Delayed Primary Epstein-Barr Virus Infection: Clinical and Immunologic Manifestations

Abstract & Commentary

By Richard R. Watkins, MD, MS, FACP, Division of Infectious Diseases, Akron General Medical Center, Akron, OH; Associate Professor of Internal Medicine, Northeast Ohio Medical University, Rootstown, OH. Dr. Watkins reports no financial relationships relevant to this field of study.

This article originally appeared in the February 2013 issue of Infectious Disease Alert.

Synopsis: A prospective study on Epstein-Barr virus seronegative college freshmen found that primary infection was symptomatic in 89% of cases. Kissing was the primary risk factor for infection, and blood viral load, CD8+ lymphocytosis, and IL-6 levels correlated with disease severity.

Source: Balfour HH, et al. Behavior, virologic, and immunologic factors associated with acquisition and severity of primary Epstein-Barr virus infection in university students. J Infect Dis 2013;207:80-88.

In the United States, approximately 50% of individuals develop antibodies to Epstein-Barr virus (EBV) by age 5. Infections during the first decade are usually asymptomatic, while disease is most commonly diagnosed in adolescents of higher socioeconomic status. Researchers at the University of Minnesota sought to determine the proportion of delayed primary infections that are symptomatic. Another goal was to investigate how CD8+ lymphocytosis correlated with symptomatic disease.

Two freshman classes were followed prospectively throughout their undergraduate years. Of 202 EBV antibody-negative students, 143 (71%) were enrolled in the surveillance phase. They were seen every 8 weeks while in school and during breaks if they remained in the area. The visits involved obtaining a medical history, an oral wash specimen, a 40 mL venous blood sample, and completion of a health questionnaire. Sera collected were tested for EBV antibodies. Subjects who developed signs and symptoms suggestive of acute EBV infection were seen as soon as possible and study specimens and questionnaires were obtained. Primary EBV infection was defined as a positive result of an EBV antibody test and the presence of EBV DNA in the oral and/or blood compartment of a subject who was previously negative for both EBV antibodies and EBV DNA. Primary EBV infection was classified clinically as infectious mononucleosis (with at least two of the following: sore throat, cervical lymphadenopathy, fever, and fatigue), symptomatic (symptoms present but did not fulfill the definition of infectious mononucleosis), or asymptomatic. Severity of illness was graded from 0 (asymptomatic) to 6 (essentially bedridden).

Sixty-six out of 143 students developed primary EBV infection during the 4 years of observation. The incidence of infection during the freshman year (26 cases/100 person-years) was more than twice the mean incidence during the following 3 years (10 cases per 100 person years; P = 0.002). The incidence was greater in women than men (23.6 vs 16.1 cases/person-years) but was not statisically significant. Sexual behavior was a risk factor for primary EBV infection, with students reporting deep kissing with or without coitus having similar distributions of time to infection. Infectious mononucleosis developed in 51 subjects (77%). It was symptomatic but not meeting the definition of mononucleosis in eight subjects (12%), and seven asymptomatic (11%). EBV DNAemia was documented in 42 subjects (64%). Heterophile antibodies were documented in 50 (77%) of 65 subjects, IgM antibodies in 54 (83%) of 65 subjects, and IgM antibodies were found as early as 8 days before symptoms began and persisted as long as 420 days after symptom onset.

The authors quantified CD8+ T-cell numbers and activation over time. CD8+ T-cell numbers increased the most during the first 2 weeks following symptom onset. They also observed an upregulation of CD38, HLA-DR, and granzyme B on total CD8+ T-cells in the first 2 weeks. Moreover, the investigators discovered an expansion of natural killer (NK) cells in the blood during acute disease correlated with CD8+ T-cell numbers. Severity of disease corresponded with the quantity of EBV in whole blood, CD8+ T-cell numbers and granzyme B expression. Of several cytokines evaluated during acute infection (including interferon y), only IL-6 correlated significantly with severity of disease.

Commentary

As mentioned in an accompanying commentary, what sets this study apart from others on primary EBV infection is the rigor of the prospective follow-up.1 The investigators should be commended for a study design that involved 143 participants who gave oral and blood samples every 8 weeks over a period of 4 years, and donated additional samples whenever they developed a febrile illness. Sixty-six of them acquired primary EBV infection, of which 89% were symptomatic. This result is much greater than the approximately 25-50% incidence of symptomatic primary EBV infection reported in prior studies. Thus, it seems likely the results of the present study reflect the true incidence of symptoms of primary infection in this age group. Deep kissing was identified as the main risk factor for EBV acquisition, as students who engaged in this activity had similar conversion rates whether or not they engaged in sexual intercourse, and those with no history of kissing remained seronegative.

A prior study found that NK cell numbers correlated with less severe illness, not more as the present study reported.2 This discrepancy could be due to the smaller numbers of patients in the older study, which lacked internal controls for NK cell numbers and frequency before, during, and after primary EBV infection. Furthermore, data from the current report suggest that both NK cells and CD8+ T-cells respond similarly to the intensity of viral challenge. It is possible that a particular subset of NK cells is responsible for better viral control and symptom reduction, and further research on this topic seems warranted. Indeed, future prospects for an EBV vaccine hinge on our continued elucidation of these complex host-virus interactions.

References

1. Rickinson AB, et al. Epstein-Barr virus and infectious mononucleosis: What students can teach us. J Infect Dis 2013;207:6-8.

2. Williams H, et al. The immune response to primary EBV infection: A role for natural killer cells. Br J Haematol 2005;129:266-274.