Violeta Genova, CRA

Disease

Chicken pox (Varicella)

Causative Agents

Chicken pox disease is a viral infection caused by a herpes virus called varicella zoster virus(VZV). The varicella virus belongs to family Herpesviridae ,and is also known as “chicken pox virus”, “zoster virus”, and “human herpes virus type 3”.

VZV is enveloped, double stranded linear DNA genome with an icosohedral (def)  capsid (def) and a lipid envelope (def). It has a spherical shape and a diameter from 150-200 nanometers (def).
Varicella virus affects only humans and cannot infect other animals. The only exceptions are primates such as gorillas and chimpanzees. VZV is characterized by its ability to remain in the nerve tissue and become active again after long period of time.

Epidemiology

Varicella is an epidemic infection and a common illness of childhood. The highest rate of occurring happens in the range between ages of 4 to 10 years. The mMajority of people (90%) get infected before adulthood. Only 10% of the individuals become infected as adults.

In 10%-20 % of the people, the infection can reoccur after several decades. In general, a person experiences varicella only one time throughout their life. Once infected, people are considered to be protected for life and most likely will not get the infection again. However, due to the ability of the virus to remain latent in human body for years, it can resurface years later in the form of different skin infections or eruptions. These skin eruptions are called shingles (def) or herpes zoster (def).

Even though people can get infected with varicella during the entire year, spring and winter are usually considered as varicella seasons since the virus is spread by the respiratory route. Chicken pox has no sex or racial predilection but is generally experienced to be more severe in males adults compared to female adults and children.

Before the implementation of universal vaccination, about 4 million people a year were infected in the United States. From all cases 11,000 were hospitalized and 50 - 100 resulted in death. Currently, due to the vaccine less than 10 deaths occur per year, most of them in unimmunized people.

According to the statistics for distribution of varicella worldwide 80% of children who are under age of 10 have had the infection; 95% of adults are immune and 25% of adults who have not had varicella are susceptible. Mortality rate for children between 1-14 years is 0.75 per 100,000. For people who are between 15-19 years the rate is 2.75 per 100,000 and for individuals between 30-49 years the mortality rate is 25.2 per 100,000.

Transmission

Varicella is highly contagious and easily transmitted viral infection. VZV can be isolated from the secretions of the upper respiratory tract and also from the fluid secreted by the blisters on the skin. The virus can be transmitted from person to person through the respiratory route by coughing and sneezing or through direct contact by touching the infected skin or contaminated belongings of the person with varicella. The disease can be transmitted to another person even before the infected person get to experience the first symptoms of it. The time range during which Varicella is most easily spread is a few days prior the rash sings appear up to the moment when scabs are formed. Once blisters dry up and get crusted, they cannot spread the infection anymore. The total contagions period is about 10 days.

Signs and Symptoms

 Usually, it takes about two weeks for a person who has been exposed to the infection to develop the signs. The first symptoms include slight fever, headache, feeling tired and weak, and sore throat, which are soon followed by red, itchy skin rash. Small red spots start to appear first on the abdomen or back and face, and then spread to throughout the entire body. The red spots develop into blisters which eventually dry up and form scabs.

Complications of varicella:

Usually, varicella is a mild illness but in some cases it may become a reason for developing the following complications :

• Secondary bacterial infection (def) . It is the most common complication of varicella and is typical occurrence in healthy children. It can manifest as skin diseases impetigo (def), cellulitis (def),and erycipelas (def).
• Viral pneumonia (def), encephalitis (def) and hepatitis (def). They are common in adult population and associated with greater morbidity and mortality.
• Haemorrhagic (def) chicken pox. It is more common in the immunocompromised or immunosuppressed people.
• Gullian-Barre syndrome (def) - more common among adults than children. The incidence rate increases with age.
• Rayes syndrome (def) associated with the use of aspirin and children population.

Factors that increase the risk for severe varicella:

• Neonatal period. The first month of life is risky, especially newborns whose mothers are seronegative (def)
• Neonatal period. Delivery before 28 weeks gestation
• Steroid therapy; high doses for 2 weeks or more, or even short term therapy during or before the incubation period of varicella
• Children with cancer are at high risk ,especially those with leukemia
• Anyone with weakened immune system (people with cancer, HIV (def) or those taking drugs that suppress their immune system)
• Pregnancy- early and late stages of pregnancy
  
  

Prevention and Treatment

The best way of prevention against  varicella infection is maintaining high levels of immunization. Vaccination helps people who already got the vaccine stay protected. It also prevents the spread of the illness and reduces the risk for exposure for those who for some reason were not able to be vaccinated. Varicella vaccine was developed in 1974 by Michiaki Takahashi derived from the Oka strain. Japan and Korea were the first countries that started using the vaccine for chicken pox in 1988. Almost a decade later, in 1995, the vaccine was officially approved in the United States as well.

Two shots of vaccine are recommended for children who are under age of 13. The first shot is given when the child is 12-15 months old and it is usually combined with the MMR vaccine (def). The second shot is recommended at 4-6 years. Two doses are given 4-8 weeks apart to individuals who are 13 or older.

Immunization greatly reduces the risk of children getting infected with varicella but as no vaccine is 100% guaranteed to prevent a disease, it should be kept in mind that children can still get shingles years later when they are adults.

Acyclovir is antiviral drug approved for treatment of varicella. Since healthy children and adults experience mild form of varicella , acyclovir is only recommended in cases of severe and complicated varicella or to (def) patents. Acyclovir treatment is advised, as long as it is started within 24-48 hours from the rash onset.

To prevent further spread of the infection, it is recommended that people who are already infected with chicken pox are kept isolated and limit their contacts with others as much as possible. Keeping good hygiene and avoiding scratching the blisters are other important measures as they help decrease the risk of secondary infection.

Symptoms of chicken pox can be relieved by using pain killers or creams and lotions that help soothe the itchy feeling. To ease the discomfort, an oatmeal bath might help or some people add a little bit of vinegar instead. Calamine lotion containing zinc oxide is commonly used as topical barrier and has excellent safety profile.


Bibliography

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http://www.webmd.com/a-to-z-guides/chickenpox-varicella-topic-overview 
2.Author: Parang N Mehta, MD, Variccela. Jul 31, 2009. Retrieved march 27, 2010 from
http://emedicine.medscape.com/article/969773-overview 
3.Wikipedia, Chicken pox. Retrieved March 27, 2010 from
http://en.wikipedia.org/wiki/Chickenpox 
4.Herpesviruses Slide Set, Varicella Zoster Virus. Retrieved March 27, 2010 from
http://virology-online.com/viruses/VZV.htm 
5. Abelardo J. C. Campos, M.D. ,Varicella Zoster Virus. Retrieved March 27, 2010 from
http://www.hopkinsmedicine.org/heic/ID/vzv/#Treat 
6.New York State, Department of Health,Chickenpox (varicella zoster infection. September 2008.Retrieved  March 27, 2010 from
http://www.health.state.ny.us/diseases/communicable/chickenpox/fact_sheet.htm  
7.KidsHealth/Parents/ Infections>/Skin Infections & Rashes>/Chickenpox. Retrieved March 27, 2010 from http://kidshealth.org/parent/infections/skin/chicken_pox.html