At a glance
Millions of people in developing countries die every year of conditions that are easily treatable elsewhere. They die not only because of lack of medicines and health care but also because many are so undernourished that relatively mild complaints become killers.
The most lethal diseases are AIDS, tuberculosis, pneumonia, diarrhoea and malaria. The most vulnerable to many of these are children under five years old.
Also deadly are perinatal conditions that affect children in the period from just before to soon after birth. These conditions include low birth weight, birth asphyxia and birth trauma.
But disease not only kills. It can also debilitate people for life and make it harder for them to work. This perpetuates a vicious cycle that pushes them and their families further down the poverty ladder, making them even more susceptible to illness.
Global warming is likely to change the patterns of disease and exacerbate health crises in many poor countries, resulting in many more deaths, says the World Health Organization (WHO).
One caveat to bear in mind when researching health issues is that data is patchy for Africa, the Middle East and Asia. WHO relies on member states for health statistics, but millions of births and deaths go unreported and not all countries conduct surveys. This makes it difficult to build up an accurate picture of how diseases affect countries. Many global figures are estimates, and these are not always comparable because they may be based on different methodologies.
Our In detail section has sections on the biggest killer diseases and conditions.
Below is information on some of the most lethal conditions people face in developing countries (cancer and heart disease are not included):
- Lower respiratory infections
- Perinatal conditions and maternal mortality
- Diarrhoeal diseases
Other major infectious diseases affecting developing countries include:
- Sleeping sickness
Lower respiratory infections
Millions of people die of lower respiratory infections each year – most of them children under five years old.
These includes diseases of the lungs, windpipe or bronchial tubes, the most lethal being pneumonia. Other respiratory diseases are bronchitis and Legionnaire's disease – a rare form of pneumonia.
Tuberculosis and whooping cough are also lower respiratory infections, but death tolls are tallied separately by the U.N. World Health Organization (WHO).
They are spread by coughing, sneezing, laughing or exhaling.
Infection: Half of pneumonia cases are caused by bacteria, but they can also be caused by viruses. The alveoli – microscopic air-filled sacs of the lung responsible for absorbing oxygen from the atmosphere – become inflamed and flooded with fluid.
Symptoms: Sudden onset of shivering fits, fever, chest pains and coughing. The cough starts out dry, but patients soon begin to cough up phlegm, which can be yellow or bloodstained.
Breathing can become fast and shallow and painful, and patients sometimes find themselves gasping for air. They may even start to go blue around the lips and nails due to a lack of oxygen.
Treatment: Pneumonia can be treated with antibiotics, and there is a vaccine available against the most common form of pneumonia, caused by the bacterium Streptococcus pneumoniae.
CHRONIC OBSTRUCTIVE PULMONARY DISEASE
This is a non-communicable respiratory disease that kills more than 3 million people a year. It is mostly caused by smoking and is not curable.
Tens of millions of people live with HIV, the majority in sub-Saharan Africa. In the past decade, new infection rates have stabilised or fallen in most regions, except Eastern Europe, Central Asia, the Middle East and East Asia.
Spread: The HIV virus is transmitted through unprotected sex, through blood (particularly through transfusions or intravenous drug use) and from mother to baby via pregnancy, labour or breast milk. Many people living with HIV do not know they are infected.
Treatment and prevention: There is no cure for HIV/AIDS, but its effects can be contained with drugs. However, many people living with HIV/AIDS do not have access to the necessary daily cocktail of drugs.
Condom use is the most effective form of prevention.
For more detailed information, see our HIV/AIDS crisis briefing.
Perinatal conditions and maternal mortality
These are some of the main killers and affect millions of children during the period just before and soon after birth.
Low birth weight is the most common cause of death, followed by birth asphyxia and birth trauma, according to the WHO.
The conditions develop because the mother is malnourished or in poor health, and because of a lack of proper medical care at birth.
Malnutrition and poor medical care also mean hundreds of thousands of women a year die from complications related to pregnancy or childbirth. And about 20 times that number suffer serious injury or disability - between 8 million and 20 million a year.
Diarrhoea is a symptom of gastrointestinal infection that kills hundreds of thousands of people a year, mostly children.
The best known infections are cholera and dysentery, which cause severe, sometimes life-threatening forms of diarrhoea.
Even when it is not lethal it contributes to worsening malnutrition and weakness. Two billion people a year develop diarrhoea.
It is caused by a host of bacterial, viral and parasitic organisms.
Infection is spread through contaminated food or drinking-water, or from person to person as a result of poor hygiene. The most common cause is contamination of water or food with human faeces.
Diarrhoea can be treated with oral re-hydration salts. Zinc is also now advocated as an accompanying treatment.
Infection: Cholera infects tens of thousands of people globally every year. Few die of the disease. It is an acute intestinal infection caused by the bacterium Vibrio cholerae and spread through contaminated food and water.
Sudden, large outbreaks are usually caused by a contaminated water supply. If a community is unprepared for an outbreak, as many as 50 percent of people with cholera may die because of lack of treatment.
The WHO says hygienic disposal of human faeces, an adequate supply of safe drinking water and good food hygiene are essential.
Symptoms: Develop within one to five days and include diarrhoea and vomiting that can quickly lead to severe dehydration and death if not treated promptly. But most infected people do not become ill, although the bacterium is present in their faeces for seven to 14 days.
Treatment: Cholera is easy to treat through oral rehydration salts to replace lost fluids. In severe cases, intravenous drips may be needed to save the patient's life.
There are limited supplies of two oral vaccines that provide high-level protection for several months against cholera caused by V. cholerae O1. Both are suitable for use by travellers but they have not yet been used on a large scale for public health purposes.
Dysentery is a term covering diseases that trigger inflammation of the lining of the large intestines, causing stomach pains, diarrhoea, vomiting and fever.
Infection: Dysentery is highly contagious, and caused by bacteria from contaminated food or water, or by physical contact with a person who has already been infected.
Epidemic dysentery is a particularly severe form that is caused by the bacterium Shigella dysenteriae type 1 (Sd1).
Amoebic dysentery is caused by the amoeba parasite that burrows through the intestinal wall into the bloodstream and spreads to other organs, including the liver, lungs and brain.
Symptoms: Bloody diarrhoea, abdominal cramps, fever and rectal pain.
Treatment: Adults usually only need rehydration salts to recover from dysentery caused by bacteria. Children may need antibiotics.
Amoebic dysentery however needs to be treated with a combination of drugs to kill the parasite, treat any bacterial infection, and fight infection of the liver and other tissues.
Tuberculosis (TB) is on the rise, particularly affecting Southeast Asia and Africa. A third of the world's population is infected with TB.
It kills hundreds of thousands of people a year, and is a leading killer of people living with HIV/AIDS.
Each year, millions fall ill with TB. The average TB patient loses three to four months of work time as a result of TB.
Unlike most of the diseases listed above, TB affects adults more than children.
Symptoms: These depend on where the TB bacteria grow. TB in the lungs may cause a persistent bad cough, pain in the chest or blood or sputum to be coughed up.
Other symptoms are weakness, weight loss, chills, fever and night-time sweating.
Spread: TB of the lungs or throat can be spread through the air when an infected person coughs or sneezes. But TB is usually not infectious if it has settled in other parts of the body such as the kidneys or spine.
Treatment: This takes at least six months and requires as many as four different drugs, which are often unavailable in developing countries. When available, they are effective in up to 95 percent of cases, according to the Global Fund to Fight AIDS, Tuberculosis and Malaria.
However, there are growing concerns about the rise of multi-drug resistant TB caused by inconsistent or partial treatment, which threatens TB control efforts and HIV/AIDS treatment.
Nearly half the world's population is at risk from malaria, which is spread by the female anopheles mosquito.
It affects people in most developing countries, but the vast majority of deaths occur in sub-Saharan Africa, home to the most deadly form of the virus.
An estimated 219 million people contracted malaria in 2010, and 660,000 people died of the disease.
Symptoms: Include fever and flu-like illness with headaches, muscle aches, shivering and lethargy. Nausea, vomiting, diarrhoea, anaemia and jaundice can also occur.
If not properly treated, infection with the type of malaria known as Plasmodium falciparum may cause kidney failure, seizures, coma and death within hours.
Prevention and treatment: In recent years drug-resistant strains of malaria have spread, rendering once effective – and cheap – anti-malarial drugs such as chloroquine almost useless in many areas. Almost all cases of Plasmodium falciparum in Africa are resistant to these drugs.
The best available treatment is called artemisinin combination therapy, or ACT. This more expensive treatment is derived from a Chinese herb.
But in recent years, the parasite has developed resistance to artemisinin in parts of southeast Asia. The fear is that resistance to artemisinin will spread to Africa where the majority of malaria cases and deaths occur.
Insecticide spraying and bednets help prevent the spread of malaria.
For more, read our malaria briefing.
There has been a vaccine for this childhood disease for decades, yet it is a leading cause of death for young children in developing countries. Tens of thousands of children die of the virus each year.
The virus grows in cells lining the back of the throat and lungs.
Spread: Measles is one of the most contagious diseases known, spread by coughing and sneezing, or close personal contact.
Symptoms: High fever begins about 11 days after infection, and lasts for up to a week. A runny nose, cough, red and watery eyes and small white spots inside the cheeks are early symptoms.
Later a rash develops on the face and upper neck, and can spread to the hands and feet. Children do not usually die of measles directly but of complications, including encephalitis, severe diarrhoea, ear infections and pneumonia. Blindness can also result from measles.
Human African trypanosomiasis, or sleeping sickness, is caused by a parasite that is spread by the tsetse fly. It infects thousands every year.
There are two forms:
About 95 percent of cases are Trypanosoma brucei gambiense, found in western and central Africa. Symptoms usually do not emerge for months or years after the person became infected, by which time the central nervous system is affected.
A few cases are Trypanosoma brucei rhodesiense, found in eastern and southern Africa. Symptoms emerge a few weeks or months after infection.
Symptoms: In the first stage symptoms include fever, headaches, joint pains and itching.
The second stage begins when the parasite invades the central nervous system, called the neurological stage, and this is when symptoms usually begin to appear. These include confusion, sensory disturbances, poor coordination, and disturbance of the sleep cycle.
Treatment: Without treatment, sleeping sickness is fatal. Diagnosis must be before the neurological stage in order to avoid difficult and risky treatment procedures.
Early treatment includes drugs which are generally effective and less toxic. Drugs used in the second stage have to reach the parasite, which means crossing the blood-brain barrier. These are both toxic and difficult to administer – in some cases the side effects can be fatal.
Dengue fever has spread dramatically in the past few decades, and now about half of the world's population is at risk from dengue.
It is a mosquito-borne tropical virus that infects millions of people each year, most of them in Southeast Asia and the western Pacific, and can be fatal.
Unlike the mosquitoes that cause malaria, dengue mosquitoes are daytime feeders.
Symptoms: These usually appear a week after infection, and include a sudden high fever, headaches and severe joint and muscle pain. The illness lasts up to ten days but complete recovery can take a month.
Treatment: Rest and drinking plenty of fluids. Two of the four types of dengue fever can progress to dengue haemorrhagic fever, which causes bleeding from the nose, gums and inside the body, and can be fatal.
No vaccine is currently available.
Meningitis is a serious and sometimes fatal disease that infects the membranes surrounding the brain and spinal cord. The disease affects mainly young children, but can also infect adults. The majority of cases occur in Africa's "meningitis belt" which stretches from Senegal in the west to Ethiopia in the east.
Viral or bacterial infections are the main causes of meningitis. Viral meningitis is less severe and clears up without specific treatment, but the most common form of bacterial meningitis kills 50 percent of sufferers if untreated – and up to 20 percent of survivors suffer brain damage or hearing loss.
There are vaccines against some forms of the disease but these are not always available in Africa.
Spread: It is usually passed between people by coughing and sneezing or kissing.
Symptoms: A stiff neck, severe headache, fever, vomiting and sensitivity to light. As the disease progresses, patients may experience seizures.
For more, read our meningitis briefing.
Ebola haemorrhagic fever (EHF) is a severe, often fatal disease that has appeared sporadically since it was identified in 1976. The disease is caused by infection with Ebola virus, named after a river in the Democratic Republic of Congo where it was first recognised.
Symptoms: Include a sudden onset of fever, intense weakness, muscle pain, headache and sore throat.
This is often followed by vomiting, diarrhoea, rash, impaired kidney and liver function and, in some cases, both internal and external bleeding. The fever has an incubation period of two to 21 days.
Spread: The Ebola virus is transmitted by direct contact with the blood, secretions, organs or other bodily fluids of infected people.
Burial ceremonies where mourners have direct contact with the body of the deceased person can play a significant role in the transmission of Ebola. Health care workers have frequently been infected while treating Ebola patients.
Treatment: There is no specific treatment or vaccine.
Hundreds of cases and deaths have been documented since the Ebola virus was discovered.
- Between June and November 1976, EHF infected 284 people in Sudan, causing 151 deaths. In the Democratic Republic of Congo, there were 318 cases and 280 deaths in late 1976.
- Between September 2000 and January 2001, the Sudan subtype of the Ebola virus infected 425 people, including 224 deaths, making it the largest epidemic so far of Ebola.
- From October 2001 to December 2003, several EHF outbreaks of the Zaire subtype, were reported in Gabon and the Republic of Congo, with a total of 302 cases and 254 deaths.
- In 2007, EHF of the Zaire subtype infected 264 people and killed 187 in Congo. Subtype Bundibugyo infected 149 people and killed 37 in Uganda.
Poliomyelitis (polio) is a highly infectious disease caused by a virus that invades the nervous system, and can cause total paralysis within hours.
Spread: The virus is spread through contaminated food and water, multiplies in the intestine and spreads to the nervous system.
Symptoms: Many people have no symptoms, but excrete the virus in their faeces and transmit it to others.
Visible symptoms are fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs. A few cases lead to irreversible paralysis (usually in the legs), and can be fatal.
It mainly affects children under the age of five.
Treatment and prevention: There are several vaccines that protect a child for life. However, there is no cure.
The number of cases has dropped by 99 percent since a global effort to eradicate the disease was launched in 1988 when an estimated 350,000 people developed polio. All countries – except Afghanistan, Nigeria and Pakistan – are now free of polio.
Scientists are constantly on the alert for new strains of flu which could unleash a pandemic, killing millions of people worldwide within months.
Flu viruses regularly mutate, and health experts fear that a new strain will develop to which most people will have little or no immunity. Recent scares include the bird flu pandemic which began in 2003 and swine flu which hit the headlines in 2009.
There is no cure for flu, but preventive vaccines are developed each year for specific strains.
Common seasonal flu kills between 250,000 and 500,000 people in an average year. Most deaths in industrialised countries occur among people over 65 years old, but little is known about the effects of seasonal flu in developing countries.
For more, read our Global flu pandemics briefing.
The World Health Organization (WHO) is a good place to start. It has fact sheets on a huge variety of health issues, health profiles of countries across the world, and an impressive database of statistics.
Below are links to further reading, grouped by disease.
Lower Respiratory Infections, including pneumonia
Perinatal conditions and maternal mortality
Diarrhoea diseases, including cholera and dysentery