Although undeniably effective, the current rehydration therapy for cholera could increase the toxicity of the cholera bacterium, according to a new study. The scientists behind the data propose a change in the treatment, replacing glucose with starch from rice powder.
Cholera is caused when the bacterium Vibrio cholerae infects the small intestine, causing severe diarrhoea and vomiting, which can result in dehydration and death. The main treatment involves oral rehydration therapy, where the patient drinks water mixed with salts and glucose.
Although this treatment is very effective, there are concerns that the glucose content might actually worsen the disease. A new study by researchers in Switzerland and Italy has indicated that this is indeed the case. As reported in the journal PLOS Neglected Tropical Diseases, they demonstrated that glucose increases the toxicity of the cholera bacterium, whereas replacing glucose with starch can reduce its toxicity by almost 75 per cent.
Cholera treatment: effective, but could be improved
The usual treatment for cholera comes in the form of ‘oral rehydration therapy’ packs. Essentially, it involves feeding the patient water mixed with electrolyte salts and glucose. The idea is to replace the patient’s lost fluids and essential salts, while the glucose acts as a source of carbon that helps the intestine to absorb the salts more efficiently. The patient continues the therapy until the infection has run its course.
Up to half of cholera patients would die without treatment, but oral rehydration therapy has been shown to lower the deaths to around one per cent. However, there are concerns that using glucose in the rehydration mixture can actually exacerbate the disease. The problem is that the bacterium also consumes glucose, which increases the gene activity that makes the bacterium toxic.
On the other hand, some field studies have shown that using more complex carbon sources, like starch from rice powder, might be more effective. Despite this, there has never been a decisive study linking oral rehydration recipes with their effect on how the disease spreads.
The cholera bacterium, Vibrio cholerae, infects humans by releasing a protein called the cholera toxin. Consequently, regulating the genes that produce the cholera toxin can either increase or decrease the bacterium’s capacity to spread disease.
Alternatives to glucose
In the new study, researchers led by Melanie Blokesch and Andrea Rinaldo at École Polytechnique Fédérale de Lausanne (EPFL) correlated data from a recent cholera outbreak in Haiti with the effectiveness of oral rehydration therapy. Blokesch’s team fed the cholera bacterium with different sugars, such as glucose and sucrose, as well as starch from potatoes and rice to see how each would affect the cholera toxin genes.
The scientists found that the activity of the genes, as well as the production of the cholera toxin itself, increased when the bacterium was grown on glucose but decreased by around 75 per cent when it was grown on starch from rice. One reason for this is that the type of carbohydrate, such as glucose or starch, available to the bacterium affects the mechanisms that regulate the activity of its toxin-producing genes. Ultimately, this effect influences the bacterium’s ability to infect humans.
Rinaldo’s team matched these data to the actual cholera epidemics in Haiti. Using data from the outbreak of cholera that started in 2010, they developed a mathematical model of the disease’s epidemiology. They then modified the model to include oral rehydration therapy based on rice starch instead of glucose. The results indicated that using this alternative approach could lead to 30 per cent fewer cholera cases (375,000 instead of 520,000 cases) on the island within the first 14 months of an epidemic.
The results feed into the current discussion of cholera treatment, and strongly suggest a review of current approaches. “Of course, we’re not saying ‘stop doing oral rehydration therapy with glucose right away’ because it works so well,” Blokesch says. “But still, the data suggests that the regimen can be significantly improved, and that the community needs to start discussing this possibility again – especially in areas endemic to cholera.”
– Adapted from EPFL Mediacom