Schistosomiasis: Part 4

Diagnostic Tests

Investigations to find eggs in stool smears, urine samples and bladder or rectal biopsy specimens are standard practice9 . As with many other parasitic diseases exposure histories are important to ascertain. Eosinophils also accumulate during parasitic diseases that express Th1 cytokines (such as schistosomiasis), these cells play a major role in the inflammatory response that takes place during infection. An elevated eosinophil count can be detected through blood tests in people with schistosomiasis10 . Antibody tests are also available, though they do not distinguish between current and past infections 11 .

Management and Therapy

Praziquantel (Biltricide) – an antihelmintic medication that prevents worms from growing or multiplying in the body, is the best available treatment for human schistosome infections. The Praziquantel treatment indicated for S. haematobium, S. japonicum and S. mansoni is three doses of 20 milligrams per kilogram of body weight; this dosage yields the best results when given within the space of one day 3 .

Oxamniquine is another medication that targets adult worms within the body 1 . It is cheaper, and therefore a good candidate for mass-treatment programs. More careful dosing is necessary with Oxamniquine, depending on where in the world schistosome infection was contracted 3 .

Public Health Prevention Strategies

One of the most important aspects of schistosomiasis control is prevention. Various methods have been used over the years, including education/awareness campaigns, snail removal projects, and the application of molluscicides. These chemicals have been particularly popular in China, and their use is now escalating to new levels despite several fundamental problems; molluscicides have the unfortunate side effect of killing fish, and a somewhat inconsistent and unreliable track record in actually permanently eliminating snail populations. Though molluscicides may be helpful in controlling particularly acute and focused outbreaks, they are probably not the best method of general control. The birthrate of snails is high enough that molluscicides can not eliminate populations. Their primary function can be used for acute infection outbreaks, but longer term snail abatement programs must be more permanent6 .

Slightly more effective and less damaging to the environment is the process of lining ditches and canals with concrete. This seems to greatly reduce snail presence 6 but the drawbacks here are that not all vital bodies of water can, or should be concrete-lined due to the associated high costs.

It is now felt that control regimes should generally look at intervillage connectedness to formulate cost-effective strategies of administering chemotherapy, or other viable measures in select villages 4 . One way to do this is to create Global Positioning System habitat survey maps on the ground in affected areas, and then overlay them with high resolution LandSat images. The information provided by selected local surveys and descriptions can help identify areas of probable snail habitat on larger satellite maps; a valuable tool for targeting relevant locales in places of dispersed and varied endemicity6 .

In many places simply recommending that people avoid still water is unreasonable due to economic or hygienic necessity. Niclosamide lotion, used on the skin prior to immersion in dangerous waters has been shown to be helpful 3 , though only as often as lotion is available.

One novel, culturally appropriate, and sustainable idea comes from the work of Robert Spear in Southern China. His team of researchers has developed a modified version of the traditional “anaerobic waste-digestion system” that is typically located under a villager's house, and functions both to cycle waste and produce methane gas for cooking. Spear's modifications manage to reduce schistosome egg presence in the digested waste by one hundred-fold while causing little or no degradation of the human and animal waste. The absence of degradation is fundamental for the members of small farming communities, because the waste is used as fertilizer. The process of modification costs about $200 per household, and was recently installed in 31 of 40 houses in one hamlet.

The specificity of interventions for particular villages in a region, and the importance of understanding the determinants for infection in particular villages using spectral analysis and GPS imaging is demonstrated by the differences in Schistosomiasis infection rates between natural villages in China. For example, the installation of the anaerobic waste digestion system was successful in the trial village at the top of one watershed, but unsuccessful for a similar terraced agricultural village just five kilometers away. Both villages had an initial disease prevalence of 50 to 60 percent, yet only one of the two villages saw significant declines in prevalence after the installation of the anaerobic waste digestion systems. This was probably due to the fact that one of the villages drew its water from a source contaminated by yet another settlement, uninvolved in any schistosomiasis reduction plan. So while local efforts may have reduced the schistosome egg count going into the water, they had no effect on the upstream eggs already there.

Schistosoma japonicum expert Robert Spear also claims that the biggest challenge in China will be to convince the government to think of the villages as connected clusters rather than as individual systems. He leaves for China in mid-May, 2006, to set up a demonstration project that will include 30 to 40 connected regions. He hopes to make a transition to connect public health with rural energy and to effectively follow up and implement sustainable Schistosomiasis prevention projects within the next few years. His work is a hopeful model for schistosomiasis prevention and interventions in the future.

Useful Web Links

Index

References

1 Mahmoud, Adel A. F., ed. Schistosomiasis. Tropical Medicine Science and Practice Vol. 3. Singapore: Imperial College Press, 2001.

3 John, David T and William A. Petri, Jr. Markell and Voge's Medical Parasitology. 9th ed. United States: Saunders Elsevier, 2006. 181-196.

4 Xu, Bing, Gong, Peng, Seto, Edmund, Liang, Song, Yang, Changhong, Wen, Song,Qiu, Dongchuan, Gu, Xueguang & Spear, Robert (2006) A Spatial-Temporal Model for Assessing the Effects of Intervillage Connectivity in Schistosomiasis Transmission. Annals of the Association of American Geographers 96 (1); 31-46.

6 Spear, Robert. Telephone interview. 18 May 2006.

9 Elliott, DE. 1996. "Schistosomiasis Pathophysiology, Diagnosis, and Treatment". Gastroenterol Clinical North American 25(3): 599-625.

10 Dajotoy, Terese, Pia Andersson, Anders Bjartell, Claes-Göran Löfdahl, Hans Tapper, and Arne Egesten. 2004. "Human eosinophils produce the T cell-attracting chemokines MIG and IP-10 upon stimulation with IFN-". Journal of Leukocyte Biology 76:685-691.

11 Fulford, Martha, Jay Keystone. “Schistosomiasis.” 2002 New York. Healthline. 2005-2006. Healthline. 17 May 2006.

img11 "Rice." Wikipedia. 2006. Wikipedia.org. 17 May 2006. http://wikipedia.org