Psychological Trauma in Animals
World Small Animal Veterinary Association Congress Proceedings, 2018
Franklin D. McMillan, DVM, DACAW
Best Friends Animal Society, Kanab, UT, USA

Post-traumatic Stress and PTSD

Psychological trauma in humans has been well-described for several decades. More recently, a rapidly growing body of research provides extensive evidence supporting the existence of psychological trauma and its characterization in nonhuman animals. Although post-traumatic stress disorder (PTSD) has received the most attention from both the public and researchers, a key aspect of psychological trauma is that post-traumatic psychopathology includes far more than PTSD, in 2 senses. In the first sense, PTSD constitutes the most severe outcome on a continuum of fear-based responses to a potentially traumatic experience (PTE). At the other end of this continuum mild post-traumatic fears can be found, and in between are all levels of severity of fears as well as additional important psychological changes along with the fears (such as intrusive memories, flashbacks, nightmares, and more). The diagnosis of PTSD is made only if an individual exhibits a certain number of symptoms from each of 4 quite well-defined symptom clusters over a certain period of time. As specified in the Diagnostic and Statistical Manual of Mental Disorders (DSM IV), in addition to the history of exposure to a traumatic event, the 4 symptom clusters that distinguish PTSD from other post-traumatic psychological disturbances are:

1.  Re-experiencing the trauma through intrusive memories, dissociation, flashbacks, and nightmares

2.  Avoidance of anything reminiscent of the traumatic event

3.  Negative alterations in cognition and mood

4.  Hyperarousal symptoms such as hypervigilance and increased startle response (not present before the trauma)

The criteria for children 6 years and younger - which likely have greater applicability to animals - require fewer symptoms in each of the diagnostic clusters. One of the most important lessons obtained from research is that most survivors of single, discrete traumatic events do not develop any form of psychopathology. People who experience even the most harrowing of traumatic experiences are likely to experience at least short-term distress but do not develop PTSD or any other post-traumatic psychiatric disorder. The most common trajectory is for recovery over time. Only a minority of individuals develop distress and functional impairment that rise to meet the criteria for one or more of the psychiatric disorders. Another important development in recent years is the recognition that many people exposed to a PTE show enough of the symptoms of PTSD to cause distress and functional impairment but too few symptoms to meet the diagnostic criteria for PTSD. In fact, research shows that the number of people in this category after trauma outnumber the people who receive the diagnosis of PTSD. Accordingly, numerous researchers feel that the more appropriate term for this continuum of post-traumatic responses is “post-traumatic stress”, or PTS. Here, PTSD would be the most severe form of PTS. Forms of PTS that fail to reach the threshold for a diagnosis of PTSD are referred to as “subthreshold PTSD” (also, “partial PTSD”). This conceptualization of PTS takes on even greater importance as we discuss post-traumatic conditions in animals, where meeting certain PTSD diagnostic criteria is often difficult to confirm (e.g., flashbacks and nightmares). In this way, we can refer to animals experiencing PTS without the concern of whether they strictly cross the diagnostic threshold for PTSD.

The second sense of the assertion that post-traumatic psychopathology extends well beyond PTSD is that PTSD does not capture the full spectrum of post-traumatic disorders. Post-traumatic disorders other than (or coexist with) PTSD include specific phobia, generalized anxiety disorder, and depression, among others.

Current research has identified the primary physiological system involved in PTS to be the hypothalamic-pituitary-adrenal (HPA) axis, which appears to undergo pronounced and persistent dysregulation. Studies of PTSD show that fear is the key emotion involved in the disorder and the adaptive functioning of fear conditioning, with the capability to distinguish between safe and unsafe stimuli and facilitate identification of danger, fails in this disorder. Rather than a normal level of alertness with relaxed attention, individuals with PTSD have an elevated baseline of arousal: the individual suffering from PTSD continues to function in a “red alert” status of readiness, behaviorally primed for another stressful event. To severely affected individuals, almost every place becomes perceived as unsafe, resulting in a loss of one’s sense of security.

As mentioned above, a large body of research provides compelling evidence in support of the notion that animals experience psychological trauma. But do they experience PTSD as it occurs in humans? In the laboratory, a large number of animal models of PTSD have demonstrated phenomenology that closely resembles that of PTSD in humans. However, the subjective experiences of some symptoms such as flashbacks, nightmares, and intrusive recollections cannot currently be ascertained. Most animal models of PTSD are based on exposure to stressors that the victim cannot control, that are unpredictable, or are both. In addition to the purported experimental models of PTSD, a few reports of proposed naturally occurring cases of PTSD in animals have been published.

  • Traumatic stress disorder was reported in an adult female wolf (Canis lupus) born in the wild and then placed into captivity. The wolf showed symptoms similar to those of humans with PTSD, and included generalized fear, avoidance, hypervigilance, arousal, and exaggerated startle reactions.
  • PTSD was reported in 2 sanctuary-housed female chimpanzees who had previously sustained prolonged captivity and biomedical experimentation. The animals exhibited a wide array of signs, including intense screaming, self-injurious behaviors, stereotypic rocking, trance-like states, ritualistically arranging each piece of food in a circle around oneself, sudden and unpredictable aggression, emotional instability, hypervigilance, attacking one’s own hand or foot as though it did not belong to him/her, self-isolation, and hitting oneself continually in the head.
  • Wild elephants showed signs that were interpreted as resembling PTSD symptoms and meeting the diagnostic criteria for PTSD, such as abnormal startle response, depression, unpredictable asocial behavior, and hyperaggression.
  • Several anecdotal reports describe signs of post-traumatic stress in canine and feline survivors of hurricane Katrina. Signs reported in the animals were severe personality or temperament changes, new phobias, chronic chewing or paw licking, and depression; trembling, excess salivation, pacing, aggressive behavior, loose stools, vomiting, lack of appetite, elimination in the house, avoidance of people, and twitching during sleep; and indelible fear of storms as well as nervousness, fear, or aggressive behavior in response to events reminiscent of the trauma, such as heavy winds, rain, or rushing water.
  • In a study of previously traumatized chimpanzees (traumatic events included maternal separation, social isolation, biomedical experimentation, or similar experiences), researchers used PTSD diagnostic criteria adapted for children and determined that 44% of chimpanzees in sanctuaries met the set of alternative criteria for PTSD, compared with 0.5% of chimpanzees in the wild.
  • Most recently, popular media accounts and a few scientific reports have described clinical signs in military working dogs (MWDs) which closely resemble signs seen in human PTSD. Extreme behavioral changes have been observed in an estimated 5 percent of MWDs after exposure to combat and violent events in Iraq and Afghanistan. The key to the diagnoses was that the dogs had not displayed symptoms prior to, or earlier in, deployment to war zones.

Potential Causes of Psychological Trauma in Animals (Causes of Severe Stress)

Many sources of severe stress - which have the potential to cause psychological trauma - are relatively common in animals. These include:

1.  Abuse - physical or emotional in nature

2.  Aversive confinement - such as in prolonged shelter confinement and in CBEs

3.  Multiple re-homing - involves repeated disruption of life events and social relationships, preventing the establishment of a secure base and sense of stability

4.  Hoarding - extreme stress due to competition for scarce resources

5.  Natural disasters - loss of home environment and social bonds, often including physical trauma

6.  Fighting - organized dogfighting involving abusive treatment, training stress, severe physical injury that is commonly treated by the dogs’ owners without veterinary services

7.  Racing - Greyhound dogs and racehorses, often severely stressed

8.  Forced work - for example, sled dogs, animals in entertainment (circus acts, movies and television, marine animal parks) - may be pushed beyond their limits

9.  Service and military duty - exposure to combat and explosions, search and rescue work, police work

10.  Laboratory research and testing - stress in experiments designed to cause distress as well as “routine” fears associated with laboratory confinement and manipulations

11.  Physical trauma and injury - wide variety of adverse physical conditions

Treatment of Psychological Trauma

Recommendations for treating psychological trauma in animals have not been adequately developed. Research is lacking, and the variety of traumas suggest individualized treatment programs are likely to be more effective than a single approach to trauma in general. Currently we are relegated to simply treat the signs, such as fears and phobias, with standard behavioral therapeutic approaches. Future research will determine the best methods for the individual types of traumas.


References are available from the author on request.


Speaker Information
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Franklin D. McMillan, DVM, DACAW
Best Friends Animal Society
Animal Care
Kanab, UT, USA

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