Snake Envenomation

Primary reference(s)

WHO, no date. Snakebite Envenoming. World Health Organization (WHO). Accessed 5 October 2020.

Additional scientific description

Although the exact number of snake bites is unknown, an estimated 5.4 million people are bitten each year with up to 2.7 million envenomings. Around 81,000 to 138,000 people die each year because of snake bites, and around three times as many amputations and other permanent disabilities are caused by snakebites annually. Bites by venomous snakes can cause paralysis that may prevent breathing, bleeding disorders that can lead to a fatal haemorrhage, irreversible kidney failure and tissue damage that can cause permanent disability and limb amputation. Agricultural workers and children are the most affected. Children often suffer more severe effects than adults, due to their smaller body mass (WHO, 2019).

Snake venoms contain a mixture of toxins that are species-specific and tend to have a number of cellular targets in organisms exposed to them, typically prey animals. In humans and animals, snake venoms may precipitate multi-organ system failure caused by (depending on the species of snake, and the classes of toxins present in the venom) haemorrhage and prolonged disruption of haemostasis, neuromuscular paralysis, tissue necrosis, myolysis (muscle degeneration), cardiotoxicity, acute kidney injury, thrombosis, hypovolaemic shock and several other effects. When survived, snake bites may result in life-long disablement of humans (WHO, no date).

Metrics and numeric limits

In 2019, the World Health Organization (WHO) estimated that over 5.8 billion people were at risk of encountering a venomous snake, [and thus] it is not surprising but no less tragic that almost 7400 people every day are bitten by snakes, and 220 to 380 men, women and children die as a result, adding up to about 2.7 million cases of envenoming and 81,000 to 138,000 deaths per year (WHO, 2019).

The WHO has developed a strategy to reduce mortality and disability from snakebite envenoming by 50% before 2030 with a global prevention and control programme, but metrics and numerical limits are not yet defined and data are still to be collected (WHO, 2019).

Examples of drivers, outcomes and risk management

Snake bite is a neglected public health issue in many tropical and subtropical countries. Most of these snake bites occur in Africa, Asia and Latin America. In Asia up to 2 million people are envenomed by snakes each year, while in Africa there are an estimated 435,000 to 580,000 snake bites annually that need treatment. Regional engagement by the WHO has taken place and various resources are now available. 

• The guidelines for the Prevention and Clinical Management of Snakebite in Africa were developed by the WHO Regional Office of Africa with contributions from technical experts. They are meant to assist health workers to improve medical care for snakebite victims. The guidelines discuss snakes, snake venoms and snakebites and their consequences with emphasis on the medically important snakes, namely those causing serious envenoming. The volume contains over a hundred snake photographs, clinical signs of envenoming and the consequences. The guidelines also feature various annexes and in particular the geographical distribution of African venomous snakes, as well as their classification, habitats and clinical toxinology (WHO, 2010).
• The incidence of snakebite mortality is particularly high in South-East Asia. Rational use of snake anti-venom can substantially reduce mortality and morbidity due to snakebites. These guidelines are a revised and updated version of Regional Guidelines for the Management of Snakebites published by the WHO Regional Office in South-East Asia in 2011 and updated in 2016. These guidelines aim to promote the rational management of snakebite cases in various health facilities where trained health functionaries and quality snake antivenom are available (WHO, 2016). 

Envenoming affects women, children and farmers in poor rural communities in low- and middle-income countries. The highest burden occurs in countries where health systems are weakest and medical resources are sparse (WHO, 2019). An increased incidence of snakebite envenoming may be associated with the following hazards: natural disasters (floods, earthquakes, volcanic activity, typhoons, hurricanes and cyclones, landslides, tsunami events), the extractive industry (mining, forestry), and land use (agricultural activity like rice, sugar cane, oil palm, copra, rubber, tea, coffee, banana plantations and other agribusiness involving manual labour). 

In contrast to many other serious health conditions, a highly effective treatment exists for envenoming. Most deaths and serious consequences of snake bites are entirely preventable by making safe and effective antivenoms more widely available and accessible. High quality snake antivenoms are the only effective treatment to prevent or reverse most of the venomous effects of snake bites (WHO, 2019). Issues include: 

• A significant challenge in manufacturing antivenoms is the preparation of the correct immunogens (snake venoms). At present very few countries have capacity to produce snake venoms of adequate quality for antivenom manufacture, and many manufacturers rely on common commercial sources. These may not properly reflect the geographical variation that occurs in the venoms of some widespread species. In addition, lack of regulatory capacity for the control of antivenoms in countries with significant snake bite problems results in an inability to assess the quality and appropriateness of the antivenoms (WHO, 2019).
• A combination of factors has led to the present crisis. Poor data on the number and type of snake bites have led to difficulty in estimating needs, and deficient distribution policies have further contributed to manufacturers reducing or stopping production or increasing the prices of antivenoms. Poor regulation and the marketing of inappropriate or poor quality antivenoms has also resulted in a loss of confidence in some of the available antivenoms by clinicians, health managers, and patients, which has further eroded demand (WHO, 2019).
• Snake antivenom immunoglobulins (antivenoms) are the only specific treatment for envenoming by snakebites. Antivenoms can prevent or reverse most of the snakebite envenoming effects and play a crucial role in minimising mortality and morbidity. These preparations are included in the WHO List of Essential Medicines and should be part of any primary health care package where snakebites occur. Currently, there is an urgent need to ensure availability of safe, effective and affordable antivenoms, particularly to people in developing countries, and to improve the regulatory control over the manufacture, import and sale of antivenoms (WHO, 2018). 

The WHO has taken steps to raise the awareness of health authorities and policymakers on this issue. In December 2015, a programme to evaluate the potential safety and effectiveness of current antivenom products intended for use in sub-Saharan Africa was launched by the WHO. The results of this detailed technical and laboratory assessment will provide procurement agencies with informed guidance on which antivenoms best suit their needs. Following a request by several United Nations member states, the WHO formally listed snakebite envenoming as a highest priority neglected tropical disease in June 2017 (WHO, 2019).

A Snakebite Envenoming Working Group established that same year was tasked with informing the development of a strategic WHO road map on snakebites. This strategy focuses on a 50% reduction in mortality and disability caused by snakebite envenoming by 2030. This aim will be achieved through four key objectives: empower and engage communities; ensure safe, effective treatment; strengthen health systems; and increase partnerships, coordination and resources (WHO, 2019).