MICROBIOLOGY
Changes in global disease patterns: the challenge for microbiologists
The spread of diseases from one natural habitat to another, less-conducive environment is one result of climate change, facilitated by the ease with which individuals can now move around the world. Here, Mike Wren provides a background to the likely impact on microbiological services.
The challenges that face clinical microbiologists have been listed previously and show that a higher proportion of disease is transmited by insect vectors in the tropics than in the temperate regions of the globe. A higher proportion of the diseases convey long-lasting immunity in the temperate areas than in the tropics, and animal reservoirs of disease are more frequent in the tropics. Past history has shown that this is likely to change. Most of the temperate diseases are
acute rather than slow, chronic or latent, and the patient either dies or recovers. In the tropical regions, however, diseases are more or less split between lasting for weeks, months or years. Traditionally, 25 major human pathogens originated in the Old World, with only Chagas disease originating in the New World.1 Eight of the 15 temperate diseases
probably reached humans from domestic animals, three from apes or rodents, the remaining four of unknown origins (Table 1). Historically, the spread of diseases was
driven by famine, war, slavery and the effects of colonisation. In the modern era, the spread of diseases, both of humans and animals, has followed trade routes and in particular by rapid international travel, and probably exacerbated by climate change and global warming. More recently, increased urbanisation has led to the increase of certain diseases2 Past contemporary 20th century
(Table 2).
diseases occurring in epidemic proportions have included poliomyelitis, tuberculosis, equine encephalitis, dengue, chikungunya virus, Zika virus and human immunodeficiency virus. We are now on the brink of an era in
which re-emerging and new pathogenic microorganisms can be spread by the increase in rapid global travel and connectivity, and the occurrence of global climate change.
Emergence of pathogens into human populations The spillover of animal pathogens into humans due to the destruction of animal natural habitats for farming and other crop raising has resulted in the emergence of previously restricted animal pathogens into human populations in recent decades. Subsequent human-to-human transmission has resulted in outbreaks
Intensive pig farming which spread into virgin areas containing bats resulted in Nipah virus infections in pig farmers (colourised transmission electron micrograph [TEM] of a Nipah virus particle in a Vero cell).
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