Two of the most socioeconomically devastating parasitic diseases in tropical countries — malaria and schistosomiasis — may be closely linked in their infection processes, a recent Yale study has found.
The study used mathematical modeling to consider the concurrence of malaria and schistosomiasis caused by the S. Mansoni flatworm, a waterborne parasite responsible for roughly one third of the 200 million cases of schistosomiasis worldwide. They found that incidences of S. Mansoni-caused schistosomiasis led to greater incidences of malaria, suggesting that treatment for the former may be a powerful and cost-effective tool in the elimination of the latter.
“By treating schistosomiasis we can reduce the burden of malaria on young children in Sub-Saharan Africa by a factor of two [within schistosomiasis—inflicted communities],” said Martial Ndeffo Mbah, associate research scientist in epidemiology at the School of Public Health and the study’s principal author.
The disease affects a range of ages, but is extremely concentrated in young children, Ndeffo Mbah said, leading some organizations to offer mass-schistosomiasis-treatment in schools. This study suggests that these treatments may serve a dual process — simultaneously preventing schistosomiasis and malaria in children.
According to the study, treatment for the parasite not only cures individuals of the rashes, diarrhea and liver damage caused by schistosomiasis, but also helps curtail malaria by making preventative treatments more effective and reducing the transmission of the disease. In other words, it is easier to treat a person for malaria and prevent infection if he or she does not have schistosomiasis.
The researchers focused on establishing the relationship between the two diseases, rather than the biological processes behind the relationship.
Not only are treatments more effective for malaria for those who are cured of schistosomiasis, but there is also a huge cost benefit to implementing this policy, Ndeffo Mbah said.
“Compared to malaria, schistosomiasis treatment is very cheap,” he said. “You only need 50 cents to treat the child for an entire year.”
Malaria treatment, on the other hand, costs significantly more than that at roughly $2.50 per individual per dose, according to UNICEF.
Schistosomiasis is typically caused through interaction with contaminated water, which leads to mass infection in some regions. But according to Matt Tucker, director of the Schistosoma Lab of the Biomedical Research Institute, a biomedical production laboratory, the incidence concentration depends on the portion of a population that frequently comes into contact with contaminated water sources. Workers, children who are playing in the water and people who do laundry in such water sources are among those who are most at risk of infection, Tucker noted.
The disease is curable with praziquantel, though rates of reinfection are high, and individuals may need to receive drugs three to four times a year, Tucker said. In the absence of fully effective distribution of praziquantel, the parasite is endemic in the region, causing up to 200,000 deaths per year and providing for easier transmission of malaria to humans.
He added that other curative measures include permanent vaccines currently in development and ecological treatments. The ecological method involves trying to figure out how to stop the disease from ever reaching humans in the first place. One of those strategies is to eliminate the disease-causing flatworm through destruction of their usual habitats, including irrigation ditches. The National Science Foundation, in particular, is currently supporting research projects aimed at eliminating the ecological causes of the disease.
The study focused on instances of coinfection between the two diseases. Becca Lewis, a doctoral candidate at Columbia University who researches the coinfection of malaria and salmonella, said that coinfection occurs when the two pathogens interact directly, either helping or hindering each other.
“Coinfection can change susceptibility in two ways,” she said. “How likely you are to contract the infection, for example, [or] whether the malaria can enter your body or even establish life cycles within the body. And once [one of the pathogens has entered the body], it can change your susceptibility to the pathology of the disease.”
In order to better treat malaria, Ndeffo Mbah recommended that nations and international organizations move towards more focused treatment of schistosomiasis.
According to the study, “mass praziquantel administration will generate indirect benefit in terms of reducing malaria transmission and disease burden in S. mansoni–malaria co-endemic communities.” It goes on to note that it would be extremely beneficial to scale up schistosomiasis control efforts in sub-Saharan Africa, and especially in areas were S. mansoni and malaria are highly prevalent. Taking such action would both to help eliminate the damage caused by the schistosomiasis itself and to advance the international effort against malaria, the study stated.
According to the World Health Organization, there was a 40 percent increase in treatment of schistosomiasis between 2011 and 2012.