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Thyroid hormone remained suppressed for 36 hours in dogs bitten by puff adders

Puff adder in Kruger National Park
Research · Physiology

A study of dogs naturally bitten by venomous snakes has found a rapid and prolonged change in thyroid hormone concentrations after puff adder (Bitis arietans) envenomation. In the puff adder group, total thyroxine remained significantly lower than both admission values and healthy controls 36 hours after the bite. The study was published on 21 February 2026 in the Journal of Veterinary Internal Medicine.

The researchers examined 17 privately owned dogs that had been naturally envenomed in South Africa. Eight had been bitten by puff adders and nine by snouted cobras (Naja annulifera). The dogs were compared with healthy control groups. Blood samples were taken at admission and again 12, 24 and 36 hours after envenomation.

The study focused on the body’s endocrine response to envenomation. Researchers measured total thyroxine, or TT4, which is a major thyroid hormone; thyrotropin, or TSH, which helps regulate thyroid hormone production; cortisol, an important stress hormone; and C-reactive protein, or CRP, which rises during systemic inflammation.

TT4 remained suppressed through 36 hours after puff adder bites

Across all snakebite cases, TT4 was significantly lower than in healthy control dogs at every sampling point. The puff adder group reached its lowest median TT4 concentration at 24 hours. At 36 hours, TT4 in this group was still significantly lower than at admission and significantly lower than in the healthy controls. Dogs with neurological signs after snouted cobra bites showed the same prolonged pattern, with TT4 still suppressed at 36 hours, whereas the non-neurological cobra subgroup reached its lowest values at 12 hours and had recovered to control-like levels within 24 hours.

Total thyroxine concentrations in dogs after puff adder and snouted cobra envenomation over 36 hours
Total thyroxine (TT4) remained suppressed in the puff adder group through 36 hours after envenomation. Figure 1 from Fourie-Viljoen et al. (2026), Journal of Veterinary Internal Medicine, CC BY 4.0.

Cortisol followed a different pattern. In the puff adder group, median cortisol was highest at admission and had fallen significantly by 36 hours. The strongest cortisol response in the study occurred in the subgroup of cobra-bitten dogs that showed neurological signs. Thyrotropin (TSH) did not show a clear overall difference between envenomed dogs and healthy controls, although TSH in the puff adder subgroup fell from its admission level over the following 36 hours. The authors caution that the TSH assay had limited sensitivity and several extreme outliers.

Lower TT4 was associated with stronger systemic inflammation

When all envenomed dogs were analysed together, there was a weak but statistically supported negative association between TT4 and CRP concentrations. The authors interpret this as evidence that suppression of thyroid hormone is linked to the systemic inflammatory response during acute snake envenomation. They describe the pattern as a form of endocrine disturbance associated with critical illness rather than evidence of primary thyroid disease.

The authors note several limitations, including the relatively small number of dogs, missing values at some sampling times and limited screening for concurrent illnesses. The study was also a post-hoc analysis of prospectively collected clinical data, and the original study had not included a snakebite severity score. Within the first 36 hours after envenomation, both puff adder and snouted cobra bites were associated with measurable changes in thyroid and stress-hormone responses.

Sources and image credit

  1. Fourie-Viljoen, N., Goddard, A., Thompson, P. N., Daminet, S., & Schoeman, J. P. (2026). Acute endocrine responses to snouted cobra (Naja annulifera) and African puffadder (Bitis arietans) envenomation in dogs. Journal of Veterinary Internal Medicine, 40(1), aalag005. https://doi.org/10.1093/jvimsj/aalag005Primary peer-reviewed open-access article published 21 February 2026 under CC BY 4.0. The prospective longitudinal dataset included 17 naturally envenomed client-owned dogs: eight bitten by puff adders and nine by snouted cobras. TT4 remained suppressed through 36 hours in the puff adder subgroup, and TT4 was weakly but significantly negatively correlated with CRP across cases.

Image: Tony Rebelo — puff adder (Bitis arietans) near Satara, Kruger National Park, South Africa, 8 June 2021; representative wild image, not from the canine envenomation study. Source: Wikimedia Commons. · CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ · Source

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