Water-borne Viruses Through Polluted Water

The viruses of greatest significance in the water borne transmission of infectious diseases are essentially those that multiply in the intestine of humans and are excreted in large numbers in the feces of infected individuals.

Although viruses cannot multiply outside the tissues of infected hosts, some enteric viruses appear to have a considerable ability to survive in the environment and remain infective.

Discharges of sewage and human excreta constitute the main source of human enteric viruses in the aquatic environment. With the various analytical methods currently available, wide variations are found in the numbers of viruses present in sewage.

The numbers of viruses and the species distribution will reflect the extent to which the population is carrying them. It may reduce the number of viruses by the population.

Sewage treatment may reduce the number of viruses 10-1000-fold, depending on the nature and extent of the treatment given. However, it will not eliminate them entirely, and the sludge produced during sewage treatment will often contain large numbers. As sewage mixes with receiving water, viruses are carried downstream. They remain detectable for varying periods of time, depending on the temperature, the degree to which they are absorbed onto sediments, the depth to which sunlight penetrates into the water, and other factors. Consequently, enteric viruses can be found in sewage polluted water at the intakes to water-treatment plants.

The relationship between the occurrence of viruses in water and risks to health is not a simple one. Viruses are replicating infectious agents that are among the smallest of all microorganisms. In essence, they are nucleic acid molecules that can enter cells and replicate in them, and code for proteins. They are capable of forming protective shells around them. Viruses pathogenic to humans can occur in polluted water. Some of the diseases attributed to them are listed below:

The nature of viruses:

Virus Family	Members	No.of serotypes	Diseases caused
Picorna-viridae	Human polioviruses	3	Paralysis, meningitis, fever
	Human echoviruses	32	Meningitis, respiratory disease, rash, fever, gastroenteritis
	Human coxsackie Viruses a1-22,24	23	Enteroviral vesicular pharyngitis, respiratory disease, meningitis, enteroviral vesicular stomatitis with exanthem (hand, foot and mouth disease)
	Human coxsackile viruses b1-6	6	Myocarditis, congenital heart anomalies, rash, fever, meningitis, respiratory disease, epidemic myalgia (pleurodynia)
	Human enteroviruses 68-71	4	Meningitis, encephalitis, respiratory disease, rash, acute enteroviral haemorrhagic conjunctivitis, fever
	Hepatitis A virus	1	Hepatitis A
Reo-viridae	Human reoviruses	3	Unknown
	Human rotaviruses	5	Gastroenteritis, diarrhea
Adeno-viridae	Human adenoviruses	41	Respiratory disease, conjunctivitis, gastroenteritis
Parvo-viridae	Adeno-associated viruses	4	Latent infection following integration of DNA into the cellular genome
Calici-viridae	Human caliciviruses	5	Gastroenteritis in infants and young children.
	Small round structured viruses (including norwalk virus)	14	Gastroenteritis, acute viral gastroenteropathy (winter vomiting disease)
	Hepatitis E virus		Hepatitis E
Unknown	Astroviruses	1	Gastroenteritis, neonatal necrotizing enterocolitis
Papova-viridae	Papillomaviruses	2	Planter warts

The virus particle or virion consists of genome, either RNA or DNA, that is surrounded by a protective protein shell called the capsid.This shell by itself is often enclosed within an envelope that contains both Viruses replicate only inside specific host cells. They are totally dependent on the host cell’s synthetic apparatus and energy sources, and are thus parasites at the genetic level.

Pathogen	Disease
Bacteria campylobacter jejuni	Gastroenteritis
Enteropathogenic escherichia coli	Gastroenteritis
Legionella pneumophila	Acute respiratory illness
Salmonella	Typhoid, paratyphoid, salmonellosis
Shigella	Becillary dysentery
Vibrio cholerae	Gastroenteritis
Protozoa cryptosporidium	Diarrhea
Entamoeba histolytica	Amoebic dysentery
Giardia lamblia	Diarrhea
Naegleriafowleri	Meningoencephalitis
Enteroviruses	Respiratory illness
Enteroviruses	Eye infection
Adenovirus	Gastroenteritis
Astrovirus	Gastroenteritis
Calicivirus	Gastroenteritis
Coxsackievirus A	Myocarditis, meningitis, respiratory illness
Echovirus	Meningitis, diarrhea, fever, respiratory illness
Hepatitis A virus	Infectious hepatitis
Norwalk virus	Diarrhea, vomiting, fever
Poliovirus	Meningitis, paralysis
Rotavirus	Diarrhea, vomiting

Recognition of seawater in ground water:Ground water samples taken from where there is seawater intrusion may have a chemical composition different from a simple proportional mixing of seawater and ground water. The popular belief is that, increase of total dissolved solids or chlorides alone is a valuable parameter to determine the extent of intrusion. However, the chloride-bicarbonate ratio (ratio of chlorides to the sum of carbonates and bicarbonates) is more important, which is definitely a pointer to the intrusion as given below:

Type of water	Cl/CO3 + HCO3
Normal good ground water in aquifer	1
Slightly contaminated ground water	1 to 2
Moderately contaminated ground water	2 to 5
Injuriously contaminated ground water	5 to 10
Highly contaminated ground water (near sea shore)	10 to 20
Sea water	200

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