The answer, published in Frontiers in Parasitology, is reassuring but nuanced. Freezing urine at minus 20 degrees Celsius for five to seven days caused a small but statistically significant drop in the proportion of samples testing positive for CAA, while storage under non-frozen conditions at temperatures between 4 and 25 degrees Celsius for roughly five weeks produced results that were generally comparable to those from freshly tested urine. The findings suggest that laboratories and control programs may have more flexibility in how they handle urine samples than the conventional freeze-first approach implies, though the edge of the assay’s detection range remains a fragile zone where storage choices can matter.

To understand why this matters, it helps to know what the CAA test actually measures. Circulating anodic antigen is a glycan-based molecule released by adult Schistosoma worms into the bloodstream of their host. Because it is only produced by living worms, its presence signals an active infection rather than a past one, making it a valuable marker for monitoring treatment efficacy and for surveillance in settings where egg-based microscopy misses low-intensity infections. Conventional parasitological methods such as urine filtration for Schistosoma haematobium eggs suffer from limited sensitivity precisely in the situations that matter most during elimination: after praziquantel treatment, when worm burdens are low and egg excretion is intermittent, and in low-endemic areas where most infections are light. The UCP-LF CAA test, which uses up-converting phosphor particles as a highly sensitive reporter label, has demonstrated strong performance across all known Schistosoma species, including hybrids and veterinary species, and can be run in laboratories with relatively basic equipment.

The study, led by Pytsje T. Hoekstra of the Leiden University Center for Infectious Diseases and colleagues from Leiden University Medical Center, the Public Health Laboratory-Ivo de Carneri on Pemba, the Swiss Tropical and Public Health Institute, and the University of Basel, was embedded in a larger prospective diagnostic evaluation among school-aged children in two schools on Pemba Island, conducted in February 2025. Pemba, part of the Zanzibar archipelago of the United Republic of Tanzania, is a near-elimination setting for S. haematobium, which makes it an ideal proving ground for diagnostics that must perform at the very limits of detection. The researchers collected urine from 272 children and split each sample into aliquots that followed different paths before testing.

The first aliquot was tested within four hours of collection, on the day itself, at the Public Health Laboratory-Ivo de Carneri on Pemba. The second was frozen within four hours, held at minus 20 degrees Celsius for five to seven days, thawed, and then tested at the same laboratory during the following week, reflecting the conventional approach used for CAA testing in many research and surveillance programs. A third aliquot, available for a subset of 153 samples with sufficient remaining urine volume, was stored at 4 degrees Celsius, transported to the Netherlands under cooled conditions with ice packs at the end of the second week, and tested at Leiden University Medical Center within two to three weeks of arrival, roughly five weeks after the sample was originally collected. This third condition was introduced partway through the study as a pragmatic test of a realistic field-to-laboratory workflow, mimicking what happens when freezing is not available in the field and samples must simply be refrigerated and shipped.

The assay itself follows a well-established protocol. Urine is pre-treated with trichloroacetic acid to release CAA from immune complexes and precipitate proteins, after which the clear supernatant is concentrated using centrifugal filtration devices with a 10-kilodalton cutoff. The concentrated sample is then mixed with assay buffer containing up-converting phosphor particles conjugated to anti-CAA antibodies, lyophilized into pellets for stability. Lateral flow strips bearing a test line of anti-CAA antibodies are added, and immunochromatography proceeds for at least three hours before the strips are scanned with a reader adapted for the up-converting label. Each run includes a serial dilution series of a trichloroacetic acid-treated crude adult worm antigen preparation spiked into CAA-negative urine, which serves both to validate the assay’s cut-off, set at 2 picograms per milliliter for the dry format used here, and to quantify the CAA concentration in unknown samples.

The headline numbers tell a clear story. In the full dataset of 272 samples, 44, or 16.2 percent, tested positive when urine was fresh, but only 35, or 12.9 percent, tested positive after freezing. Nine of the samples that flipped from positive to negative after freezing were low-positive samples with CAA concentrations between 2 and 5 picograms per milliliter, sitting close to the assay’s cut-off. Not a single fresh-negative sample turned positive after freezing, meaning the discordance ran entirely in one direction. A McNemar’s test on the paired proportions confirmed the difference was statistically significant, with a p-value of 0.004. Quantitative CAA concentrations showed a non-significant trend toward lower values after freezing, with a Wilcoxon signed-rank p-value of 0.051, and a Bland-Altman analysis found no statistically significant systematic bias, though fresh samples tended to have higher concentrations with a mean ratio of 1.18.

For the subset of 153 samples that also had a non-frozen stored aliquot, the picture was different in an interesting way. Positivity was 20 out of 153, or 13.1 percent, in fresh urine, 16 out of 153, or 10.5 percent, in frozen urine, and 24 out of 153, or 15.7 percent, in non-frozen stored urine, the highest of the three conditions. Compared with fresh samples, only 2 flipped from positive to negative after non-frozen storage while 6 flipped the other way, a difference that was not statistically significant. Against frozen samples, however, the non-frozen condition produced significantly more positives, with 1 sample going from positive to negative and 9 going from negative to positive, yielding a McNemar p-value of 0.02. Across all pairwise comparisons, Spearman rank correlations between quantitative CAA concentrations were strong, ranging from 0.86 to 0.93 with p-values below 0.0001, and Cohen’s kappa for qualitative agreement ranged from 0.71 to 0.87, indicating substantial to near-perfect concordance.

The authors interpret these findings with appropriate caution. The reduction in positivity after freezing was concentrated among samples with CAA concentrations close to the 2 picograms per milliliter cut-off, suggesting that analytical variability around the detection threshold, rather than wholesale degradation of the antigen, likely explains the lost positives. CAA is chemically a carbohydrate, which makes it remarkably resistant to degradation; its stability is famously illustrated by its detection in Egyptian mummies, where it has persisted for thousands of years. The comparable results between fresh and non-frozen stored samples indicate that CAA detection was maintained across a realistic field-to-laboratory workflow involving refrigerated storage, cooled transport, and international shipping, though the authors note that this comparison cannot fully separate the effect of storage from the effects of transport, timing, and laboratory conditions, since the non-frozen samples were analyzed in Leiden while the fresh and frozen ones were tested on Pemba.

Several limitations shape the conclusions. The non-frozen condition was introduced halfway through the study and assessed only in a pragmatic subset defined by available urine volume, which could have introduced bias even though selection was not based on participant characteristics or diagnostic outcomes. More fundamentally, the study was designed to compare storage conditions rather than storage durations: fresh samples were tested within four hours, frozen samples after five to seven days, and non-frozen samples after roughly five weeks, with intervals dictated by logistics rather than prospective assignment. The effects of storage condition and storage duration therefore cannot be disentangled, and no conclusions can be drawn about the impact of longer-term non-frozen storage, prolonged freezing, or repeated freeze-thaw cycles. The authors call for further studies addressing these gaps, noting that bacterial or fungal growth during prolonged non-frozen storage could potentially affect CAA detection and that standardized storage and transport procedures remain important for preserving sample integrity.

Even with those caveats, the practical implications are significant for elimination programs. The results suggest that urine storage strategies for delayed centralized CAA testing can be adapted to local circumstances: where freezers are available, samples can be frozen with the understanding that a small fraction of very low-positive results may be missed; where they are not, refrigerated storage and cooled transport over several weeks appear to preserve detection well. As schistosomiasis programs move from control toward elimination, and as the UCP-LF CAA test finds growing use in surveillance, sample pooling, post-treatment follow-up, pharmacokinetic studies, migrant health, and even controlled human infection models, knowing that the antigen in a child’s urine sample from Pemba can survive a five-week journey to a Dutch laboratory without meaningful loss of signal is the kind of unglamorous but essential knowledge on which elimination campaigns are built.

Subject of Research: Effect of urine storage conditions on circulating anodic antigen detection with the UCP-LF CAA test for schistosomiasis diagnosis

Article Title: Effect of urine storage conditions on circulating anodic antigen detection using the UCP-LF CAA test

Article References: Hoekstra, P. T., van Dam, G. J., Blokland-Flink, M., de Jong, D., Ali, S. M., Ali, M. N., Ndum, N. C., Knopp, S., Corstjens, P. L., & van Lieshout, L. (2026). Effect of urine storage conditions on circulating anodic antigen detection using the UCP-LF CAA test. Frontiers in Parasitology, 5, Article 1894516. https://doi.org/10.3389/fpara.2026.1894516

Image Credits: AI Generated

DOI: 10.3389/fpara.2026.1894516

Keywords: schistosomiasis, circulating anodic antigen, UCP-LF CAA, urine storage, diagnostics, Schistosoma haematobium, Pemba, Tanzania, elimination, freezing, surveillance, neglected tropical diseases

The research, published in the journal Discover Oceans, surveyed 113 randomly selected artisanal fishermen at three landing centers, Ruela, Chibuabuare and Chuiba, between September and November 2024. The team, led by Heráclito Comia of Lúrio University, used semi-structured questionnaires administered face to face in Portuguese and the local language Emakua, a necessity in a population where more than half of respondents had no formal schooling. The sample was drawn from 146 registered fishermen using systematic sampling with a random starting point, and the data were analyzed with descriptive statistics and chi-square tests. The survey deliberately anchored questions to the previous five years, a window that cognitive psychology research suggests minimizes recall bias while capturing meaningful trends, and one that includes the traumatic memory of Cyclones Idai and Kenneth in 2019.

The numbers tell a story of partial awareness. Just under 62 percent of respondents said they had heard of climate change, a figure well below the near-universal awareness reported among fishers in Ghana and Nigeria. But awareness of the label tells only part of the story. When asked about specific environmental changes, the fishermen’s empirical observations were strikingly sharp: 91 percent perceived rising temperatures, 82 percent noted declining rainfall, 86 percent perceived rising sea levels, and a remarkable 98 percent reported more frequent cyclones. One 52-year-old fisherman from Ruela described the shift in visceral terms, saying the sun is much hotter now than when he started fishing, and that by ten in the morning the heat burns their skin where once they could stay out until midday.

Attribution is where the scientific and traditional worlds diverge most sharply. Nearly three quarters of respondents, 72.6 percent, attributed the changes to supernatural or divine forces rather than human activity, and only 27.4 percent acknowledged potential human contributions. One 65-year-old fisherman from Chuiba explained that the changes in the sea and the winds are controlled by the spirits of the ancestors, and that when ceremonies are not performed correctly or the sea is angered, the weather turns against the community. The researchers argue this attribution pattern matters enormously for policy, because belief in human agency is often a precondition for proactive adaptation. If the weather is a moral response to human behavior, the logic of emissions reduction or coastal planning simply does not compute.

The statistical analysis added nuance to the picture. Education level was strongly associated with climate change awareness, with those holding primary education or higher significantly more likely to recognize the term than those with no formal schooling, a moderate effect size confirmed by chi-square testing. Years of fishing experience, meanwhile, predicted the adoption of adaptation strategies: fishers with more than two decades on the water were far more likely to deploy multiple responses, suggesting that accumulated local ecological knowledge is itself a form of adaptive capacity. Intriguingly, perception of warming did not vary by age group, indicating that the experience of a hotter coast is shared across generations, and awareness did not differ significantly between landing centers.

What the fishermen are actually doing in response to change is arguably the most encouraging part of the study. The most common strategy, adopted by 36 percent, was abandoning mosquito nets, a cheap but destructive fishing method, in favor of proper drift nets, a shift the fishers describe as both a reaction to declining catches and a conscious conservation choice. One 38-year-old from Chibuabuare explained that mosquito nets were cheap but the fish were disappearing, and that drift nets cost more but catch bigger fish while the small ones can grow. A quarter of respondents reported avoiding juvenile fish, and a fifth said they deliberately avoided expanding their fishing zones. One elder put the logic plainly: if you catch the babies today, there will be no food for the children tomorrow.

But the study also exposes the hard ceiling that poverty places on adaptation. Poverty was named as the primary barrier by 41.6 percent of respondents, followed by lack of access to financial resources at 20.4 percent. The dilemma is captured by a 29-year-old fisherman from Chuiba who said he knows he should buy a motor to reach deeper, cooler water, but struggles just to buy food for his family and cannot imagine saving for an engine. Other constraints included restricted access to fishing grounds during conservation closures, lack of appropriate gear, limited access to government services, and competition from foreign fishing vessels. In the IPCC’s vulnerability framework of exposure, sensitivity and adaptive capacity, the fishers of Pemba score high on the first two and dismally on the third.

The information landscape shaping these perceptions is equally revealing. Radio was the dominant source of climate information, cited by 41.6 percent of respondents, followed by fisher-to-fisher communication at 28.3 percent. Formal channels, NGOs, researchers and extension services, barely registered, each mentioned by fewer than one percent of respondents. That near-total absence of institutional contact represents a critical failure of the science-society interface, the authors argue, and simultaneously points to a solution: radio broadcasts in Emakua and Portuguese, paired with peer-to-peer education networks, could carry scientific climate information into communities through channels they already trust. The researchers also propose engaging fishers as citizen scientists to record environmental changes, co-producing knowledge that is both scientifically valid and locally credible.

The wider stakes are considerable. Mozambique’s coastal and marine environment supports roughly two million people who depend directly on fisheries, and the artisanal sub-sector accounts for about 80 percent of total marine catches. Climate projections suggest temperatures in the country could rise by 1.5 to 2.5 degrees Celsius by 2100, and the 2019 cyclone season, which killed more than 600 people and displaced millions, offered a brutal preview of what intensifying extremes mean for coastal communities. The Pemba study’s recommendations therefore extend beyond climate communication to structural change: alternative livelihood programs such as sustainable aquaculture and ecotourism, subsidies for sustainable fishing gear, microfinance access, SMS and radio early-warning systems, community climate information centers at landing sites, and social protection measures such as cash transfers during closed seasons or weather-indexed insurance.

What emerges from Pemba is a lesson that resonates far beyond northern Mozambique. Local communities living on the front lines of climate change often perceive its fingerprints with precision, sometimes more vividly than distant institutions, but perception alone does not produce effective adaptation when explanations are supernatural, information is informal and money is scarce. The researchers call for longitudinal studies tracking how perceptions evolve, comparative work across Mozambique’s coastlines, and gender-disaggregated analyses, since women dominate fish processing and marketing yet were largely absent from this survey of registered fishers. Until the structural constraints of poverty and the cultural framing of climate causation are addressed together, the fishermen of Pemba will keep reading the sea accurately, and keep waiting for the spirits to calm it.

Subject of Research: Climate change perceptions and adaptation among artisanal fishing communities in northern Mozambique

Article Title: Artisan fishers’ perception of climate change: a case study of Pemba district, Northern Mozambique

Article References: Comia, H., Achia, S., & Machaieie, S. (2026). Artisan fishers’ perception of climate change: a case study of Pemba district, Northern Mozambique. Discover Oceans, 3(1), Article 9. https://doi.org/10.1007/s44289-026-00123-7

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00123-7

Keywords: climate change perception, artisanal fisheries, Mozambique, Pemba, adaptation strategies, coastal communities, local ecological knowledge, climate communication, vulnerability, Indian Ocean cyclones, fisheries conservation, adaptive capacity