Human Herpesvirus 1

The Herpesviruses consist of 8 main virus types, ranging from HHV-1 to HHV-8. Each of these viruses causes different problems, but in this post, we are focussing on the Type 1 Herpes Simplex Virus (or Human Herpesvirus 1, HHV-1) which is primarily responsible for oral infections. HHV-2 is responsible for genital infections with similar features to HHV-1.

Structure and Viral Replication

The basic structure of the virus is highlighted in the diagram below:

Like with many viruses, the Herpesviruses have glycoproteins on their surface which allow them to bind to and enter human cells. Once inside, they uncoat and release their double-stranded DNA (dsDNA). Transcription and translation of this DNA leads to the production of new viruses which can then be released from the host cell.

Human Herpesvirus 1 – HHV 1

HHV-1 is responsible for a primary infection and a secondary infection:

• Primary – Herpetic Gingivostomatitis
• Secondary (reactivation) – Herpes Labialis

Once a patient develops the primary infection, herpetic gingivostomatitis, the virus migrates along the trigeminal nerve and then eventually lies dormant in the trigeminal ganglion. The virus can lie dormant for several years until reactivation occurs. Reactivation can occur due to stress, UV light, illness or immunosuppression. During reactivation, herpes labialis, the virus migrates from the ganglion back down to the peripheral nerves and then is actively shed via cold sores. Reactivation can occur repeatedly.

In up to 90% of patients, the primary infection of HHV-1 is asymptomatic and usually occurs in childhood. However, they can then still go and develop secondary reactivation in the future.

Herpetic Gingivostomatitis

The primary infection is quite common and as mentioned, often is asymptomatic. It is most common amongst children and tends to be very mild. However, it can occur in adults, in which case it is usually more severe. The virus has an incubation period of between 5-7 days and the infection lasts for up to 2 weeks.

Symptoms and Diagnosis

The symptoms and features of the primary infection include:

• Multiple oral vesicles, easily rupturing and sloughing
• Gingivitis with erythema and sloughing
• Drinking and eating is painful
• Halitosis
• Malaise
• Pyrexia
• Lymphadenopathy
• Profuse salivation, especially amongst children

Diagnosis is usually achieved by just the symptoms and clinical examination, and no special investigations are usually needed (although PCR may be used to identify viral DNA)

Management

Usually, the condition is self-limiting and will clear itself. When the patient presents, there isn’t usually a reason to give them medication. Advice is given as follows:

• Rest
• Fluids and a soft diet
• Systemic and Local Analgesics
• Antipyretics
• Local antiseptics e.g. chlorhexidine mouthwash
• Strict cross-infection control – the virus is easily transmissible
• If it is found early or the patient is immunocompromised then acyclovir (200mg, x5/day for 5 days) may be given

Rarely does a patient need hospitalisation but this may be necessary if they become excessively dehydrated or due to extreme pyrexia.

Herpes Labialis

When HHV-1 is reactivated later in life, the patient develops herpes labialis, or more commonly referred to as cold sores. The cold sores are the sites where the virus is actively being shed.

Features

Features are quite simple to identify:

• Patient experiences some prodromal irritation at the site that the cold sore will develop
• Vesicles commonly around the mucocutaneous junction of the lips
• Crusting lesion

Lesions usually last 7-10 days and recur at the same sites.

Management

Topical 5% acyclovir creams may be used during the prodromal irritation phase, but these have limited success.

Prophylactic treatment has shown success in immunocompromised patients. A prophylactic dose of acyclovir 600-1000mg/day, in 2 doses, has shown to be effective in reducing the frequency and severity of reactivation.

Other Complications

Herpetic Whitlow

This occurs due to unprotected hand contact with infected oral tissues, which have either a primary or secondary HHV-1 infection. It causes extremely painful lesions on the hands. It is difficult to treat and prevention by wearing gloves is the best way!

The same can occur if the eyes aren’t protected by goggles and viral contact occurs.

HSV Encephalitis

Usually affecting the frontal lobes of the brain, this has a mortality rate of up to 80% and if the patient survives, the chances of returning to normal are very small. HHV-1 most commonly affects the >50s. Symptoms include headaches, pyrexia and behavioural changes over several days.

Summary

• Human Herpesvirus 1, HHV-1, is responsible for primary and secondary oral infections
• Herpetic gingivostomatitis is the primary infection. Symptoms include multiple, sloughing, oral vesicles.
• Diagnosis is one via clinical examination and treatment is usually symptomatic
• Herpes labialis is the reactivation characterised by cold sores
• Other complications include herpetic whitlow and encephalitis.

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References and Recommended Reading

• Single Best Answer Questions for Dentistry
• Essentials of Microbiology for Dental Students
• Infectious Disease Essentials