When "People Who Hoard Animals" was published in Psychiatric Times in 2000, we were just beginning our study of this poorly understood behavior. (1) Since then, hoarding disorder (HD) has been a subject of considerable research and has become an official diagnosis in DSM-5. DSM-5 criteria for HD do not specify the types of possessions that are necessary for this diagnosis. Because animals are legally considered property (ie, possessions), the hoarding of animals would appear to qualify as HD, although this question is not yet resolved in the psychiatric literature.
In light of this development, a review of the existing literature and a new look at animal hoarding is warranted. In this article, we provide an overview of what we have learned in the past 15 years about this behavior with respect to phenomenology, etiology, and treatment. At the outset, it is important to note that our knowledge of this condition is based on a limited number of studies. Consequently, what is described here should be viewed as a set of working hypotheses.
Although animal hoarding technically fits the criteria for HD, DSM-5 fell short of listing it as an official subtype, and Mataix-Cols (2) has rightly noted that its diagnostic classification remains unclear on the basis of the available evidence. DSM-5 describes animal hoarding as a condition associated with HD and defined by "the accumulation of a large number of animals and a failure to provide minimal standards of nutrition, sanitation, and veterinary care and to act on the deteriorating condition of the animals (eg, disease, starvation, death) and the environment (eg, severe overcrowding, extremely unsanitary conditions)." Estimates from surveys of animal control agencies and humane societies suggest that there are approximately 3000 reportable cases of animal hoarding annually in the US. (3)
The most dramatic feature of this behavior is the effect it has on the home environment. Large numbers of animals, often sick, dying, or dead, are crammed into living areas of the hoarder's home. Often urine and feces cover the floors and/or walls, creating high concentrations of ammonia and aerosolized organic contaminants that pose serious health risks to occupants. (4,5) In a study of complaints to health departments, animal hoarding was found to result in significantly more unsanitary conditions than did object hoarding and posed significantly more threat to the health of human occupants of the home and to the community at large. (6) Surveys of caseworkers dealing with this problem indicate that a lack of appropriate sanitation appears in 70% to more than 90% of animal-hoarding cases, and together with the large number of animals involved, increases the likelihood of zoonotic diseases for the occupants and the community. (4,7)
Case reports indicate that between 31% and 100% of individuals who hoard animals also hoard inanimate possessions. (7,8) In these cases, the clutter and unsanitary conditions severely interfere with normal activities of daily living, such as sleeping in a bed, bathing, finding important objects, and preparing food. Often major appliances, toilets, showers, and tubs are...