A new laboratory study conducted in Viet Nam provides a sobering partial answer. Researchers used blood samples collected from thirteen dengue patients at the Hospital for Tropical Diseases in Ho Chi Minh City to feed colonies of wMel-infected Aedes aegypti, then compared how the mosquitoes fared when reared at different temperatures. The use of patient-derived viremic blood is a methodological strength, because it exposes mosquitoes to the genetically diverse, naturally circulating viruses that circulate in human populations rather than to a single laboratory-adapted strain. This design allowed the team to assess whether heat could compromise the protection that wMel affords under conditions that closely mimic natural transmission.

The central finding is that rearing temperature matters. Compared with wMel-infected mosquitoes maintained at 28 ± 4°C, those reared at 31 ± 4°C developed infectious saliva more frequently, meaning that virus reached the salivary glands and could be expectorated in a form capable of initiating a human infection. This is a critical endpoint in vector competence studies: a mosquito that never produces infectious saliva is, for practical purposes, a dead end for the virus. The elevated temperature regime therefore increased the frequency of what researchers call breakthrough infections, in which the Wolbachia-mediated block fails to prevent the virus from completing its journey through the mosquito.

Importantly, the protection was weakened but not abolished. Even at the higher rearing temperature, wMel-infected mosquitoes were still less likely to develop infectious saliva than wild-type mosquitoes exposed to the same conditions. The bacterium continued to provide a meaningful, if diminished, barrier to transmission. This distinction matters for public health planning, because it suggests that wMel deployments remain valuable even during hot periods, while also signaling that the margin of safety narrows when temperatures climb. The study thus reframes the conversation from whether Wolbachia works to under which thermal conditions it works best.

To understand the mechanism behind this temperature-dependent erosion of protection, the researchers examined Wolbachia densities in key mosquito tissues. Heat treatment reduced the density of wMel in all tissues tested, including the ovaries, midgut, and salivary glands. Wolbachia density is widely regarded as a key determinant of the strength of viral blocking, since the bacterium is thought to compete with viruses for intracellular resources and to prime antiviral immune pathways. A reduction in bacterial load in the midgut, the first site of viral amplification after a blood meal, and in the salivary glands, the final gateway to transmission, provides a plausible mechanistic explanation for the increased frequency of infectious saliva observed at higher temperatures.

The consequences for the virus itself were equally telling. Heat treatment significantly increased the amount of DENV-1 and DENV-4 replication in wMel-infected mosquitoes. In other words, the warmer conditions did not merely weaken the bacterium; they also created a more permissive environment for viral multiplication. Dengue viruses exist as four antigenically distinct serotypes, and the observation that both DENV-1 and DENV-4 replicated more abundantly under heat stress suggests that the effect is not limited to a single viral lineage. This convergence of reduced Wolbachia density and heightened viral replication paints a coherent picture of how elevated temperatures tip the balance within the mosquito toward successful transmission.

The team also looked for predictors of breakthrough at the level of individual mosquitoes. When comparing cohorts of wMel-infected mosquitoes that did or did not develop infectious saliva, the levels of dengue virus in the head and thorax were associated with increased odds of developing infectious saliva, whereas Wolbachia density itself was not statistically associated with that outcome. This finding is intriguing because it implies that once the virus has successfully disseminated beyond the midgut and established high titers in secondary tissues, the mosquito is likely to become salivary-gland infectious regardless of how much Wolbachia it carries. Dissemination, rather than bacterial load alone, may therefore be the pivotal bottleneck whose integrity is most vulnerable to heat.

These results build on earlier work showing that exposing wMel-infected Aedes aegypti to heat treatment, particularly during the larval stage, reduces wMel density in the ovaries, midgut, and salivary glands. They also echo a broader literature on the thermal biology of mosquito-borne transmission. Temperature shapes nearly every stage of the arbovirus transmission cycle, from mosquito development rates and blood-feeding frequency to viral replication kinetics within the vector. Laboratory studies with other systems have long suggested that heat stress can shorten the extrinsic incubation period of flaviviruses, and the present study extends this concern specifically to Wolbachia-based intervention strategies, which had sometimes been assumed to be relatively insensitive to environmental variation.

The authors conclude that elevated rearing temperatures increase the risk of patient-derived dengue breakthrough infections in wMel-infected Aedes aegypti, potentially because of increased viral replication within these mosquitoes. From this they draw a practical recommendation: it would be prudent to intensify surveillance in regions that rely on wMel for dengue control when daily mean temperatures remain above 30°C for multi-day periods. Such surveillance could include enhanced case detection, entomological monitoring, and, where feasible, molecular testing of mosquito samples to detect any decline in Wolbachia prevalence or density in the field. The recommendation acknowledges that the laboratory findings, while grounded in realistic patient-derived virus, will need to be reconciled with field observations across seasons and heat waves.

For the global dengue control community, the study arrives at a moment of both optimism and urgency. Wolbachia deployments have delivered striking public health gains, and no single laboratory result diminishes the value of that achievement. But the finding that sustained temperatures above 30°C can measurably weaken the wMel block underscores the need to plan for a warming world. Future work will likely focus on whether heat effects accumulate over multiple generations, whether thermotolerant Wolbachia strains can be selected or engineered, and how seasonal temperature profiles interact with mosquito population dynamics to shape transmission risk. In the meantime, the message for program managers is clear: the Wolbachia shield holds, but under a hot sun it must be watched more closely.

Subject of Research: Effect of rearing temperature on Wolbachia-mediated blocking of patient-derived dengue virus in Aedes aegypti mosquitoes

Article Title: Impact of temperature on patient-derived dengue virus breakthrough infections in w Mel-infected Aedes aegypti

Article References: da Silva Gonçalves, D., Thuy, V. T., Loterio, R. K., Tuyet, N. V., Xuan, T. H. T., Thi, G. N., Thi Thuy, V. H., LeDuyen, H., Thi, D. L., Vo, L. T., Huy, H. L. A., Thuy, N. T. V., Nguyen, P. T., Yacoub, S., Anders, K. L., Flores, H., Simmons, C. P., & Fraser, J. E. (2026). Impact of temperature on patient-derived dengue virus breakthrough infections in wMel-infected Aedes aegypti. PLOS Neglected Tropical Diseases, 20(10), e0014255. https://doi.org/10.1371/journal.pntd.0014255

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0014255

Keywords: Wolbachia, wMel, dengue virus, Aedes aegypti, temperature, vector competence, breakthrough infection, DENV-1, DENV-4, Ho Chi Minh City, salivary glands, mosquito-borne transmission

The instrument in question is the Hospital Anxiety and Depression Scale, or HADS, a fourteen-item questionnaire first developed in the 1980s by R.P. Snaith and A.S. Zigmond. Its genius lies in what it leaves out. Most depression questionnaires ask about fatigue, appetite loss, or sleep problems, but in a hospital ward or a diabetes clinic those symptoms may reflect the underlying illness rather than a mood disorder. HADS was deliberately designed to avoid physical symptoms, focusing instead on the emotional core of anxiety and depression, which is why it has become a staple in chronic disease settings around the globe. Until now, however, nobody had formally evaluated how well the Vietnamese version of the scale performs in adults with type 2 diabetes, leaving clinicians and researchers in Vietnam without clear guidance on how to interpret its scores.

To close that gap, a team led by Son Huynh of the University of Medicine and Pharmacy at Ho Chi Minh City recruited 465 adults with type 2 diabetes from three different outpatient diabetes clinics in Ho Chi Minh City. The multi-site design was not a luxury; it was a deliberate choice to see whether the questionnaire behaves consistently across different clinical settings, something single-site validation studies cannot reveal. Each participant completed the Vietnamese HADS along with the Patient Health Questionnaire-9, a well-established depression measure that served as a benchmark for comparison. The study was approved by the Ethics Committee for Biomedical Research at the University of Medicine and Pharmacy at Ho Chi Minh City, and all participants provided written informed consent.

The first question the researchers tackled was reliability: does the scale produce consistent, stable measurements? Using modern ordinal reliability coefficients, which are appropriate for the ordered response categories typical of psychological questionnaires, they found an ordinal McDonald’s omega of 0.765 for the anxiety subscale and 0.846 for the depression subscale. In practical terms, both figures fall within the range generally considered acceptable to good, meaning patients’ answers hang together coherently enough to support meaningful score interpretation. That is a foundational result, because no amount of sophisticated structural analysis can rescue a questionnaire whose items fail to measure anything consistently.

The deeper question was structural validity: does the questionnaire actually separate into the two distinct dimensions, anxiety and depression, that its design promises? The answer turned out to be more complicated than a simple yes. Exploratory factor analysis, guided by parallel analysis, initially suggested three underlying factors rather than two. But when the team inspected the third factor, they found it was fragmenting the depression items without representing a genuinely distinct psychological construct, so they retained the original two-factor solution. Confirmatory factor analysis then confirmed that two-factor structure, though only after the researchers incorporated two theory-driven correlations between residual terms, adjustments that account for overlapping wording in the Vietnamese translation. The final model showed acceptable fit, with a root mean square error of approximation of 0.084, a comparative fit index of 0.922, a Tucker-Lewis index of 0.904, and a standardized root mean square residual of 0.076.

The most technically sophisticated part of the analysis was a bifactor model, a statistical framework that asks whether a questionnaire is best understood as measuring one broad underlying dimension plus some specific subdimensions, or as several largely independent dimensions. The results were striking. A substantial general distress factor emerged, explaining a large share of the common variance: the omega hierarchical coefficient reached 0.839 and the explained common variance was 0.608. In plain language, most of what the Vietnamese HADS measures in this population is a single, broad current of psychological distress that runs through both the anxiety and depression items. At the same time, enough residual variance remained within each subscale to suggest that the anxiety and depression scores still carry some distinct, meaningful information beyond the general factor.

Construct validity testing added further nuance. Both subscales correlated moderately with the PHQ-9, supporting convergent validity, the idea that the scale is measuring something related to what similar tools measure. Discriminant validity, the ability of the two subscales to keep themselves statistically distinct, was supported for the depression subscale but not for the anxiety subscale. The square root of the average variance extracted for anxiety was 0.552, which fell below the correlation between the two subscales of 0.652. That means the anxiety and depression scores overlap so heavily in this population that they cannot be treated as cleanly separable constructs, echoing the bifactor finding that general distress dominates the measurement.

Perhaps the most practically important discovery came from an exploratory analysis of cross-site comparability. When the researchers compared item responses across the three clinics, three depression items related to anhedonia, the loss of interest or pleasure in activities, showed comparatively larger differences between sites, with eta-squared values ranging from 0.18 to 0.21. Those are sizable effects, indicating that responses to these particular questions varied noticeably depending on which clinic a patient attended. The authors caution that this heterogeneity means researchers should be careful when comparing or pooling HADS scores across different settings in multi-site studies, because some of the observed differences between sites may reflect measurement inconsistency rather than genuine differences in patient wellbeing.

So what should clinicians and researchers in Vietnam actually do with the Vietnamese HADS? The study’s conclusions are deliberately measured. The scale demonstrates acceptable structural validity and partial construct validity in Vietnamese adults with type 2 diabetes, and the bifactor results support the total score as a broad, cross-sectional index of general psychological distress. The authors recommend that the total score should be the primary measure reported, with the individual subscale scores offering useful but more limited supplementary information. Crucially, diagnostic accuracy and criterion validity, the ability of the scale to identify true clinical cases against a diagnostic gold standard, have not yet been established. The total score is therefore supported strictly as a continuous indicator of emotional burden for research and routine care, not as a formal screening or diagnostic tool.

The study also carries a broader lesson for global health measurement. Patient-reported outcome measures do not travel effortlessly across languages and cultures; every translation inherits quirks of wording, and every new clinical population can reshape how items behave. By combining classical reliability estimation, exploratory and confirmatory factor analysis, bifactor modelling, and multi-site heterogeneity checks, the Vietnamese team has modeled the kind of thorough validation that questionnaires deserve before they are used to inform care decisions. For the hundreds of millions of people worldwide living with type 2 diabetes, and for the clinicians trying to see beyond the disease to the person, having a distress measure that is trusted, transparent about its limits, and grounded in local evidence is a quiet but consequential step forward for mental health care in chronic disease.

Subject of Research: Psychometric validation of the Vietnamese Hospital Anxiety and Depression Scale in adults with type 2 diabetes

Article Title: Psychometric validation of the Vietnamese Hospital Anxiety and Depression Scale (HADS) in adults with type 2 diabetes mellitus: a multi-site cross-sectional study

Article References: Huynh, S., Pham, O., Nguyen, N., Phan, L., Le, T., Nguyen, V., & Pham, A. (2026). Psychometric validation of the Vietnamese Hospital Anxiety and Depression Scale (HADS) in adults with type 2 diabetes mellitus: a multi-site cross-sectional study. BMC Psychology. https://doi.org/10.1186/s40359-026-05608-w

Image Credits: AI Generated

DOI: 10.1186/s40359-026-05608-w

Keywords: HADS, type 2 diabetes, psychometric validation, anxiety, depression, Vietnam, bifactor analysis, psychological distress, patient-reported outcome measures, factor analysis, mental health screening, Ho Chi Minh City