People in developed countries tend to think of roundworm as just a problem for dogs and cats. But more than 800 million people around the world are infected with the parasite. The highest infections rates occur in parts of sub-Saharan Africa, Asia and south-central Latin America.
Those numbers could be brought down, since researchers in Ireland and England have identified a mechanism that could potentially turn a mouse susceptible to roundworm into one that can effectively fight the infection. Their findings are published in PLOS.
Neglected tropical diseases
Roundworm is one of many neglected tropical diseases identified by the World Health Organization and it is the most common of the three transmitted from soil. Most humans infected with roundworm do not show symptoms. People find out they are infected after passing the parasite in their stool or vomit.
Fertilized roundworm eggs are deposited in the soil from human feces. If someone ingests these eggs, they hatch in the intestine. The larvae then move into the liver where they mature further and are transported through the bloodstream into the lungs. After a few days, the now mature worms wriggle out of the lungs into the throat, where they are either swallowed or evacuated. If they make it back into the intestines, the female worms can lay up to 200,000 eggs a day which are deposited back into the soil after defecation-- starting the cycle anew.
This disease is particularly harmful for young children. The adult worms can live up to 2 years, so intestinal blockage can become severe in tiny tummies. The larvae can also cause breathing issues when they enter the lungs. The WHO combats the disease in highly affected areas with regular deworming of the population.
Researchers have noticed that some people are more susceptible to roundworm than others. But human studies are expensive. So researchers use mice that mimic this dichotomy. When infected, susceptible mice show a higher number of parasites in their lungs than those that are resistant. This led previous researchers to conclude that the liver environments in these two genetically different mice also had to be different.
Jim Carolan, a lecturer of biology at Ireland's Maynooth University, finds the roundworm parasite fascinating. “Our bodies should be able to kick that [parasite] up and down the street. But it doesn’t because the [roundworms] have evolved ways to evade … or suppress the system,” he tells VOA.
To find out how, he looked at the liver proteins in these two types of mice. In the liver cells of resistant mice, Carolan and colleagues discovered hundreds of different proteins that are associated with energy production. One of the byproducts of the higher mitochondrial processes that produce energy is chemicals containing oxygen known as reactive oxygen species (ROS).
The researchers suggest that if resistant mice have more active mitochondria, they will produce more of these ROS, which could be toxic to parasitic cells.
This work is only preliminary and Carolan stresses that more tests and research are needed before human therapies can be developed. “I like to refer to it as a sign post. It’s pointing us in a direction that we need to focus on.” They still need to determine if there are actually more mitochondria present in the resistant mice and if that mitochondria is more active. To do this they will need to count the mitochondria and measure the levels of ROS to see if it is indeed higher than in susceptible mice.
“This is the easy part. The hard part is yet to come,” says Carolan.
Bringing attention to a neglected disease
The importance of this work is twofold: it provides scientists a new avenue to investigate for fighting a disease that affects a large number of impoverished people and it brings attention to a disease that is largely ignored in developed countries.
Graham Medley is a professor of Infectious Disease Modelling at the London School of Hygiene and Tropical Medicine. He notes in an article in The Lancet that the regular deworming done in developing countries is effective at containing the disease but not at eliminating it. Medley told VOA in an email that “roundworms are a major public health problem in low income countries, and having a drug that prevents infection would be a major advance.”
Carolan notes, “If we could turn that susceptible mouse into a resistant mouse … using a strategy that could target the mitochondria in the susceptible line, then you’re well on your way of thinking of some way to do that in humans.”
So while his study is preliminary, it gives researchers a path to pursue towards fighting this neglected disease.