Posted by: Chris Maloney | February 5, 2012

The Pirate Virus: What Is Norovirus and Why Does It Keep Attacking Cruise Ships?


Noroviruses (Photo credit: AJC1)

Norovirus has struck again.  Two cruise ships down.  It’s more lethal than an Italian captain (joking).

If you want to classify norovirus, well, read the abstract at the end.  Think of norovirus as the pirate of the cruise ships, although it can spread through any semi-enclosed community.  That means hospitals, nursing homes, etc.

The trouble is that norovirus can be spread by food (cruise ship buffet, anyone?), people (see that guy coughing on the chocolate cake at the cruise ship buffet, anyone?), and fomites– which is a cool word and means ANYTHING- (want to use the same knife to cut the chocolate cake that the guy who coughed used, anyone?  Or sleep in his bunk after he’s left the ship?)  So it’s a nasty little critter that resists disinfectants and pretty much loves cruise ships.

Chances are really good that it isn’t the cruise ship’s fault.  They’ve sterilized every surface, and one or more passengers come on the ship even though they just visited their aunt in the nursing home and feel a bit queasy.  But darn it, it’s just a little upset stomach and cruises are expensive.  Bingo, Typhoid Mary and her husband, in a closed environment with everyone else for a week.  And all that sterile ship is ripe for colonization with the incoming virus.

What if, instead of bleaching everything and making it red carpet welcome mat time for norovirus, the cruise companies got smart and started swabbing passengers?  I’m sorry, here’s  a rain check for your cruise.  You’re infectious.  Well, that would make waves.

Another novel idea would be to populate the cruise ship with non-disease causing bacteria before passengers arrive and to flush passengers with probiotics during the voyage.  It’s just yogurt, but with stronger lactobacilli.  If I ran a cruise line, I would be getting researchers to start checking for norovirus resistant strains of probiotics and lay down a protective coating before and between cruises.  “Everybody off the main deck, please.  We’re doing a yogurt wash.  This one is key lime pie flavor.”


Viruses. 2010 Mar;2(3):748-81. Epub  2010 Mar 23.

Pathogenesis of noroviruses, emerging RNA viruses.


Center for Molecular and Tumor Virology, Department of Microbiology and Immunology, Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130-3932, USA; E-Mail: ; Tel.: +1-318-675-8122;


Human noroviruses in the family Caliciviridae are a major cause of epidemic gastroenteritis. They are responsible for at least 95% of viral outbreaks and over 50% of all outbreaks worldwide. Transmission of these highly infectious plus-stranded RNA viruses occurs primarily through contaminated food or water, but also through person-to-person contact and exposure to fomites. Norovirus infections are typically acute and self-limited. However, disease can be much more severe and prolonged in infants, elderly, and immunocompromised individuals. Norovirus outbreaks frequently occur in semi-closed communities such as nursing homes, military settings, schools, hospitals, cruise ships, and disaster relief situations. Noroviruses are classified as Category B biodefense agents because they are highly contagious, extremely stable in the environment, resistant to common disinfectants, and associated with debilitating illness. The number of reported norovirus outbreaks has risen sharply since 2002 suggesting the emergence of more infectious strains. There has also been increased recognition that noroviruses are important causes of childhood hospitalization. Moreover, noroviruses have recently been associated with multiple clinical outcomes other than gastroenteritis. It is unclear whether these new observations are due to improved norovirus diagnostics or to the emergence of more virulent norovirus strains. Regardless, it is clear that human noroviruses cause considerable morbidity worldwide, have significant economic impact, and are clinically important emerging pathogens. Despite the impact of human norovirus-induced disease and the potential for emergence of highly virulent strains, the pathogenic features of infection are not well understood due to the lack of a cell culture system and previous lack of animal models. This review summarizes the current understanding of norovirus pathogenesis from the histological to the molecular level, including contributions from new model systems.

PMID:  21994656

[Current topics on inactivation of norovirus].

[Article in Japanese]


Division of Biomedical Food Research, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501, Japan.


Human norovirus is the most important foodborne virus in Japan. According to the statistics of food poisoning by the Ministry of Health, Labour, and Welfare (MHLW), the number of patients infected with norovirus has accounted for half of all the patients with food poisoning in recent years. One of the most important measures for the control of infectious diseases is establishing of techniques for inactivating pathogens. For the prevention of food poisoning caused by norovirus, MHLW recommends that foods be subjected to heat treatment at 85 degrees C for 1 min or more; moreover, it recommends the use of sodium hypochlorite to inactivate (disinfect) this virus. However, application of these treatments is not always feasible because heat results in denaturation and sodium hypochlorite can be toxic to the human body and can cause discoloration. Therefore, it is necessary to develop and improve the efficacy of disinfectants and physiochemical treatments against the virus. Human norovirus cannot be propagated in cell culture or in a small animal. This matter is the greatest hindrance for testing the stability of this virus in environments or for evaluating the efficacy of disinfectants, heat treatment, pH treatment, ultraviolet or gamma irradiation, high hydrostatic pressure treatment, and other methods for the inactivation of the virus. Hence, some viruses such as human enterovirus, feline calicivirus, or mouse norovirus have been used as surrogates of human norovirus. The data on inactivation and stability of surrogate viruses are exclusively used as the data of human noroviruses. In recent years, some attempts to distinguish between infectious and noninfectious virus particles by genetic methods such as polymerase chain reaction have been made. These methods include pretreatments by RNase for digesting viral RNAs from non-intact or destroyed virus particles, or addition of a reagent such as ethidium monoazide for inhibiting PCR amplification of viral RNAs from them, before RNA extraction. Non-intact virus particles, which may represent virus particles with some damage (s) in the structural protein(s), are not necessarily synonymous with non-infectious virus particles. However, the results of methods using these treatments, compared to the results of traditional methods without these treatments, seem to be more correlated to the amount of the infectious virus particles. Although many disinfectants or physiochemical treatments have been reported, traditional techniques such as removal of virus particles by washing in running water, heat treatment, or disinfection by sodium hypochlorite are still important control measures. Establishment of control measures for human norovirus and successful propagation of the virus in cell culture are strongly desired.

PMID:  22259842
Br J Nutr. 2011 Aug;106(4):549-56. Epub  2011 Apr 27.

Effect of the continuous intake of probiotic-fermented milk containing Lactobacillus casei strain Shirota on fever in a mass outbreak of norovirus gastroenteritis and the faecal microflora in a health service facility for the aged.


Department of Laboratory for Probiotic Research, Juntendo University, Bunkyo-ku, Tokyo, Japan.


For conducting effective risk management in long-stay elderly people at a health service facility, we performed an open case-controlled study to evaluate the effect of the intake of probiotic-fermented milk containing Lactobacillus casei strain Shirota (LcS-fermented milk) on norovirus gastroenteritis occurring in the winter season during the intake period. A total of seventy-seven elderly people (mean age 84 years) were enrolled in the study. During a 1-month period, there was no significant difference in the incidence of norovirus gastroenteritis between the LcS-fermented milk-administered (n 39) and the non-administered (n 38) groups; however, the mean duration of fever of >37°C after the onset of gastroenteritis was 1·5 (SD 1·7) d in the former and 2·9 (SD 2·3) d in the latter group, showing a significant shortening in the former group (P < 0·05). RT-quantitative PCR analysis targeting ribosomal RNA showed both Bifidobacterium and Lactobacillus to be significantly dominant, whereas Enterobacteriaceae decreased in faecal samples from the administered group (n 10, mean age 83 years), with a significant increase in faecal acetic acid concentration. Continuous intake of LcS-fermented milk could positively contribute to the alleviation of fever caused by norovirus gastroenteritis by correcting the imbalance of the intestinal microflora peculiar to the elderly, although such consumption could not protect them from the disease.

PMID:  21521545

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