Exploring the Human–Animal Interaction (HAI) for Children with ASD Across Countries: A Systematic Review

Studies were identified and searched in various electronic databases, including PubMed, Scopus, ProQuest, EBSCOhost, and Web of Science. The publication period of the included papers was set from 1 January 2000 to 31 December 2023. The key search terms for these databases included a combination of at least one identifier for HAI, one identifier for animal-related terms, one identifier for children with ASD, and one identifier for social and emotional outcomes (Table 1). The designs of the identified studies could be quantitative, qualitative, or mixed methods.

The title and the abstract were initially screened for eligibility for inclusion by the first author. Studies with titles and abstracts meeting the inclusion criteria were obtained, while some required a more thorough review of the full text to examine their eligibility for inclusion. The inclusion criteria used for the review selection were as follows: (1) involved empirical data; (2) involved any type of HAI; (3) targeted children under 18 years old with a diagnosis of ASD; and (4) measured social and/or emotional outcomes.

After the initial screening, studies were further reviewed based on the full text. Studies were excluded if they: (1) were review papers or meta-analyses; (2) were not peer-reviewed; (3) were not published in English; (4) lacked a detailed methodology; (5) were not relevant to HAI; or (6) involved adult participants or children without ASD, but separate data were not generated.

Key data were identified and extracted from each study based on the objectives of this review. To examine the study characteristics, the extracted items included the country of origin, HAI terminology, type of companion animal involved, HAI format, and HAI setting. Given the cultural diversity across nations, the data were primarily summarized through country-based analysis to obtain a refined understanding of the potential cultural variations in HAI.

Figure 1 shows the flow diagram of the study selection process. The key features of HAI in the selected studies were extracted and summarized in Table 2. Sixty out of the 97 articles were published in the 2010s, while 33 were published between 2020 and 2023. Only four were published between 2000 and 2009. This may indicate a growing interest in publications on the topic of HAI for children and adolescents with ASD in recent years.

Among the 97 selected studies, 35 were conducted in Europe, while 32 were conducted in the US (Table 3). The remaining studies were conducted in Canada (n = 8), Asia (n = 6), and Australia (n = 10).

Within the selected studies, dogs were the most common type of companion animal involved (n = 41), followed by horses (n = 34) and guinea pigs (n = 7). Other animals included cats (n = 2) and dolphins (n = 4). Some studies involved unspecified companion animals or a mix of more than one type of animal (n = 9; Table 3).

As documented in the selected papers, HAI occurred in various settings. Most studies took place in home settings (n = 29) and horse riding or training centres (n = 29). Eleven studies were conducted in clinical and educational settings respectively, such as treatment centres and schools. Eight studies took place in outdoor spaces, farms, or lagoons. Three studies were conducted in experimental or laboratory settings. Two studies involved more than one setting, while the settings were not mentioned in the remaining four studies (Table 3).

Across the 97 selected studies (Table 3), two formats of HAI were identified: (1) pet ownership and (2) animal-assisted interventions. Animal-assisted intervention was the most common form of HAI (n = 73), comprising over 75% of all the selected studies. Among the AAI studies, 44 involved using companion animals with no specific training, while 29 involved trained service animals. Pet ownership was examined in 24 studies, with 14 involving untrained animals and the remaining ten involving trained animals.

The types of companion animals varied across the different HAI formats (Table 4). Dogs were primarily involved in studies on both pet ownership and AAI. All studies on pet ownership with trained animals utilized dogs as companion animals (n = 10). Among the 14 studies on pet ownership with untrained animals, the companion animals were more diverse, including dogs (n = 6), cats (n = 2), and unspecified or mixed types of animals (n = 6). Among the 29 AAI studies with trained animals, a majority involved dogs (n = 24), followed by horses (n = 3) and dolphins (n = 2). In the 44 AAI studies with untrained animals, horses were the most frequent companion animals (n = 31), followed by guinea pigs (n = 7).

The studies on HAI revealed specific patterns in the types of companion animals, settings, and formats across different countries (Table 3). Around one-third of the 41 studies involving dogs were conducted in Europe (n = 13). Nearly half of the studies with horses were from the US (n = 16), followed by Europe (n = 11). Studies on guinea pigs came from Europe (n = 4) and Australia (n = 3). Both studies involving cats were carried out in the US. Three of the four studies on dolphins were from Europe, while one was from Asia. Studies with non-specific or multiple companion animals were mainly from the US (n = 5) and Europe (n = 4).

In terms of settings across countries (Table 3), over 40% of studies conducted at home (n = 12) were based in the US, while about half of the studies carried out at horse riding or training centres (n = 14) were located in the US. Around half of the studies in clinical or treatment centres were conducted in Europe (n = 5). Among the school-based studies (n = 11), three were conducted in Asia and three in Australia. Two out of the three experimental or laboratory studies were conducted in Europe, while one took place in Asia. Among the eight studies with outdoor or farm settings, six took place in Europe. Two studies involving multiple settings were conducted in the US and Asia, respectively, while the four studies without specified settings came from the US (n = 1), Europe (n = 2) and Australia (n = 1).

Regarding HAI formats across different countries (Table 3), 40% of the pet ownership studies with trained animals were conducted in Canada (n = 4), while over 60% of the pet ownership studies with untrained animals were conducted in the US (n = 9). Around 40% of the AAI studies were from Europe, with trained animals (n = 11) and untrained animals (n = 18). Among the six studies from Asia, all were related to AAI, with five studies involving trained animals and one study involving untrained animals. These results suggest variations in research interests and approaches to HAI across different geographical locations, focusing on pet ownership in the US and therapeutic applications involving companion or service animals in Europe and Asia.

The results of this review have revealed interesting patterns regarding the formats and companion animals involved in HAI across different countries. These variations could be attributed to the cultural norms that shape attitudes towards animals.

The current review found that nearly half of the HAI studies conducted in home settings were from the US. It is believed that Western cultures tend to value companion animals more sentimentally, often anthropomorphizing them as family members who provide emotional support and love (Risley-Curtiss et al., 2006; Sheade & Chandler, 2014; Smith, 2019). This aligns with recent statistics showing that pet ownership is common in American households. According to the 2021–2022 APPA National Pet Owners Survey, around 70% of the US population owned at least one pet, with dogs being the most commonly owned companion animals. Specifically, it is a prevalent trend for American parents of children with ASD to explore complementary and alternative methods of treatment (CAM) (Volkmar et al., 2014). Among these treatments, animal-based intervention was found to be one of the most common CAM treatments, with one-quarter of children with ASD participating in AAI during childhood (Christon et al., 2010). According to Carlisle (2014), over 25% of dog-owning parents considered the benefits of dog ownership to their children with ASD to be a significant factor influencing their decision to own a dog. Hence, viewing pet ownership as a natural intervention for children with ASD likely explains the research interests in examining the daily impact of HAI on children with ASD in American household settings.

Moreover, nearly half of the HAI studies involving horses were conducted in the US. This reflects the long-standing tradition of therapeutic horseback riding as a recreational activity in the country, which helps horse riders develop skills in horseback riding and achieve both therapeutic and life goals (McDaniel Peters & Wood, 2017). Initially positioned for recreational purposes, it was adopted by occupational and speech therapists and subsequently embraced by various therapeutic professionals (Dismuke, 1984; Engel, 1984). Incorporating horses into recreational therapy is a common practice in the US, with certified therapeutic recreational specialists primarily serving individuals with neurodevelopmental disabilities such as autism (McKissock et al., 2023). Given the diverse therapeutic applications and popularity of human-horse interactions for children with ASD in the US, it is not surprising that a significant portion of relevant HAI research has been carried out in the country.

In this review, Europe was found to have the greatest number of HAI studies compared to other regions. The human–animal bond has long been considered an inherent connection with therapeutic power across European countries. Therapeutic support from animals for patients was first documented in a Belgian hospital in the eleventh century, and the involvement of companion animals has been widely used in different European healthcare institutions since the eighteenth century (Grandgeorge & Hausberger, 2011). The view of animals as sentient beings capable of experiencing emotions has further led to the enactment of various animal welfare and protection legislation in European countries like Austria, Germany, Switzerland, France, and Spain. These legal reforms have challenged the traditional view of animals as mere property, granting better protection for animals in civil codes (Cardoso et al., 2017). Hence, the focus on fostering a positive human–animal bond may have prompted further exploration of HAI through research studies, contributing to the phenomenon of a higher concentration of HAI studies conducted in Europe.

In recent years, green care has flourished across European countries, with AAI involving companion animals becoming a common type of green care intervention. Green care encompasses various therapeutic interventions that involve experiencing the natural environment and interacting with animals, such as care farming, healing gardens, eco-therapy, and AAI (Haubenhofer et al., 2010). For example, the United Kingdom has focused on horticultural therapy, while AAI with companion animals is preferred in countries like Finland, Norway, Germany, and Austria. In Germany, care farming has developed a strong link with animal husbandry, gardening, and the healthcare industry to promote physical and mental well-being through farming activities. The therapeutic context pertained to green care may explain the observation that most studies involving AAI were conducted in Europe, regardless of whether trained animals are involved.

Apart from therapeutic intentions, outdoor learning approaches have been widely adopted by many European countries, particularly in Scandinavia and the Nordic regions, where nature is considered a cultural symbol (Gullestad, 1992). Experiential education is closely tied to outdoor education in the UK and other European countries, which encompasses learning through outdoor activities, therapeutic interventions, and environmental education in natural settings (Änggård, 2010; Higgins, 2009). The emphasis on experience-based and sensory exploration in natural environments may account for the prevalence of HAI studies in outdoor spaces and natural settings in Europe. Research also suggests that dogs and horses are the most common companion animals involved in AAIs for children with ASD (Harris & Williams, 2017). While dogs are often trained as therapy animals for educational or clinical purposes, horses are widely integrated into outdoor therapeutic sessions for improving the social, behavioral, and motor skills of children with ASD. Thus, the unique therapeutic approach in Europe, which emphasizes AAI and outdoor settings, may elucidate why dogs and horses are the predominant companion animals in European HAI studies for autism interventions.

In contrast to the prevalence of HAI studies in the US and Europe, our results revealed that HAI studies were least documented in Asia. This is not surprising, as some Asian societies may be less comfortable with HAI due to certain cultural norms and demographic constraints. For example, China has a “one dog policy” that restricts the domestication of large dogs due to fears of rabies (Valiyamattam et al., 2018). In other Asian societies like Hong Kong, people are less likely to keep pets due to socioeconomic and environmental constraints, such as limited living space and the high cost of pet care (Chandler, 2022).

Although there is a growing interest in companion animals and concerns for animal welfare in Japan, the development of AAI still lags behind that of Western countries. For example, a society dedicated to therapeutic riding was established in Japan only in 2006 to support individuals with disabilities (Japan Therapeutic Riding Association, 2024). Moreover, there is a lack of research studies validating the effectiveness of equine-assisted activities and therapies for children with ASD in Japan (Kawamura et al., 2024), which may hinder the promotion of HAI in the region.

Despite the growth of therapy programs involving companion animals in Asian countries, cultural disapproval of companion animals and other practical constraints may continue to impede the development of AAI or HAI in these societies. The prevalent use of therapy animals in Asian countries may explain why most Asian studies focused primarily on AAI and service animal interactions rather than on pet ownership. Concerns and challenges related to pet ownership for children with ASD in Asian countries are underexplored and warrant examination in future studies.

In this review, patterns have been observed that reveal associations between HAI formats and companion animals’ involvement. The functional roles supported by each animal species can be considered influential factors in determining the types of companion animals involved in the corresponding HAI. Optimal matching between companion animals and children with ASD is essential for achieving therapeutic goals and meeting mutual needs during interactions. Regardless of their training, companion animals serve significant functions that can be classified as either daily supportive or therapeutic.

First, the daily supportive roles of companion animals mainly involve providing emotional support and assisting with the daily functioning of children with ASD or their families. Some companion animals may not undergo specific training, yet they can still perform supportive functions for children with ASD. These animals are seen as sources of emotional attachment and facilitators of strong family bonds (Carlisle et al., 2023). Emotional attachment to small household animals, such as dogs and cats, is common in pet ownership. Many pet owners experience emotional support and a reduction in daily stress through the presence of companion animals, which primarily function as companions or sources of recreation, bringing joy and alleviating loneliness in daily life (Mueller, 2014).

For example, Wright et al. (2015a, 2015b) emphasized that pet dogs can serve as a common topic of interest and create shared family activities such as dog walking, thereby uniting the family and strengthening family bonds. In contrast, cats generally exhibit more independent and less intrusive behaviors than dogs, which may be preferable for families with children who have ASD (Carlisle et al., 2023). Children who view pets as siblings are often more willing to disclose their feelings to pets than to human siblings (Bures et al., 2021a; Power, 2008).

Some household pets are trained as therapy animals or service animals to enhance the well-being of individuals through HAI, especially for those with physical or mental disabilities. Among HAI studies focused on children with ASD, it has been revealed that most dogs involved are certified therapy dogs or designated autism assistance dogs that provide support for these children. For example, autism assistance dogs in home settings can offer daily support for families with children who have ASD, such as facilitating public outings and promoting family harmony.

In addition to daily support, the therapeutic role is another significant function performed by companion animals during interventions. Within AAI, the therapeutic goals for children with ASD may help determine the types of companion animals involved in the corresponding format of HAI. For example, interaction with dogs is often incorporated into interventions to enhance the social competence of children with ASD. Trained therapy dogs involved in AAI exhibit playful and responsive traits that enable them to fulfill the therapeutic role of speech elicitors among children with ASD during interventions (Fung & Leung, 2014). When children with ASD display emotional meltdowns or inappropriate social behaviors, service dogs may help divert their attention and provide social support (Smyth & Slevin, 2010). This may partly explain why all HAI studies related to dogs in this review were associated with service animal interaction in the formats of pet ownership or AAI.

Although large animals, such as horses, are rarely kept as household pets, their unique characteristics enable them to fulfill other therapeutic functions, such as interventions aimed at achieving physical and social outcomes. Specifically, horseback riding is used as a treatment tool in hippotherapy to accomplish functional goals, such as improving motor balance control and facilitating social engagement (Ajzenman et al., 2013). For instance, in equine-assisted programs, grooming horses can enable children to develop social skills, such as responsibility (Mueller, 2014). While horses in rehabilitation programs need to be well-trained to perform specific gaits and exercises for individuals with motor issues (De Santis et al., 2017), horses involved in equine-assisted psychotherapy in some therapeutic centres in Australia were found to lack proper training (Nelson et al., 2016). This may explain why, in some HAI studies, untrained horses could still be involved in AAI without service animal interaction to achieve specific social and emotional outcomes among children with ASD.

Guinea pigs, a common pocket animal, are often kept as household pets. Due to their calm temperament and small size, they can assist in classroom learning in educational settings (Krskova et al., 2010). Since classroom pets need to be small animals that are easy to handle in cages or aquariums, guinea pigs are often considered one of the best classroom pets to support learning for young children (O'Haire et al., 2013b). This review showed that over half of the HAI studies related to guinea pigs were conducted in schools, where they were incorporated into reading programs and classroom activities to enhance social-emotional functioning for children with ASD (Krskova et al., 2010; O'Haire et al., 2015). Like horses, untrained guinea pigs could be involved in less formal and unstructured animal-assisted activities. This contrasts with therapies assisted by dogs, which are typically conducted by educators or facilitators skilled in fostering positive HAI for children with ASD.

Dolphins have recently emerged as companion animals in AAI due to their intellectual competence and high responsiveness. They can be trained for dolphin-assisted therapy (DAT) to help therapists in enhancing the cognitive and social competence of children with mental or intellectual disabilities, especially those with ASD. Dolphins can elicit happiness from people due to their natural, spontaneous, and playful traits (MdYusof & Chia, 2012). However, interactions with dolphins are often constrained to waterside locations like lagoons or dolphinariums, making it more challenging to incorporate them into AAI compared to other companion animals. This may explain the scarcity of HAI studies on dolphin interaction in the field.

This study has explored the distinct patterns of HAI across different countries and highlighted potential cultural influences on the formats of HAI and the types of companion animals involved among children with ASD. To facilitate effective HAI for these children, it is essential to ensure that the choice of companion animals—considering factors such as size and temperament—is suitable for achieving the expected benefits and therapeutic objectives (Sams et al., 2006). The therapeutic effects of HAI can vary significantly based on individual differences among children with ASD. For instance, in conjunction with dog ownership, more regular contact with horses has been associated with increased adaptability to daily routines, suggesting that dog ownership and exposure to various animal species may create synergistic benefits for children with ASD and their families (Hall et al., 2016). Therefore, when introducing HAI to children with ASD for positive outcomes, their personalized educational programs should be carefully tailored to address skill development, therapeutic needs, degree of autonomy, and individual preferences (Hurtb et al., 1999; Philippe-Peyroutet & Grandgeorge, 2018). In addition, effective facilitators, including therapists and parents, play a crucial role in supporting and guiding children with ASD in positive HAI, such as teaching them how to approach and build relationships with companion animals (Lisk et al., 2023). Given the constraints in various settings, it is also important to consider cultural factors and the appropriate matching of companion animals when providing adaptive HAI practices for children with ASD.

Despite the comprehensive synthesis of cultural differences in HAI presented in this review, several limitations must be addressed. First, only articles with full English texts were selected, which excluded relevant HAI studies from Asian countries that were not published in English. Moreover, the lack of published papers on HAI in certain countries may simply suggest a deficiency in research within this field. It is plausible that HAI practices are extensively adopted in those countries despite the lack of research. This may also indicate a potential discrepancy between research output and the actual implementation of HAI across countries, which could be further explored in future studies.

Second, as this paper serves as an overview of HAI studies that examined the social and emotional benefits for children with ASD, the critical search terms were limited to those related to social and emotional outcomes. However, HAI also offers other developmental benefits for children with ASD, such as positive behavioral changes and improved motor skills (Borgi et al., 2016), which are worth examining to obtain a thorough understanding of HAI for therapeutic purposes.

In addition, potentially effective therapeutic components of HAI that support children with ASD were not examined in this review. For example, the calmness and responsiveness of companion animals may facilitate social interaction among children with ASD during HAI. It would be valuable to investigate in detail how the traits of each companion animal are associated with the benefits of interaction in various formats of HAI for children with ASD.

Lastly, investigating the underlying mechanisms of HAI and how they are influenced by cultural contexts can provide a more concrete theoretical basis for understanding the cultural variations in HAI for children with ASD. Comparative studies of HAI between Eastern and Western countries could yield more rigorous validation.