Norwalk virus

Norovirus belongs to a group of Caliciviridae family viruses. It is non-enveloped, single stranded RNA virus. Discovered in city Norwalk, Ohio, in 1968, during an outbreak of gastroenteritis (stomach flu) in a local elementary school, in faeces examined using electron microscopy. There it gets its first name - Norwalk virus. Together with Sapovirus (which also belongs to a group of Caliciviridae family), it causes acute gastroenteritis, and far now humans are the only known hosts for these viruses.

Norovirus and Gastroenteritis
Norovirus is the main cause of gastroenteritis. With about 25 types of these virus, more than 20 million of people only in USA get infected each year and about thousand finishing in deaths. These viruses affecting people of all ages and an person can host it limitless times during a lifetime. Originally coming from feces, it is usually spread faecal-oral through contaminated water and food, or from person to person, but objects and surfaces too. It is extremely contagious and epidemic, especially in isolated and closed environments, schools, cruising ships, stadiums. Incubation period lasts day or two after infecting with these viruses and depends on immune system of the host as well as type of the virus.

Noroviruses commonly isolated in cases of acute gastroenteritis belong to two genogroups: genogroup I (GI) includes Norwalk virus, Desert Shield virus and Southampton virus and II (GII) which includes Bristol virus, Lordsdale virus, Toronto virus, Mexico virus, Hawaii virus and Snow Mountain virus. Infections with strains of GII tend to be more prevalent (Ando et al 2000, Hansman et al 2004, Kirkwood & Bishop 2001). Interestingly, a study of NoVs detected over a three-year period (1995-1997) in Central Australia (Schnagel et al 2000) showed a predominance of GI strains and contrasts the increased prevalence of GII strains observed in outbreaks investigated in Southeastern Australia during 1980-1996 (Wright et al 1998, White et al 2002). The dominant strain in 2004/5 in Australia was a GII/4 strain, variously referred to as the GII/4 variant strain, Grimsby strain or Farmington Hills strain, which was first detected in 2001 as the cause of a sudden increase in outbreaks in Europe and the US, and has now spread globally.

Transmission
Transmission of norovirus is very easy since there is no vaccine which can prevent this virus, nor there is medicine which can cure from it. Situations in which norovirus transmits are in most cases related to direct contact with already infected person. Indirect transmission through contaminated food, water, objects and surfaces are also common. It transmits easy by sharing foods or using the same utensils with infected person. Foods and drinks can get contaminated when infected person prepare foods, without taking care about personal hygiene after episodes of norovirus symptoms. Non-organic surfaces and objects become contaminated the same way, person can get infected when getting in touch with those surfaces and later on touch mouth. Closed places and institutions such are hotels, cruise ships, schools, stadium crowds, public transportation, restaurants are all places where norovirus can transmit from infected person to a healthy one very easy.

Symptoms
Symptoms of norovirus are almost the same like symptoms of any other cause of gastroenteritis and include watery diarrhea and frequent vomiting on the first place. These symptoms may occur separately on simultaneously. Also infected person will probably experience some of the following symptoms: low grade fever with temperature over 38C/100.4F, nausea, headache, stomach chills and cramps, fatigue, muscle ache, aching limbs. Symptoms appear in a day or two after incubation period, but in cases of low level immune system, they can appear even sooner. Norovirus symptoms lasts for a several days, with gradual reduction of symptoms. Person can spread the virus even after two, three days after relief of symptoms. Most people make a full recovery within a couple of days.

Dehydration
Norovirus may still have adverse outcomes such is severe dehydration in older people, those with frequent or other diseases, people with very low level of immune system, pregnant women and in children.

Signs of mild dehydration are: thirst, dry mouth, dry lips and eyes, headache, dark urine, lightheadedness, dizziness.

Signs of severe dehydration are: severe thirst, inability to urinate, wrinkled skin, sunken eyes, irritability, a weak pulse, cold hands and feet.

Body fluids lost during episodes of vomiting and diarrhea must be replaced, if not dehydration will get even worse and could lead to further complications of health condition, such as low blood pressure and kidney failure. In the case of dehydration the urgent medical attention is needed to prevent from worsening of the health condition!

Apart from the risk of dehydration, in general the disease is not dangerous and there are usually no long-lasting effects nor consequences. Anyway, it can be unpleasant due to exhausting norovirus symptoms.