LASSA FEVER - WEST AFRICA (37): LIBERIA, WHO

Posted on 12TH JUL 2018
tagged Lassa Fever, West Africa; Liberia

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Date: Fri 6 Jul 2018, 5:00 PM
Source: WHO Weekly Bulletin on Outbreaks and Other Emergencies [edited]
http://apps.who.int/iris/bitstream/handle/10665/273028/OEW27-30060607201...

Event Description
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Liberia has continued to experience sporadic cases of Lassa fever since the beginning of 2018. In week 25 (week ending 26 Jun 2018), 2 new confirmed Lassa fever cases were reported in Nimba County, the only county with active transmission currently. Nimba County has reported 5 confirmed Lassa fever cases since [12 May 2018]. In the latest event (the 2 confirmed cases in week 25), the 1st case-patient, a 59-year- old male from Gbehlay Geh district, fell ill on [4 Jun 2018] and was treated with antimalarials and antibiotics at a local clinic. On [20 Jun 2018], the case-patient presented to a public hospital with fever and other constitutional symptoms, and had bleeding from a venepuncture site. On [21 Jun 2018], a blood specimen was collected and sent to the National Public Health Reference Laboratory (NPHRL). The test result released on [26 Jun 2018] was positive for Lassa fever virus infection. The 2nd case-patient, a 41-year-old female, is the wife of the first case-patient (described above). She developed illness on [17 Jun 2018] and was admitted to the same hospital on [20 June 2018] with fever and other constitutional symptoms. Being a known contact, a blood specimen was collected on [21 Jun 2018] and the test result released on [26 Jun 2018] was positive for Lassa fever. The 2 case-patients are admitted under barrier nursing and ribavirin treatment initiated. A total of 26 contacts, including 13 health workers, have been line listed and are being followed up.

Between [1 Jan 2018] and [27 Jun 2018], a total of 130 suspected Lassa fever cases, including 33 deaths, were reported. Of these, 20 cases were laboratory confirmed, 103 were discarded (after testing negative), and 7 cases were not tested due to inadequate specimens. Of the 20 confirmed cases, 14 have died, giving a case fatality rate of 70 percent. Females make up 60 percent (12) of the confirmed cases. The age range for the confirmed cases is 1 to 65 years old, with a median of 32.5 years. The confirmed cases are from 5 counties, namely (Nimba (9), Bong (4), Montserrado (3), Margibi (2), and Grand Bassa (2).

Public Health Actions
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- The Ministry of Health and the National Public Health Institute of Liberia (NPHIL) are coordinating response activities to the Lassa fever outbreak, with support from WHO, CDC and other partners. The national epidemic preparedness and response committee (NEPRC), under the leadership of NPHIL, have been meeting weekly to review the Lassa fever outbreak situation and provide technical support to sub-national level, with technical support from WHO, and US-CDC; 15 WHO field offices are providing technical and operational support to the response.
- Active surveillance, including case search, case investigation and contact tracing are ongoing in the affected districts. A specimen transport system using couriers is available at designated points across the country to transport specimens to the NPHRL for testing.
- The Ganta United Methodist Hospital has been designated as a treatment centre, and equipped with ribavirin and other medical supplies for case management. Orientation of healthcare workers on case management protocol is ongoing.
- Healthcare workers in the country are being trained on Lassa fever case management and infection prevention and control (IPC) measures by NPHIL and MOH, with support from WHO.
- Health workers' exposure risk assessment is planned to be conducted in the clinic or hospital where the confirmed cases sought care.
- Community engagement activities are ongoing in the affected communities, including home visits and providing information on environmental cleanliness.

Situation Interpretation
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Sporadic Lassa fever cases continue to occur in certain parts of Liberia where the disease is known to be endemic. Bong, Grand Bassa, Margibi, and Nimba are among the counties that report cases annually. In 2017, a total of 30 confirmed cases were reported from 7 counties. The reason for these sporadic cases is known: the constant interaction of rats (the vector for Lassa fever virus) and people in unsanitary conditions. The national authorities and partners need to prioritize measures mitigating this exposure risk factor by improving vector and environmental management components of the response. This goes along with effective social mobilization and community engagement strategies, targeting vector control and environmental management in the communities. There is also a need to enhance capacity at the subnational levels for early case detection, case investigation, appropriate case management and its associated IPC [infection prevention and control] measures aimed at averting infection among health workers.

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Communicated by:
ProMED-mail

[The number of Lassa fever cases in Liberia continues to slowly increase. Between 1 Jan 2018 and 27 Jun 2018, 20 cases were laboratory confirmed, up from 18 cases on 1 Jun 2018. Apparently, all these Lassa fever virus infections were acquired by contact with infected rodents or their excretions. Lassa fever virus can be acquired from infected rodents or patients in the hospital but in the above report, there is no mention of Lassa fever virus nosocomial transmission. Transmission can occur in health facilities when personal protective equipment is not employed and barrier-nursing practices are not adequate to protect staff from blood and secretions of infected patients. The hospitals attending the patients mentioned above do have barrier measures in place.

As mentioned in previous posts, Lassa fever virus transmission to humans occur when people are in contact with the reservoir rodent host, the multimammate mouse (_Mastomys natalensis_ and _M. erythroleucus_) and the African wood mouse (_Hylomycus pamfi_) or their excreta, as was likely the situation in these cases. Rodent control has to be undertaken at the village level with individual households employing the preventive measures listed above. This requires an extensive and continuous public education effort.

Images of the _Mastomys natalensis_ mouse, the rodent reservoir of Lassa fever virus, can be seen at https://www.inaturalist.org/taxa/45326-Mastomys-natalensis and of _M. erythroleucus_ and _Hylomycus pamfi_ at: http://punchng.com/nigerias-large-rat-population-threatens-lassa-fever-war/.
- Mod.TY

Maps of Liberia can be accessed at: http://www.theworldmap.net/country/big/liberia/ and http://healthmap.org/promed/p/54]

See Also
Lassa fever - West Africa (33): Liberia 20180615.5858754
Lassa fever - West Africa (30): Liberia 20180604.5836574
Lassa fever - West Africa (28): Liberia 20180520.5806477
Lassa fever - West Africa (27): Liberia (MG) 20180510.5791763
Lassa fever - West Africa (23): Liberia, WHO 20180417.5753003
Lassa fever - West Africa (17): Liberia (MO, NI) 20180310.5678669
2017
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Lassa fever - West Africa (04): Liberia 20170209.4827934
2016
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Lassa fever - West Africa (29): Nigeria, Liberia 20160520.4233773
Lassa fever - West Africa (23): Sweden (VG) ex Liberia, additional information 20160406.4141321
2015
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Lassa fever - USA: (NJ) ex Liberia 20150526.3386913
2014
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Lassa fever - Nigeria, Liberia 20140328.2363217
2013
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Lassa fever - Liberia: (BG) fatal cases 20130911.1937742
2007
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Lassa fever - Liberia (03) 20070430.1406
Lassa fever - Liberia (02): confirmed 20070413.1235
Lassa Fever - Liberia: RFI 20070410.1210
2006
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Lassa fever - Liberia (02) 20061001.2812
Lassa fever - Liberia: RFI 20060929.2783
2004
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Lassa fever, imported - USA (NJ) ex Liberia (02) 20040930.2700
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