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Morphology and COI DNA Identified Pharyngomyia picta in a Free-Ranging Sambar From Kerala

Rusa unicolor female, Kanha National Park, India
Research · Disease, parasites & microbiology

Researchers in Kerala combined larval morphology with DNA sequencing to identify the nasal bot fly Pharyngomyia picta in a free-ranging sambar (Rusa unicolor). P. picta is an obligate parasite of deer and other cervids: adult females release larvae at the host’s nostrils, and the larvae develop in the nasal and pharyngeal passages. Such infestation is called nasopharyngeal myiasis. The adult female sambar was found dead in Konnakuzhy in the Vazhachal Forest Division in January 2026, and four large larvae were recovered from its trachea during necropsy.

Morphology and a mitochondrial DNA barcode agreed

The larvae were 2.5–3 centimetres long and had the body spines and crescent-shaped posterior spiracles expected in third-instar P. picta. Because closely related bot flies can be difficult to distinguish by appearance alone, the researchers also sequenced a 640-base-pair fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene. COI is widely used as a DNA-barcode region: comparing its sequence with reference material can help distinguish closely related animal species.

Diagnostic morphology of third-instar Pharyngomyia picta larvae
Diagnostic morphology of third-instar Pharyngomyia picta larvae recovered from the sambar. Figure 2 from Athira et al. (2026), The Journal of Basic and Applied Zoology, CC BY 4.0. Source.

The Kerala sequences were identified as P. picta, and the phylogenetic analysis placed the analysed Kerala sequence within the P. picta lineage and closest to previously published Spanish reference sequences. Earlier reports had already documented P. picta in sambar in South Asia on morphological grounds; the new result is the first combined morphological and molecular characterisation from a sambar in Kerala. It therefore adds a DNA reference from an Indian wildlife host for which molecular information has been scarce.

The infestation may have contributed to breathing problems

The necropsy showed pulmonary congestion and oedema — fluid accumulation in the lungs — together with nasopharyngeal myiasis, and the larvae may have contributed to respiratory compromise. The researchers nevertheless state that the available evidence cannot establish a definitive causal relationship between the infestation and the deer’s death. They call for further epidemiological and molecular work to clarify the parasite’s distribution and health effects in wild cervids.

Sources and image credit

  1. Athira, C. P., Athira, I. B., Lakshmanan, B., Deepak Mathew, D. K., Babu, L., & Dipu, M. T. (2026). Molecular identification of Pharyngomyia picta (Meigen, 1824) (Diptera: Oestridae) in sambar deer (Rusa unicolor) from Kerala, India. The Journal of Basic and Applied Zoology, 87, 68. https://doi.org/10.1186/s41936-026-00600-7Primary open-access research article published 14 June 2026. Four third-instar bot-fly larvae recovered from the trachea of a free-ranging adult female sambar in Kerala were identified morphologically and by sequencing a 640-bp mitochondrial COI fragment. The Kerala isolate clustered closely with Spanish P. picta sequences. The authors state that the infestation may have contributed to respiratory compromise but that a definitive causal relationship with mortality cannot be established.

Image: Charles J. Sharp / Wikimedia Commons — female sambar in Kanha National Park, Madhya Pradesh, India, 17 November 2017; cropped to 16:9. Representative image for this story; not presented as an animal or scene from the reported study or event. · CC BY-SA 4.0 · Source

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