Picornaviruses Flashcards
Explain the etymology of “picorna”.
pico means small, and rna stands for ribonucleic acid. Picornaviruses are small RNA viruses.
What type of genetic material do picornaviruses have?
positive-sense, single stranded DNA
Are picornaviruses enveloped or non-enveloped?
non-enveloped
What is the primary mode of transmission for enteroviruses?
fecal-oral route or respiratory route
There are five genera in the family Picornaviridae that cause human disease, namely: ____________.
(a) Enterovirus
(b) Rhinovirus
(c) Hepatovirus
(d) Parechovirus
(e) Cardiovirus
How many poliovirus serotypes are there?
3
How is Poliovirus transmitted?
Poliovirus is primarily transmitted through the fecal-oral route, but it can also be spread via contaminated water or food and respiratory droplets.
Explain the pathogenesis of polio.
Multiplication: The virus enters the body through the mouth and multiplies in the oropharynx and gastrointestinal tract.
Initial viraemia: After initial replication, the virus invades local lymphoid tissues, such as the tonsils and Peyer’s patches in the intestines. They then enter the blood stream, producing initial viraemia. The patient may form antibodies at this stage, preventing the infection from spreading (abortive infection).
Second viraemia: In patients who fail to control the initial viraemia, there is a second major viraemia from where they are disseminated in the spinal cord and brain by passage across the blood-CNS barrier. An alternative pathway may be via entry into motor neurones at peripheral neuromuscular junctions.
The virus multiplies in the neurons of the CNS and destroys anterior horn cells of the spinal cord, as well as nerve cells in the medulla oblongata and in the bulbar pons.
[Diagram 1] [Diagram 2] [Diagram 3]
Briefly discuss the following clinical manifestations of polio:
(a) abortive poliomyelitis
(b) aseptic meningitis
(c) paralytic poliomyelitis
(a) abortive poliomyelitis: This is a mild-non-specific illness. Manifestations of disease is characterized by a 2-3 day fever and influenza-like symptoms. There are no signs of CNS localization and complete recovery can be expected in less than a week.
(b) aseptic meningitis: symptoms include stiffness of the neck, back and/or legs and last from 2 to 10 days. Recovery is rapid and complete.
(c) paralytic poliomyelitis: It begins with 2 to 3 days of minor illness such as fever and influenza-like symptoms. After several days, these symptoms disappear and return within 5 to 10 days along with signs of meningeal irritation.
Flaccid paralysis ensues characterized by cramping muscle pain, spasms, coarse twitching, and tendon reflexes are diminished. Encephalitis is rare but possible. Patients do not show loss of sense or cognitive changes. Recovery is possible however paralysis lasting beyond 6 months is permanent.
Discuss methods of laboratory diagnosis of poliovirus.
☑ The virus may be recovered from throat swabs taken soon after onset of illness and from rectal swabs or stool samples collected over long periods. Cultures of human or monkey cells are inoculated and incubated. Cytopathic effect is observed in 2-3 days.
☑ The virus can also be identified more rapidly by polymerase chain reaction assays.
Briefly discuss the two types of polio vaccines.
(1) Inactivated polio vaccine (IPV) [aka. Salk vaccine]
Administration: Given by injection in the arm or leg, depending on the patient’s age.
Components: Contains inactivated (killed) poliovirus.
Schedule: 2 months, 4 months, 6-18 months, 4-6 years
It is used mainly in the US.
(2) Oral polio vaccine (OPV) [aka. Sabin vaccine]
Administration: Given orally as drops
Components: Contains live, attenuated (weakened) poliovirus.
Schedule: birth, 6 weeks, 10 weeks, 14 weeks
[There are 3 types: Trivalent, Bivalent, Monovalent]
Which picornavirus is known for causing the common cold?
Rhinovirus
Discuss the pathogenesis of rhinoviruses.
Rhinoviruses grow in the cooler environment of nasal mucosa. The virus enters through the nose, mouth or eyes and initiates upper respiratory tract infection, including throat.
clinical manifestations of rhinovirus infection
☑ incubation period is between 1-4 days
☑ nasal discharge, nasal secretions, sneezing, sore throat. In more serious cases, fever and upper respiratory infection are possible.
☑ illness usually resolves itself within a week
