Eradication of infectious diseases
Eradication is the reduction of an infectious disease's prevalence in the global human or animal host population to zero. A number of world organizations together with local governments are working to fully eradicate various diseases. 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. Also, the term eradication is sometimes used in the context of HIV and certain other viruses to describe the sought-after total removal of the virus from an individual (i.e. a cure).
ccessful program targeting smallpox 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 pork tapewor
Smallpox is the only disease to have been eradicated. It became one of the first diseases for which there was an effective vaccination when Edward Jenner demonstrated in 1798 that inoculation of humans with cowpox could protect against smallpox.
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.
Global eradication underway
Young Girl with Polio in an
in industrialized countries followed the development of a vaccine he 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.
The following world regions have been declared polio-free:
- The Americas (1994)
- Indo-West Pacific region (1997)
- Europe (1998)
- Western Pacific region, including China (2000)
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 2008, the number of global reported cases has remained between 750 and 2000 per year, with 1,654 cases in 2008. Some of these cases were the result of new importations in 27 countries which had previously interrupted transmission, leading to many subsequent outbreaks; 13 of these countries are believed to have still had active transmission in 2008. Four further countries remain in which poliovirus transmission has never been interrupted - Nigeria, India, Pakistan, and Afghanistan.
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 dracunculiasis. Eradication efforts have been based on making drinking water supplies safer and through educating people where it is endemic on safe drinking water practices. These strategies have proved successful: two decades of eradication efforts have reduced its global incidence to 4,619 cases in 2008 (provisional figures, March 2, 2009), down from an estimated 3.5 million in 1986, although 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 six countries - Sudan, Ghana, Mali, Nigeria, Niger and Ethiopia - are reported to have had domestic transmission of guinea worm in 2008.
There have been a series of campaigns to eradicate rinderpest, a viral disease of cattle belonging to the same family as measles, primarily through the use of a live attenuated vaccine. The latest of these campaigns was led by the UN Food and Agriculture Organization (FAO). As of 2008, the virus had been last seen in 2001; however, on the basis of earlier setbacks, the FAO were unwilling to declare it eradicated until the end of a period of intensive surveillance due to complete in 2010.
Regional or sub-regional elimination established or under way
Some diseases have already been eliminated from parts 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. Even after regional elimination is successful, interventions often need to continue to prevent a disease becoming re-established. Several of the diseases here listed - Lymphatic Filariasis, Measles, Mumps, 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 elimination has already been achieved in the USA, Australia and Western Europe. As of early 2009, a further 39 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 Algeria, Argentina, Armenia, Egypt, El Salvador, Iraq, Paraguay, Republic of Korea, Saudi Arabia and Turkmenistan) with a further 11 in the pre-elimination stage ( Some countries that are not yet in the elimination stage are also moving towards elimination. For instance, the elimination of malaria from the last remaining island in the Caribbean to have endemic transmission, Hispaniola, is under way. The main tools are malaria treatment, mosquito nets, and vector control. Of the two countries on the island, malaria is currently endemic throughout Haiti and in 83/143 municipalities in the Dominican Republic. China is also shifting focus from control to elimination, with an initial focus on elimination in the island province of Hainan.
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. Nearly a year later, on September 25, 2008, the Roll Back Malaria partnership unveiled the Global Malaria Action Plan, 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.
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. 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. 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. Using a combination of treatments better reduces the number of microfilariae in blood. The use of insecticide-treated mosquito bed nets also reduces the transmission of lymphatic filariasis as well as malaria, which is prevalent in many of the same communities in Africa. 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 7 remaining foci by 2010, but lymphatic filariasis is still endemic to 110/140 communes in Haiti .
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.
Measles and rubella
In the 1990s, the governments of the Americas, along with the Pan American Health Organization, launched plans to eliminate first measles and then also rubella from the region. As of December 2008, the elimination of endemic transmission of measles from the Americas has been all but achieved, with occasional small outbreaks from imported cases,, such as a recent outbreak of measles in Canada.. The WHO regional offices for Europe and for the Western Pacific are aiming to also achieve regional measles elimination by 2010 and 2012 respectively. However, the global goal remains control (a 90% reduction in measles deaths by 2010 from the 757,000 deaths in 2000).
Rubella elimination is not yet so advanced, but has also had much success - the number of reported rubella cases in the Americas fell from 135,947 in 1998 to 3,809 in 2008, and domestic rubella transmission in the Americas appeared to be confined to northern Argentina as of March 2009 
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. In most endemic African countries, the focus is currently on control, but a few, such as Uganda, are also attempting elimination.
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.
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