Infectious Aetiology of Cancer: Developing World Perspective

Infection attributable cancers contribute over 1/4th of all cancers in the developing countries (26.3%) compared to the developed countries (7.7%), (Parkin, 2006). Overwhelming majority are related to viral infections. In contrast to other carcinogens where it is usually a ‘hit and run’ kind of situation, with infectious agents particularly viruses one may precisely demonstrate and prove its presence and integration within host neoplastic cells. Oncogenic DNA viral genome incorporates itself directly into host cells DNA while oncogenic RNA viral genome is transcribed into host cell DNA by reverse transcriptase. Neoplastic transformation usually follows. Oncogenic mechanisms include acting as promoter, transforming protooncogenes into oncogenes. Credit goes to Dr Peyton Rous, a noble laureate pathologist who demonstrated that it was possible to transmit tumours from one animal to other like transmission of an infection. Human tumours with proven or proposed viral aetiology include ‘Human papillomavirus (HPV)’, Epstein-Barr Virus (EBV), Hepatitis B and C viruses, RNA retroviruses like ‘Human T-lymphotropic virus (HTLV1)’, ‘Human Herpes Virus-8 (HHV-8). Bacteria with proven carcinogenic potential include ‘Helicobacter pylori’. Among fungi aflatoxins produced by ‘Aspergillus flavus’ are potent carcinogens. Among parasites ‘Schistosoma’ and ‘Clonorchis sinensis’ are implicated in the causation of cancer.