Treatment for snail-borne schistosomiasis works best over the long haul
Monitoring for infectious snails in bodies of water near villages in coastal Kenya. Credit: J. Clennon, Emory University
Watch where you jump in for a swim or where your bath water comes from, especially if you live in Africa, Asia or South America. Snails that live in tropical freshwater in these locations are intermediaries between disease-causing parasitic worms and humans.
The worms' infectious larvae emerge from the snails, cruise in shallow water, easily penetrate human skin and mature in internal organs.
The result is schistosomiasis, the second most socioeconomically devastating disease after malaria. As of 2009, 74 developing nations had identified significant rates of schistosomiasis in human populations.
There has been much debate about how best to prevent the disease, says Charles King, a physician and researcher at Case Western Reserve University in Cleveland, Ohio. "Beyond that," he asks, "how long should treatment last once someone has schistosomiasis?"
"Current guidelines focus on suppressing the disease's effects by limiting the infection during childhood," says King. "But that may not be enough to cure it or to prevent re-infection, leaving children still at risk for stunted growth and anemia."
King and colleagues recently published results of a study of long-term treatment of schistosomiasis in the journal PLOS Neglected Tropical Diseases.
The team's work is funded by the National Science Foundation (NSF)-National Institutes of Health (NIH) Evolution and Ecology of Infectious Diseases (EEID) program.
Countries worldwide where people are at risk for the snail-borne disease schistosomiasis. Credit: CDCAt NSF, the EEID program is supported by the Directorate for Biological Sciences and Directorate for Geosciences. At NIH, it's supported through the Fogarty International Center.
Schistosomiasis is usually treated with a single dose of the oral drug praziquantel.
World Health Organization (WHO) guidelines set forth in 2006 recommend that when a village reports that more than 50 percent of its children have parasite eggs in their urine or stool—a clear sign of schistosomiasis—everyone in the village should receive treatment.
When 10 to 50 percent of children are affected, say the guidelines, only school-age children should be treated—every two years. With less than 10 percent, mass treatment is not suggested.
But because of the long-term health effects of schistosomiasis, says King, "we now think it's better to provide regular yearly treatment."
People who work in rice fields are exposed for many hours to snail-infested waters. Credit: U. Kitron, Emory UniversityHe and scientists Xiaoxia Wang, David Gurarie and Peter Mungai of Case Western Reserve University; Eric Muchiri of the Ministry of Public Health and Sanitation in Nairobi, Kenya; and Uriel Kitron of Emory University in Atlanta, Georgia, used data collected in 10 villages in southeastern Kenya to run advanced models of village-level schistosomiasis transmission.
They scored the number of years each of the 10 villages would be projected to remain below a 10 percent infection level during a simulated 10-to-20-year treatment program.
GIS map showing four communities in Kenya that are at high risk for schistosomiasis. Credit: Charles King, Case Western Reserve University et al.All strategies that included an initial four annual treatments reduced community prevalence of the disease to less than 10 percent. Programs with gaps in treatment, however, didn't reach this objective in half the villages.
At typical levels of treatment, the researchers found, current WHO recommendations likely could not achieve full suppression of schistosomiasis.
"With more aggressive annual intervention that lasts at least four years," says King, "some communities might be able to continue without further treatment for 8 to 10 years.
"But in higher-risk villages, repeated annual treatment may be necessary for an indefinite period—until the eco-social factors that foster the disease [such as poor wastewater treatment] are removed."
In high-risk places, ongoing surveillance for the disease and annual drug treatment, the scientists say, need to become the mainstays of control.
In short, these villages require what they call "re-worming after de-worming."
But what happens if townspeople move to a more arid location, one with less freshwater and fewer snails?
In drier landscapes, schistosomiasis is a rare event that happens only during floods. Response to treatment therefore may be much better. Unless or until another flood occurs.
Although drier locales carry less risk for the disease, they're by no means free and clear. Even in arid locations, people would likely need to be treated more than once to get rid of the parasites.
"This research demonstrates the value of understanding where disease-causing organisms are in the environment," says Sam Scheiner, NSF program officer for EEID.
"Such knowledge can reduce human diseases much more effectively and at a lower cost than simply focusing on treatment."
The best goal, says King, is complete eradication of schistosomiasis.
To achieve that, scientists need to determine what makes a "wormy village," how often therapy is needed to prevent disease in such locations—and what can be done to change the environment such that a high-risk village becomes a low-risk one.
Journal reference: PLoS Neglected Tropical Diseases
Provided by National Science Foundation
- Brazil claims successful test of parasite vaccine Jun 13, 2012 | not rated yet | 0
- Small-scale agricultural changes may help eradicate widespread disease May 31, 2007 | not rated yet | 0
- Combating urinary schistosomiasis: Both metrifonate and praziquantel can be used Jul 16, 2008 | not rated yet | 0
- Case Western Reserve professor helps control infectious diseases with models and math Dec 19, 2008 | not rated yet | 0
- Sustainable interventions key to successful schistosomiasis control May 05, 2009 | not rated yet | 0
- Motion perception revisited: High Phi effect challenges established motion perception assumptions Apr 23, 2013 | 3 / 5 (2) | 2
- Anything you can do I can do better: Neuromolecular foundations of the superiority illusion (Update) Apr 02, 2013 | 4.5 / 5 (11) | 5
- The visual system as economist: Neural resource allocation in visual adaptation Mar 30, 2013 | 5 / 5 (2) | 9
- Separate lives: Neuronal and organismal lifespans decoupled Mar 27, 2013 | 4.9 / 5 (8) | 0
- Sizing things up: The evolutionary neurobiology of scale invariance Feb 28, 2013 | 4.8 / 5 (10) | 14
Classical and Quantum Mechanics via Lie algebras
Apr 15, 2011 I'd like to open a discussion thread for version 2 of the draft of my book ''Classical and Quantum Mechanics via Lie algebras'', available online at http://lanl.arxiv.org/abs/0810.1019 , and for the...
- More from Physics Forums - Independent Research
More news stories
(HealthDay)—Few randomized clinical trials have been done to assess clinical prediction rules for patients with lower back pain, and the trials that have been done are of low quality and do not provide ...
Diseases, Conditions, Syndromes 20 hours ago | not rated yet | 0 |
A new, highly sensitive blood test that quickly detects even the lowest levels of malaria parasites in the body could make a dramatic difference in efforts to tackle the disease in the UK and across the world, according to ...
Diseases, Conditions, Syndromes May 17, 2013 | not rated yet | 0
(AP)—The World Health Organization says a yellow fever booster vaccination given 10 years after the initial shot isn't necessary.
Diseases, Conditions, Syndromes May 17, 2013 | not rated yet | 0
(AP)—Twenty-three youths have died in the past nine days at initiation ceremonies that include circumcisions and survival tests, South African police said Friday.
Diseases, Conditions, Syndromes May 17, 2013 | 5 / 5 (1) | 3
The United States government public health agency, the CDC, pledges "To base all public health decisions on the highest quality scientific data, openly and objectively derived." But Peter Doshi, a postdoctoral fellow at Johns ...
Diseases, Conditions, Syndromes May 16, 2013 | not rated yet | 0
An increasing number of U.S. children are experiencing gastrointestinal issues that require interventions to resolve, according to research presented at Digestive Disease Week (DDW).
57 minutes ago | not rated yet | 0 |
A ground-breaking advance in colonoscopy technology signals the future of colorectal care, according to research presented today at Digestive Disease Week(DDW). Additional research focuses on optimizing the minimal withdrawal ...
55 minutes ago | not rated yet | 0
Big names in medicine are set to give an upbeat assessment of the war on AIDS on Tuesday, 30 years after French researchers identified the virus that causes the disease.
9 hours ago | 5 / 5 (1) | 0
For combat veterans suffering from post-traumatic stress disorder, 'fear circuitry' in the brain never rests
Chronic trauma can inflict lasting damage to brain regions associated with fear and anxiety. Previous imaging studies of people with post-traumatic stress disorder, or PTSD, have shown that these brain regions can over-or ...
10 hours ago | not rated yet | 0 |
(Medical Xpress)—What if the quality of your work depends more on your focus on the piano keys or canvas or laptop than your musical or painting or computing skills? If target users can be convinced, they ...
21 hours ago | 3.7 / 5 (3) | 0 |
The neural machinery underlying our olfactory sense continues to be an enigma for neuroscience. A recent review in Neuron seeks to expand traditional ideas about how neurons in the olfactory bulb might encode information about ...
21 hours ago | not rated yet | 0 |