Chickenpox
Chickenpox, also known as varicella, is a highly contagious disease caused by varicella zoster virus, a member of the herpesvirus family. The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab over. It usually starts on the chest, back, and face. It then spreads to the rest of the body. The rash and other symptoms, such as fever, tiredness, and headaches, usually last five to seven days. Complications may occasionally include pneumonia, inflammation of the brain, and bacterial skin infections. The disease is usually more severe in adults than in children.
Chickenpox is an airborne disease which easily spreads via human-to-human transmission, typically through the coughs and sneezes of an infected person. The incubation period is 10–21 days, after which the characteristic rash appears. It may be spread from one to two days before the rash appears until all lesions have crusted over. It may also spread through contact with the blisters. Those with shingles may spread chickenpox to those who are not immune through contact with the blisters. The disease can usually be diagnosed based on the presenting symptom; however, in unusual cases it may be confirmed by polymerase chain reaction testing of the blister fluid or scabs. Testing for antibodies may be done to determine if a person is immune. People usually only get chickenpox once. Although reinfections by the virus occur, these reinfections usually do not cause any symptoms.
Since its introduction in 1995 in the United States, the varicella vaccine has resulted in a decrease in the number of cases and complications from the disease. It protects about 70–90 percent of people from disease with a greater benefit for severe disease. Routine immunization of children is recommended in many countries. Immunization within three days of exposure may improve outcomes in children. Treatment of those infected may include calamine lotion to help with itching, keeping the fingernails short to decrease injury from scratching, and the use of paracetamol to help with fevers. For those at increased risk of complications, antiviral medication such as aciclovir is recommended.
Chickenpox occurs in all parts of the world. In 2013, there were 140 million cases of chickenpox and shingles worldwide. Before routine immunization the number of cases occurring each year was similar to the number of people born. Since immunization the number of infections in the United States has decreased nearly 90%. In 2015 chickenpox resulted in 6,400 deaths globally – down from 8,900 in 1990. Death occurs in about 1 per 60,000 cases. Chickenpox was not separated from smallpox until the late 19th century. In 1888 its connection to shingles was determined. The first documented use of the term chicken pox was in 1658. Various explanations have been suggested for the use of "chicken" in the name, one being the relative mildness of the disease.
Signs and symptoms
The early 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 signals the presence of the disease. Oral manifestations of the disease not uncommonly may precede the external rash. 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 10–12 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 and tonsil areas in the form of small ulcers which can be painful, itchy, or both; this enanthem can precede the exanthem 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 and enanthem by one to two days, the infected person becomes contagious one to two days before recognition of the disease. Contagiousness persists until all vesicular lesions have become dry crusts, which usually entails four or five days, by which time nasal shedding of live virus ceases. The condition usually resolves by itself within a week or two. The rash may, however, last for up to one month.
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 associated with chickenpox in the previous year accounts for nearly one-third of childhood AIS. The most common late complication of chickenpox is shingles, caused by reactivation of the varicella zoster virus decades after the initial, often childhood, chickenpox infection.
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 have severe symptoms. For pregnant women, antibodies produced as a result of immunization or previous infection are transferred via the placenta to the fetus. Varicella infection in pregnant women could lead to spread 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. Effects on the fetus can range in severity from underdeveloped toes and fingers to severe anal and bladder malformation. Possible problems include:- Damage to the 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: skin lesions, hypopigmentation
Pathophysiology
Exposure to VZV in a healthy child initiates the production of host immunoglobulin G, immunoglobulin M, and immunoglobulin A 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, 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.Shingles
After a chickenpox infection, the virus remains dormant in the body's nerve tissues for about 50 years. However, this does not mean that VZV cannot be contracted later in life. The immune system usually keeps the virus at bay, but it can still manifest itself at any given age causing a different form of the viral infection called shingles. Since the efficacy of the human immune system decreases with age, the United States Advisory Committee on Immunization Practices suggests that every adult over the age of 50 years get the herpes zoster vaccine. In England a routine shingles vaccination programme for adults aged 70—80 began in 2013.Shingles affects one in five adults infected with chickenpox as children, especially those who are immune-suppressed, particularly from cancer, HIV, or other conditions. Stress can bring on shingles as well, although scientists are still researching the connection. Adults over the age of 60 who had chickenpox but not shingles are the most prone age demographic.
Diagnosis
The diagnosis of chickenpox is primarily based on the signs and symptoms, with typical early symptoms followed by a characteristic rash. Confirmation of the diagnosis is by 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 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 or previous infection and subsequent immunity.
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 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's developing fetal varicella syndrome.