Prevalence of Anti-Human Herpes Virus Type 7 IgG Positivity Rate among Children with Fever and Skin Rash in Diyala Province, Iraq

1. Introduction

The HHV-7 is a member of the Roseolovirus genus within the Betaherpesvirinae subfamily of the herpesviriodae family. It was first detected from purified, activated CD4⁺ T lymphocytes from the peripheral blood of a healthy individual ( 1 ). HHV-7 is closely related to human herpesviruses-6 (HHV-6). HHV-7 infection occurs in early childhood and causes a short febrile disease frequently associated with a skin rash called exanthema subitum or roseola infantum ( 2 ). HHV-7 infection also leads to or is associated with a number of other symptoms, including acute febrile respiratory disease, vomiting, diarrhea, low lymphocyte counts, and febrile seizures ( 3 ). The clinical manifestations of primary and reactivated HHV-7 infections are similar, except those seizures occurred more frequently in reactivated infections. These findings, previously unrecognized in otherwise healthy children, suggest that HHV-7 viremia can represent primary or reactivated infection and may be affected by the interaction between HHV-6 and HHV-7 ( 4 ). It has been found that HHV-7 is associated with the classic fever of unknown origin (FUO) ( 5 ).

The HHV-7 is ubiquitous and is responsible for lifelong latent infections in macrophages and T-lymphocytes, most often asymptomatic. It resides primarily in CD4⁺ T cells since it uses the CD4 and possibly some cell-surface glycoproteins to enter CD4⁺ T cells ( 6 ). Reactivation of latent HHV-7 may cause a mononucleosis-like syndrome. HHV-7 is highly prevalent in the healthy population, with over 90% of adults being seropositive to the virus ( 7 ). Primary infections frequently occur in early childhood. Anti-HHV-7 antibodies were detected in infants under 2 years old or later. Seroconversion occurs in 3- to 4-year-old ( 8 ): the HHV-7 infects T cells, monocytes-macrophages, epithelial cells, and central nervous system cells. The latent viral persistent infection is established in salivary glands, and the virus is continuously shed through the saliva ( 9 ). So, it has been readily detected in the saliva of healthy adults, suggesting that saliva plays a role in the horizontal transmission of the virus via close contact between parents and children ( 2 ). Additionally, breastfeeding may be a possible route of transmission ( 10 ).

The seroprevalence of HHV-7 reaches 75% in 3- to 6-year-old children and 98% in adults ( 11 ). Anti-HHV-7 antibody titers are high (94.4%) in children in the first 2 months, possibly due to maternal antibodies, followed by a reduction to 30% between 6-7 months. Then re-increased after 8 months ( 8 ). The prevalence of antibodies to HHV-7 increases with age; 60% of young adolescents have detectable titers. The anti-HHV-7 antibodies are sustained into adulthood, as sera from 92% of healthy adults are seropositive ( 12 ).

Most of the studies affirm the higher role of HHV-6 in the causation of roseola infantum in children compared to HHV-7 ( 13 ). In this regard, it has been found that more than half of the children were infected with HHV-6B prior to HHV-7 ( 14 ). However, the distinction between the primary role in the causation of roseola infantum, whether HHV-6 or HHV-7 and the cross-reactivity of these viral antibodies are still puzzling worldwide ( 15 ).

2. Materials and Methods

2.1. Study Design and Sampling

The current study is a cross-sectional conducted in Diyala province from July 2020 to March 2021. A total of 180 child patients with fever and skin rash were included. Their age range was 1 -14 years. Additionally, 60 healthy children were enrolled as the control group aged 1-14. Patients were allocated and collected from Al-Batool Teaching Hospital for Maternity and Children and other Healthcare centres in the Diyala Directory of Health. A special questionnaire form was reconstructed for this study which includes socio-demographic information plus clinical notes and the results of a complete blood count. Blood specimen was aspirated from all patient and control groups. Sera were separated and kept at -20 0C until testing. An ELISA kit for the detection of anti-HHV-7 (Mybiosource-China) was used.

2.2. Statistical Analysis

Statistical analysis was done using Statistical Package of Social Science (SPSS) version 27, and the P-value was considered significant wherever it was less than 0.05.

3. Results

Concerning the any-HHV-7 IgG positivity rate, the results showed that 33 (19.4%) of the patients were positive versus 137 (80.6%) were negative, while in the healthy group, 19 (31.7%) were positive for anti-HHV-7 IgG and 41 (68.3%) were negative. However, the difference between the two groups was insignificant statistically (P=0.051) (Table 1).

The results in a table 2 found that one patient who was positive for anti-HHV-7 IgM was also positive for anti-HHV-7 IgG against 26 (96.3%) who were negative for anti-HHV-7 IgM but positive for anti-HHV-7 IgG. So, the difference was statistically significant (P=0.038). In the healthy group, only one individual who was positive for anti-HHV-7 IgM was also positive for anti-HHV-7 IgG, while 18 (94.7%) were negative for anti-HHV-7 IgM but positive for anti-HHV-7 IgG, with a statistically insignificant difference (P=0.405).

Data in table 3 found that the HHV-7 IgG positivity rate (20.0%) among patients 1-4 years old was insignificant higher compared to other age groups (P=0.678). In the control group, the HHV-7 IgG positivity rate among those 1-4 years old was insignificantly higher (P=0.675). Regarding gender, the anti-HHV-7 IgG positivity rate was insignificantly different between male and female patients (16.7% Vs 21.7%, P=0.405) and between healthy males and females (34.5% Vs 29.0%, P=0.650). Concerning the residence, the HHV-7 IgG positivity rate among urban patients (20.1%) was insignificantly higher (P=0.463). Among the healthy, only those residing in the urban areas had a 31.7% positivity rate of anti-HHV-7 IgG. Concerning the number of children in the family, the results of patients revealed that families with four children had the highest anti-HHV-7 IgG positivity but with an insignificant difference (P=0.124). In the healthy control group, families with 5 or more children had the highest anti-HHV-7 IgG positivity (35.0%) but with an insignificant difference (P=0.839).

The Association of anti-HHV-7 IgG with CBC parameters is shown in table 4. Regarding the mean±SD concentration of hemoglobulin (Hb), there was a slight insignificant increase of Hb in patients with negative anti-HHV-7 IgG compared to their positive counterparts (11.7±15 Vs 11.2±1.2) (P=0.746). Similarly, in the healthy, there was a slightly increased in the mean ± SD of Hb concentration among individuals with negative anti-HHV-7 IgG compared to their positive counterparts (11.9±1.1 Vs 11.3±0.9) (P=0.987). Concerning the mean±SD of PCV, the patients' results showed an insignificant increase in patients with negative anti-HHV-7 IgG compared to their positive counterparts (36.8±3.7 Vs 35.6±3.6) (P=0.821). In the healthy group, individuals with negative anti-HHV-7 IgG had higher PCV than their positive counterparts (37.7±1.2 Vs 35.9±1.4), but the difference was statistically insignificant (P=0.088).

In connection with the total WBC count, patients with positive anti-HHV-7 IgG had higher but insignificant mean±SD of WBC count compared to their negative counterparts (8.7±1.4 Vs 7.6±1.6) (P=0.975). Similarly, individuals in the healthy group with positive anti-HHV-7 IgG had insignificantly higher counts than their negative counterparts (6.8±2.6 Vs 6.4±2.3) (P= 0.945). Concerning the lymphocyte count, the mean±SD count in patients with positive anti-HHV-7 IgG was insignificantly higher than in their negative counterparts (3074.4±1302 Vs 2914.2±1194) (P=0.241). In the healthy group, individuals positive for anti-HHV-7 IgG had insignificantly higher than their negative counterparts (2914.2±1194 Vs 2640.1±891), (P=0.344). Lastly, patients with positive anti-HHV-7 IgG had insignificantly lower platelet counts than their negative counterparts (302.9±82.8 Vs 302.9±82.8) (P=0.328). In comparison, healthy individuals with positive anti-HHV-7 IgG had insignificantly higher than their negative counterparts (338.9±94 Vs 310.5±82) (P=0.710).

4. Discussion

This study is emerging from the importance of roseola infantum, a common illness in childhood caused by a primary infection by HHV-6 and/or HHV-7. It is also known as exanthema subitum or the sixth disease because it ranks as the sixth condition, following measles, scarlet fever, rubella, Duke's disease, and parvovirus B19, causing skin rash in infants ( 3 ).

To explore the prevalence of roseola infantum among Diyala children, the contribution of both causative viruses, HHV-6 and HHV-7, should be investigated. We started with the HHV-6 in 2018; at that time, the anti- HHV-6 IgM positivity rate among children 6-24 months who complained of fever and skin rash was 45.6%, and the highest positivity rate was among the age group 1-6 months. Additionally, the anti- HHV-6 IgM positivity was higher among children with breast milk and those whose mothers complained of infection during pregnancy ( 16 ). On the other hand, the anti-HHV6 IgG positivity among apparently healthy infants was 43.9%. The highest positivity was among those 19-24 months old, and a significantly higher anti-HHV6 IgG positivity was found among infants whose families had a recent history of positive cases ( 9 ). After that, to complete the epidemiological picture of roseola infantum, the prevalence of HHV-7 was explored in the present study.

The current study found that the anti-HHV-7 IgG positivity rate among child patients with fever and skin rash was 19.4% versus 80.6 % who were negative, while among healthy control, the positivity rate was 31.7% and 68.3% were negative. It was well documented that the seroprevalence of HHV-7 and HHV-6 was greatly variable worldwide and that almost all people are exposed firstly to HHV-6 and secondly to HHV-7 during childhood ( 17 ). Because HHV-6 and HHV-7 are closely related in genome organization and sequence, the cross-reactive antibody responses between HHV-6 and HHV-7 have been reported.

In a study that included sera of healthy blood donors from nine countries using indirect immunofluorescent assays, Lan and Luo ( 17 ) reported that the prevalence of anti- HHV-7 antibodies is high (75–98%) in all countries except for Northern Japan (44%). There were regions of low, intermediate and high mean antibody titers against HHV-7 such as 78.5–91.3 for Belgium, Israel, Japan, USA and Australia, 175.4–182.6 for Mexico and Cologne/Germany, and 389.2 for South Africa for which geographic characteristics may be responsible, suggesting that HHV-7, similar to HHV-6, is a widespread human herpesvirus with elevated antibody titers in the healthy human population. Additionally, among Mexican blood donors using the indirect immunofluorescence test, the anti-HHV-7 positivity rate was 98.5%, and nearly 85% had high titers ( 18 ). Therefore, a future study to explore the anti-HHV-7 titers among the general population is recommended to recognize which region Iraq belongs to.

Among healthy Hungarian children aged 6 - 18 months, the anti- HHV-7 was found in 19.0% of children before 12 months, but the majority were infected after that age. More than half of the children were infected with HHV-6B prior to HHV-7. Anti- HHV-7 antibodies were higher in girls compared to boys ( 15 ). The present study found that 20% of children had anti-HHV-7 IgG at 1-4 years old, and females and urbanites had insignificantly higher HHV-7 IgG positivity than their counterparts. Thus, a comprehensive study is suggested to address the seroprevalence of all betaherpesviruses among Iraqi children.

Furthermore, in a seroprevalence study, children aged 3 months to 6 years and from cord blood were tested. The HHV-6 seropositivity rate increased from 19% to 79.3% in the first eighteen months of life, while the HHV-7 seroprevalence reached a similar level (75.9%) in children aged 3-6 years. These results show that HHV-7, like HHV-6, is a prevalent virus in infancy. In cord blood sera, a similar value for the two viruses (78.9% for HHV-6 and 76.3% for HHV-7) was found, affirming that HHV-6 primary infection generally precedes that by HHV-7 ( 11 ). It was found that the HHV-7 prevalence in the USA population was >85%; however, in Japan, a low prevalence was reported. The primary infection of HHV-7 appears later in life than HHV-6, while HHV-7 can be more readily isolated from the saliva than HHV-6 ( 19 ).

Molecular and epidemiological analysis revealed that HHV-7 was transmitted horizontally from grandparents to parents and children through close contact within a household. Of note, either parent can transmit HHV-7 to the children. A follow-up study on saliva samples revealed that the titer of HHV-7 DNA differed in each individual and that "high producers" and "low producers" can be recognized. Maternal antibodies against HHV-7 tended to be higher and remain longer after birth than those of HHV-6. Thus, these findings are consistent with the clinical observation affirming that HHV-6 infection occurs earlier than HHV-7 infection ( 20 ). This is very important in our community since kissing of newly born or infants by his/her parents, grandparents, brothers/sisters, or even relatives is an inherited custom among Iraqi families. These may form the main route for transmission of all betaherpesviruses to offspring. Another important clinical feature of HHV-7 infection is that most infections during childhood remain apparent ( 21 ). Although it was insignificant, the results in this study found that the presence of four children in the family increases the chance of infection by HHV-7, suggesting that siblings in the family may infect each other.

In Japan, the positivity rate of anti-HHV-7 antibody was 40% in the first 2 months of life, which declined during the first 6 months, then gradually increased to 45% at 1-4 years till it reached the highest level (60%) at 11-13 years of age that was maintained until the end of the third decade, then decreased after that ( 22 ). In the present limited study, the highest ant-HHV-7 positivity rate was among those 5-9 years old. Thus, more extensive studies are required among immunocompetent or immunocompromised people to clarify this feature more precisely.

Numerous neurological manifestations have been associated with HHV-7 primary infection in children and occasionally in immunocompromised adult patients ( 22 ). Additionally, reactivation of latent HHV-7 may cause CNS disease in immunocompetent adults, as detected by the presence of HHV-7 DNA in CSF ( 23 ). Besides the possible role of HHV-7 in certain myelo radiculo neuropathy and malignancies ( 24 ) and hemiconvulsion-hemiplegia-epilepsy syndrome. Collectively, these observations make this virus of serious concern, and thus future molecular or immunological studies are recommended to address these query points in the community.

There are several reports on the association of roseola viruses and the development of drug-induced hypersensitivity syndrome or some tines called drug reaction with eosinophilia and systemic syndrome ( 24 ). Additionally, lymphadenopathy was found in 54% of patients with drug-induced hypersensitivity syndrome ( 25 ). It is well known that HHV-7 is a lymphotropic virus that infects and resides in CD4⁺ T lymphocytes using the CD4⁺ molecule. At the same time, HHV-7 has a number of effects on these cells, including membrane leaking, lytic syncytia, occasional apoptosis, supporting of latent infection, up or downregulating levels of specific cytokines and enhancement of natural killer cell cytotoxicity ( 26 ). These effects collectively and gradually decrease the number of circulatory lymphocytes affirming the lymphopenia found in this study.

Another result obtained by this study is the significantly lower mean platelets count (thrombocytopenia) in patients compared to the control. This result is consistent with a fact reported that the HHV-7 has the potential to infect hematopoietic stem and progenitor cells and impair hematopoietic stem and progenitor cells' survival and proliferation, presumably via lysis or induced cell death. Since all blood cells develop from the hematopoietic stem cells in the bone marrow through a process called hematopoiesis. Notably, hematopoietic stem cells give rise to red and white blood cells and platelets in a tightly regulated process ( 26 ). These mechanisms are responsible for the significant drop down of platelets and insignificant decrease in hemoglobin concentration (Hb) obtained in this study ( 27 ). The HHV-6 infection suppressed the three lineages of hematopoiesis; erythroid, granulocyte/macrophage, and megakaryocyte using the hematopoietic colony assays ( 22 ).

Authors' Contribution

Study concept and design: A. SH. H.

Acquisition of data: S. A. A.

Analysis and interpretation of data: K. L.

Drafting of the manuscript: A. SH. H.

Critical revision of the manuscript for important intellectual content: A. SH. H.

Statistical analysis: S. A. A.

Administrative, technical, and material support: K. L.

Ethics

The study was scientifically and ethically approved by the Committees in the College of Medicine-Diyala University and Diyala Directory of Health. Human privacy was esteemed by obtaining the parent's verbal approval.

Conflict of Interest

The authors declare that they have no conflict of interest.

References

1. Patel SJ, Zhao G, Penna VR, Park E, Lauron EJ, Harvey IB, et al. A Murine Herpesvirus Closely Related to Ubiquitous Human Herpesviruses Causes T-Cell Depletion. J Virol. 2017; 91(9)
2. Adekola HA, Abdullahi IN, Emeribe AU, Faruku N, Uzairue L, Adeyemi Billyrose OM, et al. Sero-survey of measles virus antibodies among symptomatic children attending Abuja Teaching Hospital, Nigeria. GMS Hygiene Infect Control. 2021; 16
3. Ongrádi J, Ablashi DV, Yoshikawa T, Stercz B, Ogata M. Roseolovirus-associated encephalitis in immunocompetent and immunocompromised individuals. J Neurovirol. 2017; 23(1):1-19.
4. Lee JS, Lacerda EM, Nacul L, Kingdon CC, Norris J, O'Boyle S, et al. Salivary DNA Loads for Human Herpesviruses 6 and 7 Are Correlated With Disease Phenotype in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Front Med. 2021; 8
5. Jallow MM, Fall A, Wade SF, Fall NS, Kiori D, Sy S, et al. Molecular Detection of Human Herpes Viruses in Suspected Measles Serum Samples from Senegal, 2014 to 2017. Am J Trop Med. 2021; 104(6):2224-8.
6. Agut H, Bonnafous P, Gautheret-Dejean A. Update on infections with human herpesviruses 6A, 6B, and 7. Med Mal Infect. 2017; 47(2):83-91.
7. Krumina A, Chapenko S, Kenina V, Mihailova M, Logina I, Rasa S, et al. Correction to: The role of HHV-6 and HHV-7 infections in the development of fibromyalgia. J Neurovirol. 2019; 25(4):617.
8. Munawwar A, Singh S. Human Herpesviruses as Copathogens of HIV Infection, Their Role in HIV Transmission, and Disease Progression. J Lab Physicians. 2016; 8(1):5-18.
9. Asha K, Sharma-Walia N. Targeting Host Cellular Factors as a Strategy of Therapeutic Intervention for Herpesvirus Infections. Front Cell Infect Microbiol. 2021; 11:603309.
10. Mayer BT, Krantz EM, Swan D, Ferrenberg J, Simmons K, Selke S, et al. Transient Oral Human Cytomegalovirus Infections Indicate Inefficient Viral Spread from Very Few Initially Infected Cells. J Virol. 2017; 91(12)
11. Fölster-Holst R, Zawar V, Chuh A. [Paraviral exanthems]. Der Hautarzt; Zeitschrift fur Dermatologie, Venerologie, und verwandte Gebiete. 2017; 68(3):211-6.
12. Pavletić B, Runzheimer K, Siems K, Koch S, Cortesão M, Ramos-Nascimento A, et al. Spaceflight Virology: What Do We Know about Viral Threats in the Spaceflight Environment?. Astrobiology. 2022; 22(2):210-24.
13. Carneiro VCS, Alves-Leon SV, Sarmento DJS, Coelho W, Moreira ODC, Salvio AL, et al. Herpesvirus and neurological manifestations in patients with severe coronavirus disease. Virol J. 2022; 19(1):101.
14. Blostein F, Foote S, Salzman E, McNeil DW, Marazita ML, Martin ET, et al. Associations Between Salivary Bacteriome Diversity and Salivary Human Herpesvirus Detection in Early Childhood: A Prospective Cohort Study. J Pediatric Infect Dis Soc. 2021; 10(8):856-63.
15. Hill JA, Ikoma M, Zerr DM, Basom RS, Peddu V, Huang ML, et al. RNA Sequencing of the In Vivo Human Herpesvirus 6B Transcriptome To Identify Targets for Clinical Assays Distinguishing between Latent and Active Infections. J Virol. 2019; 93(3)
16. Hasan AS, Mehdi S, Noor AH. The Seropositivity Rate of Human Herpesvirus Type 6 among Infants in Diyala Province, Iraq. J Biosci Med. 2019; 7(6):9.
17. Lan K, Luo MH. Herpesviruses: epidemiology, pathogenesis, and interventions. Virol Sin. 2017; 32(5):347-8.
18. Krueger GR, Koch B, Leyssens N, Berneman Z, Rojo J, Horwitz C, et al. Comparison of seroprevalences of human herpesvirus-6 and -7 in healthy blood donors from nine countries. Vox Sang. 1998; 75(3):193-7.
19. Ablashi DV, Berneman ZN, Kramarsky B, Whitman J, Asano Y, Pearson GR. Human herpesvirus-7 (HHV-7): current status. Clin Diagn Virol. 1995; 4(1):1-13.
20. Yamada M. Human herpesviruses 6 and 7: effects on hematopoiesis and mode of transmission. Jpn J Infect Dis. 2001; 54(2):47-54.
21. Aburakawa Y, Katayama T, Saito T, Sawada J, Suzutani T, Aizawa H, et al. Limbic Encephalitis Associated with Human Herpesvirus-7 (HHV-7) in an Immunocompetent Adult: The First Reported Case in Japan. Intern Med. 2017; 56(14):1919-23.
22. Yoshikawa T, Asano Y, Kobayashi I, Nakashima T, Yazaki T, Suga S, et al. Seroepidemiology of human herpesvirus 7 in healthy children and adults in Japan. J Med Virol. 1993; 41(4):319-23.
23. Houldcroft CJ. Human Herpesvirus Sequencing in the Genomic Era: The Growing Ranks of the Herpetic Legion. Pathogens (Basel, Switzerland). 2019; 8(4)
24. Shanehsazzadeh M, Rad JS, Pourazar A, Behbahani M. Epidemiology of herpes human virus 6 and 7 infections in salivary gland neoplasms in isfahan, iran. Med Arch (Sarajevo, Bosnia and Herzegovina). 2014; 68(4):276-8.
25. Hindosh N, Kotala R, Probasco L, Bal S. Terbinafine Induced Lupus Erythematosus With Progression to Lupus Nephritis. Cureus. 2022; 14(4):23887.
26. Hamid O, Hoffner B, Gasal E, Hong J, Carvajal RD. Oncolytic immunotherapy: unlocking the potential of viruses to help target cancer. Cancer Immunol. 2017; 66(10):1249-64.
27. Pascutti MF, Erkelens MN, Nolte MA. Impact of Viral Infections on Hematopoiesis: From Beneficial to Detrimental Effects on Bone Marrow Output. Front Immunol. 2016; 7:364.