Although Lassa fever is endemic in a number of West African nations, this year has seen a surge in cases (see ECDC: Rapid Risk Assessment On Lassa Fever In Nigeria, Benin, Togo, Germany & USA), along with reports suggesting unusually high fatality rates.
Cases have been exported to both Germany and Sweden, and at least one case was evacuated to a U.S. facility for treatment.
The Lassa virus is commonly carried by multimammate rats, a local rodent that often likes to enter human dwellings. Exposure is typically through the urine or dried feces of infected rodents, although human-to-human transmission is possible.
Normally, 80% who are infected only experience mild symptoms, and the overall mortality rate is believed to be in the 1% to 2% range (although it runs higher (15%-20%) among those sick enough to be hospitalized).
Today the World Health Organization reports on (now lab confirmed) Lassa cases in Liberia.
Since 1 January 2016, WHO has been notified of at least 38 suspected cases of Lassa fever in Liberia.
Suspected cases were reported from 6 prefectures: Bong (17 cases, including 9 deaths), Nimba (14 cases, including 6 deaths), Gbarpolu (4 cases), Lofa (1 case), Margibi (1 case) and Montserrado (1 case).
Between 1 January and 3 April 2016, samples from 24 suspected cases were received for laboratory testing. Of these 24 suspected cases, 7 are reported to have tested positive for Lassa fever:
All the Lassa fever confirmed cases tested negative for Ebola virus disease. Since there are no designated laboratories in Liberia that can test samples for Lassa fever by PCR, specimens are currently sent for testing to Kenema, Sierra Leone.
- 2 cases were identified by polymerase chain reaction (PCR);
- 2 cases were identified through the detection of IgM antibodies using enzyme-linked immunosorbent assay (ELISA);
- 2 cases were identified through the detection of Lassa virus antigens using ELISA;
- information on the type of testing employed to identify the seventh case is not currently available.
Public health responseTo date, 134 contacts have completed the 21-day follow-up period. A total of 17 additional contacts are being monitored. None of these contacts have so far developed symptoms.
Appropriate outbreak response measures, including case management, infection prevention and control, community engagement and health education, have been put in place by the national authorities with the support of WHO and partner organizations.
WHO risk assessmentLassa fever is endemic in Liberia and causes outbreaks almost every year in different parts of the country. Based on experiences from previous similar events, it is expected that additional cases will be reported.
Although occasional travel-associated cases of Lassa fever have been reported in the past (see DON published on 27 and 8 April 2016), the risk of disease spread from Liberia to non-endemic countries is considered to be low. WHO continues to monitor the epidemiological situation and conduct risk assessments based on the latest available information.