Poliovirus

2021-08-16 06:33 PM

Motor neurons of the spinal cord or of the cerebral cortex can be destroyed and thus cause flaccid paralysis

Enterovirus belongs to the family Picornaviridae, this family includes 2 genera: Enterovirus and Rhinovirus. Common features are small, single-stranded RNA, cuboidal symmetrical capsid, no envelope.

Enterovirus genus includes 4 species

Poliovirus: includes 3 types, causing polio, meningitis.

Coxsackievirus: includes 29 types, causes aseptic meningitis, myocarditis, aphthous pharyngitis, skin rash...

Echovirus: includes 32 types, causing aseptic meningitis, respiratory infection, encephalitis, enteritis, myocarditis,...

Enterovirus type 68-71 causes hemorrhagic conjunctivitis, bronchiolitis; Type 72 of Enterovirus causes acute hepatitis (Hepatitis A virus).

Similar Rhinovirus

Causes upper respiratory tract infection.

Poliovirus infects the pharynx and intestine, so it can be isolated in both places. It consists of 3 types: 1, 2, 3.

Poliovirus causes polio, an acute illness that affects the central nervous system. The motor neurons of the spinal cord or of the cerebral cortex can be destroyed and thus cause flaccid paralysis. In an outbreak 90-93% of cases were latent, 4-8% had a mild illness with respiratory and intestinal symptoms, only 1-2% had polio syndrome.

Virological characteristics

Virus morphology

The poliovirus is one of the smallest known viruses, 28 nm in diameter. The virus contains single-stranded RNA, the cuboidal symmetric capsid consists of 32 capsomeres. Single-stranded RNA molecules make up 30% of the viral particle's weight. RNA molecules can detach from viral particles and retain the ability to infect cell cultures. Capsid protects nucleic acids, helps the virus to fix on the surface of receptor cells, and carries specific antigens to form immunity to the virus.

Resistance abilities

The virus is resistant to ethers and bleach, stable at pH 4 - 10 but inactivated at 56 0C for 30 minutes or treated with formalin, Cl2, H2O2, KMnO4. At normal temperatures, the virus can survive in human feces from 1 day to many weeks depending on the amount of virus, pH, and moisture content of the stool. The virus remains infectious for a relatively long time in water, milk, and other foods.

Viral Culture properties

People can infect Rhesus monkeys, Cynomolgus monkeys when injected into the spinal cord, into the brain or instilled into the nose. Poliovirus can be transmitted by the gastrointestinal tract when the virus is transmitted to monkeys through the mouth. Animals are no longer used to diagnose viruses but are used to test vaccines.

Most Poliovirus strains can grow in human or monkey kidney cells, or in permanent cells such as HeLa cells. Poliovirus causes in cell culture a characteristic pathological effect: cells become round, optically refractive, and the nucleus shrinks before degenerating.

Antigen structure

Poliovirus includes 3 types: 1, 2, 3 identified by neutralization reaction, complement combination reaction, and precipitation reaction in gel medium. Neutralizing antigens and complement-conjugated antigens can be extracted from cell cultures or from virally infected CNS.

Possibility to cause disease

Path of disease transmission

Polio is a highly contagious disease that can be transmitted by the gastrointestinal tract and respiratory tract, but mainly by the gastrointestinal tract. People get the virus by eating food contaminated with the virus or coming into contact with contaminated objects or breathing in small droplets containing the virus.

The growth of the virus in the body

After entering the body, the virus infects the oropharynx and intestines, replicating there and in lymph nodes in the neck and mesentery. After 2 or 3 days the virus is released into the bloodstream and secondary infection occurs in sensitive tissues other than the nervous system and the central nervous system. Replication of viruses at the primary sites and subsequent viremia, in many cases asymptomatic or indicative of a nonspecific, important disease called poliomyelitis occurs after viremia and is the result of viral replication and cellular destruction at secondary sites. The incubation period is from 7-14 days, sometimes shorter than 3 days or longer than 35 days.

Clinical features

The infection does not manifest

About 90-95% of Poliovirus infections show no symptoms. In these cases, the infection is confined to the gastrointestinal tract and can only be identified by fecal virus isolation or by serological tests.

Mild illness

Patients have moderate fever for 24-48 hours; mild illness precedes severe illness. Symptoms: headache, anorexia, vomiting, nasal and pharyngeal congestion, sore throat, and sometimes gastrointestinal disturbances. Mild illness is not a common feature of polio and occurs in only one-third of children and less in adults among those diagnosed with polio.

Mild illness is considered a clinical manifestation of viremia after which the patient recovers. The syndrome is called preterm polio and accounts for about 4-8% of all Poliovirus infections.

Serious illness

Appears 1-3 days after mild illness or occurs without mild illness.

Pre-polio phase: disease reflecting poliovirus infection of the central nervous system, presenting the first clinical signs of infection in most cases. Features: fever, headache, nausea, vomiting, and signs of moderate irritation of the meninges causing pain and stiffness in the neck and back, possibly also in the extremities. In a few patients, the disease stops here without developing into paralysis and is called non-paralytic polio.

Paralytic phase: 1-5 days after the onset of severe illness or sometimes longer, the patient develops flaccid paralysis in specific muscle groups. Muscle paralysis develops over the next 3 days, the extent of which depends on the location and condition of the lesions in the central nervous system. Recovery begins after the disease stops developing. The functioning of the paralyzed muscles may improve over the next 4-6 weeks, with any improvement usually complete within 6 months. Physical therapy can help with recovery. Rarely, the second phase of paralysis occurs 3 to 4 days after the first episode. About 1-2% of people infected with Poliovirus develop severe illness.

Forms of polio

Paralytic lesions commonly occur in the cells of the anterior horns of the spinal cord (spinal palsy). Similar lesions can occur in areas of the spinal cord and brain (medullary palsy) and in the cerebral cortex (cerebral palsy). Medullary palsy is particularly serious because damage to the cranial nerves paralyzes the muscles of the trachea, larynx, and palate, inability to swallow, and rapidly impedes breathing if left untreated. suitable. Injury to the respiratory and vasomotor centers can lead to respiratory failure and cardiovascular collapse, so bulbar palsy has a high mortality rate.

Immunity

Permanent immunity to the Poliovirus type that causes the infection. However, there may be a low degree of resistance between types 1 and 2, especially between types 1 and 2. Anti-polio antibodies passed on to the baby gradually disappear during the first 6 months of the baby's life. Antibodies injected into the body only last for 3-5 weeks.

Neutralizing antibodies form about 7 days after the body is exposed to Poliovirus and persist for life. Because the virus in the brain and spinal cord is not affected by antibodies in the blood, immunostaining is only valid when done before the onset of symptoms related to the nervous system.

It has long been known that polio resistance is closely related to the tonsils. Recent surveys have shown that after tonsillectomy, antibody levels in the mouth and throat are markedly reduced, especially in male children. In children with tonsillectomy, the response to polio vaccine is slow and the antibody titre is lower than in children with intact tonsils.

Laboratory diagnostics

Cerebrospinal water

White blood cells increase 10 - 200 /mm3, rarely 500 /mm3. In the early stages of the disease, the polymorphonuclear leukocyte/lymphocyte ratio is high, but within a few days, the ratio reverses. The total cell count slowly returned to normal. Cerebrospinal fluid protein is moderately increased, averaging 40-50 mg/100ml, and remains this way for several weeks before the cell count declines. Normal glucose levels.

Virus isolation and identification

Specimens:

It is a cotton swab to swab the throat during the outbreak, but it can be used to pick up the anus or collect stool for a longer time. The probability of finding the virus depends on the course of the disease: 80% in the first 2 weeks but only 25% in the 3rd week. In the case of the patient's death, brain and colonic contents are taken. Specimens should be refrigerated as soon as possible and, if sent to the laboratory for more than 1 day, should be kept frozen.

Isolation and identification:

Cultured in monkey kidney or amniotic cells or standing cells (Hela, KB, WI-38). The poliovirus causes a characteristic cytopathological effect. Type determination by neutralization reaction.

Serum reaction:

Double serum collection: the first time after a disease outbreak, the second time, 2-3 weeks later to find antibody dynamics. Complement combination reaction, neutralization reaction can be used. Complement-conjugated antibodies change over the course of the disease. Neutralizing antibodies appear early and are usually detectable during the patient's hospital stay. Type-specific precipitated antibodies develop during recovery and are of little use in diagnostic testing.

The serological reaction is not only valuable for the diagnosis of the disease, but also for determining the status of viral infection (hidden form) in the community and determining the effectiveness of the vaccine.

Prevention and treatment

Treatment

There is no specific drug.

Prevent

By general measures that are difficult to implement, mainly by very effective vaccines. There are two types of vaccines: the Salk vaccine and the Sabin vaccine.

Vaccine Salk:

A dead vaccine containing 3 virulent virus types was cultured in monkey kidney cells and killed with formol and bpropiolactone. Intradermal injection of the vaccine induces humoral immunity to prevent the virus from infecting the central nervous system. Vaccines are safe and effective if used correctly. However, this vaccine has some disadvantages: it does not create local immunity, so the virus can still multiply in the intestines, so it does not reduce the risk of spreading the virus. more expensive.

Vaccine Sabin:

It is a live attenuated vaccine. This is a complete live vaccine containing 3 attenuated poliovirus types 1, 2, and 3. The virus replicates in the enterocytes to form local antibodies. Harvested immunity not only prevents virulent wild viruses from infecting the nervous system but also inhibits the invasion and replication of those viruses in the gut. Moreover, the Sabin vaccine is about 100 times cheaper than the Salk vaccine and easy to implement because it can be given orally or put a few drops into a sugar stick and then sucked.