Chickenpox: Epidemiology, Pathogenesis, Diagnosis, Treatment, and Prevention

Medically reviewed: 15, February 2024

Read Time:17 Minute

Chickenpox: A Review of Epidemiology, Pathogenesis, Diagnosis, Treatment, and Prevention

Chickenpox, caused by the varicella-zoster virus (VZV) in the herpesvirus family, is an extremely contagious infection. While it typically affects children, it can also impact adolescents and adults. The infection presents as a rash that is itchy and filled with fluid-filled blisters.

It is important to note that chickenpox can lead to serious complications, particularly in individuals with weakened immune systems, pregnant women, and newborns.

Fortunately, there is a highly effective method of prevention available: vaccination. Extensive research has shown that vaccination is not only safe but also significantly reduces both the frequency and severity of chickenpox. This article aims to provide a comprehensive overview of chickenpox, covering its epidemiology, pathogenesis, diagnosis, treatment, and prevention. Moreover, it places a strong emphasis on current recommendations and guidelines for clinical practice.

What is Chickenpox (Virus Zoster)?

Chickenpox, also known as varicella, is a common childhood infection that affects millions of people worldwide every year.

Varicella-zoster virus (VZV), a type of DNA virus that falls under the Alphaherpesvirinae subfamily, is the main cause of this condition. This virus is closely related to herpes simplex virus types 1 and 2, as well as cytomegalovirus.

The transmission of VZV occurs through respiratory droplets or direct contact with the skin lesions of infected individuals. After exposure, the incubation period typically lasts between 10 to 21 days, though the average duration is around 14 to 16 days. It is during this time that the virus remains dormant before symptoms begin to manifest.

The contagious period of the disease starts about 1 to 2 days before the rash appears and continues until all the lesions have crusted over, which generally happens within 5 to 10 days.

The primary infection results in chickenpox, which is typically a self-limited illness characterized by fever, malaise, and a generalized, pruritic, vesicular rash. The rash usually appears first on the trunk and face, and then spreads to the extremities, including the scalp, mucous membranes, and genitalia.

The rash evolves through three stages: papules, vesicles, and crusts.

The number and distribution of lesions vary widely, from a few to several hundred. The lesions tend to be more severe and extensive in older children and adults than in young children. The rash is usually accompanied by itching, which can be severe and distressing. The virus can also affect other organs, such as the lungs, liver, brain, and eyes, causing various complications.

Chickenpox commonly leads to additional problems such as bacterial infections in the skin and soft tissues, which are often caused by Staphylococcus aureus or Streptococcus pyogenes. Moreover, there are other complications that can arise from this viral infection, including pneumonia, encephalitis, cerebellar ataxia, hepatitis, nephritis, myocarditis, arthritis, and Reye’s syndrome.

The risk of complications is higher in certain groups of people, such as those with immunodeficiency, chronic diseases, pregnancy, and neonates. The mortality rate of chickenpox is low, ranging from 2 to 4 per 100, 000 cases in developed countries, but can be higher in developing countries and in adults. The virus establishes latency in the sensory nerve ganglia after the primary infection, and can reactivate later in life, causing herpes zoster (shingles), a painful, unilateral, dermatomal rash.

The reactivation can be triggered by various factors, such as aging, stress, immunosuppression, or trauma. The incidence of herpes zoster increases with age, and is estimated to affect 10 to 20% of people who have had chickenpox. The most common complication of herpes zoster is postherpetic neuralgia, a chronic, debilitating pain that persists after the resolution of the rash.

Other complications include ocular involvement, cranial nerve palsies, meningitis, and stroke. The diagnosis of chickenpox is usually based on the clinical presentation and history of exposure. Laboratory tests, such as polymerase chain reaction (PCR), viral culture, or serology, can be used to confirm the diagnosis or to differentiate it from other conditions that cause similar rashes, such as measles, rubella, erythema infectiosum, or drug eruptions.

The treatment of chickenpox is mainly supportive, and includes antipyretics, antihistamines, analgesics, and topical agents to relieve fever, itching, and pain.

Antiviral medications like acyclovir, valacyclovir, and famciclovir have the potential to effectively decrease the length and intensity of symptoms caused by viral infections, and to prevent or treat complications, especially in high-risk groups. Antiviral therapy should be initiated within 24 to 72 hours of rash onset to be effective.

Symptoms of Chickenpox in children and adults

The symptoms of chickenpox usually appear 10 to 21 days after exposure to the varicella-zoster virus (VZV), with an average of 14 to 16 days. The symptoms can be divided into two phases: prodromal and eruptive.

Prodromal phase

The prodromal phase is the period before the rash appears, and may last from a few hours to a few days. During this phase, some people may experience:

  • Fever, which may range from mild to high
  • Headache, which may be severe or throbbing
  • Malaise, which is a general feeling of being unwell or sick
  • Loss of appetite, which may lead to weight loss or dehydration
  • Sore throat, which may cause difficulty swallowing or speaking
  • Cough, which may be dry or productive
  • Abdominal pain, which may be crampy or colicky
  • Joint pain, which may affect the knees, elbows, or wrists
  • Lymphadenopathy, which is the swelling of the lymph nodes, especially in the neck, armpits, or groin

Not everyone with chickenpox will have prodromal symptoms, and some people may have only mild or nonspecific symptoms. The prodromal phase is more common and severe in adults than in children.

Eruptive phase

The eruptive phase, which refers to the time when the rash becomes visible on the skin, typically spans a duration of around 5 to 10 days.

The rash usually starts on the trunk and face, and then spreads to the limbs, including the scalp, palms, soles, and mucous membranes. Skin rash consists of small, red, itchy bumps (papules) that quickly turn into clear, fluid-filled blisters (vesicles) that break and crust over. It progresses in crops, meaning that new lesions appear while old ones are healing. The number and distribution of lesions vary widely, from a few to several hundred. The lesions tend to be more numerous and severe in older children and adults than in young children.

The rash is usually accompanied by intense itching, which can cause scratching and secondary bacterial infections. The rash can also cause pain, burning, or tingling sensations in the affected areas. The rash can affect any part of the body, but some areas may be more prone to complications, such as:

  • The eyes, which may develop conjunctivitis, keratitis, uveitis, or corneal scarring
  • The ears, which may develop otitis media, mastoiditis, or facial nerve palsy
  • The mouth, which may develop gingivostomatitis, pharyngitis, or laryngitis
  • The genitals, which may develop vulvovaginitis, balanitis, or urethritis
  • The anus, which may develop proctitis or anal fissures

The rash usually resolves without scarring, unless there is severe scratching, infection, or inflammation. However, some people may develop hypopigmentation (lightening) or hyperpigmentation (darkening) of the skin in the areas where the lesions were.

Chickenpox Treatment

The treatment of chickenpox is mainly supportive, and aims to relieve the symptoms and prevent the complications of the infection. The treatment may vary depending on the age, health status, and severity of the disease of the affected person. The following are some of the common treatment options for chickenpox:

Home remedies against Chickenpox

Most cases of chickenpox can be managed at home with simple measures, such as:

  • Drinking plenty of fluids to prevent dehydration
  • Taking acetaminophen (Tylenol) to reduce fever and pain.
  • It is highly advised to refrain from administering aspirin or any products containing aspirin to children or teenagers who have chickenpox, as doing so can potentially lead to the development of a severe medical condition referred to as Reye’s syndrome.
  • Applying calamine lotion, oatmeal baths, or cool compresses to soothe the itching and inflammation of the rash
  • Keeping the nails trimmed and wearing gloves or mittens to prevent scratching and skin infections
  • Wearing loose-fitting, cotton clothing to avoid irritation of the skin
  • Avoiding contact with other people, especially those who are at high risk of complications, such as pregnant women, newborns, and immunocompromised individuals, until the rash has crusted over

Antiviral drugs

Antiviral drugs, such as acyclovir (Zovirax), valacyclovir (Valtrex), or famciclovir (Famvir), can be used to reduce the duration and severity of chickenpox, and to prevent or treat complications, especially in high-risk groups. Antiviral drugs work by inhibiting the replication of the varicella-zoster virus (VZV) in the body. They are most effective when started within 24 to 72 hours of the onset of the rash. These drugs are usually given orally, but may also be given intravenously in severe cases or in hospitalized patients.

If you take antiviral drugs, it may have some side effects, such as nausea, vomiting, headache, or rash, and may interact with other medications. Therefore, they should be used under the guidance and prescription of a healthcare provider.

Antibiotics for chickenpox treatment

Antibiotics are used to treat bacterial infections that may occur as a result of chickenpox, such as skin infections, pneumonia, or sepsis. Antibiotics do not work against viral infections, and should not be used to treat chickenpox itself.

Antibiotics are usually given orally, but may also be given intravenously in severe cases or in hospitalized patients. It may have some side effects, such as diarrhea, allergic reactions, or yeast infections, and may interact with other medications. Therefore, they should be used under the guidance and prescription of a healthcare provider.

Immunoglobulin for chickenpox

Immunoglobulin is a preparation of antibodies that can provide passive immunity against VZV. Immunoglobulin can be used for post-exposure prophylaxis, to prevent or modify the disease in people who have been exposed to chickenpox and who are at high risk of complications, such as pregnant women, newborns, and immunocompromised individuals.

Immunoglobulin can also be used for treatment, to reduce the severity and duration of chickenpox, and to prevent or treat complications, especially in immunocompromised individuals. Immunoglobulin is usually given intramuscularly or intravenously, depending on the product and the indication. Immunoglobulin should be given as soon as possible after exposure or onset of symptoms, preferably within 96 hours.

Immunoglobulin may have some side effects, such as pain, swelling, or redness at the injection site, fever, chills, headache, or allergic reactions, and may interfere with the response to live vaccines. Therefore, it should be used under the guidance and prescription of a healthcare provider.

Chickenpox Prevention and Risks

The prevention and risks of chickenpox are related to the exposure, susceptibility, and vaccination status of the individuals and the population. The following are some of the factors that influence the prevention and risks of chickenpox:

Exposure for the chickenpox virus

Exposure to the varicella-zoster virus (VZV) can occur through respiratory droplets or direct contact with skin lesions of infected individuals. The virus can also spread through contaminated objects or surfaces, such as clothing, bedding, or toys. The virus can survive in the environment for several hours, depending on the temperature and humidity. The disease is most contagious from 1 to 2 days before the onset of rash until all the lesions have crusted over, usually within 5 to 10 days. However, some people may be contagious for longer, especially if they have a weakened immune system or if they receive antiviral therapy.

The risk of exposure to VZV can be reduced by:

  • Avoiding contact with people who have chickenpox or herpes zoster, especially if they have active lesions or blisters
  • Covering the mouth and nose when coughing or sneezing, and washing the hands frequently with soap and water or alcohol-based hand sanitizer
  • Cleaning and disinfecting objects and surfaces that may be contaminated with VZV, such as toys, utensils, or furniture
  • Isolating people who have chickenpox or herpes zoster from others, especially from high-risk groups, such as pregnant women, newborns, and immunocompromised individuals, until the rash has crusted over
    Reporting cases of chickenpox or herpes zoster to the local health authorities, and following their recommendations for outbreak control and prevention

Susceptibility

Susceptibility to VZV depends on the immune status and the history of infection or vaccination of the individuals. People who have never had chickenpox or who have not been vaccinated against it are susceptible to VZV, and can develop chickenpox if they are exposed to the virus.

Those who have been vaccinated against it are usually immune to VZV, and are unlikely to develop chickenpox if they are exposed to the virus. However, some people may have a partial or waning immunity to VZV, and may develop a mild or modified form of chickenpox, with fewer or no blisters, and low or no fever. This is more common in people who have been vaccinated than in people who have had natural infection.

The risk of susceptibility to VZV can be reduced by:

  • Vaccination against chickenpox, which can provide long-lasting immunity to VZV and prevent or reduce the severity of the disease
  • Getting a booster dose of chickenpox vaccine, if recommended by a healthcare provider, to boost the immunity against VZV and prevent breakthrough infections
  • Getting tested for immunity to VZV, if unsure of the history of infection or vaccination, and getting vaccinated if not immune
  • Getting vaccinated against herpes zoster, which can prevent or reduce the severity of herpes zoster and its complications, and may also boost the immunity against VZV

Vaccination against chickenpox

The prevention of chickenpox is achieved through vaccination, which has been shown to be safe and effective in reducing the incidence and severity of the disease.

The chickenpox vaccine is a live, attenuated strain of VZV, which induces both humoral and cellular immunity. The vaccine is recommended for all children aged 12 to 15 months, with a second dose at 4 to 6 years of age. The vaccine is also recommended for adolescents and adults who have not had chickenpox or who are not immune to VZV, with two doses given 4 to 8 weeks apart.

The vaccine can also be used for post-exposure prophylaxis, if given within 3 to 5 days of exposure, to prevent or modify the disease. The vaccine has been shown to be 70 to 90% effective in preventing chickenpox, and 95 to 100% effective in preventing severe disease. The vaccine has also reduced the incidence of herpes zoster and its complications, by preventing the primary infection or boosting the immunity against VZV.

The vaccine is generally well tolerated, with mild and transient adverse effects, such as injection site reactions, fever, and rash. Serious adverse events, such as anaphylaxis, encephalitis, or disseminated infection, are rare. The vaccine does not contain thimerosal, a mercury-containing preservative, and does not cause autism or other neurodevelopmental disorders. The vaccine is contraindicated in people who have a history of severe allergic reaction to any component of the vaccine, who are pregnant or planning to become pregnant, who have a severe immunodeficiency, or who have recently received blood products or immunoglobulin.

The vaccine should be used with caution in people who have a moderate immunodeficiency, who have a history of thrombocytopenia, or who are taking salicylates or antiviral drugs.

It does not interfere with the routine childhood immunization schedule, and can be given simultaneously or at any interval with other vaccines. It also does not affect the results of tuberculin skin testing, and can be given before or after the test.

The vaccine does not protect against other herpesviruses, such as herpes simplex virus or cytomegalovirus, and does not affect the risk of acquiring or transmitting these infections.

It does not prevent the reactivation of latent VZV, and does not treat or prevent herpes zoster.

However, there is a separate vaccine for herpes zoster, which is recommended for people aged 50 years and older, regardless of their history of chickenpox or herpes zoster. The herpes zoster vaccine is a higher dose of the same strain of VZV used in the chickenpox vaccine, and is given as a single dose.

The herpes zoster vaccine has been shown to reduce the incidence of herpes zoster by 50 to 70%, and the incidence of postherpetic neuralgia by 60 to 70%. The herpes zoster vaccine is also generally well tolerated, with similar adverse effects as the chickenpox vaccine. It is contraindicated in the same groups of people as the chickenpox vaccine, and should not be given to people who have active herpes zoster or who are receiving antiviral therapy. Such vaccine can be given at the same time or at any interval with other vaccines, except for the chickenpox vaccine, which should be given at least 4 weeks apart. The herpes zoster vaccine does not affect the results of tuberculin skin testing, and can be given before or after the test.

Chickenpox is a common and usually benign infection, but it can cause serious complications and mortality in some groups of people. Here are some things to consider about vaccination:

  • The availability of a safe and effective vaccine has greatly reduced the burden of the disease and its sequelae. The vaccination of children, adolescents, and adults who are susceptible to VZV is recommended as a public health measure to prevent chickenpox and its complications.
  • The vaccination of older adults who are at risk of herpes zoster is also recommended to prevent this painful and debilitating condition and its complications.
  • Chickenpox vaccination of pregnant women who are not immune to VZV is not recommended, but they should avoid exposure to people with chickenpox or herpes zoster, and seek medical attention if they develop symptoms.
  • The vaccination of people with immunodeficiency or other contraindications should be done under the guidance of a specialist, and they should be monitored closely for adverse events.
  • Vaccination of those who have had chickenpox or herpes zoster is not necessary, but it is not harmful, and may boost their immunity against VZV.
  • Vaccination of people who are unsure of their immunity status can be done after serological testing or without testing, depending on the clinical situation and the availability of resources.
  • The vaccination of people who have been exposed to VZV can be done as post-exposure prophylaxis, if given within a certain time frame, to prevent or modify the disease.
  • The vaccination of people who have active chickenpox or herpes zoster is not indicated, and should be deferred until the resolution of the infection.

Vaccination serves as the utmost efficient method in shielding individuals against chickenpox and its potential complications. The chickenpox vaccine, formulated with a weakened strain of the varicella-zoster virus (VZV), prompts the development of both humoral and cellular immune responses.

It is strongly advised for all children between the ages of 12 and 15 months to receive the initial dose, followed by a second administration between the ages of 4 and 6 years.

The vaccine is also recommended for adolescents and adults who have not had chickenpox or who are not immune to VZV, with two doses given 4 to 8 weeks apart. The vaccine can also be used for post-exposure prophylaxis, if given within 3 to 5 days of exposure, to prevent or modify the disease.

The benefits of vaccination include:

  1. Reducing the incidence and severity of chickenpox and its complications, especially in high-risk groups, such as pregnant women, newborns, and immunocompromised individuals
  2. Reducing the transmission and spread of VZV in the population, and achieving herd immunity
  3. Reducing the incidence and severity of herpes zoster and its complications, by preventing the primary infection or boosting the immunity against VZV
  4. Reducing the economic and social burden of chickenpox and herpes zoster, by saving healthcare costs and productivity losses

The risks of vaccination against chickenpox:

  • Mild and transient adverse effects, such as injection site reactions, fever, and rash, which occur in 10 to 20% of vaccine recipients
  • Serious adverse events, such as anaphylaxis, encephalitis, or disseminated infection, which occur in less than 1 in 1 million vaccine recipients
  • Breakthrough infections, which occur in 1 to 4% of vaccine recipients, and are usually mild or asymptomatic, but may be contagious
  • Interference with the response to live vaccines, such as measles, mumps, rubella, or yellow fever, which should be given at least 4 weeks before or after the chickenpox vaccine
  • Interference with the results of tuberculin skin testing, which should be done before or at the same time as the chickenpox vaccine, or 4 to 6 weeks after the vaccine

The contraindications of vaccination include:

  • History of severe allergic reaction to any component of the vaccine, such as gelatin or neomycin
    Pregnancy or planning to become pregnant within 1 month of vaccination
  • Severe immunodeficiency, such as HIV/AIDS, cancer, transplant, chemotherapy, immunosuppressive medications, or long-term use of steroids
  • Recent receipt of blood products or immunoglobulin, which may interfere with the immune response to the vaccine

The precautions of vaccination include:

  • Moderate immunodeficiency, such as chronic diseases, malnutrition, or age
  • History of thrombocytopenia, which may increase the risk of bleeding
  • Use of salicylates or antiviral drugs, which may reduce the effectiveness of the vaccine.

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