Medical biology, microbiology, virology, immunology

department

By as. E.V. Pokryshko

  Genera of Picornaviruses

Enterovirus Polio, types 1-3 Coxsackie A , types 1-24Coxsackie B, types 1-6Echo, types 1-34Other enteroviruses, types 68-71

Diseases of the human (and other) alimentary tract (e.g. polio virus)

Rhinovirus,          types 1-115

Disease of the nasopharyngeal region (e.g. common cold virus)

Cardiovirus Murine encephalomyocarditis, Theiler's murine encephalomyelitis virus

Aphthovirus Foot and mouth disease in cloven footed animals

Hepatovirus Human hepatitis virus AOthers Drosophila C virus, equine rhinoviruses, cricket

paralysis virus

Pathogenesis of enterovirus infection

Rhino,echo,coxsackie,polio

Replication in oropharynx

Primary viremia

Target Tissue Secondary viremia

Skin Muscle Brain Meninges Liver

Echo

Coxsackie

A

Echo

Coxsackie

A, B

Polio

Coxsackie

Echo

Polio

Coxsackie

Echo

Coxsackie

Clinical Picornavirus Syndromes Virus Diseases (Virus Type)

Polioviruses

(types 1-3)

Undifferentiated febrile illnesses (types 1-3)Aseptic memingitis (types 1-3)Paralisis and encephalitic diseases (types 1-3)

Coxsackievirus group A

(A1-A, A-24)*

Acute hemorrhagic conjunctivitis (type 24)Herpangina (types 2-6, 8, 10, 22)Exanthem (types 4, 5, 6, 9, 16)Hand-foot-mouth disease (types 5, 10, 16)Aseptic memingitis (types 1, 2, 4-7, 9, 10, 14, 16, 22)Paralysis and encephalitic diseases (occasional types 4, 7, 9, 10)Hepatitis (types 4, 9)

Virus Diseases (Virus Type)

Coxsackievirus group A (A1-A, A-24)*

Upper and lower respiratory illnesses (types 9, 10, 16, 21, 24) Lymphonodular pharyngitis (10)Infantile diarrhea (types 18, 20, 21, 22, 24 variant)Undifferentiated febrile illnesses (types 1-6)Pleurodinia (types 1-5)Pericarditis, myocarditis (types 1-5) Aseptic meningitis types (1-6)Paralysis and encephalitic diseases (occasional types 1-5)Severe systemic infection in infants, meningoencephalitis and myocarditis (types 1-5)Upper and lower respiratory illnesses (types 4, 5) Exanthem, hepatitis, diarrhea (types 5)

Virus Diseases (Virus Type)

Echoviruses (1-7, 9, 11, 29-33)*

Aseptic meningitis (many seroypes ) Paralysis and encephalitic diseases (occasional types 1, 2, 4, 6, 7, 9, 11, 14-16, 18, 22, 30)

Exanthem (types 1-9, 11, 14, 16, 18, 19, 25, 30, 32)

Hand-foot-mouth disease (19)

Pericarditis, myocarditis (types 1, 6, 9, 19, 22)

Upper and lower respiratory illnesses (types 4, 9, 11, 20, 22, 25)

Neanatal diarrhea (types 11, 14, 18, 20, 32)

Epidemic mialgia (types 1, 6, 9)

Hepatitis (types 4, 9)

Virus Diseases (Virus Type)

New enteroviruses

Pneumonia and bronchiolitis (types 68, 69)

Acute hemorrhagic conjunctivitis (type 70)

Aseptic meningitis, meningoencephalitisHand-foot-mouth disease (71)

Hepatitis (type 72)

Rhinoviruses (1-115)

Upper and lower respiratory illnesses (types 1-115)

Hepatovirus (Hepatitis A)

Gastroenteritis and hepatitis A

* Reclassification of coxsackievirus A23 as echovirus 9, echovirus 8 as 1, echovirus 10 as reovirus, echovirus 28 as rhinovirus type 1A, and echovirus 34 as coxsackievirus A24.

Properties of enteroviruses

Property Enteroviruses

Size (nm)Capsid form PolypeptideRNA typeAcidOptimal temperature for growth(oC)

22-30Icosahedral VP1, VP2, VP3, VP4‘+’, single stainStable37

RNA

POLIOMYELITIS

“Picornavirus” 3 types: Poliovirus

1,2,3 Ingested, spread by

alimentary route: Commoner in areas of poor sanitation

Infants protected by maternal antibodies

Poliomyelitis is an acute infectious disease that in its serious form affects the central nervous system. The destruction of motor neurons in the spinal cord results in flaccid paralysis (less than 0.1%). However, most poliovirus infections are subclinical.

During epidemic outbreaks, type I is most frequently isolated (in 65-95 per cent of cases) while types II and III account for the remaining 5-35 per cent of cases.

The virus is 30 nm in size and forms intranuclear inclusions. The virion is icosahedral and consists of a single sense-strand RNA and a protein capsid containing 32 spherical subunits (capsomeres).

This genome RNA serves as an mRNA and initiates the synthesis of virus macromolecules.

The poliomyelitis virus has neither an outer membrane nor lipids and is therefore not sensitive to the effect of ether and sodium desoxycholate.

Morphology.

Morphology.

Poliomielitis virus

The poliomyelitis virus is cultivated on kidney cells of green African monkeys and on diploid human cells devoid of latent SV40 viruses.

The cytopathic effect is attended by destruction and the formation of granules in the infected cells.

Cultivation. SPE.

The virus is extremely resistant to photodynamic inactivation. It survives in sterile water at room temperature for a period of more than 100 days, in milk for 90 days, in faeces in the cold for more than 6 months, and in sewage for several months. It withstands exposure to 0.5-1 per cent phenol solutions and remains viable for several weeks at pH 3.8-8.5.

The poliomyelitis virus is sensitive to calcium chlorate lime, chloramine, formalin, potassium permanganate, and hydrogen peroxide solutions.

It is rapidly killed on boiling.

Resistance.

Pathogenesis

Source of infection: Apparent and subclinical patients

Incubation: is usually 7-14 days, but it may range from 3 to 35 days.

Transmission

Fecal – oral route: poor hygiene, dirty diapers (especially in day-care settings)

Ingestion via contaminated food and water

Contact with infected hands Inhalation of infectious aerosols

Pathogenesis1. The mouth is the portal of entry of the virus. 2. The virus first multiplies in the tonsils, the lymph nodes

of the neck, Peyer's patches, and the small intestine. The virus is regularly present in the throat and in the

stools before the onset of illness. One week after onset there is little virus in the throat, but virus continues to be excreted in the stools for several weeks, even though high antibody levels are present in the blood.

3. ViremiaThe virus may be found in the blood of patients with

abortive and nonparalytic poliomyelitis.4. The central nervous system may then be invaded by

way of the circulating blood.

PathogenesisPoliovirus can spread along axons of peripheral nerves to

the central nervous system, and there it continues to progress along the fibers of the lower motor neurons to increasingly involve the spinal cord or the brain. Poliovirus invades certain types of nerve cells, and in the process of its intracellular multiplication it may damage or completely destroy these cells. The anterior horn cells of the spinal cord are most prominently involved, but in severe cases the intermediate gray ganglia and even the posterior horn and dorsal root ganglia are often involved. In the brain, the reticular formation, vestibular nuclei, and deep cerebellar nuclei are most often affected. The cortex is virtually spared, with the exception of the motor cortex along the precentral gyms.

Clinical Findings. When an individual susceptible to infection is exposed to the virus, one of the following responses may occur:

inapparent infection without symptoms (asymptomatic illness), the minor illness – 90% infected people

aseptic meningitis – 1%-2% of patients with poliovirus infections,

paralytic poliomyelitis, the major illness 0.1% to 2% of persons with poliovirus

Only about 1% of infections are recognized clinically.

Abortive Poliomyelitis. This is the commonest form of the disease. The patient has only the minor illness, characterized by fever, malaise, drowsiness, headache, nausea, vomiting, constipation, and sore throat in various combinations. The patient recovers in a few days. The diagnosis of abortive poliomyelitis can be made only when the virus is isolated or antibody development is measured.

Nonparalytic Poliomyelitis (Aseptic Meningitis). In addition to the above symptoms and signs, the patient with the nonparalytic form presents stiffness and pain in the back and neck. The disease lasts 2-10 days, and recovery is rapid and complete. In a small percentage of cases, the disease advances to paralysis.

Paralytic Poliomyelitis. The major illness usually follows the minor illness described above, but it may occur without the antecedent first phase. The predominating complaint is flaccid paralysis resulting from lower motor neuron damage. The maximal recovery usually occurs within 6 months, with residual paralysis lasting much longer.

Child with polio sequelae

ImmunityImmunitysIgA and neutralizing antibody (IgG, IgA, IgM) persist for life spanImmunity is permanent to the type causing the infection. There may be a low degree of heterotypic resistance induced by infection, especially between type 1 and type 2 polioviruses.Passive immunity is transferred from mother to offspring. The maternal antibodies gradually disappear during the first 6 months of life. Passively administered antibody lasts only 3-5 weeks.

Lab DiagnosisLab Diagnosis Definitive diagnosis is made by osolation of

the virus from stool, CFS, oropharyngeal secretions

Cell culture involves fibroblastic MRC-5 cellsCPE is usually evident within 36 hours Serotyping is based on neutralization of CPE

by standardized antisera using intersecting pool followed by specific sera.

ELISA IFA neutralizing Test CFT

TreatmentTreatmentThere is no specific treatment. Treatment involves reduction of pain and muscle spasm and maintenance of respiration and hydration. When the fever subsides, early mobilization and active exercise are begun. There is no role for antiserum. Early injections of gamma-globulin, blood transfusion, wide use of vitamins C and B,-, amino acids (leucine, glutamic acid), analgesics (analgine, amidopyrine, pantopon, etc.), mediators, and stimulants (proserine, galanthamine, dibazol, etc.) are recommended. An orthopaedic regimen is set up from the first day that paralysis develops to prevent contractures and deformations, and exercise therapy is carried out during the rehabilitation period. An apparatus for artificial respiration is employed when there are respiration disturbances.

Prevention

Both oral polio vaccine (OPV live, attenuated ， Sabin, 1957) and inactivated poliovirus vaccine (IPV, Salk, 1954) are avilable

IPV is used for adult immunization and Immunocopromised patients

Both killed and live virus vaccines induce antibodies and protect the central nervous system from subsequent invasion by wild virus. Low levels of antibody resulting from killed vaccine have little effect on intestinal carriage of virus. The gut develops a far greater degree of resistance after live virus vaccine, which seems to be dependent on the extent of initial vaccine virus multiplication in the alimentary tract rather than on serum antibody level.

Advantages and disadvantages of OPV

Advantages Effectiveness Lifelong immunity Induction of secretory antibody

response similar to that of natural infection

Possibility of attenuated virus circulating in community by spread to contacts (indirect immunization)(herd immunity)

Ease of administration Lack of need for repeated boosters

Advantages and disadvantages of OPV

Disadvantages Risk of vaccine-associated

poliomyelites in vaccine recipients or contacts

Spread of vaccine to contacts without their consent

Unsafe administration for immunodeficient patients

Advantages and disadvantages of IPV

AdvantagesAdvantagesEffectivenessGood stability during transport and

in storage Safe administration in

immunodeficient patientsNo risk of vaccine-related disease

Advantages and disadvantages of IPV

Disadvantages Lack of induction of local (gut)

immunity Need for booster vaccine for

lifelong immunity Fact that injection is more painful

than oral administration Fact that higher community

immunization levels are needed than with live vaccine

COXSACKIEVIRUSESCOXSACKIEVIRUSES

The coxsackieviruses comprise a large subgroup of the enteroviruses. They produce a variety of illnesses in human beings, including aseptic meningitis, herpangina, pleurodynia, hand, foot, and mouth disease, myo- and pericarditis, common colds, and possibly diabetes. Coxsackieviruses have been divided into 2 groups, A and B, having different pathogenic potentials for mice.

Group A viruses produce widespread myositis in the skeletal muscles of newborn mice, resulting in flaccid paralysis without other observable lesions.

Group B viruses may produce spasticity effect in sucking mice, focal myositis, encephalitis, and, most typically, necrotizing steatitis involving mainly fetal fat lobules. Some B strains also produce pancreatitis, myocarditis, endocarditis, and hepatitis in both suckling and adult mice.

Normal adult mice tolerate infections with group B coxsackieviruses.

Herpangina: There is an abrupt onset of fever, sore throat, anorexia, dysphagia, vomiting, or abdominal pain. The pharynx is usually hyperaemic, and characteristic discrete vesicles occur on the anterior pillars of the fauces, the palate, uvula, tonsils, or tongue. The illness is self-limited and most frequent in small children.

Exanthems – Rubelliform rashes

Hand, Foot, and Mouth Disease: The syndrome is characterized by oral and pharyngeal ulcerations and a vesicular rash of the palms and soles that may spread to the arms and legs. Vesicles heal without crusting, which clinically differentiates them from the vesicles of herpes- and pox-viruses. The rare deaths are caused by pneumonia.

Hand-foot-and-mouth disease

Hand-foot-and-mouth

disease: mostly coxackie A

fever, malaise, sore

throat, vesicles on bucсal

mucosa, tongue, hands,

feet, buttocks

highly infectious

resolution – 1w

ECHOVIRUSES

The echoviruses (enteric cytopathogenic human orphan viruses) are grouped together because they infect the human enteric tract and because they can be recovered from humans only by inoculation of certain tissue cultures. Over 30 serotypes are known, but not all cause human illness. Aseptic meningitis, febrile illnesses with or without rash, common colds, and acute hemorrhagic conjunctivitis are among the diseases caused by echoviruses.

Properties of the Viruses

General Properties. Echoviruses are typical enteroviruses measuring 24-30 nm.

Important Characteristics

Not produce diseases in sucking mice, rabbits, or monkeys;

Cause aseptic meningitis, infantile diarrhea,

Monkey kidney and human embryonated kidney cell culture

Growth of Virus. Monkey kidney cell culture is the method of choice for the isolation of these agents. Some also multiply in human amnion cells and cell lines such as HeLa.

Certain echoviruses agglutinate human group 0 erythrocytes. The hemagglutinins are associated with the infectious virus particle but are not affected by neuraminidase.

Initially, echoviruses were distinguished from coxsackieviruses by their failure to produce pathologic changes in new-born mice, but echovirus-9 can produce paralysis in new-born mice. Conversely, strains of some coxsackievirus types (especially A9) lack mouse pathogenicity and thus resemble echoviruses. This variability in biologic properties is the chief reason why new enteroviruses are no longer being subclassified as echo- or coxsackieviruses,

Antigenic Properties. Over 30 different antigenic types have been identified. The different types may be separated on the basis of cross-Nt or cross-CF tests. Variants exist that do not behave exactly like the prototypes. After human infections, Nt antibodies persist longer than CF antibodies.

Animal Susceptibility. To be included in the echo group, prototype strains must not produce disease in suckling mice, rabbits, or monkeys. In the chimpanzee, no apparent illness is produced, but infection can be demonstrated by the presence and persistence of virus in the throat and in the feces and by the type-specific antibody responses.

Epidemiology. The epidemiology of echoviruses is similar to that of other enteroviruses. They occur in all parts of the globe. Unlike the enterobacteria, which are constantly present in the intestinal tract, the enteroviruses produce only transitory infections. They are more apt to be found in the young than in the old. In the temperate zone, infections occur chiefly in summer and autumn and are about 5 times more prevalent in children of lower income families than in those living in more favourable circumstances.

Studies of families into which enteroviruses were introduced demonstrate the ease with which these agents spread and the high frequency, of infection in persons who had formed no antibodies from earlier exposures. This is true for all enteroviruses.

Wide dissemination is the rule. In a period when 149 inhabitants of a city of 740,000 were hospitalized with echo-9 disease, approximately 6% of the population, or 45,000 persons, had a compatible illness.

Pathogenesis & Pathology. The pathogenesis of the alimentary infection is similar to that of the other enteroviruses. Virus may be recovered from the throat and stools: in certain types (4, 5. 6, 9, 14. and IS) associated with aseptic meningitis, the virus has been recovered from the cerebrospinal fluid.

Clinical Findings. To establish etiologic association of echovirus with disease, the following criteria are used; (1) There is a much higher rate of recovery of virus from patients with the disease than from healthy individuals of the same age and socioeconomic level living in the same area at the same time. (2) Antibodies against the virus develop during the course of the disease. If the clinical syndrome can be caused by other known agents, then virologic or serologic evidence must be negative for concurrent infection with such agents. (3) The virus is isolated from body fluids or tissues manifesting lesions, e.g., from the cerebrospinal fluid in cases of aseptic meningitis.

Echoviruses 4, 6, 9, 11, 14, 16, 18, and others have been associated with aseptic meningitis. Rashes are common in types 9, 16 ("Boston exanthem disease"), 18, and 4. Rashes are commonest in young children. Occasionally, there is conjunctivitis, muscle weakness, and spasm (types 6,9, and others). Infantile diarrhea may be associated with some types (e.g., 18, 20). Echovirus type 28 isolated from upper respiratory illness causes "colds" in volunteers and has been reclassified as rhinovirus type 1. For many echoviruses (and some coxsackieviruses), no disease entities have been defined.

With the virtual elimination of polio in developed countries, the central nervous system syndromes associated with echo- and coxsackieviruses have assumed greater prominence. The latter in children under age 1 may lead to neurologic sequelae and mental impairment. This does not appear to happen in older children.

Laboratory Diagnosis

It is impossible in an individual case to diagnose an echovirus infection on clinical grounds. However, in the following epidemic situations, echoviruses must be considered: (1) summer outbreaks of aseptic meningitis; (2) summer epidemics, especially in young children, of a febrile illness with rash; and (3) out breaks of diarrheal disease in young infants from whom no pathogenic enterobacteria can be recovered.

The diagnosis is dependent upon laboratory tests. The procedure of choice is isolation of virus from throat swabs, stools, rectal swabs, and, in aseptic meningitis, cerebrospinal fluid. Serologic tests are impractical — because of the many different virus types — unless a virus has been isolated from a patient or during an outbreak, of typical clinical illness. Nt and HI antibodies are type-specific and may persist for years. CF antibodies give many heterotypic responses.

If an agent is isolated in tissue culture, it is tested against different pools of antisera against enteroviruses. Determination of the type of virus present depends upon neutralization by a single serum. Infection with 2 or more enteroviruses may occur simultaneously.

Control. Avoidance of contact with patients exhibiting acute febrile illness, especially those with a rash, is advisable for very young children. Members of institutional staffs responsible for caring for infants should be tested to determine whether they are carriers of enteroviruses. This is particularly important during out breaks of diarrheal disease among infants.

OTHER ENTEROVIRUS TYPES

Four enteroviruses (types 68-71) grow in mon key kidney cultures, and 3 of them cause human disease.

Enterovirus 68 was isolated from the respiratory tracts of children with bronchiolitis or pneumonia.

Enterovirus 70 is the chief cause of acute hemorrhagic conjunctivitis. It was isolated from the conjunctiva of patients with this striking eye disease, which occurred in pandemic form in 1969-1971 in Africa and Southeast Asia. It was not diagnosed in the USA until its importation into Florida in 1981. Acute hemorrhagic conjunctivitis has a sudden onset of subconjunctival hemorrhage ranging from small petechiae to large blotches covering the bulbar conjunctiva. There may also be epithelial keratitis and occasionally lumbar radiculomyelopathy. The disease is commonest in adults, with an incubation period of 1 day and a duration of 8-10 days. Complete recovery is the rule. The virus is highly communicable and spreads rapidly under crowded or unhygienic conditions. There is no effective treatment.

Enterovirus 71 was isolated from patients with meningitis, encephalitis, and paralysis resembling poliomyelitis. It continues to be one of the main causes of central nervous system disease, sometimes fatal, around the world. In some areas, particularly in Japan and Sweden, the virus has caused outbreaks of hand, foot, and mouth disease.

RHINOVIRUS GROUP

Rhinoviruses are isolated commonly from the nose and throat but very rarely from feces. These viruses, as well as coronaviruses and some reo-, adeno-, entero-, parainfluenza, and influenza viruses, cause upper respiratory tract infections, including the "common cold."

General Properties: Rhinoviruses are picornaviruses similar to enteroviruses but differing from them in having a CsCI buoyant density of 1.40 g/mL and in being acid-labile.

Animal Susceptibility and Growth of Virus. These viruses are infectious only for humans and chimpanzees. They have been grown in cultures of human embryonic lung fibroblasts (WI-38) and in organ cultures of ferret and human trachea! epithelium. They are grown best at 33 °C in rolled cultures.

Antigenic Properties: Over 100 serotypes are known. Some cross-react (e.g., types 9 and 32).

Pathogenesis & Pathology. The virus enters via the upper respiratory tract. High titers of virus in nasal secretions — which can be found as early as 2-4 days after exposure – are associated with maximal illness. Thereafter, viral titers fall, although illness persists.

Histopathologic changes are limited to the submucosa and surface epithelium. These include engorgement of blood vessels, oedema, mild cellular infiltration, and desquamation of surface epithelium, which is complete by the third day. Nasal secretion increases in quantity and in protein concentration.

Experiments under controlled conditions have shown that chilling, including the wearing of wet clothes, does not produce a cold or increase susceptibility to the virus. Chilliness is an early symptom of the common cold.

Epidemiology. The disease occurs throughout the world. In the temperate zones, the attack rates are highest in early fall and winter, declining in the late spring. Members of isolated communities form highly susceptible groups.

The virus is believed to be transmitted through close contact, by large droplets. Under some circum stances, transmission of the virus by self-inoculation through hand contamination may be a more important mode of spread than that by airborne particles.

Colds in children spread more easily to others than do colds in adults. Adults in households with a child in school have twice as many colds as adults in households without school children.

In a single community, many rhinovirus serotypes cause outbreaks of disease in a single season, and different serotypes predominate during different respiratory disease seasons.

Clinical Findings. The incubation period is brief, from 2 to 4 days, and the acute illness usually lasts for 7 days although a non-productive cough may persist for 2-3 weeks. The average adult has 1-2 attacks each year. Usual symptoms in adults include irritation in the upper respiratory tract, nasal discharge, headache, mild cough, malaise, and a chilly sensation. There is little or no fever. The nasal and nasopharyngeal mucosa become red and swollen, and the sense of smell becomes less keen. Mild hoarseness may be present. Prominent cervical adenopathy does not occur. Secondary bacterial infection may produce acute otitis media, sinusitis, bronchitis, or pneumonitis, especially in children. Type-specific antibodies appear or rise with each infection.