• Vaccine is a biological preparation that improves immunity to a particular disease. They are molecules, usually but not necessarily proteins, that elicits an immune response, thereby providing protective immunity against a potential pathogen.
• Vaccine is used to boost the body’s immune system and prevent the serious life threatening diseases.
• Vaccine can be prepared against bacteria or even eukaryotic protozoans, however most successful vaccines have been developed against viruses.
• The first human vaccine was smallpox vaccine, using cowpox as vaccine.
• Rabies was the first virus attenuated in a lab to create a vaccine for humans.

Characteristics of Vaccine:

Following are the properties that an ideal vaccine should possesses;

1. Safe: Vaccine must be safe and must not itself causes illness or death
2. Protective: vaccine must protect against illness resulting from exposure to live pathogen
3. Sustained protection: protection against illness must last for years
4. Induce neutralizing antibodies
5. Induce protective T cells
6. Low cost
7. Biological stability
8. Ease of administration
9. No side effect or Very few side effects

Types of vaccines

1, Live attenuated vaccines:

• Live attenuated vaccines contain living microorganisms that has been weakened in the lab so it can’t cause disease. These vaccine evoke immune system of the host preventing form the diseases.
• Live attenuated vaccines are relatively easy to create for certain viruses.
• Vaccines against measles, mumps, and chickenpox, for example, are made by this method.
• Live attenuated vaccines are more difficult to create for bacteria. Bacteria have thousands of genes and thus are much harder to control. However, this approach has been used to create a vaccine against Vibrio cholerae.
• Live attenuated vaccine use whole organism as vaccine and are prepared from attenuated strains that almost or completely devoid of pathogenicity but are capable of inducing a protective immune response. They multiply in the human host and provide continuous antigenic stimulation over a period of time.
• Examples: BCG, Typhoid vaccine, Measles vaccine, mumps vaccine, Sabin’s polio vaccine, VAR vaccine, Yellow fever vaccine, Rota virus vaccine etc

2. Killed or Inactivated vaccines: 

• Disease-causing microorganisms are killed with chemicals, heat, or radiation. Such vaccines are more stable and safer than live vaccines because the dead microorganisms can’t mutate back to their disease-causing state.
• There are the easiest preparations to use. Such vaccines are simply inactivated or killed microorganisms.
• Preparation of killed vaccine may take the route of heat or chemicals. The chemicals used includes formaldehyde or beta-propiolactone. The traditional agent for inactivation of virus is formalin.
• Excessive treatment can destroy immunogenicity whereas insufficient treatment can leave infectious microorganisms capable of causing disease.
• The inactivated vaccines usually don’t require refrigeration, and they can be easily stored and transported in a freeze-dried form, which makes them accessible to people in developing countries.
• Example: Salk polio vaccine, Anthrax vaccine, Cholera vaccine, Purtusis vaccine, Plague vaccine, Influenza vaccine, Hepatitis A vaccine, Rabies vaccine, Rubella vaccine etc

3. Subunit vaccines:

• Instead of the entire microorganisms, subunit vaccines include only the antigens that best stimulate the immune system and used in vaccine preparation.
• Vaccine that consists of specific, purified macromolecules derived from pathogen are known as subunit vaccine.
• The general forms of such vaccine are in current use: Purified capsular polysaccharides, inactivated exotoxin (Toxoid), recombinant microbial antigen, synthetic peptide.

i. Purified capsular polysaccharide vaccine:

• The virulence of some pathogenic bacteria depends primarily on the anti-phagocytic property of their hydrophobic polysaccharide capsule.
• These are generally conjugate vaccine.
• In some gran negative bacteria, LPS is the outermost covering which protect the bacteria from binding with the antibody. So that the immature immune systems of infants and younger children can’t recognize or respond to them. For this conjugate vaccine is used.
• Examples: Hib vaccine (The vaccine that protects against Haemophilus influenzae type B (Hib) is a conjugate vaccine), Vaccine for Streptococcus pneumoniae, vaccine for Neisseria meningitides

ii. Toxoid vaccines:

• For some bacteria that secrete toxins, or harmful chemicals, a toxoid vaccine is made.
• The toxins are inactivated by treating with formalin, such detoxified toxin is known as toxoid, which is used as vaccine.
• Vaccination with toxoid induces anti-toxoid antibodies, which are capable of binding the toxin and neutralizing its effect.
• Conditions for the production of toxoid vaccines must be closely controlled to achieve detoxification without excessive modification of the epitope structure. Sufficient quantities of the purified toxins is prepared by cloning the exotoxin genes and then expressing them in easily grown host cells, purified and subsequently inactivated.
• Vaccines against diphtheria and tetanus are examples of toxoid vaccines.

iii. Recombinant vaccine:

• Recombinant vector vaccines are experimental vaccines similar to DNA vaccines, but they use an attenuated virus or bacterium to introduce microbial DNA to cells of the body.
• Attenuated bacteria also can be used as vectors.
• The gene coding for immunogenic protein is inserted into plasmid vector and then transformed it into suitable host cell such as bacteria, yeast, mammal cell etc.
• In this case, the inserted genetic material causes the bacteria to display the antigens of other microbes on its surface.
• In effect, the harmless bacterium mimics a harmful microbe, provoking an immune response.
• Recombinant hepatitis B vaccine is the only recombinant vaccine licensed at present.

iv. Synthetic peptide vaccine:

• The development of synthetic peptides that might be useful as vaccines depends on the identification of immunogenic sites.
• The best example is Foot and mouth disease where protection was achieved by immunizing animals with a linear sequences of 20 aminoacids.
• Synthetic peptide vaccine would have many advantages. They are stable and relatively cheap to manufacture. Furthermore, less quality assurance is required.
• Synthetic peptides so not readily stimulate t cells. It was generally assume that, because of their small size, peptides would behave like haptens and would therefore require coupling to a protein carrier which is recognized by T cells.
• It is now known that synthetic peptides can be highly immunogenic in their free form provided they contain, in addition to the B cells epitope, T cell epitope recognized by T-helper cells. Such T cell epitope can be provided by carrier protein molecules, foreign antigens or within the synthetic peptide molecule itself.
• Synthetic peptide vaccine is not applicable for all viruses. For example, it is not applicable for Polio virus because important antigenic sites were made up of 2 or more different viral capsid protein.

4. DNA vaccines:

• DNA vaccine is DNA sequence used as vaccine.
• This DNA sequence codes for antigenic protein of pathogen.
• When the genes for a microbe’s antigens are introduced into the body, some cells will take up that DNA. The DNA then instructs those cells to make the antigen molecules. The cells secrete the antigens and display them on their surfaces. In other words, the body’s own cells become vaccine-making factories, creating the antigens necessary to stimulate the immune system.
• As this DNA inserted into cells it is translated to form antigenic protein. As this protein is foreign to cells, immune response raised against this protein. In this way, DNA vaccine provide immunity against that pathogen.
• Recently, encouraging results were reported for DNA vaccines whereas DNA coding for the foreign antigen is directly injected into the animal so that foreign antigen is directly produced by the host cells.
• In theory these vaccines would be extremely safe and devoid of side effects since the foreign antigens would be directly produced by the host animal.
• In addition, DNA is relatively inexpensive and easier to produce than conventional vaccines and thus this technology may one day increase the availability of vaccines to developing countries.
• The time for development of DNA vaccine is relatively short which enable timely immunization against emerging infectious diseases.
• Also, DNA vaccines can theoretically result in more long term production of an antigenic protein when introduced into a relatively non dividing tissue such as muscles.
• Examples,  DNA Vaccine Against West Nile Virus, Influenza and Herpes virus

Vaccine: Characteristics and types of vaccine

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Characteristics of Poliovirus

• Family: Picornaviridae
• Genus: Enterovirus
• Poliovirus are small, hexagonal, +ssRNA virus
• Symmetry: Icosahedral capsid composed of 60 capsomere
• Each capsomere consists of four viral protein (VP1- VP4)
• Size: 22-30nm
• Shape: spherical
• Genome: positive sense single stranded RNA (+ssRNA).
• The genome is polyadenylated at 3’ end and
• Non-enveloped

Other characteristics of polio virus

• Poliovirus can survive for 4-6 months in cold water.
• It can be inactivated by pasteurization temperature, 0.3% formaldehyde, 0.1M HCL, residual cholorine of (0.3-0.5) ppm
• It is resistant to lipid soluble agents such as Ether, Chloroform, bile and proteolytic enzymes of intestine
• It can survive in faeces for months at 4° C and for years at -20°

Epidemiology:

• WHO recorded Polio cases have decreased by over 99% since 1988, from an estimated 350 000 cases in more than 125 endemic countries then, to 37 reported cases in 2016.
• Of the 3 strains of wild poliovirus (type 1, type 2, and type 3), wild poliovirus type 2 was eradicated in 1999 and no case of wild poliovirus type 3 has been found since the last reported case in Nigeria in November 2012.
• Pakistan , Afghanistan and Nigeria are endemic to poliovirus

Serotypes of Poliovirus:

On the basis of neutralization test poliovirus is divided into three serotypes.

• Poliovirus 1: it is most common and virulent type. It is frequent isolated from patients with poliomyelitis and causes epidemics
• poliovirus 2: it is usually associated with endemic infection
• poliovirus 3: it causes occasional endemic infection

Mode of transmission

• Human are only natural host for Poliovirus
• primarily by: Faeco-oral route by Ingestion of virus contaminated food and water
• Droplet infection, inhalation

Pathogenesis

1. Initial multiplication:

• in oropharynx and intestinal epithelium
• Incubation period: 9-12 days
• Virus regularly present in throat and in stool of patient before clinical symptoms

2. Primary viremia:

• Virus enter the lymphatic and blood from oropharynx and intestinal epithelium producing primary viremia
• In most of the case, primary viremia is cleared by host defense. But in children who fail to control primary viremia develop Poliomyelitis.

3. Secondary viremia:

• When primary viremia is not controlled then there is a secondary viremia
• After multiplication in reticuloendothelial syetem, it envades the blood stream again causing major or secondary viremia.
• During secondary viremia, virus crosses the blood-brain barrier and gain access to brain and spinal cord.
• Virus multiply in nerve cell of CNS and damage anterior horn of spinal cord as well as nerve cell of medulla oblongata, pons etc. therefore patients suffer from neurological symptoms

Clinical manifestation:

Few suffer from minor illness, very few suffer from meningitis and less than 1% suffer from major paralytic disease

1. Asymptomatic illness:

• In most of the infection is asymptomatic and self-limiting

2. Abortive poliomyelitis:

• Non-specific symptoms such as headache, fever, sore throat, loss of appetite
• Disease last for 5 days

3. Non paralytic poliomyelitis

• Very few patients suffer from non-paralytic poliomyelitis
• Stiffness of neck
• Pain in back and neck
• Disease last for 2-10 days

4. Paralytic Poliomyelitis:

• Less than 1% patients suffer from major paralytic poliomyelitis
• It damages the motor nerves causing oedema and muscle paralysis
• Malaise
• Anorexia
• Nausea and vomiting
• Sore throat
• Constipation
• Abdominal pain
• Headache and fever
• Flaccid paralysis: motor neuron damage
• Bulbar paralysis: respiratory paralysis

5. Post poliomyelitis muscle atropy:

• Muscle wasting
• Loss of neuromuscular function
• Physically Disabled

6. Death is rare. And if occur it is due to respiratory paralysis

Lab diagnosis:

Specimen: nasal secretion, faecal samples, throat swab, CSF

1. Electron Microscopy: virus detection
2. Virus isolation: culture on monkey kidney cell line, Human amnion, HeLA, Hep-2, Buffalo green monkey (BGM), MRC-5 cell line
3. Antibody detection: ELISA, complement fixation test
4. Antigen detection: neutralization test
5. Molecular diagnosis: PCR

Treatment: no antiviral drus

Prevention and control:

1. Vaccination

i. Salk’s killed polio vaccine:

• Prepared by Jonas Salk in 1956
• Also known as Inactivated poliovirus vaccine (IPV)
• Prepared by formalin inactivation of poliovirus
• It is injected deep subcutaneous or intramuscular
• Given to child at age of 2 months, 4 months, at school entry age
• Effective against all serotype of poliovirus

ii. Sabin’s vaccine: live attenuated vaccine

• Developed by Albert Sabin in 1962
• Contains live attenuated strain of all serotypes of poliovirus
• It is administered Orally at 2 months of age simultaneously with first DPT
• It is recommended for all children below 5 years
• In endemic countries monovalent oral poliovirus type I vaccine (MOPvI) is introduced to eliminate the last reservoir of poliovirus

2. proper sanitation

3. safe drinking water

References

1. http://polioeradication.org/where-we-work/polio-endemic-countries/
2. https://www.cdc.gov/polio/about/
3. http://polioeradication.org/polio-today/polio-prevention/the-virus/
4. http://www.who.int/mediacentre/factsheets/fs114/en/
5. http://www.who.int/biologicals/areas/vaccines/poliomyelitis/en/

Poliovirus: Characteristics, Epidemiology, Serotypes, Mode of transmission, Pathogenesis, Clinical manifestation, laboratory diagnosis, Prevention and control

The post Poliovirus: Characteristics, Epidemiology, Serotypes, Mode of transmission, Pathogenesis, Clinical manifestation, laboratory diagnosis, Prevention and control appeared first on Online Biology Notes.