Structure and composition 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.
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 bound to the 5`end. The positive-sense genomic RNA is infectious.
Enterovirus structure Surface cleft – attachment to cellular receptors: Immunoglobulin superfamily, integrins, ICAM-1
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.
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 was first identified in 1909 by inoculation of specimens into monkeys. The virus was first grown in cell culture in 1949 which became the basis for vaccines
Poliovirus may cause poliomyelitis , which is an infectious disease that in its serious form affects the central nervous system. However, most poliovirus infect-ions are 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
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 Isolation • Mainstay of diagnosis of poliovirus infection • poliovirus can be readily isolated from throat swabs, faeces, and rectal swabs, but rarely from the CSF • Can be readily grown and identified in cell culture • Requires molecular techniquesto 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
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 sucklingrather 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