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Measles eradication
The WHO has set regional elimination goals for measles virus (MV) eradication to be achieved by 2020 or earlier. Global mortality due to measles has been reduced by 78%, from an estimated 733,000 deaths in 2000 to an estimated 164,000 deaths in 2008. The WHO Region of the Americas has sustained measles elimination since 2002 and four of the five remaining WHO regions have set regional elimination goals to be achieved by 2020 or earlier [1]. In view of the close genetic relationship of MV to the veterinary members of the same morbillivirus genus, when MV is eradicated and if vaccination is discontinued, an opportunity for zoonosis may arise. Morbilliviruses are highly contagious pathogens that cause some devastating viral diseases in humans and animals. Each morbillivirus is monoserotypic, and there are shared sequences and hence epitopes between all members of the genus. Therefore, infection with one virus provides varying degrees of protection to the others. Therefore, at present immunity to MV in the human population is likely to decrease the risk of infection with the veterinary viruses and their subsequent adaptation. Lessons have been learned from animal-to-human virus transmission, i.e., HIV, and more recently from severe acute respiratory syndrome and avian influenza virus infections. We are therefore alerted to the risk of zoonosis from the veterinary morbilliviruses. In this review the evidence from viral genomics, animal studies and cell culture experiments will be evaluated to assess the possibility of cross-infection of humans with these viruses.
Phylogenetic relationship of morbilliviruses
Morbilliviruses constitute a genus within the family Paramyxoviridae , subfamily Paramyxovirinae . Members of the genus include MV, canine distemper virus (CDV), rinderpest virus (RPV), peste des petits ruminants virus (PPRV) and the more recently identified marine morbilliviruses, phocine distemper virus (PDV), dolphin morbillivirus (DMV) and porpoise morbillivirus. The morbilliviruses are thought to have a common ancestor that adapted to different species. The cattle virus, RPV, shares closest identity to MV, with PPRV (natural host sheep and goats) being more distant. Phylogenetic evidence suggests that MV may have evolved from RPV following the domestication of cattle [2]. RPV is now eradicated [3], but humans may be susceptible to one or more of the other veterinary morbilliviruses. Due to their close sequence similarity, PDV...