IÂ spoke withÂ virologist Ian Goodfellow, whose laboratory works on noroviruses, about why he went to Sierra Leone to establish an Ebolavirus diagnostic and sequencing laboratory. The obstacles he encountered were considerable, but the results were very useful.Â Recorded at the Emerging Infectious Diseases A to Z (EIDA2Z) conference hosted by the National Emerging Infectious Diseases Laboratories (NEIDL).
Lassa virus origin and evolution
I have a soft spot in my heart for Lassa virus: a non-fictional account of itsÂ discoveryÂ in Africa in 1969Â inspired meÂ to become a virologist. Hence papers on this virus always catch my attention, such as one describing itsÂ origin and evolution.
Lassa virus, a member of the Arenavirus family, is very different from Ebolavirus (a filovirus), but both are zoonotic pathogens that mayÂ cause hemorrhagic fever. It is responsible for tens of thousands of hospitalizations, and thousands of deaths each year, mainly in Sierra Leone, Guinea, Liberia, and Nigeria. Most human Lassa virus outbreaksÂ are caused by multiple exposures to urine or feces from the multimammate mouse, Mastomys natalensis, which is the reservoir of the virus in nature. In contrast, outbreaks of Ebolavirus infection typically originate with a crossover from an animal reservoir, followed by human to human transmission. Despite being studied for nearly 50 years, until recently the nucleotide sequences of only 12 Lassa virus genomes had been determined.
To remedy this lack of Lassa virus genome information, the authors collected clinical samples from patients in Sierra Leone and Nigeria between 2008 and 2013. From these and other sources they determined the sequences of 183 Lassa virus genomes from humans, 11 viral genomes from M. natalensis, and two viral genomes from laboratory stocks. All the data are publicly available at NCBI. Analysis of the data lead to the following conclusions:
- Lassa virus forms four clades, three in Nigeria and one in Sierra Leona/Liberia (members of a clade evolved from a common ancestor).
- Most Lassa virus infections are a consequence of multiple, independent transmissions from the rodent reservoir.
- Modern-day Lassa virus Â strains probably originated at leastÂ 1,000 years ago in Nigeria, then spread to Sierra Leone as recently as 150 years ago. The lineage is most likely much older, but how much cannot be calculated from the data.
- The genetic diversity of Lassa virus in individual hosts is an order of magnitude greater than the diversityÂ of Ebolavirus. Furthermore, Lassa virusÂ diversity in the rodent host is greater than in humans, likely a consequence of the longer, persistent infections that take place in the mouse.
- The gene encoding the Lassa virus glycoprotein is subject to high selection in hosts, leading to variants that interfere with antibody binding.
- Genetic variants that arise in one rodent are not transmitted to another.
Perhaps the most important result from this work is the establishment of laboratories in Sierra Leone and Nigeria that can safely collect and process samples from patients infected with Lassa virus, a BSL-4 pathogen.
TWiV 341: Ebolavirus experiences
On episode #341 of the science show This Week in Virology,Â Vincent returns to the University of Glasgow MRC-Center for Virus Research and speaks with Emma, Gillian, and Adam about their ebolavirus experiences: caring for an infected patient, working in an Ebola treatment center in Sierra Leone, and making epidemiological predictions about the outbreak in west Africa.
You can find TWiV #341 at www.microbe.tv/twiv.
TWiV 307: Ebola aetiology
On episode #307 of the science show This Week in Virology, Tara Smith joins the TWiEBOVsters toÂ discuss the Ebola virus outbreak in west Africa, spread of the disease to and within the US, transmission of the virus, and much more.
You can find TWiV #307 at www.microbe.tv/twiv.
TWiV 306: This Week in Ebolavirus
On episode #306 of the science show This Week in Virology, the Grand Masters of the TWiVÂ discuss Ebola virus transmission, air travel from West Africa, Ebola virus infectivity on surfaces, the Dallas Ebola virus patient, and Ebola virus in dogs.
You can find TWiV #306 at www.microbe.tv/twiv.
TWiV 305: Rhymes with shinola
On episode #305 of the science show This Week in Virology,Â Vincent, Alan, and Kathy continue their coverageÂ of the Ebola virus outbreak in West Africa, with a discussion of case fatality ratio, reproductive index, a conspiracy theory, and spread of theÂ virus to the United States.
You can find TWiV #305 at www.microbe.tv/twiv.