Disease Burden

Available information about the epidemiology of DDW is generally incomplete, oftentimes the reliability is uncertain, and the data difficult to compare because methodologies, criteria, and end points vary from study to study. Thus, increased disease surveillance and well-designed epidemiological data collection, along with improved diagnostic tools, are needed for a clearer and more accurate assessment of DDW disease burden. The most common parameter to define burden of disease (BOD) is the disability-adjusted life year (DALY), which can be thought of as one lost year of "healthy" life (http://www.who.int/healthinfo/global_burden_disease/ metrics_daly/en/). The DALY is a complex parameter, calculated from the sum of years of life lost (YLL) due to mortality and years lived with disability (YLD) due to morbidity. Although imperfect, the DALY parameter allows one to quantify and compare the impact of disease on the health of populations across endemic areas

[5, 6]. This parameter is mainly driven by mortality rates [7], but also takes into consideration the impact of morbidity. Different studies using different methodological criteria report different BOD data [8]. BOD data included in Tables 1-3 are based on the WHO report "The Global Burden of Disease. 2004 Update", published in 2008.1 Infectious and parasitic diseases are the second cause of death worldwide, second only to cardiovascular diseases and ahead of cancers (Table 1). The main health impact, in terms of DALYs, is produced by respiratory tract infections, diarrheal diseases, and the "big three" (Table 2). However, the combined impact of the most neglected diseases, including leishmaniasis, Chagas disease, human African trypanosomiasis (HAT), and the helminthes infection is comparable to that caused by each one of the big three [9] (Table 3).

Diarrhea is a common symptom of gastrointestinal infections caused by a wide range of pathogens, including viruses (e.g., rotavirus), bacteria (e.g., Escherichia coli, Shigella, Campylobacter, and Salmonella, along with Vibrio cholerae during epidemics), and protozoa (e.g., Cryptosporidium). The burden of diarrheal disease is the highest among DDW2,3 (Table 2) [10], killing 1.8 million children with

Table l Leading causes of death, worldwide 2004 Disease

% of total deaths

Cardio vascular diseases Infections and parasitic diseases Cancers

Respiratory infections Respiratory diseases

WHO - The global burden of disease. 2004 update. WHO Geneva 2008

Table 2 Global health impact of major diseases of the developing worlda

Disease

Global

Clinical

Global deaths (in

Global DALY (in

prevalence

incidence/year

developing countries)

developing countries)

Millions

Millions

Millions

Millions

Lower resp. inf.

-

429.2

4.2 (2.9)

94.5 (76.9)

Diarrheal disease

-

4620.4

2.2(1.8)

72.8 (59.2)

HIV/AIDS

31.4

2.8

2.0(1.5)

58.5 (42.9)

Malaria

-

241.3

0.9 (0.9)

34.0 (32.8)

Tuberculosis

13.9

7.8

1.5 (0.9)

34.2 (22.4)

Dengue

50

9.0

0.019

0.7

aThe global burden of disease, 2004 update WHO, Geneva 2008

aThe global burden of disease, 2004 update WHO, Geneva 2008

'Global burden of disease 2004. WHO 2008 (http://www.who.int/healthinfo/global_burden_ disease/2004_report_update/en/index.html).

2Diarrheal disease web page. WHO (http://www.who.int/mediacentre/factsheets/fs330/en/).

3Diarrhea: Why children are still dying and what can be done. The United Nations Children's Fund (UNICEF)/World Health Organization (WHO), New York, Geneva (2009).

Table 3 Impact of neglected tropical diseasesa'b

Disease

Approximate global

Global no. of deaths

Global DALYs

prevalence (millions)

(thousands)

(millions)

Intestinal nematode

151

6

4.0

infections

Hook worm disease

576

0

1.1

Ascariasis

807

2

1.8

Trichuriasis

604

2

1.0

Lymphatic filariasis

65

0

5.9

Onchocerciasis

0.9

0

0.4

Schistosomiasis

2.61

41

1.7

Trachoma

6.3

0

1.3

Leishmaniasis

12

47

1.9

Human African

Trypanosomiasis

<0.1

52

1.7

Chagas disease

65

11

0.4

Leprosy

0.4

5

0.2

Dengue

50

18

0.7

aThe global burden of disease, 2004 update WHO, Geneva, 2008 bRef. [1]

aThe global burden of disease, 2004 update WHO, Geneva, 2008 bRef. [1]

approximately 4.6 billion episodes a year. According to WHO 2004 estimates, rotavirus accounts annually for an estimated two million hospitalized cases of severe diarrheal disease in children, and kills an estimated 527,000 children per year. Rotavirus infection is ubiquitous, occurs worldwide, and affects nearly all children (95%) by the age of 5 years. Although the incidence of rotavirus disease is similar between industrialized and developing countries, adverse outcomes are more likely in children from the latter. The estimated number of deaths from diarrhea has fallen dramatically over the past two decades as a result of improved treatment with oral rehydration therapy, sanitation, and water interventions.

In spite of the tremendous toll of death and disability produced by these diseases (Tables 1-3), there are some promising signs of progress. As described in WHO's "World Malaria Report 2009",4 more than one-third of the 108 malarious countries reported reductions in malaria cases of >50% in 2008 compared to 2000. Ten countries are implementing nationwide elimination programs, of which six entered the elimination phase in 2009. Eight countries are in the pre-elimination stage and a further nine countries have interrupted transmission and are in the phase of preventing reintroduction of malaria. Nevertheless, in 2008 there were an estimated 243 million cases of malaria, which produced estimated 863,000 deaths. The biggest problem is caused by Plasmodium falciparum in sub-Saharan Africa. However, Plasmodium vivax is geographically the most widely distributed cause of malaria, with up to 2.5 billion people at risk and many million clinical cases every year [11].

4World malaria Report 2009. WHO Geneva 2009. http://www.who.int/malaria/world_malaria_ report_2009/en/index.html.

Tuberculosis also makes a large contribution to mortality and morbidity in developing nations. Thus, in 2008 there were an estimated 8.9-9.9 million new cases of TB, 1.1-1.7 million deaths among HIV-negative people, and an additional 0.45-0.62 million among HIV-positive people. Almost 30,000 cases of multidrug-resistant TB (MDR-TB) were identified in 2008 (11% of the estimated total number of cases). In the last few years, new and very virulent strains, including the extremely resistant XDR TB and the totally drug-resistant TB for which there is no treatment [12, 13], have been reported. Much of this mortality occurs in African children [14].5 However, there have been some improvements in TB. Based on WHO's 2009 data,6 in the last 10 years, the tuberculosis case-detection rate increased from an estimated 11% in 1995 to 63% in 2007, and data on treatment success rates under the current tuberculosis treatment paradigm, directly observed treatment short-course (DOTS) indicates consistent improvement, with successful treatment rising from 79% in 1990 to 85% in 2006.7 Nonetheless, TB continues to be a major health burden in the developing world.

Dengue infection [15-17] is transmitted by mosquitoes and often produces a self-limited febrile illness called dengue fever (DF), which can lead to the severe forms of dengue: hemorrhagic fever (DHF) and dengue shock syndrome (DSS). Dengue is caused by four different dengue virus serotypes: DEN1, DEN2, DEN3, and DEN4. Severe forms of the disease occur in 5-10% of DF patients. Patients with DHF require hospitalization, and 30-40% of children with DHF progress to DSS. The case-fatality rate for DHF/DSS can be as high as 5%. Importantly, those who recover from DF possess life-long immunity to the dengue virus serotype that infected them. An estimated 2.5 billion people are at risk for dengue infection and DHF, primarily in urban tropical and subtropical regions, but also increasingly in rural areas. In the latter part of the twentieth century, endemic areas suffered unprecedented global dengue epidemics with large numbers of fatalities. WHO estimates 500,000 cases of DHF annually.

The diseases produced by helminthes are responsible for approximately 200,000 deaths annually, although some experts estimate much higher numbers [18]. Virtually all of the 1.4 billion people living on less than US $1.25 per day (the World Bank's poverty line) are infected with helminthes, which ruin their health, hinder education, and impair agricultural productivity [19-21]. The health toll of helminth infections is immense, with the soil-transmitted helminthes (e.g., ascariasis, roundworm), trichuriasis (whipworm, and hookworm) alone accounting for 4 million DALYs, with lymphatic filariasis and onchocerciasis contributing another 5.9 million and 0.4 million DALYs, respectively. Fortunately, large-scale treatment programs have been established in response to these diseases. For example, in 2007, 546 million

5Guidance for National Tuberculosis Programmes on the Management of Tuberculosis in Children. World Health Organization, Geneva, WHO/HTM/TB/2006.371, WHO/FCH/CAH/2006.7.

6Global tuberculosis control: a short update to the 2009 report. WHO Geneva 2009 (http://www. who.int/tb/publications/global_report/2009/update/en/index.html).

7World Health Statistics 2009. WHO Geneva 2009 (http://www.who.int/whosis/whostat/2009/en/ index.html).

people were treated to prevent transmission of lymphatic filariasis. These mass drug administration (MDA) programs will be discussed in more detail below.

The disease burden figures for leishmaniasis [22-24], endemic in 88 countries with two million new cases per year (1.5 million for cutaneous leishmaniasis and 500,000 for visceral leishmaniasis); HAT, endemic in 36 countries with 60 million people at risk and 70,000 existing cases8 [25-27]; and Chagas disease [28, 29] with 200,000 new cases per year, are dramatic. Significant reduction in infection rates and mortality for Chagas disease has been achieved in recent years through vector control measures. For example, in the Southern Cone, between 1990 and 2000 the number of new cases per year decreased from 700,000 to 200,000 and the number of deaths from more than 45,000 to 21,000. Likewise, the burden of HAT in Africa has decreased significantly the last 10 years, with reported number of new cases each year in the 10,000 range for 2008. Unfortunately, disease control has been more complicated for leishmaniasis due to a number of factors, including the nature and habitat of the vector and the nature of the disease.

Was this article helpful?

0 0

Post a comment