Urban Cerrado marmosets show low helminth richness in AJVR study
Bottom line
Low helminth richness in an urban Brazilian marmoset population may reflect more than a narrow parasite list. In a new American Journal of Veterinary Research study, researchers examined gastrointestinal helminths from 21 black-tailed marmosets, Mico melanurus, found dead in Cuiabá, Brazil, between October 2020 and February 2022, and identified just two nematode taxa: Primasubulura jacchi in 18 samples and Trypanoxyuris spp. in two. One degraded sample was excluded. The authors paired those findings with morphologic and morphometric descriptions and argue that the low parasite richness seen in this fragmented urban Cerrado habitat may signal ecological imbalance rather than a simple absence of exposure. M. melanurus is a Near Threatened primate associated with the Cerrado, and the paper adds to a sparse parasite record for the genus Mico. (preprints.org)
Why it matters: For veterinary professionals, especially those working in wildlife health, zoo and conservation medicine, and One Health surveillance, the study is a reminder that “low diversity” findings can still carry clinical and ecological significance. P. jacchi reached a reported mean intensity of 34.22 parasites per positive sample and was found in about 90% of analyzed marmosets, while Trypanoxyuris spp. had lower prevalence but can still be associated with intestinal mucosal lesions and inflammatory responses in heavier infestations. The authors also note that no zoonotic gastrointestinal helminths were identified in this cohort, but they frame the results within ongoing habitat fragmentation and increased contact among wildlife, domestic animals, and people in urbanized landscapes. (preprints.org)
What to watch: Follow-up work using broader sampling and, ideally, molecular identification could clarify whether urban fragmentation is consistently linked to reduced helminth richness in free-ranging neotropical primates and whether that shift tracks changes in host health or zoonotic risk. (preprints.org)
Key facts
- Study
- American Journal of Veterinary Research study
- Species
- Black-tailed marmosets, Mico melanurus
- Location
- Cuiabá, Brazil
- Study period
- October 2020 to February 2022
- Sample size
- 21 carcasses; 20 evaluable samples
- Main finding
- Only two nematode taxa were identified: Primasubulura jacchi and Trypanoxyuris spp.
- Key result
- Primasubulura jacchi was found in 18 samples, with a mean intensity of 34.22 parasites per positive sample
- Interpretation
- Low helminth richness may reflect environmental disruption in a fragmented urban Cerrado habitat
- Host status
- Mico melanurus is listed as Near Threatened
A new study in the American Journal of Veterinary Research reports a surprisingly narrow gastrointestinal helminth profile in black-tailed marmosets, Mico melanurus, from a fragmented urban area of Brazil’s Cerrado biome. Across 21 opportunistically collected carcasses from Cuiabá, researchers identified only two nematode taxa, with Primasubulura jacchi dominating and Trypanoxyuris spp. appearing in just two samples. Their central interpretation is that low helminth richness in this setting may reflect environmental disruption in an anthropized landscape, not simply low infection pressure. (preprints.org)
That matters in part because Mico melanurus is an understudied host. The species is a black-tailed marmoset distributed across parts of Brazil, Bolivia, and Paraguay, and recent reference sources list it as Near Threatened. The authors note that Brazil’s primate helminth fauna remains incompletely described, with many species lacking parasite records altogether, and they position this work as a baseline contribution for a native primate living in habitat increasingly shaped by urban expansion, agriculture, fires, and livestock pressure. (preprints.org)
The study used helminths collected from 21 M. melanurus specimens found dead within Cuiabá’s urban perimeter from 2021 to 2022 under Brazilian ethics approval and collection license. One sample was too degenerated to classify, leaving 20 evaluable cases. In those, the team recovered P. jacchi from 18 samples and Trypanoxyuris spp. from two, then deposited specimens in the Helminthological Collection of the Federal University of Jataí. Reported parasite burdens varied widely: P. jacchi counts ranged from 1 to 132 individuals per sample, with a mean intensity of 34.22 and mean abundance of 30.8, while Trypanoxyuris spp. ranged from 11 to 115 individuals, with a mean intensity of 63 and mean abundance of 6.3. (preprints.org)
The paper also provides useful diagnostic detail. The authors identified P. jacchi by male and female morphology, while Trypanoxyuris could only be assigned to genus because only female worms were recovered. That distinction matters because female Trypanoxyuris are morphologically similar across species, and species-level confirmation typically depends on male reproductive structures. The authors suggest the parasite may be T. callithricis, which has been reported previously in Mico and other primates in Mato Grosso, but they stop short of confirming that without male specimens. (preprints.org)
In interpreting the findings, the researchers tie parasite ecology to host behavior and landscape change. They note that P. jacchi is commonly reported in primates and may be sustained by insect consumption, since arthropods can serve as intermediate hosts. That fits the feeding ecology of M. melanurus, which consumes substantial amounts of invertebrates. At the same time, the authors say they expected to find additional helminth groups with indirect life cycles, including acanthocephalans or Spirurida nematodes, but did not. Their inference is that habitat fragmentation may be altering ecological relationships within the biome, reducing parasite richness while increasing pressure on native host populations. (preprints.org)
There doesn’t appear to be a separate institutional press release or formal outside commentary on this paper yet, but related literature supports the broader One Health framing. A 2025 study of marmosets in southern Brazil reported parasites with zoonotic potential in anthropized settings and argued for continued surveillance at the human-animal-environment interface. Separately, a 2022 report documented natural SARS-CoV-2 infection in a free-ranging M. melanurus from an urban area in midwestern Brazil, underscoring how these primates already sit within overlapping wildlife, domestic animal, and human exposure networks. (onlinelibrary.wiley.com)
Why it matters: For veterinary professionals, this is less a parasite inventory story than a surveillance and interpretation story. In wildlife and conservation medicine, a short pathogen list can be easy to dismiss, but this study suggests low helminth richness itself may be biologically meaningful in fragmented habitats. Clinically, P. jacchi has been associated with diarrhea and ulcerative intestinal lesions in some primates, though infections may also be asymptomatic, potentially allowing reservoir persistence. From a population-health standpoint, the paper adds evidence that urban-adapted primates need parasite monitoring that connects pathology, ecology, and land-use change rather than treating those domains separately. (preprints.org)
What to watch: The next step will likely be whether future studies expand beyond morphology to molecular characterization, add fecal and live-animal surveillance, and compare urban-fragmented versus less disturbed Cerrado habitats. That would help determine whether the low richness reported here is a repeatable ecological signal, a sampling artifact of opportunistic necropsy, or an early marker of changing disease dynamics in a Near Threatened primate living close to people. (preprints.org)