Eradication of infectious diseases


Eradication of infectious diseases

Eradication is the reduction of an infectious disease's prevalence in the global host population to zero.[1] It is sometimes confused with elimination, which describes either the reduction of an infectious disease's prevalence in a regional population to zero, or the reduction of the global prevalence to a negligible amount. Further confusion arises from the use of the term eradication to refer to the total removal of a given pathogen from an individual (also known as clearance of an infection), particularly in the context of HIV and certain other viruses where such cures are sought.

Eight attempts have been made to date to eradicate infectious diseases—four aborted programs targeting hookworm, malaria, yaws, and yellow fever, two successful programs targeting smallpox and rinderpest, and two ongoing programs targeting poliomyelitis and dracunculiasis. Five more infectious diseases have been identified as of April 2008 as potentially eradicable with current technology by the Carter Center International Task Force for Disease Eradication—measles, mumps, rubella, lymphatic filariasis and cysticercosis.[2]

Contents

Eradicated

So far, two diseases have been successfully eradicated—one specifically affecting humans (smallpox), and one affecting a wide range of ruminants (rinderpest).

Smallpox

Smallpox is the first disease, and so far the only infectious disease of humans, to have been eradicated by human undertakings. It became the first disease for which there was an effective vaccination when Edward Jenner demonstrated in 1798 that inoculation of humans with cowpox could protect against smallpox.[3]

The virus causing smallpox, Variola vera, has two variants: variola major, with a mortality rate around 30 percent, and variola minor, with a mortality rate less than 1 percent. The last naturally occurring case of variola major was diagnosed in October 1975 in Bangladesh, and the last naturally occurring case of variola minor was diagnosed in October 1977 in Somalia. The global eradication of smallpox was certified by a commission of scientists on December 9, 1979 and endorsed by the World Health Assembly on May 8, 1980.[3]

Rinderpest

During the 20th century, there were a series of campaigns to eradicate rinderpest, a viral disease which infected cattle and other ruminants and belonged to the same family as measles, primarily through the use of a live attenuated vaccine.[4] The final, successful campaign was led by the Food and Agriculture Organization (FAO) of the United Nations. On 14 October 2010, with no diagnoses for nine years, the FAO announced that the disease had been completely eradicated,[5] making this the first (and so far the only) disease of livestock to have been eradicated by human undertakings.

Global eradication underway

Poliomyelitis (polio)

International Polio Cases by Year
Year Estimated Recorded
1975 - 49,293
1980 400,000 52,552
1985 - 38,637
1988 350,000 35,251
1990 - 23,484
1993 100,000 10,487
1995 - 7,035
2000 - 2,971[6]
2001 - 483
2002 - 1,922
2003 - 784
2004 - 1,258
2005 - 1,998
2006 - 1,985
2007 - 1,315
2008 - 1,652
2009 - 1,606
2010 - 1,349
References:[7][8][9][10][11]

A dramatic reduction of the incidence of poliomyelitis in industrialized countries followed the development of a vaccine in the 1950s. In 1960, Czechoslovakia became the first country certified to have eliminated polio.

In 1988, the World Health Organization (WHO), Rotary International, the United Nations Children's Fund (UNICEF), and the U.S. Centers for Disease Control and Prevention (CDC) passed the Global Polio Eradication Initiative. Its goal was to eradicate polio by the year 2000. The updated strategic plan for 2004–2008 expects to achieve global eradication by interrupting poliovirus transmission, using the strategies of routine immunization, supplementary immunization campaigns, and surveillance of possible outbreaks. The WHO estimates that global savings from eradication, due to forgone treatment and disability costs, could exceed one billion U.S. dollars per year.[12]

The following world regions have been declared polio-free:

The lowest annual polio prevalence seen so far was in 2001, with 483 reported cases. However, following interruption of vaccination in Nigeria in 2003–4 and a reduction in immunisation in India in 2001–2, there was a resurgence of polio transmission: in the period of 2002 to 2009, the number of global reported cases has remained between 750 and 2000 per year, with 1,606 cases in 2009. Some of these cases were the result of new importations in 31 countries which had previously interrupted transmission, leading to many subsequent outbreaks; 19 of these countries reported cases in 2009. Four further countries remain in which poliovirus transmission has never been interrupted (Nigeria, India, Pakistan, and Afghanistan).[13][14] The current provisional total for 2010 stands at 1,294 cases from 20 countries.[9] However, as of June 15, 2011, the total cases-to-date has dropped to 205 (compared to 349 in 2010), which may result in a new record for lowest annual polio prevalence.[15]

Dracunculiasis

International Guinea Worm Cases by Year [16][17]
Year Reported Cases Countries
1989 892,055 16
1995 129,852 19
2000 75,223 16
2001 63,717 16
2002 54,638 14
2003 32,193 13
2004 16,026 13
2005 10,674 12
2006 25,217 [18] 10
2007 9,585 9
2008 4,619 7
2009 3,190 5
2010 1,797 6

Dracunculiasis, also called guinea worm disease, is a painful and disabling parasitic disease caused by a worm, Dracunculus medinensis. It is spread through consumption of drinking water infested with copepods hosting Dracunculus larvae. The Carter Center has led the effort to eradicate the disease, along with the CDC, the WHO, UNICEF, and the Bill and Melinda Gates Foundation.

Unlike diseases such as smallpox and polio, there is no vaccine nor drug therapy for guinea worm. Eradication efforts have been based on making drinking water supplies safer (e.g. by provision of borehole wells, or through treating the water with larvicide), on containment of infection and on education for safe drinking water practices. These strategies have produced many successes: two decades of eradication efforts have reduced guinea worm's global incidence to 1,797 cases in 2010, down from an estimated 3.5 million in 1986. Success has been slower than was hoped—the original goal for eradication was 1995. The WHO has certified 180 countries free of the disease, and only five countries—Sudan, Ghana, Mali, Ethiopia and Chad—reported domestic transmission of guinea worm in 2010 (one further country, Niger, reported imported cases). 94% of all cases reported in 2010 were in southern Sudan.[17][19] As of 2010, the WHO predicted it would be "a few years yet" before eradication is achieved, on the basis that it took 6–12 years for the countries that have so far eliminated guinea worm transmission to do so after reporting a similar number of cases to that reported by Sudan in 2009.[20]

Regional elimination established or under way

Some diseases have already been eliminated from large regions of the world, and/or are currently being targeted for regional elimination. This is sometimes described as "eradication", although technically the term only applies when this is achieved on a global scale.[21] Even after regional elimination is successful, interventions often need to continue to prevent a disease becoming re-established. Three of the diseases here listed (Lymphatic Filariasis, Measles, and Rubella) are among the diseases believed to be potentially eradicable by the International Task Force for Disease Eradication, and if successful, regional elimination programs may yet prove a stepping stone to later global eradication programs.

This section does not cover elimination where it is used to mean control programs sufficiently tight to reduce the burden of an infectious disease or other health problem to a level where they may be deemed to have little impact on public health, such as the leprosy, neonatal tetanus, or obstetric fistula campaigns.

Malaria

Malaria elimination has already been achieved in most of Europe, North America, Australasia, North Africa and the Caribbean, and parts of South America, Asia and Southern Africa, according to the Malaria Elimination Group at UCSF.[22] As of 2011, a further 32 countries were in the process of eliminating malaria from all or part of their territory. The WHO define elimination as having no domestic transmission for the past three years. They also define an "elimination stage" when a country is on the verge of eliminating malaria, as being <1 case per 1000 people at risk per year. According to the 2010 WHO world malaria report, 27 countries are certified as having eliminated malaria, seven countries appear to be malaria free but steps still need to be taken to ensure they do not re-establish transmission, 10 countries are in the elimination stage and nine the pre-elimination stage (<5 cases per 1000 people at risk per year).[23]

There has also been a discussion of moving to global eradication. At the Gates Foundation Malaria Forum in October 2007, Bill and Melinda Gates called for a new plan for malaria eradication, by going as far as possible with existing tools while also investing in new ones.[24][25] Nearly a year later, on September 25, 2008, the Roll Back Malaria (RBM) Partnership unveiled the Global Malaria Action Plan (GMAP), in which a series of measures were proposed to eliminate malaria as a global public health concern by 2015, eliminate all malaria transmission within 8–10 countries by the same deadline, and build towards its eventual global eradication.[26]

Lymphatic filariasis

Lymphatic filariasis is an infection of the lymph system by mosquito-borne microfilarial worms which can cause elephantiasis. Studies have demonstrated that transmission of the infection can be broken when a single dose of combined oral medicines is consistently maintained annually for approximately seven years.[27] The strategy for eliminating transmission of lymphatic filariasis is mass distribution of medicines that kill the microfilariae and stop transmission of the parasite by mosquitoes in endemic communities.[27] In sub-Saharan Africa, albendazole (donated by GlaxoSmithKline) is being used with ivermectin (donated by Merck & Co.) to treat the disease, whereas elsewhere in the world albendazole is used with diethylcarbamazine.[28] Using a combination of treatments better reduces the number of microfilariae in blood.[27] Avoiding mosquito bites, such as by using insecticide-treated mosquito bed nets, also reduces the transmission of lymphatic filariasis.[27][29] In the Americas, >90% of the burden of lymphatic filariasis is on the island of Hispaniola (comprising Haiti and the Dominican Republic). An elimination effort to address this is currently under way alongside the malaria effort described above; the Dominican Republic expects to eliminate its seven remaining foci by 2010, but lymphatic filariasis is still endemic to 110 of 140 communes in Haiti.[30]

As of October 2008, the efforts of the Global Programme to Eliminate LF are estimated to have already prevented 6.6 million new filariasis cases from developing in children, and to have stopped the progression of the disease in another 9.5 million people who have already contracted it. Overall, of 83 endemic countries, mass treatment has been rolled out in 48, and elimination of transmission reportedly achieved in 21.[31]

Measles

Five out of six WHO regions have goals to eliminate measles, and at the 63rd World Health Assembly in May 2010, delegates agreed to move towards eventual eradication, although no specific global target date has yet been agreed.[32][33][34] The Americas set a goal in 1994 to eliminate measles and rubella transmission by 2000, and successfully achieved regional measles elimination in 2002, although there have been occasional small outbreaks from imported cases since then.[35] Europe had set a goal to eliminate measles transmission by 2010, but were hindered by the MMR vaccine controversy and by low uptake in certain groups, and despite achieving low levels by 2008, European countries have since experienced a small resurgence in cases. The Eastern Mediterranean also had goals to eliminate measles by 2010, The Western Pacific aims to eliminate the disease by 2012, and in 2009 the regional committee for Africa agreed a goal of measles elimination by 2020. As of May 2010, only the South-East Asian region has yet to set a target date for elimination of measles transmission.[32]

In 2005, a global target was agreed for a 90% reduction in measles deaths by 2010 from the 757,000 deaths in 2000; estimates for 2008 show a 78% decline so far to 164,000 deaths.[36] However, some have been pushing to attempt global eradication.[37] This was updated at the 2010 world health assembly to a targeted 95% reduction in mortality by 2015, alongside specific vaccination and structural targets,[32][33] and in a meeting in November 2010, the Strategic Advisory Group of Experts on Immunization "concluded that measles can and should be eradicated".[38] A study of the costs of eradicating measles compared to the costs of maintaining indefinite control was commissioned in 2009 by the WHO and the Bill and Melinda Gates Foundation.[39]

Rubella

Two WHO regions have set 2010 as a target for rubella elimination. The WHO region of the Americas set itself a target for regional elimination of rubella and congenital rubella syndrome by 2010. As of 2010, the last confirmed endemic case of rubella in the Americas was in Argentina in February 2009[40] and verification of regional elimination is currently under way and due to complete by 2012.[41] The WHO European region also set a target of 2010.[42] However, as of 2008 there were still 20,579 reported cases of rubella, 311 of which were laboratory confirmed, just among the 27 countries reporting data to EUVAC.[43]

Onchocerciasis

Onchocerciasis (river blindness) is the world's second leading cause of infectious blindness. It is caused by the nematode Onchocerca volvulus, which is transmitted to people via the bite of a black fly. Elimination of this disease is under way in the region of the Americas, where this disease is endemic to Brazil, Colombia, Ecuador, Guatemala, Mexico and Venezuela. The principal tool being used is mass ivermectin treatment. If successful, the only remaining endemic countries would be in Africa and Yemen.[44] In Africa, it is estimated that >102 million people in 19 countries are at high risk of onchocerciasis infection, and in 2008, 56.7 million people in 15 of these countries received community-directed treatment with ivermectin. Since adopting such treatment measures in 1997, the African Programme for Onchocerciasis Control reports a reduction in the prevalence of onchocerciasis in the countries under its mandate from a pre-intervention level of 46.5% in 1995 to 28.5% in 2008.[45] Some African countries, such as Uganda,[46] are also attempting elimination and successful elimination was reported in 2009 from two endemic foci in Mali and Senegal.[47]

Yaws

Yaws is a rarely fatal but highly disfiguring disease caused by the spiral-shaped bacterium (spirochete) Treponema pertenue, a relative of the syphilis bacteria Treponema pallidum, spread through skin to skin contact with infectious lesions. The global prevalence of this disease and the other endemic trematoses, Bejel and Pinta, was reduced by the Global Control of Treponematoses (TCP) programme between 1952 and 1964 from about 50 million cases to about 2.5 million (a 95% reduction). However, following the cessation of this program these diseases remained at a low prevalence in parts of Asia, Africa and the Americas with sporadic outbreaks. Yaws is currently targeted by the South-East Asian Regional Office of the WHO for elimination from the remaining endemic countries in this region (India, Indonesia and East Timor) by 2010, and so far, this appears to have met with some success, since no cases have been seen in India since 2004.[48][49]

Bovine spongiform encephalopathy (BSE) and new variant Creutzfeldt–Jakob disease (vCJD)

Following an epidemic of vCJD in the UK in the 1990s, there have been campaigns to eliminate BSE in cattle across the EU and beyond which appear to have achieved large reductions in the number of cattle with this disease.[50] Cases of vCJD have also fallen since then, for instance from an annual peak in the UK of 28 cases in 2000 to 3 cases in 2010.[51]

Following the ongoing eradication effort, only 45 cases of BSE were reported worldwide in 2010, the fewest since at least 1988.[52][53]

In fiction

Futures and futuristic alien civilizations in which some or all infectious diseases have been eradicated are a staple of science fiction. Examples include:

The War of the Worlds by H. G. Wells, in which the Martian race have long eradicated their own infectious diseases, leaving them vulnerable to Earth pathogens following the atrophy of their natural defences.

The Evitable Conflict, by Isaac Asimov, describes a future run by Machines in the manner which they see as most conducive to man's best interests, in which "we have eradicated the anopheles mosquito and the tsetse fly".

See also

References

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