The Attenuation of Herpes Zoster

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Herpes zoster is a viral infection that mainly affects the older people. Its symptoms are a painful skin rash often accompanied by blisters on one area of skin. The virus that causes this dermal condition is the same as that which causes chicken pox (varicella). The only difference is that chicken pox is mainly as a result of initial contact with the virus while zoster is more of a secondary effect. Chicken pox mainly affects children and young people and it is infectious. When it clears, the viruses do not leave the human body completely but instead remain latent and for some reasons these may reactivate causing zoster in the later years. In most cases the viruses resurface when the body’s immune system can no longer contain the virus replication (Eastern, J & Elston, M. n.d) available on . Herpes zoster vaccine is a drug used to prevent Herpes Zoster outbreaks in adults aged 60 years and above. It is recommended for use in the United States targeting individuals who have a history of chickenpox. However, experts recommend that all persons over the age of 60 get the vaccine, provided their immunity has not been compromised as in the case of HIV/AIDS victims or cancer patients undergoing chemotherapy. Its use in immunocompromised persons may result in undesirable side effects (PMC 2008) available on . The vaccine is endorsed by the Food and Drug Administration. This vaccine is given subcutaneously and is a single dose. It should not be used in children (Center for Disease Control and Prevention n.d.)

The zoster virus is identical to varicella virus, the virus that causes chicken pox. The vaccine is also closely related to varivax, the vaccine against chicken pox. Its components are similar to those of varicella vaccine but has got a higher virus concentration. Herpes Zoster manifests as a dermal disorder setting itself apart from varicella by the clinical symptoms it exhibits. Persons who have had an earlier exposure to varicella are at a greater risk of developing herpes zoster than those with no exposure.

The vaccine is dispensed as Zostavax and is normally stored frozen in temperatures of about -50. It is only removed for reconstitution for injection a few minutes before administration. The reconstituted vaccine should be used within 30 minutes and any remainders discarded. This is owing to the fact that it comprises of live attenuated varicella virus, and must be kept alive for efficacy.

The study of the viral behavior of varicella zoster was carried out on human tissue implanted on the SCID-hu mouse. Infection of these skin implants formed the basis for study of the virus and hence the foundation of its attenuation. V-Oka is the strain of varicella- zoster virus used to generate the vaccine. To begin with its pathogenicity was analyzed against that of its parent, P-Oka, and two other strains of varicella-zoster virus; VZV-S (varicella-zoster virus Schenke) which is a clinical isolate strain with low-passage and VZV-Ellen, which is a standard strain used in the laboratory (American Society for Microbiology 1998) which can be found at (). All these strains of the virus replicated positively in tissue culture and only the low-passage strains were infective in skin. This was investigated by an analysis of the character of glycoprotein C in infection of the human skin. The analysis was carried out using gC negative mutants of V-Oka and VZV-Ellen.

Analysis of infectious virus yields and of human skin tissue implants for VZV DNA and viral protein synthesis revealed that only low passage strains were virulent in the human skin. Comparison of the infectivity of V-Oka and P-Oka revealed that V-Oka was generally weaker and it was eventually nullified by lack of glycoprotein C. This formed the basis for clinical attenuation of V-Oka, owing to the fact that it has reduced replication in skin and passage through tissue culture decreases the infectivity of VZV on the human skin. The efficacy of this vaccine was investigated in a study on a sample population in the US. The study was carried out on healthy persons aged 60 and above who had had an earlier infection of chicken pox or had lived in the United States for over 30 years. These people were given the herpes Zoster vaccine as a 0.5ml of live attenuated herpes virus as a single subcutaneous injection or a placebo. Follow up on the patients indicated that the severity and duration of the disease was reduced significantly in the vaccinated individuals as compared to previous data on the disease.

The side effects were more pronounced in the vaccinated group than in the group that was given a placebo.

Zostavax is contraindicated in pregnancy and breastfeeding though no conclusive study has been carried out to confirm if zostavax is secreted in milk. This is owing to the fact that the drug indications exempt children. People in the child bearing age are advised not to use this vaccine. It is also important to note that Zostavax is not used to treat zoster herpes. Neither is it used as a vaccine against chicken pox.

Herpes zoster vaccine can offer protection for about 4 years. Protection beyond four years is not confirmed. However, booster dosage is not recommended but this may change with advancement of studies (Public Health Agency of Canada 2010) ).

References

American Society for Microbiology 1998. Web.

Eastern, J & Elston, M. n.dWeb.

Center for Disease Control and Prevention n.d. Herpes Zoster Vaccination for Healthcare Professionals. Web.

PMC 2008.Live, . Web.

Public Health Agency of Canada 2010. Statement on the Recommended Use of Herpes Zoster Vaccine. Web.

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