Varicella-Zoster Virus (aka, HHV-3)

Herpesviruses 3 & 4

General Features:

Large viruses, with double-stranded DNA housed in enveloped icosahedral capsids. Enveloped capsid viruses; vulnerable to acids, detergents, and drying.

Herpesviruses cause lytic, persistent, and latent infections. Additionally, the Epstein-Barr virus, which we'll learn about in this tutorial, can cause immortalizing infections.

Treatment & Prevention

Vaccines for VZV and HZV
Acyclovir for Shingles

Varicella-Zoster Virus

Aka, Human Herpesvirus 3

In Children: causes mild respiratory illness with successive crops of maculopapular rash. (chicken pox)

In Adults: Infection can be more severe and widespread in adults, who may also develop complications such as interstitial pneumonia.

Pathogenesis:

Transmission & Entry: the virus typically enters the new host via respiratory droplets; transmission can also occur via secretions from the pustules.

Viral replication occurs within the tonsils and respiratory tract.

Viremia: The virions travel in the bloodstream and lymphatics to the liver, spleen, and other reticuloendothelial organs.

Secondary viremia delivers the virus to the T-cells; viremia produces symptoms such as fever and malaise.

Epithelial cells: T-cells become infected and deliver the virus to the epithelial cells.

Rash: Infection of the epithelia produces the characteristic vesiculopustular rash, particularly on the scalp, head, and trunk.

The virus establishes latent infection in trigeminal and dorsal root ganglia.

Herpes-Zoster Virus

Shingles:

Some individuals will develop shingles, which is caused by reactivation of the virus; the re-activated form is called Herpes-Zoster Virus.

Replication and release of the virus along neural pathways produces skin lesions that follow dermatomes; these infections can be very painful.

Epstein-Barr virus

Aka, Human Herpesvirus 4

This virus has been characterized as a B-cell parasite because of its tropism for these immune cells.

"Kissing disease.": Because it is transmitted in saliva, the virus is sometimes referred to as the "kissing disease." The virus can also be transmitted via saliva on shared cups or utensils.

The virus is very common: approximately 90% of adults have formed antibodies against the Epstein-Barr Virus (EBV).

Infection is usually mild or asymptomatic; we'll focus the rest of the tutorial on some important exceptions.

Infectious Mononucleosis

Most often develops in older children and adolescents.

Active infection of B cells leads to B-cell proliferation and T-cell activation.

Activated B cells produce heterophile antibodies – Can be useful for diagnostic purposes.

Downey Cells: EBV-activated T-cells. They have an irregular, almost fluttery appearance that some have compared to a ballerina's tutu.

Mononucleosis Symptoms – Swollen lymph nodes, especially in the neck – Pharyngitis, due to the presence of infection in the tonsils – Splenomegaly, which, in rare cases, can lead to splenic rupture (this is why patients are advised to avoid contact sports or other activities that increase the risk of rupture). – Fatigue – Neurologic complications are possible: Meningoencephalitis and Gullain-Barr Syndrome.

Following primary infection, latent infection is established; reactivation of the virus promotes its shedding.

Lymphomas caused by HHV-4

Lymphomas EBV is associated with some lymphomas, including Burkitt lymphoma, African Burkitt lymphoma, and Hodgkin lymphomas – Risk: Poor T-cell immunity

Burkitt Lymphoma:

https://en.m.wikipedia.org/wiki/File:Burkitt's_lymphoma.jpg

Post-transplant lymphoproliferative disorder In transplant recipients, EBV is associated with post-transplant lymphoproliferative disorder.

Nasopharyngeal carcinoma

In some Asian populations, the virus is associated with nasopharyngeal carcinoma.

Hairy oral leukoplakia In AIDS patients, the virus is associated with hairy oral leukoplakia, which is characterized by whitish plaques in the oral cavity.

Varicella-Zoster Virus (aka, HHV-3)

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