Statement of the Problem

Two cats were evaluated because of aggression toward each other and their owners.

Signalment

The cats were a 2-year-old 7-kg (15.4-lb) castrated male domestic shorthair (cat 1) and a 2-year-old 4-kg (8.8-lb) castrated male domestic shorthair (cat 2).

History

The current owners of the 2 cats had adopted them at 8 weeks from different households. The owners consisted of a young couple living in a small apartment. The cats were kept indoors all the time.

Prior to the onset of the present problem, the relationship between the cats had been good, as inferred from the presence of allogrooming, allorubbing, mutual play, and a common resting location. No signs of aggression had been observed prior to the onset of the present problem.

Three episodes of aggression were initially reported by the owners. The first took place when a relative came into the house with her own cat. Cat 1 attacked the visiting cat as soon as it came out of its cage. According to the owner, cat 1 adopted a defensive posture, including an arched lateral display, flattened ears, an inverted U-shaped tail, piloerection, hissing, and a high pitch meow. The visiting cat tried to escape, showing also a defensive posture without any clear signals of aggression. The owners managed to interrupt the fight, and the visiting cat was immediately removed from the household.

The second episode took place an hour after the first, when the relative came back to the house, this time without her cat. At this time, cat 1 suddenly attacked cat 2, adopting an attitude similar to that described for the first episode. Cat 2 responded with defensive aggression, including signals such as an arched tail, piloerection, flattened ears, pupillary dilation, and hissing. The owners again managed to separate the cats and placed them in different locations within the apartment.

After 2 days, the owners tried to reintroduce the cats to each other. Initially, although no clear signs of aggression were observed, the owners described a high state of arousal and vigilant attitude in both cats. After 2 days, a loud medium- to high-frequency sound from the television triggered an aggressive reaction from cat 2 toward cat 1. The husband tried to separate the cats, and cat 2 severely attacked the wife, who was standing in the same room, but at some distance from the husband and cat 1. The cats were again separated within the apartment. After 2 weeks, cat 2 still showed clear signs of defensive aggression whenever approached by the owners, who decided to seek professional help.

Physical Examination Findings and Laboratory Results

No specific medical tests were performed at the time of the behavioral consultation. Results of a complete physical examination performed 2 months earlier prior to routine vaccination had been unremarkable.

The behavioral examination revealed that cat 2 had always reacted with aggression toward the owners in 2 contexts. After being petted for a while, the cat showed an inhibited bite and ran away. Also, the cat hid from time to time in various locations and attacked its owners' legs and ankles as they were passing by.

Diagnosis

A diagnosis of feline aggression can be made on the basis of 3 basic diagnostic criteria: target of the attacks, context in which the aggression occurs, and communicative signals during episodes of aggression.¹ The 3 episodes of aggression initially reported by the owners could be explained in terms of 2 categories of aggression: fear-related aggression and redirected aggression.¹ Regarding the first episode, territorial aggression was ruled out on the basis of the cat's posture, which was clearly defensive.

Fear-related aggression is displayed toward a social stimulus that is perceived to be a threat by the cat, whether the stimulus is indeed threatening or not. Typically the problem has an acute onset and sometimes develops in response to a single aversive event.^1,2 Redirected aggression is considered one of the most common types of aggression in cats and can be observed in any situation during which an attack is prevented or the primary target is not available.^1–3 The resultant state of aggressive arousal lasts for some time and can be easily directed to a substitute target. The most common triggering stimuli for redirected aggression are the sight, sound, or odor of an unfamiliar person or cat. Also, the occurrence of loud and high-pitched sounds has been described as a possible eliciting stimulus for redirected aggression in cats.^1–3 The differential diagnosis for redirected aggression includes pain-related aggression and organic conditions such as neurologic problems (eg, meningioma) and hormonal disorders (eg, hyperthyroidism).^4,5

To rule out medical conditions, a thorough medical examination should be performed in all cats referred because of aggression.⁵ In the present case, medical tests were postponed to avoid stressing the cats as well as to prevent new episodes of aggression that could occur if the cats had been handled by their owners or the veterinarian. All forms of aggression described by the owners of these 2 cats met well-established criteria for diagnostic categories in behavioral medicine, and episodes of aggression could be clearly linked to environmental cues. Difficulties in performing a complete medical examination in patients referred for behavioral problems have been described previously.^6–8

Although not the owners' primary complaint, the behavioral history revealed that cat 2 displayed play-related aggression and petting-related aggression. Play-related aggression is one of the more common types of aggression toward people. Attacks are usually observed when the owner passes by the cat or in response to sudden hand or leg movements.^5,9 Petting-related aggression, also called irritable aggression, is recognized by an increasing number of authors as a common form of aggression toward owners. After a period of tolerance to being petted, some cats suddenly bite the owner and jump down.⁹

Treatment and Follow-up

The unpredictable and uninhibited nature of the attacks make redirected aggression one of the most dangerous forms of feline aggression toward people.¹⁰ Redirected attacks often cause multiple and severe wounds and can be particularly hazardous for children, disabled people, and persons suffering from immunosuppressive or vascular diseases.¹⁰

Any treatment plan for cats with aggression problems must deal first with human safety. Risk factors for feline aggression include those related to the cat's behavior and those related to its social environment. Uninhibited and unpredictable attacks are particularly dangerous, especially when children are present. Consequently, in some cases, euthanasia may be the only reasonable recommendation.^11,12 Nevertheless, it is important for the attending veterinarian to analyze all possible treatment options and discuss risk factors with the owner. In the end, owners should make their decision on the basis of their level of comfort with the risk of other aggressive episodes occurring.

According to the owners' initial description, cat 2 showed a very unpredictable form of human-directed aggression. However, as a result of the behavioral history, triggering stimuli could be identified and avoided. This finding, together with the family composition, allowed the initiation of a treatment protocol that included behavior modification and use of synthetic feline pheromones.

The proposed treatment plan could be divided in 2 parts. First, recommendations were made to prevent redirected aggression and to reestablish social tolerance between the cats. Second, measures were taken to address play-related and petting-related aggression.

The owners were instructed to avoid or diminish the presence of potential arousing stimuli, such as visiting cats and loud, high-pitched sounds. Also, information about how to recognize signals of arousal and aggression, such us a stiff body posture, piloerection, tail twitching, and dilated pupils,¹³ was provided. Whenever aggression was suspected, the owners were advised to carefully isolate the cat in a dark room and avoid any kind of physical interaction until some behavior incompatible with aggression, such as eating, grooming, or resting, was observed.^1,3

A type of counterconditioning known as systematic desensitization was used to change the cats' perception of each other as a threatening stimulus. The procedure involved exposing the 2 cats to increasing levels of interaction. First, cats were separated in 2 areas and had neither physical nor visual contact. Olfactory habituation was allowed by interchanging the cat's territories from time to time and also by alternatively rubbing each cat with the same towel. After 2 weeks, when no signs of distress were observed, cats were allowed to have visual contact through a mesh door. To encourage close proximity between the cats in a positive context, highly palatable food was placed on both sides of the door. After 2 more weeks, when no indicators of anxiety were observed, the owners were instructed to remove the mesh door for progressively longer periods. Initially, whenever the door was opened, food bowls with preferred foods were placed at a distance far enough to avoid any aggression or distress response in either cat. Provided that both cats showed a relaxed attitude, food bowls were moved closer and closer until physical contact was possible. At the beginning of this stage, cats were separated as soon as food was consumed. Eventually, the time the cats were allowed to stay close to each other after eating the food was progressively increased until separation was no longer required. It was emphasized to the owners that the duration of each stage of the systematic desensitization program would depend on the progress shown by each cat, and thus could differ from 1 stage to another.

In addition to the behavior modification program, a synthetic pheromone diffuser^a was used to reduce the level of anxiety of the cats. Synthetic feline facial pheromones have proven to be effective in a variety of situations where a stress reaction is likely to be present, such as in some forms of urinary marking, hospitalization, and transportation.^14–16 Regarding play-related aggression, owners were encouraged to play more with cat 2 with interactive toys that move and stimulate chasing, stalking, pouncing, grabbing, and swatting behaviors.¹⁷

To prevent further episodes of petting-related aggression, physical contact was only allowed when the cat actively sought attention. Once initiated, all interactions had to be of short duration to prevent an aggressive response.

After 1 year of treatment, no more episodes of aggression toward people or between the cats were reported. Regarding the relationship between the cats, affiliative behaviors, such as allogrooming and allorubing, were progressively regained through the first 6 weeks of treatment. Interestingly, cat 1 showed an increased level of arousal any time someone came into the house after having been in contact with other cats. In such situations, the owners were always able to calm the cat by diverting its attention with play or food. As additional preventive measures, the owners were advised to avoid as much as possible loud and high-pitched sounds and to remind the cat-owning relative to wash her hands and change her clothes whenever she came back to the house.

Discussion

Redirected aggression is a common behavior problem that can be diagnosed only after performing a thorough behavioral examination. In the cats described in the present report, the momentary introduction of another cat was the primary cause of aggression, which induced a long-lasting social conflict between the resident cats and a problem of aggression toward the owners in 1 cat. In addition to redirected aggression, play-related aggression and petting-related aggression were identified. Multiple diagnoses of aggression are common in behavioral medicine,⁵ and each of them must be assessed independently. Once all forms of aggression have been characterized, a comprehensive treatment protocol can be designed. In this case, treatment encompassed 3 main strategies: removing or avoiding the triggering stimuli, teaching the owners to anticipate the attacks, and addressing the consequences attacks had on the social relationships between the cats and with the owners.³ Also, additional measures were taken to correct the problems of play-related and petting-related aggression.