Behavioural changes secondary to organic diseases are relatively common and justify a careful clinical examination during a consultation for behavioural problems (Fig. 1).
In the light of the model proposed by P. Pageat, the diagnosis of a behavioural disorder is a differential diagnosis, not a “hold all” diagnosis when an organic disease cannot be identified. An organic disease should be particularly suspected when:
- a behavioural disorder appears abruptly or evolves rapidly without apparent cause;
- there is rapid exploitation of the aggressive behaviours;
- phobias appear unexpectedly, with no traumatic cause, in an adult dog;
- there is worsening of already present phobias characterized by symptoms that suddenly become “very productive”;
- the animal’s symptoms do not fit into a well-defined clinical picture or there is inconsistency in the origin of the behavioural disorder.
The veterinarian should suspect the presence of an organic disease, whose symptoms mimic a behavioural disorder, when: (i) it is not possible to make a nosographic diagnosis (name the disease), but only a functional one (the presence of a pathological state such as phobia, anxiety, depression, dysthymia and so on); (ii) the symptoms shown by the animal appear to be “inconsistent” with the normal behavioural pattern of the species under examination; and (iii) the symptoms appear “unexpectedly”, with no history of prior behavioural disorders.
In clinical practice, aggressive behaviour in the dog represents a non-pathognomonic sign of a dermatological condition. Pruritus and/or pain secondary to dermatological disorders can increase the irritability of an animal, favouring the onset of irritation- or hierarchy-elicited aggression. The animal tends to isolate itself and anticipate physical contact. The symptoms can evolve towards secondary hyper-aggressiveness (the sequence of the aggressive behaviours is altered – the intimidation phase disappears leaving only the consummatory phase) or a state of chronic depression.
INFECTIONS OF PHEROMONE-PRODUCING GLANDS
Infections of glands producing pheromones can cause the development of dog-directed aggression. The glands involved are the anal glands (in the dog, the anal sacs contain sebaceous and ceruminous glands), the para-anal glands and, in bitches, structures within the vulva. The glands that secrete pheromones play an important role in social and sexual interactions and in situations of stress (there are alarm pheromones). Fungi and bacteria normally present on the skin modify pre-pheromones (precursors of pheromones) into biologically active substances through esterification and hydrolysis. Following an inflammatory process, endocrine disease or administration of some drugs (cortisones, progestins) pheromones can be “modified” by changes in the local microflora.
After having explored the secretory areas, dogs can show irritation-elicited aggression in response to the presence of an anomalous message. In the case of inflammation of the anal sacs of a dog, other dogs living with it can mount the affected animal (in a state of sexual obnubilation: the mounting behaviour becomes extremely frequent) and attack it after having sniffed places in which the animal was crouched. Numerous studies have shown a relationship between castration and altered pheromone secretion since prolactin and testosterone control the secretion of sebaceous glands.
AGGRESSIVE BEHAVIOUR AND SENSORY DEFECTS
In clinical practice, aggressive behaviour is a non-pathognomonic sign of a sensory defect. Sight, hearing, smell, touch, and taste play very important roles in the life of animals. Numerous researchers have shown that touch and hearing can compensate, in part, for the loss of sight. In fact, in humans the senses of touch, hearing and sight allow the perceptions made with one sense to be transferred to another in order to acquire information on the surrounding environment. Animals have a mechanism that allows them to make interactions between sensory information: Stein and Meredith demonstrated that the use of one sensory system influences the perception acquired through another. For example, according to the authors, a single sense is not able to trigger a predatory response: both sight and hearing are necessary.
Sight
In humans eidola (visual hallucinations) have been described in patients with dystrophic photoreceptors. Affected people describe incongruous images superimposed on real ones; however, thanks to the important role of the cerebral cortex in humans, the individual manages not to respond to the false visual stimuli. An animal, on the other hand, treats the visual information as true and develops aggressive behaviour (irritation- or fear-elicited, small prey predatory sequence), which is unexpected and incomprehensible to the entourage. The main signs of the syndrome of visual hallucinations in dogs with dystrophic receptors are aggressive behaviour and a tendency to avoid poorly illuminated places. The dog tries to catch an imaginary, small prey, demonstrating irritation-elicited aggression towards its owners (during physical contact) which is rapidly exploited. In some cases the animal shows fear-induced aggression towards passers-by. Owners describe that the aggressive events occur more frequently at dusk, in dim places and at the border between a light area and a dim one.
Research carried out in 2002 (S. Giussani) showed that dogs are not able to manage their environment well in the 4 months following loss of vision (whether sudden or progressive). Furthermore, their relationship with their owners changes. Exploratory and aggressive behaviours (predatory, hierarchy, irritation-elicited) decrease considerably, hypervigilance appears, playing disappears, the search for physical contact increases and sleep increases. Furthermore, the animals that show stronger emotional manifestations from the start of the visual disorder seem to have greater difficulty adapting, while animals with weaker emotional manifestations seem to adapt better.
Hearing
Deafness in the dog is usually caused by cochlear disorders, probably of a genetic origin. During intrauterine life or in the first few weeks after birth cochlear degeneration may cause deafness in one or both of the ears. Numerous breeds, particularly white-coated ones, can be affected by this condition: Dalmatian, Argentine Dogo, Border Collie, etc. Other types of deafness are related to transmission defects of the external and middle ear, secondary to otitis.
Unilateral deafness does not cause behavioural changes, even if it prevents the dog from localising sources of sound correctly in the environment. Bilateral deafness induces behavioural signs related to the animal’s difficulty in collecting/transmitting auditory information. As far as concerns communicating with other dogs, an adult dog correctly socialised with other dogs will manage to receive and send the information correctly; puppies, on the other hand, should be helped because they must learn to use other senses to make up for the deficit. A puppy could be the victim of irritation-elicited aggression because the sounds it makes (barking, growling) are often not concordant with its body language. Furthermore, the lack of perception of vocal messages from other dogs (barking, growling) could induce irritation aggression in these latter. Following a traumatic experience the puppy might itself develop aggressive behaviour (which it tends to exploit rapidly) when meeting another dog. As far as concerns communication with humans, the deaf dog is not able to respond promptly and correctly to verbal requests from its owner. This can lead to punishment which becomes the basis for development of pathological relations between the animal and human. The dog can then respond with irritation-elicited aggression (which it exploits rapidly) in those occasions in which communication with the owner is incorrect.
Suggested readings
- BERNARDINI M, Neurologia del cane e del gatto, Poletto editore, 2002, Gaggiano (Mi);
COLANGELI R, GIUSSANI S, Medicina comportamentale del cane e del gatto, Poletto editore, 2005 Gaggiano (Mi); - DAMINT S, BEATA C, (2005) Endocrinology and behaviour, About Hierarchy, Behaviour and Internal Medicine ESVCE, Marseille 8 – 9 october;
- DODDS WJ, (2004) Behavioral issues and thyroiditis: theory and case review. Proceedings American Holistic Veterinary Medical Association;
- DODMAN NH, SHUSTER L, Farmacologia comportamentale veterinaria, Masson s. p. a., 2000, Milano;
- FATJO’ J., MANTECA X. (1999) “Problemas de comportamiento en perros y gatos”. Dal: Seminario Iberoamericano de Comportamiento en Perros y Gattos, Univ. de Ciencias Aplicadas y Ambientales (U.D.C.A), Facultad de Ciencias Agropecuarias, Carrera de Medicina Veterinaria - Universtad Autónoma de Barcelona (U.A.B.). 4 e 5 Novembre 1999, Santa Fe de Bogotà, D.C;
- FERRIERE C, Eduquer un chien sourd, La communication, collection Zoopsychiatrie, 2005, Solal Editeur;
- GIUSSANI S, Perte de la vision et modifications comportementales chez les carnivores domestiques, Mémoire pour l’obtention du diplome de Vétérinaire Comportementaliste del Ecoles Nationales Vétérinaires, 2002 Nantes;
- HOPKINS S.G., Schulbert T.A., Hart B.L. (1976) Castration of adult male dogs: effects on roaming, aggression, urine making and mounting;
- MEGE C, BEAUMONT – GRAFF E, BEATA C, DIAZ T, HABRAN T, MARLOIS N, MULLER G, Patologia comportamentale del cane, Masson s. p. a ed EV s. r. l., Milano/ Cremona, 2006 prima edizione;
- Neilson J.C., Eckstein, R.A., Hart B.L. (1997) Effects of castration on problem behaviors in male dogs with reference to age and duration of behavior. J Am Vet Med Assoc 1997 Jul 15;211(2);
- O'Farrell V, Peachey E.. Behavioural effects of ovariohysterectomy on bitches. J Small Anim Pract. 1990;.
- OVERALL KL, La clinica comportamentale del cane e del gatto, C. G. Edizioni Medico Scientifiche s. r. l., Torino, prima edizione italiana;
- PAGEAT P, “La patologia comportamentale del cane” – Edizione Le Point Veterinaire Italie Milano 2000;
- SALMERI, K.R., BLOOMBERG, M.S., SCRUGGS,S.L., SCHILLE, V. (1991) Gonadectomy in immature dogs: effects on skeletal, physical, and behavioural development. J. Am. Vet. Med. Assoc.