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Mysterious Death of a Songbird Reveals a Novel Coxiella Species

By Xueyan Xu, PhD

When a colorful passerine bird, the Violaceous Euphonia (Euphonia violacea), mysteriously died at a US Zoo, the cause wasn’t clear. Veterinarians noticed severe brain lesions and sent tissue samples to MiDOG for Next-Generation Sequencing (NGS) analysis.

The results were astonishing: Over 93% of the bacterial DNA came from a previously unknown species of Coxiella, a genus of bacteria that includes the notorious Coxiella burnetii, the cause of Q fever in humans This finding marks a rare and potentially significant avian infection by a novel Coxiella species, adding a new twist to the story of this elusive genus. The genus Coxiella includes Coxiella burnetii, the etiological agent of Q fever in humans, Coxiella cheraxi, a pathogen of redclaw crayfish, and tick endosymbionts (1, 2, 3). Despite their diversity, all Coxiella species share one trait: they are hard to detect and even harder to grow in the lab. That’s where advanced molecular tools like NGS come in.

Coxiella burnetii Infection in Humans and Animals

Coxiella burnetii is a Gram-negative, obligate intracellular pathogen that infects monocytes and macrophages. It is highly infectious due to its environmental stability, and low infectious dose (4). C. burnetii causes Q fever in humans and coxiellosis in animals. Infections occur in a wide range of hosts, including mammals, birds, reptiles, and arthropods. Primary animal reservoirs include sheep, goats, and cattle. Humans become infected through inhalation of aerosols contaminated by bacteria shed in the feces, urine, milk, or birth products of infected animals. People who work with farm animals or animal products are at greater risk of contracting Q fever (5).

Many infected humans and animals show no clinical signs. C. burnetii infection in ruminants can cause anorexia, late-term abortion, and necrotizing placentitis (5). In birds, C. burnetii has been isolated from the brain and liver of roosters, kidneys of pigeons and sparrows, and spleen and liver of a redstart and a white wagtail (6). Diagnosis of coxiellosis in animals includes microscopic evaluation of tissue smears, immunohistochemical testing, PCR assay, ELISA testing, and culture of tissue samples. However, seasonal variability in bacterial shedding can complicate result interpretation (6).

Emerging Coxiella-Like Infections in Birds

Coxiella-like agents distinct from C. burnetii have also been reported sporadically in diseased and dead birds. Infected birds often exhibited lethargy, emaciation, and neurological signs prior to death. Bacteria were isolated from multiple organs, including brain lesions, and identified as novel Coxiella species using molecular analysis (6, 7, 8, 9, 10). Coxiella-like species have also been isolated from ticks (11). While the pathogenicity of these tick endosymbionts remains unknown, Coxiella infections in birds were likely acquired through tick bites. Culturing these tick endosymbionts has never been achieved, and identification relies on PCR and microscopy.

The Coxiella species identified in our case is likely a novel species, similar to Coxiella pathogens previously associated with bird deaths. Given that there are only a few reports of Coxiella spp. causing disease in birds, its presence in the US Zoo is surprising. If the infection is contagious or tick-borne, it could pose a threat to local birds and animals.

NGS: A Powerful Tool for Pathogen Discovery

Traditional diagnostic tools, culture, PCR, ELISA, often fail when bacteria are shed intermittently or cannot be cultured. MiDOG’s NGS platform overcomes these challenges by identifying all DNA present in a sample, revealing both known and novel pathogens.

This technology allows veterinarians, zookeepers, and researchers to:

  • Detect hidden infections early,
  • Trace emerging zoonotic threats, and
  • Improve wildlife health surveillance.

In this case, NGS not only solved a mystery, it uncovered a new bacterial species that might otherwise have gone unnoticed.

Why This Discovery Matters

This discovery underscores the critical role of molecular diagnostics in modern veterinary and wildlife medicine, revealing how advanced tools like NGS can uncover pathogens that traditional methods often miss. It also broadens our understanding of the diverse Coxiella genus, highlighting its complex relationships across species and environments. Most importantly, it serves as a reminder that zoonotic threats can arise from the most unexpected places, even from a small, vibrant songbird, emphasizing the need for continued vigilance and innovation in disease surveillance.

References:

  1. Eldin, C., Mélenotte, C., Mediannikov, O., Ghigo, E., Million, M., Edouard, S., … & Raoult, D. (2017). From Q fever to Coxiella burnetii infection: a paradigm change. Clinical microbiology reviews, 30(1), 115-190.
  2. Ruth Elliman, J., & Owens, L. (2020). Confirmation that candidatus Coxiella cheraxi from redclaw crayfish (Cherax quadricarinatus) is a close relative of Coxiella burnetii, the agent of Q‐Letters in applied microbiology, 71(3), 320-326.
  3. Brenner, A. E., Muñoz-Leal, S., Sachan, M., Labruna, M. B., & Raghavan, R. (2021). Coxiella burnetii and related tick endosymbionts evolved from pathogenic ancestors. Genome Biology and Evolution, 13(7), evab108.
  4. Kazar, J. (2005). Coxiella burnetii infection. Annals of the New York Academy of Sciences, 1063(1), 105-114.
  5. Coxiellosis in Animals. https://www.merckvetmanual.com/infectious-diseases/coxiellosis/coxiellosis-in-animals
  6. Ebani, V. V., & Mancianti, F. (2022). Potential Role of Birds in the Epidemiology of Coxiella burnetii, Coxiella-like Agents and Hepatozoon spp. Pathogens, 11(3), 298.
  7. Shivaprasad, H. L., Cadenas, M. B., Diab, S. S., Nordhausen, R., Bradway, D., Crespo, R., & Breitschwerdt, E. B. (2008). Coxiella-like infection in psittacines and a toucan. Avian diseases, 52(3), 426-432.
  8. Vapniarsky N., Barr B.C., Murphy B. Systemic Coxiella-like infection with myocarditis and hepatitis in an eclectus parrot (Eclectus roratus) Vet. Pathol. 2012;49:717–722. doi: 10.1177/0300985811409251.
  9. Flanders A.J., Rosenberg J.F., Bercier M., Leissinger M.K., Black L.J., Giglio R.F., Craft S.L.M., Zoll W.M., Childress A.L., Wellehan J.F.X. Antemortem Diagnosis of Coxiellosis in a Blue and Gold Macaw (Ara ararauna) J. Avian Med. Surg. 2017;31:364–372. doi: 10.1647/2016-224.
  10. Needle D.B., Agnew D.W., Bradway D.S., Nordhausen R.W., Garner M.M. Avian coxiellosis in nine psittacine birds, one black-browed barbet, and one paradise tanager. Avian Pathol. 2020;49:268–274. doi: 10.1080/03079457.2020.1729956.
  11. Trinachartvanit W., Maneewong S., Kaenkan W., Usananan P., Baimai V., Ahantarig A. Coxiella-like bacteria in fowl ticks from Thailand. Parasites Vectors. 2018;11:670. doi: 10.1186/s13071-018-3259-9.