Laboratory Diagnosis - Poliovirus Infections

Laboratory Diagnosis

◗ Specimens

Stool, throat swab, and cerebrospinal fluid (CSF) are the specimens used for isolation of the viruses. Viruses can be isolated from feces for more than 30 days during the illness and from the throat swab during the first few days of the illness. The virus is isolated rarely from the CSF specimens.

◗ Microscopy

Microscopy of the CSF shows a predominantly lymphocytic pleocytosis with the presence of 25–500 cells/mm3. The virus is rarely demonstrated in the CSF.

◗ Isolation of the virus

Isolation of viruses from clinical specimen by tissue culture is the most specific method in the diagnosis of poliomyelitis.

Cell culture: Virus isolation from feces and throat swab is car-ried out by cultivation on monkey kidney, human amnion, HeLa, Hep-2, Buffalo green monkey (BGM), MRC-5, and other cell cul-tures. The cytopathic effects produced by the virus are observed within 48 hours. These consist of cell retraction, increased refractivity, cytoplasmic granularity, and nuclear pyknosis. Identification of serotype is carried out by performing neutral-ization test. Differentiation of a wild virulent virus strain from that of an attenuated vaccine strain can be done by virulence test in the monkeys and by performing polymerase chain reac-tion (PCR). Isolation of poliovirus from feces does not indicate a diagnosis of poliomyelitis, as large numbers of asymptomatic ill-nesses are seen. Hence, isolation of poliomyelitis virus from feces needs to be interpreted carefully along with clinical presentation of the disease.

◗ Serodiagnosis

Serodiagnosis is based on demonstration of a fourfold increase in the antibody titer of the serum collected at the time of acute illness and the period of convalescence. Neutralization or complement fixation test is carried out to demonstrate anti-bodies. Neutralizing antibodies appear early and are present throughout life. However, serodiagnosis is less frequently used for diagnosis of poliomyelitis.