Picornaviruses

Taxonomy Note Be aware that there are hundreds of picornaviruses, and their taxonomy has undergone significant re-organization, and intertextual variation is very common. Picornaviruses are named for their size and genome type: Small (pico) RNA (rna) Viruses. The genome is single-stranded positive sense; during replication, the RNA is translated to a polyprotein that is then cleaved. The naked genome by itself is infectious. Picornaviruses are naked icosahedral capsid viruses. # Includes non-respiratory and respiratory enteroviruses. Non-Respiratory enteroviruses – Resist harsh conditions, including stomach acids and sewage. – Usually transmitted via the fecal-oral route. – Replication occurs most effectively at 37 degrees Celsius (internal body temperature); – Asymptomatic infections; exceptions to this can be quite severe. Respiratory enteroviruses Formerly categorized in a separate Rhinovirus genus. Rhinoviruses – Cannot survive acidic environments. – Survive on hands and hard surfaces, which facilitates their transmission to mucosa of the respiratory tract or conjunctiva. – Replicate most effectively at 33 degrees Celsius – Infection is initiated in the epithelia of the nasopharynx. # Hepatovirus A – Fecal-oral transmission – Often spread via contaminated water. Most often infect children. Most cases are asymptomatic, particularly when infection is limited to the pharynx and gastrointestinal tract. In approximately 5% of cases, nonspecific flu-like symptoms occur and subside within a week. 1 in 200 cases will involve the central nervous system. Virus reaches the CNS via viremia and retrograde neuronal travel. Replicates in the spinal cord (motor neurons of the anterior horn). Meningitis can develop in some individuals. Poliomyelitis occurs in 1 out of 200 poliovirus infections: Temporary or permanent paralysis that typically involves the limbs; when the muscles involving respiration are involved, infection can be fatal. "Iron lung" = Emerson Respirator used to mechanically support respiration in polio patients. Post-polio syndrome occurs when nerve dysfunction occurs 30-40 years after initial poliomyelitis. Vaccination can prevent this crippling and potentially fatal disease. – The inactivated polio vaccine (IPV) is currently given to children in the United States and to adults at increased risk (travelers, laboratory and health care workers, etc.). – The live attenuated oral polio vaccine (OPV) is still available in some countries. Coxsackieviruses A is associated with the following: Herpangina is a self-limiting, acute febrile illness. – Characterized by fever, vomiting, and small painful lesions or ulcers in the mouth, especially in the oropharynx. – Most commonly affects children. Hand-foot-and-mouth disease – Characterized by oral sores and a rash on the hands and feet, and other nonspecific symptoms. – Self-limiting. – Typically occurs in children. – Aphthovirus also causes hand-foot-and-mouth disease. Coxsackieviruses B is associated with the following: Pleurodynia, aka, Bornholm disease – Inflammation of the pleura, often accompanied by fever. – Patients experience mild to severe muscle pain the in thorax and abdomen, especially during deep breathing. – Usually*self-limiting. Myocarditis, particularly in newborns. Paralysis (occasionally). Type 1 Diabetes development via destruction of pancreatic islet cells. Enterovirus 68 is primarily associated with respiratory illnesses, however, it has also been associated with paralysis. – Vulnerable to acid and replicates best at lower temperatures. Echovirus 11 is associated with aseptic meningitis. Human parechoviruses (formerly known as echoviruses 22 and 23), produce asymptomatic infection or gastrointestinal and respiratory illnesses. – In infants, infection can cause fever, rash, and irritability – aka, "hot, red, angry babies." – CNS infections, including seizures, meningitis, and encephalitis, as well as myocarditis (less frequent). Respiratory enterovirus Be aware that many texts continue to refer as rhinoviruses as their own genus. Responsible for > 50% of all "common colds," which are upper respiratory tract illnesses. There are over 100 rhinovirus serotypes, which is why it has been impossible to produce a protective vaccine (so far). Typically confined to the upper respiratory tract. – Recent evidence shows that they can replicate in some portions of the lower respiratory tract as well. – Limited range is due to need for lower temperatures for optimal replication. Also associated with pneumonia and exacerbation of existing pulmonary diseases – Asthma and chronic obstructive pulmonary disease (COPD). Infection of epithelial cells triggers the innate immune system. – Inflammatory chemokines and cytokines contribute to the symptoms of the common cold. Antibodies are produced, but only provide transient protection against the specific serotype responsible for the infection. However, these antibodies are insufficient protection against the other rhinovirus serotypes, so it's not unusual for a person to suffer from multiple "colds" during the year. Acute infection after ingestion of contaminated food or water, or close contact with an infected person. Most commonly occurs in children, in whom it is usually asymptomatic. Older children and adults are more likely to experience nonspecific symptoms, pain, and jaundice. – Typically subside on their own within a couple of months. More serious complications, including liver failure, renal failure, and pancreatitis can also occur. – Infection can be fatal in the elderly and/or patients with liver disease. Antibodies are produced that protect from future infections. Vaccination to prevent Hepatitis A is recommended for all children at 1 year of age.