| Chickenpox | |
|---|---|
| Classification and external resources | |
Child with varicella disease |
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| ICD-10 | B01 |
| ICD-9 | 052 |
| DiseasesDB | 29118 |
| MedlinePlus | 001592 |
| eMedicine | ped/2385 derm/74, emerg/367 |
| MeSH | C02.256.466.175 |
Chickenpox or chicken pox is a highly contagious illness caused by primary infection with varicella zoster virus (VZV).[1] It usually starts with vesicular skin rash mainly on the body and head rather than at the periphery and becomes itchy, raw pockmarks, which mostly heal without scarring. On examination, the observer typically finds lesions at various stages of healing.
Chickenpox is an airborne disease spread easily through coughing or sneezing of 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.[2] They remain contagious until all lesions have crusted over (this takes approximately six days)[3]. Immunocompromised patients are contagious during the entire period as new lesions keep appearing. Crusted lesions are not contagious.[4]
It takes from 10 to 21 days after initial infection for the disease to develop.
The onset of illness with chickenpox is often characterized by symptoms including myalgia, itching, nausea, fever, headache, sore throat, pain in both ears, complaints of pressure in head or swollen face, and malaise in adolescents and adults. In children, the first symptom is usually the development of a papular rash, followed by development of malaise, fever (a body temperature of 38 °C (100 °F), but may be as high as 42 °C (108 °F) in rare cases), sometimes severe back pains to the lower back, and anorexia (loss of appetite, not to be confused with anorexia nervosa). Typically, the disease is more severe in adults.[5] Chickenpox is rarely fatal, although it is generally more severe in adult males than in adult females or children. Non-immune pregnant women and those with a suppressed immune system are at highest risk of serious complications. Chickenpox is believed to be the cause of one third of stroke cases in children.[6] The most common late complication of chickenpox is shingles, caused by reactivation of the varicella zoster virus decades after the initial episode of chickenpox.
Chickenpox has been observed in other primates, including chimpanzees[7] and gorillas.[8]
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The diagnosis of varicella is primarily clinical, with typical early "prodromal" symptoms, and then the characteristic rash. 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 Tsanck smear, or better with examination 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).[9]
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.[10]
Primary varicella is a disease that is endemic to all countries worldwide. Varicella has a prevalence that is stable from generation to generation.[11]
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 4–10 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 but 10% of young adults remain susceptible.
In the tropics, chickenpox often occurs in older people and may cause more serious disease.[12] In adults the pock marks are darker and the scars more prominent than in children.[13]
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.
For pregnant women, antibodies produced as a result of immunization or previous infection are transferred via the placenta to the fetus.[14] 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.[15]
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).[16] Effects on the fetus can range in severity from underdeveloped toes and fingers to severe anal and bladder malformation. Possible problems include:
Infection late in gestation or immediately following birth is referred to as "neonatal varicella".[18] 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.[10]
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).[19]
Many adults who have had chicken pox as children are susceptible to shingles as adults, often with the accompanying condition postherpetic neuralgia, a painful condition that make it difficult to sleep. Even after the shingles rash has gone away, there can be night pain in the area affected by the rash.[20]
Shingles affect one in three adults, 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. [21]
A shingles vaccine is available for adults over 50 for both adults who had childhood chickenpox or who previously had shingles. [22] The vaccine for shingles lessens the impact of shingles and its side effects.
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.[23] The chickenpox virus (VZV) is susceptible to disinfectants, notably chlorine bleach (i.e., sodium hypochlorite). Also, like all enveloped viruses, VZV is sensitive to desiccation, heat and detergents. Therefore these viruses are relatively easy to kill.
A varicella vaccine was first developed by Michiaki Takahashi in 1974 derived from the Oka strain. It has been available in the U.S. 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,[24] which is currently part of the routine immunization schedule in the US.[25] 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 person who already took the vaccine is more likely to have only a few chickenpox.[26]
Varicella 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 clears the virus from 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.[27] 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.[28] Also, staying in a cold surrounding can help in easing the itching as heat and sweat makes it worse.
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.[29] It is important to maintain good hygiene and daily cleaning of skin with warm water to avoid secondary bacterial infection.[30] Scratching may also increase the risk of secondary infection.[31]
To relieve the symptoms of chickenpox, people commonly use anti-itching creams and lotions. These lotions are not to be used on the face or close to the eyes. Neem leaves can be made into paste form and can be applied on the rashes. Warm water bath with neem leaves may be helpful. Water bath may be done at least seven days from the onset of the vesicles. It should be done so because the vesicles contains the virus and may splash while bathing and it may cause the vesicles to appear on subsequent regions. An oatmeal bath also might help ease discomfort.[32]
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 if they are not suffering from another medical condition which would put them at risk of developing complications.[33]
Treatment of chickenpox in children is aimed at symptoms whilst 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 deep scratch their blisters.[34]
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.[35]
Some parents believe that it is better for children to contact chickenpox than get the vaccine. They even go the extent of exposing their children to others who have the disease – even by taking them to “chicken pox parties.” Doctors counter that children are safer getting the vaccine, which is weakened form of the virus, than by getting the disease, which can be fatal.[36]
Infection in otherwise healthy adults tends to be more severe and may be fatal. Treatment with antiviral drugs (e.g. acyclovir or valacyclovir) is generally advised, as long as it is started within 24–48 hours from rash onset.[33] 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 itch and may be used in cases where the itch 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.[37]
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.[38]
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.[39] 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.[40]
In adults, the disease is more severe,[41] though the incidence is much less common. Infection in adults is associated with greater morbidity and mortality due to pneumonia,[42] 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.[10] Inflammation of the brain, or encephalitis, can occur in immunocompromised individuals, although the risk is higher with herpes zoster.[43] Necrotizing fasciitis is also a rare complication.[44]
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 immunosuppressive therapies.[45] Varicella is a particular problem in hospitals, especially when there are patients with immune systems weakened by drugs (e.g., high-dose steroids) or HIV.[46]
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.[47]
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 etiology of these hemorrhagic chickenpox syndromes is not known.[47]
Chickenpox was first identified by the Persian scientist Muhammad ibn Zakariya ar-Razi (865–925), known to the West as "Rhazes", who clearly distinguished it from smallpox and measles.[48] Giovanni Filippo (1510–1580) of Palermo later provided a more detailed description of varicella (chickenpox).
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