The research team, led by Hamidou Lazoumar Ramatoulaye of the Centre de Recherche Médicale et Sanitaire in Niamey together with colleagues at the CNTS, the Institut Pasteur de Paris and partner institutions, conducted a cross-sectional serosurvey between October 2021 and March 2022. This window captured a period when the Delta variant was driving waves across West Africa and vaccination campaigns were only beginning to reach significant fractions of the population. Rather than relying on patients who sought care, the investigators turned to blood donors, a population that is largely healthy, well characterized demographically, and already giving blood samples for routine screening.

The methodological design was straightforward but rigorous. Using systematic random sampling with a sampling interval of six, the team enrolled 3,656 blood donors at the CNTS. Each participant completed a structured questionnaire covering socio-demographic characteristics, possible prior exposure to SARS-CoV-2, symptoms experienced during the pandemic, and preventive practices. Blood samples drawn during donation were then tested for antibodies against the virus, allowing the researchers to distinguish prior infection and vaccine-induced immunity from the naive immune profiles of people who had never encountered the virus. Statistical associations between categorical variables were assessed with chi-square and Fisher’s exact tests, and multivariate analysis was used to identify factors independently associated with seropositivity.

The demographic profile of the cohort reflected the realities of blood donation in Niger. The sex ratio was heavily skewed, with 4.1 male donors for every female donor, a pattern consistent with donation practices in many West African settings. Only 12 percent of participants had received at least one dose of a COVID-19 vaccine, meaning that the vast majority of antibodies detected in the study reflected genuine infection rather than immunization. This distinction proved crucial for interpreting the results, because it allowed the team to estimate how extensively the virus had circulated silently through the urban population of Niamey.

The headline finding was striking. Overall seroprevalence reached 65 percent among vaccinated donors and 53 percent among those who had never been vaccinated, a difference that was statistically significant with a p-value below 0.01. In other words, even setting aside vaccine recipients entirely, more than half of unvaccinated healthy adults had been infected with SARS-CoV-2 by early 2022. Given that symptomatic testing in Niger had identified only a small fraction of this number, the results imply that the overwhelming majority of infections, likely the asymptomatic and mild cases that never reached a clinic, escaped detection entirely. This pattern mirrors what serosurveys in other countries have shown, but the gap between confirmed cases and true exposure appears especially wide in this setting.

Age patterns within the vaccinated group added further nuance. Among vaccinated donors, seropositivity climbed to 87 percent in the over-fifty age group, a rate significantly higher than in younger participants. This may reflect a combination of longer cumulative exposure over the course of the pandemic and greater likelihood that older adults who chose vaccination had also experienced prior infection, producing antibody responses detectable by the assays used. Intriguingly, no such age gradient appeared among unvaccinated donors, where seropositivity rates were statistically indistinguishable across age groups (p-value = 0.54). The authors suggest this uniformity points to intense, widespread community transmission that affected all adult age bands similarly, rather than the age-stratified waves seen in countries where early containment measures altered transmission dynamics.

Blood group emerged as an unexpected variable in the analysis. Among vaccinated donors, individuals with the O negative blood group showed lower seropositivity than other groups, at 46 percent, while among the unvaccinated it was the O positive group that was less frequently seropositive, at 48 percent. The biological interpretation of such associations remains debated in the literature. Some studies have proposed that ABO blood type influences susceptibility to SARS-CoV-2 infection or the severity of disease, potentially through effects on viral binding or on the clotting and inflammatory cascades that accompany infection. The Niamey findings add a data point from a West African population, though the authors are careful to present these as observational associations rather than proof of a protective mechanism.

The multivariate analysis identified two symptoms independently associated with seropositivity: headache and anorexia. This is consistent with the clinical spectrum of COVID-19 as documented worldwide, where headache is among the most commonly reported symptoms and loss of appetite frequently accompanies systemic infection. The association suggests that even in a population where most infections were silent, those who did experience certain symptoms were more likely to have mounted an antibody response detectable at the time of the survey. At the same time, the fact that most seropositive donors reported no distinctive illness at all underscores how easily the virus moved through the community without triggering clinical suspicion.

Beyond the specific numbers, the study carries an important message about surveillance strategy. The authors argue that blood donor seroprevalence studies provide a rapid, scalable, and ethically deployable form of surveillance that is particularly suited to tracking respiratory viruses with high rates of asymptomatic carriage. Blood collection infrastructure already exists in most countries, samples are drawn routinely, and donors give informed consent as part of standard practice. Tapping into this system allowed the Nigerien team to generate population-level exposure data at a fraction of the cost and logistical complexity of a dedicated household serosurvey, and to do so in a setting where diagnostic testing capacity was limited.

The implications extend to pandemic preparedness across the region. If more than half of healthy adults in Niamey had been infected by early 2022 while official counts captured only a sliver of that burden, then case-based surveillance alone is a poor guide to the true state of an epidemic in similar settings. Periodic serosurveys anchored in transfusion centers could help health authorities estimate the susceptible fraction of the population, time vaccination campaigns and other mitigation measures more effectively, and monitor the emergence of new variants. As the authors conclude, making the circulation of the virus visible in healthy people is an essential step toward implementing strategies that reduce transmission, and the humble blood donation bag may prove to be one of public health’s most valuable windows into hidden epidemics.

Subject of Research: SARS-CoV-2 seroprevalence among blood donors in Niamey, Niger

Article Title: Seroprevalence against SARS-CoV-2 among blood donors in Niamey, Niger, from October 2021 to March 2022

Article References: Ramatoulaye, H. L., Ibrahim, K. D., Mayaki, Z., Oumar, A. A. D., Sylviane, F. C. A., Moussa, A., Oumarou, G. I., Sidikou, B. A., Zeinabou, A. K. A., Barkiré, F. H., Alhassane, Z. D., Djamila, Z. S., Aminou, E. Y. Y. M., Seini, S. H., Testa, J., Richard, V., & Jambou, R. (2026). Seroprevalence against SARS-CoV-2 among blood donors in Niamey, Niger, from October 2021 to March 2022. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14590-y

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14590-y

Keywords: SARS-CoV-2, seroprevalence, blood donors, Niger, Niamey, COVID-19, surveillance, asymptomatic infection, serosurvey, public health, vaccination, West Africa

The temporal profile reported in the study also illustrates a well-known feature of fungal physiology in solid-state culture. Enzyme secretion by filamentous fungi typically follows a pattern in which activity rises during the early exponential growth phase, peaks as the fungus encounters nutrient limitation or accumulates metabolic by-products, and then declines as proteolysis, substrate depletion, or product inhibition erode the accumulated enzyme pool. The observed rise from 4.68 units per milliliter on day two to 11.96 units per milliliter on day four, followed by a gradual decline to roughly 8.5 to 8.9 units per milliliter by days eight and ten, is consistent with this classical pattern. The rapid early increase suggests that the fungus germinated quickly on the moistened cake and that the cellulose fraction of the substrate was sufficiently accessible to induce cellulase synthesis. Induction of cellulase genes in Aspergillus species is generally triggered by the presence of cellulose or soluble cellulose derivatives, while high concentrations of glucose repress expression through carbon catabolite repression. The fact that activity climbed steeply between days two and four implies that the readily available sugars in the palm kernel cake were consumed early, relieving repression and allowing the cellulolytic system to be fully expressed.

The decline in activity after the day-four peak can be interpreted through several non-exclusive mechanisms. Proteases secreted by the fungus during later growth stages can degrade cellulases, particularly in substrates containing modest nitrogen reserves. The physical structure of the substrate also changes over time; as the fungus consumes the more digestible polysaccharide fractions, the remaining material becomes increasingly recalcitrant, reducing the stimulus for continued enzyme production. Additionally, the accumulation of soluble hydrolysis products can exert feedback inhibition on the enzymes themselves, and the crude extract measured at each time point reflects a dynamic balance between ongoing secretion and in situ degradation. The stabilization observed between days eight and ten may indicate that the culture had entered a quiescent state in which residual enzyme activity persisted without further net production. For process design, this plateau is informative because it suggests a window of several days during which harvest would yield comparable activity, providing operational flexibility even though the statistical analysis identified day four as the optimum.

The assay methodology used in the study merits some elaboration for readers less familiar with cellulase measurement. The dinitrosalicylic acid method detects reducing sugars released from a substrate, and when carboxymethylcellulose is used as the substrate, the measured activity corresponds primarily to endoglucanase activity. Endoglucanases cleave internal glycosidic bonds within amorphous regions of cellulose chains, generating new chain ends and reducing polymer length. This is only one component of the complete cellulolytic system, which also includes exoglucanases that processively release cellobiose from chain ends and beta-glucosidases that cleave cellobiose into glucose. A full characterization of the secreted enzyme cocktail would require additional assays, such as filter paper activity for total cellulase capacity or p-nitrophenyl-beta-D-glucopyranoside assays for beta-glucosidase. Because palm kernel cake contains substantial hemicellulose in addition to cellulose, the fungus likely secreted xylanases and other accessory enzymes as well, and these could be valuable co-products in their own right. The single-enzyme measurement reported therefore represents a conservative lower bound on the total hydrolytic value of the crude extract.

The normalization of activity to dry substrate weight, expressed as units per gram of dry substrate, is an important methodological detail that facilitates comparison across the solid-state fermentation literature. Reported cellulase yields on lignocellulosic residues vary widely depending on substrate composition, particle size, moisture regime, inoculum density, and fungal strain, and expressing results per gram of dry substrate rather than per milliliter of extract removes one major source of ambiguity. The extraction procedure used, involving shaking with distilled water followed by centrifugation, is a standard approach for recovering extracellular enzymes from fermented solids, though extraction efficiency is rarely complete and can itself depend on incubation time as the enzyme distribution between solid and liquid phases shifts. Readers comparing these results with other studies should therefore attend to whether activities were measured in crude extracts or in culture filtrates, and whether the assay temperature and pH matched those used here.

The moisture content of eighty percent deserves comment because water activity is among the most influential parameters in solid-state fermentation. Filamentous fungi tolerate lower water activities than bacteria, which is one reason solid-state culture favors fungal enzyme production and reduces bacterial contamination risk. Too little water limits swelling of the substrate, diffusion of nutrients, and mass transfer of secreted enzymes; too much water fills the interparticle spaces, reduces oxygen availability, and can effectively convert the process toward submerged conditions with their attendant disadvantages. The level chosen in this study sits within the range commonly reported for fungal solid-state fermentation of lignocellulosic substrates, but it was held constant, so the interaction between moisture and incubation time remains unexplored. Similarly, the ambient laboratory temperature, which in Kumasi typically falls in the mid-twenties to low thirties Celsius, was not actively controlled, meaning that the reported kinetics reflect a realistic but variable thermal environment. Future work that systematically varies moisture, temperature, particle size, and inoculum density, ideally through a factorial or response-surface design, would be needed to identify the true optimum and to quantify interactions among these parameters.

The absence of an uninoculated control, which the authors acknowledge, is worth considering from the standpoint of experimental interpretation. Because the substrate was autoclaved before inoculation, the contribution of native microbial communities to the measured activity is likely minimal, and the steep rise in activity coinciding with fungal growth supports the attribution of cellulase production to Aspergillus niger. Nevertheless, palm kernel cake may contain residual enzymes or heat-stable reducing sugars that could contribute to background reducing sugar release in the assay, and a substrate-only control would have allowed this background to be subtracted. Similarly, a heat-inactivated or killed-mycelium control would help distinguish enzyme activity from abiotic sugar release. These considerations do not undermine the central finding, given the clear temporal dynamics, but they define the boundaries within which the quantitative values should be interpreted.

From an applied perspective, the crude enzyme produced on palm kernel cake would be most immediately useful in applications that tolerate impurities and variable composition. In textile bioprocessing, bio-polishing of cotton fabrics, and in the softening of denim, crude cellulase preparations are routinely used and substrate-derived impurities are of limited concern. In the saccharification of agricultural residues for bioethanol, the enzyme cocktail would act on the same class of substrates on which it was induced, potentially providing good activity against local residues such as cassava peels, cocoa pod husk fiber, or rice husk. The co-secretion of xylanases by the fungus would be advantageous in these contexts because hemicellulose often shields cellulose fibers and its removal improves overall hydrolysis efficiency. For higher-value applications such as pharmaceutical or food-grade enzymes, additional purification and quality assurance would be required, but the fermentation step demonstrated here would remain the foundation of the process.

The circular economy framing of the work connects it to a wider agenda of agro-industrial waste valorization across West Africa. Palm oil processing generates several distinct residue streams, including empty fruit bunches, palm oil mill effluent, palm kernel shells, and palm kernel cake, each with different composition and potential uses. Palm kernel cake is already used to a limited extent as animal feed because of its residual protein and fat content, but its high fiber fraction limits its digestibility for monogastric animals. Enzymatic treatment or solid-state fermentation of the cake could serve a dual purpose: producing cellulase as a harvestable product while simultaneously upgrading the residual solid as a feed ingredient with improved fiber digestibility. Such integrated biorefinery concepts, in which a single substrate yields sequential or co-located products, are increasingly viewed as the most economically viable route for small-scale biotechnology in developing regions, because no single low-value product carries the entire process cost.

Finally, the study’s identification of day four as the optimal harvest point provides a concrete anchor for subsequent optimization and scale-up efforts. In industrial practice, the productivity of a fermentation process, expressed as units produced per liter per day, often matters more than the peak titer itself, and a short four-day cycle with high activity compares favorably with longer fermentations that achieve only modestly higher peaks. The single-factor design used here is an appropriate first step, establishing the temporal baseline against which the effects of other variables can be measured. As multifactorial studies build on this foundation, and as strain improvement and medium supplementation are explored, the combination of a GRAS-status producer, a locally sourced substrate, and a defined production window offers a credible starting point for developing cellulase production capacity within Ghana and, by extension, a template applicable to other palm-processing regions facing similar waste management and enzyme import challenges.

Subject of Research: Cellulase production by Aspergillus niger using palm kernel cake in solid state fermentation

Article Title: Cellulase production by Aspergillus niger using palm kernel cake in solid state fermentation

Article References: Sam Barko, P., Cofie, H., Danquah, B., Bentil, J. A., & Ofosu, M. (2026). Cellulase production by Aspergillus niger using palm kernel cake in solid state fermentation. Discover Biotechnology, 3(1), Article 10. https://doi.org/10.1007/s44340-026-00056-z

Image Credits: AI Generated

DOI: 10.1007/s44340-026-00056-z

Keywords: Cellulase, production, Aspergillus, niger, palm, kernel, cake, solid, state, fermentation, scientific research