Understanding the Varicella-Zoster Virus (VZV)
Have you ever wondered what causes that common childhood illness known as chickenpox? Or perhaps you're curious about shingles, a condition that can cause much discomfort in adults?
If you nodded or thought 'yes', you're in for an informative read. 
Today, we're going to delve into a specific virus called the Varicella-Zoster Virus (VZV).
What is Varicella-Zoster Virus (VZV)?
The Varicella-Zoster Virus (VZV) is an alpha herpes virus that only infects humans1. It's part of the larger α-herpesvirus family1. So what does this virus do? Let's find out.
Varicella-Zoster Virus (VZV) and Diseases it Causes
Chickenpox (Varicella)
The VZV virus is responsible for causing chickenpox, a frequent and highly contagious disease, particularly in childhood2. It's characterised by a maculopapular, vesicular rash that can be pruritic and transforms into dried crusts (scabs) over a 3- to 7-day period2.
Shingles (Herpes Zoster)
VZV doesn't disappear after causing chickenpox. Instead, it remains dormant within the body, hiding in sensory nerve ganglia1.
The reactivation of this dormant virus results in shingles, a painful dermatomal rash, often followed by pain in the distribution of the rash (postherpetic neuralgia)2.
Prevention Measures
Prevention is always better than cure, especially when it comes to infectious diseases. For chickenpox, a highly effective vaccine is available and is often administered during childhood. It's the first line of defence against VZV.
As for shingles, there's also a vaccine called the Shingles or Zoster Vaccine. It's generally recommended for adults over the age of 50, even if they've had shingles before.
These vaccines don't guarantee complete protection, as evidenced by breakthrough varicella, but they significantly reduce the severity of the disease.
Regular hand hygiene and avoiding close contact with infected individuals are other measures to prevent the spread of VZV.
Related: Can a Parent of a Child with Chickenpox Pass It On?
Transmission and Geographical Distribution of VZV
VZV spreads either by aerosolized respiratory droplets or by contact with the virus in varicella or zoster skin lesions2. Its reach is not limited to any specific region - it occurs worldwide3.
Breakthrough Varicella Explained
Interestingly, even after vaccination against VZV, one might experience a mild infection, termed breakthrough varicella. This happens when wild-type VZV infects a vaccinated individual more than 42 days after vaccination1.
Seriousness of the Varicella-Zoster Virus (VZV)
Is the Varicella-Zoster Virus serious? The answer is yes. Although chickenpox is typically a mild disease, shingles can be particularly debilitating, especially for older adults. Moreover, breakthrough varicella can occur even after vaccination, although it is generally mild.
The Biological Aspects of VZV
Where VZV is Most Likely to be Found
After primary infection, VZV establishes latency in the dorsal root ganglia, a cluster of nerve cell bodies1.
VZV Latency and Virus Pathogenesis
The ability of VZV to remain dormant within the body and later reactivate is an essential aspect of its pathogenesis. It's a fascinating, yet complex, aspect of the virus' lifecycle that warrants deeper exploration.
VZV Infection and Virus Replication Cycle
As part of its infectious cycle, the virus replicates within the host's cells. During this cycle, it moves through several stages, including attachment, penetration, biosynthesis, maturation, and release.
Understanding the VZV Virus Structure
The VZV is a complex virus with a specific structure essential for its function and ability to cause infection.
Understanding this structure helps scientists develop treatments and vaccines against diseases it causes.
Measures Against VZV and Ongoing Research
Varicella Zoster Immune Globulin
To prevent complications after exposure to VZV, a substance known as varicella zoster immune globulin is used. This substance is purified from individuals who have high levels of immunity to varicella3.
VZV Research Developments
There is ongoing research on VZV, including the development of a monkey model of varicella3. By understanding VZV better, we get closer to finding more effective treatments and perhaps even eradicating the diseases it causes.
Treatment Options
Once VZV infection occurs, treatment primarily focuses on alleviating symptoms and preventing complications. For chickenpox, over-the-counter medication can help with itchiness caused by the rash, while more severe cases might require antiviral drugs1.
When it comes to shingles, antiviral medication is important to shorten the duration of the virus and reduce the risk of complications. Pain management, including the use of over-the-counter pain relievers and prescription medication, is often necessary due to the painful rash associated with shingles2.
For people at high risk, such as those with weakened immune systems or pregnant women exposed to VZV, Varicella Zoster Immune Globulin may be administered to help prevent severe disease3.
As science and medicine continue to evolve, the hope is to continue improving these treatments and preventive measures, creating a healthier future for all.
The Global Impact of VZV
Varicella-zoster virus (VZV) has a significant global impact due to the high morbidity and mortality associated with chickenpox and shingles (123).
The epidemiology of VZV is worldwide, and the virus is highly contagious (45). The burden of VZV infection is higher in low-income countries, where there is a lack of data on the epidemiology of VZV (2).
The HIV/AIDS pandemic is also expected to impact the epidemiology of VZV in Africa (2).
In 2014, the World Health Organization estimated that there were approximately 4.2 million cases of varicella with severe complications and around 4200 related deaths occurring per year worldwide (5).
The spread of the virus can be decreased dramatically by the widespread use of the varicella vaccine, particularly in a worldwide vaccination program (3).
There are several varicella vaccines available worldwide, and their efficacy and safety have been well established (6).
The varicella vaccination program has been successful in reducing the incidence of varicella and its complications in many countries (6).
The Prevalence of Varicella-zoster Virus (VZV)
Varicella-zoster virus (VZV) is a DNA virus that causes two distinct diseases: varicella (chickenpox) and herpes zoster (shingles) (1).
Here are some key points about the prevalence of VZV-related diseases:
- Varicella: Before the introduction of the varicella vaccine, varicella was a common and highly contagious disease that affected nearly all susceptible children before adolescence (2). The annual incidence was estimated at 80-90 million cases worldwide (2). However, the incidence of varicella has declined significantly since the vaccine was introduced (1).
- Herpes zoster: Herpes zoster is a common disease among older individuals, with a lifetime risk of 10% to 30% that rises to 50% among those living to ≥85 years (3). The incidence of herpes zoster varies by age and is approximately 2-9 cases per 1,000 US population annually (4). Infection in immunocompromised individuals often causes severe, disseminated disease (5). A person's risk for herpes zoster and related complications sharply increases after 50 years of age (4).
- Populations most affected: Children who receive the varicella vaccine have a lower risk of herpes zoster compared with children who were infected with wild-type VZV (4). Adults age 20 years or older accounted for only 7% of varicella cases (1). Those aged 60 years and above have a higher immunity to VZV infections, with 50% of the rural population and 78.9% of the urban population being immune (6). Adolescents, adults, and pregnant patients are at increased risk for severe disease and are often treated with antivirals (2). Children who are immunocompromised, those who are otherwise at risk for severe disease, and those who already have severe disease require specific treatment (2).
Impact of Vaccination Programmes
The introduction of varicella vaccination has significantly changed the landscape of VZV-related diseases.
Here are some ways vaccination programs have impacted VZV-related diseases:
- Varicella: The incidence of varicella has declined significantly since the vaccine was introduced, with an average of 97% decline in incidence from pre-vaccine years based on data from four states that have been tracking varicella incidence (1). The vaccine has been shown to be highly effective in preventing varicella, with a two-dose regimen providing even greater protection (2). Vaccinated children are less likely to become infected with wild-type VZV (3).
- Herpes zoster: The impact of varicella vaccination on the incidence of herpes zoster is still being studied, but some studies suggest that vaccinated children have a lower risk of herpes zoster compared with children who were infected with wild-type VZV (3). There is no definitive and consistent association between vaccination and the increase in herpes zoster incidence in the elderly (4).
Overall, the disease burden and the viral transmission of VZV are reduced by the routine use of varicella vaccine in children (5).
The introduction of universal vaccination has led to reductions in the incidence of the disease and hospitalizations and has been shown to be cost-effective (4).
In Summary
The Varicella-Zoster Virus is an intricate virus that causes two well-known diseases, has a unique lifecycle, and calls for ongoing research to tackle the health problems it causes.
It's an example of how a tiny organism can have a significant impact on human health.