Asia, home to over half the world's population, has seen significant socioeconomic and urban transitions in recent decades, leading to increased wealth and living standards in many areas. However, this improvement is unevenly distributed, resulting in disparities in life expectancy and disease burden. Infectious diseases, particularly those caused by zoonotic parasites carried by animals like dogs and cats (e.g., fleas, soil-transmitted helminths), pose a significant and ongoing challenge, especially in disadvantaged communities. The rise in companion animal ownership in urban Asia, correlated with modern lifestyles, raises concerns about zoonotic pathogen transmission. While some parasitic diseases in humans are well-known in Asia, data on the prevalence, distribution, and risk factors of zoonotic parasites in companion animals in metropolitan areas are limited. This study investigates the hypothesis that human living standards, along with animal characteristics and environmental factors, predict the risk of zoonotic parasite exposure in companion animals across various Asian cities.

Existing literature highlights the significant global burden of zoonotic parasitic infections, emphasizing the need for comprehensive studies, especially in regions like Asia with high population density and diverse ecological settings. Previous research has documented the association between specific parasites and companion animals, but large-scale epidemiological data on zoonotic parasite prevalence and risk factors in Asian metropolitan areas are scarce. Studies have shown the impact of urbanization and socioeconomic factors on infectious disease patterns, but the interplay between these factors and zoonotic parasite transmission in companion animals remains understudied. This research gap necessitates a comprehensive investigation into the complex relationships between human social conditions, environmental factors, and zoonotic parasite infections in companion animals to develop effective control strategies.

This international collaborative study, spanning eight East and Southeast Asian countries, involved academic institutions and private veterinary facilities. Data collection occurred monthly from June 2017 to July 2018, encompassing a total of 2381 client-owned dogs and cats. Inclusion criteria included regular outdoor access and absence of recent antiparasitic treatment. Informed consent was obtained from all pet owners. A standardized questionnaire collected data on animal characteristics (age, sex, neuter status, species), husbandry (rural/urban environment, household type), and clinical status. Diagnostic testing included ectoparasite collection, blood sampling, and fecal analysis. Ectoparasite detection and vector-borne pathogen identification methods are detailed in a previous publication (Colella et al., 2020). Endoparasite detection used flotation, sedimentation, and Baermann-Wetzel techniques. Species identification of *Ancylostoma* spp. utilized a multiplex qPCR assay. A comprehensive set of risk indicators, encompassing animal characteristics, husbandry practices, bioclimatic factors (annual mean temperature and precipitation), and socioeconomic factors (human population density, pet-human population ratio, and human life expectancy), were analyzed. Statistical analyses were performed using R, employing Cramér's V, multiple correspondence analysis (MCA), and multivariable mixed-effects logistic regression to identify significant predictors of parasite infection.

Overall, 44.9% of the animals harbored at least one parasite. Ectoparasites, vector-borne pathogens (VBPs), and endoparasites were detected in 31.4%, 13.1%, and 13.5% of animals, respectively. Prevalence varied significantly across geographical locations. The most common endoparasites were hookworms (Ancylostomatidae), followed by ascaridoid nematodes and coccidians. Molecular analysis identified *Ancylostoma ceylanicum* and *A. braziliense* in a significant proportion of hookworm-positive samples. Statistical analysis revealed that several factors significantly influenced parasite infection status. Increased human life expectancy was associated with a lower risk of overall parasite infection and VBP exposure (OR 0.86). Neutered animals had significantly lower odds of overall parasite infection (OR 0.61) and ectoparasite infestation (OR 0.53). Urban animals had lower odds of overall parasite infection (OR 0.36) and ectoparasite infestation (OR 0.28) compared to rural animals. Younger (<5 years) and older (>15 years) animals had higher odds of overall parasite infection compared to adult animals (5-15 years). Annual mean temperature positively correlated with overall parasite and VBP exposure. Dogs were significantly more likely than cats to be infected with VBPs (OR 34.1). Hookworm infections were more prevalent in dogs and in younger and older animals. Analysis of ticks and fleas revealed similar trends with respect to life expectancy and neutering status.

The study's findings highlight the impact of human social conditions on zoonotic parasite transmission in companion animals. Increased human life expectancy, reflecting better living standards and access to healthcare, is significantly associated with reduced parasite risk. Similarly, the strong association between neutering and lower parasite prevalence underscores the importance of access to veterinary care. The higher prevalence of parasites in younger and older animals highlights age-related vulnerabilities. The significant geographical variation in parasite prevalence underlines the need for region-specific control strategies. The identification of *A. ceylanicum* and *A. braziliense* underscores the importance of using molecular tools for accurate diagnosis and highlights the potential zoonotic risks associated with these hookworms. These results emphasize the need for a One Health approach, integrating human and animal health interventions.

This study demonstrates that human life expectancy and access to veterinary care are crucial factors influencing the risk of zoonotic parasite infections in companion animals in East and Southeast Asia. Future research should focus on further investigating the socio-economic drivers of parasite prevalence, exploring the effectiveness of targeted interventions, and expanding research to include a wider range of parasites and geographical locations. Enhanced collaboration between human and veterinary health professionals is vital for effective zoonotic disease control and prevention.

The study's focus on client-owned animals in urban areas might limit the generalizability of findings to rural populations or free-roaming animals, which may experience higher parasite burdens. The cross-sectional design limits causal inference. Diagnostic methods may have underestimated the true prevalence of some parasites, particularly protists. Variation in technical expertise across different sites could have influenced the accuracy of parasite detection.