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Invertebrate medicine for the general practitioner
  1. John Chitty

Abstract

Invertebrates are routinely kept in captivity, yet are rarely presented to veterinarians, who often have limited knowledge on these species. The range of invertebrates is wide, the size is generally small, and the conservation status can often be high. This article covers the basics of invertebrate medicine, focusing on terrestrial ‘pet’ species.

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John Chitty qualified from the Royal Veterinary College in 1990 and gained an RCVS Certificate in zoological medicine in 2000. He is an RCVS Advanced Practitioner in zoological medicine and is currently the co-director of a small animal/exotics practice in Andover, Hampshire. He is the secretary of the European Association of Avian Veterinarians and is also on editorial board of the Journal of Exotic Pet Medicine.

INVERTEBRATE species are rarely presented to veterinary surgeons. This does not reflect a lack of disease in captive invertebrates and has more to do with the generally low individual cost of each individual or group of animals. There are various reasons why invertebrates kept in captivity, as summarised in Table 1.

Table 1:

Reasons for keeping invertebrates in captivity

Fig 1:

Macleay's spectre (Extatosoma tiaratum) is a robust and easy-to-handle stick insect species. For this reason, it is frequently used in zoos as a handling animal

The lack of involvement may also be a result of an overall lack of veterinary knowledge of these species and, perhaps, a perceived lack of interest by veterinarians. In addition, invertebrate welfare (except cephalopods) is not covered by any legislation in the UK; for example, invertebrates are not covered by the Veterinary Surgeons Act (1966) or the Animal Welfare Act (2007). They are, however, included in zoo legislation (Zoo Licensing Act [1981- amended 2002]) and by medicines legislation (Veterinary Medicines Regulations 2011). This does lead to some apparent discrepancies, especially in beekeeping where there is no requirement for a veterinary surgeon to diagnose a problem (in spite of them being a food-producing species), yet only a veterinary surgeon (under whose care the bees are) can prescribe prescription-only medications.

For veterinarians, one of the more daunting aspects is the sheer number and diversity of species, even though the range kept in zoos and others is miniscule in comparison to the vast number of invertebrate species. For this reason, this article will focus on ‘pet’ species and restrict itself to terrestrial species (aquatic species being the province only of specialist keepers, zoos and research establishments).

Another daunting aspect is the size of these animals. Being so small, handling may be difficult and the clinical investigations, accordingly, be limited. Additionally, veterinary surgeons should be aware that they may be presented with certain species in this group that may have high conservation value (eg, in zoos) or high financial and emotional value to owners, especially the longer-lived arachnid species.

Invertebrate pets

Invertebrates may represent a non-intensive pet that is not intrusive on owner time. There has also always been a fascination with invertebrate collecting. It has become less acceptable to kill them and pin them to boards, and so live keeping has increased. Invertebrates are often kept by children and may be deemed ‘easy to keep’, although this is often not the case. Nonetheless, as species kept to introduce children to petkeeping, they will also introduce these children to an animal's needs and welfare, and of course, to the veterinarian. However, some invertebrate species are sold as toys rather than pets, raising ethical issues regarding the role of these creatures in the pet trade.

As with reptiles, there is sometimes a ‘shock’ value to invertebrate pets, and venomous spiders or scorpions may appeal to some who hold alternative outlooks. However, clients cannot be categorised and, as mentioned earlier, these arachnids are relatively long-lived for invertebrates and owners can often form an emotional bond with these pets and be very committed to their welfare.

Husbandry and feeding

Some examples of common species kept and their needs are provided in Table 2.

Table 2:

Terrestrial invertebrate species commonly kept in the UK

Fig 2:

Madagascan hissing cockroaches. Note the presence of wood in the substrate as these are lignin feeders. Young are not born with the digestive enzyme lignase but must acquire this from ‘parents’, making these some of the few invertebrates receiving parental care. Importantly, breeders should allow eggs to develop and hatch in the main vivarium with adults

Fig 3:

Hermit crabs require water and solid ground in their vivaria. In addition, water quality must be closely monitored

In general, it is essential for owners to research the species being kept before getting it. Research should look at both the species' natural environment and diet, and experiences of other keepers. The following areas should always be looked at when designing an enclosure:

▪ Enclosure shape, size and materials (Fig 4)

▪ Heat (and gradient)

▪ Humidity (and gradient)

▪ Substrate (and animal's use of the substrate)

▪ Need for ultra-violet light

▪ Need for cover (Fig 5)

▪ Water requirement and how to provide this.

Fig 4:

Plastic pet carrier boxes kept on heat mats make excellent vivaria for ground-dwelling terrestrial invertebrates. They should be large enough for the number of animals kept and to allow sufficient environmental enrichment

Fig 5:

The importance of cover cannot be over-emphasised as many of these species are quite shy. In this case, bark and kitchen roll inners are most effective for Assassin bugs

In all cases, enclosures should be designed with the Five Freedoms in mind - particularly with respect to avoidance of fear and distress, and allowing the performance of natural behaviours. Most invertebrate species kept in captivity are predated on in the wild and this means they will require shelter and hiding places. How this is provided will depend on their natural behaviours – arboreal species (eg, stick insects) require branches to climb along with plenty of foliage, whereas leaf litter foragers (eg, millipedes) require deep litter in which to hide and forage.

Diet will always be a compromise between what the animal eats in nature, and what is easily available to the keeper. Live invertebrate food can be provided for carnivores (few adapt well to killed prey). Any uneaten prey items should always be removed from the vivarium as soon as possible – as with reptiles, prey damage is regularly seen. Live vertebrates should not be given. Herbivores should be given organic (or unsprayed ‘wild’) material – many non-organic fruit and vegetables are covered in traces of pesticides and these may have a profound effect on the insect colony. In the event of sudden-onset toxicity following addition of a contaminated foodstuff, the vivarium should be completely cleaned out and substrate changed and the affected animals thoroughly washed in a steady stream of warm water. Uneaten food should always be promptly removed to reduce the chances of vinegar fly or fruit fly ‘strike’.

Biosecurity

The investigation and control of infectious disease is discussed later. In general, it is better avoided as there is often little that can be done once an infectious agent has entered a colony. As with other species, generalisations can be made in terms of biosecurity (Box 1).

Box 1

Infectious disease preventive measures

Provide optimal husbandry and stocking rate for that species.

Provide a hygienic environment – regular cleaning will help reduce numbers of potential/ opportunistic pathogenic organisms.

Care should be taken when introducing new specimens – ideally these should be quarantined for a month before entering the environment. If in doubt, they can be washed or sprayed with disinfectant before entering the main colony.

Prey source – invertebrate prey is capable of introducing pathogens to captive invertebrates. Live prey should be obtained fresh from a single respected source.

Wash wild plant material before placing it in the vivarium.

Leaf litter is a source of wild invertebrates and pathogens – litter can be thoroughly washed and dried before use, or can be microwaved.

Handling and special risks

Handling of these species does come with some risk; however, this is species dependent. Some species are highly venomous or toxic (certain spiders, scorpions, centipedes) and simply should not be handled. Others may carry significant, though more minor, risks (Table 3).

Table 3:

Handling risks of terrestrial invertebrates

Fig 6:

(a) The urticating hair of a Chile rose spider. The barbs enable the hair to grip and ‘track’ forming a very irritating intense lesion. (b) Hair loss on the back of a South American spider, indicating excessive shedding of uriticating hairs – probably a response to over-handling or a stressful environment. South American spiders should not be handled with bare hands unless the handler is experienced and the spider very tractable; instead they should be examined in glass or clear plastic jars (or goggles should be worn)

Fig 7:

This scorpion needs handling with great care – the small claws indicate it is likely to harbour a potent venom in the sting which is restrained with forceps. Ideally, the forcep tips should be padded

Examination and history taking

Examination and history taking can be particularly problematic compared to other species groups; however, some things are similar. A history should always be taken (Table 4). Clinical examination can be greatly facilitated by using magnification. This will enable a thorough examination of the external surface. In most species, it is impossible to do more in the conscious animal. Palpation is rarely possible either in small delicate species or those protected by a rigid exoskeleton. Isoflurane anaesthesia may enable some examination of orifices, dangerous species or those parts protected by curling or by joints (eg, the ventral surface of a millipede). Further investigations can be carried out in some species (Table 5).

Table 4:

Relevant aspects of clinical history

Table 5:

Further investigations used in invertebrate medicine

Fig 8:

Barium study in a giant African land snail. (Photograph: David Williams and Jo Astrup)

Anaesthesia

For terrestrial species, the simplest means of anaesthesia is to place the invertebrate into a secure scavenged chamber and use isoflurane. Induction will often take 20 to 30 minutes and recovery will appear prolonged. Monitoring is difficult, although an 8 MHz Doppler probe has been used to monitor anaesthetic depth in snails (Fig 9).

Fig 9:

Use of a 8 MHz Doppler probe to monitor anaesthesia in a giant land snail

Surgery

Limited surgery is possible in invertebrate species. For the most part, surgery is limited to repair of injuries in larger specimens.

Wound and shell repair

Initially, the aim is to reduce loss of haemolymph (the fluid in the open circulatory system of arthropods and insects) – simple pressure with a cotton bud may help. For shallow wounds, topical antibiotic powders or suspensions may be applied. For deeper wounds, the animal should be anaesthetised and the defect closed using tissue glue (or in spiders even sutures – 8/0 or 5/0 monofilament sutures are recommended. These should be removed after four weeks, or sooner if the animal shows signs of going into shed).

In snails, shell damage may be repaired using tissue glue or epoxy resin; anaesthesia is not usually required. For a harder repair, alternate layers of baking soda and super glue should be applied. This gives a good cosmetic and hard-wearing repair.

Many wounds are actually the result of poor husbandry and these issues should also be corrected. With spiders, climbing areas should be avoided to ensure the animal does not fall and ‘split’. With snails, shell quality may be affected by diet. In large groups, some individuals, if ‘calcium-deficient’, will rasp the shell of others, producing lesions or thinning the shell so that it is easily damaged.

Limb damage

Damaged limbs can be autotomised in many ‘soft’ species, although the technique is best described in spiders. It does not appear appropriate in those with hard exoskeletons. It should be performed in conscious animals as part of the autotomy is an active casting off of the limb. In essence, the limb should be grasped near its base with forceps and pulled sharply. The limb will normally grow back.

In species that do not autotomise, damaged limbs can still be removed in the same fashion. However, the animal should be anaesthetised first and the open wound closed to avoid excessive loss of haemolymph.

Dysecdysis (shedding)

Dysecdysis is commonly a reason for contacting a vet. Normally, involves an upside-down spider and there is no actual problem, although the situation should be closely monitored. Otherwise, the shedding process may seem to be occurring slowly but, again, usually there is no actual problem as shedding may take several days.

On occasion, shedding may go wrong – several limbs may be observed to have shed the exoskeleton while one may not have. Intervention should be attempted with care. If just one limb is affected, it can be autotomised and may then grow back. If larger areas are affected, then soaking of the animal combined with gentle teasing away of the retained material may help. However, this should be done with great care as the new exoskeleton will be soft and easily damaged (Fig 10).

Fig 10:

The recently shed cockroach is easily visible; the skeleton will harden and colour-up over the next few days. However, at this stage the new exoskeleton is very soft and easily damaged

Fluid therapy

Oral fluids can be very effective - simply placing the animal in a shallow (covered) dish of warm water will give it the opportunity to drink. Alternatively, spiders can be given small pieces of soaked sponge or gauze. Plain water is generally effective, although hypotonic or isotonic Hartmann's solution can also be used via leg or body. It is appropriate to use standard isotonic fluids at a rate of 20 ml/kg as a bolus. In general, the author will use Hartmann's solution (Fig 11).

Fig 11:

Injecting fluids into spider haemolymph. By preference, the limb is used rather than the body to avoid hitting the heart (which sits in the dorsal coelomic cavity). After placement of the needle, a few drops of haemolymph can also be extracted for culture/cytology

Parasite control

Ectoparasites

Many ectoparasites are actually commensal species and removing them may lead to problems. For example, the mites found on millipedes are of great benefit as they feed on accumulated debris around the millipede's joints. Removal of the mites results in excessive build-up of debris and fungal/bacterial infections. In other species, for example spiders, they are of little or no harm and the difficulties in removing the mites may outweigh the advantages. It is also important to check that the mites seen are genuinely ectoparasites and not simply environmental or forage mites. It is also worth checking that what might be thought to be parasites are not, in fact, something else (Fig 12).

Fig 12.

These were found moving (in large numbers) in a Partula snail colony vivarium. It was initially suspected these 3 to 7 mm strands were parasitic or environmental worms. However, investigation revealed them to be discarded ‘love darts’ left after mating. The movement was due to contraction of the protein strands, making the darts appear to wriggle

Therapy

A simple environmental change will often remove the bulk of the mites. Otherwise:

▪ Arachnids – obviously, chemicals cannot be used as the host and parasites are related. In these cases, environmental changes should be combined with manual removal of mites using a soft brush. Anaesthesia of the spider will greatly assist this process.

▪ Insects – use of environmental change plus flumethrin strips (Bayvarol; Bayer) is effective. The strips should be placed on the floor of the vivarium, but should not cover more than 50 per cent of the surface area.

Myiasis

Fly strike is usually caused by a build up of uneaten food in the vivarium. However, the invertebrates will rapidly become struck and rarely survive. A full environmental change should be instigated as soon as possible. Struck invertebrates should be culled if severely affected. If the larvae have not penetrated the cuticle of the host, they may be washed off or physically removed. However, the affected host should be maintained in a separate vivarium until you are sure there are no more maggots on or in the host.

Endoparasites

Endoparasites may be a cause of wasting, especially in spiders. Diagnosis is by clinical signs and the finding of ova/larvae in faeces. Concerned owners often contact a vet regarding nematodes found in the environment. These are rarely of clinical concern other than indicating possible environment unsuitability – a complete environmental change is indicated.

Therapy

Avermectins should not be used. However, benzimidazoles may be appropriate. The author uses oxfendazole (Bovex; Chanelle) at the rate of one drop per spider.

Infectious diseases

It must first be decided whether or not the disease is truly infectious. In most cases, high morbidity or mortality represents defects in the environment or husbandry. A full history should be taken and faults corrected before the conclusion is drawn that the problems are genuinely infectious.

In infectious disease cases, the stocking rate should be considered. There are rarely set recommendations for stocking rates; however, it is often fairly obvious that extremely large numbers of animals are being kept in a restricted environment.

Other aspects that should be considered in the history include:

▪ Hygiene. Consider frequency of cleaning out and disinfection methods used. Compare the owner's description with the current appearance of the vivarium.

▪ Recent introductions of animals, especially if obtained from dealers/pet shops.

If infectious disease is suspected, affected animals should be culled and submitted for examination, namely:

▪ Histopathology. Place entire animals in alcohol (open the body cavity of large animals).

▪ Cytology (Fig 13). If lesions are present, these may be sampled directly.

▪ Virology. Whole animals may be submitted for electron microscopy.

▪ Bacterial culture. Whole animals may be submitted. However, in larger invertebrates, swabs may be taken from mouth and/or cloaca.

Fig 13.

Spider haemocytes (from haemolymph) – the appearance of these cells can vary greatly and the presence of ‘free’ bacteria may also be normal. However, observing phagocytosis of bacteria by these cells may indicate systemic infection

The problem with sampling is that normal commensal organisms are rarely understood, which makes the finding of bacteria/viruses harder to interpret. Also, many of the ‘pathogens’ are in fact opportunistic environmental organisms. For these reasons, histopathology is essential in placing the cultured organisms with lesions. Nonetheless, many apparent infections remain hard to type and, therefore, treat.

In an ‘outbreak’, unaffected animals should be separated and monitored closely. Spraying with non-irritant disinfectant (eg, F10SC [Health & Hygiene]) 1:500 dilution may help (Fig 14).

Fig 14:

A Macleay's spectre stick insect with brown stains on the cutice and around the joints, representing fungal infections (determined by cytology). Control in the colony was by environmental changing/disinfection, culling of severely affected individuals and spraying the others with dilute F10 SC (1:500) every two to three days

In valuable individuals (ie, those with emotional or financial value), broad-spectrum antibiotics may be used. The author generally uses either marbofloxacin at 5 mg/kg intracoelomic or orally daily, or trimethoprim-sulphonamide orally or intracoelomic at 30 mg/kg daily. In fungal disease, itraconazole may be used orally at 10 mg/kg daily.

Summary

There is little information available on the treatment of pet invertebrate species. However, these may represent the first species kept by a child and it is important that veterinarians show an interest and provide what help they can. Basic investigation techniques used in other exotic species along with some specific species knowledge can enable treatment or correction of faulty husbandry, which is often the root of the problems.

Further information and reading

As described, there is little specific information available on these species. However, a body of information is growing and the following may contain useful information. The book ‘Invertebrate Medicine’, edited by G. A. Lewbart (2012) is particularly recommended to anyone developing an interest in this area.

There are many books aimed at the keeper – many are highly anecdotal; however, Krieger publish some excellent texts and anything by Chris Mattison can be recommended.

A number of journals regularly publish invertebrate-related papers, eg, Veterinary Clinics of North America. Exotic Animal Practice, Exotic DVM, and Journal of Exotic Pet Medicine.

There are also groups producing useful, particularly management guidelines for livefood species, and on invertebrate euthanasia: Zoo Working Groups/TAGs (eg Terrestrial Invertebrate Working Group in UK [via www.biaza.org.uk] and Terrestrial Invertebrate Taxon Advisory Group [TITAG] in Europe [www.eaza.net]).

The Veterinary Invertebrate Society has been inactive for several years. However, recent attempts have been made to revive this group and its journal. Readers interested in joining (or providing material and case studies for inclusion in the journal) can contact the author.

References

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