New research shows that parasitic nematodes, which are responsible for infecting more than a billion people worldwide, carry viruses that could solve the puzzle of why some cause serious illness.
A study led by the Liverpool School of Tropical Medicine (LSTM) used advanced bioinformatic data mining techniques to identify 91 RNA viruses in 28 species of parasitic nematodes, representing 70% of the species that infect humans and animals. Often these are asymptomatic or not serious, but some can lead to a serious, life-changing illness.
Nematode worms are the most common animals on Earth and occur on all continents around the world, with several species infecting humans as well as agriculturally and economically important animals and crops. And yet, in several cases, scientists don’t know how some nematodes cause certain diseases.
The new research, published in Natural microbiologyopens the door for further research into whether these newly discovered viruses – only five of which were previously known to science – could contribute to many chronic, debilitating conditions. If a link can be proven, it could pave the way for more effective treatments in the future.
Mark Taylor, Professor of Parasitology at LSTM, said: “This is a truly exciting discovery and could change our understanding of the millions of infections caused by parasitic nematodes. Finding an RNA virus in any organism is of great importance, because these types of viruses are well-known pathogens. When these worms that live in us release these viruses, they spread through the blood and tissues and cause an immune response.
“This raises the question of whether any of the diseases for which these parasites are responsible could be caused by the virus rather than directly by the parasitic nematode.”
Parasitic nematodes, including hookworms and whipworms, can cause severe abdominal problems and bloody diarrhea, developmental delay and anemia. Infection with filarial worms can lead to disfiguring conditions such as lymphedema, or ‘elephantiasis’, and onchocerciasis, or ‘river blindness’, which leads to blindness and skin diseases.
The study authors propose that these newly identified viruses may play a role in some of these conditions. For example, onchocerciasis-associated epilepsy (OAE), which occurs in children and adolescents in sub-Saharan Africa, has recently been linked to onchocerciasis, but it is not known why it causes neurological symptoms such as uncontrollable repetitive head nodding, as well as severe growth retardation. , delayed puberty and impaired mental health.
One of the viruses in the parasites that cause onchocerciasis identified in the new study is a rhabdovirus — the type that causes rabies. The study authors suggest that if this virus infects or damages human nerve or brain tissue, it could explain the symptoms of OAE.
The full extent and diversity of the viruses living in parasitic nematodes, how they affect nematode biology, and whether they act as drivers of disease in humans and animals now require further investigation.
The illuminating discovery of these widespread but previously hidden viruses was first made by Dr. Shannon Quek, a postdoctoral research associate at LSTM and lead author of the new study, who had initially used the same data mining method to screen for viruses in mosquitoes that spread disease, before deciding to investigate nematodes.
Dr. Quek, who comes from Indonesia, a country plagued by many parasitic nematodes, said: “As a child, I saw many people infected with these diseases and I suffered from dengue virus three times. That made me interested in tropical areas. Diseases caused by parasitic nematodes are very long-lasting, lifelong diseases that continually affect humans. The disease has a significant impact on people’s quality of life, their economic performance and their mental health.
“Many studies have been done on the microbiomes of mosquitoes, and how the bacteria that live in them can block the spread of viruses, which could stop vector-borne diseases like dengue. This interaction between organisms in the same host led me to think: – what else could be in parasitic nematodes? Which will now be the focus of our research after my discovery.”
