#18,966
On the heels of yesterday's report on Flies as potential vectors for HPAI H5N1, we've a preprint which finds the first evidence of carriage of HPAI H5 in a soft tick (Ornithodoros maritimus); recovered from a naturally infected Slender-billed Gull from the south of France in 2023.While this report has the potential to launch a thousand clickbait headlines, it should be stressed that there is currently no evidence that ticks are a meaningful or efficient vector of the HPAI virus.
That said, we know that some ticks can carry and transmit similar RNA viruses - including Thogotoviruses - like the Bourbon Virus found a decade ago in the American Midwest or the more recently discovered Oz Virus in Japan.
In recent years, we've seen a growing interest in tickborne diseases, with new threats continuing to emerge (see Japan: Suspected Animal-to-Human Transmission of SFTS in Veterinarian's Death).
From a tangentially related 2020 study (see Infestation of small seabirds by Ornithodoros maritimus ticks: Effects on chick body condition, reproduction and associated infectious agents) we learn:
Ticks are divided into two groups: hard ticks (Ixodidae) and soft ticks (Argasidae). Both families can potentially transmit numerous pathogens of medical and veterinary interest (Dietrich et al., 2011 and references therein). However, those transmitted by soft ticks have been less studied due to the specialization of Argasidae to hidden habitats (i.e. crevices) and the short time they spend for blood feeding on the host compared to hard ticks (Vial, 2009).
First they washed the `outside' of the tick, but no external virus was detected. Next, they `homogenized the larvae', and inoculated embryonic eggs, where subsequently low to moderate titers of the virus was detected.Since we've seen previous evidence of copious viral shedding via feathers (also supported by this report), this two-pronged process helped to confirm ingestion (as opposed to external contamination) of the virus.
The relatively low titers, however, were more consistent with the passive carriage, rather than replication, of the virus in the tick's gut.
The authors do suggest some ways that limited mechanical transmission of the virus - including via allopreening - might occur among birds. But how much of a factor this really is remains unknown.
It's a fascinating report, and while I've only posted the abstract and a small excerpt, is very much worth reading in its entirety.
Detection and isolation of H5N1 clade 2.3.4.4b high pathogenicity avian influenza virus from ticks (Ornithodoros maritimus) recovered from a naturally infected slender-billed gull (Chroicocephalus genei)
Dylan Andrieux, Manuela Crispo, Malorie Dirat, Laura Lebouteiller, Mathilda Walch, Emmanuel Liénard, Guillaume Croville, Maxime Fusade-Boyer, Loïc Palumbo, Julien Hirschinger, Guillaume Le Loc’h, Jean-Luc Guérin, Sébastien Soubies, Nicolas Gaide
doi: https://doi.org/10.1101/2025.11.28.689408
This article is a preprint and has not been certified by peer review
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ABSTRACT
Laridae birds, such as gulls, are known reservoirs of H13 and H16 low pathogenic avian influenza subtypes. However, during the recent outbreaks linked to the reemergence of high pathogenicity avian influenza virus (HPAIV) H5N1 clade 2.3.4.4b of the Goose/Guangdong lineage, European populations of those birds suffered significant losses. HPAI cases were registered not only along the coastlines but also inland areas, particularly in France and Central Europe.
During a diagnostic investigation of a group of Laridae birds, part of a HPAIV outbreak registered in the South of France in 2023, larval stages of Ornithodoros maritimus, a nidicolous soft tick parasitizing seabirds, were recovered from a slender-billed gull (Chroicocephalus genei).
Affected birds exhibited gross and histopathological lesions consistent with systemic HPAI infection. Immunohistochemistry revealed marked neurotropism, oculotropism and multicentric epitheliotropism. Viral isolation and sequencing analysis confirmed the presence of HPAI H5N1 clade 2.3.4.4b in both the gull and ectoparasites, showing from 98.505% to 99.989% nucleotide identity across six out of eight RNA segments.
While additional research is needed to properly assess the vector competence of O. maritimus, ticks may represent an interesting non-invasive surveillance tool for HPAIV surveillance. This is the first time a HPAIV is successfully isolated from ticks larvae. These findings represent a first step toward understanding the potential role played by ticks in the diffusion of avian influenza viruses within marine bird colonies and among other ecosystems, considering the occurrence of specific behavioral traits, such as kleptoparasitim and the position of gulls at the interface between wild and domestic species.(SNIP)
(SNIP)(Continue . . . )Additional research is needed to properly assess the vector competence of O. maritimus, both mechanically and biologically. On the one hand, mechanical transmission may result from external contamination of the tick’s rostrum or through allopreening, which can facilitate the removal of ectoparasites. On the other hand, biological transmission, which is not supported by current literature on avian influenza or our data, would require efficient viral replication within the tick.Addressing these questions would require additional studies, which are beyond the scope of this report.Our results show that ticks may represent an environmental sample of interest for HPAIV surveillance. Harvesting engorged ticks in seabird nests may be a suitable and practical method to assess the circulation of HPAIV in a bird colony. The presence of HPAIV in other tick species should also be explored to understand if their collection and testing could be used as an additional and non-invasive surveillance tool for influenza in wild birds.
