21: Viruses of relevance to dentistry

Chapter 21 Viruses of relevance to dentistry

This chapter gives an outline of the viruses that are of special relevance to dentistry. The DNA viruses are described first, followed by the RNA viruses (see Table 4.1).

DNA viruses

Papovaviruses

These DNA viruses infect both humans and animals; however, human disease is infrequent.

Human papillomavirus

Human papillomavirus (HPV) mainly causes skin warts (verrucae); it is also associated with a number of lesions including oral papillomas, oral verrucous carcinomas and focal epithelial hyperplasia. There are more than 70 serological types of HPV, some of which are more closely associated with lesions (both benign and cancerous) than others.

Skin warts

• Clinical features: warts typically are benign epithelial tumours. Specific serological types of HPV are associated with anogenital warts (condylomata acuminata) and are seen in all cervical biopsies that show precancerous change.
• Epidemiology: warts are generally more common in children than in adults. The virus is likely to be transmitted by direct contact or autoinoculation.

Oral infections with HPV

Over 40% of healthy individuals have HPV in the normal oral mucosa, suggesting that this is a reservoir of the virus.

Oral squamous papillomas and warts

• Clinical features: most are single, small (1 cm), pedunculated, exophytic lesions (Fig. 21.1). They rarely, if ever, progress to carcinomas.
• Epidemiology: occur mainly in the third to fifth decade of life, with a male preponderance.
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Fig. 21.1 A papilloma at the angle of the mouth.

Verrucous carcinoma

There is evidence to indicate that HPV is associated with human carcinomas, on the basis of:

• the frequent malignant change in virus-induced warts in epidermodysplasia verruciformis
• the frequent association of HPV-16, -18 and -33 with invasive cervical cancer
• development of cancer in vulvar warts in women with lymphoma.

Adenoviruses

These DNA viruses induce latent infections of the tonsils, adenoids and other lymphoid tissues of humans. However, most infections caused by adenoviruses are acute and self-limiting.

Adenoviral diseases

Acute respiratory disease is the most common adenovirus infection. It is an influenza-like illness seen commonly in military training camps. Clinically, the main symptoms are pharyngitis and conjunctivitis. Although self-limiting, acute respiratory disease may be complicated by pneumonia in some cases. Other infections caused by these viruses include pharyngoconjunctival fever (a disease of infants and children), epidemic keratoconjunctivitis, pneumonia and gastroenteritis.

Epidemiology

Adenoviruses are ubiquitous, and human beings are the only known reservoir for the human strains. The infections are spread from person to person by respiratory and ocular secretions. Adequate chlorination of pools may help decrease the spread of pharyngoconjunctival fever.

Herpesviruses

There are a range of different human herpesviruses, currently numbered 1–8 (see Table 4.3). All of them are structurally similar (enveloped, icosahedral with double-stranded DNA) and infect both humans and animals. They are the most common causes of human viral infections. All have the important property of remaining latent, with the ability to reinfect the host a variable period after the primary infection. Important human pathogens include herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), varicella-zoster virus (VZV), cytomegalovirus (CMV) and Epstein–Barr virus (EBV) (see Chapter 4). Students of dentistry should be thoroughly conversant with the herpes group of viruses as the majority of them either cause oral infection or are intimately associated with orofacial tissues and saliva.

Structure

See Chapter 4.

HSV (human herpesviruses 1 and 2)

There are two types of HSV: HSV-1 and HSV-2. They can be differentiated by serotyping, by DNA homology and, to some extent, by clinical disease pattern.

Clinical disease

Disease due to HSV can be either a primary infection, due to first encounter with the virus, or a reactivation or recurrent infection, due to activation of the latent virus.

Primary infection

There is an incubation period of 2–20 days, depending upon the infected site and the infecting strain of virus. The lesions include:

• primary gingivostomatitis with lesions on the lips and mouth; very common (see Chapter 35)
• genital herpes: vesicular eruption of the genitalia, mostly due to HSV-2 (but up to a third of the cases may be due to HSV-1)
• herpetic whitlow: infection of the fingers, acquired by dentists and nurses as a result of contamination of the hands by virus-laced saliva or other secretions (Fig. 21.2)
• conjunctivitis and keratitis: less commonly, HSV infections involve the eyes, sometimes leading to blindness
• encephalitis: a result of either primary or recurrent infection; may lead to permanent defects or death.
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Fig. 21.2 A herpetic whitlow in a dentist caused by herpes simplex virus.

Recurrent infections

Recurrence or reactivation of HSV entails activation of the non-infectious form of the latent virus residing in the neurons of either the trigeminal ganglion (Fig. 21.3) or the sacral ganglia. Reactivation is provoked by menstruation, stress, sunlight (possibly ultraviolet rays), local trauma, etc.; the lesions tend to recur at the site of the primary lesion. HSV has been implicated in Bell’s palsy.

image image

Fig. 21.3 Herpes labialis: (A) recurrence of facial herpes infection due to reactivation of the latent virus in the trigeminal ganglion; (B) clinical presentation of herpes labialis on the mucocutaneous junction of the upper lip.

Epidemiology

Humans are the only known reservoir for HSV-1 and HSV-2; experimental infection can be induced in animals and cell cultures. As the virus is highly labile, most primary infections are acquired through direct contact with a lesion or contaminated secretions. In general, HSV-1 causes orofacial lesions or lesions ‘above the belt’, while HSV-2 causes lesions ‘below the belt’, i.e. genital herpes (Fig. 21.4). However, because of sexual promiscuity or for other reasons, this may not be always true. HSV-1 is acquired early in life, while HSV-2 appears after the onset of sexual activity.

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Fig. 21.4 Predominant distribution of infection with herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), in different age groups.

As recurrent infection is common in the presence of high antibody titres, circulating antibodies appear to be unhelpful in controlling HSV infection. One reason for this may be the contiguous cell-to-cell spread of the virus, which cannot be prevented by antibody. Reactivation is not accompanied by a rise in herpes antibody titre.

Diagnosis

Diagnosis is usually achieved clinically; laboratory diagnosis is useful to confirm infection, especially in compromised patients. This entails:

• direct demonstration of viral antigens in vesicular fluid or scrapings by electron microscopy or immunofluorescence (Fig. 21.5)
• demonstration of characteristic multinuclear giant cells in scrapings from lesions – simple but not always successful
• propagation of virus in tissue culture.
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Fig. 21.5 Positive immunofluorescence of a smear taken from the lip lesion shown in Figure 21.3B (stained with anti-herpes antibody tagged to a fluorescing chemical), indicating that the patient has herpes labialis.

However, the foregoing traditional techniques are now supplanted by polymerase chain reaction-based rapid diagnostic methods.

Prevention

Control is difficult because of the high frequency of asymptomatic infection. It is important to avoid contact with acute herpetic lesions and contaminated body fluid (e.g. saliva) by routine wearing of gloves. No vaccine is available.

Treatment

The course of primary infection can be altered significantly with drugs that interfere with viral DNA synthesis, such as aciclovir and vidarabine, but these should be administered in the early prodromal phase of the disease for best results (see also Chapter 35).

Varicella-zoster virus (human herpesvirus 3)

This organism causes both varicella (chickenpox) and herpes zoster (shingles) – two different diseases due to an identical organism. Chickenpox is the primary infection, and herpes zoster is the reactivation of illness.

Clinical disease

Varicella

A common childhood fever, varicella is mild and self-limiting. The disease is more severe if contracted in adulthood. After a 2-week incubation period, fever develops, followed by a papular rash of the skin and mucous membranes, including the oral mucosa. The papules rapidly become vesicular and itchy but painless (in contrast to the rash in zoster).

Zoster (shingles)

Occurs primarily as a reactivation of the virus in dorsal root or cranial nerve (usually trigeminal) ganglia (Fig. 21.6). The disease usually affects adults, and the virus is reactivated despite circulating antibodies. Zoster is triggered by trauma, drugs, neoplastic disease or immunosuppression.

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Fig. 21.6 Pathogenesis and sequelae of varicella-zoster virus (VZV) infection.

The virus remains latent in ganglionic nerve cells and, after activation, travels back along the nerve fibre to the skin. Thoracic nerves supplying the chest wall are most often affected, and the lesion presents as a unilateral, painful vesicular rash, which extends in a horizontal strip from the middle of the back around the side of the chest wall (‘belt of roses from hell’). Fever and malaise accompany the lesion. The rash may last for 2–4 weeks, with pain (post-herpetic neuralgia) persisting for weeks or months.

The trigeminal nerve is affected in about 15% of cases, with involvement of the ophthalmic, maxillary and mandibular divisions (in that order of precedence). Severe localized oral pain precedes the rash and may be easily confused with toothache (see Chapter 35). Involvement of the ophthalmic nerve may lead to eye lesions and sometimes blindness.

Ramsay Hunt syndrome is a rare manifestation of zoster, with a vesicular rash on the tympanic membrane and the external auditory canal, together with unilateral facial nerve palsy.

Epidemiology

Shingles is primarily a disease of older adults and immunocompromised persons; it is rare in children. The incidence increases with advancing age and with decreasing degree of immunocompetence. It is a highly contagious infection in a host not previously exposed to the virus. Transmission occurs by direct contact with skin lesions or droplet infection from infectious saliva.

Diagnosis

The clinical picture is pathognomonic, as the lesion distribution overlaps and accurately maps the distribution of the sensory nerve (Fig. 21.7). Serology, if needed, entails detecting a fourfold rise in antibody titre in paired sera (compare herpes simplex reactivation, where antibody rise is not significant).

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Fig. 21.7 Herpes zoster infection of the tongue: note the sharp midline demarcation of the lesion (due to reactivation of the virus travelling via the lingual branch of the right trigeminal nerve).

Treatment

Chickenpox is self-limiting and requires symptomatic treatment, if any. Disseminated zoster in immunocompromised patients requires antiviral drugs (e.g. aciclovir, vidarabine), which interfere with herpesvirus DNA replication. Varicella-zoster virus is less sensitive to aciclovir than is HSV, and hence, a higher dosage is required; therapy should start within 72 h of onset. Systemic aciclovir may reduce the duration of the early infective phase and the associated pain. In addition, it may reduce the prevalence of post-herpetic neuralgia.

Prevention

Passive immunization with varicella-zoster immune globulin (VZIG) may be indicated for persons at high risk of severe infection. A vaccine for chickenpox is now available.

EBV (human herpesvirus 4)

EBV is widespread in humans, and most adults have antibody to the virus. The virus persists in latent form within lymphocytes after primary infection (lymphotrophic, unlike HSV and varicella-zoster virus, which are neurotrophic). The genome resides in a latent form in B cells; latent EBV infection is common in the population. It is the aetiological agent of a number of diseases:

• infectious mononucleosis (glandular fever)
• Burkitt’s lymphoma and other B cell lymphomas
• nasopharyngeal carcinoma (especially in southern Chinese populations)
• oral hairy leukoplakia
• post-transplant lymphoproliferative diseases.

Infectious mononucleosis

An acute infection affecting lymphoid tissue throughout the body, infectious mononucleosis is commonly seen in teenagers, with a peak incidence at 15–20 years of age. The organism is present in saliva and is postulated to be transmitted during kissing – hence, it is called the ‘kissing disease’.

Incubation period

Incubation is 4–7 weeks; possibly shorter (10–40 days) in young children.

Signs and symptoms

Low-grade fever with generalized lymphadenopathy and abnormal lymphocytes in the blood (note that a similar illness, glandular fever-like syndrome, develops during the first fortnight after infection with human immunodeficiency virus (HIV)). Fever, tonsillitis and fatigue are common, and many patients have splenomegaly. Lymphocytosis is a characteristic feature, hence the term ‘mononucleosis’; some 10% of the lymphocytes are atypical, with enlarged misshapen nuclei and increased cytoplasm (Fig. 21.8).

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Fig. 21.8 Infectious mononucleosis: characteristic blood film with many mononuclear cells.

Chronic, persistent or reactivated EBV infection

This may take many clinical forms and is less common than acute mononucleosis, described above. The syndrome is characterized by persistent fatigue, with or without physical or laboratory findings.

Epidemiology

The virus is ubiquitous, and humans are its only known host. Spread of EBV is via respiratory secretions, primarily through oral contact. Those from lower socioeconomic classes are exposed to EBV at an early age and typically develop asy/>

Related posts:

  1. 16: Vibrios, campylobacters and Wolinella
  2. 18: Fusobacteria, Leptotrichia and spirochaetes
  3. 17: Bacteroides, Tannerella, Porphyromonas and Prevotella
  4. 9: The immune response
  5. 26: Infections of the gastrointestinal tract
  6. 4: Viruses and prions

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Jan 4, 2015 | Posted by in General Dentistry | Comments Off on 21: Viruses of relevance to dentistry

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