Avian malaria is caused by hemosporidian parasites, single-celled organisms related to the agents of human malaria that are transmitted by biting insects. In birds, Plasmodium is spread by mosquitoes, Haemoproteus chiefly by biting midges and louse flies, and Leucocytozoon by black flies. Urbanization is widely recognized as a driver of increased pathogen transmission, primarily through landscape modification and heightened contact rates between hosts and vectors, which can elevate parasite prevalence and virulence. Urban environments can enhance vector distribution and increase host contact rates, and are often associated with adverse effects on bird health, including compromised body condition due to exposure to pollutants and lower-quality food sources.

Research on the relationship between urbanization and avian malaria has produced varied findings. Most studies report higher infection rates in urban bird populations, while others find no significant differences between habitat types. These differences likely reflect the influence of local environmental conditions that shape malaria transmission dynamics, including vegetation cover, land use, and especially water availability, which has been shown to be a strong predictor of hemosporidian infection in wild birds. Although rural or more natural areas are generally assumed to experience lower transmission due to reduced human impact, agricultural activities and habitat disturbance can still influence infection risk. Degraded or transitional landscapes, which are increasingly common, may not fit neatly into rural–urban categories.

Understanding these transmission patterns is particularly crucial in regions where native bird species already face multiple threats. Habitat loss, climate change, and the introduction of novel pathogens can compound the effects of avian malaria, making disease outbreaks even more detrimental. In New Zealand, avian malaria has been implicated in the decline of native bird populations, with studies linking higher parasitemia levels to increased mortality risk. In Hawaii, rising temperatures and shifting precipitation patterns have contributed to an increase in avian malaria prevalence, further endangering endemic bird species. In Central America, extensive land-use changes over recent decades—driven by large-scale agricultural expansion, cattle ranching, infrastructure development, and illegal deforestation—have led to widespread degradation and loss of dry forests, potentially altering vector distributions and host–pathogen interactions. Yet avian malaria research in the region remains sparse.

The survey was carried out in the Motagua Valley region, located in the department of Zacapa at elevations ranging from 300 to 900 meters above sea level. The valley has a tropical subhumid climate, with an average annual temperature of 26.9 °C and average annual precipitation of 815 mm, and a pronounced dry season lasting up to five months from November to May. The landscape comprises a mosaic of tropical dry forest patches with varying levels of anthropogenic disturbance, surrounded by human settlements and land uses centered on crop cultivation, pastures, grazing areas and urban development. The team assessed twelve distinct sites, nine in rural environments and six in urban areas.

Wild birds were captured via six 12-meter mist nets over two-day periods between March and October 2021, from 6:30 am to 11:30 am, and backyard birds were captured directly at their breeding sites. Blood samples of 20–40 microliters were drawn from the sub-brachial wing vein, never exceeding one percent of a bird’s body weight, preserved in EDTA and stored at −20 °C. Each bird underwent sex determination, weight measurement and comprehensive morphometrics, including wing, tail and beak dimensions. Blood smears were fixed with ethanol, stained with Giemsa and screened under a light microscope. When infection was detected, parasitemia was estimated by counting infected erythrocytes in ten randomly selected fields, each typically containing between 1,000 and 5,000 red blood cells, and classified as low, moderate, moderate to high, or high.

Total DNA was extracted from each blood sample, and multiplex PCR was performed with genus-specific primer sets for Plasmodium, Haemoproteus and Leucocytozoon. Thermocycling conditions included a hot-start denaturation at 94 °C, 35 cycles of denaturation, annealing at 54.5 °C and extension at 72 °C, followed by a final extension step. Amplification products were run on 1.5 percent agarose gels and visualized on a transilluminator. Associations between prevalence and habitat type were assessed with Fisher’s exact test, and a binomial logistic regression model was used to determine whether malaria prevalence differed between urban and rural sites.

The results revealed a moderate overall prevalence of 38 percent, with Plasmodium spp. being the most prevalent, followed by Haemoproteus spp. Notably, no Leucocytozoon infections were detected. Among positive samples, 26 were infected with Plasmodium, 14 with Haemoproteus, and two had mixed infections—a Baltimore oriole and a turquoise-browed motmot carried parasites of both genera. The Inca dove (Columbina inca) was the most heavily sampled species, with 13 of 30 individuals infected. Microscopic examination of 209 blood smear slides found 33 positive, and approximately 69 percent of these presented a moderate level of parasitemia. Most infected birds exhibited low to intermediate parasitemia, a pattern consistent with chronic infections that promote long-term parasite survival within populations, as certain bird species, including members of the Columbidae family and some Passeriformes, are considered chronic hosts of hemosporidian parasites.

Statistically, the study found no significant difference in overall prevalence between habitat types, with an odds ratio of 1.04 for urban sites compared to rural sites, indicating a negligible difference in infection probability. However, Plasmodium prevalence varied significantly across habitat types, with higher prevalence in urban areas, while no significant variation was observed for Haemoproteus. The overall prevalence is consistent with previous studies in arid ecosystems of the Neotropical region, where rates typically range from 30 to 50 percent, such as 32 percent in the southern Chihuahuan Desert and 35 percent in tropical dry forests of Brazil. The absence of Leucocytozoon, transmitted by black flies, aligns with its low prevalence in the Neotropics and likely reflects unfavorable conditions for these vectors at the valley’s low altitude.

The number of infections detected via PCR differed from those identified through microscopy, consistent with previous research comparing the two methods. PCR can detect infections even at extremely low parasite loads—fewer than one parasite per million host cells—a threshold unlikely to be captured in standard microscopic examinations, which typically analyze 10,000 to 100,000 cells. Conversely, some PCR-detected infections may be controlled by the host and never progress to stages circulating in the bloodstream. Low parasitemia levels in mist-netted birds may also reflect a capture bias, since high parasitemia significantly impairs bird mobility, reducing the likelihood of heavily infected individuals being captured. This suggests that, in natural conditions, avian populations may experience more severe impacts from malaria than mist-net surveys reveal. The researchers conclude that habitat type does not necessarily correlate with overall prevalence or parasitemia intensity, and that future longitudinal studies across diverse habitats will be essential to comprehend the temporal and spatial dynamics of avian malaria, especially in regions experiencing rapid environmental change.

Subject of Research: Prevalence and parasitemia of avian malaria parasites in wild birds across urban and rural tropical dry forest habitats in eastern Guatemala

Article Title: Avian malaria in wild birds within a tropical dry forest area in Guatemala

Article References: Bustamante-Castillo, M., De León-Robles, E., Barrios-Izas, M. A., & Calderón-Aguirre, L. A. (2025). Avian malaria in wild birds within a tropical dry forest area in Guatemala. Neotropical Biology and Conservation, 20(3), 205-219. https://doi.org/10.3897/neotropical.20.e153327

Image Credits: AI Generated

DOI: 10.3897/neotropical.20.e153327

Keywords: avian malaria, Plasmodium, Haemoproteus, wild birds, tropical dry forest, Guatemala, urbanization, parasitemia, PCR, microscopy, vector-borne disease, Motagua Valley

Avian haemosporidians are a group of apicomplexan parasites belonging chiefly to three genera: Plasmodium, Haemoproteus, and Leucocytozoon. In birds, these organisms can behave much like the malaria parasites that afflict humans, invading blood cells and internal organs, sapping host condition, and in severe cases reducing survival and reproductive success. Their effects ripple outward into population dynamics, migration behavior, and even the structure of whole bird communities. For decades, ecologists have worked to map which insect vectors carry which parasite lineages, because transmission is the hinge on which the entire host-parasite system turns. Mosquitoes, Culicoides biting midges, louse flies, and black flies are the recognized vectors, each genus of parasite showing affinities for particular insect groups and particular bird hosts.

Leptoconops is a genus of haematophagous biting midges in the family Ceratopogonidae, closely related to the better-known Culicoides midges that are established vectors of avian Haemoproteus. Despite this kinship, Leptoconops midges have never been systematically implicated in avian malaria transmission, and no previous study had molecularly screened them for haemosporidian infections. That gap is precisely what motivated the research team, led by Javier Carbonero and Martina Ferraguti of the Estación Biológica de Doñana, a research institute of the Spanish National Research Council (CSIC) in Seville, together with colleagues affiliated with the Centro de Investigación Biomédica en Red de Epidemiología y Salud Pública.

The scale of the fieldwork reflects the difficulty of the question. During 2024, the researchers collected a total of 5,417 female Leptoconops midges across sites in Andalusia, taking advantage of the fact that only female midges take blood meals and can therefore plausibly acquire and transmit blood parasites. Each specimen was morphologically identified to species, a labor-intensive step that matters because vector competence and host preferences can differ sharply even between close relatives. The midges were then grouped into 203 pools for molecular analysis, a pooling strategy that balances laboratory workload against the sensitivity needed to detect low-level infections in wild-caught insects.

The molecular heart of the study is a nested polymerase chain reaction (PCR) protocol targeting the cytochrome b gene, the standard DNA barcode region for avian haemosporidians. Nested PCR uses two successive rounds of amplification with two pairs of primers, dramatically increasing sensitivity and allowing researchers to detect the minute quantities of parasite DNA that may persist in an insect after a blood meal has been digested. Positive amplicons were then sequenced, and the resulting DNA barcodes were compared against reference databases to assign each parasite to a genus and, where possible, to a known lineage with a documented host range. This lineage-level resolution is what gives the study its ecological punch: many haemosporidian lineages have been catalogued from specific bird species, so finding a lineage inside a midge hints at which birds the midge may have bitten.

Eight of the 203 pools tested positive for haemosporidian DNA. The positive pools corresponded to two of the Leptoconops species examined, Leptoconops communis and Leptoconops nigrithorax, indicating that more than one member of the genus encounters these parasites in the wild. The identified parasites spanned all three target genera. Among the Haemoproteus detections were Haemoproteus noctuae, corresponding to the lineage CIRCUM01, and an unidentified Haemoproteus species of the lineage COLPAL01. The Plasmodium findings included Plasmodium matutinum, the well-characterized lineage LINN1, while Leucocytozoon was represented by the lineages COLIV04 and AEMO02. In addition to these known barcodes, the team uncovered two lineages that had never been recorded before, which they designated Plasmodium P_LEPTO01 and Haemoproteus H_LEPTO01, expanding the global catalogue of avian haemosporidian genetic diversity.

The known host associations of the detected lineages are where the story becomes genuinely suggestive. Haemoproteus noctuae, for example, is a parasite associated with owls and other birds, and lineages such as LINN1 and COLIV04 have been documented from particular avian hosts in previous surveys. By matching the lineages found in the midges to their known bird hosts, the researchers can infer, indirectly, which avian species Leptoconops midges may have fed upon. This approach, sometimes framed within the broader use of insect-derived DNA as a sampling tool, effectively turns each infected midge into a tiny record of both a bird-parasite interaction and a midge feeding choice. It is an indirect inference rather than a direct blood-meal identification, but it provides testable hypotheses about the feeding ecology of a genus whose biting habits remain poorly documented in many regions.

The authors are careful, and appropriately so, about what the results do and do not demonstrate. Detecting parasite DNA in an insect does not establish vector competence, the ability of a vector to support the parasite’s full developmental cycle and transmit it to a new host. Haemosporidian parasites undergo a complex development within a competent vector, including sexual reproduction, invasion of the insect’s gut wall, production of infective sporozoites, and migration to the salivary glands. Parasite DNA could, in principle, simply reflect the digestion of an infected blood meal without any subsequent parasite development. The researchers explicitly state that vector competence has not been demonstrated and that the potential role of Leptoconops in transmission is unknown and merits further investigation. Disentangling genuine biological transmission from mere mechanical carriage of DNA will require experimental infection studies, dissection of midge tissues, and detection of parasite developmental stages rather than DNA alone.

Even with those caveats, the study carries weight for several reasons. First, it establishes a previously unrecorded interaction between a widespread genus of biting midges and avian haemosporidian parasites, adding Leptoconops to the short list of insect groups in which these parasites have been molecularly detected. Second, the diversity of parasites found, spanning Plasmodium, Haemoproteus, and Leucocytozoon, suggests that the encounters are not a rare accident of a single parasite species but a broader pattern involving multiple parasite lineages and at least two midge species. Third, the discovery of two novel lineages underscores how much undocumented parasite diversity circulates in wild bird communities and their vectors, and how vector-focused sampling can surface it. Fourth, the work has practical implications: if Leptoconops midges prove to be competent vectors, current models of avian malaria transmission, which lean heavily on mosquitoes and Culicoides, would need revision, with consequences for understanding disease dynamics in bird populations, the risks faced by vulnerable species, and even the epidemiology of zoonotic or wildlife pathogens in shared landscapes.

The research was conducted by a team based at the Estación Biológica de Doñana in Seville, with funding from projects including ARBOPREVENT, supported by Fundación La Caixa, a national research project financed by Spain’s Ministry of Science and European regional funds, and the Severo Ochoa excellence program. The work formed part of a broader research effort on vector ecology in southern Spain, where wetland habitats concentrate both bird diversity and biting insects. As the authors conclude, the findings suggest real interactions between Leptoconops midges and infected avian hosts, and they call for further studies to determine whether these midges are incidental carriers or genuine players in the transmission of avian malaria. For now, a genus of tiny midges, long noted mainly for the irritating bites of its females, has earned a place on the watch list of avian disease ecology, and the search for its true role in the parasite’s life cycle is only beginning.

Subject of Research: Molecular detection of avian haemosporidian parasites in Leptoconops biting midges

Article Title: First molecular detection of avian haemosporidian parasites in Leptoconops (Diptera: Ceratopogonidae) biting midges

Article References: Carbonero, J., González, M. A., Magallanes, S., Paun-Tanase, D. I., Martínez-de la Puente, J., Figuerola, J., & Ferraguti, M. (2026). First molecular detection of avian haemosporidian parasites in Leptoconops (Diptera: Ceratopogonidae) biting midges. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07713-6

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07713-6

Keywords: avian malaria, haemosporidian parasites, Leptoconops, biting midges, Ceratopogonidae, Plasmodium, Haemoproteus, Leucocytozoon, vector ecology, cytochrome b, nested PCR, Andalusia