Malaria status & challenges of the epidemic

3. How many people were affected by malaria in 2006?

• 3.1 Where are people at risk of being infected with malaria?
• 3.2 How many malaria cases and deaths were there in 2006?
• 3.3 Why is there a wide range of estimates?

3.1 Where are people at risk of being infected with malaria?

About half of the world population lives in areas where there is some risk of being infected with malaria. In 109 countries or territories worldwide, malaria is either constantly present (endemic) or not present anymore but with a risk of coming back. These countries are at different stages in the process of malaria elimination. The remaining countries are certified malaria-free or have had no local infections for over a decade (see Map).

The largest populations at any risk of malaria live in the WHO South-East Asia and Western Pacific Regions although the magnitude of the risk varies from one region to another (see Fig. 3.2).

One fifth of the world population is at high risk of contracting malaria, living in areas with one or more new malaria cases per 1000 inhabitants per year. Nearly 50% of all persons at risk of malaria infection live in the WHO African Region and 37% in the WHO South-East Asia Region.

The vast majority of people at low risk of malaria infection live outside Africa in areas with one or more new malaria cases per 1000 inhabitants per year. Although low risk areas cover one third of the world population living across a huge area, they account for less than 3% of all reported malaria cases.

Table 3.1: Estimates of populations at risk of malaria, number of cases and deaths

This text is a summary of: WHO, World Malaria Report (2008) ,
3. Estimated burden of malaria in 2006, Population at risk, p.9

3.2 How many malaria cases and deaths were there in 2006?

The numbers of malaria cases and deaths are difficult to determine with accuracy. In 2006, there were an estimated 247 million malaria cases but the real value could be lower than 200 million or over 300 million. That year, an estimated 881 000 people died from malaria (see Table of estimates by region).

Malaria cases in the WHO African Region are mostly caused by the parasite Plasmodium falciparum. Outside Africa, other Plasmodium species are more common.

In 2006 the vast majority of cases and deaths occurred in the WHO African Region (86% and 90% respectively), followed by the South-East Asia (9% and 4%) and Eastern Mediterranean WHO Regions (3% and 4%).

In the WHO African Region, 90% of the malaria cases occurred in the 19 countries with the largest populations and over half were in just five countries: Nigeria, Democratic Republic of the Congo, Ethiopia, Tanzania and Kenya (see number of cases and number of deaths by country).

Outside the WHO African Region: ten countries accounted for 90% of the malaria cases: mainly India, which accounted for a third of cases, followed by Sudan, Myanmar, Bangladesh, Indonesia, Papua New Guinea, Pakistan, Brazil, Somalia and Afghanistan (see Fig. 3.6 for number of cases and Fig.3.10 for number of deaths).

The majority of the malaria deaths (85%) occurred in children under five years of age. The proportion is much higher in the African and Eastern Mediterranean WHO Regions than in other regions (see Table of estimates by region).

According to data and estimates, only one in five malaria deaths was reported worldwide in 2006.

This text is a summary of: WHO, World Malaria Report (2008) ,
3. Estimated burden of malaria in 2006, Malaria cases, Malaria Deaths, p.10-12

3.3 Why is there a wide range of estimates?

It is very hard to calculate the number of malaria cases and deaths accurately.

Estimates are based, in part, on the numbers of cases reported by national malaria control programmes. Therefore, whether or not reported cases are a true reflection of the number of malaria cases in a region depends on three factors:

• The quality of reports from routine surveillance systems.
• The proportion of patients that use public health facilities compared to those that use private health facilities or who do not seek treatment at all. For instance, in South-East Asia a large number of patients use private services, which results in official statistics that often report too few new malaria cases.
• The proportion of cases with a confirmed diagnosis. For instance, in the WHO African Region only a small number of samples from patients are sent for laboratory analysis, and diagnosis is only based on malaria symptoms such as fever, headache, vomiting and diarrhoea. This is likely to result in too many cases being reported because not everyone with signs that could be attributed to a malaria infection really has the disease.

In 2006, the WHO estimated that 1.2 billion people were at high risk of being infected with malaria and a further 2.1 billion were at low risk. These figures are consistent with those from studies carried out in 2003 and 2005 where similar data and techniques were used. Estimates of the number of deaths (around 1 million deaths per year) are also broadly consistent with those obtained in a study in 2004. The main difference is that the new estimates include fewer deaths in the WHO Western Pacific Region, mainly because malaria seems to have declined in Cambodia and Viet Nam.

However, the figures are not consistent with those from studies carried out in the 1990s and from a publication from 2008. Some of the discrepancies can be due to differences in the way data are analysed. Others could be due to the way in which results were analysed or to a true decline in the number of malaria cases since the 1990s.

With all methods, the calculated values for the number of cases and deaths are very uncertain. This affects estimates for each country and the ranking of countries within regions. There are two methods to calculate the numbers of malaria cases and deaths: by estimating the likely values from limited data, or by using routine surveillance data. This latter method is better but depends critically on the information that each country gives to the WHO and on data from published surveys. If information is incomplete but the number of missing reports is registered, the estimates can be adjusted properly. However, if these records are not kept, the adjustments could overestimate or underestimate the number of malaria cases and deaths. Unfortunately, surveillance systems and registration is weakest in countries most affected by malaria and that could lead to very large differences between calculated and actual values.

This text is a summary of: WHO, World Malaria Report (2008) ,
3. Estimated burden of malaria in 2006, Comment, p.12-15