Enterovirus 68

Enteroviruses are a group of positive-sense single stranded RNA viruses that are known to cause certain human diseases (positive-sense just means 5’ to 3’; and can be directly translated to viral proteins; and that RNA complementary strand is not needed; and thus do not need RNA polymerase). One example of an enterovirus is Polio, however many non-polio strains also exist.

It affects millions of people per year and the virus is found in respiratory secretions.

It was first isolated in California in 1962 from pediatric patients but later on considered rare, however it has been on the news the past few months and is getting some traction; the late 2000s had a dramatic increase of EV68. It most severely affects children under the age of 5 years that have respiratory illnesses.

EV68 shares properties with rhinoviruses, which are the most common viral infective agents in humans and are the predominant cause of the common cold.

Thus far, the mechanisms for EV68 has been relatively unknown.

EV68 can cause mild symptoms such as fever, runny nose, sneezing, cough and body/muscle aches. It can cause severe symptoms such as wheezing and extreme difficulty breathing. It is spread via fluid secretions like saliva, mucus or sputum.

Summer is the most probable time to get sick and by late fall the percentage of EV-68 infections decrease. EV68 is not normally common but in 2014 there have been increased number of cases. Kids are most likely to get ill because they do not have immunity from previous exposure to these viruses, however, adults may experience no or mild symptoms most of the time; asthmatic children are most at risk.

Since the exact mechanism of enterovirus 68 is unknown, it is speculated that they share many features with other +ssRNA viruses. The mechanism is as follows.

In the first step of viral replication, early proteins are made. An example of an early protein is viral replicase. This is an RNA-dependent RNA polymerase (RdRp), meaning that it uses RNA as a template to make more RNA. In step 2, the RdRp copies the original positive-sense RNA strand to make a double-stranded RNA replicative complex. The newly made negative-sense RNA strand is used as a guide to make more single strands of positive-sense RNA (step 3). These single strands of positive-sense RNA can be used as mRNA to make the structural proteins (step 4) or will be packaged into the final virions. Step 5 shows that the structural proteins and the positive-sense single strands of RNA are packaged together (as indicated by the dotted green arrow) to bud out or exit the cell when it lyses (explodes)

This research team aimed to study the antigenicity and receptor binding of EV68 detected in “recent” years as opposed to the prototype “Fermon” strain, this is because the underlying molecular mechanisms for this trend are still unknown; in a way it makes sense because EV68 was not really considered so lethal, so resources were not allocated to researching it as much as something much more prevalent.

Hemaglutination inhibition (HI) and neutralization (NT) were used. The Fermon strand (first detected) had lowest HI compared to recent EV68 strains. This showed that the different antigenicity may account for increases in EV 68 detection in recent years.

Also, EV68 preferably binds to alpha2-6 sialic acids, which suggests that EV68 may have an affinity for the upper respiratory tract; this is the first report describing the properties of EV68 receptor binding to specific types of sialic acids; recall that sialic acids are N- or O- substituted derivatives of neuraminic acid, a monosaccharide with a nine-carbon backbone and in this case they are the receptors

Proposed mechanism: EV68 inhibits Toll-like receptor 3 (TLR3)-mediated innate immune responses by targeting the TIR domain-containing adaptor inducing interferon regulatory factor (TRIF), in infected HeLa cells (cell type in the immortal cell line) EV68 inhibits poly(1-C)(a prototype TLR3 agonist) induced beta interferon regulatory factor 3 (IRF3) activation and beta interferon (IFN-B) expression; both IRF3 and IFN-B are extremely important in fighting viral infections using the innate immune system response.

Further investigations revealed that TRIF, a critical adaptor downstream of TLR3, is targeted by EV68. • When expressed alone, 3Cpro, an EV68-encoded protease cleaves TRIF at Q312 and Q653 with its cysteine protease activity, which are the sites in the amino- and carboxyl-terminal domains, respectively

This cleavage of TRIF may be the mechanism by which EV68 evades host innate immune responses

EV-D68 appears to spread via droplets and direct contact like other respiratory viruses. (unlike most enteroviruses) EV-D68 can be present in respiratory secretions from the nose and throat and can spread from an infected person when they cough or sneeze. Touching surfaces or objects contaminated with these secretions may also result in infection if the virus then gets into the body by touching the mouth, nose or eyes.

There is no vaccine or specific antiviral treatment for EV-D68. Most people don’t require any treatment and will get better on their own, but symptoms like wheezing and fever can be treated (aspirin should be avoided in children). Patients who have difficulty breathing may require hospital admission and those with severe breathing problems may require treatment in an intensive care unit including being placed on a ventilator.

In mid-August 2014, the US Centers for Disease Control and Prevention (CDC) began investigating clusters of children with severe respiratory illness in Missouri and Illinois. Laboratory testing indicated that EV-D68 was the cause of these illnesses. The CDC has since reported an increasing number of laboratory-confirmed cases of EV-D68 from an increasing number of states. As of September 15, 2014, laboratory-confirmed cases have been reported in Canada.

The actual number of cases of EV-D68 is not known as people with viral infections often don’t seek medical care and swabs to test for viral infections are not routinely done. As well, not all laboratories test for EV-D68 or other respiratory viruses, and most respiratory infections are not reportable to public health. For most viruses, knowing the specific type of virus does not change patient care.

• Most of the news coverage on enterovirus-d68 are in America, as the outbreak seems to be larger there. Right now it is unknown how many cases there are in Canada because people haven’t been keeping track. It’s not a disease that is required to be reported to public health departments, and not everyone goes to the hospital for the symptoms that enterovirus-68 shows. • The first death in Canada occurred just two weeks ago in BC. Surprisingly, the person that died was not a child but in fact a man in his 20s. He had severe asthma – goes to show that although it is more commonly serious for young children, it can affect others (especially those with existing respiratory illnesses), so everyone should take precautions.

• Clean your hands frequently with soap and water or an alcohol-based hand rub, including after touching commonly touched objects and surfaces, before touching your face, before preparing food and before eating; • Avoid touching your face as much as possible; • Stay at least two metres (six feet) away from people who are ill; • Frequently clean surfaces and objects that are commonly touched.

Enterovirus D68. (2014). Retrieved October 22, 2014, from  http:/www.publichealthontario.ca

Enterovirus D68. (2014, September 25). Retrieved October 15, 2014 ffrom http://www.cdc.gov

Imamura, T., Okamoto, M., Nakakita, S. I., Suzuki, A., Saito, M., Tamaki, R.,… & Oshitani, H. (2014). Antigenic and receptor binding properties of Enterovirus 68. Journal of virology, 88(5), 2374-2384.

Rybicki, E. (2003, May 12). Viral Replication Strategy in Positive-Sense Single-Stranded RNA Viruses - Library. Retrieved October 19, 2014, from http://www.microbelibrary.org

Xiang, Z., Li, L., Lei, X., Zhou, H., Zhou, Z., He, B., & Wang, J. (2014). Enterovirus 68 3C Protease Cleaves TRIF To Attenuate Antiviral Responses Mediated by Toll-Like Receptor 3. Journal of virology, 88(12), 6650-6659.