Herpesvirales

Herpes(PHIL 1573 lores)

Duck plague victim

Herpesvirales is an order of viruses that includes several important families of viruses affecting humans, animals, and marine life. The most well-known and studied family within this order is the Herpesviridae, which includes viruses responsible for diseases such as herpes simplex virus (HSV) causing cold sores and genital herpes, varicella-zoster virus (VZV) causing chickenpox and shingles, and Epstein-Barr virus (EBV) associated with infectious mononucleosis, among others. Herpesvirales are characterized by their ability to establish latent infections, a period during which the virus is present in the body but not actively replicating. This ability contributes to the lifelong persistence of these viruses in their hosts.

Classification

The order Herpesvirales is divided into several families, of which the most notable include:

• Herpesviridae: This family is the most studied and includes viruses infecting humans and other mammals. It is further subdivided into three subfamilies: Alphaherpesvirinae, Betaherpesvirinae, and Gammaherpesvirinae.
• Alloherpesviridae: This family primarily includes viruses that infect fish and amphibians.
• Malacoherpesviridae: Viruses in this family infect mollusks.

Each family is further divided into genera and species, based on their genetic makeup and the specific hosts they infect.

Structure and Genome

Viruses in the order Herpesvirales share a common structure: a large double-stranded DNA genome enclosed within an icosahedral capsid, which is itself wrapped in a lipid bilayer envelope. This envelope contains viral glycoproteins essential for the virus's ability to enter host cells. The size and complexity of their genomes allow these viruses to encode a large number of proteins, including those involved in DNA replication, viral assembly, and evasion of the host immune response.

Pathogenesis and Diseases

Herpesvirales are capable of causing a wide range of diseases in humans and animals. In humans, diseases can range from mild skin conditions to severe systemic infections. For example, HSV-1 typically causes cold sores, while HSV-2 is associated with genital herpes. VZV causes both chickenpox in children and shingles in adults, while EBV is known for causing infectious mononucleosis and is associated with certain types of cancer.

In animals, diseases caused by members of the Herpesvirales order can affect both wild and domesticated species, leading to significant economic losses in agriculture and aquaculture. For example, infectious salmon anemia virus (ISAV), a member of the Alloherpesviridae family, causes a lethal disease in farmed salmon.

Latency and Reactivation

A hallmark of Herpesvirales infections is their ability to establish latent infections within their hosts. After the initial acute infection, the virus can enter a dormant state within specific cell types. For example, HSV can remain latent in neuronal cells, while EBV can do so in B cells. Under certain conditions, such as stress, immunosuppression, or hormonal changes, these viruses can reactivate, leading to recurrent disease symptoms.

Prevention and Treatment

Prevention of Herpesvirales infections includes the use of vaccines, such as the VZV vaccine for chickenpox and shingles, and practicing safe hygiene and sexual practices to reduce the transmission of HSV. Treatment options for herpesvirus infections primarily involve antiviral medications that inhibit viral DNA replication, such as acyclovir and its derivatives. However, there is currently no cure for these infections, and treatment focuses on managing symptoms and reducing the frequency of reactivation.