Anatomy of Snake Bite

The Anatomy of a snake bite in the dog….

How I do it at Serpentine Vet

Dr Belinda Beynon

Hi all, this is a summary of the way I, personally, approach dogs who have, or who MAY have been bitten by a snake. I am not saying it is the only way, or the right way, but it’s what I do, and it’s based on my years in Emergency at Murdoch, and tempered with working in the real world without all the machines that go ping.

I wrote it between 0400 and 0500 this morning, so please forgive any typos or ‘brain farts’.

Our pics below are of a patient yesterday, and show her after treatment with antivenom, and after her breathing tube was removed. You can see her tongue still isn’t working, and in her case you can see the strike location, which is actually uncommon.

In Perth and surrounds we have a multitude of snakes, many of whom are not at all venomous to us or our pets. The main three who ARE venomous are Brown snakes (Dugites), Tiger Snakes and, in the Ranges, Death Adders.

This chat will be about Browns and Tigers, and will not be super sciency.

It is a fallacy that snake bite is something that only occurs in the semi rural areas. Snakes are amazing at adapting to urban areas and can be found in most suburbs.

They are incredibly peaceful animals unless provoked. However their definition of provocation is often very different to ours.

Despite most opinions, snakes are not naturally aggressive, but can become so if they believe they are under attack or cannot escape. Anecdotally Tigers can be more aggressive than Browns, but this is a very subjective opinion.

Snakes are protected by law in WA and it is illegal to kill them.

However our pets don’t know this, and they often have a jolly good attempt at either playing with, or killing a snake, and this is when they get struck.

Let’s stick to dogs for the moment. We can talk about cats later if the interest is there. They are a wee bit different.

When a dog is struck by a snake it may either be non-envenomated (a dry strike) where the snake has struck and made contact but not released venom, it may have a ‘mild’ envenomation, where the sacs were low in quantity or quality venom, or it may receive a heavy envenomation.

The key here is that NOT ALL BITES envenomate.

Many Vets believe this is where the myth about Vitamin C curing snake bite has come from (that a dog receives a dry bite, the owners give vitamin C and voila, the dog is better). It’s wrong. It doesn’t work. Science has proved it and people need to stop.

The toxins in elapid snakes (which is what Tigers and Browns are) are similar but different. Both have neurotoxins, which causes paralysis of the muscles via loss of nerve function.

The victim dies of suffocation.

They both have procoagulants, which cause the blood to start clotting microscopically throughout the body, using up all of the clotting factors, which then causes haemorrhage anywhere at all, potentially, in the body (Browns are worse for this).

The patient dies of the bleeding…whether a mass loss (in the abdomen) or a smaller loss in a very unfortunate location (brain, heart sac, lungs etc)

Tigers also have myolysins which damage the muscle cells, causing leakage of muscle proteins (myoglobin) in to the blood and then urine via the kidneys. They caused a direct loss of smooth muscle function in a way that Browns don’t seem to.

IMPORTANT…….

If your dog vomits, passes diarrhoea, or collapses and then recovers after an interaction with a snake, then it has probably received a potentially FATAL dose of venom and needs urgent care.

If your dog is seen with a snake, but does not do any of these things, it still needs to be taken to a vet for monitoring, because even a low dose envenomation can still be fatal…..just less acutely and  dramatically, if left untreated.

In summary….

Browns: Stop breathing, cause bleeding.

Tigers: Stop breathing, cause bleeding, damage muscles.

I don’t think I’ve forgotten anything here.

The treatment of snake bite depends on whether the pet HAS BEEN envenomated, what snake is involved, how severely the dog has been envenomated.

It will involve a combination of any of the below depending on its state.

1: Patient walks in under its own steam, and clinical exam is normal:

EITHER

IV catheter placement and clotting test. If Clotting Test is prolonged, patient receives IV fluids and either a venom detection urine test (if snake not identified) followed by apporopriate antivenom, or just combined tiger brown antivenom. Multi brown is cheaper than tiger brown, so is preferred if the snake is confirmed as a brown snake.

OR

IV catheter placement and clotting test, with normal clotting test, followed by waiting and repeat clotting test in 6-8 hours. If normal then, can be discharged, was not envenomated. This option may include IV fluids the client budget permits.

2: Patient walks in and is mildly symptomatic …. examination reveals it is weak, wobbly, ataxic, decreased throat gag, decreased pupillary (eye) response, dilated pupils, ‘lower motor neuron’ signs. In this case there is NO NEED to do a clotting test on arrival.

This patient requires antivenom. If the snake is identified by the VET to be a brown, then multi brown antivenom is used. If the snake is not able to be identified then combined tiger brown antivenom is used. If the snake is identified by the VET as a Tiger then combined tiger brown antivenom is used. One to two vials may be used. IV fluids support is used, and patient is hospitalised until all the above clinical signs resolve. Clotting times will be monitored, and referral for overnight care may be needed if it’s at that end if the day. The patient is not out of danger until clotting is normal.

3:Patient is collapsed, has grey gums, may or not be breathing.

This patient does NOT need a blood test. If completely paralysed this patient needs an airway placed FIRST, and control of its airway is required. It must be breathed for manually or mechanically if it is not breathing itself. The breathing is the MOST important part. Before any tests, before any conversations, before ANYTHING else.

Then an IV Catheter will be placed…sometimes this may be needed first in order to allow sedation for airway control. These dogs are conscious and can be panicking if there is any residual muscular ability.

The patient is premeditated (to reduce risk of anaphylaxis to the antivenom)  …this is Vet preference…and TWO vials of antivenom will be administered over twenty minutes, and high levels of IV fluids given to counteract any physical shock or fluids losses from possible earlier vomiting and diarrhoea.

The airway and support will be maintained until the antivenom is effective which maybe be several hours. Some patients will require mechanical ventilation, which is a specialist procedure.

Most will not, and our staff or the owners can breathe for the Pet using the bag on the anaesthetic machine.

During this time a few additional tests may be performed depending on the dogs state and the history. IF the dog has killed the snake and it has been left at home, the owner can go home, and carefully retrieve the snake for the vet to ID.

Colour and patterns on Tigers and Browns can be very similar at different ages, stages and locations. Owners are not always right in their ID. We look at the ventral scales behind the vent. If they are divided it’s a brown snake, if they are single, it’s a Tiger.

Don’t try this at home, kids.

Cleverer vets than I can also ID using the snakes facial scales.

If the snake is not available, and it is felt that further antivenom is needed, then a venom detection test can be performed. This is a commercially available kit that uses urine, ideally. It’s a test that take up to twenty minutes to run, so you don’t use it if an animal is clinically affected without starting a multivalent antivenom first.

Some times an ultrasound might be used to check the heart sac for bleeding, the chest for bleeding or the abdomen for bleeding.

If we can obtain urine then we look for red cells versus pigment, and to ensure that we have diluted the urine significantly to protect the kidneys. This is particularly important with tiger bites as the muscle pigment released can damage the kidneys.

Once the patient can breath on its own then they don’t need manual or  mechanical support any more.

Once they are able to drink and walk they are through the worst of the event.

However until any coagulopathy has fully resolved they ARE still at risk of a bleeding event.

And in the case of Tigers some patients may suffer residual complications with their oesophagus or  gullet, such as regurgitation.

Once at this point, we will often refer to WAVES for ongoing fluids, and clotting tests, and they do FINAL discharge when the patient is safe.

And now…….the inevitable TALK.

Treating snake envenomated patients is expensive. Very expensive.

Our most recent case (pictured) came in paralysed, not breathing and cyanotic, but with a heart beat. She walked out, under her own steam, four hours later to go to WAVES for ongoing assessment of her coagulopathy and support overnight.

Her bill, with us, was enough to buy a small, old, beaten up but driveable second hand vehicle.

That cost is made up of antivenom, drugs, fluids, professional services and intensive care. For most of the four hours she was with us, we did nothing but look after her. There is an opportunity cost too, where other patients aren’t seen, in a small veterinary practice, but perhaps less so in multi vet practices.

When a dog comes in collapsed, with snake envenomation, Vets will immediately ask you about whether you want to treat. We all know that you WANT to treat, but sometimes these sorts of costs can be prohibitive. We have to ask upfront because there is no time to waste.

If, like most of us, you live paycheck to paycheck, please prepare in advance for a crisis like this, by getting preauthorisation for credit with a group like Vetpay, and check that your vet is registered with them (we are). Or have a separate credit card that is ONLY for this sort of crisis. Please don’t ask for credit from your vet.

In our case, last year, we treated three dogs at once, two of whom had been envenomated (and saved them) for a desperate client who promised us the money. We saw half of it and are still chasing the balance. We are a small family owned clinic. We can’t do it, and it’s not fair to ask small businesses to fund these emergencies for you.

We are Vets, we love the animals and we care for you, but we cannot be your bank.

Oh, a final reminder…..and this is important….

If you find your dog, collapsed on the ground near a snake….and it (the dog) looks dead, remember that IF the dog has a heartbeat then it CAN potentially be saved. Remember these guys are paralysed, NOT unconscious. They can hear you and know you are there. They can’t blink, they can’t move but they can hear and feel. If you act fast the might have a chance.

Call your vet, get someone else to drive, and give mouth to nose resuscitation to keep oxygen in the system. Hold the dogs mouth closed with your hand, place your entire mouth over the nose and blow, forcefully, every five seconds.

The toxins don’t have a direct effect on the heart, but without oxygen it will soon stop working and so will the brain.