Continued from the previous page
Re-emerging infectious diseases are due to the reappearance and increase in the number of infections from a known disease which had formerly caused so few infections that it had no longer been considered a public health problem.
Cholera can emerge afresh where water and sanitation systems have deteriorated and food safety measures are not adequate. In 1991, the seventh cholera pandemic reached the Americas where cholera had not been registered for a century; over 390,000 cases were notified in over 10 South American countries, two thirds of the world total. In 1997, cholera outbreaks chiefly affected Eastern Africa. While overall numbers have declined since 1991, over 147,000 cases were reported globally in 1997. In 1998, the epidemic spread over eastern and southern Africa; new outbreaks occurred in South America.
Dengue fever has spread in many parts of South-East Asia since the 1950s and re-emerged in the Americas in the 1990s following deterioration in active mosquito control and spread of the vector into urban areas. Infection with dengue virus has often resulted in dengue haemorrhagic fever (DHF) in Asia but rarely in the Americas until a severe outbreak in Cuba in 1981. DHF has since spread, and during the epidemics in Central and South America in 1995-1997, DHF was reported in 24 countries.
Diphtheria re-emerged in the Russian Federation and some other republics of the former Soviet Union in 1994 and culminated in 1995 with over 50,000 cases reported. The re-emergence was linked to a dramatic decline in the immunization programmes following the disruption of health services during the unsettled times immediately after the break-up of the Soviet Union. Since then, immunization services have been re-established, reversing the upward trend: in 1996, 13,687 cases were reported in the Russian Federation.
Meningococcal meningitis occurs worldwide, but devastating, large-scale epidemics have mainly been in the dry Sub-Saharan regions of Africa, designated the "African meningitis belt". Since the mid-1990s, epidemics in this area have been on an unprecedented scale, and epidemic meningitis has also emerged in countries south of the Ameningitis belt". A new strain of Neisseria meningitidis (serogroup A clone III.1), which was first seen in the 1980s in Nepal and China, has spread west and has now been diagnosed in major meningitis outbreaks in Africa.
Rift Valley fever (RVF) is a zoonotic disease typically affecting sheep and cattle in Africa. Mosquitoes are the principal means by which RVF virus is transmitted among animals and to humans. Persons in contact with sick animals occasionally become infected. The disease in humans is typified by fever and myalgia but, in some cases, progresses to retinitis, encephalitis or haemorrhage. Following abnormally heavy rainfall in Kenya and Somalia in late 1997 and early 1998, RVF occurred over vast areas, producing disease in livestock and causing haemorrhagic fever and death among the human population. The extent of the outbreak and the severity of the disease was probably due to many factors, including climatic conditions, malnutrition and possibly route of infection.
Yellow fever (YF) is an example of a disease for which an effective vaccine exists but, because it is not widely used in many areas at risk, epidemics continue to occur. The threat of YF is present in 33 countries in Africa and 8 in South America. Since the mid-1980s, there has been a steady increase in the number of cases or of countries reporting cases (up to 5,300 per year worldwide); yet, the true number of cases occurring could be many times higher, as outbreaks in general occur in remote areas and miss the attention of health services. YF is typically a disease of the tropical forest areas where the virus survives in monkeys. Humans bring it back to their villages and, if a suitable mosquito vector is present, the disease will spread quickly and kill a large proportion of the population which has no immunity.
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POINT OF FACT:
All but one of the diseases known to humankind still exist. Tuberculosis, once considered forgotten, has re-emerged as a global emergency.
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Number 1 1999
