25 Enterovirus

The virion of enterovirus consists of a capsid shell of 60 subunites ,each of four proteins(vp1-vp4)arranged with icosahedral symmetry around a genome made up of a single strand of positive –sense RNA.

Structure and composition

Morphology

27nm, icosahedral symmetry, no envelope

The molecular structure :

The three largest viral proteins,vp1-vp3,have a very similar core structure, in which the peptide backbone of the protein loops back on itself to form a barrel of eight strands held together by hydrogen bonds(the beta barrel).

The amino acid chain between the beta barrel and the N and C terminal proteins of the protein contains a series of loops. These loops include the main antigenic sites that are found on the surface of the viron and involved in the neutralization of viral infection.

The genome RNA is in size about 7.4kb .The

genome is polyadenylated at the 3` end and has

a small viral coded protein(VPg) covalently bo

und to the 5`end. The positive-sense genomic R

NA is infectious.

Surface cleft – attachment to cellular receptors:Immunoglobulin superfamily, integrins, ICAM-1

Enterovirus structure

Classification Enteroviruses include the following :

(1)polioviruses,type 1-3;

(2) coxsakieviruses of group A, types 1-24 (there is no type 23);

(3) coxsakieviruses of group B, types 1-6;

(4) echoviruses, types 1-33 (no types 10,22,23,or 28);

(5) enteroviruses, types 68-71.

Enteroviruses Serotypes

肠道病毒的特点

小球形病毒（ ~ 30 nm），无包膜核酸为 +ssRNA，有感染性衣壳有 VP1—VP4四种蛋白， VP1—VP3分布在表面， VP4与内部 RNA结合

耐酸耐乙醚，但鼻病毒除外在胞浆增殖，有明显 CPE，破胞释放引起多种疾病：麻痹性疾病、无菌性脑膜炎、心肌损伤、腹泻、皮疹等

Poliovirus

Poliovirus was Poliovirus was first identified in first identified in 19091909 by by inoculation of specimens into monkeys. inoculation of specimens into monkeys. The virus was first grown in cell culture in The virus was first grown in cell culture in 19491949 which became the basis for which became the basis for vaccinesvaccines

Poliovirus may cause poliomyelitis , w

hich is an infectious disease that in its seri

ous form affects the central nervous syste

m. However, most poliovirus infect-ions a

re subclinical.

General properties:

Poliovirus particle are typical enterovirus.

They are inactivated when heated at 550c for

30min,by a chlorine concentration of 0.1ppm

Poliovirus are not affected ether or sodium deoxycholate

Animal susceptibility and growth of virus:

Polioviruses have a very restricted host range .Most strains will infect monkeys when inoculated directly into the brain or spinal cord.

Most strains can be grown in primary or continuous cell line cultures derived from a variety of human tissues or from monk- ey kidney, testis, or muscle ,but not from tissues of lower animals.

Antigenic propertis:

There are three antigenic types

Two type-specific Ag (D and C)are contained in poliovirus preparation and can be detected by ELISA.

The D form can be converted to the C form by heating . The D form repres-ents full particles containing RNA; the C form ,empty particles.

Pathogenesis Pathology﹠ :

The mouth is the portal of entry of the virus and primary multiplication takes place in the oropharynx or intestine.

The virus is regularly present in the throat and in the stools before the onset of illness.

The virus may be found in the blood of patients with nonparalytic poliomyelitis. Ab to the virus appear early in the disease, usually before paralysis occurs

The virus first multiplies in tonsil, the lymph nodes of the neck, Peyer’ s paches, and the small intestine.

The central nervous system may be invaded by way of the circulating blood. Large amounts of anti-body are necessary to prevent passage of the virus along nerve fiber.

Poliovirus can spread along axons of peripheral ner-ves to the central nervous system, along the fibers of the lower motor neurons to the spinal cord or the br-ain.

Virus invades certain types of nerve cell, and may da-mage or completely destroy these cells for its intracell-ular multiplication.

Transmission

Fecal – oral route

via hands and objects

via food and water

Clinical findings:

Abortive poliomyelitis

Nonparalytic poliomyelitis

Paralytix poliomyelitis

Progressive postpoliomylitis muscle atrophy

Clinical Manifestations

Most infections asymptomatic, 95%

Abortive polio (minor illness), 5%: fever, malaise, sore throat,

myalgia, headache)

Aseptic meningitis (non paralytic polio), 1%

Paralytic polio (major illness), 0.1%: asymetric flaccid paralysis /

paresis. Lower, or upper extremities, thoracic, abdominal, bulbar.

Involvement : spinal cord anterior horn cells, motor cortex, dorsal

root ganglia

neurologic sequela (2/3)

Post-polio syndrome: progressive atrophy years later

Perhaps the first written record of a virus infection consists of a heiroglyph from Memphis, drawn in approximately 1400BC, which depicts a temple priest called Siptah showing typical clinical signs of paralytic poliomyelitis

Victims of paralytic polio

Child with polio sequelae

Franklin D. Roosevelt Born in 1882 at Hyde Park, New York--now a

national historic site--he attended Harvard University and Columbia Law School. On St. Patrick's Day, 1905, he married Eleanor Roosevelt.

Following the example of his fifth cousin, President Theodore Roosevelt, whom he greatly admired, Franklin D. Roosevelt entered public service through politics, but as a Democrat. He won election to the New York Senate in 1910. President Wilson appointed him Assistant Secretary of the Navy, and he was the Democratic nominee for Vice President in 1920.

In the summer of 1921, when he was 39, disaster hit-he was stricken with poliomyelitis. Demonstrating indomitable courage, he fought to regain the use of his legs, particularly through swimming. At the 1924 Democratic Convention he dramatically appeared on crutches to nominate Alfred E. Smith as "the Happy Warrior." In 1928 Roosevelt became Governor of New York.

He was elected President in November 1932, to the first of four terms.

Laboratory diagnosis:

The virus may be recovered from throat swabs, rectal swabs, or stool samples.

Specimens should be kept frozen during transit to the laboratory

Cultures of human or monkey cells

Paired serum specimens are required to show rise in antibody titer during the course of disease.

Laboratory Diagnosis

Virus IsolationMainstay of diagnosis of poliovirus infectionpoliovirus can be readily isolated from throat swabs,

faeces, and rectal swabs, but rarely from the CSFCan be readily grown and identified in cell cultureRequires molecular techniques to differentiate

between the wild type and the vaccine type Serology

Very rarely used for diagnosis since cell culture is efficient. Occasionally used for immune status screening for immunocompromised individuals

Immunity:

Immunity is permanent to the type cau-sing the infection.

Passive immunity is transferred from mother to offspring, which gradually disappear during the first 6 months of life.

Virus-neutralizing antibody forms soon after exposure to the virus, often before the onset of illness.

Epidemiology:

Poliomyelitis occurs worldwide – year-round in tropics and during summer and fall in tem-perate zone. Winter outbreaks are rare.

The disease occurs in all age groups ,but chil-dren are more susceptible than adult because of the acquired immunity of the adult popula-tion.

Human are the only known reservoir of infect-ion.

Prevention control:﹠Both live-virus and killed-virus vaccines are avail-able . They induce antibody and protect the central nervous system from subsequent invasion by wild virus.

A potential limiting factor for oral vaccine is interfer-ence, and for vaccine-associated disease, a switch to the use of only inactivated poliovaccine (four doses) for children

Immune globulin can provide protection for a few weeks against the paralytic disease but does not prevent subclinical infection.

The application of recombinant DNA

Vaccines Available

Intramuscular Poliovirus Vaccine (IPV) consists of formalin inactivated virus of all 3 poliovirus

serotypes (Salk) Produces serum antibodies only: does not induce local

immunity and thus will not prevent local infection of the gut However, it will prevent paralytic poliomyelitis since viraemia is

essential for the pathogenesis of the disease Oral Poliovirus Vaccine (OPV)

Consists of live attenuated virus of all 3 serotypes (Sabin). Produces local immunity through the induction of an IgA

response as well as systemic immunity Rarely causes paralytic poliomyelitis, around 1 in 3 million

doses

Most countries use OPV because of its ability to induce local immunity and also it is much cheaper to produce than IPV

The normal response rate to OPV is close to 100%.

OPV is used for the WHO poliovirus eradication campaign

Because of the slight risk of paralytic poliomyelitis, some Scandinavian countries have reverted to using IPV. Because of the lack of local immunity, small community outbreaks of poliovirus infections have been reported

Current Status of Wild Poliovirus Transmission

我国政府规定每年 12月 5日和 1月 5日为脊灰疫苗日。

柯萨奇病毒（ Coxsackievirus）

从 1948年美国纽约州 Coxsackie镇一名疑似脊髓灰质炎的患儿粪便中用乳鼠接种的方法分离发现

Coxsackieviruses - In 1948, a new group of agents were identified by inoculation into newborn mice from two children with paralytic disease. These agents were named coxsackieviruses after the town in New York State. Coxsackieviruses A and B were identified on the basis of the histopathological changes they produced in Newborn mice and their capacity to grow in cell cultures

Coxsackieviruses are distinguished from other enteroviruses by their pathogenicity for suckling rather than adult mice. They are divided into 2 groups on the basis of the lesions observed in suckling mice.

Group A viruses (23 types) produce a diffuse myositis with acute inflammation and necrosis of fibers of voluntary muscles.

Group B viruses (6 types) produce focal areas of degeneration in the brain, necrosis in the skeletal muscles, and inflammatory changes in the dorsal fat pads, the pancreas and occasionally the myocardium.

In addition, all from group B and one from group A (A9) share a group Ag. Cross-reactivities have also been demonstrated between several group A viruses but no common group antigen has been found.

Pathogenesis

Fecal-Oral route trasmission Spread in the body like polioviruses

Disease Associations Paralytic Disease - most commonly associated with polioviruses but

other enteroviruses may also be responsible, notably enterovirus 71 Meningitis - caused by all groups of enteroviruses, most commonly

seen in children under 5 years of age. Encephalitis - focal or generalized encephalitis may accompany

meningitis. Most patients recover completely with no neurological deficit.

Undifferentiated febrile illness - may be seen with all groups of enteroviruses.

Hand foot mouth disease - usually caused by group A coxsackieviruses although group B coxsackieviruses and other enteroviruses have been caused outbreaks.

Herpangina - caused by group A coxsackieviruses. Epidemic Pleurodynia (Bornholm disease) - normally caused by group

B coxsackieviruses.

Myocarditis - group B coxsackieviruses are the major cause of myocarditis, although it may be caused by other enteroviruses. It may present in neonates as part of neonatal infection and is often fatal. In adults, the disease is rarely fatal.

Respiratory Infections - several enteroviruses are associated with the common cold.

Rubelliform rashes - a rash disease resembling rubella may be seen with several coxsackie A, B, and echoviruses.

Neonatal Infection - some coxsackie B viruses and echoviruses may cause infection in newborn infants. The virus is usually transmitted perinatally during the birth process and symptoms vary from a mild febrile illness to a severe fulminating multisystem disease and death.

Conjunctivitis - associated with several types of enteroviruses, notably Coxsackie A24 and Enterovirus 70 (haemorrhagic conjunctivitis)

Pancreatitis/Diabetes - associated with Coxsackie B virus infection. The extent of the role of the virus in diabetes is unknown.

Exanthems - Rubelliform rashes

- EV leading cause in summer & fall. All types of rash

Hand-foot-and-mouth disease

Hand-foot-and-mouth

disease: mostly coxackie A

fever, malaise, sore throat,

vesicles on bucal mucosa,

tongue, hands, feet, buttocks

highly infectious

resolution – 1w

Herpangina

Herpangina – usually coxackie A

acute onset, fever, sore throat,

dysphagia

lesions – posterior pharynx

can persist w’s

no gingivitis

Laboratory Diagnosis

Virus Isolation Mainstay of diagnosis of enterovirus infection Coxsackie B and Echoviruses can be readily grown in cell

culture from throat swabs, faeces, and rectal swabs. They can also be isolated from the CSF

Coxsackie A viruses cannot be easily isolated in cell culture. They can be isolated readily in suckling mice but this is not offered by most diagnostic laboratories because of practical considerations. Molecular techniques may provide a better alternative.

Serology Very rarely used for diagnosis since cell culture is efficient. Neutralization tests or EIAs are used but are very cumbersome

and thus not offered by most diagnostic laboratories

Management and Prevention

There is no specific antiviral therapy available against enteroviruses other than polio.

Some authorities use IVIG in the treatment of neonatal infections or severe infections in immunocompromised individuals. However, the efficacy is uncertain.

HNIG have been to prevent outbreaks of neonatal infection with good results.

There is no vaccine available mainly because of the multiplicity of serotypes. There is little interest in developing a vaccine except against enterovirus 71 and coxsackie B viruses.

Echoviruses

The first echoviruses were accidentally discovered in 1951 from human faeces, unassociated with human disease during epidemiological studies of polioviruses. The viruses were named echoviruses (enteric, cytopathic, human, orphan viruses).

These viruses were produced CPE in cell cultures, but did not induce detectable pathological lesions in suckling mice.

Types

Altogether, There are 32 echoviruses (types 1-34; echovirus 10 and 28 were found to be other viruses and thus the numbers are unused)

There is no group echovirus Ag but heterotypic cross-reactions occur between a few pairs.

Pathogenesis

致病性与柯萨奇病毒类似，呈多样性。主要是无菌性脑炎、类脊髓灰质炎等

感染后对同型病毒可产生持久免疫诊断困难，对可疑患者可采粪便、 CSF等标本做病毒分离和中和试验

尚无疫苗。预防以隔离为主

New Enteroviruses Newly identified picornaviruses that are not polioviruses are no

longer classified separated into the species coxsackie and echovirus because of the ambiguities presented by overlapping host range variations.

4 new enteroviruses have been identified (68 - 72). Enterovirus 70 is the causative agent epidemics of acute haemorrhagic conjunctivitis that swept through Africa, Asia, India and Europe from 1969 to 1974. The virus is occasionally neurovirulent.

Enterovirus 71 appears to be highly pathogenic and has been associated with epidemics of a variety of acute diseases, including aseptic meningitis, encephalitis, paralytic poliomyelitis-like disease and hand-foot-mouth disease.

Enterovirus 72 was originally assigned to hepatitis A virus, but it had now been assigned to a new family called heptoviruses.

Gastrointestinal Viruses

Viral Gastroenteritis It is thought that viruses are responsible for up to

3/4 of all infective diarrhoeas. Viral gastroenteritis is the second most common

viral illness after upper respiratory tract infection.

In developing countries, viral gastroenteritis is a major killer of infants who are undernourished. Rotaviruses are responsible for half a million deaths a year.

Many different types of viruses are found in the gut but only some are associated with gastroenteritis.

Associated with gastroenteritis

Rotaviruses Adenoviruses 40 41 Caliciviruses Norwalk like viruses or SRSV (Small

Round Structured Viruses) Astroviruses SRV (Small Round Viruses) Coronaviruses Toroviruses

Found in the gut, not normally associated with

gastroenteritis Polio Coxsackie A Coxsackie B Echo Enteroviruses 68-71 Hepatitis A Hepatitis E Adenoviruses 1-39 Reoviruses

Found in the gut as opportunistic infection

CMV HSV VZV HIV

Gastrointestinal VirusesVirus Genome Typical disease incubation Duration

Rotaviruses:Group A, B, C

ds-segmented RNA

Major cause of diarrhea in children

1-3 days24-56 h

5-8 days3-7 days

CalicivirusesNorwalk agents

ssRNA Infects adults and childrenEpidemic viral gastroenteritis

1-3 days18-24 h

1-3 days12-48 h

EAd 40,41 Linear dsRNA

diarrhea in children

7-8 days 8-12 d

Astrovirus +ssRNA Infects mainly children and elderly

1-4 days 1-4 d

Gastrointestinal Viruses

Infants:

Rotavirus A; Adenovirus 40,41; Coxsackie A24 virus

Infants, children, and adults

Norwalk virus; Calicivirus嵌杯样病毒属 ; astrovirus; Rotavirus B; Reovirus.

Human Rotavirus

Important Characteristics

70 nm round, double shelled, enclosing a genome of 11 segments of double stranded RNA.

Groups of Rotaviruses

Group A subtypes 1, 2, 3, 4 (main human pathogens)(Further 7 subtypes) also infect animals (monkey, calf, mouse)

Group B Infects pigs and ratsFound to cause extensive outbreaks in China in past decade

Group C Infects Pigs (Occasionally Man) Group D Infects birds Group E Infects pigs

Pathogenesis

Essentially an ingestion disease (faecal-oral route)

Incubation is short : 1 to 3 days Illness: Sudden onset watery

diarrhoea, with or without vomiting. May last up to 6 days (or longer if immunocompromised). The disease is self limiting.

Complications: Dehydration may result, this can be severe and life threatening in young children.

Pathogenesis

Group A: Main pathogen of infantile diarrhea

Group B : Cause epidemic adult diarrhea

Group C: Cause human or animal sporadic diarrhea

Immunity: sIgA

Lab. Diagnosis IEM, Cell culture, PAGE of RNA segments, PCR Latex agglutination Elisa

Treatment

Treatment is aimed at prevention and/or treatment of dehydration by oral and/or intravenous fluids and electrolytes

Prevention

Non specific factors: improved hygiene, education, clean waterSpecific - Breast feeding helps to provide passive immunity in the newborn (from maternal antibodies), Vaccination is still experimental.

Enteric Adenoviruses

Naked DNA viruses, 75 nm in diameter. Fastidious enteric adenovirus types 40 and 41 are associated

with gastroenteritis. Associated with cases of endemic gastroenteritis, usually in

young children and neonates. Can cause occasional outbreaks. Possibly the second most common viral cause of gastroenteritis

(7-15% of all endemic cases). Similar disease to rotaviruses Most people have antibodies against enteric adenoviruses by

the age of three. Diagnosed by electron microscopy or by the detection of

adenovirus antigens in faeces by ELISA or other assays.

Astroviruses

Small RNA viruses, named because of star-shaped surface morphology, 28 nm in diameter.

Associated with cases of endemic gastroenteritis, usually in young children and neonates. Can cause occasional outbreaks.

Responsible for up to 10% of cases of gastroenteritis.

Similar disease to rota and adenoviruses.

Most people have antibodies by the age of three. Diagnosed by electron microscopy only, often very

difficult because of small size.

Caliciviruses

Small RNA viruses, characteristic surface morphology consisting of hollows. particles 35 nm in diameter.

Associated mainly with epidemic outbreaks of gastroenteritis, although occasionally responsible for endemic cases.

Like Norwalk type viruses, vomiting is the prominent feature of disease.

Majority of children have antibodies against caliciviruses by the age of three.

Diagnosed by electron microscopy only, often difficult to diagnose because of small size.

Norwalk-like Viruses

Small RNA viruses, with ragged surface, 35 nm in diameter, now classified as caliciviruses.

Always associated with epidemic outbreaks of gastroenteritis, adults more commonly affected than children.

Associated with consumption of shellfish and other contaminated foods. Aerosol spread possible as well as faecal-oral spread.

Also named "winter vomiting disease", with vomiting being the prominent symptom, diarrhoea usually mild.

Antibodies acquired later in life, in the US, only 50% of adults are seropositive by the age of 50.

Diagnosis is made by electron microscopy and by PCR.

Other Possible Diarrhoeal Viruses

Coronaviruses RNA viruses with a crown-like appearance

Not convincing associated with gastroenteritis at

present

Small Round Viruses Small virus-like particles with a smooth surface, 22-

28nm in diameter

May possibly be parvoviruses, enteroviruses, or cubic bacteriophages

Occasionally seen in the faeces of endemic or epidemic cases of gastroenteritis

Gastrointestinal VirusesVirus Genome Typical disease incubation Duration

Rotaviruses:Group A, B, C

ds-segmented RNA

Major cause of diarrhea in children

1-3 days24-56 h

5-8 days3-7 days

CalicivirusesNorwalk agents

ssRNA Infects adults and childrenEpidemic viral gastroenteritis

1-3 days18-24 h

1-3 days12-48 h

EAd 40,41 Linear dsRNA

diarrhea in children

7-8 days 8-12 d

Astrovirus +ssRNA Infects mainly children and elderly

1-4 days 1-4 d

问题肠道病毒有哪些？是不是肠道感染的所有病毒都称为肠道病毒？

简要说明肠道病毒的特性脊髓灰质炎病毒的传播途径、致病机制是什么？如何预防脊灰？

B组柯萨奇病毒的致病有何特点？ ECHO病毒、轮状病毒、杯状病毒、小圆结构病毒分别与哪些疾病有关？