Non-human primates (NHPs) are known to possess a high genetic relationship with humans, which makes them useful biomedical research models. NHPs might be vulnerable to human diseases, thereby acting as zoonotic reservoirs [8, 10]. In 1997, the first case of transference of E. bieneusi infection was recorded between a human (afflicted with AIDS) and a rhesus monkey (afflicted with simian immunodeficiency virus) [11]. However, until 2011, there was a lack of studies on the occurrence of E. bieneusi in non-human primates at the genotype level [10]. Zhao et al., summarized 16 studies on the infection of E. bieneusi in NHPs from seven countries [8, 12]. Among them, seven studies included M. mulatta, and they were all from China, with a prevalence range from 4.2 to 31.1% [12–18]. For the first time, our study has detected E. bieneusi in wild M. mulatta from the Hainan Province of China, with a prevalence of 15.0%. Generally, E. bieneusi has been found to be more prevalent in wild M. mulatta here than other wild NHPs, such as baboons from Kenya (12.3%) [10], chimpanzees from Cameroon (4.5%) and Kenya (2.6%) [21], gorillas from the Central African Republic (4.0%) [20], orangutans from Indonesia (2.0%) [19], and five captive species of wild NHPs from the Qinling Mountains of China [17]. Our study showed that E. bieneusi was more prevalent in M. mulatta than farm monkeys from Henan (6.8%), Guangxi (8.5%), Sichuan (10.5%), and zoo monkeys from Henan (12.5%) in China [14–16, 22]. However, the prevalence of E. bieneusi in monkeys from Rwanda (18.0%) and some cities in China, like Shanxi (18.2%), Shanghai (26.7%), Hebei (27.0%), and Beijing (29.2%) was higher than that observed in our study [14–16, 20, 22]. Additionally, there are two more studies that identified E. bieneusi infection in laboratory macaques in Beijing (25.6%) and Guangxi (18.5%), China, which were both higher compared with this study [13, 23]. In fact, in Hainan, two studies were reported on captive long-tailed macaques infected with E. bieneusi, which were also more than that observed in our study [8, 24]. Similar to humans and farm animals, age substantially increases the risk E. bieneusi infection in NHPs [8]. Here, we identified a elevated E. bieneusi infection rate in young M. mulatta compared with adults, which agreed with the results of captive long-tailed macaque and laboratory macaques from Hainan, China and North China, respectively [8, 14]. In addition to age, the health of the hosts, the detection methods, sample size, the experimental design, animal practices, etc. could cause the increase in prevalence.
Among the five known genotypes in our study, the genotype PigEbITS7 was detected in 76.9% (20/26) of E. bieneusi isolates, which shows predominance in the investigated wild M. mulatta. This genotype was initially detected in pigs from the USA [7] and it has been confirmed to have a broad host range, even in humans [3]. In China, PigEBITS7 was detected in some patients, including AIDS and hospitalized children, and several animals such as rodents, NHPs, and urban wastewater [5, 8, 25–27].
Additionally, previous studies have reported the presence of four other genotypes (Type IV, Peru6, D, and Henan-III) in humans and animals around the world, of which genotypes D and Type IV are commonly found in E. bieneusi- induced microsporidiosis in humans [3, 28]. Both genotypes D and Type IV have been detected in infants, HIV-positive patients, and HIV-negative patients in China [25, 29–33]. Meanwhile, they have been found in NHPs, pigs, dogs, snakes, cats, hippopotamus, Pere David’s deer, chinchillas, Siberian tiger, lions, Fischer's lovebird, red foxes, wastewater, and lake water [3].
Genotypes Peru 6 (syn. PtEbI, PtEbVII) (from Peru and Portugal) and Henan-III (from Malaysia and China) have been spread across limited geographical area as well as small number of E. bieneusi-infected human cases compared with genotypes D and Type I [34–36]. Meanwhile, genotype Peru 6 has been identified in sheep, goats, reindeers, and wastewater [37–40], whereas genotype Henan-III has been found in NHPs, pet snakes, pigs, and birds in China [41–44]. Therefore, the above shreds of evidence suggest the possible zoonotic transmission of these genotypes from the wild M. mulatta to humans.
In this study, the novel genotype HNM-IX was genetically closely related to the human-pathogenic genotype EbpC which was commonly found in humans from Iran, Czech Republic, Peru, China, Thailand, and Vietnam [29, 45–48]. It was also found in more than 15 animal species and in environmental samples [3, 49]. From the phylogenetic analysis, the six genotypes identified here were all categorized into group 1. Group 1 had almost all human-pathogenic genotypes and possessed 94% of the known E. bieneusi ITS sequences [3]. Therefore, the genotypes in wild macaques investigated including the novel one could have a sizeable zoonotic possibility.