Chickenpox is a highly contagious disease caused by primary infection with varicella zoster virus (VZV). It usually starts with a vesicular skin rash mainly on the body and head rather than on the limbs. The rash develops into itchy, raw pockmarks, which mostly heal without scarring. On examination, the observer typically finds skin lesions at various stages of healing, and ulcers in the oral cavity and tonsil areas. The disease is most commonly observed in children.
Chickenpox is an airborne disease which spreads easily through coughing or sneezing by ill individuals or through direct contact with secretions from the rash. A person with chickenpox is infectious one to two days before the rash appears. They remain contagious until all lesions have crusted over (this takes approximately six days). Immunocompromised patients are contagious during the entire period as new lesions keep appearing. Crusted lesions are not contagious.
Chickenpox has been observed in other primates, including chimpanzees and gorillas.
The origin of the term chicken pox, which is recorded as being used since 1684, is not reliably known. It has been said to be derived from chickpeas, based on resemblance of the vesicles to chickpeas, or to come from the rash resembling chicken pecks. Other suggestions include the designation chicken for a child (i.e., literally 'child pox'), a corruption of itching-pox, or the idea that the disease may have originated in chickens. Samuel Johnson explained the designation as "from its being of no very great danger."
Signs and symptoms
The early (prodromal) symptoms in adolescents and adults are nausea, loss of appetite, aching muscles, and headache. This is followed by the characteristic rash or oral sores, malaise, and a low-grade fever that signal the presence of the disease. Oral manifestations of the disease (enanthem) not uncommonly may precede the external rash (exanthem). In children the illness is not usually preceded by prodromal symptoms, and the first sign is the rash or the spots in the oral cavity. The rash begins as small red dots on the face, scalp, torso, upper arms and legs; progressing over 10â€"12 hours to small bumps, blisters and pustules; followed by umbilication and the formation of scabs.
At the blister stage, intense itching is usually present. Blisters may also occur on the palms, soles, and genital area. Commonly, visible evidence of the disease develops in the oral cavity & tonsil areas in the form of small ulcers which can be painful or itchy or both; this enanthem (internal rash) can precede the exanthem (external rash) by 1 to 3 days or can be concurrent. These symptoms of chickenpox appear 10 to 21 days after exposure to a contagious person. Adults may have a more widespread rash and longer fever, and they are more likely to experience complications, such as varicella pneumonia.
Because watery nasal discharge containing live virus usually precedes both exanthem (external rash) and enanthem (oral ulcers) by 1 to 2 days, the infected person actually becomes contagious one to two days prior to recognition of the disease. Contagiousness persists until all vesicular lesions have become dry crusts (scabs), which usually entails four or five days, by which time nasal shedding of live virus also ceases.
Chickenpox is rarely fatal, although it is generally more severe in adult men than in women or children. Non-immune pregnant women and those with a suppressed immune system are at highest risk of serious complications. Arterial ischemic stroke (AIS) associated with chickenpox in the previous year accounts for nearly one third of childhood AIS. The most common late complication of chickenpox is shingles (herpes zoster), caused by reactivation of the varicella zoster virus decades after the initial, often childhood, chickenpox infection.
Diagnosis
The diagnosis of varicella is primarily clinical, with typical early "prodromal" symptoms, and then the characteristic rash and oral-cavity sores. Confirmation of the diagnosis can be sought through either examination of the fluid within the vesicles of the rash, or by testing blood for evidence of an acute immunologic response.
Vesicular fluid can be examined with a Tzanck smear, or better by testing for 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.
Pathophysiology
Exposure to VZV in a healthy child initiates the production of host immunoglobulin G (IgG), immunoglobulin M (IgM), and immunoglobulin A (IgA) antibodies; IgG antibodies persist for life and confer immunity. Cell-mediated immune responses are also important in limiting the scope and the duration of primary varicella infection. After primary infection, VZV is hypothesized to spread from mucosal and epidermal lesions to local sensory nerves. VZV then remains latent in the dorsal ganglion cells of the sensory nerves. Reactivation of VZV results in the clinically distinct syndrome of herpes zoster (i.e., shingles), postherpetic neuralgia, and sometimes Ramsay Hunt syndrome type II. Varicella zoster can affect the arteries in the neck and head, producing stroke, either during childhood, or after a latency period of many years.
Pregnancy and neonates
During pregnancy the dangers to the fetus associated with a primary VZV infection are greater in the first six months. In the third trimester, the mother is more likely to suffer from the adverse effects of the infection. For pregnant women, antibodies produced as a result of immunization or previous infection are transferred via the placenta to the fetus. Women who are immune to chickenpox cannot become infected and do not need to be concerned about it for themselves or their infant during pregnancy.
Varicella infection in pregnant women could lead to viral transmission via the placenta and infection of the fetus. If infection occurs during the first 28 weeks of gestation, this can lead to fetal varicella syndrome (also known as congenital varicella syndrome). Effects on the fetus can range in severity from underdeveloped toes and fingers to severe anal and bladder malformation. Possible problems include:
- Damage to brain: encephalitis, microcephaly, hydrocephaly, aplasia of brain
- Damage to the eye: optic stalk, optic cup, and lens vesicles, microphthalmia, cataracts, chorioretinitis, optic atrophy
- Other neurological disorder: damage to cervical and lumbosacral spinal cord, motor/sensory deficits, absent deep tendon reflexes, anisocoria/Horner's syndrome
- Damage to body: hypoplasia of upper/lower extremities, anal and bladder sphincter dysfunction
- Skin disorders: (cicatricial) skin lesions, hypopigmentation
Infection late in gestation or immediately following birth is referred to as "neonatal varicella". Maternal infection is associated with premature delivery. The risk of the baby developing the disease is greatest following exposure to infection in the period 7 days prior to delivery and up to 7 days following the birth. The baby may also be exposed to the virus via infectious siblings or other contacts, but this is of less concern if the mother is immune. Newborns who develop symptoms are at a high risk of pneumonia and other serious complications of the disease.
Shingles
After a chickenpox infection, the virus remains dormant in the body's nerve tissues. The immune system keeps the virus at bay, but later in life, usually as an adult, it can be reactivated and cause a different form of the viral infection called shingles (scientifically known as herpes zoster). The United States Advisory Committee on Immunization Practices (ACIP) suggests that any adult over the age of 60 years gets the herpes zoster vaccine as a part of their normal medical check ups.
Many adults who have had chickenpox as children are susceptible to shingles as adults, often with the accompanying condition postherpetic neuralgia, a painful condition that makes it difficult to sleep. Even after the shingles rash has gone away, there can be night pain in the area affected by the rash.
Shingles affects one in five adults infected with chickenpox as children, especially those who are immune suppressed, particularly from cancer, HIV, or other conditions. However, stress can bring on shingles as well, although scientists are still researching the connection.
Shingles are most commonly found in adults over the age of 60 who were diagnosed with chickenpox when they were under the age of 1.
A shingles vaccine is available for adults over 50 who have had childhood chickenpox or who have previously had shingles.
Prevention
Hygiene measures
The spread of chickenpox can be prevented by isolating affected individuals. Contagion is by exposure to respiratory droplets, or direct contact with lesions, within a period lasting from three days prior to the onset of the rash, to four days after the onset of the rash. The chickenpox virus is susceptible to disinfectants, notably chlorine bleach (i.e., sodium hypochlorite). Also, like all enveloped viruses, it is sensitive to desiccation, heat and detergents.
Vaccine
A varicella vaccine was first developed by Michiaki Takahashi in 1974 derived from the Oka strain. It has been available in the US since 1995 to inoculate against the disease. Some countries require the varicella vaccination or an exemption before entering elementary school. Protection from one dose is not lifelong and a second dose is necessary five years after the initial immunization, which is currently part of the routine immunization schedule in the US. The chickenpox vaccine is not part of the routine childhood vaccination schedule in the UK. In the UK, the vaccine is currently only offered to people who are particularly vulnerable to chickenpox. A vaccinated person is likely to have a milder case of chickenpox if infected.
Treatment
Treatment mainly consists of easing the symptoms as there is no actual cure of the condition. Some treatments are however available for relieving the symptoms while the immune system suppresses the virus in the body. As a protective measure, patients are usually required to stay at home while they are infectious to avoid spreading the disease to others. Also, sufferers are frequently asked to cut their nails short or to wear gloves to prevent scratching and to minimize the risk of secondary infections.
The condition resolves by itself within a couple of weeks but meanwhile patients must pay attention to their personal hygiene. The rash caused by varicella zoster virus may however last for up to one month, although the infectious stage does not take longer than a week or two.
Although there have been no formal clinical studies evaluating the effectiveness of topical application of calamine lotion, a topical barrier preparation containing zinc oxide and one of the most commonly used interventions, it has an excellent safety profile. It is important to maintain good hygiene and daily cleaning of skin with warm water to avoid secondary bacterial infection. Scratching may also increase the risk of secondary infection.
Acetaminophen (paracetamol) but not aspirin may be used to reduce fever. Aspirin use by someone with chickenpox may cause the serious, sometimes fatal disease of the liver and brain, Reye syndrome. People at risk of developing severe complications who have had significant exposure to the virus may be given intra-muscular varicella zoster immune globulin (VZIG), a preparation containing high titres of antibodies to varicella zoster virus, to ward off the disease.
Antivirals are sometimes used.
Children
If oral acyclovir is started within 24 hours of rash onset it decreases symptoms by one day but has no effect on complication rates. Use of acyclovir therefore is not currently recommended for immunocompetent individuals (i.e., otherwise healthy persons without known immunodeficiency or on immunosuppressive medication). Children younger than 12 years old and older than one month are not meant to receive antiviral medication unless they are suffering from another medical condition which would put them at risk of developing complications.
Treatment of chickenpox in children is aimed at symptoms while the immune system deals with the virus. With children younger than 12 years cutting nails and keeping them clean is an important part of treatment as they are more likely to scratch their blisters more deeply than adults.
Aspirin is highly contraindicated in children younger than 16 years as it has been related with a potentially fatal condition known as Reye's syndrome.
Some parents believe that it is better for children to contract chickenpox than to get the vaccine, and they deliberately expose their children to the virus, sometimes by taking them to "chickenpox parties." Some doctors counter that children are safer getting the vaccine, which is a weakened form of the virus, than getting the disease, which can be fatal.
Adults
Infection in otherwise healthy adults tends to be more severe. Treatment with antiviral drugs (e.g. acyclovir or valacyclovir) is generally advised, as long as it is started within 24â€"48 hours from rash onset. Remedies to ease the symptoms of chickenpox in adults are basically the same as those used on children. Adults are more often prescribed antiviral medication as it is effective in reducing the severity of the condition and the likelihood of developing complications. Antiviral medicines do not kill the virus, but stop it from multiplying. Adults are also advised to increase water intake to reduce dehydration and to relieve headaches. Painkillers such as paracetamol (acetaminophen) are also recommended as they are effective in relieving itching and other symptoms such as fever or pains. Antihistamines relieve itches and may be used in cases where the itches prevents sleep, because they are also sedative. As with children, antiviral medication is considered more useful for those adults who are more prone to develop complications. These include pregnant women or people who have a weakened immune system.
Sorivudine, a nucleoside analogue has been reported to be effective in the treatment of primary varicella in healthy adults (case reports only), but large-scale clinical trials are still needed to demonstrate its efficacy.
After recovering from chickenpox, it is recommended by doctors that adults take one injection of VZV immune globulin and one injection of varicella vaccine or herpes zoster vaccine.
Prognosis
The duration of the visible blistering caused by varicella zoster virus varies in children usually from 4 to 7 days, and the appearance of new blisters begins to subside after the 5th day. Chickenpox infection is milder in young children, and symptomatic treatment, with sodium bicarbonate baths or antihistamine medication may ease itching, it is recommended to keep new infants from birth up to age 6 months away from an infected person for 10 to 21 days as their immune systems are not developed enough to handle the stress it can bring on. Paracetamol (acetaminophen) is widely used to reduce fever. Aspirin, or products containing aspirin, should not be given to children with chickenpox as it can cause Reye's Syndrome.
In adults, the disease is more severe, though the incidence is much less common. Infection in adults is associated with greater morbidity and mortality due to pneumonia (either direct viral pneumonia or secondary bacterial pneumonia), bronchitis (either viral bronchitis or secondary bacterial bronchitis), hepatitis, and encephalitis. In particular, up to 10% of pregnant women with chickenpox develop pneumonia, the severity of which increases with onset later in gestation. In England and Wales, 75% of deaths due to chickenpox are in adults. Inflammation of the brain, or encephalitis, can occur in immunocompromised individuals, although the risk is higher with herpes zoster. Necrotizing fasciitis is also a rare complication.
Varicella can be lethal to adults with impaired immunity. The number of people in this high-risk group has increased, due to the HIV epidemic and the increased use of immunosuppressive therapies. Varicella is a particular problem in hospitals, when there are patients with immune systems weakened by drugs (e.g., high-dose steroids) or HIV.
Secondary bacterial infection of skin lesions, manifesting as impetigo, cellulitis, and erysipelas, is the most common complication in healthy children. Disseminated primary varicella infection usually seen in the immunocompromised may have high morbidity. Ninety percent of cases of varicella pneumonia occur in the adult population. Rarer complications of disseminated chickenpox also include myocarditis, hepatitis, and glomerulonephritis.
Hemorrhagic complications are more common in the immunocompromised or immunosuppressed populations, although healthy children and adults have been affected. Five major clinical syndromes have been described: febrile purpura, malignant chickenpox with purpura, postinfectious purpura, purpura fulminans, and anaphylactoid purpura. These syndromes have variable courses, with febrile purpura being the most benign of the syndromes and having an uncomplicated outcome. In contrast, malignant chickenpox with purpura is a grave clinical condition that has a mortality rate of greater than 70%. The cause of these hemorrhagic chickenpox syndromes is not known.
Epidemiology
Primary varicella occurs in all countries worldwide. Varicella has a prevalence that is stable from generation to generation. As of 2010 it caused about 6,800 deaths, down from 11,200 in 1990.
In temperate countries, chickenpox is primarily a disease of children, with most cases occurring during the winter and spring, most likely due to school contact. It is one of the classic diseases of childhood, with the highest prevalence in the 4â€"10 year old age group. Like rubella, it is uncommon in preschool children. Varicella is highly communicable, with an infection rate of 90% in close contacts. In temperate countries, most people become infected before adulthood, and 10% of young adults remain susceptible.
In the tropics, chickenpox often occurs in older people and may cause more serious disease. In adults the pock marks are darker and the scars more prominent than in children.
In the United States, the Centers for Disease Control and Prevention (CDC) does not require state health departments to report infections of chicken pox, and only 31 states currently volunteer this information. However, in a 2013 study conducted by the social media disease surveillance tool called Sickweather, anecdotal reports of chickenpox infections on Facebook and Twitter were used to measure and rank states with the most infections per capita, with Maryland, Tennessee and Illinois in the top 3.