APPROACHES TO INVERTEBRATES

Transcription

1 Vet Times The website for the veterinary profession APPROACHES TO INVERTEBRATES Author : JOHN E COOPER, MARGARET E COOPER Categories : Vets Date : September 15, 2008 JOHN E COOPER, MARGARET E COOPER argue that instead of fearing insects and their ilk, it s time for veterinarians to show some backbone when treating animals without one THE invertebrates, the animals without backbones, constitute nearly 90 per cent of the animal kingdom and comprise millions of species, many of which are still unknown to science. To the veterinary profession, invertebrates have traditionally been considered as pests, parasites and intermediate hosts of parasites. The aim of most veterinary surgeons has been to kill or destroy invertebrates, with little attention usually paid to their biology or their numerous contributions to biodiversity. In the past few years, thinking has changed, and a more enlightened approach has evolved. While some taxa of invertebrates are still considered to be pests, necessitating control, there has been increased veterinary interest in studying host-to-parasite relations and in applying this information to more rational treatment strategies. Certain terrestrial species of invertebrates are important because they contribute to the well-being of humans. Examples include the honey bee (Apis mellifera), the silkworm (Bombyx mori), giant land snails (Achatina and Archachatina species) and various other edible species of insects (especially members of the Lepidoptera, Orthoptera and Isoptera orders). Veterinary attention for such species is sometimes needed. Some invertebrates benefit humans indirectly because they are managed as part of a conservation or education programme for example, the farming of butterflies or the captive breeding of endangered species of snails. These animals come under 1 / 12

2 veterinary care when they are in ill health or fail to thrive, or if, as they are in the UK, such collections are open to the public and, therefore, required by zoo legislation to be inspected 1. Invertebrates of veterinary importance The categories of terrestrial invertebrates that are of particular relevance to veterinary practitioners comprise those species that are kept as companion animals. Although there has long been interest in keeping and breeding certain insects, such as butterflies, the past few years have seen an increase in the maintenance of more exotic species, such as scorpions, mygalomorph spiders, praying mantids, giant cockroaches and tropical grasshoppers. Veterinary attention for such companion animals is increasingly sought and the profession is expected to be able to provide advice. A number of texts, books and papers have been published on the care of these creatures and new ones are appearing regularly 2, 3, 4, 5, 6, 7. Another facet of the profession s responsibility towards invertebrates is attention to the large numbers that are kept for research. Here, disease control is an essential part of good management and a prerequisite to good science. Any captive invertebrate is dependent upon its keeper, and there is a clear need to ensure not only that it remains in good health, but also that its welfare is not unduly compromised. A key part of working with such animals is for the veterinary surgeon to be familiar with their biology and natural history, and to make every effort to gain practical experience of handling them this will also impress the client. The best way of achieving this is to keep some invertebrates oneself. Management Captive invertebrates requirements vary, depending on whether they are terrestrial or aquatic, breathe atmospheric air or use gills, or live in temperate or tropical areas. Important considerations in the management of captive invertebrates are to provide the animals with: An environment that simulates their wild environment, especially the temperature, relative humidity and substrate. Desert species (such as certain scorpions) may need sand and a dry environment, while arboreal invertebrates (such as stick insects) will probably require foliage and possibly a higher relative humidity. A diet that is either natural or contains the appropriate nutrients for that species. Invertebrates vary greatly in their feeding habits. Some taxa, such as spiders, are obligate carnivores and require living prey. Others, such as the larvae of butterflies, feed only on certain plants. A few for example, cockroaches will eat a variety of different foods of both plant and animal origin. Some herbivorous species are very selective, such as larvae of certain moths that feed on only one food plant. Other Lepidoptera may be more open in their tastes and will accept a variety. If there is 2 / 12

3 doubt over the appropriate vegetation or prey species to give invertebrates, a selection should be offered. Adequate space and opportunity for the animals to perform most normal functions, including breeding. Invertebrates that can fly need to be able to do so. Spiders that build large webs should have an appropriately sized enclosure. It should be noted that record keeping is a crucial part of good invertebrate management 1 and should be coupled with a comprehensive health programme. Handling and restraint Methods of handling and restraint depend upon the species. Some invertebrates have to be manipulated with care because they are toxic or can present physical dangers. Gloves, nets and plastic or cloth bags are useful aids to handling. Restraint of invertebrates can be physical an extension of handling or chemical, using anaesthetic agents, such as isoflurane, carbon dioxide or (for aquatic species or life stages of otherwise terrestrial invertebrates) benzocaine, or tricaine methanesulphonate. Physical restraint must be carried out with care, as many invertebrate species are delicate. Some are readily damaged by a fall; rupture of the chitinous exoskeleton of spiders, for example, can lead to rapid, often fatal, loss of haemolymph 2. Lepidoptera, in particular, will readily lose limbs or surface scales if they are roughly handled. Chemical restraint often has much to commend it and can be used safely and effectively to facilitate the examination of dangerous species. Anaesthesia Anaesthesia of terrestrial invertebrates follows basic principles. Inhalation agents are generally used 8. The animal should be examined carefully before induction. An assessment of the depth of anaesthesia is often not easy. Some species and individuals will take time (hours, not minutes) to recover. Hypothermia can be used to facilitate the handling of invertebrates and to take samples, but it can prove fatal in some sensitive species, such as solifuges, and should not be employed for procedures that may cause pain. Disease control Many invertebrate diseases are recognised and these can be broadly divided into infectious and non-infectious. Often there is overlap. For example, damage to an animal s calcareous or chitinous 3 / 12

4 exoskeleton may permit the ingress of infectious agents. There are few specific therapies for infectious diseases, and exclusion of pathogens should be the aim. Non-infectious conditions are often attributable to a sub-optimal environment and attention to management can halt morbidity and/or mortality. Infectious agents that can cause disease in invertebrates include metazoan parasites (mites, hymenopterous and dipterous insects), viruses, fungi, bacteria and other organisms. Spread of pathogens is enhanced when large numbers of invertebrates are kept together such as in a laboratory or butterfly house 1. Signs of ill health in terrestrial invertebrates include anorexia, lethargy, change of colour, discharges and dysecdysis (difficulty in shedding the skin). Behavioural changes may also be seen; for example, mealworms (Tenebrio molitor) will assemble on the surface of their container if the carbon dioxide concentration is high. However, some apparently aberrant behaviour may be perfectly normal; for example, a mygalomorph spider shedding its skin may lie on its back and appear to be dead or dying. A full investigation of any incident involving morbidity or mortality of captive invertebrates must be carried out promptly and details taken of the history and method of management. The animals should be handled and examined individually. Even small invertebrates can be seen in detail using a hand lens. Clients who keep invertebrates should be encouraged to maintain detailed records and also to save shed skins and empty egg and pupal cases, so that these can be examined later by the veterinary surgeon for parasites or lesions. Exclusion of infectious diseases from collections of invertebrates hinges upon: quarantining incoming stock; isolating sick animals; and practising good hygiene. Veterinarians who deal with invertebrates, especially in large collections, should familiarise themselves with the ways in which the various pathogens can spread and infect stock, and take appropriate precautions. For example, butterfly larvae are susceptible to attack by parasitic wasps and flies, and exclusion of the adult wasps and flies is essential. This is likely to require double layers of fine netting. Eggs of incoming insects may be contaminated with microorganisms requiring them to be washed, on arrival and when transferred elsewhere, in dilute hypochlorite. 4 / 12

5 Treatment Treatment of individual invertebrates is certainly possible, but is generally restricted to larger species. Wounds can be cleaned and the escape of haemolymph can be stemmed. The administration of fluids can be a life saver, especially in spiders that rapidly become dehydrated. Minor surgery is feasible and may include amputation of limbs or debridement of wounds and infected orifices. Anaesthesia may be needed (see earlier). Little is known about the efficacy or safety of most agents that might be used to treat captive invertebrates, although some proven data is available on the use of antibiotics and certain other drugs in honey bees and a few laboratory species. Increasingly, clinical reports are appearing about the safe and apparently successful use of a variety of medicinal compounds in a range of different invertebrates6. Whenever a new product is tried, initial test therapy on a small number of animals in the group or, if there is only one patient, on some other healthy invertebrates, is advisable. Changes in management will often arrest mortality in captive invertebrates. For this reason, if a number of animals are affected, the veterinary surgeon should suggest that some are separated and kept under different conditions pending proper diagnosis. Altering the temperature, relative humidity or terrain may, in itself, prove beneficial. Hygienic precautions play an important part in disease control, especially among arthropods, where many micro-organisms are recognised pathogens. In a few cases, there may be a risk of transmission of infectious agents to the keeper. Regular cleaning of cages and removal of sloughed skins and faeces will help to minimise the risk of this or an epizootic in the animals. Care must be taken with some species; giant land snails (Achatina species), for example, appear to prefer dirty conditions and often thrive in the presence of decaying vegetation. Similarly, overripe fruit is a favoured food of adult Lepidoptera and is regularly provided in many butterfly houses. One must, therefore, be selective when implementing apparently standard hygienic measures. Diagnostic tests Swabs and brushings can be cultured or examined directly. In some cases it may be possible to withdraw blood (haemolymph) or remove biopsies. Laboratory techniques developed for work on insect pests can often be used or modified for veterinary diagnostic purposes 10. Necropsy Postmortem examination of invertebrates can prove useful and is recommended as a routine 9. 5 / 12

6 Even if the veterinary surgeon is not familiar with the pathology of the species, he or she should know something of the normal anatomy and be able to detect gross lesions, demonstrate the presence of parasites and take appropriate samples for microbiology and histopathology. Euthanasia Although individual invertebrates can be killed physically, these animals are then unsuitable for postmortem examination. It is preferable to use gaseous agents, such as isoflurane or carbon dioxide. The National Federation of Zoological Gardens (now called BIAZA) has produced guidelines on this topic and other subjects relating to the humane care of invertebrates 1. Conclusions The veterinary profession has had a rightful and long-standing concern about invertebrates as parasites and pests. Now, however, veterinary surgeons are beginning to recognise that many insects, other arthropods and molluscs are of intrinsic interest and may even be of use to the human race. The provision of medical care to such a diverse group of animals is not easy, but brings with it much interest and intellectual stimulation and the opportunity for the practitioner to contribute to new fields of animal health and welfare. References 1. Collins N M (ed; 1990). The Management and Welfare of Invertebrates in Captivity, National Federation of Zoological Gardens, London. 2. Cooper J E (1987). A veterinary approach to spiders, The Journal of Small Animal Practice 28: Cooper J E (1987). Wirbellose (Invertebraten). In Gabrisch K and Zwart, P (eds), Krankheiten der Wildtiere, Schlütersche, Hannover. 4. Cooper J E (2004). Invertebrate care, Vet Clinics Exotic Anim Pract 7: Frye F L (1992). Captive Invertebrates: A Guide to Their Biology and Husbandry, Krieger, Melbourne, Florida. 6. Lewbart G A (ed; 2006). Invertebrate Medicine, Blackwell Publishing, Ames, Iowa. 7. Williams D L (2002). Invertebrates. In Meredith A and Redrobe S (eds) Manual of Exotic Pets, BSAVA, Gloucester. 8. Cooper J E (2001). Invertebrate anesthesia, Vet Clinics Exotic Anim Pract 4: Cooper J E and Cunningham A A (1991). Pathological examination of captive invertebrates, Int Zoo Yearbook 30: Davidson E W (ed; 1981). Pathogenesis of Invertebrate Microbial Diseases, Allanheld and Osmun, Totowa, New Jersey. 6 / 12

7 Left: a tarantula (mygalomorph) spider in close proximity to the book on invertebrate medicine edited by Gregory Lewbart. Photos courtesy of MARGARET ECOOPER. 7 / 12

8 Right: spiders and other invertebrates can be given fluids using a spoon. Photos courtesy of MARGARET ECOOPER. 8 / 12

9 Butterfly houses are popular in many areas. These insects are at risk from various infectious and non-infectious diseases. 9 / 12

10 Millipedes generally fare well in captivity and feed exclusively on vegetable matter. This is a mating pair. 10 / 12

11 There are many species of giant snail. This one, from South America, lays small numbers of large eggs (see left of picture). 11 / 12

12 Powered by TCPDF ( Grasshoppers are prevalent insects. Some, such as this one, exhibit interesting morphological adaptations. All are susceptible to disease when kept in captivity, especially parasitic (nematode and protozoan) infestations. 12 / 12