Hepatitis E virus (HEV) is recognized as one of the most important agents of acute viral hepatitis worldwide. According to estimates of the World Health Organization (WHO) , every year there are around 20 million infections, 3 million of symptomatic cases of HEV and more than 50,000 deaths in the planet.
While in industrialized countries HEV infections normally lead to sporadic zoonotic or foodborne cases of acute hepatitis, in developing regions HEV causes large recurrent outbreaks affecting several hundred to several thousand persons. Such outbreaks are caused by consumption or use of fecally contaminated water. HEV waterborne outbreaks often occur in areas with limited access to clean water, or with low levels of water sanitation and hygiene. In addition, HEV waterborne outbreaks frequently strike areas of civil conflict or emergency such as refugee camps, where its control may be challenging and the disease outcomes more dramatic.
HEV particles are small (approximately 27-34 nm in diameter), non-enveloped, and contain a single-stranded RNA (ssRNA) genome of 7.2 kilobases (kb). HEV is currently classified within the Hepeviridae family and the Orthohepevirus genus. Based on genetic analyses, human isolates of HEV are classified in four genotypes and several subtypes. Genotypes 1 and 2 are responsible for the occurrence of large waterborne outbreaks in tropical and some subtropical regions. Specifically, genotype 1 has been detected in Asian countries (Bangladesh, Cambodia, China, India, Kyrgyzstan, Myanmar, Nepal, Pakistan, Uzbekistan, and Vietnam) as well as in Africa (Algeria, the Central African Republic, Chad, Djibouti, Morocco, Sudan, Tunisia, Namibia, Egypt, and South Africa). Genotype 2 was initially detected in an epidemic in Mexico, but more recently it has also been reported in African countries (Central African Republic, Chad, Democratic Republic of the Congo, Egypt, Namibia, and Nigeria). Genotypes 3 and 4 have been identified in sporadic acute hepatitis E cases in the United States, Europe, China and Japan, and are only associated with cases of zoonotic origin.
HEV outbreaks are thought to occur after events of heavy rainfall and floods, which may magnify the contamination with human feces of the water used for multiple purposes (drinking, cooking, personal hygiene, religious rituals, etc.), or in hot and dry months, possibly due to lower water levels which lead to an increased concentration of enteric pathogens. These observations suggest that climatic factors may be of major importance for the efficient transmission of HEV and the occurrence of outbreaks. However, the specific environmental conditions influencing HEV spatiotemporal dynamics remain largely unknown. It is therefore currently not possible to anticipate the spatiotemporal occurrence of HEV epidemics. In a context of climatic change, it is urgently needed to better understand the ecology of waterborne pathogens in order to increase our preparedness toward future HEV outbreaks.