Lassa fever is an acute viral haemorrhagic fever caused by the Lassa virus. Although it is not as well-known as its relative Ebola virus, it is deadly. From 300,000 to 500,000 people are infected every year, most of them In Africa. Prognosis is that 15-20% of hospitalized people with Lassa fever will die and it results in approximately 5,000 deaths every year. Now international team of scientists discovered ancient roots of the Lassa virus and have an explanation of how it has changed over time.
It is a major breakthrough in the research of this virus. Scientists say that results of this research provided them with important knowledge of how Lassa virus is evolving, which is very important in order to develop vaccines and therapies. Science did know how virus spreads even before this research, since the Lassa virus was first described in Nigeria in 1969.
The disease can spread from human to human, but some of the sufferers from Lassa virus get infected through contact with urine and droppings from infected Mastomys natalensis rodents, which are considered to be natural “reservoir” of the virus. However, scientists also wanted to understand the evolution of the virus, in order to make effective vaccines.
In order to get this critical knowledge about the virus, international team of researchers was formed. These scientists work in a variety of different science institutions: Harvard University, Broad Institute, Tulane University, Nigeria’s Irrua Specialist Teaching Hospital and Sierra Leone’s Kenema Government Hospital.
Scientists used a technique called next-generation sequencing to analyse genomes of Lassa virus samples taken from wild Mastomys natalensis and human patients in Nigeria and Sierra Leone. The results were surprising – the virus has ancient root in the exact place where it was first described. The team of researchers found that far-flung strains of Lassa virus share a common ancestor that can be traced back more than 1,000 years to the territory we now call Nigeria.
The research showed that Lassa virus spread out of Nigeria about 400 years ago. During the past two centuries it moved into territories today known as Guinea, Liberia and Sierra Leone. It is interesting that it is the exact same area, where the largest outbreak of Ebola virus has been happening since 2013. Spreading of the Lassa virus, allowed it to mutate and adapt to mammalian hosts.
This new research provided other important knowledge as well. It turns out that although virus can spread from human to human, most of people are infected from the wild rodent reservoir. Kristian G. Andersen, a researcher at The Scripps Research Institute and lead author of the study, explained that “the reason Lassa hasn’t yet grown into this huge epidemic is because there is limited transmission between humans”. He also said this feature of the virus is “a major difference between Lassa virus and Ebola virus”.
Now scientists will have to make further steps in order to control and prevent Lassa fever and local scientists in West Africa are crucial in this process. Next step is going to be bettering the understanding how the Lassa virus mutates within individual hosts as it confronts the immune system. Although this is only the beginning of the journey towards effective vaccines against Lassa virus, this research already provided science with very important knowledge and may eventually lead to better control of the spread of the Lassa fever.