What and how does it work , all answers are in this article .. Thank you
THE Picornaviruses are the smallest viruses yet identified and all have
RNA as the nucleic acid. In 1957 the Polio, Coxsackie A, Coxsackie B
and ECHO viruses were grouped together as the Enteroviruses and
in 1962 the Picornavirus group was named to include all viruses with
similar properties. The name was constructed from "pico" meaning
"small" and RNA, from their nucleic acid.
The human members are the Enteroviruses, the Rhino or "common
cold" viruses and a variety of unclassified strains which will eventually
take their place in one or other of the above sub-groups. To date there
are approximately 80 distinct human Picornaviruses with many others
awaiting full serological identification. During a period of four years
in the North East of Scotland the author found no less than six viruses
belonging to this group, which he was unable to identify. One has
since been classified as ECHO 30 and the remainder will no doubt prove
to be identical with other types throughout the world. In fact there is
no reason to suppose that we are yet anywhere near total recognition of
all the members of this important group.
A similar situation exists among the lower animals. The types
affecting animals must already be reaching 100. Enteroviruses, similar
to, but antigenically different from the human types, have been demonstrated
in monkeys, swine, cattle, cats, mice and fowls. Some of these
viruses, like Teschen virus or swine poliomyelitis, cause well-defined
disease, while others have been found only in the faeces of healthy
animals. The most important are probably those causing Foot and
Mouth Disease of Cattle. Finally there are the viruses which cause
encephalomyocarditis (EMC) in mice
All of the sub-groups of the Picornavirus family are sufficiently alike
to be considered together
The properties of the Picornavirus group have been defined as They are small in size—15-30 íáì in diameter, They are resistant to ether and chloroform, The nucleic acid is RNA Those which have been studied show cubic symmetry, possibly icosahedral, but the number of capsomeres is not yet established.The particle size of representative strains of each of the sub-groups
Has been determined and all fall within the range 23-29 ôçì in diamete
4-9 The Enteroviruses are uniformly 28 m the EMC viruses
vary between 25 and 29 m the Foot and Mouth Disease viruses are
23 m/i.7
Biochemical analysis of the virus particles has only been performed
on the Polioviruses and one strain of EMC virus. The polioviruses
all contain 20-25% RNA and 75-80% protein
with a molecular weight of 6-8 x 106. Results obtained for EMC virus
correspond closely with these, being 30% RNA and 70% protein
The amino-acid composition of the protein of Poliovirus type 1 has been
determined and differs only in the proportions from animal proteins
The bases in all three types of Poliovirus are in similar proportions but
no other members have been studied in such detail
In any given suspension of Poliovirus only 1 in 30 to 1 in 260 of the
virus particles is infective but most adsorb to susceptible cells at
4°C.On warming to 37°C, 50-60% of the particles are eluted and can
no longer adsorb to cells although infectious RNA can be extracted.
Possibly minor variations in surface structure account for this, and also
for part of the non-infectivity of the majority of the virus particle
The inactivation of infectivity of the different viruses in acid media
varies considerably and is a dividing feature within the group. Each
determination has been made using different times and temperatures of
exposure
It is clear from these results that the Enteroviruses, excepting ECHO
, form a homogenous group while ECHO 28, the Rhinoviruses and
FMDV form another. Such results as are available for the other animal
viruses indicate that they belong to the former group.
All the Picornaviruses are rapidly inactivated by formalin at all
temperatures above freezing point The Enteroviruses are also
inactivated by oxidising agents and desiccation, while EMC strains
are destroyed by high concentrations of halogen ions. These properties
are probably common to all members of the group. Although
heating to 61°C rapidly destroys the infectivity of all these viruses the
stability at lower temperatures varies not only between the sub-group
but also between individual strains of each antigenic type In
general, the Enteroviruses and the EMC viruses are less stable to heating
than the Rhinoviruses, FMDV and ECHO 28. The wide range is seen
when the half life of the Enteroviruses at 37°C varies from 2*5 to 40
hours. An example of the effects of different temperatures on one
strain of FMDV shows that 90% inactivation occurs in 30 seconds at
61°C, in 2 mins. at 55°C, in 21 hours at 37°C but only after 18 weeks at
4°C. A small proportion of any suspension of FMDV has enhanced
heat stability and serial passage of this fraction increases the amount of
resistant virus. At — 70°C all the Picornaviruses can be preserved
indefinitely and in most cases they are stable at — 20°C for several years.
Certain strains become non-infective after only a few months at — 20°C
and stock strains have to be preserved at lower temperatures, e.g.,
ECHO . (Enteric Cytopathic Human Orphan.)
High concentrations of such cations as Mg++, Ca++ and Na+ inhibit
the thermal inactivation of the Enteroviruses and EMC viruses.6»29 This
property has been called the cationic stabilisation of viruses and occurs
with at least 35 of the Enteroviruses, covering all the subdivisions.4 The
EMC viruses are stabilised at 56°C by monovalent cations, even in the
presence of large amounts of halogen ions, but they have not yet been
tested with the divalent cations. On the other hand, the Enteroviruses
are stabilised by the divalent cations at all temperatures between 4°C
and 50°C but the monovalent cations are selective in their temperature
range. At 50°C, molar MgCl2 or CaCl2 completely prevents inactivation
of these viruses for 3 hours whereas 2 molar NaCl only stabilises them
for one hour. Preliminary studies with the Rhinoviruses show that
molar MgCl2 only partially stabilises them to heating at 50°C.8 For a
human Picornavirus to be accepted into the Enterovirus sub-group it
must show complete cationic stabilisation for 3 hours at 50°C
Soluble antigens have been reported for all strains studied in sufficient
detail, but with the exception of FMDV they are not always formed and
little is known of their properties.7»30 The FMDV soluble antigen is
present in every suspension of virus. It is non-infectious, has a particle
diameter of 8 ðéì7 and is distinct from the infectious particle antigen
This infectious particle is specific for each antigenic type. The soluble
antigen is common to all types when tested by the complement fixation
test but by agar-gel diffusion it shows type specificity
Two distinct antibodies react with the soluble antigen one being the
type-specific antibody which also combines with the infectious particle
The EMC viruses are all closely related antigenically and vary only in
pathogenicity
By far the greatest amount of work has been done on the Poliovirus
