Cryptosporidium and Giardia infections in humans in Tigray, Northern Ethiopia: an unexpectedly low occurrence of anthropozoonotic transmission

Enteric protozoans Cryptosporidium spp. and Giardia duodenalis are among the leading causes of diarrhoea in children. These parasites have particular impact in low- and middle-income countries. In these countries, people often live in close contact with their animals, highlighting the potential role of zoonotic routes of transmission in disease spread. The occurrence and species/genotypes of Cryptosporidium and Giardia duodenalis infecting humans in Tigray, Ethiopia were investigated, along with the risk associated with infection. Stool samples from 249 asymptomatic people (4-80 years of age) in four rural districts in Tigray and 58 from symptomatic young children (1-33 months) attending health centres in Mekelle, Tigray's main city, were analysed for Cryptosporidium oocysts and Giardia cysts. Participants in the rural areas completed questionnaires regarding potential risk factors, with emphasis on livestock contact and sources of water. The occurrence of Cryptosporidium infection was 6% and 5% in people in the rural districts and young children from Mekelle, respectively; equivalent figures for Giardia infection were 29% and 14%. Molecular characterization of Cryptosporidium isolates revealed C. ubiquitum, subtype XIIa in a sample from rural districts, and C. hominis subtype IdA17 (1 sample) and IbA9G3 (2 samples) in infants from Mekelle with diarrhoea. For Giardia, Assemblage B predominated (22/25; 88%), but we also identified three samples with Assemblage A (AII). Our major finding was that, despite the close contact between people and livestock in our rural study sites, transmission of Cryptosporidium and Giardia between humans and their animals seems to be surprisingly uncommon. Our results are discussed in relation to other relevant studies, and also draws attention to the possibility that introduction of zoonotic species and/or subtypes, such as C. parvum, could have serious consequences for both human and animal health. As our study was conducted in Tigray, further investigation in different settings in Ethiopia could provide relevant information on transmission and zoonotic potential, and the potential for spread of zoonotic transmission. In addition, given the importance of these two parasites in causing diarrhoea in children, this information is vital for developing effective appropriate interventions against transmission that can be applied not only in Tigray or Ethiopia, but throughout Africa and beyond.