Herpes viruses Summarized - Part I

Namaste!

Today in Virology, we are discussing one of the most common and widespread clan of viruses i.e. Herpesviruses. Since this is a major topic, we will discuss this in two separate parts. Also, as this is only a summary, I will only talk about the major, key points.

Lets dive!

Herpesvirus clan contains mostly enveloped, DNA viruses.

First list all the family members.

1. Herpes Simplex
2. Varicella Zoster (Childhood - Chicken Pox)
3. Herpes Zoster (Old age - Shingles)

To be discussed in the next part.

1. Epstein Barr virus
2. Cytomegalovirus

HERPES SIMPLEX:

• Two types - HSV 1 (isolated from the lesions around mouth and buccal cavity) and HSV 2 (usually responsible for genital herpes).
• Humans are the natural hosts and the sources of infection are of course, skin lesions. Aslo saliva and respiratory secretions form a major mode of transmission. 
• Entry occurs through cuts in skin or mucous membranes and spreads locally via cell to cell transmission. These viruses also transport themselves to nerve fibers and remain latent in the ganglia (Particularly in trigeminal and sacral nerves) only to get reactivated periodically and cause lesions (This is what is called 'Recurrent Chicken pox' in layman language). In sensitive patients, minor stimuli like cold, exposure to sun or even menses can cause such reactivation.
• Typical herpes lesions are thin walled, which breaks down leaving tiny superficial ulcers. HSV1 causes lesions above the waist area while HSV 2 causes lesions below the waist area (Quite a good understanding between the buddies, cute no!) Recurrent infections are more localised.
• It is also a common cause of corneal blindness. Keratoconjunctivitis, or follicular conjunctivitis on the eyelids is another manifestation. 
• Prophylaxis - 1)Valaciclovir and Famciclovir - oral infections. 2) Idoxyuridine - Eye and skin infections. 3) Acyclovir and Vidarabine - deep and systemic infections.

VARICELLA ZOSTER

• Varicella Zoster Virus was first isolated by Thomas Weller in human embryonic tissue culture.
• VZV is similar in morphology with Herpes Simplex Virus. In fact, Varicella (chickenpox) and Herpes Zoster are the same manifestations of the same virus. The only difference being, Varicella follows primary infection in a nonimmune individual, while Herpes Zoster is a reactivation of a latent viral infection when the immunity of an individual falls below ineffective levels. Thus chickenpox is a contagious disease (happens due to contact with infected individual), herpes zoster doesn't spread through contact.
• The portal of entry is always respiratory tract or conjunctiva. The rashes usually start appearing on the trunk after an incubation period of 5-20 days, thereby spreading in a centripetal pattern in the rest of the body.
• Other complications like myocarditis, nephritis, acute cerebellar ataxia, meningitis and encephalitis may occur, especially in elderly people.
• Chickenpox if happened during pregnancy can be dangerous for both mother and baby with enhanced risk of pneumonia. In case, the mother develops chickenpox a week before the delivery, the baby would receive the viral infection from the mother, but not the antibodies. In such cases, the babies are given VZV antiserum and/or chemotherapy right after the birth.
• Prophylaxis - Acyclovir and Famciclovir are found effective in the treatment after infection.

HERPES ZOSTER

• Herpes Zoster usually occurs in individuals who have had chicken pox earlier. The virus remains latent and causes lesions many years alter when the residual immunity of the individual is lost.
• The rash is typically lateral and confined to the area supplied by the particular reactivated nerve. The lesions are identical to varicella lesions. Healing of the rash may take as long as two weeks whereas pain and paresthesia in the affected area may persist for months.
• The Rampant Hunt syndrome is a are form zoster manifestation, which affects the facial nerve and external auditory canal, leading to facial palsy.
• Herpes Zoster is an evolutionary form of Varicella Zoster. But in most communities, this virus is completely eliminated by varicella infection in childhood and thus the chances of it to reappear is low. Recurrent Zoster infections are most commonly observed in HIV patients.
• Treatment remains the same as that done in chickenpox.