Varicella-Zoster Virus Infections
VZV is a member of family Herpesviridae is a DNA virus. It causes two distinct entities:
Varicella (chickenpox)
Herpes zoster (shingles)
Pathogenesis: Transmitted via respiratory route. Viremia manifests as exanthematous lesions. Vesicles involve the corium and dermis with degenerative changes characterized by ballooning, the presence of multinucleated giant cells and eosinophilic intranuclear inclusions. Vesicular fluid becomes turbid as PMNs accumulate, and eventually burst releasing their fluid (which includes infectious virus) or are gradually absorbed.
Reactivation of VZV results in herpes zoster. Presumably the virus infects the dorsal root ganglia.
Humans are the only known reservoir for VZV. It is highly contagious. Occurs in late winter and early spring.
Incubation period: 12-21 days but is usually 14-17 days.
Individuals are infectious ~48 hours before the onset of the vesicular rash, during the period of vesicle formation (which generally last 4-5 days), and until all vesicles are crusted.
Clinically presents as rash, low grade fever, malaise. Pt's develop a prodrome 1-2 days before the onset of the exanthem. Fever of 37.8°C-39.4°C of 3-5 days' duration. Maculopapules, vesicles, and scabs in various stages of evolution, evolve over hours to days, appear on the trunk and face and rapidly spread to involve other areas of the body. Most are small, have an erythematous base with a diameter of 5-10 mm in diameter. Successive crops appear over 2-4 day period. Lesions can be found on the oral mucosa or the vagina.
Most common infectious complication of varicella is secondary bacterial superinfection of the skin, which is usually caused by Streptococcus pyogenes or Staphylococcus aureus, including strains that are methicillin resistant. Skin infection occurs from excoriation of lesions after scratching. Gram stain of the skin lesion is often helpful in determining the etiology of the infected lesions.
Most common extracutaneous site of involvement in children is the CNS. The syndrome of acute cerebellar ataxia and meningeal inflammation generally appears ~21 days after the onset of rash. Usually no complication, but aseptic meningitis, encephalitis, transverse myelitis, GB syndrome, and Reye's syndrome can also occur.
Varicella pneumonia is a serious complication following chickenpox, develops more commonly in adults, is particularly severe in pregnant women. Occurs 3-5 days into the illness and is associated with tachpnea, cough, dyspnea, and fever. Cyanosis, peluritic chest pain, and hemoptysis are common. CXR shows nodular infiltrates and interstitial pneumonitis.
Other complications of chicken pox: myocarditis, corneal lesions, nephritis, arthritis, bleeding diatheses, acute GN, and hepatitis.
Ramsay Hunt syndrome: Pain and vesicles appear in the external auditory canal, and patients lose their sense of taste in the anterior two-thirds of the tongue while developing ipsilateral facial palsy. The geniculate ganglion of the sensory branch of the facial nerve is involved.
CNS involvement may follow localized herpes zoster. Many Pts without signs of meningeal irritation have CSF pelocytosis and moderately elevated levels of CSF protein. Symptomatically meningoencephalitis. Granulomatous angitis with contralater hemiplegia.
Transverse myelitis.
DDx: disseminated HSV, disseminated rash of coxsackievirus inf, echovirus inf, or atypical measles. These rashes or more commonly morbiliform with a H'gic component rather than vesicular or vesiculopapular. Lesions of small pox are larger than that of chickenpox and all are the same at any given time.
LABS: VZV DNA by PCR. Direct immunofluorescent staining of cells from the lesion base or detection of viral antigens by other assays is also useful. The most frequently employed serologic tools for assessing host response are the immunofluorescent detection of antibodies to VZV membrane antigens, the fluorescent antibody to membrane antigen (FAMA) test, ELISA.
VZV management:
Good hygiene, daily baths and soaks.
Skin care, close cropping of fingernails
Antipruritic drugs, bendaryl
Tepid water baths and wet compressess.
No ASA to children.
For adolescent and adults with chicken pos >24 hrs duration: Acyclovir 800 mg PO five times a day for 5-7 days.
Aluminum acetate soaks for the management of herpes zoster can be both soothing and cleansing.
Famciclovir 500 mg PO tid x 7 days.
Valacylovir 1 gm PO tid for 5-7 days.
Acyclovir 10-25 mg/kg IV q8hr x 7 days
VZIG to individuals who are susceptible. Given within 96hr (preferably >72h) of the exposure.
Disseminated multidermatomal V. Zoster:
Acyclovir 5-10 mg/kg IV q8h can change to Valtrex 1 g PO tid for a total duration of 7 days.
Respiratory isolation - not contact isolation for disseminated zoster x 48 h after starting acyclovir.
If Pt. has recurrent Zoster outbreaks, start suppression therapy:
Acyclovir 400 mg PO tid or Valtrex 1 gm PO qd.
Acyclovir:
HSV: 400 mg PO q8h; 5-10mg/kg IV q8h for severe HSV infections including HSV encephalitis.
Prophylaxis in patients who have frequent HSV recurrences: 400 mg PO q12h.
Acyclovir adverse events: Reversible crystalline nephropathy may occur; preexisting renal failure, dehydration, and IV bolus dosing increase the risk of this effect. Rare cases of CNS disturbances, including delirium, tremors, and seizures, may also occur, particularly with high doses, in patients with renal failure and in the elderly.
Valacylovir.
HZV: 1 g PO q8h
HSV initial episode of genital infection: 1 g PO q12h
Recurrent episodes of HSV: 500 mg PO q12 or 1 g PO q24h.
Adverse event: Nausea. Rare CNS disturbances. High doses 8 g/d have been associated with development of hemolytic-uremic syndrome/thrombotic thrombocytopenic purpura in immunocompromised patients, including those with HIV and bone marrow and solid organ transplants
Famciclovir
HZV: 500 mg PO q8h
HSV initial episode of genital infection: 250 mg PO q8h
Recurrent episodes of HSV: 125 mg PO q12 .
Adverse event: HA, nausea, and diarrhea