Bite First, Bleed Later: Philippine Pitvipers and the Hidden Dangers of Coagulotoxic Venom
The Philippines is home to a rich diversity of venomous snakes, yet almost nothing is known about how most of their venoms affect the human body. Outside of the Philippine cobra, there are no country-specific antivenoms, and treatment guidelines remain frustratingly vague. In our study, we focused on two Philippine pitvipers—Trimeresurus flavomaculatus and Trimeresurus mcgregori—to uncover what their venoms actually do in the blood, and whether any existing antivenoms can offer protection.
Venoms that make clots—and then break them
Both species’ venoms were able to clot human plasma and fibrinogen much faster than normal. At first glance this might sound like a procoagulant effect. But closer analysis revealed the opposite. The clots formed were weak and unstable, breaking down quickly and depleting fibrinogen levels. This “pseudo-procoagulant” or thrombin-like activity leaves the blood unable to clot properly, creating a net anticoagulant state. The result for a bite victim is a high risk of internal bleeding and hemorrhagic shock.
Adding to the effect, both venoms also inhibited key clotting factors—Factor IXa and Factor Xa. Of the two species, T. mcgregori proved the stronger inhibitor, suggesting it could drive victims into an even more severe anticoagulant state.
Can antivenoms help?
Since the Philippines has no antivenoms for pitviper bites, we tested cross-neutralization by antivenoms made in Thailand. Both the Green Tree PitViper Antivenom (monovalent) and the Hemato Polyvalent Antivenom (raised against several viperid species) were effective to varying degrees. Importantly, the polyvalent antivenom consistently performed better, rescuing fibrinogen clotting more strongly across both species.
This is encouraging. It means that, in the absence of a dedicated Philippine pitviper antivenom, existing Thai antivenoms could provide at least partial protection. For regions of the Philippines where these snakes are common, having access to such products could make the difference between life and death.
A neglected problem
Snakebite is a neglected tropical disease worldwide, and the Philippines illustrates why. There are more than 40 venomous snake species in the archipelago, yet the only available antivenom is for the cobra. Pitviper bites are treated under generic snakebite advisories, leaving clinicians without clear guidance and patients without effective therapy. In rural areas, people often turn to faith healers or traditional remedies simply because hospital care is too far away or too expensive.
Our findings argue strongly that this situation needs to change. At the very least, non-specific but effective antivenoms such as those from Thailand should be stocked in high-risk regions until locally tailored antivenoms can be developed.
The bigger picture
What we see in these Philippine pitvipers is another reminder that snake venoms are sophisticated, dynamic biochemical weapons. They don’t just cause clotting or bleeding in simple ways—they hijack the system, creating unstable clots that collapse into uncontrolled bleeding. For toxinologists, this is fascinating biology. For public health officials, it is a call to action.
Until the Philippines develops its own antivenoms for medically important pitvipers, cross-neutralizing products remain the only lifeline. Better reporting, stronger treatment guidelines, and improved access to effective antivenoms are essential steps if we are to reduce the hidden burden of snakebite across the islands.