to restoring imperiled amphibians

Article References: Climate refuges may be key to restoring imperiled amphibians. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: amphibian chytrid fungus, harlequin toads, Atelopus, climate refugia, Panama, reintroduction, conservation biology, Smithsonian, Batrachochytrium dendrobatidis, captive breeding, disease ecology, climate change