By Kelly A. Reynolds, MSPH, Ph.D.
One of the world’s most hideous waterborne diseases is about to be eradicated–that is, gone from the earth forever. While scientists have mapped out the theoretical process for disease eradication, many more failures than successes have been realized.
In fact, only one infectious disease, smallpox, has been successfully extinguished from the globe. However, concerns of bioterrorism and a population lacking immunity raise the question: is it really gone for good?
Steps for eradication
According to Dowdle’s “Principles of Disease Elimination and Eradication,” eradication is defined in various ways including:
- Extinction of the disease pathogen.
- Elimination of the occurrence of a given disease, even in the absence of all preventative measures.
- Control of an infection to the point at which transmission ceased within a specified area.
- Reduction of the worldwide incidence of a disease to zero as a result of deliberate efforts, obviating the need for further control measures.
In the early 1990s, the International Task Force for Disease Eradication considered more than 80 infectious disease agents for the likelihood of successful eradication, determining that only six were candidates. Consideration of the social, biological, political and economic characteristics and impacts of initiating an eradication program are essential for determining how and when such efforts should be forwarded.
A pathogen not considered eradicable today may be a candidate tomorrow with the rapid advancement of science, education and social policies. Dowdle identified three indicators of primary importance for successful eradication:1
- An effective intervention is available to interrupt transmission of the agent
- Practical diagnostic tools with sufficient sensitivity and specificity are available to detect levels of infection that can lead to transmission.
- Humans are essential for the life cycle of the agent, which has no vertebrate reservoir and does not amplify in the environment.
To date, smallpox is the only disease that has been completely eradicated from the globe via a targeted eradication program, with the last documented case occurring in 1977. Although estimated to have killed a half a billion people in the 20th century, the development of a vaccine and being a human-specific virus aided in the elimination of the disease.
Success with Guinea worm
On the brink of elimination is Guinea worm disease. Guinea worm is truly an ancient disease. Organisms have been isolated from Egyptian mummies and the disease is thought to be referenced in the Old Testament of the Bible.
The parasite is spread by ingesting drinking water containing the larvae hosted by freshwater copepods. After about two weeks following ingestion, the larvae develop into a human infectious stage, eventually growing into large intestinal worms that emerge painfully from the surface of the skin, usually in the lower limbs. Infected persons wading in waters enable emerging worms to lay eggs that continue the cycle of infection. (See WC&P, On Tap, September 2007 for more details on Guinea worm.)
Mature Guinea worms are removed from patients physically either via surgery or by pulling the worm out a few centimeters a day over a period of weeks or even months. The worm, similar in size to a cooked spaghetti noodle, is wrapped around a stick as it slowly emerges.
Infection results in much pain, debilitating treatment and often permanent scarring or crippling effects. On average, persons with emerging Guinea worms are unable to work or participate in normal activities for three months. Immunity is not acquired following infection and in endemic regions, individuals may become repeatedly infected over their lifetime.
Guinea worm infections result in painful, debilitating and sometimes recurring disease, often leading to serious economic and social burdens in affected families and communities. Although the impacted regions of Guinea worm infections are poor, rural settings, breaking the cycle of infection can be achieved by simple, POU water treatment methods such as boiling and crude filtration, including passing drinking water through a cloth filter.
People with Guinea worm infections should not be allowed to bathe in drinking water sources and water should be consumed only from protected ground water sources. Commercial larvicides are available that can kill the copepods present in contaminated but necessary drinking water sources.
In 1986, 3.5 million people were estimated to be infected annually. However by December 2008, infections of Guinea worm disease reportedly reached an all time low with an estimated 5,000 cases in the world remaining. This year (2009) promises to be the year when no cases are reported.
As early as 2003, there were more than 32,000 cases reported in 12 countries, all in Africa. The Carter Center, along with others (The Bill and Melinda Gates Foundation, CDC, UNICEF, WHO), was instrumental in the control of Guinea worm infections via a focused eradication effort.
Reductions in Guinea worm infections have not occurred due to medical interventions or vaccines but rather via grassroots educational public health initiatives and crude-method source water protection and filtration. Success, however, was not inexpensive. An estimated 225 million (USD) has been invested in endemic African communities over the last two decades on Guinea worm eradication.
Guinea worm is the second infectious disease to be eradicated and the first parasitic disease. Attempts to eradicate malaria, yellow fever and yaws have not been successful to date, falling short of the eradication timeline goals.
These technically failed programs, however, provided essential insights into the difficulties in disease extinction. Even after dramatic reductions in disease rates, complete eradication is difficult, if not impossible, to achieve.
In 1988, various US and global health agencies launched the Global Poliovirus Eradication Initiative, with the goal to eliminate polio by the year 2000. The primary control strategy is through vaccination programs, originally started in the 1950s. Although endemic only to Nigeria, India, Pakistan and Afghanistan, approximately 2,000 cases a year continue to be reported.
Many of the primary infectious disease concerns today have a waterborne or water-related route of transmission. The list of complexities associated with waterborne pathogens and their possible eradication is daunting: worldwide spread; mutant strains; lack of sanitation; untreated animal wastes; multiple hosts; antibiotic resistance; and emerging infections.
These roadblocks have played a role in the persistence of historic diseases that still plague our society, including typhoid and cholera. This despite our having greatly advanced the tools for monitoring, diagnostics and intervention, particularly in terms of water treatment and purification.
In addition to polio and Guinea worm disease, future and current candidates proposed for eradication are: malaria; lymphatic filariasis (mosquito borne cause of elephantitis); mumps, measles, and rubella (regional elimination); onchocerciasis (river blindness); yaws (skin infection caused by bacterium, low prevalence in Asia, Africa and Americas); Trypanosomiasis (sleeping sickness); and tapeworm infections from pork.
Another future concern is how to preventing the return of eradicated diseases. Continuing to monitor population health and source water quality in some of the most remote regions of the world may be necessary for continued success of Guinea worm initiatives while the security of stockpiles for smallpox viruses have been the subject of heated debates over the years.
Following smallpox eradication, only two viable stocks of the smallpox virus were maintained, housed at the Centers for Disease Control and Prevention (CDCP) in Atlanta and the Research Institute for Viral Preparations in Moscow. The latter was transferred to Novosibirsk in central Siberia after the fall of the Soviet Union. Smallpox vaccinations in the U.S. were halted in 1972 and thus, the immunity of the population continues to wane.
While eradication programs are necessary, they are slow to gain success and new diseases continue to emerge. Therefore, minimizing exposure to infectious agents continues to be a primary, individual defense both locally and globally.
- Dowdle, W.R. 1999. The Principles of disease Elimination and Eradication. MMWR. Centers for Disease Control. 48 (SU01); 23-27.
- United Nationals Maxims News Network. Former President Carter on Eradicating Fuinea Worm Disease: Exclusive Interview by Marisha Wojciechowska-Shibuya. December 9, 208.
- Barry, M. (2007) The tail end of Guinea worm—global eradication without a drug or a vaccine. New England Journal of Medicine. 356:2561-2564.
- Garrett, L. 2000. Betrayal of Trust:The Collapse of Global Purblic Health. New York, Hyperion.
About the author
Dr. Kelly A. Reynolds is an associate professor at the University of Arizona College of Public Health. She holds a Master of Science degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds has been a member of the WC&P Technical Review Committee since 1997. She can be reached via email at [email protected].