Human Beings and Venom

Humans have had a fear of venomous animals for a very long time. In Indonesia, the slow loris is still regarded as fatal and dangerous. In some of the communities, it is believed that if the blood or semen of slow lorises touched the ground, a landslide will occur afterwards. In another region, if the lorises' placenta touches the ground, the locals believe that nothing can grow there again. In one of the Indonesian communities, before their ancestors went to war, they would smear their swords in loris blood. Apparently, this would cause their enemies' wounds to fester when they were stabbed (Nekaris, et al., 2013).

A slow loris having its teeth removed by a pet trader (Image 1).

Nowadays, venoms have the potential to be used as medicine. Vampire bat venom, because of its anticoagulant properties, is a candidate for thrombolytic therapy (treatment for heart attacks and strokes) (Ligabue-Braun, Verli, & Carlini, 2012). The most common use for venom in the medical community is for the creation of antivenom. Snake envenomation is a highly relevant public issue. It is difficult to  estimate the numbers of attacks that occur, as, in many countries, the attacks are not appropriately reported or treated. Adequate treatment is critically dependent on the ability of antivenoms to reverse venom-induced haemorrhage, hypotensive shock, coagulopathy (the inability of the blood to clot) and other symptoms. Antivenom is made by using animals (such as horses, sheep or rabbits) to produce antibodies to counteract the venom. This is done by injecting extremely small amounts of venom into the animal on a regular basis for a long period of time. After 10 to 12 months, a small portion of the animal's blood is removed and the plasma (which contains the antibodies) is extracted (Calvete, et al., 2009).

A snake being milked for venom (Image 2).

A short documentary 'The Making of Antivenom' can be watched here: http://www.biocsl.com.au/bites-app. 

References

Calvete, et al. (2009). Venoms, venomics, antivenomics. FEBS Letters , 583 (11), 1736-1743.

Ligabue-Braun, R., Verli, H., & Carlini, C. (2012). Venomous mammals: A review. Toxicon , 59, 680-695.

Nekaris, K., et al. (2013). Mad, bad and dangerous to know: the biochemistry, ecology and evolution of slow loris venom. Journal of Venomous Animals and Toxins including Tropical Diseases , 19 (21).

Images

Image 1 - http://upload.wikimedia.org/wikipedia/commons/thumb/8/8e/Nycticebus_tooth_removal_01.jpg/220px-Nycticebus_tooth_removal_01.jpg. Accessed on 12/05/14.

Image 2 - http://dxline.info/img/term/antivenin-1067_3.jpg. Accessed on 12/05/14. 

Vampire Bat Venom

The saliva of vampire bats is considered to be a subtype of venom. Common vampire bats (Desmodus rotundus), Hairy-legged vampire bats (Diphylla ecaudata) and White-winged vampire bats (Diaemus youngi) are found from Mexico to southern Argentina. They produce saliva with anticoagulant properties to help them feed on the blood of their prey (Ligabue-Braun, Verli, & Carlini, 2012).

A Common Vampire Bat (Image 1).

The purpose of the vampire bat's venom is to thin the blood of its prey and to anaethetise the area, allowing the bat to feed for extended amounts of time (up to several hours) without being noticed. It has been suggested that rather than the venom causing the painless bite, the young bats how to bite without inflicting pain through trial and error. These bats mostly feed on farm animals - such as cattle, horses, goats, pigs and sheep - but they will also feed on poultry, wild prey and humans. To reduce the risk of the bat being injured, it will normally feed when its prey is asleep. Vampire bats have large, sharp upper incisor teeth that produce a crater-like, sharply circumscribed wound that is approximately 4 mm wide. The bite is inflicted on the bare skin, with the victim's hair being combed or parted by the bat. The saliva enters the body and thins the blood, ensuring that it does not clot. The bat then uses its tongue to lap up the blood. There are two classes of anticoagulants in the vampire bat's saliva. The major class is called plasminogen activators and they produce the localised breakdown of proteins in tissue remodelling, wound healing and neuronal plasticity. This class is made up of many proteins and it is used by the bat to degrade blood clots. Besides the blood thinning effects, the vampire bat venom also causes an immune response on preys frequently fed upon (Ligabue-Braun, Verli, & Carlini, 2012).

A vampire bat feeding (Image 2).

A vampire bat's skull (Image 3).

Vampire bats have modified physiology that enables them to use blood as their only source of food and water. Their gastroesophageal-duodenal junction is T-shaped and their stomach is tubular. This allows the ingested blood to first enter the intestine and then overflow into the stomach. The stomach is used to store blood and absorb water. After the blood is ingested, most of the water is eliminated by instant urine production. The highly nitrogenous blood remains are then processed with very little water, so the bats are able to cope with high levels of urea in their urine (equivalent levels are seen in desert mammals). The bats have a reduced metabolism whilst they digest and they lack storage fat tissue, so they must feed daily to survive (Ligabue-Braun, Verli, & Carlini, 2012).

References

Ligabue-Braun, R., Verli, H., & Carlini, C. (2012). Venomous mammals: A review. Toxicon , 59, 680-695.

Images

Image 1 - http://images.nationalgeographic.com/wpf/media-live/photos/000/005/cache/common-vampire-bat_505_600x450.jpg . Accessed on 5/5/14.

Image 2 - http://i1.ytimg.com/vi/iLp-ls8AoaU/maxresdefault.jpg . Accessed on 5/5/14

Image 3 - http://www.faunaparaguay.com/Diaemus%20youngii%20skull%20lateral%20www.pybio.org.jpg . Accessed on 5/5/14.

Slow Loris Venom

Slow lorises are the only venomous primates. They do not have venom glands; instead, their saliver mixes with the secretion of their brachial glands on their arms to produce the venomous fluid. Their anterior incisors, or tooth comb, are normally used for feeding and grooming, but are also an effective venom delivery system. When threatened, the slow loris raises its arms above its head, allowing it to move its mouth to its glands to combine fluids if need be. The fluid is either applied to the top of the head for defence, or kept in the mouth to bite the threat (Nekaris, et al., 2013).

Slow loris bites are intensely painful and the wound can retain fluid, fester and heal very slowly. There is also a high chance the wound will scar. Due to the illegal pet trade in Asia, people are often bitten by slow lorises. There have been two cases where owners have almost died because they were bitten by their pet lorises. These people, who were allergic to cats, went into anaphylactic shock because the loris' gland extract shares a high degree of sequence similarity with cat allergens (Nekaris, et al., 2013).

A slow loris (Image 1).

A slow loris' brachial gland and mouth which makes up its venom system (Image 2).

A slow loris in its defensive position (Image 3).

There are many potential reasons why slow lorises use their venom. It was thought that the lorises used venom to subdue their prey; however, the lorises consume their prey very rapidly and do not appear to need venom to paralyse them. Lorises have been seen using their venom to defend against predators. Female lorises will cover their offspring with their fluid before 'parking' them for a few hours whilst they forage. The venom has also repelled cats, sun bears and civets, which are some of the slow loris' predators. Whilst the loris is going through a period of torpor, it decreases its social behaviour. Venom could provide an essential line of defence against ectoparasites during this time, as the loris is not grooming itself. Lorises may also use the venom as a seasonal, offensive weapon during the breeding season. This could explain why venom is only sometimes potent. During the few days which mating can occur, there is intense competition and feeding between males and females (Nekaris, et al., 2013).


One theory about slow lorises is that they evoled to mimic the spectacled cobra. Many animals possess protective colouration that deceives predators, but it is extremely rare in mammals. Multiple researchers have pointed out that lorises have snake-like characteristics in regards to their defensive postures and serpentine gait. Their grunt that they make during aggressive encounters also resembles the hiss of a cobra during threatening displays. Lorises also have facial markings similar to the eyespots and stripes of the spectacled cobra, and their dorsal stripes closely resembles the body of the cobra, particularly when viewed from above. It is thought that this mimicry evolved during a period of co-existance between these two species, at a time when environmental pressures would have favoured its selection. Ten million years ago, when the spectacled cobra and slow loris were moving into Asia, the climate underwent a number of fluctuations, causing a band of drier woodland to run from the Malay Peninsula down to Java, replacing the tropical forests. This change in habitat may have benefited some animals, as it made migrations easier. Being arboreal, slow lorises dislike travelling on the ground, as it increases the risk of predation. The drying out of the land forced the lorises to travel on the ground. They experienced a change in predation pressure, which caused them to develop these mimicking features to put off aerial predators (Nekaris, et al., 2013).

Potential mimicry of specatacled cobras in slow lorises (Image 4).

 References

Nekaris, K., et al. (2013). Mad, bad and dangerous to know: the biochemistry, ecology and evolution of slow loris venom. Journal of Venomous Animals and Toxins including Tropical Diseases , 19 (21).

Images

Image 1 - http://ichef.bbci.co.uk/naturelibrary/images/ic/credit/640x395/s/sl/slow_loris/slow_loris_1.jpg. Accessed on 29/4/14.

Image 2 -https://taxo4254.wikispaces.com/file/view/brachial%20gland%20and%20incisors.jpg/384315024/brachial%20gland%20and%20incisors.jpg. Accessed on 29/4/14.

Image 3 - http://www.nocturama.org/wp-content/uploads/2012/03/Nekaris_c.jpg. Accessed on 29/4/14.

Image 4 - Retrieved from Nekaris, K. et al. (2013) on 29/4/14.