Human herpesvirus 6 (HHV-6) belongs to the Herpesviridae family and is closely related to cytomegalovirus (CMV) (1). The infection associated with this virus has been described as frequent in solid organ transplant recipients and it usually results from the reactivation of a previous latent infection (2). In the general population, about 90% of people have been infected with HHV-6 by the end of the first two years of life (3, 4). The primary infection with this virus in childhood is usually symptomatic, presenting as acute benign febrile illness. After infection, HHV-6 remains latent, but immunosuppressive states can induce replication. In immunosuppressed patients, infection with HHV-6 can be life-threatening, due to the presentation of severe forms of end-organ disease as intersticial pneumonitis, (5) encephalitis (6, 7) and severe aplasia (8). Moreover, as with CMV, HHV-6 infection in transplant recipients can lead to indirect effects such as the induction of acute rejection episodes, (2) and coinfection with other viruses such as CMV (9–11) among other complications (12).
Without prophylaxis, CMV-seronegative recipients from CMV-seropositive donors (D+/R−) have a risk of contracting primary CMV disease of up to 50% and about 18% with 100-days of ganciclovir or valganciclovir prophylaxis (13). Currently, the pp65 antigenemia assay or plasmatic viral-DNA monitoring are the best strategies to control the spread of infection with this virus in CMV-seropositive recipients. With regards to HHV-6 there is a lack of information about the incidence of primary infection in seronegative-solid organ transplant recipients and the cost-effectiveness of HHV-6 viral load monitoring in this context. For these reasons we aimed to prospectively evaluate the risk of HHV-6 infection in seronegative-solid organ transplant recipients.
We conducted a prospective cohort study at the Hospital Clinic, a 850-bed tertiary-care center in Barcelona, Spain. Between January 2004 and December 2004, all patients undergoing solid-organ transplantation in our center were included for follow-up.
For each patient, the variables of age, gender, type of transplant, immunosuppressive therapy, acute rejection episodes and prophylaxis or treatment either with ganciclovir or valganciclovir were prospectively collected.
Blood samples were obtained immediately pretransplant, and at 7, 14, 21, 28, 45, 60, 75, and 90 days posttransplant.
The presence of immunoglobulin (Ig) G antibodies against HHV-6 was determined pretransplant and one year posttransplant in recipients and in donors by means of an indirect immunofluorescence method (PANBIO Inc, Columbia, MD). Negative results were repeated to confirm the results. Indeterminate or low-positive results were categorized as positive serology.
HHV-6 and CMV Viral Load Measurement
We determined the HHV-6 and CMV viral load in transplant recipients with negative Ig G antibodies against HHV-6. HHV-6 and CMV viral load was determined by a commercial kit (Affigene HHV-6 VL and Affigene CMV VL tests, Bromma, Sweden), based on the amplification and detection of a sequence located in the U22 gene for HHV-6 and in the major immediate early gene for CMV. After specimen preparation, DNA was PCR amplified using HHV-6 and CMV specific complimentary primers, respectively. Hybridation of the amplified products to oligonucleotide and detection of the amplified products was done by colorimetric determination.
The study design was approved by the Institutional Review Board of the Barcelona Hospital Clínic. Patients gave informed consent for clinical data and collection of blood samples.
For comparison between groups, we used chi-square test (or Fisher exact test if necessary). A probability value <.05 was considered to be significant.
In all, 193 consecutive solid-organ transplant patients were included in the study (99 kidney, 64 liver, 20 heart and 10 kidney-pancreas). All patients received surgical antibiotic prophylaxis. Prophylaxis for Pneumocystis jiroveci with trimethoprim-sulfamethoxazole (160 mg/800 mg) was administered every day during the first six months posttransplantation. Table 1 show the immunosuppressive schemes of the studied population.
Seven patients had negative Ig G antibodies against HHV-6 (prevalence 3.6%). Looking at the type of transplant, seronegativity was more frequent in kidney recipients (6%) than in other recipients (Table 2). Gender and mean age (51.22 vs. 51.31 years, respectively) between HHV-6 positive and negative recipients showed no statistical differences. Demographic and transplant features are shown in Table 1. We analyzed eight samples from each of the seven seronegative patients.
Donor HHV-6 Serology
Ig G antibodies against HHV-6 were available for four donors, of which only one was positive.
CMV Viral Load
Four patients had positive CMV viral load measurements. The highest viral load was 1,075 copies. None of the seven HHV-6 seronegative patients had CMV disease.
One-year Follow-up Antibodies against HHV-6
Four patients (57%) had positive HHV-6 serology in the follow-up. Of them, only one patient had positive HHV-6 viral load determinations.
Clinical Course of the Patient with a Primary HHV-6 Infection
Patient two received urgent heart transplantation due to a massive left ventricular acute myocardial infarction. Posttransplant prophylactic treatments were administered following our internal guidelines. Itraconazole was administered in the first four days posttransplantation and was switched to intravenous liposomal amphotericin B due to prolonged orotracheal intubation and prolonged broad-spectrum antibiotic prophylaxis. After 10 days posttransplant, the patient was started on oral acyclovir and oral itraconazole was reintroduced. He did not receive CMV prophylactic treatment. On day 16 posttransplant the patient developed mild cholestatic hepatitis (AST 126 IU/L, ALT 214 IU/L, Alkaline phosphatase 1011 IU/L), pain in the upper-right abdomen, nausea, vomiting and diarrhea, without fever. An abdominal ultrasound showed a slightly enlarged gallbladder without signs of cholecystitis. The abdominal computed tomograph (CT) scan and retrograde endoscopic cholangiography were normal. No liver biopsy was performed. On day 23, HHV-6 viral load was 78,002 copies/ml (4.89 viral load logs), and in the next 24 hr he was started on intravenous ganciclovir. CMV pp65 antigenemia was negative. On day 44, he was started on oral valganciclovir. The patient required parenteral nutrition and the digestive symptoms progressively improved so oral nutrition was reintroduced. On day 88 posttransplantation, he was discharged from the hospital.
Our main findings were: i) the prevalence of HHV-6 seronegativity in transplant recipients is very low, and ii) symptomatic HHV-6 primary infection is not frequent in adult solid-organ transplant patients.
In contrast with CMV primary infection, primary HHV-6 infection in seronegative recipients has some unresolved questions due to a lack of information: the incidence and severity of infections, the usefulness of monitoring HHV-6 replication and the need for prophylaxis with ganciclovir or valganciclovir. We decided to investigate the incidence of primary HHV-6 infection in our patients because of a previous experience that had a fatal outcome in one kidney-pancreas transplant patient (6). In our cohort of transplanted patients, primary HHV-6 infection was detected in only one patient. Thus, the incidence of symptomatic primary HHV-6 infection is probably less frequent than the rates reported for primary CMV infection. Furthermore, the only infected patient did not exhibit severe end-organ disease. Whether cholestatic hepatitis in this patient is secondary to HHV-6 infection is uncertain due to the absence of histological analysis of a liver biopsy. Furthermore, to attribute the rest of nonspecific symptoms of this patient to HHV-6 infection is controversial in the setting of a recent transplanted patient. In our series, HHV-6 infection in seronegative patients reached 57% (4 patients), with positive antibodies after one year. This high rate of asymptomatic HHV-6 primary infection could be due to the use of ganciclovir and valganciclovir prophylaxis in our transplanted patients. Thus, is reasonable to use prophylactic treatment in HHV-6 seronegative recipients, although we found no severe infections of this virus in our patients.
A recent study found an incidence of HHV-6 infection of about 14% in solid-organ transplant patients receiving either oral ganciclovir or valganciclovir for the prophylaxis of CMV D+/R− serostatus (14). Although pretransplant serology was unknown, this study shows that the incidence of HHV-6 infection in that cohort was higher than in ours. In our study, four of seven HHV-6 seronegative patients received ganciclovir or valganciclovir prophylaxis (the patient with a primary infection received intravenous ganciclovir after the first detection of a positive HHV-6 viral load). The clinical manifestations in the patient with HHV-6 primary infection were unspecific: predominating digestive symptoms, and no fever. A lack of specific symptoms can lead to misdiagnosis and unnecessary complementary explorations. The use of specific tests for the diagnosis of HHV-6 replication must be taken into account in atypical symptoms or signs in seronegative transplant patients. However, in our opinion, HHV-6 viral load monitoring in this group of patients is not cost effective.
The greatest limitation of our study is the small sample of patients studied due to the low prevalence of HHV-6 seronegativity in patients undergoing transplantation. The inability to differentiate between variant A and B of HHV-6 strains is another limitation. Whether the A or B variant of HHV-6 causes more or less severe infections is uncertain in transplanted patients. Larger cohorts of patients with HHV-6 replication monitoring allowing for the differentiation of variants A and B are needed to clarify this point.
In conclusion, we found a low rate of symptomatic primary HHV-6 infection in solid organ transplant patients, although more than half got infected with this virus during follow-up. However, a larger study is needed in order to define the risk and the spectrum of this infection in seronegative patients.
1. Campadelli-Fiuma G, Mirandola P, Menotti L. Human herpesvirus 6: an emerging pathogen. Emerg Infect Dis
1999; 5: 353.
2. Humar A, Kumar D, Caliendo AM, et al. Clinical impact of human herpesvirus 6 infection after liver transplantation. Transplantation
2002; 73(4): 599.
3. Okuno T, Takahashi K, Balachandra K, et al. Seroepidemiology of human herpesvirus 6 infection in normal children and adults. J Clin Microbiol
1989; 27: 651.
4. Zerr DM, Meier AS, Selke SS, et al. A population-based study of primary human herpesvirus 6 infection. N Engl J Med
2005; 352: 768.
5. Singh N, Donald C, Timothy G, Marino I. Human herpesvirus-6 infection in liver transplant recipients: documentation of pathogenicity. Transplantation
1997; 64: 674.
6. Benito N, Ricart MJ, Pumarola T, et al. Infection with human herpesvirus 6 after kidney-pancreas transplant. Am J Transplant
2004; 4(7): 1197.
7. Singh N, Paterson DL. Encephalitis caused by human herpesvirus-6 in transplant recipients: relevance of a novel neurotropic virus. Transplantation
2000; 69: 2474–2479
8. Rossi C, Delforge ML, Jacobs F, et al. Fatal primary infection due to human herpesvirus 6 variant A in a renal transplant recipient. Transplantation
2001; 71: 288.
9. Humar A, Malkan G, Moussa G, et al. Human herpesvirus-6 is associated with cytomegalovirus reactivation in liver transplant recipients. J Infect Dis
2000; 181: 1450.
10. DesJardin J, Cho E, Supran S, et al. Association of human herpesvirus 6 reactivation with severe cytomegalovirus-associated disease in orthotopic liver transplant recipients. Clin Infect Dis
2001; 33: 1358.
11. Dockrell DH, Prada J, Jones MF, et al. Seroconversion to human herpesvirus 6 following liver transplantation is a marker of cytomegalovirus disease. J Infect Dis
1997; 176: 1135.
12. Benito N, Moreno A, Pumarola T, Marcos MA. Human herpesvirus type 6 and type 7 in transplant recipients. Enferm Infecc Microbiol Clin
2003; 21: 424.
13. Humar A, Payá C, Pescovitz MD, et al. Clinical utility of cytomegalovirus viral load testing for predicting CMV disease in D+/R− solid organ transplant recipients. Am J Transplant
2004; 4(4): 644.
14. Razonable RR, Brown RA, Humar A, et al. Herpesvirus infections in solid organ transplant patients at high risk of primary cytomegalovirus disease. J Infect Dis
2005; 192: 1331.