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THE Picornaviruses probably cause more clinical illness than any
other group of viruses. Poliomyelitis, Foot and Mouth Disease and the
"common cold" are actual or potential scourges of both man and
animals. Vaccines have controlled poliomyelitis and in the case of
FMD a combination of vaccine and slaughter is containing the disease.
But by far the greatest number of illnesses caused by this group are
non-specific respiratory infections or cases of general "malaise".
Nevertheless, specific clinical entities are associated with certain subgroups.
Poliomyelitis was known in the days of the Pharaohs if one can judge
from pictures and descriptions. In the early part of this century 80 % of
the cases of paralytic poliomyelitis in the U.S.A. occurred in children
under school age, whereas in 1950 only one third belonged to this
group. This change in incidence, attended by an increase in severity
with advancing age, is almost certainly due to the improved sanitation
and living conditions, which prevent the disease from becoming endemic
among the infant population. Today two types of vaccine are in use
and have considerably reduced the incidence of the disease. The first
vaccine in use was a formalin-inactivated vaccine developed by Salk
while the second and more important was the Sabin live-attenuated
vaccine
Although transmission of Poliovirus to an experimental animal was
reported it was not until that the antigenic homogeneity
of Poliovirus was questioned. the three antigenic types had
been defined and in 1951 it was assumed that these were the only viruses
causing paralysis. Since then many of the other Enteroviruses have
been associated with cases of paralytic poliomyelitis. A future rise in
poliomyelitis can therefore be expected with the subsequent addition of
more and more antigenic types to the trivalent vaccines rendering them
less efficient. In the case of the "common cold" there are already so
many distinct Rhinoviruses that any hope of an efficient vaccine must
unfortunately be discarded.
Diseases of Humans
The Enteroviruses and Rhinoviruses cause illness ranging from mild
upper respiratory tract infections and diarrhoea to paralytic poliomyelitis
and fatal myocarditis. Most of the illnesses involve either the
respiratory tract or the central nervous system (CNS). Each clinicalentity will be considered in turn, starting with those illnesses caused
solely by the Enteroviruses.
ASEPTIC MENINGITIS or non-paralytic polio is the commonest
CNS disease associated with the Picornaviruses. Widespread outbreaks
occur in the summer and autumn in temperate zones but appear at any
time in tropical climates. The majority of the Enteroviruses can and
do cause meningitis, but only some give rise to outbreaks.
The onset of illness is sudden after an incubation period of 6 to 20
days. Severe headache is followed by general malaise, fever, vomiting,
drowsiness and neck stiffness. When the onset is gradual the first signs
are general malaise, loss of appetite and nausea followed by the above
symptoms. There is a wide variation in the severity of the illness but all
cases show these symptoms. The fever may be anything from 99 to
103°F lasting from 2-14 days, but 4-5 days are more usual. Other
symptoms which occur less frequently are photophobia, myalgia,
lymphadenopathy, back stiffness, conjunctivitis, diarrhoea and
rashes.10-14 Diagnosis is confirmed by the presence of the Kernig and
Brudzinski signs, either or both of which are positive.
Usually there is
an increase in leucocytes in the cerebro-spinal fluid (CSF) and lymphocytes
exceed polymorphs. This increase in white cells ranges from 12 to
2,000 but rarely exceeds 500 per cu. mm. In the initial stages of illness
the CSF findings may be reversed.The protein content of the CSF
is normal or only slightly raised. The illness is never fatal unless it
progresses to either of the following two syndromes.
Epidemics of meningitis have been recorded all over the world and
involve distinct Enteroviruses, not counting the three Polioviruses.
In Europe and America Coxsackie A types 7 and 9,15»16 Coxsackie B
types 1 to 517"21and ECHO have
all caused epidemics. Sporadic cases are associated with Coxsackie A
PARALYTIC POLIOMYELITIS has retained its notoriety although
it is at present relatively uncommon in Europe and America as a result
of vaccination. Like aseptic meningitis it occurs during the summer and
autumn in temperate climates causing large epidemics. The initial
symptoms are identical with aseptic meningitis and only a variable
proportion of cases actually develop paralysis, the remainder passing
off as meningitis. The incidence of paralysis depends on the virulence
of the strain but mostly on the age of the population at risk with paralysis
at its worst in the adolescent age group and among the more active
members of the community.32»33'34 In the tropics where Poliovirus is
endemic, danger exists only for the indigenous infant population because
all older persons have been infected. Here the ratio of paralytic to nonparalytic
infections can be as low as 1
Between 2 and 4 days after the onset of meningitis, two selected muscle
gn^ps can become paralysed. Spinal paralysis, the most common,involves a flaccid paralysis of the limbs or trunk and is the result of
lesions of the anterior horn cells. The other form of paralysis occurs
when the medulla is attacked. This bulbar paralysis, as it is called, is
manifest in paralysis of the palate, pharynx and larynx and is usually the
more severe illness. The fever continues longer and the mortality rate is
higher. Direct respiratory failure can occur due either to disturbance of
the respiratory control centres in the medulla, or to paralysis of the
intercostal and diaphragm muscles. With non-bulbar paralysis the
mortality rate is relatively low, but residual paralysis is common.
Widespread outbreaks are caused by Poliovirus types 1, 2 and 3 and
small outbreaks by Coxsackie A7.9>15>36 Sporadic cases have been
reported due to Coxsackie A types 2, 4 and 9,29 Coxsackie B types 2, 3, 4
and 5,21>37'38'39 and ECHO types 2, 4, 6, 9, 11, 16 and 30.21>31>38>39>40
ENCEPHALITIS occurs sometimes in association with and sometimes
in the absence of meningeal symptoms. The onset of illness is
insidious and the typical clinical picture is one of intense headache,
hallucinations, lethargy, mental confusion, paresis of the cranial
nerves, blurred vision, papilloedema, hyperacusis and hypertension.
Only sporadic cases are seen but there afe occasional deaths.
Probably most of the Enteroviruses causing meningitis also cause
encephalitis but so far only some have been reported. The three types of
Poliovirus are involved, together with Coxsackie A types 2, 5 and 6,
Coxsackie B types 2, 3, 4 and 5, and ECHO types 7, 9, 11 and 14
RASHES are commonly seen and fall into two distinct groups. The
most important is the petechial rash associated with meningitis, which
can be confused with a meningococcal septicaemia.10 Although uncommon,
physicians can expect to see it occasionally during outbreaks
of meningitis due to ECHO types 7 and 9, and Coxsackie A9.10'44-47
The more common rash however, is a maculopapular rash also
associated with meningitis. It varies in severity and duration from a
scanty rash disappearing in several hours to an almost confluent rash
lasting several days. There is no post-exanthematous scaling which is
typical of measles and with which it may be confused. In many cases,
especially those due to ECHO 16, the rash appears late in the illness
and is of very short duration.48 This rash is a feature of ECHO 9 outbreaks,
usually accompanied by generalised lymphadenopathy.
Children are more frequently affected than adults and in children the
illness is less severe if there is a rash.49 In outbreaks of Coxsackie B
types 2 and 3 and ECHO types 7 and 11 this rash can be expected.
HERPANGINA is a very unpleasant illness characterised by painful
lesions of the palate and tonsillar pillars. The palate lesions first appear
as vesicles surrounded by an erythematous zone, but soon burst giving a
typical appearance of punched out ulcers about 5 mm in diameter. An
accompanying systemic illness is usual and the symptoms are fever,
vomiting and abdominal pain.The fever lasts from 1 to 4 days and thelesions continue for a varying length of time but never less than a week.
The illness is never fatal and is caused by Coxsackie A types
BORNHOLM DISEASE' pleurodynia or epidemic myalgia are the
names frequently used to describe a very common and unpleasant
illness caused by the Coxsackie B viruses. The patient feels a sudden
severe pain in the muscles of the thorax and abdomen or sometimes in
the back and limbs. This pain is followed by fever, sweating, headache,
anorexia, nausea, sore throat and vomiting. The duration of illness is
from 6 to 40 days with relapses occurring up to six months after the
initial symptoms. It is never fatal.
It is not uncommon for cases of pleurodynia to be mistaken for acute
appendicitis if the pain is localised in the abdominal muscles, or myocardial
infarction if it is only thoracic. Only Coxsackie B types 1, 2, 3, 4
and 5 have so far been associated with this illness
PERICARDITIS is an illness characterised by sudden precordial
pain and a loud friction rub. Sometimes pericardial effusion is present.
These cases are usually sporadic, occurring during outbreaks of pleurodynia
or meningitis. They have been associated with a variety of
Coxsackie viruses namely—Coxsackie A type 1, and Coxsackie B
types 2, 3, 4 and 5.42>58-64
MYOCARDITIS is mainly a disease of newborn infants in nurseries.
Shortly after birth the babies have loose stools followed 3-8 days later
by fever, tachycardia and the electrocardiographic changes of myocarditis.
65'66 The illness is caused by Coxsackie B types 2, 3 and 4.66-68
The cases are sporadic and when seen in older children they are usually
much less severe. In babies the mortality rate is high.
DIARRHOEA in epidemic form may be caused by the Enteroviruses.
Most outbreaks affect young children in closed communities although
older persons can be involved. Vomiting and fever are commonly
seen in addition to a severe diarrhoea of semi-liquid and mucous stools.
This is not usually a particularly serious illness but occasional deaths
have been reported. The viruses causing these outbreaks are Poliovirus
types 2 and 3, Coxsackie B type 3 and ECHO types 7, 9, 11, 14
UPPER RESPIRATORY TRACT INFECTIONS can be caused by
virtually all of the human Picornaviruses. The most common as its
name suggests is the "common cold," characterised by a watery nasal
discharge and stuffiness with occasionally, a sore throat and cough.74
Most "common colds" are caused by the Rhinoviruses and ECHO
28.75'76 To date the number of Rhinoviruses fully identified is small
compared with the rapidly increasing number known.
Other well defined Picornaviruses causing outbreaks of respiratory
tract illness are Coxsackie A21 or Coe virus and ECHO types 11 and 20.
The illness caused by Coxsackie A21 is more severe than the "common
cold" with mild fever and headache as well as the nasopharyngeal
