American Journal of Microbiological Research, 2025, Vol. 13, No. 3, 38-44 Available online at http://pubs.sciepub.com/ajmr/13/3/1 Published by Science and Education Publishing DOI:10.12691/ajmr-13-3-1 Emergence of Aspergillus terreus as a Notable Fungal Pathogen of Human and Animal Health Dhwani Upadhyay 1 , Prasad Andhare 1 , Mahendra Pal 2,* 1 Department of Life Sciences, School of Sciences, GSFC University, Vadodara, Gujarat, India 2 Narayan Consultancy of Veterinary Public Health and Microbiology, Bharuch, Gujarat, India *Corresponding author: Received April 18, 2025; Revised May 19, 2025; Accepted May 27, 2025 Abstract Aspergillus terreus, historically considered an environmental saprophyte, is now known to be an important opportunistic pathogen in human and veterinary medicine. Its increasing occurrence, particularly in immunocompromised individuals, emphasises its clinical relevance. Importantly, A. terreus demonstrates inherent resistance to the key antifungal, amphotericin B, which further complicates treatment options and is associated with increased morbidity and mortality. The virulence of the pathogen is enhanced by its production of various mycotoxins, another type of secondary metabolite that may alter host–pathogen interactions, and statins. Here, we review the current understanding of the taxonomy, ecology, and pathogenicity of A. terreus and its specific morphologic characteristics and resistance profiles. We explored their transmission dynamics, highlighting their environmental reservoirs and possible zoonotic routes. Infections caused by this fungus can cause a variety of clinical manifestations, from superficial to invasive diseases; therefore, a high index of suspicion is required to make a diagnosis. The phenotypic diversity of the organism along with traditional identification methods is a challenge for diagnosis." Therapeutically, the resistance of A. terreus to amphotericin B requires alternative antifungal regimens, with voriconazole and posaconazole demonstrating variable activity. This review further discusses breakthroughs in diagnostic modalities and therapeutic approaches with the potential to improve patient outcomes. We also highlight preventive strategies, such as environmental control and infection surveillance, to reduce the risk of A. terreus infection. This review intends to bring together the current knowledge and offer valuable insights related to the emerging pathogen A. terreus and its clinical importance. Keywords: Antifungal resistance, Aspergillus terreus, Emerging fungal pathogen, Invasive aspergillosis, Public health Cite This Article: Dhwani Upadhyay, Prasad Andhare, and Mahendra Pal, “Emergence of Aspergillus terreus as a Notable Fungal Pathogen of Human and Animal Health.” American Journal of Microbiological Research, vol. 13, no. 3 (2025): 38-44. doi: 10.12691/ajmr-13-3-1. 1. Introduction Aspergillus terreus was first recognised as an opportunistic, ubiquitous environmental saprobe and was initially known to colonise ecological niches present in soil, decaying vegetation, and compost, and as such, played an essential role in recycling organic matter. Originally considered to be of limited clinical relevance, it has now become one of the most relevant opportunistic pathogens in immunocompromised hosts and is a frequent cause of life-threatening infections in patients receiving chemotherapy, organ transplants, or prolonged corticosteroid therapy [1]. Traditionally deemed an incidental contaminant of clinical specimens, increasing evidence supports the role of A. terreus as a pathogen initiating severe infections, including invasive aspergillosis (IA), particularly in haematological malignancy and transplant populations. This paradigm shift mirrors a greater appreciation for the organism’s distinguishing pathogenic factors, including inherent resistance to amphotericin B, as well as the production of biologically active metabolites such as terreic acid, which may influence host immunity and microbiota competition [2]. Basic taxonomic classification places A. terreus in the section Terrei, characterised by biseriate conidiophores and smooth-walled conidia, but morphological similarities with other Aspergillus species in clinical identification can lead to misidentification [3]. The setting of A. terreus as an emerging pathogen is within the synchronising of the One Health paradigm, which is defined as seeking equitable improvement and optimal health for humans, animals, and the environment, and recognising the interrelationship among these three components [4]. Isolations of this ubiquitous fungus from veterinary patients have been on the rise, particularly among canines and equines, suggesting both zoonotic potential and environmental persistence across multiple ecosystems [5]. Nosocomial presence, particularly in construction-affected healthcare settings, underscores the role of environmental disruption in pathogenic emergence.