Venoms and the blood

Dani Bancroft gets to grips with the haemotoxins released by organisms to defend themselves against threats or to kill prey

The stinger of a honeybee

The stinger of a honeybee.


Spike Walker/Wellcome Images

Venom is a fluid mixture of chemicals; venoms have evolved as a defence mechanism in many different organisms. Some components of venoms, called neurotoxins, affect the nervous system (see ‘Venoms and the nervous system’); others, called haemotoxins, affect the blood.

What do haemotoxins do?

Some venoms reduce the level of clotting (coagulation) of blood, including some snake venoms (for example, those of the twig snake or boomslang). Some haemotoxins have been chemically developed into anticoagulation drugs. These can be used alongside other medications, such as aspirin and warfarin, to treat patients who have suffered a heart attack by helping to break down any blood clots.

Bee venom

A honeybee sting delivers the protein apitoxin in its venom. The pain and swelling caused by a sting is the inflammatory response of the immune system to other foreign proteins in the venom, but the haemotoxin is actually useful as it also prevents clotting and improves blood flow in the tissues surrounding the skin.

For this reason, apitoxin has been developed into a therapeutic treatment for rheumatism (a type of arthritis caused by inflammation of the joints) to relieve the painful swelling caused by the condition. By thinning the blood, the treatment improves circulation. Bee venom has also been included in small doses in some beauty products, such as anti-ageing creams.

Snake venoms

Although some venoms reduce the clotting (coagulation) of the blood, certain toxins from venomous snakes (including rattlesnakes and other vipers) trigger rapid clotting. This causes blood vessels to become blocked.

Some haemotoxins are used in medical diagnosis. The Textarin–Ecarin clotting test uses snake venom to determine the presence of anticoagulants in the blood that are produced by autoimmune diseases such as lupus. In the test, samples of a patient’s blood are exposed to the snake toxins textarin and ecarin (from the Australian brown snake and the Indian saw-scaled viper, respectively).

These toxins cause clotting by activating the clotting factor cascade (specifically prothrombin) to form multiple blood clots. The time taken for each toxin to make the blood sample solidify is measured and compared to a control. If present, lupus antibodies slow down the coagulation time and therefore provide a very sensitive indicator in the diagnosis of lupus.


Further reading

About this resource

This resource was first published in ‘Proteins’ in January 2014.

Cell biology, Health, infection and disease, Biotechnology and engineering
Education levels:
16–19, Continuing professional development