According to the Nigeria Centre for Disease Control (NCDC), from 1st January to 11th March 2018, a total of 1386 suspected Lassa fever cases have been reported, including 114 deaths (365/81 laboratory confirmed).
19 states have recorded at least one confirmed case across 55 Local Government Areas with 84% of all confirmed cases reported from three states–Edo (43%) Ondo (25%) and Ebonyi (16%) states.
In an interview with Nigerian news source, Premium Times, Chief Executive Officer of the Nigeria Centre for Disease Control, Chikwe Ihekweazu was asked what is behind the rapid spread of the disease and what efforts are you taking to stem the tide?
Ihekweazu said, “There is no magic bullet for Lassa fever, unfortunately. Lassa is endemic in our environment. The virus is with us. The host animals, (the multimamate rat) is in our environment. In a way, there is no magic bullet and this is really a marathon and not a sprint.
“Why are we having a big outbreak this year, is the question on everybody’s mind. The three possible causes – it could be a change in the virus, it could be a change in the rat or it could just be that we have improved our surveillance system so much that we are now finding cases that were previously not being found.
“This is at the heart of the work my colleagues are doing at the moment – epidemiologist, virologist, everyone working together to get to the bottom of what is driving this epidemic and work out preventing them in the future. There are many unknown questions about Lassa and there are lots of efforts now to find answers to the questions”.
NCDC released some early results of Lassa virus sequencing and this is what they found:
On the 10th March 2018, the analysis of a first set of seven Lassa virus draft sequences derived from the blood of seven laboratory-confirmed Lassa fever patients from Edo, Ondo, Ebonyi, and Imo States was completed. In addition, 83 unpublished sequences obtained during previous years from various parts of Nigeria were made available for comparison with the sequences of the 2018 outbreak. From the analysis, of these results, we can draw the following preliminary conclusions:
• No new virus lineages have so far been detected, meaning that the circulating viruses appear to be very similar to the viruses from previous years;
• Lassa fever cases appear to be mostly caused by viruses that are not epidemiologically linked;
• The viruses circulating in 2018 appear to originate from the pool of lineages and strains known to be circulating in Nigeria and are consistent with previous outbreaks;
• The most likely route of transmission continues to be spill over of viruses from the rodent reservoir to humans rather than extensive human-to-human transmission.
The most important question being investigated at the moment is what has caused an outbreak of this magnitude, at this time? One of the possible answers to this question is the emergence of a new Lassa virus lineage or strain with increased virulence or transmissibility. Evidence from this work, although limited to seven viruses at the moment suggests that this is unlikely to be the case.