Can you see my heart beating? A snake with a very big problem!

Snake transport box

I received an unusual phone call recently from the owner of an 18 month old False Water Cobra (Hydrodynastes gigas), a South American rear-fanged, mildly venomous species of snake (http://www.reptilesmagazine.com/Snake-Species/False-Water-Cobra/). The owner had noticed shortly after acquiring the snake that it had what was described as a wound on it’s underside through which you could see it’s insides! Naturally, I was quite worried so asked for the snake to be brought in for examination, and in the meantime they emailed me some photos and reassurance that the snake was acting perfectly normally, eating and defaecating fine and didn’t seem in any way bothered by the strange ‘wound’.

False Water Cobra Hospital Vivarium on AdmissionFalse Water Cobra Hospital Vivarium on Admission 1

Having examined the animal, it appeared that she had a defect in the body wall on her ventral surface or belly with a large hole visible in the ventral muscles. Bizarrely, this defect was at the level of the heart about a third of her length down her body. The only tissue separating her visibly beating heart from the outside world was a thin membranous layer of body cavity lining and some connective tissue which was quite transparent. I have seen some similar lesions in reptiles at the umbilicus or site where the blood vessels carry nutrients into the growing embryo from the egg or from maternal tissues in the case of live bearing species. Sometimes when these animals hatch or are born the hole in the body wall fails to close completely and an umbilical hernia or body wall defect is left behind. However, I have never seen or even heard of such a defect high up on the body overlying the heart! I concluded that this must be a congenital problem that the snake was born with, perhaps a fluke genetic mutation or a developmental insult during incubation of the egg which disrupted the normal growth of the embryo resulting in a physical abnormality at birth. Having spoken to a few reptile enthusiasts in the UK who keep this species of snake, it turns out there have been a few reported with the exact same defect in the exact same place, so it looks likely this is a genetic problem, most likely caused by inbreeding in certain lines due to relatively low genetic diversity in the UK population.

Snake membranous hernia before surgery

The risk of leaving the snake in this condition was that during the course of her life she may snag this fragile membrane protecting her heart and eviscerate herself or worse still puncture her heart. Although this risk was small, it would be safer to carry out a surgery now than always wonder and worry if she might do some damage and seriously injure herself, when pulling off her shed skin for example. I admitted her and set her up in our reptile ward in a heated vivarium to bring her body temperature up to preferred range. Once her temperature was correct I injected her with a combination of sedative drugs into the muscle in her back. I say I injected her, but actually I restrained her with a thick pair of gloves whilst my nurse Justyna gave her the injection. She was very feisty, strong, and objected to restraint, trying to bite the gloves. Obviously considering her potential to give a painful bite and possible envenomation we took great care at this stage. Rear fanged snakes are different to other venomous species in that they have modified salivary glands and teeth at the back of their mouth, with which they chew their prey in order to inject and subdue it. Therefore it would be difficult to get a dangerous bite  from a rear fanged species unless you allowed the snake to chew on you. Front fanged species can deliver a dry or wet bite from the front of the mouth with a rapid strike and minimal contact so are far more dangerous to work with and handle. After her injection we left her back in her hospital vivarium in the correct temperature to allow her to metabolise the drugs efficiently. Ectothermic or ‘cold-blooded’ animals such as reptiles rely on external temperature to control their biological functions and metabolic rate, so it is vital when treating ill specimens and indeed when undertaking anaesthesia and surgery to maintain their body temperature in the correct range so everything runs smoothly and drug dosages work effectively. After about a 20-30 minute induction period, now nice and relaxed after her sedation we removed her and placed her into an anaesthetic gas chamber so she fell further asleep and we could position and prepare her for surgery. She was maintained under anaesthesia by using a gas mask delivering a safe gaseous drug called Sevoflurane. Normally for a prolonged surgical procedure in a snake I would intubate the animal with a solid plastic or rubber tube placed into the windpipe or trachea for better control and access to her airway should she stop breathing for instance, but in the case of venomous species I prefer not to mess around in the mouth due to the risk of accidental envenomation. A correct sized mask with her head taped inside in place and sealing the entrance provides the next best option and is safer for all involved.

Snake anaesthesia preparing for surgery

 

Here’s a video link showing the heart visibly beating underneath the membranous layer of the abdominal wall defect:

Once Justyna prepped her with a surgical scrub and insulating layers to maintain her body temperature lying belly up on a surgical heat mat, I was ready to begin. I carefully dissected away the thin membrane covering her heart from the scales on either side of the deficit. I had to be extremely careful as this layer of tissue was so thin and the heart was literally beating against it directly underneath. Tiny blades and scissors were required, and I cut in time between the beats to avoid cutting at the moment the heart filled to maximum capacity with blood. Myself, Justyna and the veterinary student who is seeing practice with us this week to learn more about exotic pet medicine were all holding our breaths at times. Credit to the student Conor for taking the photographs while I operated by the way. Justyna found this anaesthetic very easy to monitor throughout as we were literally watching the heart beating throughout so she could record heart rate and strength with the naked eye for a change! Often we use sensitive probes to monitor heart rate through the body wall but not needed in this case.

And here is a video during the surgery when I had carefully dissected away the thin tissue revealing the heart beating underneath before I began to suture the defect closed:

Once the tissue had been separated away from the half sized scales lining either side of the lesion I set about suturing the hole back together, bringing the soft tissue of the internal body wall and the edges of the scales together to meet in the middle and form a tight seal which would heal and protect the heart and blood vessels underneath. I was quite happy with a neat and tidy job at the end. She was given a long acting pain medication and anti-inflammatory by injection, and a reversal drug for the sedatives given earlier and placed back in a clean dry cage with paper substrate to recover. We turned up the heat temporarily to boost her metabolic rate and aid her clearance of the anaesthetic drugs, and within 20 minutes she was groggy but wandering around her cage getting her bearings again. It always surprises me how tough these animals are. Reptiles have been around for millions of years and they really are quite resilient and remarkable in what they can withstand. Many of my clients fret and worry about anaesthetic risk in particular if their pet reptile needs a surgery for example. Although the general risk is higher than in dogs and cats I find them to be remarkably sturdy anaesthetic patients for the most part, so the risk is still quite low as long as you seek out an experienced and knowledgeable reptile vet.

Snake repair after closure

 

In terms of aftercare, she just needs to be kept clean and dry. No antibiotics were prescribed as it was a sterile op and good hygiene practices should prevent infection from here. Being a semi-aquatic species that likes to bathe in water, I’ve specified that she is not allowed a water dish in which she could submerge as the wound could act as an entry point for water and bacteria or other contamination into the body cavity if she submerged in the coming week or so. I will keep her in overnight and send her home tomorrow. So far she is making an excellent recovery. The sutures I placed are dissolvable over time and should slough off the next time she sheds her skin or possibly after that, so I just need to recheck her in a week to make sure the wound looks good, is healing well and is free of infection. Problem solved!

Snake in recovery

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Lungworm in dogs, but what about in reptiles?

Throughout the UK we are seeing a rise in the number of lungworm cases in dogs, which is a life threatening condition if left untreated, and is carried by slugs, snails and foxes. More information here:

http://www.richmondvets.co.uk/slugs-snails-and-puppy-dog-tales/

However, I’ve recently been asked about the risks of lungworm for pet reptiles on an exotic forum I contribute to. Some reptile keepers were discussing feeding snails to their lizards and wondered if this parasite could be passed on considering slugs and snails in the UK are the intermediate host for canine lungworm (Angiostrongylus vasorum). I have to admit my answer was I didn’t know for certain what the risk was if any, but I did know that amphibians such as frogs could act as an intermediate host when preying on infected slugs and snails. I also knew of certain other parasites of the lungs and circulatory system that specifically infect reptiles so thought I would write a short blog post to clear up any concerns.

The canine lungworm (A. vasorum) requires that the eggs shed in faeces of the primary mammalian host (dog or fox) are ingested in the environment by an intermediate mollusc host such as a slug or snail. The parasite then undergoes a further stage of development in the snail host before shedding infective cysts into the environment in the hope that these are ingested again by a canine such as a dog or fox. However, there is evidence that UK common frogs act as a host for the parasite also, either as an intermediate host like the snail or as a paratenic host depending which infective stage it becomes infected by (http://link.springer.com/article/10.1007%2FBF00931834?LI=true).

Lungworm cycle with frogThe term paratenic describes a host which is not essential for the development of the parasite, but can maintain the parasite and shed infective stages until the next part of the life cycle can resume. So in this example the snail and canine host can continue the cycle from ingestion of infective stages in frog faeces. Similarly, frogs can infect dogs directly if they are ingested. In most paratenic hosts there are no discernible ill effects of infection, as they merely act as a vector of infective stages to the required hosts by environmental transmission. However, it is well recognised in the field of parasitology that intermediate and paratenic hosts can undergo subtle changes in behaviour and physiology engineered by the parasite itself, that ultimately lead to an increased likelihood of ingestion by the definitive or primary host. So for example, it has been shown that mice (intermediate host) infected with certain nematodes show increased diurnal activity and diminished predator avoidance behaviours leading to increased death by predation in infected individuals, thus aiding transmission to the mammalian or avian predator (definitive host). For these reasons, if we can avoid infecting our captive reptile pets with potentially harmful parasites we should make a substantial effort to do so. As an aside, this was the topic for my undergraduate dissertation, so parasitology and parasite behaviour is a fascinating area for me. Here’s some amazing evolutionary adaptations of parasites and their hosts if you are interested:

http://essaybank.degree-essays.com/biology/host-behaviour-manipulation-by-helminths.php

Anyway, back to canine lungworm and feeding snails to pet reptiles, or amphibians for that matter. There have not been many studies into the effects of this parasite on reptiles mainly because there are no apparent economic reasons to undertake such studies, although it has been recognised that they can act as paratenic hosts. Because the common frog has been proven to act as both paratenic and intermediate host, presumably with the subsequent changes associated with infection above, I would warn against feeding native wild caught slugs and snails to captive reptiles and amphibians as a result. If the frog can act as both intermediate and paratenic host then it is likely that native reptiles can, and by default I would suggest that non-native amphibians and reptiles could also be at risk. The likelihood is that even if captive reptiles do not have any ill effects, over time the parasite burden may become heavy resulting in debilitation or complicating other health issues, and could even act as a reservoir of infection for dogs in the household. Equally, as the effects of infection are not known it is better to be safe than sorry, and so finding alternatives to using wild snails and slugs is probably the safest option. One method would be culturing your own mollusc supply, using either Giant African Land Snails which are readily available and easy to culture, or obtaining a supply of edible snails from the restaurant supply trade and culturing these at home as a food source for your reptile pets, many of which specialise or at least are adapted to consuming such prey in the wild. Caiman Lizards, skinks, certain Chameleons, salamanders and frogs all relish snails and slugs in their diet. If you are considering feeding such items a captive bred clean supply is probably the best source. It is also important to beware feeding wild snails and slugs due to the risk of slug bait poisons and insecticide or herbicide residues, even if you don’t use them in your own garden. You would be surprised how far a hungry slug can travel, and can’t always be sure your neighbours are as environmentally-minded or pet-conscious with their use of chemicals.
Apart from the possible risk of infection with canine lungworm, reptiles and amhibians can become infected with specialised lungworm parasites of their own leading to ill health and even death in some cases. It is important to be aware of the risk of parasites in general in captive reptiles, and routine parasite screens should be carried out on any new additions to a collection as well as annual or biannual screening tests in large collections. Protozoan infections, roundworms, tapeworms and pinworms are the most common offenders, but lungworm infections are also being diagnosed more and more frequently in the reptile trade. Reptile lungworms include Rhabdias spp. in snakes and Entamelas spp. in lizards. They are spread by direct transmission, differing from the canine lungworm in that they have no intermediate host. Eggs shed in faeces are directly infectious to the host reptile and other uninfected individuals that come in contact with this environmental contamination. Infection occurs through ingestion of faecal contaminated material or direct penetration by the larvae through the skin of the host. This mode of transmission means it is extremely easy to unwittingly spread the parasite widely through a large reptile collection. The most common findings in infected individuals are respiratory signs such as gaping, wheezing, foamy secretions from the airway and respiratory distress resulting from pneumonia. It is important to consider this parasite as a potential factor in respiratory infections that are longstanding or do not respond to standard effective treatments. As with most parasites, the eggs of the parasite are easily found on routine faecal examination or sometimes by examining saliva and respiratory secretions under the microscope. Reptiles that show these symptoms should always be isolated from healthy animals. Quarantining wild-caught or new additions to a collection is always recommended. If any of the above symptoms are noticed or if your reptile is generally unwell and fails to thrive a faecal parasite screen and examination by a competent, experienced vet is recommended.

I hope this topic was of interest and if you have any other suggestions for blog topics please leave them in the comments or on our Facebook or Twitter pages at Sean McCormack Mvb and @ExoticPetVet.

All the best,

Sean.