Cerebrospinal fluid (CSF) specimens from 22 allogeneic bone marrow transplant patients with central nervous system (CNS) symptoms (cases) and 107 patients who were immunocompromised but did not have CNS symptoms (controls) were assayed for human herpesvirus 6 (HHV-6) DNA. HHV-6 exhibits a wide cell tropism in vivo and, like other herpesviruses, induces a lifelong latent infection in humans. They establish latency after primary infection, and viral reactivation has been associated with a variety of complications in immunocompromised patients, especially after allogeneic hematopoietic cell transplantation (HCT). He had no notable medical history; in particular, there were no signs of a preexisting immunodeficiency. The productive nature of the infection was confirmed by electron microscopy and immunohistochemical staining. Recently we reported that 1% of newborns have congenital human herpesvirus 6 (HHV-6) infection and that most of these congenital infections (86%) resulted from chromosomally integrated HHV6 (CI-HHV-6) [1, 2]. A reativação do herpesvírus humano 6 (HHV-6), em um hospedeiro com AIDS, pode resultar em meningoencefalite aguda difusa.
Nós descrevemos a epidemiologia, a clínica e resultados encontrados em cinco pacientes com diagnóstico de HIV/AIDS e comprometimento do sistema nervoso central (SNC) devido ao HHV-6. Hall’s research suggests that a quarter of all emergency-room visits for children less than a year old are due to HHV-6 infection. HHV-6 was found in most explanted livers of patients with ALF of unknown cause. A reação em cadeia da polimerase (PCR) de amostras do líquor foi positiva para HHV-6 em todos os pacientes. O HHV-6 deve ser incluído entre os patógenos emergentes oportunistas que comprometem o SNC de pacientes com AIDS. Human herpesvirus 6 (HHV-6) is a member of the Betaherpesvirinae subfamily and was discovered to be a cause of a lymphoproliferative syndrome in 1986 by Salahuddin et al1. Like other members of this family, HHV-6 causes a primary infection during childhood that can be asymptomatic or can manifest as a febrile illness with or without exanthem subitum.
The seroprevalence of HHV-6 IgG antibodies in children over two years of age is as high as 80%2. HHH-6 has been classified into two variants, A and B. Variant B is related to roseola infantum and febrile illness in children; variant A is generally associated with lymphoproliferative disorders and central nervous system involvement in immunocompromised patients2. Discovery and ClassificationHHV-6 was first isolated from the peripheral blood mononuclear cells of patients with lymphoproliferative disorders in attempts to characterize novel lymphotropic human viruses (1). Recently, HHV-6 has been associated as an emerging pathogen in patients with AIDS and recipients of bone marrow and solid organ transplants. However, there are few reports related HHV-6 to the immunodeficiency caused by HIV/AIDS4. Several lines of evidence suggest that HHV-6 may also function as a cofactor in AIDS, accelerating the progression towards the full-blown disease.
Of the saliva samples which were collected from the children from 2 to 25 months of age, HHV-6 DNA was identified in 47%, but the HHV-6 DNA was not consistently detected among any child’s samples. Clinical and neurological examinations were performed on all the patients. All patients included in the study displayed neurological signs or symptoms during the physical examination and showed no contraindications for undergoing a lumbar puncture. may produce disease far more serious . Blood cultures for common bacteria, fungi and mycobacteria and CD4 + T cell counts were made for all the patients. Magnetic resonance image MRI was available from three patients. The definitive diagnosis was made by DNA detection of HHV-6 in CSF by polymerase chain reaction (PCR).
Aliquots of CSF samples were stored at -70°C until they were analyzed by HVM (Herplex, Genomica, Spain). Specimens were tested by HVM following the manufacturer’s instructions. The HVM is a multiplex PCR device that amplifies and detects the genomes of Herpes simplex-1 (HSV-1) and 2 (HSV-2) and Herpes varicella-zoster (HVZ) in a single tube as well as the genomes of cytomegalovirus (CMV), Epstein-Barr virus (EBV) and HHV-6. Every tube has an internal amplification control, and the amplified products are detected by hybridization with specific probes in a microplate. The analytical sensitivity reported by the manufacturer is two genome equivalents for HSV-1, HSV-2 and EBV, and between 2 and 20 genome equivalents for HVZ, HHV-6 and CMV4. The one near the left end of each DR contains reiterations of the hexanucleotide GGGTTA interspersed by related but different sequences, constituting the heterogeneous telomeric-like region het(GGGTTA)n. The median age at the time of HHV-6 meningoencephalitis diagnosis was 42 years, and the median CD4 T cell counts was 70 cells/µL.
The primary risk factor for HIV (human immunodeficiency virus) infection was intravenous drug use (IVDU) in 2 patients, unprotected homosexual contact in two and unprotected heterosexual contact in one. This strain was found to replicate efficiently in Thy/ Liv implants and to induce severe depletion of thymocytes, supporting the hypothesis that it may act as an immunosuppressive agent in vivo. Two of them presented histories of disseminated cryptococcosis with meningeal involvement; the other three had been diagnosed with disseminated tuberculosis, and one of them had had meningeal involvement. Laboratory findings confirmed that there was no evidence of activity associated with these AIDS-defining illnesses. None of the patients had received antiretroviral therapy. Pellett speculated there may even be one or two undiscovered types lurking in human cells. Three of them had signs and symptoms of meningeal compromise (headache, photophobia, vomiting and neck stiffness).
Only one of them presented seizures, and another one had signs of encephalitis (agitation, confusion and temporo-spacial disorientation). Biochemical examination of CSF samples showed hyperproteinorrachia in three of them, and there were normal levels between 15 and 45mg in the other two. Examinations of the CSF samples for common bacteria, fungi and parasites were negative. The polysaccharide cryptococcal capsular antigen in the CSF was negative in the two patients with a history of meningeal cryptococcosis. Imaging techniques like MRI were available for three of the patients. The images showed cortex and cerebellar atrophy related to advanced HIV/AIDS in two patients, and in one of them, the neuroimages were compatible with vasculitis. PCR by the HVM of CSF specimens was positive for HHV-6 and negative for HSV-1, HSV-2, VZV, EBV and CMV in all the patients.
This genetic polymorphism can be analyzed at three different levels of complexity. After PCR confirmed the presence of HHV-6, only one patient was able to receive specific treatment with ganciclovir plus foscarnet during a six-week course of both antiviral treatment, resulting in the improvement of neurological symptoms. After that, this patient was started on a secondary prophylaxis regimen with the same two antiviral drugs and highly active antiretroviral therapy (HAART). The cells were counted in a Coulter counter and divided into aliquots for the different assays. Two years later, this patient remains in good clinical condition; the secondary prophylaxis can be interrupted, the CD4 T cell count is >350 cells/µL and the plasma RNA-HIV viral load is undetectable. The human herpesvirus 6 meningoencephalitis diagnosis was confirmed postmortem by PCR of CSF samples in patients 2, 3 and 4. For this reason, it was not possible to initiate antiviral therapy.
Intravenous acyclovir therapy plus ceftriaxone was initiated for possible HSV-1 meningoencephalitis in patient 1, who died four days after admission (Table 1). To our knowledge, there are only a few reports of HHV-6-induced meningoencephalitis in HIV patients in the medical literature. However, the role of HHV-6 in the pathogenesis of CNS disease remains unclear4,5. Bossolasco et al.5 evaluated the frequency of HHV-6 DNA detection in the CSF of patients infected with HIV/AIDS and its possible relation to neurological disease. HHV-6 was found by PCR in only 2.2% of 365 patients. The detection rate was substantially lower than those found for CMV, EBV and JCV (16%, 12% and 9%, respectively)4. Liedke et al.6, in contrast, reported that HHV-6 DNA was found in the CSF samples of 30% of HIV-infected patients with neurological disease.
Even though two of the patients in our series had histories of cryptococcal meningitis and three had previous diagnoses of disseminated tuberculosis, no evidence of these pathogens was found in the laboratory specimens. The evidence suggesting a relation between HHV-6 and CNS disease is based on the detection of HHV-6 DNA in the CSF. At least one component of the cell receptor permitting virus anchorage to the cell surface differs according to HHV-6 species: HHV-6A uses CD46, a regulator of complement activation expressed on all nucleated cells, while CD134 (also called OX40), a member of the tumor necrosis factor (TNF) receptor superfamily present only on activated T lymphocytes, functions as a specific entry receptor for HHV-6B (39, 40). The fact that HHV-6 was found in all of the CSF samples taken from our patients suggest that, at least in these patients, this finding is not incidental. HIV and HHV-6 may have a synergistic activity; both of them infect and replicate in T CD4 lymphocytes, and furthermore, HIV may enhance the replication and dissemination of HHV-62. DNA was extracted from frozen pellets by proteinase K digestion and purified by phenol-chloroform extraction by standard techniques. HHV-6 may be considered an emergent pathogen in AIDS patients that can act directly or indirectly or can interfere in different components of the immune system4-6.
Moreover, infection with HHV-6 may predispose patients to superinfection with other viruses, especially EBV, CMV and HHV-75,6. Clinical reactivation in the CNS leads to an asymptomatic infection or a severe meningoencephalitis with fever, headache, seizures, demyelinating lesions and, rarely, an acute transverse myelitis with dysesthesia of the lower extremities, dysuria and dyschezia. The majority of immunodepressed patients with HHV-6-induced meningoencephalitis presented with fever, seizures, focal neurological signs and varying degrees of altered consciousness5. This is the most frequent clinical presentation of HHV-6 neurological involvement in this kind of patients. The most common clinical picture in our series was meningeal syndrome associated with fever and seizures. Diagnosis of HHV-6 meningoencephalitis includes neurological manifestations, CSF analysis positive for HHV-6 DNA and the absence of any other identifiable pathogens. All of the patients described in this report presented these three clinical and laboratory findings.
Less frequently, HHV-6 infection of the CNS can present with neuropsychiatric manifestations, including dementia3. MRI generally reveals the meningeal contrast-enhance signal intensity abnormality in the medial temporal lobe and hyperintense lesions in the insula region, the amygdale and the inferior frontal lobe similar to herpes simplex type 1. Some patients can present periventricular lesions hypointense in T1 and hyperintense in T2 compatible with vasculitis damage7,8. However, MRI brain findings might be completely normal in some cases, especially in immunocompromised patients. Those genes are transcribed in the absence of de novo protein synthesis, and this step is followed by the transcription/expression of early (E) and late (L) genes. If MRI changes of hypointensities in T1 and hyperintensity in T2 are not specific for vasculitis, the pathogenic effect of all neuroherpesvirus infections is consistent with these findings. Since its introduction in 1990, the PCR technique has contributed to the diagnosis of neurological infection caused by herpesvirus and is the standard method for the diagnosis of this agent.
1). The profit advantage with this technique is increased when affected patients have CSF alterations such as pleocitosis and protein elevation. However, there are some reports of meningoencephalitis in immunosuppressed hosts with normal CSF. For all these reasons, PCR has displaced the serological tests and the intratecal synthesis of antibodies for the diagnosis of neuroherpesvirus infections. When the sample is taken within the first ten days of the onset of the neurological symptoms, the rate of PCR-positive results is higher than after ten days have elapsed. In relation to the diagnosis of CNS infection due to HHV-6, PCR is highly sensitive and specific for the detection of etiological agents, nearly 98% and 94%, respectively9. HHV-6 is often detected in plasma, suggesting that the virus may spread to the CNS from the blood.
However, Bossolasco el al.5 affirm that the target discrepancies between the CSF and plasma HHV-6 findings support the hypothesis of an active brain infection by herpesvirus, rather than a spread across the blood-brain barrier. Also, these authors hypothesize that HHV-6 may be found after reactivation. If all the patients included in this series had been given HAART, it was their own decision not to follow the indicated treatment. The last patient was started on HAART after the acute period of HHV-6 disease, and he presented a good virological, clinical and immunological response with immune restoration. He can stop the secondary prophylaxis for HHV-6. Ganciclovir and foscarnet, either alone or in combination, proved to be the most effective therapy for immunosuppressed patients with HHV-6 related to neurological disease9. This phenomenon was further reported to be present in human cells in vivo, including cells which can be transmitted as germinal cells to offspring and hematopoietic stem cells transferred to a transplant recipient (64, 65).
None of our patients were treated with cidofovir, because this antiviral agent is not available in Argentina. In our opinion, CNS involvement due to HHV-6 should be considered in all patients with a diagnosis of meningoencephalitis, advanced HIV/AIDS disease and T CD4 cell counts less than 200 cells/µL. Transmission electron microscopy of a Thy/Liv implant harvested 11 d after inoculation with HHV-6AGS. MRI can show, in some cases, vasculitic lesions or demyelination of the white matter, as can be seen with other neuroviruses. The diagnosis is confirmed by the detection of the genome of HHV-6 by PCR. Early diagnosis followed by specific therapy based on ganciclovir and foscarnet plus HAART can improve the poor prognosis of this type of patient.