The Kinetics of Herpes Simplex Virus Type 1 Viremia in Children with Eczema Herpeticum

Roberto P. Santos, Thusa Sabapathy, Seela Nattanmai, Martha L. Lepow, Kathleen A. Stellrecht

Children’s Hospital at Albany Medical Center, Albany, NY

INTRODUCTION

ABSTRACT (Updated)

METHODS

CONCLUSION

ID Week 2012

BACKGOUND: Eczema herpeticum (EH) is a dermatologic

emergency associated with herpes simplex virus (HSV) type 1

viremia. Determination of HSV viral load (VL) kinetics from blood by

polymerase chain reaction (PCR) in children with EH has not been

previously reported. We describe the decline in HSV viremia with

increasing immunoglobulin G (IgG) and absolute lymphocyte count

(ALC) while on therapy. We report three male children (Patient A, 4

months; Patient B, 7 years; and Patient C, 10 months) with atopic

dermatitis exacerbations and generalized vesicular rash with fever

consistent with EH. Because of worsening disease (Patient A, with

MSSA bacteremia; Patients B & C with diffuse facial cellulitis

involving both eyelids due to MSSA) while on acyclovir regimen

(15-17 mg/kg IV every 8h), serial HSV PCR from blood were

performed.

METHODS: Quantitative real-time PCR was performed using MGB

Alert® HSV Primers and Probe targeting the gD gene of HSV 1 with

a reproducible lower limit of detection of 250 copies/mL of plasma.

HSV typing was performed by amplification of the gB gene followed

by restriction length polymorphism analysis. HSV VL (log copies/

mL) and HSV viremia were characterized. Serum IgG titers and CBC

with differential were determined at various time points.

RESULTS: The decline of HSV VL over time in all patients while on

acyclovir therapy (Figure 1) suggests a linear kinetics (R2 = 0.81-

0.97). The maximum VL ranges from 6.0-7.2 log copies/mL and the

minimum VL before becoming undetectable (>8 days on acyclovir

therapy) ranges from 3.5-5.9 log copies/mL. The elimination rate

constant was 0.03-0.04 h-1 with a half life (assuming minimum VL =

trough) of 17-23 hrs. HSV VL decreased by ~0.5 log copies/mL in 24

hrs. The decrease in HSV viremia coincides with increasing IgG and

ALC in Patients A & C at >2 weeks of illness. All patients improved

after completing at least 2 weeks of IV acyclovir and ~10 days of

antimicrobial therapy (Patient A, cefazolin 75 mg/kg/day; B, clinda

mycin 30 mg/kg/day; and C, cefazolin 83 mg/kg/day). No recurrence

of EH while on suppressive acyclovir regimen (10 mg/kg PO BID)

and vitamin D supplements.

CONCLUSION: We describe the kinetics of HSV type 1 viremia and

noted the decline in HSV VL corresponds with increasing IgG &

ALC. These may be useful in monitoring treatment response to

acyclovir among children with disseminated disease associated

with EH.

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Email: SantosR@mail.amc.edu

Real‐time HSV PCR was performed on the SmartCycler

(Cepheid) using MGB Alert® HSV Primers and Probe (EPOCH

Bioscience) targeting the gD gene of HSV 1 & 2 with a reprodu

cible lower limit of detection of 250 copies/mL of plasma.

Quantification of viral DNA was accomplished by

establishing a standard curve from known amounts of HSV

DNA (EPOCH).

Viral DNA was extracted from plasma samples on the

NucliSens easyMAG extractor (bio Merieux) with internal

control DNA (IC2, EPOCH) added to each sample after nucleic

acid lysis.

HSV typing was performed by amplification of a 148bp

region of the gB gene using the forward primer 5’‐GCATCGTC

GAGGAGGTGGAC‐3’ and the reverse primer 5’‐TTGAAGCGG

TCGGCGGCGTA‐‘3 followed by restriction enzyme digestion

of the amplicon with Bsr I enzyme which recognizes a

sequence polymorphism between the HSV types.

HSV viral load was reported as log copies/mL and the

decline in viremia was characterized.

HSV viremia kinetics: maximum & minimum VL ranges were

the highest and lowest reported viral copies; elimination rate

constant & half life were determined as previously described.

(Atkinson AJ, et al. 2007; Winter ME, 2004)

Serum IgG titers and CBC with differential were determined

at various time points.

FIGURE 1 CASE SERIES

Herpes simplex virus (HSV) viremia had been rarely described

in immunocompetent and more commonly among

immunocompromised children (Stanberry LR, et al. 1994;

Diamond C, et al. 1999) and adults. (Narqi S, et al. 1976;

Berrington WR, et al. 2009)

Disseminated HSV infection had been reported among children

with eczema herpeticum (EH). (Wollenberg A, et al. 2003; Cathcart

SD & Theos A, 2011; Frisch S & Siegfried EC, 2011)

The morbidity and mortality in patients with EH was described

to be associated with HSV viremia. (Wheeler CE, et al. 1966;

Sanderson IR, et al. 1987) This may be due to viral infection of

different organs like the brain, gastrointestinal tract, liver, and

lungs.

Determination of HSV viral load (VL) kinetics from blood by

polymerase chain reaction (PCR) in children with EH has not been

previously reported.

We describe the HSV type 1 viremia kinetics in children with

EH and the decline in HSV VL with increasing IgG and ALC.

We report 3 male children (Patient A, 4 months; Patient B, 7

years; and Patient C, 10 months) with atopic dermatitis

exacerbation and generalized vesicular rash with fever

consistent with EH. Because of worsening disease (Patient A,

with MSSA bacteremia; Patients B & C with diffuse facial

cellulitis involving both eyelids due to MSSA) while on

acyclovir regimen (15-17 mg/kg IV every 8h), serial HSV PCR

from blood were performed.

All patients improved after completing at least 2 weeks of IV

acyclovir and ~10 days of antimicrobial therapy (Patient A,

cefazolin 75 mg/kg/day; B, clindamycin 30 mg/kg/day; and C,

cefazolin 83 mg/kg/day). No recurrence of EH while on

suppressive acyclovir regimen (10 mg/kg PO BID) and vitamin

D supplements (25-OH Vit D<29 ng/mL at presentation).

RESULTS

The decline of HSV VL over time in all patients while on

acyclovir therapy (Figure 1) suggests a linear kinetics (R2 =

0.87-0.97).

Maximum VL range: 6.0-7.2 log copies/ mL

Minimum VL before becoming undetectable (>8 days on

acyclovir therapy) range: 3.5-5.9 log copies/ mL.

Elimination rate constant : 0.03-0.04 h-1

Half life (assuming minimum VL = trough): 17-23 hrs

HSV VL decreased by ~0.5 log copies/ mL in 24 h.

The decrease in HSV viremia coincides with increasing IgG

(from 191-264 mg/dL to 368-374 mg/dL) as well as increasing

absolute lymphocyte counts (ALC, from 3800-6400 cells/μL to

4900-7200 cells/μL) in Patients A & C at >2 weeks of illness.

DISCUSSION

We described the linear kinetics of HSV type 1 viremia in

children with eczema herpeticum and noted the decline in HSV

VL corresponds with increasing IgG and ALC while on therapy.

These may be useful in monitoring treatment response

among children with disseminated HSV disease.

Figure 1. Serial herpes simplex virus (HSV) type 1 determinations by quantitative real-time polymerase chain reaction and

intravenous acyclovir therapy in children with eczema herpeticum. The decline in HSV viral load (, log copies/mL) while on

acyclovir regimen (Days on Acyclovir) suggests a linear kinetics (R2=0.81-0.97, trend line —). HSV viral load decreased by ~0.5 log

copies/mL within 24 hours on acyclovir treatment. The HSV viremia kinetics profile are written as maximum & minimum viral loads

(log copies/ mL), elimination rate constant (h-1), and half life. Other kinetics parameters (volume of distribution, body clearance,

and area-under the concentration time curve) are not determined in the absence of actual viral concentration at start of infection.

We quantified and characterized the HSV type 1 viremia

kinetics in children with eczema herpeticum.

The decline in HSV type 1 viral load while on acyclovir

therapy suggests linear kinetics. There is proportional

decrease in HSV viremia with similar elimination rate

constants and half lives in all patients.

Serial HSV viral load determinations were fitted with a trend

line and showed linear decay over time. (Figure 1) This may be

a function of the antiviral regimen together with other host

factors. There was a decrease in febrile episodes in all

patients with increasing absolute lymphocyte count and IgG

(in Patients A & C) with decreasing HSV viremia.

If either the half life (t ½, ~17-23 hrs) of HSV viremia or the

time at which there is a significant decline (~0.5 log

copies/mL) in HSV viral load are characterized then we may

obtain a repeat blood HSV PCR to guide clinicians in

monitoring response to antiviral therapy.

After ~17-23 hours on adequate antiviral regimen assuming

no viral resistance then the amount of HSV viremia

(copies/mL) should be at least half compared to baseline.

In all patients there was a significant decrease in HSV

viremia (~0.5 log copies/mL) at ~24 hours of treatment. This

occurred before clinical improvement was observed and

becoming afebrile ~72 hours later.

The other HSV kinetics profile may have clinical application.

We determined the HSV VL on day 7 of acyclovir therapy and

assumed that it was the minimum viral load before becoming

undetectable (trough).

By day 7 of treatment there were no fever episodes in all

patients, no new skin lesions, and with increasing leukocytes

in their CBC. This corresponds to at least day 9 of illness in all

patients.

Improved clinical outcome requires prompt recognition of

EH since delayed (>1 day) acyclovir initiation is associated

with prolonged length of hospital stay. (Aronson PL, et al.

2011) In our patients, systemic antiviral agents were given

within 24-48 hours of clinical presentation.

More research is needed to validate our preliminary results

i.e. involving more patients including pregnant women,

newborns, and the immunosuppressed as well as those

associated with HSV type 2 infection.