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Human herpesvirus 6: A virus in search of a disease
Clinical Microbiology Newsletter February 15, 1993
Vol. 15, No. 4
Human Herpesvirus 6: A Virus in Search of a Disease Olajide Agbede, Ph.D. Department of Pathology University of Texas Medical Branch Galveston, Texas 77555-0743
The discovery of human herpesvims type 6 (I-IHV-6), formerly known as human B-lymphotropic virus (HBLV), followed attempts to cultivate peripheral blood mononuclear cells from patients with lymphoproliferative disorders (1). The suspicion that large, refractile cells bearing intranuclear and/or intracytoplasmic inclusion bodies in culture contain virus was confirmed by electron microscopic examination. These refractile, often binucleated cells were reproduced on transmission of the initial viral isolates to freshly isolated phytohemagglutin-stimulated human leukocytes obtained from umbilical cord blood, adult peripheral blood, bone marrow, and spleen. The detection of viral signals by in situ nucleic acid hybridization and the presence of viral antigens in culture as detected by indirect immunofluorescence are indications that the virus productively infects cells. Infected lymphocytes are lysed upon release of the virus. Other tissue culture properties of the virus include maturation in the nucleus of infected cells and release of abundant viral particles into the extracellular fluid. Although the virus was originally isolated from B cells, phenotypic characterization of the target cells for virus production showed that the majority of them possessed features descriptive of immature T-lymphocytes as demonstrated by the expression of CD7, CD2, and CD4 surface antigens (2). SubCMNEEJ 15(4)25-32,1993
sequent studies showed a propensity of the virus to infect a wide array of cell lines of hematopoietic origin, including megakaryocytes (3). In addition, the virus has shown tropism for glioblastoma cells (4).
The V i r u s Human herpesvirus type 6 has an icosahedral core symmetry of 162 capsomers enveloped in a lipid membrane. Its genome is a double-stranded DNA of at least 110 kilobase pairs, and its restriction endonuclease cleavage products show it to be distinct from other well-characterized human herpesviruses and animal lymphotrophic herpesviruses (5). The mode of transmission of HHV-6 is not known. Like the cytomegalovirus (CMV) with which it shares some genetic properties (6--8) and the ability to produce asymptomatic primary and recurrent infections (8), HHV-6 is widespread among the general population (9-11). The virus is excreted into the saliva, as shown by the 100% isolation rate from infected persons reported by two groups of investigators (12,13). Interestingly, the presence of the virus in the saliva precludes the ability to detect HIV-1 from this anatomic site, perhaps because they compete for similar cell receptors. Seroepidemiologic studies conducted by many investigators (11, 14) have shown that viral antibody is very common among healthy infants and adults. Infection is probably acquired very early in life as demonstrated by the findings of a study of children under age 5. Virusspecific antibodies are detectable as Elsevier
early as 1 mo after birth. Thereafter, prevalence of antibodies in this population declines over the ensuing 4 to 6 mo, presumably because they are passively acquired maternal antibodies; by 11 mo of age, antibody prevalence rises to a level above 60% and finally to a level of 98% among 17-yr-olds. Defining a D i s e a s e State There has been significant controversy in defining the disease manifestation caused by HHV-6 in humans. Although the virus has been implicated as the causative agent of exanthem subiturn-roseola infantum (15), a childhood disease rarely seen in children beyond the age of 3, it has not been possible to attribute unequivocally a disease entity to the presence of the virus in the adult population. Consequently, a number of
In This Issue Human Herpesvirus 6: A Virus in Search of a Disease . . . . . . . . . . . . .
25
Is this a virus with multiple disease entities or is it just associated with other viral diseases?
Gas Gangrene Caused by
Clostridium bOrermentans in an Immunodeficient Patient . . . . . . . . A case report
28
Letters to the Editor . . . . . . . . . . . .
30
Erratum . . . . . . . . . . . . . . . . . . . . . .
32
T.W. Klein. Psychoimmunology and Infection. CMN 15(3):17-22. February 1, 1993 0196-4399/93/$0.00 + 06.00
syndromes have been described in which the presence of the virus directly or indirectly provides the basis for an etiologic association with the pathogenesis of the respective syndromes. Human herpesvirus type 6 was originally isolated from the peripheral blood mononuclear cells of adult patients with lymphoproliferative disorders. High titers of antibodies to the virus exist in patients with Hodgkin's disease, African Burkitt's lymphoma, acute lymphoblastic leukemia, acute sarcoidosis, and Sjogren's syndrome (16). Apparently, it shares with CMV the ability to produce opportunistic infections in the immunocompromised host. Evidence for the ability of the virus to cause infection in immunocompromised hosts stems from studies conducted by Krueger and colleagues (17) on the pathogenesis of lymphoproliferative disorders in AIDS patients. Malignancies in these patients resembled those observed in allotransplantation and other immunodeficient states in which reactivation of Epstein-Barr virus (EBV), another herpesvirus, is thought to play a role. This observation reinforces the suggestion that HHV-6 might similarly be involved in the pathogenesis of lymphoproliferative disorders (18,19). Two histologically distinct lesions, atypical polyclonal lymphoproliferation (APL) and malignant lymphoma (ML), were associated with the presence of HHV-6. Using the Southern blotting technique and polymerase chain reaction (PCR), the genome of the virus was demonstrated in these lesions. Indeed, the serologic prevalence of HHV-6 antibody in all APL cases supported the virologic evidence of an infection and argues for a case of viral reactivation in affected tissues. HHV-6 has also been studied along with the other lymphotropic herpesviruses, EBV, and CMV, in the search for a distinct disease entity associated with the virus. Acute EBV infection is
mostly asymptomatic, leading to the speculation that HHV-6 might behave similarly. About 80-90% of children above 3 yr of age show serologic evidence of past infection by HHV-6. Eartier in the course of studies to explore the possible acute infections in the adult population attributable to HHV-6, an association with a chronic mononucleosis-like illness was established. The features of the disease strongly suggest one previously described in connection with epidemic neuromyasthenia (20, 21). It is characterized by chronic fatigue, myalgia, headache, fever, and psychiatric symptoms (22). Its immunologic markers are atypical lymphocytosis and a high ratio of helper to suppressor lymphocytes, and abnormalities related to immunoglobulin production. Significant increase in antibodies to a number of related and unrelated viruses, including human herpes simplex virus (HSV), CMV, EBV, and measles virus, have been described in these patients. Nevertheless, the production of heterophile antibody is not associated with HHV-6 infection (23). Recent reports indicate that HHV-6 might be responsible for active viral hepatitis in some patients presenting with a mononucleosis-like syndrome that cannot be attributed to other agents of sporadic viral hepatitis by existing clinical and laboratory criteria (6). An evaluation of the laboratory data of 27 patients with mononucleosis-like illness, in which EBV and CMV have been excluded on the basis of negative heterophile antibody test and patterns of immunologic response, showed that the patients have had active viral hepatitis, a syndrome typically accompanied by hepatic cell necrosis. The blood of the patients displayed atypical lymphocytosis and abnormally high aspartate aminotransferase level. Serum bilirubin levels were conspicuously high in these patients. Serologic tests for syphilis, hepatitis A virus (HAV), hepatitis B vi-
rus (HBV), CMV, and EBV were all negative. The mechanism by which HHV-6 produces the aforementioned syndromes is not clearly understood. On one hand, the virus has been associated with infectious mononucleosis (IM), which apparently represents the manifestation of an immunologically competent host to the presence of the virus. IM-like syndromes have been known to accompany infections with many other viruses and may not indicate a disease entity unique to the virus. It is generally seen in infections of lymphocytes, including those caused by CMV, EBV, varicella zoster, and vaccinia viruses. It is possible that IM resulting from primary HHV-6 infection, unaccompanied by any other viral infection, would have passed unnoticed, as is frequently the case with acute infections of human herpesvirus (22). On the other hand, APL, with which the virus has also been associated, represents the response of an immunodeficient host to the persistence of virus in tissues. HHV-6 was seen in association with HIV-1 in lymphoid tissues of APL and ML cases studied by Krueger et al. (17). However, immunosuppression does not appear to account fully for the pathogenic role of the virus in the development of lymphoproliferative diseases seen in HIV-positive patients because similar disease occurred in HIV-negative patients. Presumably, these lymphoproliferative diseases occurred as a result of some underlying immune defect(s) in these patients. The observation that EBV presents similar lymphoid diseases in HIV patients suggests an indirect effect of both viruses on cellular proliferation.
Effect on T Cells Recent reports indicate that HHV-6 has the ability to modulate the expression of surface antigenic determinants of T lymphocytes (24). In an experi-
No responsibility is assumed by the Publisher for a n y injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from a n y u s e or operation of any methods, products, iustmctions or ideas contained in the material herein. No suggested test or procedure should be carried out unless, in the reader's judgment, its risk is justified. Because of rapid advances in medical seiencas, we recommend that the independent verification of diagnoses and drug dosages should be made. Discussions, views, and recommendations as to medical procedures, choice of drugs, and drag dosages are the responsibility of the authors. NOTE:
Clinical Microbiology Newsletter (ISSN 0196-4399) is issued twice monthly in one indexed volume per year by Elsevier Science Publishing Co., Inc., 655 Avenue of the Americas, New York, NY 10010. Subscription price per year. $145.00 including postage and handing in the United States, Canada, and Mexico. Add $56.00 for postage in the rest of the world. Second-class postage paid at New York, NY and at additional mailing offices. Post~naster:. Send address changes to Clinical Microbiology Newsletter, Elsevier Science Publishing Co., Inc., 655 Avenue of the Americas, New York, NY 10010.
26
0196-4399/93/$0.00 + 06.00
© 1993 Elsevier Science Publishing Co., Inc.
Clinical Microbiology Newsletter 15:4,1993
ment to define the target population of cells within the immune system that are infected by the virus, it was shown that the two major subpopulations of T cells bearing the post-thymic stage markers CD3 ÷, CD4 ÷, C D 8 and CD3 ÷, CD4-, CD8 ÷ were susceptible to productive infection by the virus (25). Productive infection of cells carrying C I M , CD8 ÷ phenotypic markers induced de novo expression of CD4 without any alteration of the expression of the CD8 surface antigenic marker. This phenomenon has implications for dual infections involving HHV-6 and another virus that is dependent on the expression of CD4 molecules to initiate an infectious process. Under such circumstances up-regulation of the expression of CIM would expand the range of T cells susceptible to infection. This would accelerate the cytopathic effect of cells as has been reported in HHV-6 infection of normal T lymphocytes with CD4-, CD8 ÷ phenotypic markers subsequently exposed to HIV-1 (26). At the same time, the depletion of CD4 ÷ T cells in dual infections involving HHV6 and another virus would result in serious consequences for the "helper" function of the immune system. HHV-6 down-regulates the expression of C D 3 T cell antigen receptor (CD3/TCR) complex, another membrane marker that plays a vital role in the normal functioning of mature T cells (25). The down-regulatory effect of the virus on the expression of this protein complex is observed only in T cells infected by the virus and is not seen in cells infected by other human herpesviruses. CD3/I'RC complex promotes antigen recognition of immunocompetent T cells and also acts as a signal lransducer to effect the cascade of intracellular events that culminate in responsiveness to proliferative signals (27). Therefore, down-regulation may compromise the interaction of T cells with other components of the immune system. Immunologic defects could ensue as a result of the imbalance created by shutting off the antigen recognition function of the T cells. Immunologic defects have been reported in many conditions in which high titers of antibody to HHV-6 have been found (17, 22, 24, 28). It is not always clear whether such Clinical Microbiology Newsletter 15:4,1993
defects represent part of the outcome of the disease or whether they are part of the consequences of reactivation infection by HHV-6, in which case some degree of immunosuppression would have preceded the reactivation of the virus. Summary It is abundantly evident that HHV-6 infects a variety of cells in the immunologic system and that a variety of symptoms or manifestations are produced, many nonspecific, chronic, or self-limited. Serologic evidence would suggest that patients with mononucleosis-like syndrome and hepatitis described in association with HHV-6 are immunocompetent individuals with acute infection. Serologic diagnosis of infection by viruses with potential for chronicity and latency as HHV-6 may be difficult because the occurrence of IgG and IgM antibodies may not always indicate primary infection. The need for sensitive and specific diagnostic assays is necessary as clinicians become increasingly aware of the potential for acute infections by this viIllS.
References 1.
2.
3.
4.
5.
6.
7.
8.
Salahuddln, S. Z. et al. 1986. Isolation of a new virus, HBLV, in patients with lymphoproliferative disorders. Science 234:596-601. Lusso, P. et al. 1987. Diverse tropism of human B-lymphotropic virus (human herpesvirus 6). Lancet 2:743-744. Lusso, P. et al. 1988 In vitro cellular tropism of human B-lymphotropic virus (human herpesvirus-6). J. Exp. Med. 167:1659-1670. Ablashi, D. V. et al. 1987. HBLV (or HHV-6) in human cell lines. Nature 329:207. Josephs, S. F. et al. 1986. Genomic analysis of the human B-lymphotropic virus (I-[BLV). Science 234:601-603. Biberfeld, P. et al. 1987. Ultrastructural characterization of a new human Blymphotropic DNA virus (human herpesvirus 6) isolated from patients with lymphoproliferative disease. J. Natl. Cancer Inst. 79:933-941. Efstathiou, S. et al. 1988. DNA homology between a novel human herpesvirus (HHV-6) and human cytomegalovirus. Lancet 2:63-64. Steeper, T. A. et al. 1990. The spectrum © 1993 Elsevier Science Publishing Co., Inc.
of clinical and laboratory f'mdings resuiting from human herpesvirus-6 (HHV-6) in patients with mononucleosis-like illnesses not resulting from Epstein-Barr virus or cytomegalovirus. Am. J. Clln. Pathol. 93:776-783. 9. Irving, W. L. and A. L. Gunningham. 1990. Serological diagnosis of infection with human herpesvirus type 6. Br. Med. J. 300:156-159. 10. Morris, D. J. et al. 1989. Human herpesvirus 6 infection in renal transplant recipients. N. Engl. J.Med.320:1560-1561. 11. Briggs, M., J. Fox, and R. S. Tedder. 1988. Age prevalence of antibody to human herpesvirus 6. lancet 1:1058-1059. 12. Pietroboni, G. R. et al. 1988. Antibody to human herpesvirus 6 in saliva. Lancet 1:1059. 13. Harnett, G. B. et al. 1990. Frequent shedding of human herpesvirus 6 in saliva. J. Med. Virol. 30:128-130. 14. Knowles, W. A. and S. D. Gardner. 1988. High prevalence of antibody to human herpesvirus-6 and seroconversion associated with rash in two infants. Lancet 2:912-913. 15. Yamanishi, K. et al. 1988. Identification of human herpesvirus 6 as a causal agent for exanthem subitum. Lancet 1:1065-1067. 16. Ablashi, D. V. et al. 1988. Human Blymphotropic virus (human herpesvirus6). J. Virol. Methods 21:29-48. 17. Krueger, G. F. R. et al. 1989. Persistent active herpesvirus infection associated with atypical polyclonal lymphoproliferation (APL) and malignant lymphoma. Anticancer Res. 9:1457-1476. 18. Josephs, S. F. et al. 1988. Detection of human B-lymphotropic virus (human herpesvirus 6) sequences in B cell lymphoma tissues of three patients. Leukemia 2:132-135. 19. Krueger, G. R. F. et al. 1988. Diagnosis and differential diagnosis of progressive lymphoproliferation and malignant lymphoma in persistent active herpesvirus infection. J. Virol. Methods 21:255-264. 20. Gilliam, A. G. 1938. Epidemiologic study of an epidemic diagnosed as poliomyelitis, occurring among personnel of Los Angeles County General Hospital during the summer of 1934. Bulletin no. 240. Washington D.C.: US Public Health Service, Division of Infectious Disease, Institute of Health. 1-90. 21. Acheson, E. D. 1959. The clinical syndrome variously called benign myalgic encephalomyelitis, Iceland disease, and epidemic neuromyasthenia. Am. J.
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27
Med. 26:569-595. 22. Straus, S. E. 1988. The chronic mononucleosis syndrome. J. Infect. Dis. 157:405--412. 23. Downing, R. G. et al. 1987. Isolation of human lymphotropic herpesviruses from Uganda. Lancet 2:390. 24. Lusso, P. et al. 1991. Induction of CD4 and susceptibility to HIV-1 infection in
human CD8 ÷ T lymphocytes by human herpesvirus 6. Nature 349:533-535. 25. Lusso, P. et al. 1991. Productive infection of CD4 ÷ and CD8 ÷ mature T cell populations and clones by human herpesvirus 6 transcriptional down-regulation ofCD3. J. Inununol. 147:685-691. 26. Lusso, P. et al. 1989. Productive dual infection of human CIM÷T lymphocytes by
HIV-1 and HHV-6. Nature 337:370--373. 27. Meuer, S. C. et al. 1987. Antigen-like effects of monoclonal antibodies directed at receptors on human T-cell clones. J. Exp. Med. 158:988. 28. Gupta, S. and B. Vayuvegula. 1991. A comprehensive inununological analysis in chronic fatigue syndrome. Scand. J. Immunol. 33:319--327.
gard, we report C. bifermentans-associated gas gangrene in an immunodeficient patient.
13 cm x 13 cm indurated, edematous, exquisitely tender lesion with central bronzing of the skin surrounding a 7 cm horizontal laceration and a 2 cm puncture wound and vertical laceration of his right lower leg. Serosanguinous material drained from the suture sites; no crepitation was elicited. Radiographs of the right lower leg revealed scattered, subcutaneous, radiolucent areas consistent with gas formation. Immediately after the gas gangrene was recognized, the patient was taken to the operating room for irrigation, fasciotomy, and surgical debridement of the wounds. Intraoperatively, there was some necrotic-looking fat in the region of the puncture wound as well as the larger laceration, and a large amount of serous fluid overlying the fascia. A portion of the underlying tibialis anterior muscle was pale-grey and necrotic-looking. Antimicrobial therapy that included penicillin G, nafcillin, and ceftazidine was given. The patient recovered from gas gangrene uneventfully.
Case Report
Gas Gangrene Caused by Clostridium bif ermentans in an Immunodeficient Patient Kent A. Taub, M.D. Janak Patel, M.D.
Department of lnfectious Diseases Children's Hospital Edward Bannister,
Ph.D.
Department of Clinical Microbiology Armond Goldman, M.D.
Department of Allergy and Immunology Children's Hospital University of Texas Medical Branch Galveston, Texas 77555-0743 Clostridial wound infections resulting in gas gangrene are uncommon in non-wartime situations, even though clostridial species are often recovered from traumatic wounds as contaminants from soil and clothing. About 80 to 95% of cases of clostridial gas gangrene are caused by Clostridium perfringens; the other more frequent causative agents are Clostridium noyvi and Clostridium septicum (1-5). In contrast, gas gangrene associated with Clostridium bifermentans has been reported rarely (3-5). These reports suggest that C. bifermentans is less virulent than other clostridia, and as a sole agent, does not induce gas gangrene. In that re28
0196-4399/93/$0.00 + 06.00
Case Report A 17-yr-old male was admitted to the Children's Hospital of the University of Texas Medical Branch in Galveston, on August 29, 1991, with a past medical history of hyper-IgM immunodeficiency and chronic active hepatitis of unknown etiology. This patient lacked the ability to produce IgG antibody response to specific antigens. One day after receiving his monthly intravenous infusion of human IgG, he sustained lacerations of his right leg by falling on rusty wire. That same day he was seen in a local emergency room where his wounds were cleaned and sutured, and he was given an injection of human tetanus antitoxin. He was released on oral cephalexin and penicillin VK therapy. Two days later, he was admitted with fevers to 40.6°C, a shaking chill, and increasing pain and redness of the right lower leg. On examination, he was apprehensive, slightly jaundiced, and small for his age. His temperature was 38.3°C, pulse was 112 beats per min, respiratory rate was 28 breaths per min, and blood pressure was 113/60 mm Hg. The liver span was 6 cm; spleen was palpablel3 cm below the left costal margin in the mid-clavicular line. There was a © 1993 Elsevier Science Publishing Co., Inc.
Special Microbiologic
Investigations Blood cultures yielded no growth under aerobic and anaerobic conditions. Gram stain of material from the wound revealed large, box-shaped gram-positive bacilli with central, oval, and large spores and minimal white blood cells. Clinical Microbiology Newsletter 15:4,1993
Vol. 15, No. 4
Human Herpesvirus 6: A Virus in Search of a Disease Olajide Agbede, Ph.D. Department of Pathology University of Texas Medical Branch Galveston, Texas 77555-0743
The discovery of human herpesvims type 6 (I-IHV-6), formerly known as human B-lymphotropic virus (HBLV), followed attempts to cultivate peripheral blood mononuclear cells from patients with lymphoproliferative disorders (1). The suspicion that large, refractile cells bearing intranuclear and/or intracytoplasmic inclusion bodies in culture contain virus was confirmed by electron microscopic examination. These refractile, often binucleated cells were reproduced on transmission of the initial viral isolates to freshly isolated phytohemagglutin-stimulated human leukocytes obtained from umbilical cord blood, adult peripheral blood, bone marrow, and spleen. The detection of viral signals by in situ nucleic acid hybridization and the presence of viral antigens in culture as detected by indirect immunofluorescence are indications that the virus productively infects cells. Infected lymphocytes are lysed upon release of the virus. Other tissue culture properties of the virus include maturation in the nucleus of infected cells and release of abundant viral particles into the extracellular fluid. Although the virus was originally isolated from B cells, phenotypic characterization of the target cells for virus production showed that the majority of them possessed features descriptive of immature T-lymphocytes as demonstrated by the expression of CD7, CD2, and CD4 surface antigens (2). SubCMNEEJ 15(4)25-32,1993
sequent studies showed a propensity of the virus to infect a wide array of cell lines of hematopoietic origin, including megakaryocytes (3). In addition, the virus has shown tropism for glioblastoma cells (4).
The V i r u s Human herpesvirus type 6 has an icosahedral core symmetry of 162 capsomers enveloped in a lipid membrane. Its genome is a double-stranded DNA of at least 110 kilobase pairs, and its restriction endonuclease cleavage products show it to be distinct from other well-characterized human herpesviruses and animal lymphotrophic herpesviruses (5). The mode of transmission of HHV-6 is not known. Like the cytomegalovirus (CMV) with which it shares some genetic properties (6--8) and the ability to produce asymptomatic primary and recurrent infections (8), HHV-6 is widespread among the general population (9-11). The virus is excreted into the saliva, as shown by the 100% isolation rate from infected persons reported by two groups of investigators (12,13). Interestingly, the presence of the virus in the saliva precludes the ability to detect HIV-1 from this anatomic site, perhaps because they compete for similar cell receptors. Seroepidemiologic studies conducted by many investigators (11, 14) have shown that viral antibody is very common among healthy infants and adults. Infection is probably acquired very early in life as demonstrated by the findings of a study of children under age 5. Virusspecific antibodies are detectable as Elsevier
early as 1 mo after birth. Thereafter, prevalence of antibodies in this population declines over the ensuing 4 to 6 mo, presumably because they are passively acquired maternal antibodies; by 11 mo of age, antibody prevalence rises to a level above 60% and finally to a level of 98% among 17-yr-olds. Defining a D i s e a s e State There has been significant controversy in defining the disease manifestation caused by HHV-6 in humans. Although the virus has been implicated as the causative agent of exanthem subiturn-roseola infantum (15), a childhood disease rarely seen in children beyond the age of 3, it has not been possible to attribute unequivocally a disease entity to the presence of the virus in the adult population. Consequently, a number of
In This Issue Human Herpesvirus 6: A Virus in Search of a Disease . . . . . . . . . . . . .
25
Is this a virus with multiple disease entities or is it just associated with other viral diseases?
Gas Gangrene Caused by
Clostridium bOrermentans in an Immunodeficient Patient . . . . . . . . A case report
28
Letters to the Editor . . . . . . . . . . . .
30
Erratum . . . . . . . . . . . . . . . . . . . . . .
32
T.W. Klein. Psychoimmunology and Infection. CMN 15(3):17-22. February 1, 1993 0196-4399/93/$0.00 + 06.00
syndromes have been described in which the presence of the virus directly or indirectly provides the basis for an etiologic association with the pathogenesis of the respective syndromes. Human herpesvirus type 6 was originally isolated from the peripheral blood mononuclear cells of adult patients with lymphoproliferative disorders. High titers of antibodies to the virus exist in patients with Hodgkin's disease, African Burkitt's lymphoma, acute lymphoblastic leukemia, acute sarcoidosis, and Sjogren's syndrome (16). Apparently, it shares with CMV the ability to produce opportunistic infections in the immunocompromised host. Evidence for the ability of the virus to cause infection in immunocompromised hosts stems from studies conducted by Krueger and colleagues (17) on the pathogenesis of lymphoproliferative disorders in AIDS patients. Malignancies in these patients resembled those observed in allotransplantation and other immunodeficient states in which reactivation of Epstein-Barr virus (EBV), another herpesvirus, is thought to play a role. This observation reinforces the suggestion that HHV-6 might similarly be involved in the pathogenesis of lymphoproliferative disorders (18,19). Two histologically distinct lesions, atypical polyclonal lymphoproliferation (APL) and malignant lymphoma (ML), were associated with the presence of HHV-6. Using the Southern blotting technique and polymerase chain reaction (PCR), the genome of the virus was demonstrated in these lesions. Indeed, the serologic prevalence of HHV-6 antibody in all APL cases supported the virologic evidence of an infection and argues for a case of viral reactivation in affected tissues. HHV-6 has also been studied along with the other lymphotropic herpesviruses, EBV, and CMV, in the search for a distinct disease entity associated with the virus. Acute EBV infection is
mostly asymptomatic, leading to the speculation that HHV-6 might behave similarly. About 80-90% of children above 3 yr of age show serologic evidence of past infection by HHV-6. Eartier in the course of studies to explore the possible acute infections in the adult population attributable to HHV-6, an association with a chronic mononucleosis-like illness was established. The features of the disease strongly suggest one previously described in connection with epidemic neuromyasthenia (20, 21). It is characterized by chronic fatigue, myalgia, headache, fever, and psychiatric symptoms (22). Its immunologic markers are atypical lymphocytosis and a high ratio of helper to suppressor lymphocytes, and abnormalities related to immunoglobulin production. Significant increase in antibodies to a number of related and unrelated viruses, including human herpes simplex virus (HSV), CMV, EBV, and measles virus, have been described in these patients. Nevertheless, the production of heterophile antibody is not associated with HHV-6 infection (23). Recent reports indicate that HHV-6 might be responsible for active viral hepatitis in some patients presenting with a mononucleosis-like syndrome that cannot be attributed to other agents of sporadic viral hepatitis by existing clinical and laboratory criteria (6). An evaluation of the laboratory data of 27 patients with mononucleosis-like illness, in which EBV and CMV have been excluded on the basis of negative heterophile antibody test and patterns of immunologic response, showed that the patients have had active viral hepatitis, a syndrome typically accompanied by hepatic cell necrosis. The blood of the patients displayed atypical lymphocytosis and abnormally high aspartate aminotransferase level. Serum bilirubin levels were conspicuously high in these patients. Serologic tests for syphilis, hepatitis A virus (HAV), hepatitis B vi-
rus (HBV), CMV, and EBV were all negative. The mechanism by which HHV-6 produces the aforementioned syndromes is not clearly understood. On one hand, the virus has been associated with infectious mononucleosis (IM), which apparently represents the manifestation of an immunologically competent host to the presence of the virus. IM-like syndromes have been known to accompany infections with many other viruses and may not indicate a disease entity unique to the virus. It is generally seen in infections of lymphocytes, including those caused by CMV, EBV, varicella zoster, and vaccinia viruses. It is possible that IM resulting from primary HHV-6 infection, unaccompanied by any other viral infection, would have passed unnoticed, as is frequently the case with acute infections of human herpesvirus (22). On the other hand, APL, with which the virus has also been associated, represents the response of an immunodeficient host to the persistence of virus in tissues. HHV-6 was seen in association with HIV-1 in lymphoid tissues of APL and ML cases studied by Krueger et al. (17). However, immunosuppression does not appear to account fully for the pathogenic role of the virus in the development of lymphoproliferative diseases seen in HIV-positive patients because similar disease occurred in HIV-negative patients. Presumably, these lymphoproliferative diseases occurred as a result of some underlying immune defect(s) in these patients. The observation that EBV presents similar lymphoid diseases in HIV patients suggests an indirect effect of both viruses on cellular proliferation.
Effect on T Cells Recent reports indicate that HHV-6 has the ability to modulate the expression of surface antigenic determinants of T lymphocytes (24). In an experi-
No responsibility is assumed by the Publisher for a n y injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from a n y u s e or operation of any methods, products, iustmctions or ideas contained in the material herein. No suggested test or procedure should be carried out unless, in the reader's judgment, its risk is justified. Because of rapid advances in medical seiencas, we recommend that the independent verification of diagnoses and drug dosages should be made. Discussions, views, and recommendations as to medical procedures, choice of drugs, and drag dosages are the responsibility of the authors. NOTE:
Clinical Microbiology Newsletter (ISSN 0196-4399) is issued twice monthly in one indexed volume per year by Elsevier Science Publishing Co., Inc., 655 Avenue of the Americas, New York, NY 10010. Subscription price per year. $145.00 including postage and handing in the United States, Canada, and Mexico. Add $56.00 for postage in the rest of the world. Second-class postage paid at New York, NY and at additional mailing offices. Post~naster:. Send address changes to Clinical Microbiology Newsletter, Elsevier Science Publishing Co., Inc., 655 Avenue of the Americas, New York, NY 10010.
26
0196-4399/93/$0.00 + 06.00
© 1993 Elsevier Science Publishing Co., Inc.
Clinical Microbiology Newsletter 15:4,1993
ment to define the target population of cells within the immune system that are infected by the virus, it was shown that the two major subpopulations of T cells bearing the post-thymic stage markers CD3 ÷, CD4 ÷, C D 8 and CD3 ÷, CD4-, CD8 ÷ were susceptible to productive infection by the virus (25). Productive infection of cells carrying C I M , CD8 ÷ phenotypic markers induced de novo expression of CD4 without any alteration of the expression of the CD8 surface antigenic marker. This phenomenon has implications for dual infections involving HHV-6 and another virus that is dependent on the expression of CD4 molecules to initiate an infectious process. Under such circumstances up-regulation of the expression of CIM would expand the range of T cells susceptible to infection. This would accelerate the cytopathic effect of cells as has been reported in HHV-6 infection of normal T lymphocytes with CD4-, CD8 ÷ phenotypic markers subsequently exposed to HIV-1 (26). At the same time, the depletion of CD4 ÷ T cells in dual infections involving HHV6 and another virus would result in serious consequences for the "helper" function of the immune system. HHV-6 down-regulates the expression of C D 3 T cell antigen receptor (CD3/TCR) complex, another membrane marker that plays a vital role in the normal functioning of mature T cells (25). The down-regulatory effect of the virus on the expression of this protein complex is observed only in T cells infected by the virus and is not seen in cells infected by other human herpesviruses. CD3/I'RC complex promotes antigen recognition of immunocompetent T cells and also acts as a signal lransducer to effect the cascade of intracellular events that culminate in responsiveness to proliferative signals (27). Therefore, down-regulation may compromise the interaction of T cells with other components of the immune system. Immunologic defects could ensue as a result of the imbalance created by shutting off the antigen recognition function of the T cells. Immunologic defects have been reported in many conditions in which high titers of antibody to HHV-6 have been found (17, 22, 24, 28). It is not always clear whether such Clinical Microbiology Newsletter 15:4,1993
defects represent part of the outcome of the disease or whether they are part of the consequences of reactivation infection by HHV-6, in which case some degree of immunosuppression would have preceded the reactivation of the virus. Summary It is abundantly evident that HHV-6 infects a variety of cells in the immunologic system and that a variety of symptoms or manifestations are produced, many nonspecific, chronic, or self-limited. Serologic evidence would suggest that patients with mononucleosis-like syndrome and hepatitis described in association with HHV-6 are immunocompetent individuals with acute infection. Serologic diagnosis of infection by viruses with potential for chronicity and latency as HHV-6 may be difficult because the occurrence of IgG and IgM antibodies may not always indicate primary infection. The need for sensitive and specific diagnostic assays is necessary as clinicians become increasingly aware of the potential for acute infections by this viIllS.
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Salahuddln, S. Z. et al. 1986. Isolation of a new virus, HBLV, in patients with lymphoproliferative disorders. Science 234:596-601. Lusso, P. et al. 1987. Diverse tropism of human B-lymphotropic virus (human herpesvirus 6). Lancet 2:743-744. Lusso, P. et al. 1988 In vitro cellular tropism of human B-lymphotropic virus (human herpesvirus-6). J. Exp. Med. 167:1659-1670. Ablashi, D. V. et al. 1987. HBLV (or HHV-6) in human cell lines. Nature 329:207. Josephs, S. F. et al. 1986. Genomic analysis of the human B-lymphotropic virus (I-[BLV). Science 234:601-603. Biberfeld, P. et al. 1987. Ultrastructural characterization of a new human Blymphotropic DNA virus (human herpesvirus 6) isolated from patients with lymphoproliferative disease. J. Natl. Cancer Inst. 79:933-941. Efstathiou, S. et al. 1988. DNA homology between a novel human herpesvirus (HHV-6) and human cytomegalovirus. Lancet 2:63-64. Steeper, T. A. et al. 1990. The spectrum © 1993 Elsevier Science Publishing Co., Inc.
of clinical and laboratory f'mdings resuiting from human herpesvirus-6 (HHV-6) in patients with mononucleosis-like illnesses not resulting from Epstein-Barr virus or cytomegalovirus. Am. J. Clln. Pathol. 93:776-783. 9. Irving, W. L. and A. L. Gunningham. 1990. Serological diagnosis of infection with human herpesvirus type 6. Br. Med. J. 300:156-159. 10. Morris, D. J. et al. 1989. Human herpesvirus 6 infection in renal transplant recipients. N. Engl. J.Med.320:1560-1561. 11. Briggs, M., J. Fox, and R. S. Tedder. 1988. Age prevalence of antibody to human herpesvirus 6. lancet 1:1058-1059. 12. Pietroboni, G. R. et al. 1988. Antibody to human herpesvirus 6 in saliva. Lancet 1:1059. 13. Harnett, G. B. et al. 1990. Frequent shedding of human herpesvirus 6 in saliva. J. Med. Virol. 30:128-130. 14. Knowles, W. A. and S. D. Gardner. 1988. High prevalence of antibody to human herpesvirus-6 and seroconversion associated with rash in two infants. Lancet 2:912-913. 15. Yamanishi, K. et al. 1988. Identification of human herpesvirus 6 as a causal agent for exanthem subitum. Lancet 1:1065-1067. 16. Ablashi, D. V. et al. 1988. Human Blymphotropic virus (human herpesvirus6). J. Virol. Methods 21:29-48. 17. Krueger, G. F. R. et al. 1989. Persistent active herpesvirus infection associated with atypical polyclonal lymphoproliferation (APL) and malignant lymphoma. Anticancer Res. 9:1457-1476. 18. Josephs, S. F. et al. 1988. Detection of human B-lymphotropic virus (human herpesvirus 6) sequences in B cell lymphoma tissues of three patients. Leukemia 2:132-135. 19. Krueger, G. R. F. et al. 1988. Diagnosis and differential diagnosis of progressive lymphoproliferation and malignant lymphoma in persistent active herpesvirus infection. J. Virol. Methods 21:255-264. 20. Gilliam, A. G. 1938. Epidemiologic study of an epidemic diagnosed as poliomyelitis, occurring among personnel of Los Angeles County General Hospital during the summer of 1934. Bulletin no. 240. Washington D.C.: US Public Health Service, Division of Infectious Disease, Institute of Health. 1-90. 21. Acheson, E. D. 1959. The clinical syndrome variously called benign myalgic encephalomyelitis, Iceland disease, and epidemic neuromyasthenia. Am. J.
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human CD8 ÷ T lymphocytes by human herpesvirus 6. Nature 349:533-535. 25. Lusso, P. et al. 1991. Productive infection of CD4 ÷ and CD8 ÷ mature T cell populations and clones by human herpesvirus 6 transcriptional down-regulation ofCD3. J. Inununol. 147:685-691. 26. Lusso, P. et al. 1989. Productive dual infection of human CIM÷T lymphocytes by
HIV-1 and HHV-6. Nature 337:370--373. 27. Meuer, S. C. et al. 1987. Antigen-like effects of monoclonal antibodies directed at receptors on human T-cell clones. J. Exp. Med. 158:988. 28. Gupta, S. and B. Vayuvegula. 1991. A comprehensive inununological analysis in chronic fatigue syndrome. Scand. J. Immunol. 33:319--327.
gard, we report C. bifermentans-associated gas gangrene in an immunodeficient patient.
13 cm x 13 cm indurated, edematous, exquisitely tender lesion with central bronzing of the skin surrounding a 7 cm horizontal laceration and a 2 cm puncture wound and vertical laceration of his right lower leg. Serosanguinous material drained from the suture sites; no crepitation was elicited. Radiographs of the right lower leg revealed scattered, subcutaneous, radiolucent areas consistent with gas formation. Immediately after the gas gangrene was recognized, the patient was taken to the operating room for irrigation, fasciotomy, and surgical debridement of the wounds. Intraoperatively, there was some necrotic-looking fat in the region of the puncture wound as well as the larger laceration, and a large amount of serous fluid overlying the fascia. A portion of the underlying tibialis anterior muscle was pale-grey and necrotic-looking. Antimicrobial therapy that included penicillin G, nafcillin, and ceftazidine was given. The patient recovered from gas gangrene uneventfully.
Case Report
Gas Gangrene Caused by Clostridium bif ermentans in an Immunodeficient Patient Kent A. Taub, M.D. Janak Patel, M.D.
Department of lnfectious Diseases Children's Hospital Edward Bannister,
Ph.D.
Department of Clinical Microbiology Armond Goldman, M.D.
Department of Allergy and Immunology Children's Hospital University of Texas Medical Branch Galveston, Texas 77555-0743 Clostridial wound infections resulting in gas gangrene are uncommon in non-wartime situations, even though clostridial species are often recovered from traumatic wounds as contaminants from soil and clothing. About 80 to 95% of cases of clostridial gas gangrene are caused by Clostridium perfringens; the other more frequent causative agents are Clostridium noyvi and Clostridium septicum (1-5). In contrast, gas gangrene associated with Clostridium bifermentans has been reported rarely (3-5). These reports suggest that C. bifermentans is less virulent than other clostridia, and as a sole agent, does not induce gas gangrene. In that re28
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Case Report A 17-yr-old male was admitted to the Children's Hospital of the University of Texas Medical Branch in Galveston, on August 29, 1991, with a past medical history of hyper-IgM immunodeficiency and chronic active hepatitis of unknown etiology. This patient lacked the ability to produce IgG antibody response to specific antigens. One day after receiving his monthly intravenous infusion of human IgG, he sustained lacerations of his right leg by falling on rusty wire. That same day he was seen in a local emergency room where his wounds were cleaned and sutured, and he was given an injection of human tetanus antitoxin. He was released on oral cephalexin and penicillin VK therapy. Two days later, he was admitted with fevers to 40.6°C, a shaking chill, and increasing pain and redness of the right lower leg. On examination, he was apprehensive, slightly jaundiced, and small for his age. His temperature was 38.3°C, pulse was 112 beats per min, respiratory rate was 28 breaths per min, and blood pressure was 113/60 mm Hg. The liver span was 6 cm; spleen was palpablel3 cm below the left costal margin in the mid-clavicular line. There was a © 1993 Elsevier Science Publishing Co., Inc.
Special Microbiologic
Investigations Blood cultures yielded no growth under aerobic and anaerobic conditions. Gram stain of material from the wound revealed large, box-shaped gram-positive bacilli with central, oval, and large spores and minimal white blood cells. Clinical Microbiology Newsletter 15:4,1993