The prevalence of Cryptosporidium spp. reported in this study (6.99%) is consistent with results from other studies, which demonstrated its prevalence in Africa to occur in the range of 3-20% (Current and Garcia 1991). Our study show that Cryptosporidium is one of the most common gastrointestinal pathogen in humans, with a prevalence of 9.8%, almost similar to the 9% infection rates reported among children in Tanzania (Cegielski et al. 1999). However, higher infection rates of cryptosporidiosis have been reported in other studies, which include 17% in Egypt (Abdel-Messih et al. 2005) and 32% among children in Guatemala (Laubach et al. 2004).
This study identified nine species of Cryptosporidium through sequencing. These species include; C. parvum, C. hominis, C. andersoni, C. ubiquitum, C. meleagridis, C. bovis, C. muris, C. viatorum and C. xiaoi. In our study, majority of human infections were caused by C. hominis and the cattle genotype, C. parvum. These results are in agreement with those of a documented genotypic survey on the prevalence of Cryptosporidiosis among children with persistent diarrhea at Mulago Hospital in Uganda (Tumwine et al. 2003). The afore-mentioned Ugandan study demonstrated that 73.7% of the infections were caused by C. hominis, 18.4% were due to C. parvum while 3.9% were mixed infections with both species. Elsewhere, an epidemiologic study of cryptosporidiosis among children in Malawi illustrated that out of 43 cases, C. hominis was responsible for two with C. parvum (Morse et al. 2007) causing 41 cases. Because C. hominis and the cattle genotype C. parvum cause majority of human infections, the sources of these species are the main reservoirs of human cryptosporidiosis (Razakandrainibe et al. 2018). While humans are the only notable source of C. hominis, both humans and ruminants are the principal sources of the cattle genotype, C. parvum (Xiao et al. 2001). The cattle genotype of C. parvum has been found in other mammals. However, infected humans, cattle and sheep shed high numbers of oocysts, especially when infected during infancy; this probably poses a major risk to the environmental contamination (Putignani and Menichella 2010).
According to Pumipuntu and Piratae (2018), transmission of cryptosporidiosis occurs through direct or indirect contact with stools of animals. Outbreaks occur through various routes of transmission: person-to person contact in institutions, animal contact during farm visits, and contact with recreational waters, swimming pools, municipal drinking water and food (Chalmers 2012). Previous studies identified human-to-human contact as the most common means of transmission (Cordell and Addiss 1994). This is illustrated by the increased risk of outbreaks in areas where there is routine crowding, such as day-care centers and schools, or patient-patient and patient-staff transmission in hospitals and the ultimate spread to the family members of the attending children or staff (Casemore 1990; Cordell and Addiss 1994). C. parvum is the most documented Cryptosporidium spp. involved in zoonotic transmission (Zahedi et al. 2016). Most of the reported cases of outbreaks of cryptosporidiosis in schoolchildren after exposure to calves or lambs are because of C. parvum (Casemore 1990; Casemore et al. 1997). C. parvum cryptosporidiosis has also been implicated in infection resulting from occupational exposure to infected animals (Current, 1994; Casemore et al. 1997). Furthermore, evidence from genetic analysis has proven that only the cattle genotype of C. parvum is capable of zoonotic transmission (Sulaiman et al. 1999). However, this genotype has also been found in many other host species such as humans, cattle, pigs and sheep (Putignani and Menichella 2010). The high prevalence of the C. parvum in cattle and sheep coupled with the high numbers of oocysts shed by infected animals, especially newborns, make cattle and sheep important sources of environmental pollution with Cryptosporidium oocysts, which are capable of infecting humans (Uga et al. 2000).
The present study also detected C. parvum in sheep and chickens. This is in contrast with many past studies which had demonstrated a rare occurrence of C. parvum in small ruminants and birds in Africa (Robertson et al. 2020); with C. xiaoi predominating in sheep and goats in Ghana (Squire et al. 2017) and C. ubiquitum predominating in lambs under 5 years in Ethiopia (Wegayehu et al. 2017).
Although C. ubiquitum has a zoonotic potential, human infections in Africa have only been detected on rare occasions (Li et al. 2014). The present study established the existence of this species in goats, sheep and chickens. However, since these animals are likely to ingest C. ubiquitum oocysts in feces of infected children while feeding on grass, zoonotic transmission of this species is feasible in this case (Pumipuntu and Piratae 2018).
This study identified C. andersoni sp. in some of the chicken and human samples analyzed. Recent studies have demonstrated the emergence of C. andersoni as a major species causing cattle cryptosporidiosis, after C. parvum especially in calves (Wang et al. 2019). C. andersoni has also been detected in other animal species, such as cattle, sheep, horses, camels, and ostriches (Liu et al. 2020). In this study, the human C. andersoni was identical to the SSU rRNA gene of two C. andersoni isolates derived from chicken and cattle (XVaA3h and XVaA3g). The same subtypes have been identified in humans (Braima et al. 2019; Xu et al. 2020) and rats (Chen et al. 2019). Results reported in the study indicated that C. andersoni has a significant zoonotic potential.
The present study discovered a novel isolate of Cryptosporidium viatorum in human in Njoro Sub County, Kenya. This therefore increases the number of countries in which C. viatorum has been detected to 10: “Australia (n = 1) (Braima et al. 2019), China (n = 1) (Xu et al. 2020), Colombia (n = 1) (Sánchez et al. 2017), Ethiopia (n = 12) (Adamu et al. 2014; Stensvold et al. 2015; de Lucio et al. 2016), India (n = 2) (Khalil et al. 2017; Khalil et al. 2018), Myanmar (n = 1), Nigeria (n = 2) (Ayinmode et al. 2014; Ukwah et al. 2017), Sweden (n = 3) (Insulander et al. 2013; Stensvold et al. 2015), and the UK (n = 14) (Elwin et al. 2012; Stensvold et al. 2015),” and presently Kenya (n = 1). Currently, the source of infection of C. viatorum in Njoro Sub County is unknown. C. viatorum was initially thought to occur exclusively in humans. However, its detection has also been made in some rat species in Australia (Koehler et al. 2018) and China (Chen et al. 2019; Zhao et al. 2019).
Several studies in Africa have reported the presence of C. meleagridis infections in both immunocompromised and non-immunocompromised individuals, especially children (Hunter and Nichols 2002; Robertson et al. 2020). In this study, chicken were the sources of C. meleagridis and because this species has been identified as a zoonotic Cryptosporidium sp, (Zahedi et al. 2016), chickens may be a potential reservoir. This observation is similar with findings from Côte d'Ivoire (Berrilli et al. 2012) and Nigeria (Ayinmode et al. 2018) which suggested that there existed an association with chicken but in contrast with numerous other studies from Africa which did not indicate any association with infected animals or birds (Mbae et al. 2015) and instead emphasized human to human transmission.
This study identified C. baileyi, C. muris, and C. xiaoi, each from a single source. Species such as C. muris and C. xiaoi have been previously detected and identified in immunocompromised individuals (Chappell et al. 2015); while C. bovis, and C. muris have been detected in immunocompetent humans, especially children (Azami et al. 2007).