NEWS | April 27, 2015

Navy Researchers Explore Genetic Diversity of Lassa Virus in West Africa

By Donna McKinney

Lassa virus is widespread in parts of West Africa and causes the often deadly hemorrhagic fever. Scientists at the U.S. Naval Research Laboratory (NRL) are studying the genetic diversity of the virus with hopes that their work can aid the development of vaccines, diagnostic tests, and possibly antiviral drugs, explains Dr. Tomasz Leski, a research biologist and the lead author of the study. The research is published in the April issue of Emerging Infectious Diseases journal.

The Lassa virus (LASV) is usually spread to people through contact with rodents or their excretions. To obtain a more complete and updated picture of the LASV strains circulating in Sierra Leone, the NRL researchers isolated viruses from rodents collected from eight locations and examined the viruses at the genetic level.

Human cases of Lassa fever have been found in Guinea, Sierra Leone, Liberia, Mali, Burkina Faso, and Nigeria. Estimates suggest that 300,000 to 500,000 cases of Lassa fever cause 5,000 to 10,000 deaths each year in West Africa. Some estimates even project there could be 3 million cases each year with 67,000 deaths. The multimammate rat, a common African rodent, is a natural host and reservoir for the virus. Humans probably get infected by eating contaminated food, by inhaling virus-contaminated aerosols, or while butchering infected rat meat. The virus can also be transmitted in person-to-person contact.

The researchers used a combination of techniques including NRL-developed microarray for detection of biothreat agents (RPM technology) and polymerase chain reaction (PCR) to detect Lassa virus in tissues of rodents captured in several locations in Southern and Eastern provinces of Sierra Leone. Fragments of the viral genome of detected viruses were analyzed using DNA sequencing and similarity of the viral strains was compared using Bayesian statistics. The obtained results allowed the researchers to construct genealogical trees revealing the degree of diversity and relationship between groups of Lassa strains circulating in multimammate rats in Sierra Leone.

The NRL research team found that the viruses were more genetically diverse than expected, varying by location. These findings underscore how much we can still learn about this deadly virus, which was discovered more that 45 years ago. Data generated in the course of this study will help in designing better virus detection methods. They may also help in finding low virulence viral strains that may be potentially used for developing a Lassa vaccine, says Leski.

In addition to Leski, the research team members consist of Michael Stockelman, David Stenger, and Baochuan Lin from NRL's Center for Bio/Molecular Science and Engineering; Lina Moses and Daniel Bausch from Tulane University; Matthew Park from Thomas Jefferson High School, Alexandria, Virginia; and Rashid Ansumana from Njala University, Sierra Leone.