Research progress in molecular epidemiology of Cryptosporidium in non-human primates

Tian-Ming Ma, Yu Qiang, Guang-Xu Ren, Gang Lv

Key Laboratory of Translational Medicine for Tropical Diseases; NHC Key Laboratory of Control of Tropical Diseases; Hainan Medical University-The University of Hong Kong Joint Laboratory of Tropical Infectious Diseases; Department of Pathogenic Biology, Hainan Medical University, Haikou 571199, China

Keywords:Cryptosporidium Non-human primates Genotype Zoonotic

ABSTRACT Cryptosporidium is an emerging single-cell zoonotic pathogen. By invading human and animal small intestinal epithelial cells, the host produces a variety of clinical symptoms, mainly diarrhea. Spores of Cryptosporidium can be transmitted through water-borne, food-borne,and mutual transmission between hosts, which has important public health significance.Studies have shown that non-human primates can be infected with multiple Cryptosporidium genotypes. Moreover, this species has a high genetic similarity with humans, so it needs to be taken seriously. This article reviews the infection rates, genotypes, and zoonotic risk of Cryptosporidium in non-human primates.

Cryptosporidium is an important zoonotic intestinal protozoa,which is widely parasitic in humans and animals, and can cause Cryptosporidiosis [1] that causes a variety of gastrointestinal symptoms mainly diarrhea [2,3] in the hosts. Cryptosporidium infection in normal immune population often causes self-limited diarrhea [4], and causes severe diarrhea even death in Neonatal and people with immunodeficiency, which is listed as one of the suspected indicators of AIDS by WHO [5,6]. Cryptosporidium has a wide range of genetic diversity, and different species /genotypes have different host range, pathogenicity and transmission characteristics. To date, 42 Cryptosporidium species and more than 40 genotypes have been identified, of which more than 20 species and genotypes can infect human [7]. Among them, C. parvum(Cryptosporidium parvum) and C. hominis (Cryptosporidium hominis)are the most common [8]. It is generally believed that C. parvum in human body mainly comes from animal transmission, showing the characteristics of zoonosis, while C. hominis is human to human transmission [9]. In recent years, with the deepening of molecular epidemiological investigation, C. hominis has been identified in a variety of animals, and non-human primates are the most common infection (see Table 1). Therefore, the source and transmission route of C. hominis in human body need to be re-recognized. In addition,nine Cryptosporidium species have been isolated from non-human primates, all of which are zoonotic. Based on the genetic diversity of Cryptosporidium carried by non-human primates and its important public health significance, this paper reviewed the infection rates,genotypes and zoonotic risks of Cryptosporidium infection in nonhuman primates, so as to provide reference for tracing the source of Cryptosporidium infection in human body and other animals, as well as the prevention and control of Cryptosporidiosis.

1. Prevalence

At present, 21 studies in 9 countries have reported Cryptosporidium infection in non-human primates. The infection rate ranges from 0.5% to 20.7%, and the total infection rate is 4.6% (263 / 5734)(see Table 1). The average infection rates of Cryptosporidium in non-human primates were 0.5% (1 / 201), 2.7% (8 / 298), 2.6% (6/ 235), 4.0% (4 / 100), 1.0% (2 / 200), 16.0% (21 / 131) and 4.0%(4 / 100) in Central African Republic, Indonesia, Kenya, Rwanda,Thailand, Tanzania and Uganda, respectively. In USA, one case of Cryptosporidium infection was found in Macaca mulatta and Propithecus coquereli [10-18]. In China, the average infection rate of Cryptosporidium in non-human primates was 4.8% (215 / 4467) (see Table 1). They were: Hainan 8.7% (143 / 1645), Qinling Mountains 7.0% (6 / 86), Guizhou 10.9% (45 / 411), Henan 0.6% (5 / 786),Guangdong 1.8% (1 / 57), Guangxi 1.0% (11 / 1079), Shanghai 0.7% (2 / 290), and some small-sample areas [19-25]. In terms of geographical distribution, the infection rate of Cryptosporidium in non-human primates in Western China is higher than that in eastern China. In addition to geographical factors, the environment and age of non-human primates were also important factors affecting the infection rate of Cryptosporidium. Karim et al. [24] found that the infection rate of Cryptosporidium in non-human primates in captivity was 1.1% (12 / 1110), which was different from that of free stocking(0.6%). Zhao et al. [19] (5.7%, 11 / 193 and 0%, 0 / 30) and Chen et al. [20] (10.7%, 118 / 1102 and 4.0%) in Hainan in 2018, In addition,Li et al. [26] also reported that the infection rate of Cryptosporidium in young group was higher than that in old group.

In addition, the infection rates of Cryptosporidium in different kinds of non-human primates were also different. As of June 2019, the average infection rates of Cryptosporidium in China were as follows:Long tailed macaque (5.8%, 152 / 2628), rhesus monkey (3.3%, 60/ 1813), Slow Lorises (10.0%, 1 / 10) and Francois' leaf monkeys(6.7%, 1 / 15) [19-25]. At present, due to the small sample size of some species in non-human primates (n ＜ 50), the infection rate and difference of Cryptosporidium in different species of non-human primates need to be studied.

Therefore, the infection rate of Cryptosporidium in non-human primates may be related to regional, species, age and environmental differences, which needs further study by scholars all over the world.

2. Species and Genotypes

Non-human primates can be infected by many Cryptosporidium species and have high genetic diversity. To date, nine Cryptosporidium species have been isolated and identified in the world, including C. hominis, C. parvum, C. felis, C. muris, C. suis, C. ubiquitum, C.meleagridis, C. bovis and C. andersoni. C. hominis was the main infection species (see Table 1). Non-human primates carrying Cryptosporidium species have been found to be able to infect human, among which C. parvum and C. hominis were the most common. C. parvum subtype family IIa-IIp was mainly distributed in developed countries, and IId family was the main subtype family of Cryptosporidium infection in Chinese people [7]. Ia, Ib, Id and Ie were the main subtypes of C. hominis subtypes, and Ib subtype family was widely distributed in the world [7]. As early as 1999, nizeyi et al. [27]first found Cryptosporidium in gorilla feces, which was identified as C. parvum. In 2002 and 2003, Dubey et al. [28] and Warren et al. [29]found C. muris, which was different from C. parvum in cynomolgus monkeys. In 2011, Li et al. [26] identified C. hominis from baboons in Kenya, and analyzed the subtype of C. hominis for the first time, and obtained three subtypes: IbA9G3, IfA12G2 and IiA14. In 2012, ye et al. [24] found C. fells, C. hominis, C. parvum in Chinese macaques.The subtype IIc family of C. parvum was found to exist in both human and non-human primates. In 2015, Parsons et al. [15] identified C. hominis in baboons, chimpanzees and people living in the same environment in Tanzania, and identified the zoonotic subtype IfA12G2. In 2018 and 2019, Zhao et al. And Chen et al. studied cynomolgus monkeys in Hainan, China, and showed that C. hominis was the main infection species [19,20]. In addition, other species of Cryptosporidium in non-human primate has been identified. At first,human was considered as the natural host of C. hominis, but it has been confirmed that non-human primates, horses, donkeys, cattle,yaks, sheep, goats, kangaroos, rodents, hedgehogs, dogs and pigs can be infected with C. hominis [7]. Therefore, the natural host of C.hominis needs to be further studied.

3. Zoonotic Risk

The same species and genotype of Cryptosporidium in human and non-human primates have been confirmed one after another[7]. Cryptosporidium infection in human may be from non-human primates. Ye et al. [25] carried out Cryptosporidium detection on macaques freely released in a park in Guizhou Province in 2012,and found that most of the genotypes in macaques have zoonotic characteristics. The researchers speculated that they could pose a threat to tourists who were in close contact with them, polluted water sources and caused public health impacts. Karim et al.[24] found that zoonotic genotypes were prevalent in non-human primates in zoos of four provinces in China. C. homoni subtype Iia has been reported in Chinese cynomolgus monkeys, two Swedes who have been to Thailand monkey farm and American rhesus monkey [16,23,30]. In 2015, a study in Tanzania National Park showed that both baboons and chimpanzees could be infected with the same subtype IfA12G2 of C. hominis, and the infection was assessed to be the same as that in the living areas of human beings and animals, and there was a statistical correlation [15]. Therefore, non-human primates may be one of the transmission sources of human infection with Cryptosporidium. The non-human primates that have been infected with Cryptosporidium pose a health threat to tourists, laboratory researchers and breeders who are in close contact with them.

4. Prospects

In view of the important clinical and public health significance of Cryptosporidium, the pathogen has been listed as a class B biocontrol pathogen that must be reported by the National Institutes of health(USA), and was also listed as a microbial pollutant that can cause water-borne outbreaks by the American Environmental Protection Association (EPA) [31]. Non-human primates have attracted much attention in the field of medicine and scientific research due to their special kinship with human beings. Recent research results have revealed the risk of Cryptosporidium spreading between non-human primates and human beings, and the possibility of human as a natural host to spread to non-human primates and other animals [7]. With the deepening of the investigation on the molecular epidemiological distribution of Cryptosporidium, the improvement of genotype data, and the accurate analysis of its population genetic characteristics combined with Multilocus sequence typing(MLST), it is expected that in the near future, the natural host can be traced back and effective control can be carried out.

Table1 Prevalence and genotype distribution of Cryptosporidium in non-human primates worldwide