World health report

Executive summary

Disease trends

Of more than 50 million deaths worldwide in 1997, about one-third were due to infectious and parasitic diseases such as acute lower respiratory diseases, tuberculosis, diarrhoea, HIV/AIDS and malaria; about 30% were due to circulatory diseases such as coronary heart disease and cerebrovascular diseases, and about 12% were due to cancers. While deaths due to circulatory diseases declined from 51% to 46% of total deaths in the developed world during the period 1985-1997, they increased from 16% to 24% of total deaths in the developing world. Cancer deaths increased from 6% to 9% of total deaths in the developing world but they formed a constant proportion of 21% of total deaths in the developed world. Infectious and parasitic diseases decreased from 5% to 1% of total deaths in the developed world and from 45% to 43% of total deaths in the developing world.

During the last few decades, substantial progress has been made in controlling some major infectious diseases. Some have disappeared or are almost eliminated as public 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 last four decades, largely due to the impact of antibiotics and 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 and 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. The African Programme for Onchocerciasis Control began in January 1996 and covers 19 additional countries. The Onchocerciasis Elimination Programme in the Americas was stated in 1991 in six Latin American countries and aims to eliminate severe pathological manifestations of the disease and to reduce morbidity in the Americas through the distribution of ivermectin. 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 2010.

There has been an important recrudescence of sleeping sickness (African trypanosomiasis), particularly in central Africa, where reported cases have more than doubled over the past few years. In 1997, the World Health Assembly acknowledged the danger of epidemics in a number of African countries.

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 over 90% since the campaign for global eradication by the year 2000 was launched in 1988.

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

Progress towards the elimination of dracunculiasis (guinea-worm disease) in the past decade has been spectacular, with the number of cases falling dramatically worldwide and 21 formerly endemic countries being certified free of dracunculiasis transmission.

The outlook for filariasis control and elimination is encouraging, and in 1997 the World 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 1 million children a year.

Tetanus of the newborn is the third killer of children (after measles and pertussis) among the six EPI vaccine preventable disease, and is a concern in all WHO regions except Europe.

Once also 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 last three decades led control programmes to be run down 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 increase in incidence during the last 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 last 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 (DHF), 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 of leishmaniasis infections. The disease is related to economic development and environmental changes which increase exposure to the sandfly vector. More recently the combination of visceral leishmaniasis and AIDS has appeared with the spread of the AIDS pandemic.

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 worldwide is not well known, but WHO estimates that 3% of the world population is infected with HCV nd 170 million individuals are chronic carriers at risk of developing liver cirrhosis and liver cancer.

The increased life expectancy recorded in recent decades, together with changes in lifestyle stemming from socioeconomic development, have paradoxically favoured non-communicable diseases, especially circulatory disorders, cancer, and some forms of mental illness. Coronary heart disease and stroke account for 12 million deaths a year, cancer kills 6 million, and 3 million deaths are due to chronic obstructive pulmonary disease (COPD). These and other noncommunicable diseases now cause nearly 40% of all deaths in developing countries, where they affect younger people than in industrialized countries. The epidemiological transition, with its double burden of infectious and noncommunicable diseases, is common to many developing countries, where 64% of deaths due to circulatory diseases, 60% of cancer deaths and 67% of COPD deaths now occur. In many parts of the world, dramatic shifts in cancer occurrence are being observed. In several newly industrialized regions cancer has become, unexpectedly quickly, one of the leading causes of death. Cancer of the breast, colon and prostate have emerged in several countries in which they were hardly known 20-30 years ago. For all countries, breast cancer is the most common in women, followed in affluent countries by colorectal, lung and stomach cancers. In developing areas, cervical cancer is second, followed by stomach cancer. The most remarkable changes in the rankings compared to 10 years ago are the steep upward trend of prostate cancer (partly due to the introduction of early detection programmes), the increase in breast cancer, especially in developing countries, and the increase in lung cancer worldwide.

Population ageing, unhealthy diets, obesity and a sedentary lifestyle are the main factors that explain the alarming upward trend in recent years in diabetes mellitus. Along with increased longevity and socioeconomic development has come an increase in some forms of mental disorders in the last two or three decades. Social and environmental factors play a role, particularly in explaining increases in alcohol and drug abuse, suicide, violence and other behavioural problems.

During the last 20 years numerous new infectious diseases have emerged and others have re-emerged in many parts of the world. Of these, the human immunodeficiency virus (HIV) that causes AIDS has had by far the most profound global impact. Other new diseases include Legionnaires' disease, Ebola haemorrhagic fever, Rift Valley fever, monkeypox, and the new variant of Creutzfeldt-Jakob disease (nvCJD).

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.