Extracts from the World Health Report 1998
Life in the 21st century: a vision for all

Disease Trends

Of more than 50 million deaths worldwide in 1997, about one-third were caused by infectious and parasitic diseases such as acute lower respiratory tract diseases, tuberculosis, diarrhoea, HIV/AIDS and malaria; about 30% were caused by circulatory diseases such as coronary and cerebro-vascular diseases; and about 12% by cancers.

During the past few decades, substantial progress has been made in controlling some major infectious diseases. Some have disappeared or are almost eliminated as pubic health problems, but others remain daunting threats.

Global eradication of smallpox was declared in 1980 at the end of an eradication campaign which began in 1967.

The tropical disease yaws, which mainly affects the skin and bones, has virtually disappeared.

The latest in a series of cholera pandemics has been affecting much of the world since the 1960s and the disease is still endemic in some 80 countries.

The global threat of plague has declined in the past four decades, largely due to the impact of antibiotics, insecticides and other control measures, but cyclical epidemics still occur.

The largest yellow fever epidemic ever recorded was in Ethiopia in 1960-1962, causing about 30,000 deaths. There are about 30 000 deaths globally every year among about 200,000 annual cases, a decline largely due to immunization. However, since the late 1980s there has been a dramatic resurgence of yellow fever in Africa and the Americas.

Improvements in sanitation and hygiene standards in recent decades have made outbreaks of relapsing fever transmitted by lice rare; they are most likely to occur in unhygienic and crowded conditions arising from wars or natural disasters.

Recent environmental changes closely linked to water resources development and increases in population densities, have led to the spread of schistosomiasis to previously low-endemic or non-endemic areas. The disease remains endemic in 74 developing countries, mostly in Africa.

The onchocerciasis control programme which began in West Africa in 1974 has since protected an estimated 36 million people from the disease. It is expected that the global elimination of onchocerciasis as a public health problem will be achieved before 2008.

Chagas disease occurs only in the Americas from Mexico to Argentina, and the disease is targeted for elimination of transmission in the Southern Cone countries of Latin America by 2003.

There has been a significant recrudescence of sleeping sickness (African trypanosomiasis) particularly in central Africa, where reported cases have more than doubled over the past few years.

Since the first effective injectable vaccines against poliomyelitis were introduced in 1955, the disease has gradually been eliminated in much of the world, with cases declining by more than 90% since the campaign for global eradication by the year 2000 was launched in 1988.

WHO developed and promoted a multidrug therapy for leprosy, which it began to recommend in 1981. The global leprosy burden has since been reduced greatly. WHO’s goal is to eliminate leprosy as a public health problem by 2000.

Progress towards elimination of dracunculiasis (guinea-worm disease) in the past decade has been spectacular, with the number of cases falling dramatically worldwide; it is now confined to 17 countries, 16 of which are in sub-Saharan Africa.

The outlook for filariasis control and elimination is encouraging, and in 1997 the Health Assembly called for the elimination of lymphatic filariasis as a public health problem globally.

For the blinding disease trachoma the target is elimination by 2020 through long-lasting antibiotics.

Although there is hope of eliminating measles by the year 2000, it still kills nearly one million children a year.

Tetanus of the newborn is the third major killer of children (after measles and pertussis) among the six vaccine-preventable diseases of the Expanded Programme on Immunization, and is a concern in all WHO regions except Europe.

Once a target for eradication, malaria remains a major threat, and the disease is endemic in 100 countries. The aim of the current global malaria strategy is to reduce mortality by at least 20% compared to 1995 in at least 75% of affected countries by the year 2000.Complacency towards tuberculosis in the past three decades led to a decline in control programmes in many countries. The result has been a powerful resurgence of the disease, now estimated to kill 2.9 million people a year. One-third of the incidence in the past five years can be attributed to co-infection with HIV.

Epidemic meningitis is a recurrent problem in the “meningitis belt” of Africa stretching from Senegal to Ethiopia and including all or part of at least 15 countries with an estimated population of 300 million people.

Increasing urbanization during the past decades has led to an increase in the prevalence of dengue and dengue haemorrhagic fever. These conditions are reported from over 100 countries in all WHO regions except Europe. Dengue fever, and in particular life-threatening dengue haemorrhagic fever, often occurs in massive epidemics. WHO’s strategy continues to be based on prevention of transmission by controlling the vector.

There is a disturbing increase in the number cases of leishmaniasis infections. The disease is related to developmental and environmental changes which increase exposure to the sandfly vector. More recently the combination of visceral leishmaniasis and AIDS has appeared.

The hepatitis B virus infection(HBV) is a global problem, with 75% of the world’s population living in areas where there are high levels of infection. More than 2 billion people worldwide have evidence of past or current HBV infection, and 350 million are chronic carriers of the virus.

First identified in 1989, the hepatitis C virus (HCV) has now become a major public health problem. The incidence of HCV infection is now well known but WHO estimates 30% of the world population is infected and 170 million individuals are chronic carriers, at risk of developing liver cirrhosis and liver cancer.

During the past 20 years numerous new infectious diseases have emerged and others have re-emerged in many parts of the world. Of these, HIV, has had by far the most profound global impact. Others include Legionnaires’ disease, Ebola haemorrhagic fever, Rift Valley fever, monkeypox, and the new variant of Creutzfeldt-Jakob disease.

The appearance in humans of a new influenza virus, A(H5N1), in Hong Kong at the end of 1997, whose animal source is suspected to be poultry, was a reminder of the need for continuing strong global influenza surveillance.

Reproduced from and with acknowledgement to the report from WHO - March 1998