Page 346 - Review of Medical Microbiology and Immunology ( PDFDrive )

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CHAPTER 40 RNA Nonenveloped Viruses
paralysis of the muscles innervated by those neurons.
Paralysis is not due to virus infection of muscle cells. The
(Table 40–3). Both vaccines induce humoral antibodies,
which neutralize virus entering the blood and hence pre-
virus also affects the brainstem, leading to “bulbar” polio-
myelitis (with respiratory paralysis), but rarely damages the
vent central nervous system infection and disease. Both
the killed and the live vaccines contain all three serotypes.
cerebral cortex.
At present, the inactivated vaccine is preferred for reasons
In infected individuals, the immune response consists of
that are described later.
both intestinal IgA and humoral IgG to the specific sero-
type. Infection provides lifelong type-specific immunity.
The current version of the inactivated vaccine is called
enhanced polio vaccine, or eIPV. It has a higher sero-
Clinical Findings
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conversion rate and induces a higher titer of antibody
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than the previous IPV. eIPV also induces some mucosal
The range of responses to poliovirus infection includes
immunity IgA, making it capable of interrupting trans-
(1) inapparent, asymptomatic infection; (2) abortive polio-
myelitis; (3) nonparalytic poliomyelitis; and (4) paralytic
eIPV is significantly less than the amount induced by
poliomyelitis. Asymptomatic infection is quite common.
OPV. OPV is therefore preferred for eradication efforts.
Roughly 1% of infections are clinically apparent. The incu-
The only version of polio vaccine currently produced and
bation period is usually 10 to 14 days.
used in the United States is eIPV. In certain countries
The most common clinical form is abortive poliomyelitis,
where polio remains endemic (e.g., India), a monovalent
which is a mild, febrile illness characterized by headache,
oral polio vaccine is used because the rate of seroconver-
sore throat, nausea, and vomiting. Most patients recover
spontaneously. Nonparalytic poliomyelitis manifests as asep-
trivalent one.
tic meningitis with fever, headache, and a stiff neck. This also
In the past, the live vaccine was preferred in the United
usually resolves spontaneously. In paralytic poliomyelitis, sion is higher with the monovalent vaccine than with the
States for two main reasons: (1) It interrupts fecal–oral
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flaccid paralysis is the predominant finding, but brainstem
transmission by inducing secretory IgA in the gastrointes-
involvement can lead to life-threatening respiratory paraly-
tinal tract. (2) It is given orally and so is more readily
sis. Painful muscle spasms also occur. The motor nerve dam-
age is permanent, but some recovery of muscle function
The live vaccine has four disadvantages: (1) Rarely,
occurs as other nerve cells take over. In paralytic polio, both
reversion of the attenuated virus to virulence will occur,
the meninges and the brain parenchyma (meningoencepha-
and disease may ensue (especially for the type 3 virus).
litis) are often involved. If the spinal cord is also involved, the
(2) It can cause disease in immunodeficient persons and
term meningomyeloencephalitis is often used.
therefore should not be given to them. (3) Infection of the
A postpolio syndrome that occurs many years after the
acute illness has been described. Marked deterioration of
the residual function of the affected muscles occurs many
years after the acute phase. The cause of this deterioration
is unknown. TABLE 40–3 Important Features of Poliovirus
Vaccines
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No permanent carrier state occurs following infection
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by poliovirus, but virus excretion in the feces can occur for
Attribute
Live (Sabin)
Killed (Salk)
several months.
Yes
No
Yes
Interrupts transmission
Laboratory Diagnosis
Yes
Yes
Induces humoral IgG
The diagnosis is made either by isolation of the virus or by
Yes
Induces intestinal IgA
No
a rise in antibody titer. Virus can be recovered from the
Yes
No
Affords secondary protection by
throat, stool, or spinal fluid by inoculation of cell cultures.
spread to others
The virus causes a cytopathic effect (CPE) and can be iden-
No
Interferes with replication of viru-
Yes
tified by neutralization of the CPE with specific antisera.
lent virus in gut
Treatment
Reverts to virulence
No
Yes (rarely)
Yes
There is no antiviral therapy. Treatment is limited to symp-
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ruses may impair immunization
tomatic relief and respiratory support, if needed. Physio-
Yes
No
Can cause disease in the
therapy for the affected muscles is important.
immunocompromised
Route of administration
Prevention
Oral
Injection
No
Requires refrigeration
Yes
Poliomyelitis can be prevented by both the killed vaccine
Longer
Shorter
Duration of immunity
(Salk vaccine, inactivated vaccine, IPV) and the live,
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