Chickenpox overview
Michael Maddaleni, B.S.
Aravind Reddy Kothagadi M.B.B.S

# Overview
Chickenpox is the common name for varicella zoster, and it is classically one of the childhood infectious diseases caught by and survived by almost every child. It is one of the most contagious infectious diseases. The affected child or adult may develop hundreds of itchy, fluid-filled blisters that burst and form crusts. Chickenpox is caused by varicella-zoster virus, a member of the herpes virus family. The same virus also causes shingles (herpes zoster) in adults. There is no racial or sexual predilection for chickenpox. Only symptomatic treatment is advised for chickenpox except in immunocompromised patients.

# Historical Perspective
Chickenpox was first described by Razi, an Iranian physician. In the mid-1500s, Giovanni Filippo described it in more detail. In 1767, William Heberden from England, differentiated chickenpox from smallpox. The live attenuated vaccine for chickenpox was introduced in 1974.

# Classification
There is no established classification system for chickenpox.

# Pathophysiology
Chickenpox is a highly contagious disease contracted by the inhalation of aerosolized nasopharyngeal secretions droplets or through direct contact with the vesicles from an infected host. It takes from 10 to 21 days after exposure to a person with chickenpox or shingles for someone to develop chickenpox. Viral proliferation occurs in regional lymph nodes of the upper respiratory tract leading to viremia. Viremia is characterized by diffuse viral invasion of capillary endothelial cells and the epidermis. VZV infection of cells of the malpighian layer produces both intercellular and intracellular edema, resulting in the characteristic vesicles.

# Causes
Chickenpox is caused by the varicella-zoster virus, also known as human herpes virus 3 (HHV-3), one of the eight herpes viruses known to affect humans. Transmission of the disease from an infected individual occurs by droplet transmission of nasopharyngeal secretions and contact with vesicle fluid from the skin lesions.

# Differentiating Chickenpox from other Diseases
Different rash-like conditions can be confused with chickenpox and are thus included in its differential diagnosis. There are many active considerations that need to be ruled out to diagnose chickenpox. The one exception to this is Smallpox.

# Epidemiology and Demographics
Chickenpox is an endemic disease spread mainly by the respiratory route. Cases are observed all through the year but mostly in the winter and early spring. In tropical regions, cases of varicella infection have been reported to be more common among adults than children.

# Risk Factors
Risk factors which increase the likelihood of contracting chickenpox are people without a history of chickenpox in the past, individuals who are not immunized against chickenpox, newborns, especially those born prematurely, less than 1 month or born to mothers who never contracted chickenpox prior to pregnancy, immunocompromised individuals, cancer patients and the use of immunosuppressant drugs.

# Screening
According to Center for Disease Control and Prevention (CDC), there is insufficient evidence to recommend routine screening among general population. Children are vaccinatedagainst chickenpox and most adults generally may have been infected with VZV in their early years. Screening is recommended for specific populations which include, healthcare workers, pregnant women, newborns, HIV/AIDS patients and for people prior to organ transplantation.

# Natural History, Complications and Prognosis
If left untreated, skin irritation from repeatedly scratching chickenpox sores allows the bacteria to invade the skin resulting in cellulitis. In some cases, varicella infection can spread to the lungs causing pneumonia and can be proven fatal. The disease is usually mild, although serious complications sometimes occur. Two of the most common complications are bacterial infections of the skin and soft tissues in children and pneumonia in adults. Primary varicella is a common childhood disease in the western countries. Anyone who has recovered from chickenpox may develop shingles; even children can get shingles. Chickenpox is rarely fatal (usually from varicella pneumonia), with pregnant women and those with a suppressed immune systems being more at risk. Pregnant women not known to be immune and who come into contact with chickenpox may need urgent treatment as the virus can cause serious problems for the baby. This is less of an issue after 20 weeks.

# Diagnosis

## History and Symptoms
Patient with chickenpox presents with the characteristic rash and numerous spread out of lesions. Symptoms usually start as low-grade fever and skin manifestations appear by 1-2 days. Rash initially appears on the head, trunk and then spreads to the rest of the body with intense pruritus, headache, malaise, anorexia, cough, coryza, tiredness and loss of appetite.

## Physical Examination
The diagnosis of varicella is primarily made by clinical findings. In a non-immunized individual with the appropriate appearing rash occurring in "crops", no further investigation would normally be undertaken. For further investigation, examination of the fluid within the vesicles, or by testing blood for evidence of an acute immunologic response. Vesicle fluid can be examined with a tzanck smear, or better with examination for the direct fluorescent antibody. The fluid can also be "cultured", whereby attempts are made to grow the virus from a fluid sample. Blood tests can be used to identify a response to acute infection (IgM) or previous infection and subsequent immunity (IgG). Prenatal diagnosis of fetal varicella infection can be performed using ultrasound, though a delay of 5 weeks following primary maternal infection is advised. A PCR (DNA) test of the mother's amniotic fluid can also be performed, though the risk of spontaneous abortion due to the amniocentesis procedure is higher than the risk of the baby developing fetal varicella syndrome.

## Laboratory Findings
Diagnosis of chickenpox is usually based upon signs and symptoms of the affected individual. Laboratory tests are not routinely used to diagnose active cases of chickenpox and shingles, which are caused by the varicella zoster virus (VZV). Children are nowadays vaccinated and most adults generally may have been infected with VZV in their early years. Hence, general population screening is not done usually. Anyhow, testing for VZV or for the antibodies produced in response to VZV infection may be performed in when required for screening purposes. Also, screening may be advised for newborns, pregnant women, prior to organ transplantation, and in those with HIV/AIDS. Testing may be used to determine if someone has been previously exposed to varicella zoster virus either through past infection or had received vaccination and has developed immunity to the disease.

## Chest X Ray
Pneumonia, as a complication of chickenpox, rarely occurs in children, but occurs in about one-fifth of adults. Chest x-ray shows cloudiness throughout the lungs, caused by acute pneumonia following chickenpox.

## CT scan
CT Scan has a minimal diagnostic value in diagnosing chickenpox unless complications arise such as in varicella pneumonia.

## MRI
There are no MRI findings associated with chickenpox.

## Ultrasound
There are no ultrasound findings associated with chickenpox.

## Other Imaging Findings
There are no other specific imaging findings for chickenpox.

## Other Diagnostic Studies
There are no additional diagnostic findings for chickenpox.

# Treatment

## Medical Therapy
Chickenpox usually doesn't require any medical therapy in otherwise healthy individuals. Only symptomatic treatment is usually prescribed to ease the discomfort. The complexity of the therapy grows when many risk factors are involved.

## Surgery
Surgical intervention is not recommended for the management of chickenpox.

## Primary Prevention
Vaccination is recommended for children as well as adults who haven't been vaccinated previously to prevent chickenpox. Two doses of varicella vaccine are recommended for children who never have contracted chickenpox at the following intervals. The first dose is recommended between 12-15 months of age. The second dose is recommended around 4-6 years of age and also it may be given earlier if the gap between the doses is at least three months from the first dose. In adults, a vaccine is recommended for people who are 13 years of age or older. There should be a gap of at least 28 days between the two doses.

## Secondary Prevention
There are several things that can be done at home to help relieve the symptoms and prevent skin infections. Calamine lotion and colloidal oatmeal baths may help relieve some of the itching. Keeping fingernails trimmed short may help prevent skin infections caused by scratching blisters.