Diseases that need new drugs: Need of the hour
7
travel has an important role in bringing people into contact with infectious agents (Cliff et al., 2002). An increase in travel-associated diseases, anticipated in 1933 (Massey, 1933), is now demonstrated by an international airline hub-to-hub pandemic spread of acute haemorrhagic conjunctivitis in 1981 (Morens, 1998), epidemics of meningococcal meningitis associated with the Hajj, exportation of epidemic SARS from Guangdong Province of China to Hong Kong to Beijing, Hanoi, Singapore, Toronto and elsewhere (Peiris et al, 2003), Bird flu and swine flu from Europe to Asia in 2006 and 2009. The persistent spread of HIV along air trucking, drug-trafficking and troop-deployment routes is a deadly variation on this theme (Quinn, 1994; Daley et al, 1999; Ronald, 1995).
Prion diseases A prion is an abnormal, transmissible agent that induces abnormal folding of normal cellular proteins in the brain, leading to rapidly progressive brain damage and death. Prion diseases or transmissible spongiform encephalopathies (TSEs) are a family of rare progressive neurodegenerative disorders that affect man and animals, with a long incubation periods, spongiform changes with neuronal loss, that failed to induce inflammatory response (Aguzzi & Heikenwalder, 2006). Injections of ground-up brain tissue from an affected animal or man into another animal transmit the disease, suggesting that the disease is caused by a virus like agent. But no genome was identified from such brain tissues, and treatment with UV light (that destroy DNA) does not reduce its infectiousness, indicate that the causative agent is not a virus. To date, the evidence indicates that the infectious agent of TSEs is a protein (Aguzzi & Heikenwalder, 2006), called “prion proteins� (PrP) or simply prions by Stanley Prusiner that bring him the Nobel Prize in 1997 (Prusiner, 2001). The normal cellular protein (PrPC) are transmembrane glycoprotein on the surface of certain cells (neural and hematopoietic stem cells) is easily soluble, digested by proteases and is encoded by a gene PRNP located on chromosome no 20. While the abnormal, diseaseproducing protein PrPSc (for scrapie) has the same amino acid sequence in their primary structure but secondary structure contain beta conformation, insoluble in solvents (except the strongest solvents) and resistant to proteases. When PrPSc comes in contact with PrPC, it converts the three-dimensional configuration of PrPC into more of itself, and bind to each other forming aggregates (Mead, 2006). It is not clear whether these aggregates directly cause the cell damage or are cellular dame is a side effect of the disease process. Prion diseases are either inherited or infectious. Inherited Prion Diseases are spontaneous and inherited with infectious maladies. It includes (i) Creutzfeldt-Jakob disease (CJD): 10–15% are inherited (the patient comes from a family in which the disease has appeared