The global burden of neglected tropical diseases
The global burden of neglected tropical diseases
School of Public Health, Imperial College, London
The first comprehensive study on the global burden of disease and risk factors was
commissioned by the World Bank in 1992. A follow-up study was performed in 2005, and
another iteration was commissioned by the World Health Organization in 2010, due forpublication in 2011. The author suggests that the global burden of neglected tropical
diseases (NTDs) has been seriously underestimated. The way forward is the integration of
control efforts, with programmes coming together to deliver a package of drugs against
NTDs. Barriers to continent-wide coverage of drugs against NTDs are political will (missing
in those countries with poor governance), funding (approximately half of the $1.5e2 billion
is needed) and human resources. However, if the donors who give so much to malaria,
tuberculosis and human immunodeficiency virus would share just 10% of the amountallocated to the big three, the most common NTDs could become diseases of the past. Thiscould well happen within 7 years, and the targets of GET2020 (Global Elimination ofTrachoma by 2020) to eliminate trachoma and GAELF (the Global Alliance to EliminateLymphatic Filariasis) to eliminate lymphatic filariasis by 2020 are achievable.
ª 2011 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.
The first comprehensive study on the global burden of disease
In the first study on the global burden of disease and risk
and risk factors was commissioned by the World Bank in
factors, the weightings allocated to the various neglected
tropical diseases (NTDs), listed in were significantly
another iteration was commissioned by the World Health
lower than these diseases merited in the opinion of NTD
Organization (WHO) in 2010, due for publication in
experts. Several peer reviewed publications have subse-
Disability-adjusted life years (DALYs) represent an attempt
quently attempted to make the case for a significant increase
to quantify the burden of each disease, calculated as the sum
in the disability Indeed, since 2006, the investi-
of life years lost through early death (YLL) plus the years lost to
gators working on many of these NTDs have come together
disability (YLD). YLL is estimated for each disease. The
thanks to a WHO initiative. By combining their global burden,
disability caused by each disease is allocated a value from 0 to
the result is that the combined burden of disease due to NTDs
1, and YLD is calculated as the years lived with the disability
has been estimated at 56.6 DALYs, compared with malaria at
Morbidity and mortality due to NTDs were underestimated
as long-term disabilities were not always attributed to an early
Unfortunately, the DALY allocation, which forms the basis
NTD infection, nor were they given a high rating, thus leading
for research and controls funding allocations, is considered by
to low YLD. Almost all deaths which are known to be due to
some to be somewhat arbitrary, and therefore is not always
longstanding parasitic infections were, in fact, not recognized
as such and so were not attributed to the childhood infection
0033-3506/$ e see front matter ª 2011 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.
MDG6 calls for treatment of human immunodeficiency
Table 1 e The core 13 neglected tropical diseases.
virus (HIV), malaria and other diseases. NTDs are an impor-
tant constituent of the ‘other diseases’.
Estimates of those infected with intestinal worms suggest
that over 800 million individuals worldwide harbour Ascaris
infections, 600 million have Trichuris worms, and 600 million
have one or another of the hookworm species. The worms infect
children from 2 years of age, but the consequences of infection
can be prevented by early treatment with either albendazole or
mebendazole. Regular treatment during childhood may be
needed in areas where sanitation and human hygiene is poor in
order to prevent long-term effects, especially those suffered by
the 10% of individuals who harbour heavy infections.
Interestingly, hookworm tends to infect adults as well as
children, whereas the other worms are not usually found inadults. A meta-analysis by Smith and showed that
which led to the patient’s death some 25
soil-transmitted helminths cause significant weight loss and
reality, the visual impact of the appalling stigma, disfigure-
anaemia, while Miguel and Kremer showed that treated chil-
ment, blindness and disabilities caused by NTDs only needs to
dren soon achieve a better attendance record at
be seen to convince most people of the importance of these
Another study showed that a single round of deworming led
diseases. It is shameful that their public health importance
has not already attracted more effort to reduce the horrific
Since 1973, publications on schistosomiasis have quoted
a worldwide prevalence of approximately 200 million.Today,
Seven NTDs listed (marked with a star) in infect
this is likely to be the minimum because the stool examination
many millions of the poorest of the poor (‘the bottom billion’),
and urine test which leads to these figures are so insensitiv
and many infected individuals suffer the indignity of co-
Since 1971, the global distribution of schistosomiasis has
changed because China, Egypt and Brazil have all embarked on
The G8 and G20 have committed to reaching the Millen-
effective control programmes. The numbers infected in these
nium Development Goals (MDGs) by 2015, but how
three countries have declined sharply. Sadly, as the population
can these goals be achieved when so many people suffer
in Sub-Saharan Africa has increased, so has the number of
parasitic infestaHow can poverty be reduced (MDG1)
infected people on this continent. In 2011, approximately 85%
when a billion people are caught in the cycle of poverty and
of all cases of schistosomiasis (over 200 million) are found in
disease: NTDs promote poverty and poverty promotes NTDs.
Sub-Saharan A very strong and convincing case has
How can universal primary education be achieved (MDG2)
been made for an upward revision of the disability weighting
when millions of children are undernourished and stunted?
Many children are hungry and anaemic, and have their
The subtle morbidity caused by early and low-intensity long-
cognitive ability impaired because they are infected with one
term infections has previously been ignored but is significant.
or more intestinal worms. Children suffer because the worms
Equally, several more serious conditions (bladder fibrosis, liver
consume the food that the child eats and/or feed off blood
fibrosis, portal hypertension) and deaths that occur many years
from the Infected children are too weak to go to school
after infection (bladder cancer, haematemesis) are often not
or unable to concentrate when they are there. These children
recognized as being due to childhood infection with schistoso-
are frequently labelled as ‘lazy’ or ‘unintelligent’ when in fact
miasis. Finally, urogenital schistosomiasis causes cervical
they have been parasitized since an early age.
lesions which may lead to higher infections with HIV among
How can child mortality be reduced (MDG4) and maternal
younger women; all this when schistosomiasis is preventable
health be improved (MDG5) when one of the major causes of
poor birth outcomes is anaemia, caused in turn by the para-
Two NTDs (trachoma and onchocerciasis) cause blindness e
sitic infections carried by millions of women of childbearing
the former simply because after a Chlamydia infection and
conjunctivitis, the eyelashes turn down and scrape the cornea.
This is so easily prevented, yet an estimated 8 million peopletoday are unnecessarily visually impaired. Today, eliminationcampaigns are being led by governments and non-government
organizations (NGOs) using the SAFE strategy and drugs
donated by Pfizer through the International Trachoma Initiative
1. Eradicate extreme poverty and hunger.
). Onchocerciasis (river blindness) does not
2. Achieve universal primary education.
3. Promote gender equality and empower women.
cause anywhere near as much blindness today compared with
60 years ago thanks to two programmes e the Onchocerciasis
Control Project, and its successor, the African Programme for the
6. Combat HIV/AIDS, malaria and other diseases.
Control of Onchocerciasis (APOC). Meanwhile, in the Americas,
7. Ensure environmental sustainability.
onchocerciasis is close to elimination because of the Oncho
8. Develop a global partnership for development.
Elimination Programme for the Americas. This success is due to
Force for Global Health (in Atlanta), several drug donation pro-
Table 3 e More accurate estimation of disability-adjusted
grammes are now in place ). As such, the pharmaceu-
life years (DALYs) attributed to neglected tropical
tical industry has laid the foundation for either disease
elimination or morbidity control of six of the seven diseases
All that is needed is the funding for in-country logis-
tics: mapping; planning; training, information, education and
communication materials; drug distribution; and monitoring
and evaluation. It has been estimated that, on average, a cost of
$0.50 per person per year would fund the programmes in full,
and even less would be needed in areas free of schistosomiasis.
In Uganda, the overall economic cost per child treated in six
districts was US$0.54, and the cost-effectiveness was US$3.19per case of anaemia avertedFor Sub-Saharan Africa witha total target population of approximately 500 million, an esti-
the donation of ivermectin (Mectizan) by Merck. Back in 1960,
mated $1.5e2 billion over the next 7 years would probably be
people living and working on vast tracts of land near the major
enough to take these diseases off the burden of disease list.
rivers in Africa were so heavily infected that over 50% of middle-
Already, thanks to WHO’s leadership and financial donations
aged adults were blind due to the migrating larvae of the
from the US Agency for International Development (USAID), the
onchocerciasis worm. What disability weighting do these NTDs
UK Department for International Development, and the Bill and
Melinda Gates Foundation, progress has been made. By 2010, 600
Lymphatic filariasis (LF) does not kill, but for many years,
million people were receiving albendazole every year against LF.
the millions of sufferers with grossly deformed limbs and the
In Africa, almost 100 million every year also receive Mectizan,
men with hydrocoeles probably wished that they were not
while in the Far East and Indian subcontinent, albendazole is
forced to live with their afflictions. For different reasons, both
given with diethylcarbamazine. Within 6 years of these annual
men and women were denied marriage and were unable to
drug distributions, LF transmission should cease, as has been
work. They hid their shame caused by their swollen, infected
achieved in Egypt and on Zanzibar. Surgery for hydrocoeles and
and disfigured limbs and scrotum. Globally, approximately
more washing of deformed limbs is needed to complete the
600 million individuals are still at risk of contracting LF, an
elimination of LF. One word of warning for areas where the
estimated 120 million are infected and some 40 million suffer
filarial worm Loa Loa is prevalent e albendazole and Mectizan
can cause serious adverse events if dispensed to an individual
This article has not touched upon the horrific consequences
infected with L. Loa. This has delayed national coverage of LF
of some other NTDs, including leprosy, Chaga’s disease, rabies,
control in several countries in Africa, including Cameroon and
sleeping sickness, leishmaniasis and buruli ulcer.
the Democratic Republic of the Congo.
Returning to the seven NTDs described in detail, their
APOC with NGO partners is helping the governments of 19
contribution to the 56.6 DALYs is so unnecessary. There are safe
countries to deliver 40 million doses of Mectizan every year to
oral drugs that, if delivered annually, can remove these diseases
prevent onchocerciasis. The elimination of onchocerciasis by
as a major public health problem. However, these drugs are
increasing the frequency of drug deliveries is currently being
unaffordable for the billion people who are infected, who live on
tested. In the Americas, the elimination of onchocerciasis is
less than $2 per day. The pharmaceutical industry has now
almost complete thanks to the efforts of the gvernments, the
recognized this fact, and in conjunction with WHO and the Task
CarterCenter and Mectizan donations.
Table 4 e Contribution of the pharmaceutical industry to the control of neglected tropical diseases.
Reconfirmed their commitment to donate Mectizan for as long as neededfor both onchocerciasis and filariasis in Africa.
Already donated almost 2 billion tablets of albendazole for lymphatic filariasisand will continue until elimination is achieved.
In October 2010, they committed an additional 400 million tablets per year for5 years to deworm school-aged children in Africa.
Donated up to 50 million tablets of mebendazole per year for intestinal wormsfor several years. Next year, this will be increased to 200 million tablets per year.
Committed to provide doses of azithromycin for trachoma.
In 2009 alone, they donated 50 million. In 2011, that number will reach 70 million.
Committed to provide multidrug treatment for leprosy.
In October 2010, EISAI committed to provide 2 billion tablets of diethylcarbamazinefor lymphatic filariasis which is used with albendazole outside of Africa.
Both Medpharm (a generic manufacturer) and E. Merck have donated praziquantel. E. Merckhave committed to provide 200 million tablets over 10 years.
Meanwhile, the International Trachoma Initiative acts as
the agent to assist Pfizer with their donation of Zithromaxagainst trachoma. In 2011, it is estimated that 70 million doseswill reach populations with trachoma, and elimination after 3
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