1. Introduction

Even though the term “One Health” could sound like a modern concept, it dates back to the 19th century, when the father of the One Health theory Rudolf Virchow, investigating swine roundworm, Trichinella spiralis, highlighted the linkages between human and veterinary medicine and coined the term “zoonosis” to indicate an infectious disease passing between humans and animals. In these circumstances, Virchow stated that “Between animal and human medicine there are no dividing lines—or should there be. The object is different, but the experience obtained constitutes the basis of all medicine.” This last sentence, which could be called Virchow’s paradigm, in 2021 is still valid; in fact, it has been estimated that, globally, about one billion cases of illness and millions of deaths occur every year for zoonoses [1]. In the last three decades, over 30 new human pathogens have been detected, and 73% of the currently emerging and re-emerging pathogenic agents may cause zoonoses ^[2][3][2,3]. The transmission of zoonotic disease occurs at the human-animal interface through direct or indirect exposure of humans to animals, their products (i.e., meat, milk, eggs), the same vectors, and/or sharing the same environment ^[4][5][4,5]. Environment plays a crucial role in zoonosis transmission and spread. In fact, on the one hand, a healthy environment (in which humans, animals, and the environment are in a perfect balance) could mitigate the spread of infectious diseases [6]; on the other hand, environmental changes, including changes in climate, landscape, and communities of hosts and vectors, have all been implicated in the spread of zoonotic diseases directly (i.e., by modulating immunocompetence) or indirectly (i.e., by modifying the vectors composition and density) ^[4][7][4,7]. Land use modifications, for instance, intensive livestock farming, urbanization, encroachment into wildlife habitats, and agricultural changes, account for around 50% of all zoonotic emerging infectious diseases [8]. Pathogens traditionally spilled over from animals to humans; however, as testified by the SARS-CoV-2 pandemic, human encroachment into wildlife habitats, exponential human population growth, and exploitation of the environment make spillover more likely, with potentially devastating consequences [9]. 

The neglected tropical diseases (NTDs) could be defined as a diverse group of diseases whose health and the economic burden falls most heavily on the poorest people and communities ^[10][17]. Some of these are neglected tropical zoonoses (NTZs) which severely impact the environment, animal, and human health and create severe economic losses. NTZs have been at the cornerstone of the One Health/Ecohealth approach, with an estimated amount of $20 billion in direct costs and over $200 in indirect losses ^[11][18]. Nowadays, as stated above, the threat of the NTDs emergence due to climate changes, employment of natural resources, the constant increase of the world population, and their new lifestyle are increased worldwide. Some NTZs, for instance, soil-transmitted helminths, dirofilariasis, onchocerciasis, dengue, chikungunya, and schistosomiasis, as well as rabies and leishmaniosis, have been extensively studied due to their high pathogenic relevance ^{[12][13][14][15]}[19,20,21,22]. Furthermore, the linkages and effects that make them relevant to all the SDGs and how the efforts to mitigate their impact will have a direct influence on overall SDGs progress have been investigated ^[16][15]. By contrast, other NTZs, such as balantidiasis, despite their wide distribution, have been poorly investigated ^[17][18][19][23,24,25].

Balantidiasis is a parasitic disease caused by the ciliated protozoa Balantidium coli (also known as Neobalantidium coli or Balantioides coli), which affects a variety of hosts including domestic pigs, ruminants, guinea pigs, and rats ^[18][24]. Balantidium coli features a direct lifecycle with fecal-oral route transmission that occurs mainly by ingestion of food and water contaminated with cysts ^[20][21][26,27]. This parasite has a worldwide distribution; however, it is more common in the subtropical and tropical regions of the world ^[22][28]. The reservoir hosts are the domestic and wild pigs, in which the parasite inhabits mainly the villi or lumen of the large intestine ^[17][23]. In its reservoir host, the prevalence of the infection ranges from 0.7% to 100% depending on the animals’ reader system, geographic origin of animals, and, mainly, the breeding hygienic conditions ^{[17][18][19][23][24]}[23,24,25,29,30]. In a reservoir host, B. coli is commonly considered nonpathogenic; however, in symptomatic animals, the clinical presentation is characterized by fetid watery diarrhea, appetite loss, dehydration, loss of body condition, and retarded growth, inevitably leading to economic losses ^[25][31].

In developing countries, due to poor hygienic conditions, close contact between humans and farmed animals, malnutrition, concomitant infections, and debilitating diseases, B. coli could also represent a serious threat to human health ^[20][21][26,27]. In fact, as is well-known, balantidiasis could be considered a relevant NTZ, and particularly in the poorest countries, B. coli is regarded as one of the most underestimated food- and waterborne parasitosis ^[17][23], while in the developed countries, B. coli spread could be occasional and related to contamination or a process failure within water utilities or recreational waters (i.e., in swimming pools, water parks) ^[26][27][32,33]. Moreover, this pathogen could be transmitted by the consumption of raw or undercooked meat following carcass contamination during slaughtering ^[17][28][29][23,34,35]. In humans, B. coli infection could outcome in an asymptomatic way or generate a severe syndrome characterized by mucosal ulceration accompanied by diarrhea and dysentery with possible fatal outcomes ^[30][36]. This last scenario is mainly linked to other debilitating conditions, for instance, immunodepression, chronic and infectious diseases ^[31][37].

2. The Social Perspective