Global Alert and Response (GAR)

WHO Report on Global Surveillance of Epidemic-prone Infectious Diseases - Introduction


Modern times, rapid change - how this impacts on infectious diseases

Rapid change is one of the hallmarks of current times. This includes rapidly changing environments for microbes as well as humans. For example, there has been unprecedented population growth, accompanied by rapid, unplanned urbanization. This has resulted in large increases in urban slums without adequate water and waste management. In addition many of the people living in slums are migrants from rural areas, with little immunity to urban diseases. These changes create an excellent environment for communicable diseases to flourish. For example, rapid urbanization combined with lack of vector control (or in the case of South America the cessation of vector control), has lead to increased spread of Aedes aegypti mosquitos and consequently increased risk of both dengue and yellow fever epidemics.

The aeroplane is another hallmark of modern times. Air travel has become common place, and fast. The result is increased potential for rapid dispersion of infectious diseases to new environments. Other factors of the modern age that have increased the threat from communicable diseases include changes in land use and agriculture, and increased encroachment of people on forest and woodlands areas.

Civil unrest and war contribute to the spread of infectious disease. During wars, troops and equipment as well as displaced persons are constantly moving from one place to another, carrying with them infectious disease organisms and vectors. This is coupled with destruction of the physical and often economic infrastructure of the area. For example, dengue increased in South-East Asia during the Second World War and the immediate post-war period, due to the spread of mosquitos and different virus strains throughout the region. Wars have also been very important in the spread of plague. The deforestation associated with the Viet Nam War in the 1970s, coupled with the collapse of the local infrastructure, is considered to be the cause of a large epidemic of plague during the 1970s and early 1980s.

Wars also spur widespread mass migrations. Migrants may have no immunity to diseases endemic in the new area; in addition, they may bring with them diseases that are common in their former home but which are not endemic in the new area. Migrants are stressed, often physically and emotionally. This combination of conditions especially in crowded makeshift refugee camps may lead to disease epidemics, such as the cholera epidemic in Goma, Democratic Republic of the Congo, which killed thousands of people in a short period of time during 1994.

Natural disasters, such as earthquakes and flooding often create conditions that are favourable to outbreaks of communicable disease. For example, in 1997, heavy rain and floods in the Horn of Africa were followed by outbreaks of cholera. In 1998 in Central America, unusual weather patterns, including hurricane Mitch were followed by a resurgence of cholera. The 1994 outbreak of plague in Surat, India was preceded by flooding.

On the positive side, there have been tremendous strides in the control and elimination of some communicable diseases especially for vaccine preventable diseases. Smallpox has been eradicated from the world, and major efforts are being made towards the eradication of polio. In many countries, living conditions have improved substantially with associated health benefits. There have also been considerable gains in life expectancy, especially in under-five mortality rates. Scientific knowledge about the disease process has advanced markedly in recent years, especially in areas such as molecular biology.

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