Durban — The African Snakebite Institute (ASI) has provided insight into the various snakebites, the injuries they cause, the role of antivenom and its lack thereof.
The ASI revealed this in its February 2023 newsletter.
The ASI said the South African Vaccine Producers (SAVP), part of our National Health Laboratories, produces two antivenoms for snakebite – a monovalent antivenom for the venom of the boomslang, and a polyvalent antivenom which is manufactured using the venom of 10 snake species – black mamba, green mamba, East African Jameson’s mamba, snouted cobra, forest cobra, Cape cobra, Mozambique spitting cobra, rinkhals, puff adder and gaboon adder.
While the venom of the black spitting cobra, black-necked spitting cobra and zebra cobra are not part of the mix, there may be some cross-coverage for their venoms, but to what degree the polyvalent antivenom may be useful for such bites is unclear, the ASI said.
It said bites from snakes such as the common night adder, Berg adder, Bibron’s stiletto snake and the vine snake were not covered by an antivenom, and doctors treat such bites symptomatically.
“This may be problematic, and we often see severe tissue damage in Bibron’s stiletto snake bites, sometimes even resulting in the amputation of a digit or two (many victims are bitten on a finger or thumb when handling one of these snakes),” the ASI said.
It said Berg adder bites were unique as they often present as a cytotoxic bite in the early stages – pain and swelling – but then the venom affects taste and smell, vision and after a few hours breathing may be compromised. In a study of 14 Berg adder bites over more than 20 years, every victim had to be intubated and ventilated 4 to 7 hours after the bite.
The common night adder is often considered to be mildly venomous, but the venom of this snake should never be underestimated. A bite from a large individual on a small child could result in severe pain and swelling and may require hospitalisation.
“We often see dogs bitten by night adders and several dogs are killed by this snake. We recently had a case where a 19kg dog died after a bite,” the ASI said.
It said vine snakes rarely bite and spend most of their lives well-camouflaged in trees and shrubs, but if provoked, this snake will inflate the neck region and the forepart of its body and lunge out with repeated strikes.
“To date, we have not had any recorded fatalities in South Africa, but there have been a few fatal bites further north,” the ASI said.
It said vine snake venom, like boomslang venom, was potently haemotoxic, compromising the blood clotting mechanism, causing bleeding from the fang punctures, nose, mucous membranes and eventually internal bleeding and brain haemorrhaging.
It is often thought that supplementing platelets or a full blood transfusion would be sufficient treatment, but that is not necessarily the case. In a case of severe envenomation, a bite from a vine snake could be fatal, no matter what treatment is given.
“A bite from a potentially lethal snake will not automatically result in the administration of antivenom. All snakebite victims are hospitalised and carefully observed for progressive weakness, painful progressive swelling or, in the case of a boomslang or vine snake bite, bleeding. If the symptoms are severe and justify the administration of antivenom, the treating doctor will go ahead and administer antivenom intravenously via a drip. Blood is usually drawn and sent to a laboratory for analysis,” the ASI said.
It explained that in boomslang bites, patients usually receive two vials of monovalent boomslang antivenom, but in some cases, a third vial may be necessary.
Then in cytotoxic bites, such as a bite from a puff adder, doctors will usually start with 5 or 6 vials of polyvalent antivenom but in serious neurotoxic bites, such as a bite from a black mamba or Cape cobra, the patient will initially receive about 10-12 vials of polyvalent antivenom. Patients are monitored and may require more antivenom later.
Monovalent boomslang antivenom costs R6 800 per vial while polyvalent antivenom costs R2 130 per vial.
About 10% of snakebite victims who are hospitalised require and are treated with antivenom. Most of the patients have mild symptoms that do not warrant the administration of antivenom. These patients can be easily treated symptomatically, usually with pain relief and fluids to flush the kidneys.
The correct treatment for serious snakebite envenomation is antivenom. It neutralises the venom and prevents further tissue and organ damage, but does not reverse early damage done in bites from snakes with cytotoxic venom. While drugs like neostigmine may have some benefit in some neurotoxic bites, the administration of cortisone, antihistamine and substances like vitamin K have little effect initially and are certainly not lifesaving.
“While we have excellent antivenoms they have their limitations. In a recent study published by Dr George Oosthuizen and colleagues, they showed that up to four out of 10 patients treated with SAVP antivenom had a severe allergic reaction. Once a patient goes into anaphylactic shock the administration of antivenom has to be stopped immediately and the patient stabilised. This is done partially by administering adrenaline. Because of the high incidence of anaphylaxis, antivenom is only administered in a high-care unit in a hospital where a medical team can provide the necessary treatment,” the ASI said.
“While some black mamba and Cape cobra bite victims have survived without antivenom, by being intubated and ventilated, the correct treatment for a serious snakebite remains the administration of antivenom. Snake venoms are complex mixtures of toxins and when black mamba venom is described as neurotoxic, it is not only neurotoxic but primarily neurotoxic and may contain other toxins that affect other organs.”
The ASI said in serious cytotoxic envenomation, there is no other effective treatment – the patient will benefit greatly if enough antivenom is administered. Having said that, the SAVP polyvalent antivenom is not highly effective on Mozambique spitting cobra bites and many victims, even those that receive ample antivenom, suffer severe tissue damage and often need corrective surgery over the next few months following a bite.
It said while the SAVP has had production problems over the years, it ran into serious production problems early in 2022, citing power outages and supply problems as the main contributing factors. For more than six months it has been nearly impossible to purchase antivenom and this has resulted in some areas having a severe shortage.
Vets have been particularly hard hit as they often treat dogs for serious snakebites.
“The African Snakebite Institute has been inundated with calls from doctors, hospitals and vets desperately wanting to purchase antivenom, but sadly we could not always assist. This has often led to dogs dying at veterinary practices,” the ASI said.
It said the SAVP antivenom was popular throughout much of Africa and several African countries relied on antivenom purchased from South African Vaccine Producers. This has been majorly problematic and in many instances, doctors have been reluctant to use the normal dosages of antivenom when treating snakebites – not an ideal situation.
“While progress has been made to get production back to normal there is still a massive backlog and many hospitals and veterinary clinics will struggle to obtain sufficient antivenom in months to come,” the ASI said.
Would it be an option to establish alternative antivenom producers? Not easily as any new antivenom will have to be subjected to clinical trials and this takes many years and will cost millions of rand to develop.
“We receive many calls from people asking which hospitals stock antivenom. Unfortunately, we do not know as any hospital may have antivenom when we call, use it an hour later and they may not replace it for weeks,” the ASI said.
“Important! Knowing which hospital has antivenom is not important. In the event of a snakebite, get the person to the nearest hospital with a trauma unit where the patient will be stabilised. Once out of immediate danger, and this may involve intubation and ventilation, doctors can then decide whether antivenom needs to be administered and, if not available, to either transfer the patient or obtain antivenom.”
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