DETECTION AND CHARACTERIZATION OF EPSTEIN BARR VIRUS IN NASOPHARYNGEAL CANCERS IN GHANA

ABSTRACT

Purpose: Nasopharyngeal cancer (NPC) is a malignant tumor which is commonly associated with Epstein Barr virus (EBV). Two genotypes of EBV, genotype 1 and genotype 2, which are geographically restricted, are implicated in the pathogenesis of NPC. This study aimed at detecting and characterizing EBV genotypes involved in the pathogenesis of NPC in Ghana.

Experimental design: Whole blood and biopsy samples were collected from 55 patients diagnosed of NPC by CT scan and endoscopy at the Ear, Nose and Throat Unit (ENT) of the Korle-Bu Teaching Hospital (KBTH). As control subjects, whole blood was collected from 53 individuals confirmed NPC negative or without known oncological diseases by CT scan and endoscopy. Association of NPC with risk factors such as gender, alcohol intake, smoking and consumption of salted fish, was evaluated. EBV was detected by amplification of Epstein Barr nuclear antigen 1 (EBNA-1) and genotyping by amplification of Epstein Barr nuclear antigen 2 (EBNA-2) using primers specific to genotypes 1 or 2. Viral load in blood and biopsy specimen was quantified using real-time polymerase chain reaction (PCR).

Results: Risk factors such as gender, consumption of alcohol and smoking were not significantly (p > 0.05) associated with NPC development. There was a significant association (p< 0.05) of consumption of salted fish with NPC development. The frequencies of EBV positivity were 67%, 67% and 92% in NPC blood, NPC biopsies, and control blood samples, respectively. The predominant EBV genotype in blood specimen from cases was EBV genotype 2 (52%) and that of the control group was type 1 (62%). Statistically significant difference (χ2= 72.26, p = 0.001) was observed for the frequency of EBV genotypes in the NPC blood and controls. In biopsy specimen, the predominant EBV genotype was genotype 1 (58%). Median viral load (9×107 copies/ mL) in whole blood of NPC case subjects was significantly higher than median viral load (6×104 copies/ mL) in the whole blood of control subjects (p=0.001). Significantly higher (p < 0.001) median EBV DNA load (9×107 copies/ mL) was observed in

NPC whole blood samples compared to that of NPC tumor biopsies (1.58×105 copies/mL). The median viral load of case samples infected with EBV genotype 1 was significantly higher (p = 0.001) than control samples infected with the same EBV genotype (genotype 1 median viral load in cases, 2 ×107 copies/ mL verses 29 ×103 copies/ mL genotype 1 median viral load in controls). Significantly higher (p = 0.001) median viral load was observed in cases infected with EBV genotype 2 when compared to control samples infected with the same EBV genotype (1×108 copies/ mL compared to 18 ×103 copies/ mL in cases and controls, respectively).

Conclusions: In summary, gender, consumption of alcohol and smoking were not associated with NPC development in the current study whereas association was established between NPC and salted fish consumption. The frequency of EBV was higher in control subjects than NPC patients, confirming reports suggesting large number of the world’s population being asymptomatic carriers. Gender was not a risk factor of EBV infection in this study. This study identified EBV genotype 2 infection as the virulent genotype in Ghana and a possible risk factor in the development of NPC in Ghanaian patients. EBV genotype 1 was predominant in the control group and consistent with the genotype being relatively less virulent. Detection and quantification of EBV load can be used as a non-invasive biomarker for diagnosis of NPC.