Viruses that cross borders: factors responsible for global dissemination of viral infections.

OBJECTIVE: Pandemic viral infections as emerging infectious diseases are of a great global concern. However, for some viruses, particular strains are endemic to specific areas and can be genetically distinguished from strains in other regions. In contrast, for some other viruses, genetically similar strains can spread and circulate all over the world. This study addresses global dissemination of various viral infections. METHODS: We classified 34 viruses as per their ability to cross borders by review. We also described factors responsible for and the dynamics of global dissemination. We examined biological characteristics of viruses, manners or routes of transmission, host responses and epidemiological factors. RESULTS: Factors required for viruses to cross borders include 'non-blood infection', 'short incubation period', 'short infectious period', 'frequent re-infection', 'small basic reproductive number (R(0))' and 'high annual incidence'. CONCLUSION: Knowing the factors responsible for global dissemination of pathogens is useful for controlling and/or containing both classic and emerging infectious diseases.