Estudio comparativo de los trastornos de ansiedad entre los perros y los humanos

Arbaizar B. Psiquiatria.com. 2011; 15:18.
http://hdl.handle.net/10401/4070

Revisión teórica
A brief look of comparative anxiety disorders: from dogs
to humans
Estudio comparativo de los trastornos de ansiedad entre los perros y los humanos

Beatriz Arbaizar1*, Javier Llorca2*

Resumen
Los trastornos de ansiedad son la patología mental más común en los seres humanos, e incluyen
la ansiedad de separación, las fobias específicas, y el trastorno obsesivo-compulsivo entre otros.
En perros la ansiedad de separación y las fobias a las tormentas y a los ruidos intensos son
relativamente frecuentes y parecen fenotípicamente similares a los que se ven en humanos. En
los perros como en los humanos con ansiedad de separación o fobias se aprecian los mismos
fenómenos de activación autonómica al encarar el estimulo fóbico, también en las dos especies
el trastorno obsesivo-compulsivo esta caracterizado por conductas repetitivas; es más parece
que comparten mecanismos neurobiológicos similares como es la participación del circuito
amigdalino, así como ciertos tipos de polimorfismos genéticos implicados en el metabolismo de
los neurotransmisores. En ambas especies hay también una alta co-morbilidad entre los
diferentes trastornos de ansiedad. En humanos los alelos que confieren una elevada
susceptibilidad para los diferentes trastornos a menudo están distribuidos irregularmente en la
población; los perros domésticos han sido recientemente seleccionados en más de 350
subespecies ofreciendo la ventaja de la concentración en la distribución de los halotipos cara al
estudio de los diferentes polimorfismos asociados a determinados trastornos. Concluyendo las
similitudes en los fenotipos sugiere que el estudio de los trastornos de ansiedad en perros puede
ayudarnos a profundizar en el conocimiento sobre los trastornos de ansiedad en humanos, a la
vez que apunta hacia unos posibles mecanismos neurobiológicos similares.
Palabras claves: Trastornos de ansiedad, fobias, estudios comparativos.
Abstract
Anxiety disorders are the most prevalent disorders in human beings. They include separation
anxiety disorder, specific phobias, compulsive disorders, and others. In dogs, separation anxiety
and phobias -thunderstorm or noise phobias, for instance- are also a frequent condition, and
seem to be phenotypically similar to anxiety disorders in humans. Human beings and dogs with
separation anxiety or phobias share autonomic activation when facing the stimuli, while
compulsive disorders are characterized by repetitive behavior in both species. Moreover, there
seem to be certain similarities in the neurologic mechanisms involved, such as amygdale
circuitry, and also in some genetic polymorphisms involved in the metabolism of neurotransmitters. In both species, a high co-morbidity occurs within the respective groups of anxiety
disorders. Alleles that elevate the susceptibility to certain diseases in humans are often
irregularly distributed. Domestic dogs have been recently selected in over 350 breeds, giving rise
to a narrow haplotype structure which is an added advantage in the study of the different
polymorphisms associated with several disorders. In conclusion, similarities in phenotype
suggest that a study of anxiety disorders in dogs would allow a deeper knowledge of anxiety

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Arbaizar B. Psiquiatria.com. 2011; 15:18.
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disorders in human beings, and that their respective anxiety disorder group could have the same
neurobiological underlying mechanisms.
Palabras claves: Anxiety disorders, phobias, comparative studies.

Recibido: 19/04/2011 ­ Aceptado: 23/04/2011 ­ Publicado: 26/07/2011

* Correspondencia: barbaizar@humv.es, llorcaj@unican.es
1 Unidad de Salud Mental "López Albo - II", C/ Vargas-57, 39010-Santander, Spain.
2 CIBER Epidemiología y Salud Pública (CIBERESP), Spain; Division of Epidemiology and Computational
Biology, University of Cantabria, Facultad de Medicina, Avda. Herrera Oria s/n, 39011-Santander, Spain;
and IFIMAV, Santander, Spain.

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1. Introduction
Anxiety disorders are the most common disorders in human adults, adolescents and children
[1]; they include panic disorder, agoraphobia, social phobia, specific phobias, obsessivecompulsive disorder, generalized anxiety disorder, separation anxiety disorder and others. An
increased physiological reactivity when facing novel stimuli or challenging situations is a
common epiphenomenum to phobic stimuli; while "behavioral inhibition" is a well established
risk factor for anxiety disorders, and might be a manifestation of a biological predisposition.
Dogs also suffer anxiety disorders; furthermore, separation anxiety, thunderstorm phobia, noise
phobia and compulsive behavior also seem to be the most common diseases in dogs [2]. Anxiety
disorders appear to be phenotypically similar in dogs and human beings [3]; therefore, it could
be expected that studying anxiety disorders in dogs will enlighten this group of diseases in
humans.
In this paper, we revised the similarities and differences in anxiety disorders between human
beings and dogs.

2. Diagnostic

2.1 Anxiety disorder in humans
Separation Anxiety Disorder (SAD) is defined as the development of excessive anxiety
concerning separation from home or from those the individual is attached to [4].
Specific phobias are divided [4] into:
·

Animal type
· Natural environmental type (heights, storms, water)
·Blood-injury type
·Situational type (elevators, airplanes)
·Other types (like loud sounds in children)

Obsessive-compulsive Disorder (OCD) is composed of obsessions: persistent thoughts, impulses
or images. Compulsions are repetitive behaviors or mental acts [4].

2.2 Canine separation anxiety
Dogs suffering separation anxiety exhibit considerable distress when they are separated from
their owner or are left alone. Canine responses to this comprise elimination, vocalization,
destruction, increased or decreased psychomotor activity, withdrawal, self-mutilation [3].
Separation anxiety can be the cause of some aggressive behaviors in order to prevent the owner's
departure. Dogs reach social maturity within a range of 12-36 months; separation anxiety can
appear in dogs at any age, although separation anxiety diagnosis in dogs does not occur until 6

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months because some separation distress over the weaning epoch is normal [5]. The median age
of the onset of separation anxiety in dogs is over 1.5 years [6].

2.3 Canine thunderstorm and noise phobias
Dogs with thunderstorm and noise phobia present in front of the stimulus or the anticipated
stimulus the classical reaction of fear with both physiological and behavior signs of anxiety: 1)
physiologic signs of autonomic activation, such as increased respiratory and heart rates,
increased salivation, gastrointestinal disturbances, and 2) a behavior response usually
associated with escape, avoidance or defensiveness (e.g. restlessness, paralysis, pacing, circling)
[5].

2.4 Canine compulsive behavior
Canine OCD includes repetitive ritualistic behaviors like tail-chasing, pica, self-mutilation, hairbiting, etc. Compulsive behaviors usually appear in dogs with social maturity. Pica is one of the
most frequent compulsive behaviors in dogs; it is present when the dog chooses objects without
alimentary values as the main activity disregarding other activities [2]. The cognitive aspect of
OCD cannot be evaluated in dogs. Compulsive behavior is most often found in certain dog
breeds such as bullterriers and similar breeds [3].

3. Epidemiology

3.1 Anxiety disorder in humans
The SAD prevalence rate is about 3.5%. The rate of specific phobia in humans is about 10%. The
OCD rate is about 1.7%. The data supporting that anxiety disorders are a unique category are the
high comorbidity between the different anxiety disorders; in fact, Separation Anxiety Disorder
can predict future anxiety disorders [7]. Anxiety disorders have a high risk of concurrence [8];
controlled studies have shown an association between Co2 hypersensitivity with SAD and Panic
Disorder(PD) [9][10]. It seems to suggest that the two affections can share the same latent factor
that produces both phenotypes [10].
SAD is mainly a diagnostic of children and adolescents, because it has to occur before 18 years
old; however, it has been recently identified at older ages [11]; specific phobia in human beings
is a diagnostic of middle childhood; compulsive behavior often appears in teenagers and mild­
life and its course is often chronic [3].

3.2 Canine epidemiology
Separation anxiety in dogs seems a common disorder; it is present in about 14-17% of dogs that
are brought to veterinary clinics in USA, and about 20% in United Kingdom [5]. Dogs that come
from a single owner seem to be 2.5 times more likely to suffer separation anxiety than those that
come from a home with multiple owners [12].

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88% of dogs with noise phobia and 86% of dogs with thunderstorm phobia also develop
separation anxiety; dogs with separation anxiety are more likely to present noise phobia (63%),
thunderstorm phobia (52%); a dog with a thunderstorm phobia has a 90% probability of
experiencing noise phobia; and the probability that a dog with noise phobia would have a cooccurring thunderstorm phobia is 76% [13]. The owners of dogs that present less disruptive
behaviors as response to stress (e.g. withdrawal, inactivity, or salivation) would be unlikely to be
seeking help [13]. The most disruptive behaviors may adversely affect the owner-dog bond, with
the dog ending in a shelter or even being euthanized.
Separation anxiety in dogs may occur at any age, the median age of onset in dogs being over 1.5
years [6]; 40% of thunderstorm phobia diagnostics in dogs are made earlier, within the first year
of life, and only 10% are made in dogs of 5 or more years of age [14]. Compulsive behaviors
usually appear in dogs with social maturity.

4. Etiology

4.1 Etiology in humans
Anxiety in human beings and dogs appears as a multifactorial disorder [3]. Sometimes, a
compulsive behavior has several mechanisms (i.e.: disorders are multicausal) [3]; on the other
hand, the same neurochemical factors in the presence of different environmental factors can
display different phenotypes (i.e.: causes are non specific) [3].

4.1.1 Biological model
Genetic contributions seem to play only a moderate role in anxiety disorders [15]. Some studies
propose that persons can exhibit behavioral inhibition when facing new people and situations;
these persons display similar temperamental aspects to patients that will develop anxiety
disorders [7]. Moreover, functional Magnetic Resonance Image studies have shown
hyperreactivity of the amygdale and its projections to the striatum, hypothalamus, sympathetic
chain and cardiovascular system in young and teenagers with behavioral inhibition [16].
Neurobiological factors: Some studies have shown that children experiencing parental death
and separation /desertion have a greater likelihood of presenting anxiety disorders or
depressive symptoms. However, separation/desertion is associated with other factors (for
example, neurobiological factors like a family history of anxiety and depressive disorders, and
social factors such as low socio-economical status) which can themselves increase the
probability of anxiety disorders; therefore, parental death may be the specific risk factor for
anxiety and depressive symptoms [17].
Neuroanatomical contributions suggest there is an important role played by amygdale and its
circuitry in the development of conditioning fear [18]. Neurochemical contributions would also
be involved in the development of anxiety disorder; e.g.: some alterations in serotonin,
norepinephrine, dopamine, and -aminobutyric acid [19]. Polymorphisms involved in the 5-HT
system, particularly the 5-HTTLPR genotype in the 5-HT transporter polymorphic region, NA
polymorphisms and some genotypes involved in DA function, specifically genes which code D2
and D4 receptors, seem involved in the avoidance process [20][21].

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4.1.2 Learning Theory
Raschman's theory suggests three, often overlapping, learning experiences in the development
of phobias: (a) aversive classical conditioning, (b) modeling, and (c) instruction/information
transfer; however, in some phobias, such as water phobia, these mechanisms cannot be found in
most of the patients affected. Animal phobias are very common (e.g. phobias to spiders, snakes,
or dogs); most people who develop an animal phobia have not had a previous traumatic
experience. The learning model proposes the concept of latent inhibition: people approach a
new stimulus with a prior history of associations involving the previous stimulus, and these
previous associations are determining depending on whether subsequent conditioning occurs or
not (neo-conditioning theories) [22].

4.1.3 Cognitive model
The cognitive model offers the cognitive vulnerability theory as a factor for animal phobias; in
this, the perception of the animal as uncontrollable, unpredictable, dangerous, and disgusting
may have a role in the phobia development [22].

4.1.4 Evolutionary approach
Evolutionary psychologists think that virtually universal behaviors, such as fear of snakes and
spiders, are the result of evolved adaptations. The evolutionary point of view suggests that
specific phobias, such as water, separation, spiders, heights, etc., can emerge as advantages to
our prehistoric ancestor's survivorship [23].

4.2 Canine etiology

4.2.1 Biological model
Riva et al [24] found higher levels of DA and 5HT in plasma and lower levels of 5HT in platelets
in dogs with anxiety disorders.
Thunderstorm ­ phobic dogs present an increased heart rate and also a hypothalamic-pituitaryadrenal (HPT) activation in response to stress [25]. The owners do not present HPT activation
and the dog response does not seem to be influenced by the owner-dog quality relation, but the
presence in the household of other dogs seems to facilitate the lower reactivity and the fastest
HPT recovery [26]. Thunderstorm phobia is usually associated, as in human beings, to other
anxiety disorders [13].

4.2.2 Selection approach
The domestic dog, Canis lupus familiaris, comes from the gray wolf, Canis lupus. The
domestication of the gray wolf took place between 15,000 and 40,000 years ago in central Asia.

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Dog quickly spread around the world [27]. Dogs present some behaviors and dispositions
inherited from wolves, but many of their behaviors and predispositions have been constituted by
mankind's selective breeding [28]. Dogs have shown that they have the ability to learn by simple
reinforcement like classical and operant conditioning and also by observation­imitation [28].
There are at least 350 breeds throughout the world; most of them being developed in Europe in
the last 330 years. Dogs present a wide phenotypic variation as a result of restricted gene flow
and generations of high artificial selection for several specific activities such as hunting,
sheepdog, etc [29].
Affiliative behavior facilitates proximity and intimate social interaction. Social behavior in dogs
reflects their descent from wolves which have a highly structured social organization;
domestication has probably selected these social skills that are very important for the success of
the species as is cohesion [30]. The domestication process has selected characteristics of
juvenile behavior and dependence on parental figures; as a result, adult dogs also present these
behavioral trends [31].
Alleles that promote disease susceptibility are usually irregularly distributed in human beings.
Nevertheless, domestic dogs have been recently selected in breeds, which has caused a very
restrained haplotype structure; the study of different polymorphisms in dogs associated to a
particular disorder can be an advantage; furthermore, some disorder susceptibilities are
associated with several dog breeds (i.e.: compulsive disorder, cardiomyopathies, dislocation of
the hip) [27].

4.2.3 Environment factors
Some factors that can promote separation anxiety can be: strong attachment to the owner,
separation from the owner, and moving house. Dogs that come from a shelter appear to be more
prone to developing separation anxiety than those from breeders [32]. Primary attachment and
its consecutive bonding in mammals establishes a secure base where the dogs experience selfconfidence and can explore their environment [33]; feelings of security and comfort later come
up against opposite needs -such as contact with other colleagues- and a more independent
behavior progressively emerges [34]. The persistence of this primary attachment and its
immaturity characteristics beyond puberty can give rise to separation anxiety. Secondary
attachment can occur at any age in certain circumstances such as, for example, the loss of the
primary attachment figure [35]. Dogs have probably been selected on the basis of their
affectionate and socially dependent behavior [36], although owners can unwittingly facilitate
dependent behavior by reinforcement of care-soliciting behaviors [37].
Separation anxiety in dogs could be currently facilitated by our lifestyle: long owner work days,
single-individual, scarce interdog interactions [5]. Dogs could exhibit primary hyperattachment
with the owner if they maintain the puppy-like behavior patterns and a secondary
hyperattachment when, after developing as normal dogs, a change such as owner long-absence
or moving to a new house is produced [5]. Separation anxiety in dogs seems to have an
environmental factor link to the familiarity of the place: dogs placed in their usual environment
express vocalizations of distress, which is inhibited when in an unknown place [38]. The
compulsive behaviors in humans also seem to be inhibited in unknown places.

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5. Treatment
In both humans and dogs, anxiety disorders seem to have a good therapeutic response to
behavioral­cognitive therapy and selective serotonin reuptake inhibitors (SSRI) [3].
Clomipramine has been used in the treatment of separation anxiety, OCD, and noise phobia
with good results [39].
Behavior treatment in dogs includes: ignoring attention-seeking behavior, stimulating
independent behavior, reducing physical contact, and breaking the bond [40].

6. Discussion
Transmission of cultural knowledge requires the ability to identify relevant information to
retain, and selectively imitation of other partner skills. Dogs, like children, can exhibit
inferential selective imitation [41].
Curiously, one of the most common fears of children is that of loud noises [42]. The
characteristics of the noise, such as its unpredictability, appear as important factors in noise and
thunderstorm phobias in dogs [13], and are probably an important factor in child noise phobias.
The affiliative behavior selected during the domestication process of dogs promotes dependence
of parental figures, and there could be a certain similarity with the behavioral inhibition
proposed as a temperamental factor in the development of anxiety disorders in humans.
One of the specific skills that allowed dogs to adapt and become integrated in human social
groups is that they are able to recognize behavioral features characterizing human visual
attention [43][44]. Perhaps the study of this could help us to understand why dog behavior can
be used as an analog model of corresponding human behavior [45] and, specifically, why phobia
in dogs is so similar to phobia in humans.
Summarizing, anxiety disorders in dogs and human beings not only seem analogous but
probably homologous. It seems that anxiety disorders in humans and dogs are, in fact,
multifactorial: anxiety disorders in humans and separation anxiety, noise and thunderstorm
phobia could have the same neurobiological underlying mechanisms and different phenotypes
as a result of different environments and other factors.

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Correspondencia:
Javier Llorca
Facultad de Medicina
Avda. Herrera Oria s/n
39011 Santander. España.
Tel. 34-942201993
Fax. 34-942201903
E-mail: llorcaj@unican.es

Cite este artículo de la siguiente forma (estilo de Vancouver):
Arbaizar B, Llorca J. A brief look of comparative anxiety disorders: from dogs to humans.
Psiquiatria.com [Internet]. 2011 [citado 26 Jul 2011];15:18. Disponible en:
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