The research, conducted by an Argentine team from the Universidad de Buenos Aires and CONICET as part of what they call the Pampa del Indio Project, tracked T. cruzi infection in T. sordida from 2007 to 2016. The researchers had reason for suspicion. Across the Gran Chaco, where T. sordida thrives once the main vector is gone, reported infection prevalence varies wildly, from under one percent to as high as 46 percent in some Bolivian and Paraguayan settings. And the standard diagnostic tool, direct optical microscopy of the insect’s gut contents, is known to miss a substantial fraction of infections. The team hypothesized that once T. infestans was suppressed, infection in T. sordida would rise above the low levels, zero to six percent, they had previously reported.

What they found instead was remarkable stability. Out of 10,728 T. sordida collected from 528 premises over nearly a decade, 1,946 insects were tested by optical microscopy or a molecular technique called vkDNA-PCR, which targets the parasite’s kinetoplast DNA. The raw, or naive, prevalence of infection was just 1.44 percent. On average, each infested house harbored about 1.12 infected bugs, and across the entire surveillance period fewer than two percent of examined insects carried the parasite, with no more than roughly five percent of houses harboring infected specimens at any time. Infection never spiked, never crept upward, and never filled the gap left by the main vector.

The technical twist lies in the occupancy modeling. Because neither diagnostic method is perfect, the team applied single-season occupancy models, a statistical framework borrowed from ecology that jointly estimates the true probability of infection and the probability of detecting it. The models confirmed what earlier comparisons had hinted: optical microscopy detected at most 73 percent of truly infected insects, meaning it missed nearly one in every four infections. The molecular assay, by contrast, was assumed to catch essentially all of them. This method gap matters, because microscopy alone returned a prevalence of 0.65 percent while vkDNA-PCR returned 3.42 percent among tested insects, a difference that was statistically significant and that explains why older surveillance reports based on microscopy may have understated risk.

The fine structure of infection within the landscape tells its own story. Adjusted prevalence was highest in domiciles, reaching 4.72 percent, intermediate in peridomestic kitchens, storerooms and granaries at 3.30 percent, and lower in chicken-associated sites, corrals and other outbuildings. Adult bugs were far more likely to be infected than nymphs, a pattern seen across triatomine species and attributed to cumulative exposure to infected bloodmeals over a longer life and larger blood meals in later stages. Intriguingly, males showed more than twice the infection rate of females, 3.81 percent versus 1.34 percent, a finding the researchers find hard to explain given that male T. sordida live shorter lives in the laboratory and no known sex-based susceptibility differences exist. They speculate that males may feed more often or roam more widely, but the question remains open.

Spatial analysis added another layer. Global tests found no overall clustering of infection, but a local statistic pinpointed a significant hotspot in the northwestern corner of the municipality, spanning 24 houses within a radius of roughly 200 to 1,300 meters. Notably, the geography of infection shifted over time. At baseline and in the early post-intervention phase, infected bugs concentrated in that northwestern zone; by the late phase, the handful of infections appeared in the central and eastern sections instead. Baseline prevalence, adjusted to 2.65 percent, was about double the prevalence in both post-intervention phases, and the difference between baseline and pooled post-intervention data was statistically significant.

Molecular epidemiology offers a plausible explanation for that spatial and temporal shift. Trypanosoma cruzi is a genetically diverse parasite with several discrete typing units, or DTUs, that occupy different transmission cycles. In the Argentine Chaco, hybrid lineages such as TcV and TcVI dominate the domestic cycle, while TcI prevails in sylvatic settings, often linked to opossums. In Pampa del Indio, TcI predominated among infected T. sordida throughout the study, and hybrid lineages were detected only at baseline and early post-intervention, when domestic transmission by T. infestans still simmered. Once that domestic cycle was suppressed, the remaining infections in T. sordida appear to have flowed entirely from the sylvatic cycle, with molecular fingerprinting previously linking the TcI parasites in these bugs to local white-eared opossums, Didelphis albiventris, captured near the hotspot.

The blood-feeding habits of T. sordida likely dampen its threat. Chickens and other poultry, which are refractory to T. cruzi infection, rank among its favorite hosts in peridomestic environments across the region, and infected bugs in Pampa del Indio were most often collected in poultry-associated sites. Combined with the species’ strong flight dispersal and opportunistic feeding, this avian-leaning diet helps explain why a bug that invades houses freely nevertheless carries so little parasite. The picture contrasts sharply with scenarios in Brazil, Paraguay, Bolivia and Colombia, where native secondary vectors, after the main vectors were removed, exhibited high infection levels and genuinely jeopardized control gains.

The authors are careful not to declare victory. Infection prevalence is only one component of transmission risk, which also depends on bug abundance, feeding behavior and the degree of contact with humans. The T. sordida complex itself contains several cryptic species that morphological identification cannot reliably separate, adding uncertainty, though recent work suggests the relevant species share similar feeding and defecation behavior. Intense deforestation and land-use change during the study period may also have reshaped sylvatic populations and their house-invasion dynamics in ways the data cannot yet resolve. Because T. cruzi transmission is enzootic, permanently circulating in wild mammals and their insects, infected T. sordida continued to appear even a decade into control.

The practical message is twofold. First, molecular diagnostics should be standard in vector surveillance, because microscopy systematically understates infection and can mislead risk assessments across the Gran Chaco. Second, successful elimination of a primary vector does not end the story; it reshapes the ecosystem of risk. The Pampa del Indio experience shows that with sustained, adaptive surveillance, a secondary invader can be monitored effectively and kept from becoming a new engine of transmission. But it also shows that vigilance cannot lapse, because the sylvatic cycle persists indefinitely at the edges of human settlement, ready to send the occasional infected bug across the threshold.

Subject of Research: Long-term variation of Trypanosoma cruzi infection in the secondary Chagas disease vector Triatoma sordida following Triatoma infestans elimination in rural Argentina

Article Title: The Pampa del Indio Project: long-term variations of Trypanosoma cruzi infection in Triatoma sordida, a non-target invasive vector

Article References: The Pampa del Indio Project: long-term variations of Trypanosoma cruzi infection in Triatoma sordida, a non-target invasive vector. (n.d.). https://doi.org/10.3389/fpara.2026.1953889

Image Credits: AI Generated

DOI: 10.3389/fpara.2026.1953889

Keywords: Chagas disease, Trypanosoma cruzi, Triatoma sordida, Triatoma infestans, Gran Chaco, vector control, occupancy models, molecular diagnostics, discrete typing units, Argentina, entomological surveillance, Didelphis albiventris

Aedes japonicus is one of several so-called Aedes invasive mosquitoes, or AIMs, that have spread rapidly across Europe in recent decades. Native to East Asia, the species has colonised large parts of central and western Europe since its first detections on the continent, establishing populations in countries including Germany, Switzerland, Austria, Belgium, the Netherlands, France and Slovenia. In Italy, the mosquito had until now been reported only in the northern part of the country, where it has been expanding alongside another Asian invader, Aedes koreicus. The presence of both species in territories bordering Tuscany raised concerns among public health entomologists that the insects would follow the main transport corridors linking northern Italy to the central regions, and the new study set out to test exactly that hypothesis.

The survey was deliberately designed around the geography of invasion. Rather than sampling randomly across Tuscany, the researchers focused on the province of Massa-Carrara, the northernmost province of the region, and specifically on small villages situated along the roads that connect Tuscany with the adjacent regions where Aedes japonicus and Aedes koreicus had already been reported. This strategy reflects a well-established principle in invasion biology: human-mediated transport along road networks is one of the principal drivers of mosquito range expansion, and the first footholds of a new species are most likely to appear along the routes that funnel traffic from invaded areas into uninvaded ones. The team conducted the fieldwork over just two days, inspecting potential breeding habitats for adult mosquitoes, larvae and pupae.

The results were unambiguous. Morphological identification of 90 adult mosquitoes and 35 larvae, combined with molecular analyses performed on eggs, larvae, pupae and one adult, confirmed the presence of Aedes japonicus japonicus in five municipalities of northern Tuscany. The molecular work relied on standard genetic markers used in mosquito identification, including the internal transcribed spacer 1 region of the nuclear genome and the cytochrome c oxidase subunit I gene of the mitochondrial genome, amplified by polymerase chain reaction. This combination of morphological and molecular confirmation is important because several invasive Aedes species are morphologically similar, particularly in their immature stages, and misidentification can lead to costly delays in surveillance and control responses.

Perhaps the most striking aspect of the finding is what it implies about how long the species has been present. Despite the extremely short duration of the survey, the researchers detected Aedes japonicus across multiple sites and in several different types of artificial breeding containers, including buckets, tyres and a fountain basin. Finding the mosquito in so many locations and habitat types within a two-day window suggests that it is not a recent arrival confined to a single introduction point but is already firmly established in the area. The detection of immature stages co-occurring with larvae of other species, including the Asian tiger mosquito Aedes albopictus, the common house mosquito Culex pipiens, Culex hortensis and Culiseta annulata, further indicates that the species is breeding successfully in its new environment rather than merely being transported there incidentally.

This ecological flexibility is a hallmark of the species and a key reason for its invasion success. Aedes japonicus thrives in container habitats of both natural and artificial origin, tolerates cooler temperatures than many other invasive mosquitoes, and can exploit a wide range of water-holding structures in both rural and peri-urban settings. The fact that the Tuscany survey found it in buckets, tyres and a fountain basin confirms this plasticity in the Italian context and suggests that the species has the potential to spread further south, where it may encounter increasingly favourable climatic conditions during the cooler parts of the year. The coexistence of Aedes japonicus with the Asian tiger mosquito, which is now ubiquitous across Italy, also raises ecological questions about competition between the two invaders, since both exploit similar larval habitats.

From a public health perspective, the establishment of Aedes japonicus in Central Italy carries two main implications. The first is nuisance: the species is an aggressive day-biting mosquito whose females readily feed on humans, and its presence in residential areas can significantly degrade quality of life during the warm season. The second, and more consequential, is its potential role as a disease vector. While Aedes japonicus is not as efficient a vector of dengue or chikungunya as Aedes albopictus, it has been shown experimentally and in field studies to be competent for a range of arboviruses, including West Nile virus, and it has been implicated in the transmission ecology of other pathogens in its native and invaded ranges. The introduction of an additional competent vector into a region that already circulates West Nile virus and other mosquito-borne pathogens adds a new layer of complexity to vector-borne disease risk assessment in Italy.

The authors of the study argue that these findings highlight the need for active surveillance specifically targeting Aedes invasive mosquitoes in Central Italy. Traditional mosquito monitoring in Italy has historically centred on the Asian tiger mosquito, which arrived in the country in the early 1990s and is now monitored through extensive ovitrap networks. However, the detection methods and thresholds optimised for Aedes albopictus are not necessarily suited to detecting a newly arriving species at low density. The Tuscany survey demonstrates the value of a different approach: targeted sampling along invasion corridors, informed by the known distribution of the species in neighbouring territories, can detect a new arrival quickly. The researchers acknowledge the contribution of colleagues from neighbouring regions who provided information on the distribution of invasive Aedes mosquitoes near the Tuscan border and offered suggestions on sampling strategies for the timely detection of Aedes japonicus and Aedes koreicus.

The study was supported by the Tuscany region through a fund dedicated to the regional entomological network for the protection of public health, developed and restructured for the 2026 to 2027 biennium. This institutional backing reflects a growing recognition among Italian regional authorities that invasive mosquito surveillance is a core public health function rather than a purely academic exercise. As climate change alters temperature and precipitation patterns across the Mediterranean, and as international trade and travel continue to move mosquitoes and their eggs across borders, the window for early detection and response is shrinking. The rapid spread of Aedes koreicus through northern Italy in recent years, following a pattern similar to that of Aedes japonicus elsewhere in Europe, illustrates how quickly an established invader can consolidate its range once it gains a foothold.

The first report of Aedes japonicus in Central Italy is therefore best understood not as an isolated discovery but as a milestone in an ongoing continental invasion. The species has now bridged the gap between its northern Italian strongholds and the central regions of the peninsula, and its presence in five municipalities of northern Tuscany, confirmed by both morphology and genetics, indicates that the invasion front has moved decisively southward. Whether the mosquito will establish permanent populations further into Tuscany and beyond will depend on climatic suitability, the availability of breeding habitats and the effectiveness of the surveillance and control measures that regional authorities put in place. What is already clear, the researchers conclude, is that the species is firmly established in northern Tuscany, that it exploits the same artificial containers that have fuelled the spread of other invasive mosquitoes, and that sustained, targeted monitoring is now essential to track and, where possible, contain its further expansion.

Subject of Research: First detection of the invasive mosquito Aedes japonicus in Central Italy and its implications for surveillance and public health

Article Title: New evidence of an ongoing invasion: first report of Aedes japonicus in Central Italy

Article References: Del Lesto, I., Chiavacci, M., De Liberato, C., Rondón, S., Ottolini, N., Carioti, V., Magliano, A., Porchia, B. R., & Romiti, F. (2026). New evidence of an ongoing invasion: first report of Aedes japonicus in Central Italy. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07709-2

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07709-2

Keywords: Aedes japonicus, Asian bush mosquito, invasive mosquitoes, Tuscany, Italy, vector-borne disease, entomological surveillance, biological invasion, Aedes albopictus, public health, mosquito vectors, Massa-Carrara