Adults Harbor Hidden Worm Burdens in Cameroon’s Rainforest, Threatening Parasite Elimination Goals

Deep in the rainforest communities of Cameroon’s Nkam-Wouri River Basin, a quiet reservoir of parasitic worms is undermining more than two decades of mass drug administration campaigns. A new study published in PLOS Neglected Tropical Diseases has found that more than four in ten adults living in rural villages across the Littoral Region carry at least one helminth infection, a burden that persists despite years of preventive chemotherapy programs that have focused overwhelmingly on school-aged children. The findings suggest that elimination strategies built around pediatric treatment may be leaving a critical gap in the transmission cycle, one that adult populations could be quietly filling.

The research team, led by scientists working with communities across four health districts in the Littoral Region, set out to answer a deceptively simple question: how common are helminth infections among adults, and where are they concentrated? Chronic worm infections are known to cause serious long-term health problems, including lymphatic damage, blindness, anemia, and impaired cognitive development, yet reliable prevalence data for adult populations in this part of Central Africa have been scarce. Without such data, health ministries cannot accurately target interventions or assess whether elimination goals are within reach.

To fill this gap, the investigators recruited adults aged 18 to 65 years who had resided in their communities for at least five years, spanning four health districts that differ dramatically in ecology. Some districts are densely forested, others are wetland forest plantations, and still others are degraded or mosaic plantation landscapes. This environmental gradient was central to the study’s hypothesis: the researchers predicted that infection prevalences would be significantly higher in densely forested and wetland plantation districts compared to areas where forest cover has been fragmented or removed, even after more than twenty years of preventive chemotherapy.

The diagnostic approach was deliberately comprehensive. Participants provided skin snips, thick blood films, and stool samples, which were examined using the Kato Katz technique for intestinal parasites and standard microscopy for blood and skin-dwelling organisms. Demographic data were analyzed in the R statistical environment. The cohort was dominated by farmers, who made up 79.9 percent of participants, with a slight male majority at 52.9 percent, and half of all participants falling between 18 and 49 years of age. This occupational and demographic profile matters, because farming in rainforest and wetland environments brings people into repeated contact with the blackflies, mosquitoes, soil, and water sources that sustain parasite transmission.

The results confirmed the study’s central hypothesis with striking clarity. Yabassi health district, the most densely forested area surveyed, recorded the highest prevalence of Loa loa and Mansonella perstans, two filarial worms transmitted by biting insects that thrive in intact forest ecosystems. Loum health district, characterized by wetland forest plantations, showed higher prevalence for other helminth groups. Overall, 41.9 percent of adults carried at least one infection, with filariasis dominating the picture at 33.3 percent. Onchocerca volvulus, the worm responsible for river blindness, was the single most common parasite at 23.9 percent, followed by M. perstans at 11.9 percent and L. loa at 8.9 percent.

Intestinal parasites, though less prevalent overall at 9.9 percent, revealed an unexpected composition. Capillaria species led at 4.6 percent, ahead of the more familiar Ascaris lumbricoides at 2.9 percent and Trichuris trichiura at 2.7 percent. The trematode findings were equally notable: Dicrocoelium dendriticum, a fluke more typically associated with livestock, was detected in 6.9 percent of participants, while Paragonimus species, lung flukes acquired through eating raw or undercooked freshwater crustaceans, infected 3.5 percent. Taenia species, tapeworms linked to undercooked meat, were the most common cestodes at 3.1 percent. The presence of these less-conventional parasites suggests that transmission pathways in the region extend beyond the classic fecal-oral and vector-borne routes typically targeted by deworming programs.

The epidemiological patterns carried important clues about who is being left behind. Infections were more frequent in males and in individuals over 40 years of age, groups that mass drug administration campaigns rarely reach, since these programs traditionally deliver drugs through schools. Filariasis risk increased with age of 50 years or older and with longer residence in the community, indicating cumulative exposure over decades. Conversely, recent deworming and higher educational attainment both reduced the odds of infection, suggesting that even modest interventions and health literacy can measurably lower risk in this adult population.

One of the study’s most technically interesting observations was the strong statistical association observed among parasites with similar life cycles. Co-infection patterns were not random: worms sharing the same vectors, environmental reservoirs, or transmission routes tended to cluster in the same individuals. This has practical implications for diagnostics and treatment, because a person infected with one forest-associated filarial parasite is substantially more likely to harbor others. It also means that monitoring a single sentinel parasite may provide a reasonable proxy for broader parasitic burden in a given ecological setting, potentially simplifying surveillance in resource-limited districts.

The implications for neglected tropical disease elimination are sobering. Cameroon has committed to eliminating or controlling multiple helminthiases through preventive chemotherapy, the strategy of periodically distributing safe, single-dose drugs such as ivermectin, albendazole, and praziquantel to entire at-risk communities without individual diagnosis. But when programs concentrate on children, adults who remain untreated continue to carry infections, contribute to environmental contamination, and sustain the vector-borne transmission cycle. The authors argue that adults may serve as transmission reservoirs in child-centred programs, effectively reseeding infections in younger generations even as school-based treatment drives down pediatric prevalence.

The study’s conclusions point toward a recalibration of elimination strategy rather than a rejection of existing tools. The researchers recommend monitoring and including adults in preventive chemotherapy programs, promoting regular deworming and community awareness, and adopting a multi-parasite, multi-pathway strategy that addresses the full spectrum of infections circulating in these persistently endemic areas. In practice, this could mean community-wide distribution campaigns that do not stop at the school gate, diagnostics capable of detecting the less familiar parasites such as Capillaria and Paragonimus, and environmental interventions tailored to the forest and wetland ecologies that sustain transmission. As global health agencies push toward the 2030 targets for neglected tropical disease elimination set by the World Health Organization, the message from the Nkam-Wouri River Basin is clear: elimination campaigns that ignore adults may never cross the finish line.

Subject of Research: Epidemiology of helminth infections in adults in rural rainforest communities of Cameroon and implications for neglected tropical disease elimination

Article Title: Epidemiology of helminth infections in adults in rural rainforest communities of the Nkam-Wouri River Basin, Littoral Region of Cameroon: Implications for NTDs elimination using preventive chemotherapies

Article References: Ebob, A. B. O., Gandjui, N. V. T., Lenz, B., Ouam, E., Foyet, J. V., Beng, A. A., Fombad, F. F., Nietcho, F. N., Ritter, M., Karunakaran, I., Mponge, N. N., Nchang, L. C., Wang, C., Tahnteng, F. B., Cho, J. F., Esum, M. E., Katcho, T. D., Hoerauf, A., Hübner, M. P., & Wanji, S. (2026). Epidemiology of helminth infections in adults in rural rainforest communities of the Nkam-Wouri River Basin, Littoral Region of Cameroon: Implications for NTDs elimination using preventive chemotherapies. PLOS Neglected Tropical Diseases, 20(10), e0014780. https://doi.org/10.1371/journal.pntd.0014780

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0014780

Keywords: helminth infections, neglected tropical diseases, Cameroon, preventive chemotherapy, filariasis, Onchocerca volvulus, Loa loa, rainforest epidemiology, mass drug administration, parasitology, public health, Nkam-Wouri River Basin