JUN 18, 2019 11:00 AM PDT

Structures of Outbreak Strains of Human Norovirus

WRITTEN BY: Dena Aruta

Norovirus infections also called the "stomach flu," are foodborne viral illnesses that are spread from person-to-person via direct contact or by consuming contaminated food or water and contact with surfaces contaminated with feces. It is highly infectious and requires as few as 18 viral particles to cause infection. They are the leading cause of foodborne illness in the U.S. and represent over 96% of all non-bacterial outbreaks worldwide. The U.S. usually sees about 21 million cases annually, which accounts for over $2 million in medical care and lost wages. Although noroviruses are responsible for widespread outbreaks, there are currently no vaccines available and no effective treatments other than supportive care. The video below provides a basic understanding of norovirus infections. 

Clinical trials are currently analyzing shells of noroviruses that are absent of genetic material as vaccine candidates. These shells were previously thought to be the same size; however, James Jung and colleagues at Cold Spring Harbor Laboratory used high-resolution (2.6- to 4.1-Å) cryoelectron microscopy (cryo-EM) to examine the sizes and surfaces of four different outbreak strains.  Since vaccines are developed based on the antibodies produced in the body after encountering the capsid (protein shell) of a virus, the shape, size, and surface structures are essential for vaccine development of each strain. 

"We need to understand what the norovirus capsid shapes actually look like, and the shape differences between different strains," said James Jung, a postdoctoral fellow in Dr. Leemor Joshua-Tor's lab at Cold Spring Harbor Laboratory (CSHL). 

Noroviruses are round, non-enveloped, ssRNA viruses and are members of the Caliciviridae family. There are at least six genogroups that are further subdivided into 30 genotypes; genogroups I, II, and IV are capable of infecting humans. Jung and his team analyzed four strains, GII.2 SMV (2.7 and 3.1 Å), GII.4 Minerva (4.1 Å), GI.7 Houston (2.9 Å), and GI.1 Norwalk (2.6 Å), using cryoelectron microscopy to gain a better understanding of the architecture of the capsid and the relationship between variations and disease development.  

"Previously, it was thought that the norovirus shells exist in single-sized assemblies consisting of 180 building blocks and 90 surface spikes. What we found was an unexpected mixture of different shell sizes and shapes. We found a smaller form, which consists of just 60 building blocks with 30 surface spikes placed further apart. We also found larger shells made out of 240 building blocks with 120 surface spikes that are lifted significantly above the base of the shell and form a two-layered architecture that could interact differently with the human cells," Jung said.

"That means each strain will interact differently with human cells," Jung explained. "The way the antibodies bind is also going to be different. Vaccines should be formulated to take into account the variations across strains and structural forms." 

Their high-resolution images with near-atomic detail, which showed variation in the sizes and shapes of the capsids as well as the surface spikes, will be invaluable as templates for future vaccine and antiviral drug development. 

About the Author
  • After earning my Bachelor of Science degree in biology/chemistry from Virginia Polytechnic Institute and State University (aka Va. Tech), I went on to complete clinical rotations in laboratory medicine at Roanoke Memorial Hospital. I spent the next 21 years working in healthcare as a clinical microbiologist. In 2015, I combined my fascination with medicine and passion for writing into a freelance career, and I haven't looked back. Even though my expertise is in microbiology and infectious diseases, I'm adept at writing about any medical topic. Being a freelance writer allows me to pursue a career where I can work at home with my two feline assistants, Luke and Grace. I'm a firm supporter of animal rights and volunteer for a local rescue during my free time. 
You May Also Like
APR 23, 2020
Cancer
APR 23, 2020
Dual Inhibition from One Chemotherapy
Acute Myeloid Leukemia, or AML, is an aggressive blood cancer with a poor 5-year prognosis. The primary targets of chemo ...
APR 23, 2020
Health & Medicine
APR 23, 2020
Study Shows Filtered Coffee is Best for Your Health
Are you drinking more coffee than usual during the COVID-19 lockdown? Navigating weeks of working from home or onsite, a ...
APR 24, 2020
Health & Medicine
APR 24, 2020
Study Shows Marijuana Withdrawal is Real
Whether or not an addiction to marijuana is a risk of the drug has been widely debated, with the general population typi ...
APR 30, 2020
Cancer
APR 30, 2020
A New microRNA for the Cancer Fighting Toolkit
MiRNAs are small snippets of genetic information that regulate gene expression thought to be able to regulate up to 60% ...
MAY 15, 2020
Cardiology
MAY 15, 2020
Cardiovascular Disease Mortality is Greater in Rural Areas
A wide variation in cardiovascular disease mortality rates has been noted among counties in the United States. Residents ...
MAY 23, 2020
Cancer
MAY 23, 2020
A New Biomarker to Identify a Triple Negative Breast Cancer Prognosis
Breast cancer, one of the most common cancers in the world, are commonly separated into one of several sub-types. These ...
Loading Comments...