Human enteroviruses can be detected in sewage sludge from treatment plants and in deep-sea sediments. Below, we explore the four most common viruses found in water.
I. Enteroviruses
Enteroviruses belong to the Picomaviridae family, encompassing poliovirus, Coxsackievirus A, Coxsackievirus B, and ECHOvirus (Enteric Cytopathogenic Human Orphanvirus).Enteroviruses are the most prevalent viruses in aquatic environments and the most extensively studied in water virology. They are often used as representative pathogens in assessing waterborne viral safety due to several key characteristics: high viral shedding rates and prolonged excretion periods in infected individuals; strong environmental resistance and extended survival times; potential for transmission through non-waterborne routes; and relative ease of detection compared to other viruses.
Enteroviruses share the following characteristics: ① Spherical virions with icosahedral symmetry, 22–39 nm in diameter, lacking an envelope; ② Single-stranded positive-sense RNA genome; ③ Resistance to ether and acids (pH 3–5), as well as bile and common disinfectants like 70% ethanol and 5% lysol;They are sensitive to oxidizing agents like 1% potassium permanganate, 1% hydrogen peroxide, and chlorine-based disinfectants. Additionally, they are vulnerable to high temperatures, desiccation, and ultraviolet light; exposure to 56°C for 30 minutes inactivates the virus. Viruses can survive for months in feces and sewage; ④ All can replicate in the intestinal tract and invade the bloodstream to cause viremia, leading to various clinical syndromes.
1. Poliovirus
This virus is a spherical, small virus measuring 8–30 nm in diameter, belonging to the enterovirus family. Poliomyelitis is an acute infectious disease. Infection often causes fever and limb pain, with primary lesions affecting the nervous system. Consequently, some patients may develop paralysis, and severe cases may result in residual paralysis.The disease predominantly affects children, hence its alternative name, infantile paralysis.
Infected individuals shed the virus in both nasopharyngeal secretions and feces. Food and water may become contaminated through fecal transmission, making oral ingestion the primary route of infection. Contaminated water sources can facilitate large-scale outbreaks.
The virus exhibits strong viability outside the human body, surviving for months in water and feces. It can persist long-term at low temperatures but is sensitive to heat and dryness. Heating to 60°C (140°F) or exposure to ultraviolet light inactivates it within 0.5 to 1 hour. Various chlorinating agents, 2% iodine tincture, formaldehyde, and mercuric chloride also provide effective disinfection.Disinfection with residual chlorine at 0.3–0.5 mg/L for 1 hour of contact can inactivate this virus. 2. Other Enteroviruses Besides poliovirus, enteroviruses include Coxsackie and Echovirus. These two viruses are also widely distributed globally, primarily affecting children.They typically circulate more frequently during summer and autumn. Both viruses exhibit the characteristic of transiently colonizing the human intestinal tract. These viruses are relatively small, generally less than 30 nm in diameter, and possess strong resistance. They can withstand exposure to ether, 70% ethanol, and 5% coal tar soap solution, but are highly sensitive to oxidizing agents.
The clinical manifestations caused by these viruses are complex and variable. Viruses of the same serotype can induce different syndromes, while viruses of different serotypes may cause similar clinical presentations. Common symptoms include: aseptic meningitis, encephalitis; acute myocarditis and pericarditis; epidemic pleurisy; herpangina; exanthematous diseases; respiratory infections; and childhood diarrhea.
II. Hepatitis Viruses
Viral hepatitis is generally classified into hepatitis A (infectious hepatitis or short-incubation-period hepatitis) and hepatitis B (serum hepatitis or incubation-period hepatitis), with both exhibiting essentially identical pathological changes and clinical manifestations.Primary clinical symptoms include loss of appetite, nausea, upper abdominal discomfort (or hepatic region pain), and fatigue. Some patients develop jaundice and fever, with most exhibiting hepatomegaly accompanied by impaired liver function.
Hepatitis A virus (HAV) is a picornavirus that exhibits significant morphological differences from other members of its genus. Classified as Enterovirus 72 in 1981, it was recently reclassified into the Hepamavirus family due to its distinct characteristics from enteroviruses in many aspects.
HAV is primarily shed in feces and transmitted via the fecal-oral route. Contamination of water sources or food can lead to epidemic outbreaks.
The hepatitis virus exhibits strong resistance to common chemical disinfectants and can survive for months or years in dry or frozen conditions. It is inactivated by ultraviolet irradiation for 1 hour or boiling for 30 minutes or longer. Chlorine disinfection also provides some inactivation effect.
III. Rotavirus
Rotavirus belongs to the genus Rotavirus within the family Reoviridae. It was first isolated from duodenal epithelial cells of a diarrhea patient by Bishop et al. in Australia in 1973. The viral particle is spherical with a double-layered capsid, each layer forming an icosahedron.The inner capsid particles are arranged radially along the viral periphery, resembling wheel spokes. The intact virus measures approximately 70–75 nm, while the rough particles lacking an outer capsid are 50–60 nm in size. Only the double-layered capsid virus is infectious.
Rotavirus is one of the most common causes of acute diarrhea in children worldwide. It is estimated that over 140 million children globally contract rotavirus gastroenteritis annually, resulting in hundreds of thousands of deaths. Its peak incidence occurs primarily in autumn and winter, hence it is often termed autumn diarrhea.
Rotavirus exhibits strong resistance to various physical and chemical factors, surviving in feces for days or months.The virus retains infectivity after treatment with ether, chloroform, repeated freeze-thaw cycles, ultrasonication, incubation at 37°C for 1 hour, or at room temperature (25°C) for 24 hours. It is acid- and alkali-resistant, maintaining infectivity across a pH range of 3.5 to 10.0. 95% ethanol is most effective for inactivation, and heating at 56°C for 30 minutes also eliminates the virus.
Rotavirus primarily spreads through the fecal-oral route, transmitted via ingestion of contaminated water or food, or contact with contaminated objects. The 1981 rotavirus outbreak in Colorado, USA, was linked to municipal water supply contamination. Since 1982, China has experienced several large outbreaks of group B rotavirus infecting hundreds of people, caused by sewage contamination of drinking water.
IV. SARS Coronavirus (SARS-CoV)
The first case of severe acute respiratory syndrome (SARS, commonly known as atypical pneumonia) was identified in Guangdong Province, China, in late 2002. By June 2003, SARS had spread to 380 countries and regions, with over 8,000 confirmed cases and more than 800 deaths.Initial symptoms typically include fever exceeding 38°C accompanied by chills, headache, fatigue, and muscle pain. Later stages manifest as dry cough without phlegm and respiratory distress. Transmission primarily occurs through close-range droplet spread, though contact with respiratory secretions via hands can also lead to infection through the mouth, nose, or eyes.
Current research identifies the SARS pathogen as SARS coronavirus, classified under the order Nidovirales and family Coronaviridae, belonging to the group of single-stranded RNA viruses. The virus has a diameter of 80–140 nm.
Over 100 types of viruses found in untreated sewage have been detected in human feces.Each gram of human feces can contain over one million viruses, and infectious viral particles in sewage can reach concentrations as high as 500,000 per liter. These viruses are the root cause of disease transmission. To reduce incidence rates, it is essential not only to maintain personal hygiene and food safety but also to address the source by purifying water bodies and minimizing the discharge of domestic sewage and industrial wastewater into water sources.