Trombiculiosis caused by chigger mites in floodplain forest birds in Central Amazon

Conga, D.F.; Silva, G.L.; Prestes, A.; Pedroza, D.; Lopes, G.P.; Santos, T.C.M.; Maranhão, L.

doi:10.1590/1678-4162-13553

RESUMO

Os ácaros trombiculídeos estão entre os menores artrópodes, e muitas dessas espécies são capazes de produzir reações cutâneas leves a graves, além de participar da transmissão de patógenos. Portanto, conhecer seus hospedeiros e as espécies envolvidas na natureza é o primeiro passo em estudos de ecossaúde. Aves foram capturadas usando-se redes de neblina em florestas alagáveis na Reserva Mamirauá. Após a captura, foi realizado um exame externo para detectar ectoparasitas. Os espécimes observados foram cuidadosamente coletados e preservados. Além disso, fragmentos de pele infestada foram fixados em formalina e corados com hematoxilina-eosina para exame histopatológico. Ectoparasitas foram observados em seis espécies de aves, com infestação por larvas de ácaros trombiculídeos firmemente aderidas à pele. Os locais parasitados consistiam em formações crostosas e evidências de dermatite focal moderada com infiltração leve de células mononucleares e heterófilos. De acordo com as características morfológicas observadas, as larvas foram compatíveis com os gêneros Blankaartia e Neoschoengastia. Ácaros trombiculídeos são ectoparasitas de importância médica e veterinária, atingindo sua maior diversidade em zonas tropicais e subtropicais. No presente estudo, proporcionamos registros de ácaros em novos hospedeiros e novas áreas geográficas na Amazônia Central.

Palavras-chave:
Mamirauá; várzea; ectoparasitas; dermatites; Passeriformes

In the Amazon, approximately 15% of non-aquatic birds are specialists in floodplain forests (seasonally flooded) and occupy this environment almost exclusively (Remsen and Parker, 1983). In this biome, the presence of parasite arthropods occurs naturally, influencing the health and fitness of wild bird populations (Clayton et al., 2010). The chigger fauna reaches its greatest species diversity in tropical and subtropical zones and this diversity and its role in the transmission of pathogens is still scarcely studied in the Amazon region (Porras and Olivera, 2021).

Chigger mites associated with avian hosts have been studied to a much lesser proportion compared to chigger mites that infest mammals (Jacinavicius et al., 2018). The chigger mites, which infest almost exclusively birds, are the genera Hypogastia Vercammen-Grandjean, 1967, Neoschoengastia Ewing, 1929, Ornithogastia Vercammen-Grandjean, 1960, Toritrombicula Sasa, 1954 and Whartonacarus Vercammen-Grandjean, 1960 (Kalúz et al., 2016). Studies of parasites from wild animals in situ provide important information on the biodiversity of parasitic species under natural conditions. Thus, in this study, we will present records of infestation by chigger mites of the family Trombiculidae, in six species of birds from floodplain forest of the central Amazon.

Birds and chigger mites were sampled in Mamirauá Sustainable Development Reserve, Amazonas State, Brazil (2° 15′ 36″ S, 65° 40′ 48″ W). This protected area is entirely composed of floodplain forests. During the high-water season, nutrient-rich white-water rivers flood the floodplain forests, with an average annual water-level fluctuation of approximately 15 m (Goulding et al., 2003). River levels typically peak in May-June and reach their lowest points in October-November (Ramalho et al., 2009). The mean annual temperature ranges from 26 to 31°C, while annual precipitation averages between 2,200 and 2,400 mm. During the dry season, mean monthly precipitation decreases to approximately 60-80 mm (Ferreira-Ferreira et al., 2015).

The birds were captured in July 2024 in areas that were not submerged, as part of a study on the influence of floodplain forest management on understory bird diversity. On each sampling day, we used 20 mist nets (15×2.5 m, 36 mm mesh). We opened the mist nets between 6:00 am and 12:00 pm and inspected them every 30 minutes. After capturing the birds, we carried out an external assessment in an attempt to detect ectoparasites (e.g., lice, mites, and ticks). We identified the birds with the help of field guides, and the nomenclature of the birds follows Perlo (2009). Collection was carried out under Biodiversity Authorization and Information System permit (84571-1, 84571-2, 84571-3, 84571-4, 84571-5, 84571-6 and 84571-7).

The ectoparasites observed on the skin and feathers of the birds were collected using brushes and tweezers, visualized through a manual stereoscopic microscope, and preserved in 3 mL vials with 70% alcohol. In the laboratory, these specimens were slide-mounted in Hoyer’s medium. Morphological examination was performed, and measurements and photomicrographs were made using a Prime Life Science digital camera coupled to a Nikon Eclipse SI optical microscope. Additionally, a 1 cm in diameter skin sample from one of the birds infested with parasites was fixed in 10% formalin and subjected to routine hematoxylin-eosin staining for histopathological examination.

Chigger mites were observed in 10 individuals of six species: Attila bolivianus (2), Attila cinnamomeus (3), Celeus elegans (1), Dendrocolaptes radiolatus (1), Monassa nigrifrons (2) and Xiphorhynchus obsoletus (1). Externally, tiny red or orange specimens measuring approximately 1 to 2 mm in length were observed, forming clusters and firmly attached to the skin, and infesting featherless areas with a diameter of between 0.1 and 0.3 cm on the back, chest, wings, tarsus, rump, ear and neck (Fig. 1). Each parasitized bird had at least one cluster of mites and when there was more than one, they occupied different parts of the body. The site where the cluster of mites occupied consisted of crusty formations and scaling on the skin and thickened epidermis devoid of plumage. When we removed the mites from the infested site, the skin lesion had a central depression, similar to a crater. Microscopically, the infested skin revealed the mite attached to the epidermis, which was thinner (atrophied) and hyperkeratinized. In the dermis, deposition of hyaline material and the connective tissue appeared looser (edematous) with a mild infiltration of mononuclear cells and heterophils containing the stylostomes of the mites (Fig. 2).

According to the morphological characteristics, the larvae were classified into two morphotypes. The first morphotype had a red body, a subpentagonal scutum with a rounded posterior angle (Fig. 3), palpal claw trifurcate and only 1 mastitarsala III and unisetose coxae, these characteristics were compatible with the genus Blankaartia Oudemans, 1911 observed in the hosts A. bolivianus, A. cinnamomeus, D. radiolatus, M. nigrifrons, and X. obsoletus. The second morphotype observed only in the host C. elegans had an orange body, broad-ellipsoidal, subrectangular scutum with margins sinuous, cheliceral blade without accessory dorsal tooth, Sensillae expanded, and palpal tarsus with 7B. These characteristics were compatible with the genus Neoschoengastia Ewing, 1929 (Figure 3).

Chigger mites of the genera Blankaartia and Neoschoengastia have been reported in aquatic and terrestrial wild birds around the world, with more than 28 species for the genus Blankaartia and more than 70 species for the genus Neoschoengastia (Bassini-Silva et al., 2016). In Brazil, the genus Blankaartia was reported in birds of the families: Pipridae, Strigidae, Thraupidae, Troglodytidae, Turdidae, and Tyrannidae in the Northeast and Southeast (Bassini-Silva et al., 2018, 2021). While the genus Neoschoengastia was only recorded in one bird of the species Automolus infuscatus in the north of the country (Brennan, 1971). Chigger mites are parasites of medical and veterinary importance because they are sources of allergens for humans and wild animals during infestation, causing deep dermatitis and skin reactions in hosts as observed in this study, leaving the possibility of secondary infections compromising the health and survival, especially in young or newly hatched birds (Chen et al., 2022).

Despite the limited number of infested birds observed in this study, we observed that the preference of mites for a specific host species is low. These mites prefer certain geographic locations, where they feed on the hosts that inhabit them, according to observation by Zhan et al. (2013); Eamon and Courtney (2019). This low host specificity may increase the chances of contact with various hosts, as well as the transmission of bacteria such as Rickettsia spp. and Orientia tsutsugamushi (Bassini-Silva et al., 2018). Considering non-aquatic birds from protected areas, we provide in this study for the first time the presence of chigger mites of the genus Blankaartia and Neoschoengastia in floodplain forest birds in the central Amazon.

Figure 1
Patterns of chigger mite infestation on the dermal surface in understory birds. A) right ear of Attila bolivianus B) left ear of Attila cinnamomeus C-D) neck and wing of Celeus elegans (E-F), scapular region of Dendrocolaptes radiolatus and (G, H- I) chest and tarsal region of Monassa nigrifrons.

Figure 2
Histology skin of Monasa nigrifrons (hematoxylin and eosin staining). A-B) Note the feeding cavity containing stylostomes of the mites (st) beneath the larval chelicerae (ch) and palpal claw (pc) in the upper portion of the epidermis overlay by a thick stratum corneum. Scale bar: 50µm.

Figure 3
A-B) Morphology of an engorged larval, scutum and sensilla (se) of Blankaartia, C-D) Morphology of a larva, scutum and sensilla (se) of Neoschoengastia. Scale bars: A: 150 µm, B: 40 µm, C: 50 µm, D: 20 µm.

ACKNOWLEDGMENTS

We thank to the Ministério da Ciência, Tecnologia e Inovação (financial support to Instituto de Desenvolvimento Sustentável Mamirauá). We thank to the Fundação de Amparo à Pesquisa do Estado do Amazonas (Edital N. 009/2021 - PROFIX-RH & Edital N. 007/2022 - Programa Mulheres das Águas). We thank field assistants: Bruno de Aquino Neves, Eliotério Martins Alves, Eulumar Carvalho de Melo and Joney Brasil and to the Dr. Omar Gonzalez Viera for english review.

REFERENCES

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ETHICAL ASPECTS

The research was approved by the Committee for the Ethical Use of Animals (001/2022) of the Mamirauá Institute for Sustainable Development.

DATA AVAILABILITY STATEMENT

The authors confirm that the data supporting the findings of this study are available within the paper.

Corresponding author:

david.conga@mamiraua.org.br

Editor-chefe:

Marcelo Resende de Souza

Editor-científico:

Antônio de Pinho Marques Jr.

Publication Dates

Publication in this collection
23 Mar 2026
Date of issue
Mar-Apr 2026

History

Received
06 Apr 2025
Accepted
14 Oct 2025

This is an open-access article distributed under the terms of the Creative Commons Attribution License

[1] BASSINI-SILVA, R.; JACINAVICIUS, F.C.; HUANG-BASTOS, M. et al. First record of Blankaartia sinnamaryi (Floch and Fauran, 1956) (Trombidiformes: Trombiculidae) parasitizing the striped owl in Northeastern Brazil. Rev. Bras. Parasitol. Vet., v.30, p.e00312, 2021.

[2] BASSINI-SILVA, R.; JACINAVICIUS, F.C.; MATURANO, R. et al. Blankaartia sinnamaryi (Trombidiformes: Trombiculidae) parasitizing birds in southeastern Brazil, with notes on Rickettsia detection. Rev. Bras. Parasitol. Vet., v.27, p.354-362, 2018.

[3] BASSINI-SILVA, R.; JACINAVICIUS, F.C.; MENDOZA-ROLDAN, J.A. et al. Description of Blankaartia shatrovi n. sp. (Acari: Trombiculidae) from Brazil. J. Med. Entomol., v.54, p.82-90, 2016.

[4] BRENNAN, J.M. Endoparasitic chiggers. 4. Neoschoengastia esorhina sp. n. (Acarina: Trombiculidae), a second intranasal chigger of birds. J. Parasitol., v.57, p.666-667, 1971.

[5] CHEN, K.; ROE, R.M.; PONNUSAMY, L. Biology, systematics, microbiome, pathogen transmission and control of chiggers (Acari: Trombiculidae, Leeuwenhoekiidae) with Emphasis on the United States. Int. J. Environ. Res. Public Health, v.19, p.15147, 2022.

[6] CLAYTON, D.H.; KOOP, J.A.; HARBISON, C.W. et al. How birds combat ectoparasites. Open Ornithol., v.3, p.41-71, 2010.

[7] EAMON, J.H.; COURTNEY, J.C. Novel ectoparasite infestation on yuma ridgway's rails (Rallus obsoletus yumanensis). Wilson J. Ornithol., v.131, p.139-146, 2019.

[8] FERREIRA-FERREIRA, J.; SILVA, T.S.; STREHER, A.S. et al. Combining ALOS/PALSAR derived vegetation structure and inundation patterns to characterize major vegetation types in the Mamirauá Sustainable Development Reserve, Central Amazon floodplain, Brazil. Wetl. Ecol. Manag., v.23, p.41-59, 2015.

[9] GOULDING, M.; BARTHEM, R.: FERREIRA, E. The Smithsonian Atlas of the Amazon. Smithsonian Books, Washington DC. 2003.

[10] JACINAVICIUS, F.C.; BASSINI-SILVA, R.; MENDOZA-ROLDAN, J.A. et al. A checklist of chiggers from Brazil, including new records (Acari: Trombidiformes: Trombiculidae and Leeuwenhoekiidae). ZooKeys, v.743, p.1-41, 2018.

[11] KALÚZ, S.; HUNG, N.M.; CAPEK, M. et al. Two new species and new records of chiggers (Acari:Leeuwenhoekiidae, Trombiculidae) from birds in Vietnam. Zootaxa, v.4061, p.483-503, 2016.

[12] PERLO, V.B. A field guide to the birds of Brazil. New York: Oxford University Press, 2009. 465p.

[13] PORRAS, V.J.F.; OLIVERA, J.L.M. Medically important trombiculids: a systematic review of the global distribution and clinical consequences of their bites. Rev. Peru Invest. Salud, v.5, p.67-76, 2021.

[14] RAMALHO, E.E.; MACEDO, J.; VIEIRA, T.M.; VALSECCHI, J.; CALVIMONTES, J.; MARMONTEL, M.; QUEIROZ, H.L. Ciclo Hidrológico nos ambientes de várzea da Reserva de Desenvolvimento Sustentável Mamirauá - Médio Solimões, período de 1990 a 2008. Uakari v.5, p.61-87.

[15] REMSEN, J.J.; PARKER, T.A. Contribution of river-created habitats to bird species richness in Amazonia. Biotropica, v.15, p.223-231, 1983.

[16] ZHAN, Y.Z.; GUO, X.G.; SPEAKMAN, J.R. et al. Abundances and host relationships of chigger mites in Yunnan Province, China. Med. Vet. Entomol., v.27, p.194-202, 2013.