WHO - Health Systems and Services: Quality and Safety of Medicines - Blood Products and related Biologicals

Venomous snakes distribution and species risk categories

Global distribution of medically important venomous snakes

Figure: Global distribution of venomous snakes

Venomous snakes occur throughout many regions of the world and are a threat to public health, especially in the rural tropics where they are most abundant. Out of more than 3000 species of snakes in the world, some 600 are venomous and over 200 are considered to be medically important.  

A database and image library has been created by WHO to enable users to easily identify the most important venomous snakes in their country, territory or area; see the distributions of each species; and find information about antivenom products for treating envenoming caused by their bites. The database is accessible from the Database search option in the left hand site navigation menu.

In assessing the relative risk of each species, two major categories have been considered within the WHO Guidelines on production, control and regulation of snake antivenom immunoglobulins.

CATEGORY 1: Highest medical importance

Definition: Highly venomous snakes that are common or widespread and cause numerous snakebites, resulting in high levels of morbidity, disability or mortality.
CATEGORY 2: Secondary medical  importance

Definition: Highly venomous snakes capable of causing morbidity, disability or death,  for which exact epidemiological or clinical data may be lacking; and/or are less frequently implicated (due to their activity cycles, behavior, habitat preferences or occurrence in areas remote to large human populations).

The venomous snakes species listed as Category 1 are considered to cause the greatest burden of injury, disability and/or mortality attributable to snakebites in various countries, territories and other areas around the world. Species listed under this category within a country, territory or area should be considered as being of highest priority for antivenom production.

The distribution of snakes shown in the maps included in this website and their categorization are based on data available in published reference texts and scientific journals (see the WHO Guidelines above for a detailed bibliography) in addition to records held in museum collection databases, and information obtained from consultation with zoologists and other experts from many countries around the world. As more information becomes available, new species may be added to these lists, and/or some species, currently defined within Category 1 or Category 2 re-ranked.