The study, led by Patcharamai Rongthong and colleagues at the Shoklo Malaria Research Unit, part of the Mahidol-Oxford Tropical Medicine Research Unit, took the form of a cross-sectional survey conducted in September 2019 across six villages. Rather than relying on the traditional method of dissecting mosquitoes under a microscope to look for worm larvae, the team turned to molecular tools. A polymerase chain reaction assay targeting the parasites’ 5S ribosomal RNA gene allowed them to detect filarial DNA even in specimens where infection would be easy to miss morphologically. For positive Aedes specimens, the researchers went a step further, sequencing both the filarial PCR products and the mosquito cytochrome c oxidase subunit 1 gene to confirm exactly which worm species and which vector species they were dealing with.

Collecting the mosquitoes was itself a logistical feat. The team captured insects over full 24-hour diel cycles using two complementary methods: the human-landing catch, in which trained collectors allow mosquitoes to land on their exposed limbs before being trapped, and cow-baited traps, which exploit the attraction of many mosquito species to livestock. Specimens were then identified to species level using dichotomous morphological keys. This combination of approaches proved crucial, because it revealed not just which mosquitoes were infected but where and when those infected insects were actively seeking blood meals.

The headline finding was striking: 5.2 percent of the 772 mosquito specimens tested, 40 individuals in total, produced a positive filariasis PCR result. Half of those positive specimens carried DNA of Wuchereria bancrofti, the principal cause of lymphatic filariasis worldwide and the worm responsible for the vast majority of elephantiasis cases. But the survey did not stop there. Three additional zoonotic filarial species, belonging to the genera Brugia and Dirofilaria, were also identified, underscoring that these villages host a richer community of mosquito-borne nematodes than anyone had suspected. Zoonotic filariae normally circulate between animals and mosquitoes, but their presence in human-landing catches signals that people are being exposed to them as well.

The list of mosquito species carrying W. bancrofti DNA reads like a roll call of known and suspected vectors. The researchers detected the parasite in Anopheles barbirostris and Anopheles hyrcanus, both established vectors in Southeast Asia, as well as in Downsiomyia harinasutai, Finlaya poicilia and Culex sitiens. More provocatively, W. bancrofti DNA also turned up in Aedes albopictus/pseudoalbopictus, the aggressive day-biting mosquito better known globally as a dengue and chikungunya vector, and in Armigeres flavus. Finding the human filarial parasite in such a diverse array of genera, spanning Anopheles, Aedes, Culex and Armigeres, suggests that transmission in this setting is not the work of a single specialist vector but of a broad ecological network of opportunistic biters.

To quantify the risk, the team calculated the entomological inoculation rate for W. bancrofti, a standard measure of transmission intensity expressed as the number of infective bites a person receives per unit time. Their estimate came to 0.094 infective bites per person per day, with a 95 percent confidence interval of 0.049 to 0.164. While that figure may sound modest, it implies that over the course of a year a villager could plausibly receive dozens of infective bites, more than enough to sustain transmission of a parasite that requires only a handful of successful inoculations to establish infection in a susceptible host.

Perhaps the most consequential finding concerns biting behavior. Only 7.5 percent of the infected specimens, three out of forty, were captured indoors with the human-landing catch method during the classic overnight window between 9 PM and 5 AM. In other words, the overwhelming majority of infected mosquitoes were biting outdoors, or at hours outside the window that insecticide-treated bed nets are designed to protect. Bed nets have been one of the great success stories of malaria control, but this study suggests they may offer only limited protection against the filariasis vectors of Karen state, many of which appear to bite in the early evening, at dawn, or during daylight hours in the peridomestic environment.

The cow-baited traps added another layer of insight. Infected specimens were collected from these livestock-oriented traps, which points toward an intriguing intervention strategy: vector control measures that target mosquitoes at the animal interface. Because many of the vector species in this region feed opportunistically on both cattle and humans, treating livestock with insecticides or deploying traps around animal shelters could knock down mosquito populations before they ever reach their human hosts. Such veterinary-based approaches have been deployed successfully against other vector-borne diseases, and the authors argue they deserve consideration for filariasis in this setting, potentially alongside or even in place of methods that depend on indoor protection.

The detection of zoonotic filariae in specimens captured by human-landing catch deserves particular attention. Species of Brugia and Dirofilaria that normally parasitize animals were clearly biting and attempting to infect people in these villages. While zoonotic filarial infections in humans are often abortive or clinically milder than W. bancrofti infection, they can still cause disease, and their presence complicates the epidemiological picture. Any elimination campaign that focuses solely on the human parasite risks overlooking a reservoir of related worms circulating in the environment, and the molecular methods used here provide a template for surveillance programs elsewhere in Southeast Asia that may face similar hidden burdens.

The broader implications reach well beyond six villages in eastern Myanmar. Lymphatic filariasis is one of the World Health Organization’s targeted neglected tropical diseases, and global elimination efforts rest heavily on mass drug administration coupled with vector control. This study demonstrates that in ecologically complex settings, where multiple vector species with diverse biting habits coexist, the standard toolkit may need to be expanded. Outdoor and early-evening transmission, vectors attracted to livestock, and a background of zoonotic parasites all argue for interventions tailored to local entomology. The authors conclude that trials of vector control measures designed to prevent outdoor and early transmission are warranted, a call that will resonate with elimination programs across the region. For the communities of Karen state, the message is clear: the worms are there, the mosquitoes carrying them bite when and where nets cannot follow, and the next phase of the fight against filariasis will have to move outdoors.

Subject of Research: Natural filarial infections in mosquitoes and their transmission dynamics in Karen state, Myanmar

Article Title: Assessment of natural filariae infections in the mosquitoes of Karen state, Myanmar: a cross-sectional PCR survey in six villages

Article References: Rongthong, P., Kularbkeeree, T., Gloria, N., Jaruwan, N., Lee, N. Y., Trackoolchengkaew, M., Chaumeau, V., & Nosten, F. (2026). Assessment of natural filariae infections in the mosquitoes of Karen state, Myanmar: a cross-sectional PCR survey in six villages. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07649-x

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07649-x

Keywords: lymphatic filariasis, Wuchereria bancrofti, mosquito vectors, Myanmar, Karen state, PCR, Brugia, Dirofilaria, Aedes albopictus, vector control, entomological inoculation rate, bed nets

Lymphatic filariasis, one of the world’s leading causes of permanent disability, results from infection with microscopic thread-like nematodes that lodge in the lymphatic system. In its chronic form the disease produces elephantiasis, the dramatic swelling of limbs and genitals that has made it one of the most feared and stigmatized of the neglected tropical diseases. The parasite is transmitted when mosquitoes ingest microfilariae—immature worms circulating in the bloodstream of an infected person—during a blood meal. Inside the mosquito, the parasites develop over roughly one to two weeks into third-stage larvae, the infective form that can migrate to the insect’s mouthparts and be deposited on human skin during the next bite. Nigeria carries a substantial share of the global burden of this disease, and mass drug administration campaigns have been rolled out across many endemic states. Yet as the Bodinga study makes clear, drug-based treatment alone cannot interrupt transmission if the entomological and behavioral environments remain unfavorable.

To assess community readiness for elimination, the researchers administered a semi-structured questionnaire to 258 participants across three wards of Bodinga, probing knowledge, attitudes, and practices related to lymphatic filariasis and mosquito control. The results were sobering. Only 41.9 percent of respondents had ever heard of lymphatic filariasis, and even fewer could correctly describe how it is transmitted or recognize its early symptoms. This knowledge gap matters for a practical reason: mass drug administration programs depend on high compliance rates, and communities that do not understand a disease—or the reason for taking preventive chemotherapy—are far less likely to participate fully in annual treatment rounds. Previous studies from other Nigerian states, including Kano, and from endemic regions of Brazil, Indonesia, and Guinea have documented similar deficits, suggesting that the Bodinga findings reflect a broader and persistent challenge in filariasis-endemic settings rather than a local anomaly.

The entomological half of the study focused on two mosquito genera with established roles in filariasis transmission: Anopheles, the same genus responsible for malaria, and Culex, particularly the ubiquitous Culex quinquefasciatus. Larvae were collected from breeding sites across the study area, reared to adulthood in the laboratory, and subjected to susceptibility testing with the Centers for Disease Control and Prevention bottle bioassay against three widely used pyrethroid insecticides: deltamethrin, permethrin, and alphacypermethrin. The outcome was unequivocal. Both Anopheles and Culex populations proved resistant to all three compounds, with mortality rates ranging from a mere 6 percent to 44 percent—far below the 98 percent threshold the World Health Organization uses to declare a population susceptible. For a region that relies heavily on insecticide-treated nets and indoor residual spraying, this level of resistance means that the primary chemical defenses against night-biting mosquitoes may offer little practical protection.

Digging into the mechanism of that resistance produced one of the study’s most operationally significant findings. When the researchers pre-exposed the mosquitoes to piperonyl butoxide, a chemical that inhibits the detoxification enzymes known as cytochrome P450 monooxygenases, susceptibility to alphacypermethrin was almost completely restored, with mortality rebounding to 98 to 99 percent. This synergist experiment demonstrates that metabolic detoxification—the mosquito equivalent of a chemical shield built from overactive detoxifying enzymes—underlies much of the observed resistance, rather than mutations in the insecticide’s target site on the nerve membrane. The practical implication is that intervention tools engineered around PBO synergism, such as the new generation of PBO-treated bed nets, could regain much of their lost efficacy in Bodinga and similar settings. The authors also quantified expression of two detoxification genes, CYP6M2 and CYP9M10, in infected versus uninfected mosquitoes, finding both significantly downregulated in parasite-carrying insects, at 0.26-fold and 0.77-fold respectively—an intriguing hint that filarial infection itself may alter the mosquito’s metabolic capacity, echoing transcriptomic changes previously reported in Anopheles infected with malaria parasites.

The third pillar of the study was molecular xenomonitoring, a surveillance technique that searches for parasite genetic material inside mosquitoes rather than in human blood. Because it requires no invasive testing of individuals and can detect transmission even when human infection rates have fallen below the threshold of blood-smear detection, xenomonitoring is increasingly viewed as the gold standard for determining whether elimination has truly been achieved. Using a Prokopack aspirator, the team collected blood-fed resting mosquitoes from indoor surfaces and screened a total of 1,510 specimens. Microscopic dissection detected microfilariae in five mosquitoes, a pool-level infection rate of 0.33 percent. Polymerase chain reaction then confirmed Wuchereria bancrofti DNA in three of these, or 0.20 percent of the total catch. Critically, quantitative reverse transcription PCR detected the parasite’s L3 larvae—the infective stage—in confirmed mosquitoes, indicating not merely passive carriage of parasite DNA but the presence of insects capable of transmitting the disease onward. Real-time PCR testing of microscopy-negative mosquito pools returned no additional infections, suggesting the infection rate is genuinely low but not zero.

That distinction between infection and infectivity carries real weight for program managers. A mosquito carrying only early-stage larvae may reflect residual parasites in a population that is already shrinking toward elimination, whereas the detection of L3-stage larvae signals active, onward transmission. In the WHO’s transmission assessment survey framework, districts are typically eligible to stop mass drug administration after several consecutive years when antibody prevalence in children falls low enough and there is no evidence of ongoing spread. The Bodinga results suggest that, despite low parasite rates, transmission has not yet been fully interrupted in this district, and that stopping interventions prematurely could allow the parasite to resurge. The authors argue that molecular xenomonitoring should be integrated routinely into Nigeria’s filariasis surveillance architecture precisely because it can capture this residual, near-invisible transmission in a way that conventional human-based surveys cannot.

The study’s One Health framing is what elevates it beyond a conventional parasitological survey. By simultaneously measuring human knowledge and behavior, vector susceptibility and resistance mechanisms, and parasite presence in the mosquito population, the researchers captured the interlocking vulnerabilities of the entire transmission system. Each component alone would have told an incomplete story. Low awareness without resistance data might have prompted a straightforward health education campaign; resistance findings without xenomonitoring might have overstated the risk; low infection rates without behavioral data might have encouraged premature relaxation of control efforts. Together, the data indicate that Bodinga requires a coordinated response: sustained community engagement to close the knowledge gap and boost drug compliance, a transition toward PBO-based vector control tools that bypass metabolic resistance, and continued molecular surveillance to track the parasite until transmission is demonstrably halted.

The researchers, funded through the Africa Centre of Excellence for Neglected Tropical Diseases and Forensic Biotechnology with clearance from the Sokoto State Ministry of Health, recommend targeted awareness campaigns as the immediate priority, alongside expanded studies of resistance mechanisms to determine whether other pathways, such as target-site mutations or cuticular changes, also contribute alongside the confirmed metabolic component. They also note that the downregulation of CYP6M2 and CYP9M10 in infected mosquitoes raises questions about how filarial parasites interact with their vector’s detoxification machinery, an area that may deserve deeper investigation given its potential to influence both insecticide susceptibility and parasite development simultaneously.

For the global elimination campaign, which has already achieved remarkable success in countries across Asia, the Pacific, and parts of Africa, the Bodinga study offers both a warning and a template. The warning is that elimination progress can stall in districts where resistant vectors and unaware populations coexist, leaving a stubborn reservoir of transmission beneath the surface. The template is the integrated, One Health study design itself: a relatively low-cost combination of questionnaire surveys, standardized bioassays with synergist testing, and PCR-based xenomonitoring that can be deployed by national programs to identify precisely where and why transmission persists. As Nigeria pushes toward the 2030 global elimination target, studies of this kind may prove indispensable for distinguishing communities that are ready to stop treatment from those where the fight must continue.

Subject of Research: Community knowledge, pyrethroid resistance, and molecular xenomonitoring of Wuchereria bancrofti in lymphatic filariasis-endemic communities of Sokoto State, Nigeria

Article Title: Integrating Community Practices, Vector Resistance, and Molecular Xenomonitoring of Wuchereria Bancrofti: A One Health Implementation Study in Lymphatic Filariasis–Endemic Communities

Article References: Yalwa, M. A., Aliyu, M., Musa, A. I., Malami, I., Abubakar, M. B., Ndams, I. S., & Muhammad, A. (2026). Integrating Community Practices, Vector Resistance, and Molecular Xenomonitoring of Wuchereria Bancrofti: A One Health Implementation Study in Lymphatic Filariasis–Endemic Communities. Acta Parasitologica, 71(5), Article 218. https://doi.org/10.1007/s11686-026-01401-2

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01401-2

Keywords: lymphatic filariasis, Wuchereria bancrofti, molecular xenomonitoring, insecticide resistance, pyrethroids, piperonyl butoxide, cytochrome P450, Anopheles, Culex quinquefasciatus, neglected tropical diseases, One Health, Nigeria