Natural History of Cryptosporidial Infection in a Birth Cohort in a South Indian Semi-Urban Slum.

Infectious diseases are a leading cause of childhood mortality. Five of the top 10 causes of death among children living in middle and low income countries are attributed to diseases of infectious origin. Although during the past few decades (between 1970 and 2013), the number of deaths among under-five children worldwide has reduced by more than 64%, an estimated 6.3 million children under the age of five were reported to have died in 2013 and 64% of all childhood deaths have been attributed to infectious causes. In order to reach United Nations Millennium Development Goal (MDG) 4 of decreasing childhood mortality by two thirds by 2015, there is a drive to control and prevent deaths from preventable infectious diseases by prioritizing them in various child health programmes . Several aspects of cryptosporidial infections, and host factors that modify the infection amongst children in this birth cohort have been explored. The impact of the findings on public health issues, particularly relevant to control of cryptosporidial infections are highlighted here. Cryptosporidium spp. is a common cause of parasitic diarrhoea throughout the world and is one of top five pathogens causing moderate to severe diarrhoea among children in developing countries. Despite this, the epidemiology of cryptosporidiosis in endemic settings is poorly understood. This study is innovative because it is the largest birth cohort study on the natural history of childhood cryptosporidiosis. The integration of molecular and serological methods for the diagnosis of cryptosporidial infection, coupled with the intensive bi-weekly follow-up helped capture the true burden of childhood cryptosporidiosis, and found it to be higher than reported earlier. Almost all children in the study acquired cryptosporidial infection by three years of age indicating a high rate of transmission in endemic areas, most likely through asymptomatically infected individuals. This study is the first to explore whether prior natural infection offered subsequent protection from infection or disease. The study found that an earlier infection did not offer protection from infection later in life. High rates and early infection with no subsequent protection requires public health interventions aimed at routes of transmission, rather than vaccines. The results of the study provide important insights in understanding the natural history and epidemiology of cryptosporidiosis in slum communities in India where there is sustained transmission, through multiple routes. The risk factors identified in this study can help develop scientifically sound, geographically relevant and socially sustainable measures that will effectively reduce the transmission of cryptosporidiosis in this and other endemic communities. As opposed to the developed countries where water is the primary mode of transmission, in the Indian setting, the transmission of cryptosporidiosis seems to occur through multiple routes (waterborne, human-to-human and animal-to-human). Personal hygiene and safe animal handling/tethering practices hence would be the leading public health interventions in this Indian setting for short-term benefits. Social interventions such as improvement in maternal literacy, reduction of poverty and provision of basic amenities like access to safe drinking water and sanitation may also help reduce transmission in the long run, but the effect of such intervention can only be ascertained over a longer time frame. Such interventions would also involve the participation of disciplines not directly related to health, such as education, social welfare and local administration.