Herpes Simplex Viruses (HSV)

Herpes Simplex Viruses (HSV)

• There are two distinct types: HSV-1 and HSV-2
• HSV-1 and HSV-2 differ in their mode of transmission
• HSV-1 is spread by contact, usually involving infected saliva
• HSV-2 is transmitted sexually or from a maternal genital infection to a newborn
• HSV-1 infections usually stay in the oropharynx and spread by respiratory droplets/direct contact with infected saliva
• The virus must encounter mucosal surfaces or broken skin to initiate infection
• Viral replication occurs at the site of infection, then spreads via local nerve endings to dorsal root ganglia, establishing latency in the trigeminal ganglia
• Symptomatic, recurrent HSV-1 infection usually looks like cold sores (fever blisters) near the lip

Oropharyngeal Disease & Skin Infections

• Primary disease occurs most frequently in children aged 1–5 years
• It involves the buccal and gingival mucosa of the mouth
• The incubation period is short (3-5 days)
• Symptoms: fever, sore throat, vesicular/ulcerative lesions, gingivostomatitis, and malaise
• Gingivitis (swollen, tender gums) is the most striking and common lesion

Herpes Labialis (cold sores)

• Recurrent disease, characterized by a cluster of vesicles at the lip border
• Lesions progress through pustular and crusting stages, and heal without scarring in 8–10 days

Immunity for HSV

• After primary infection, the virus stays latent in the presence of antibodies
• Antibodies don't prevent reinfection or reactivation, but may change the disease

Treatment For HSV

• Antiviral drugs are effective against HSV infections, including acyclovir, which inhibits viral DNA synthesis
• Drugs may suppress clinical manifestations and shorten healing time, but HSV remains latent in sensory ganglia

Varicella-Zoster Virus (VZV)

• Varicella (chickenpox) is a mild, highly contagious disease mainly in children
• Clinically, it presents as a generalized vesicular eruption of the skin and mucous membranes
• The disease may be severe in adults and immunocompromised individuals
• Zoster (shingles) is a sporadic, incapacitating disease in elderly or immunocompromised people
• Zoster is characterized by pain and a rash limited to the skin served by a single sensory ganglion
• Both chickenpox and shingles are caused by the same virus
• Varicella is the acute disease that follows primary contact with the virus
• Zoster is the reactivation of latent varicella virus in neurons in sensory ganglia

Pathogenesis of Varicella

• The route of infection is the mucosa of the upper respiratory tract or the conjunctiva
• After initial regional lymph node replication, viremia involving infected mononuclear cells transports the virus to the skin, where the typical rash starts to show

Pathogenesis of Zoster

• The skin lesions of zoster are histologically the same as those of varicella

Clinical Findings of Varicella

• Incubation period is 10-21 days
• Earliest symptoms: malaise and fever, followed by rash
• Rash first appears on the trunk, then face, limbs, buccal and pharyngeal mucosa
• All stages of macules, papules, vesicles, and crusts may be seen at once

Clinical Findings of Zoster

• Starts with severe pain in the area of skin/mucosa served by one or more groups of sensory nerves & ganglia
• Within a few days, a crop of vesicles appears over the skin served by affected nerves
• Trunk, head, and neck are most commonly affected with the ophthalmic division of the trigeminal nerve

Immunity for VZV

• Previous varicella infection is believed to give lifelong immunity to varicella
• Zoster occurs in the presence of neutralizing antibody to varicella

Laboratory Diagnosis for VZV

• PCR assays are preferred because of their sensitivity, specificity, and rapidity
• In stained smears of scrapings or swabs of the base of vesicles (Tzanck smear), multinucleated giant cells are seen
• A rise in specific antibody titer can be detected in the patient's serum by various tests (enzyme immunoassay)

Treatment for VZV

• Antiviral compounds provide effective therapy for varicella, including acyclovir

Prevention for VZV

• A live attenuated varicella vaccine is available; two doses are recommended for children

Human Herpesvirus 6 (HHV-6)

• Infections typically occur in early childhood
• Primary infection causes exanthem subitum (roseola infantum/ "sixth disease")
• It is considered to be a mild childhood disease with a high fever lasting 3 to 5 days
• After the fever, a characteristic rash appears on the neck and trunk, resolving without any other issues several days later
• The virus is associated with febrile seizures in children
• Presumed mode of transmission is oral secretions

Measles (Rubeola) Virus

• Measles virus is a single-stranded, negative-sense, enveloped, non-segmented RNA virus within the family Paramyxoviridae
• It causes measles
• Measles is an acute, highly infectious disease with fever, respiratory symptoms, and a maculopapular rash
• Humans are the only natural hosts

Pathogenesis of Measles

• The virus enters the human body via the respiratory tract
• Viremia seeds the epithelial surfaces (skin, respiratory tract, and conjunctiva), replication occurs locally

Clinical Findings of Measles

• Measles has an incubation period of 8–15 days
• The prodromal phase has: fever, sneezing, coughing, running nose, red eyes, Koplik spots, and lymphopenia
• Cough and coryza reflect an intense inflammatory reaction involving the mucosa of the respiratory tract
• Koplik spots—pathognomonic for measles—are small, bluish-white ulcerations on the buccal mucosa opposite lower molars
• Koplik spots appear slightly before the rash
• The rash starts on the head and then spreads to the chest, trunk, and down the limbs
• Rash appears as maculopapules that coalesce to form blotches and becomes brownish in 5-10 days
• The most common complication of measles is otitis media
• Pneumonia, caused by secondary bacterial infection, is the most common life threatening complication

Immunity for Measles

• There is only one antigenic type of measles virus
• Infection usually confers lifelong immunity

Laboratory Diagnosis of Measles

• Typical measles is reliably diagnosed on clinical grounds

Treatment, Prevention, and Control of Measles

• Measles vaccine is available in combination with live attenuated rubella and mumps vaccines (MMR)