Polio is caused by a viral infection. In most cases (95% infections) there are no clinical symptoms and these infections do not need treatment.
However, these patients continue to shed the virus in their stools and act as reservoirs of infection.
Those with non-paralytic and paralytic forms of polio manifest the disease clinically.
Diagnosis of polio involves medical history, physical examination and so forth. (1-5)
Medical history of the patient includes enquiry about exposure to a case of polio. This includes travelling to an area where polio in endemic, direct contact with nasal or mucus secretions of an individual with polio infection.
History or polio vaccination is also important. Inactivated injectable polio vaccine or IPV for example has an effectiveness of around 90% protection from the infection. Individuals who are vaccinated are usually protected from the infection.
Medical history also includes feeling of illness and fever.
This involves a complete check up of the systems. The respiratory muscles are examined for function as polio affecting spinal cord and brain stem may affect respiratory muscles.
Muscle reflexes are tested. Abnormal reflexes are detected. There may be a stiff neck and stiff muscles of the back. There may be difficulty in bending the neck and difficulty in lifting the head or legs when lying flat on the back.
Acute flaccid paralysis
Acute flaccid paralysis (AFP) is a common clinical manifestation of poliomyelitis. AFP is defined as the sudden onset of flaccid paralysis in one or more limbs.
AFP is also caused by Guillain-Barré syndrome and transverse myelitis. AFP is monitored closely worldwide to detect stray cases of polio due to wild virus subtypes.
Laboratory diagnosis includes routine blood tests. There may be raised white blood cells.
Cerebrospinal fluid examination
The Cerebrospinal fluid bathes the spinal cord and the brain. This CSF is tested using a lumbar puncture. Lumbar puncture involves insertion of a long thin needle between the vertebrae. This draws out a small amount of CSF that is sent to the laboratory for evaluation.
Routine CSF examination includes assessment of cells (white blood cells, blood etc.) and levels of sugar and other chemicals in the CSF. Typically there are 10 to 200 cells/mm3 and there may be a mildly elevated protein content in CSF from 40 to 50 mg/100 ml.
Throat washing is taken and assessed for the virus. The washings are incubated at a favourable atmosphere in a culture media.
If the culture is positive for the virus it may be detected under microscope. Stool samples are also examined for polio virus. Isolation of virus from the cerebrospinal fluid (CSF) is diagnostic but is rarely possible.
Blood is tested for antibodies for polio virus. Antibodies are molecules that are produced by the body against an invading virus or bacteria.
When a person is infected with polio virus, special tests can detect the levels of polio virus specific antibodies and confirm the diagnosis.
Fingerprinting the polio virus
Once the polio virus is isolated it is tested by a special test called oligonucleotide mapping (fingerprinting) or genomic sequencing. This is essentially looking at the genetic sequence of the virus to detect if the origin of the virus is “wild type” or “vaccine like”.
Wild type virus naturally occurs in the environment and may occur as 3 subtypes – P1, P2 and P3. Vaccine like virus is derived after a spontaneous mutation of the genes of the virus in the polio vaccine.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)