Lassa Fever

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JAP members sensitizing traders in Bauchi Central Market, Bauchi State
Journalists join fight against Lassa fever in security compromised North eastern Nigeria
Nigeria
Emir of Argungu speaking on behalf of the traditional instituion
Traditional leaders intensify community sensitization as National Council on Health pledges support for early containment of Lassa fever outbreak
Nigeria
Honourable Minister of Health briefing Niger state Commissioner of Health on 14 January, 2015 after a field visit
Lassa fever outbreak in Nigeria: Federal Ministry of Health restates commitment to halt the epidemic
Nigeria
lassa-fever-transmission-rats
WHO calls for early diagnostic tests for Lassa fever

    Overview

    Lassa fever is an acute viral haemorrhagic illness caused by Lassa virus, a member of the arenavirus family of viruses. Humans usually become infected through aerosol or direct contact with excreta of infected rodents. 

    Lassa fever can also be spread between humans through direct contact with the blood, pharyngeal secretions, urine, faeces or other body secretions of an infected person. Person-to-person transmission of Lassa fever has occurred in health care settings after exposure to blood and secretions of infected patients.

    The incubation period for Lassa fever ranges from 2 to 21 days. About 80% of human Lassa fever infections are mild or asymptomatic. Fever, general weakness and malaise are usually the first symptoms to appear in symptomatic patients.

    Lassa fever is difficult to distinguish from many other diseases which cause fever, including malaria, shigellosis, typhoid fever, yellow fever and other viral haemorrhagic fevers. The overall case fatality ratio is 1% to 15% among hospitalized patients. Ribavirin is effective treatment for Lassa fever is given early in the course of clinical illness.

    Lassa fever is known to be endemic in Guinea, Liberia, Nigeria and Sierra Leone, but probably exists in other West African countries as well.

    Disease Outbreak

    NIGERIA

    Between August 2015 and 17 May 2016, WHO has been notified of 273 cases of Lassa fever, including 149 deaths in Nigeria. Of these, 165 cases and 89 deaths have been confirmed through laboratory testing (CFR: 53.9%). The cases were reported from 23 states in Nigeria.

    Since August 2015, ten health care workers (HCW) have been infected with Lassa fever virus, of which two have died. Of these ten cases, four were nosocomial infections.

    As of 17 May 2016, 8 states are currently reporting Lassa fever cases (suspected, probable, and confirmed), deaths and/or following of contacts for the maximum 21-day incubation period. Currently, 248 contacts are being followed up in the country. The other 15 previously affected states have completed the 42-day period following last known possible transmission.

     

    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:

    • 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.

    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.

    Factsheet

    Key Facts

    • Lassa fever is an acute viral haemorrhagic illness of 2-21 days duration that occurs in West Africa.
    • The Lassa virus is transmitted to humans via contact with food or household items contaminated with rodent urine or faeces.
    • Person-to-person infections and laboratory transmission can also occur, particularly in hospitals lacking adequate infection prevention and control measures.
    • Lassa fever is known to be endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, and Nigeria, but probably exists in other West African countries as well.
    • The overall case-fatality rate is 1%. Observed case-fatality rate among patients hospitalized with severe cases of Lassa fever is 15%.
    • Early supportive care with rehydration and symptomatic treatment improves survival.
    WHO calls for early diagnostic tests for Lassa fever

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    The Lassa fever virus is transmitted to humans from direct contact with infected rats through catching and preparing them for food.

    WHO/ M. Hotowossi, K. Vewonyi

    1 APRIL 2016 - Lassa fever has killed more than 160 people in West Africa, most of them in Nigeria, since November 2015. Many of these lives could have been saved if a rapid diagnostic test were available so that people could receive treatment early.

    Since November 2015, Nigeria, Benin, Sierra Leone, Liberia and Togo have reported more than 300 cases of Lassa fever and 167 deaths. Nigeria accounts for the majority of the cases with 266 cases and 138 deaths reported in 22 of the country’s 36 states as at 21 March 2016. Benin has recorded 51 cases and 25 deaths. Togo and Sierra Leone each reported 2 cases. More recently, since February, Liberia has reported seven confirmed cases including 3 deaths.

    Diagnosing Lassa fever a difficult task

    Lassa virus is carried by the Mastomys rat, which is found in parts of West Africa. The virus is transmitted to humans from direct contact with infected rats by catching and preparing them for food, or through contact with food or household items contaminated with rat faeces or urine. The virus can also be transmitted through contact with an infected person’s body fluids.

    Around 80% of people who become infected with Lassa virus have no symptoms or they have symptoms that mimic other illnesses, such as malaria, making it difficult to treat them. Symptoms include fever, fatigue, nausea, vomiting, diarrhoea, headaches, abdominal pains, sore throat and facial swelling.

    “Without early diagnosis and treatment, 1 in 5 infections result in severe disease, where the virus affects several organs such as the liver, spleen and kidneys,” explains Dr Formenty, expert in haemorrhagic fevers at WHO.

    “We need resources to invest in diagnostics to easily, accurately and safely test for Lassa fever as we do for malaria and HIV. Without a proper diagnosis, many people do not receive the correct treatment and that is why we see so many people with Lassa fever dying each year.”

    Ribavirin has been used successfully in the treatment of confirmed Lassa cases. This drug can treat infected people if it is administered as soon as the first signs appear.

    Germany reports first known Lassa infection outside Africa

    The first known case of Lassa infection outside of Africa has been reported in Germany. One person, a funeral home employee was infected after direct contact with an American who died of the disease in February 2016. The American was a medical director of a missionary hospital in Togo who was evacuated to Germany where he died.

    “This is the first time that secondary transmission of the infection is reported in Europe,” says Dr Formenty. “The risk for further transmission of Lassa fever in Germany and also West Africa is low and limited to hospital settings caring for the cases, with all contacts accounted for and monitored.”

    WHO continues to monitor the epidemiological situation and conduct risk assessments based on the latest available information.

    WHO and health partners scurry to stop the outbreak

    WHO and partners, including United Nations Children's Emergency Fund (UNICEF), Center for Disease Control and Prevention (CDC) in Atlanta, Bernard-Nocht-Institute in Hamburg, Germany and humanitarian partners, are supporting national authorities in the affected countries to take emergency measures in response to the outbreak. These include:

    • Setting up quarantine units in affected areas to isolate and treat patients.
    • Creating contact tracing systems to find those who might have been exposed to the disease.
    • Mobilizing a network of almost 200 community health workers across the country to monitor the contacts.
    • Repositioning and providing Ribavirin, in affected areas, including distributing personal protection equipment and other medical supplies.
    • Sharing information across borders.

     

    Journalists join fight against Lassa fever in security compromised North eastern Nigeria

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    Abuja, 02 February, 2016 - As part of ongoing efforts to contain the spread of Lassa fever, the World Health Organization (WHO) in collaboration with the Journalists’ Initiative Against Polio (JAP), has taken the campaign on personal and environmental hygiene to both urban and rural communities in the North East Zone (NEZ) with emphasis on infected states of Bauchi, Gombe and Taraba.

    Cumulatively in the country, 166 suspected cases (68 laboratory confirmed) and 99 deaths (43 in confirmed cases) with Case Fatality Rate (CFR) of 59.6%) have been reported from 18 states plus the Federal Capital Territory as at 01 February, 2016. In the Northeast zone, a total of 13 confirmed cases and 8 deaths in confirmed cases with CFR of 61.5% have been reported from Bauchi, Gombe and Taraba. The three states have had, ongoing transmission of the Lassa fever disease since November 2015.

    Even though the trend of transmission appears to be dropping, the Lassa fever was first discovered in Lassa village, Borno state, north eastern Nigeria in 1969.  The disease is therefore endemic in that part of the country with outbreaks recorded every year over the last five years. In order to mitigate the continuing spread of the disease within the zone, the JAP members were sensitized and engaged.

    The sensitization, which held in the conference halls of 10 media houses, focused principally on key messages on Lassa fever, the roles and responsibilities of journalists in raising public awareness to prevent epidemics and constructive reporting.

    WHO facilitated the formation of JAP in 2007 and the partnership has assisted in creating consciousness among fellow journalists and bringing to the fore, their social responsibility in increasing population immunity against vaccine preventable diseases and promoting routine immunization and community disease surveillance.

    While describing the coordinated sensitization of the JAP in the NEZ as a step in strengthening WHO’s partnership with the media, Dr Abdelrahim Khalid, the Zonal Coordinator stated that “WHO will not relent in its effort to build strong partnership with stakeholders in strengthening preventive measures and enhancing community surveillance against all epidemic prone diseases in the zone”.

    In Bauchi state for instance, members of the JAP organized and conducted series of other community sensitization activities as part of their contribution to the ongoing efforts to combat the disease. The JAP embarked on sensitization and awareness creation campaign on Lassa fever in the five high risk local government areas (LGAS) of the state and sensitized the communities on dangers, prevention and control measures of the disease.

    During the sensitization visits to secondary schools and market places in the state, they distributed copies of key messages on Lassa fever in English and local languages to students and other community members. The team rounded-off their sensitization drive in each of the high risk LGAs with 60 minutes phone-in programme on the community radio stations. 

    In a related effort to reinforce the process of community empowerment with key information on precautionary measures, the WHO also deployed over 10,000 house-to-house personnel in the zone to support the efforts of the JAP while at the same time carrying out community surveillance on Lassa fever and other epidemic prone diseases during the January round of the polio vaccination campaign conducted from 23-26 January, 2016.

    Preparatory to the engagement of the personnel for community sensitization and surveillance activities, the LGA and ward levels training opportunities were maximally utilized. Both the ward focal persons and the house-to-house teams were sensitized on the cause and prevention of Lassa fever. Copies of key messages and FAQs on Lassa fever were re-produced in local languages and distributed by the vaccination teams.

    While no case was reported during the campaign, the delivery of the key information on the disease has, nonetheless, assisted to increase the sensitivity of the index of suspicion. According to Dr Mahmud Saidu the WHO State Coordinator Borno State,  “there is no better time to conduct community sensitization and surveillance than during the campaigns when our teams are visiting all communities and every household”.

    WHO will continue to partner with government and stakeholders at all levels to provide technical support in the coordination of containment activities of the Lassa fever epidemic.

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    For more information please contact:

    • Technical contacts:

    Dr Mary Stephen: +234 816 289 9789; Email: stephenm [at] who.int

    Dr Abdelrahim Khalid; +234 803 402 1284; Email:   abdelrahimk [at] who.int

    • Media contacts:

    Ms  Charity Warigon; Tel: +234 810 221 0093; Email: warigonc [at] who.int

    Dr Mustapha Umar;  Tel: +234 803 616 9972: Email: umarm [at] who.int

    _________________________________________

    Below:

    01. JAP members sensitizing traders in Bauchi Central Market, Bauchi State

    02. School children assembled for sensitization by JAP on Lassa Fever in Toro LGA, Bauch State

     

    Traditional leaders intensify community sensitization as National Council on Health pledges support for early containment of Lassa fever outbreak

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    Abuja, 22 January 2016 - Traditional leaders from 19 Northern states have resolved to intensify community sensitization efforts in their respective domains and bring to an end, the Lassa fever outbreak, which as of 20 January 2015, recorded a total of 239 suspected cases and 44 confirmed cases, with 82 deaths from both confirmed and suspected cases in 17 states as well as  the Federal Capital Territory.

    Lassa Fever is named after Lassa town in Borno State and is endemic in most of the northern states.

    The deputy chairperson of the Northern Leaders Traditional Council (NTLC), Emir of Argungu, Alhaji Samaila Muhammadu Mera, stated that “as custodians of the people, our immediate responsibility will be to educate the general public in our respective communities on risks posed by rats, the current known reservoir of the Lassa Fever virus”.

    Th Emir pledged on behalf of all leaders present to disseminate sensitization messages from the ministry of health and World Health Organization (WHO) in mosques, churches and other community forums. He further pledged to “reinforce government’s efforts by sponsoring sensitization messages on community radio and television stations urging the general public to immediately report any strange illnesses to their nearest health facilities”.

    In a presentation to the traditional, Dr Audu Musa Idowu, the WHO State Coordinator, indicated that Isolation centers have been identified in most states while 71,000 tablets of Ribavirin, 20,750 vials of parenteral Ribavirin and 960 units of Personal Protective Equipment  were distributed to the affected states as of 20 January 2016. He informed the traditional leaders that six National laboratories with polymerase chain reaction capability are currently conducting analysis of samples collected.

    As community leaders met in Kaduna, the Federal Government, through the National Council on Health (NCH) convened an emergency meeting on 18 January, 2016, inaugurated a national Lassa Fever Eradication Committee. The communique issued at the end of deliberations reflected a collective resolve  by all 36 State Commissioners of Health and Directors of tertiary medical institutions to significantly strengthen Lassa Fever control efforts.

    During the extraordinary NCH meeting, the Honourable Minister of Health, Professor. Isaac Adewole, described the epidemic as “an embarrassment that should not be allowed to become a national shame”. He sought for strategies from the commissioners and partners that would enable the country to quickly contain the epidemic and sustain control measures to avoid another epidemic during the  next dry season.

    The minister  further pledged the establishment of additional six laboratories for Lassa Fever diagnosis. He disclosed that, worst case scenario projections, show that the epidemic could  worsen beyond that of 2012 with over 3,000 cases if the control measures are not lumped up immediately. He also indicated that about 56% of suspects with “typical Lassa Fever symptoms have turned negative for Lassa Fever virus and other haemorrhagic fever virus” and are therefore kept for further investigations.

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    Technical contacts:

    Dr Rex Mpazenje; Tel: +234 7803 960 0874; Email: mpazanjer [at] who.int

    Dr Mary Stephen; Tel: +234 816 289 9789; Email: stephenm [at] who.int

    •    Media contact:

    Ms  Charity Warigon; Tel: +234 810 221 0093; Email: warigonc [at] who.int

    ________________________________________________

    Below:

    01. Emir of Argungu speaking on behalf of the traditional instituion

    02. Dr Idowu Kaduna  WHO State Coordinator briefing traditional leaders on Lassa Fever

     

    Lassa fever outbreak in Nigeria: Federal Ministry of Health restates commitment to halt the epidemic

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    Abuja, 15 January, 2016 -- Lassa fever, which is endemic in Nigeria, has between late December 2015 and January 14, 2016 resulted in 53 deaths in 10 states and the Federal Capital Territory (FCT). 

    Lassa fever outbreak is a yearly occurrence during the dry season in Nigeria but, this year’s outbreak is more widespread with 10 states, 140 suspected and 30 confirmed cases. The case fatality rate (CFR) is significantly high at 53 or 37.9% of all cases.

    The outbreak is so far affecting Bauchi, Nasarawa, Niger, Taraba, Kano, Rivers, Edo, Oyo, Plateau states and the FCT, with Niger being the most affected with 48 cases and 16 deaths. Epidemiological link between the outbreaks of the different states has so far not been established.

    Speaking at a media briefing on 08 January 2016, the Honourable Minister of Health, Professor Isaac Adewole, declared an outbreak and reiterated the Federal Government’s commitment to quickly contain it. He assured the public that “Nigeria has the capability to diagnose Lassa fever” and that “all confirmed cases were diagnosed by the country’s laboratories”. However, because the symptoms of Lassa fever are so varied and non-specific, clinical diagnosis is often difficult, especially early in the course of the disease.

    Professor Adewole also directed all health facilities in the country to emphasize routine infection prevention and control measures and ensure all patients are treated free. Furthermore, he advised family members and health care workers to always be careful to avoid contact with blood and body fluids while caring for sick persons.

    The minister reiterated that no travel restrictions will be imposed from and to the areas currently affected. He further indicated that the World Health Organization (WHO) is being notified of all confirmed cases in line with International Health Regulations. He further thanked WHO and other partners for their support.

    Professor Adewole subsquently visited the most affected state of Niger on 14 January 2016 to mobilize local leadership and further galvanize the response.

    The WHO Officer in charge, Dr Rex Mpazanje, indicated that WHO is supporting the federal and state ministries of health through its polio structure to sensitize all health care workers in all health facilities to have a high index of suspicion and capacity to assess any suspect case that presents. Protective personal equipment, case definition materials, suspect case evaluation and documentation materials are being made available to all health facilities coupled with orientation of the service providers.

    WHO is also supporting public awareness initiatives through provision of information/ communication materials, briefing of traditional and religious leaders and airing of jingle on local radio stations.

    Furthermore, the WHO State Coordinator for Kano, Dr Bashir Abba, reported that already, 60 Disease Surveillance and Notification Officers (DSNOs), 37 secondary health facilities medical directors, 55 community health workers, 40 medical laboratory scientists and 44 nomadic representatives were sensitized on surveillance and case management of Lassa fever.

    Also, in Rivers state, WHO facilitated the reactivation of Emergency Operation Committee, chaired by the Honorable Commissioner for Health. WHO is also supporting decontamination of residences and health facilities associated with the three  cases and facilitating safe burial practices. So far, 200 contacts have been line listed and are being actively follow-up.

    Lassa fever is an acute febrile illness, with bleeding and death in severe cases, caused by the Lassa fever virus with an incubation period of 6-21 days. About 80% of human infections are asymptomatic; the remaining cases have severe multi-system disease, where the virus affects several organs in the body, such as the liver, spleen and kidneys. The onset of the disease is usually gradual, starting with fever, general weakness, and malaise followed by headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhoea, cough, and bleeding from mouth, nose, vagina or gastrointestinal tract, and low blood pressure.

    WHO fact sheet on Lassa fever

    ___________________________________

    Technical contacts:

    Dr Rex Mpazenje; Tel: +234 7803 960 0874; Email: mpazanjer [at] who.int 
    Dr Mary Stephen: +234 816 289 9789; Email: stephenm [at] who.int

    Media contact:

    Ms  Charity Warigon; Tel: +234 810 221 0093; Email: warigonc [at] who.int

    ___________________________________

    Below:

    01 Honourable Minister of Health briefing Niger state Commissioner of Health on 14 January, 2015 after a field visit

    02 Training of Disease Surveillance and Notification Officers in Kano

    03 Stakeholders meeting with the Commissioner for Health at the EOC in Rivers

     

    Lassa Fever – Nigeria

    Between August 2015 and 17 May 2016, WHO has been notified of 273 cases of Lassa fever, including 149 deaths in Nigeria. Of these, 165 cases and 89 deaths have been confirmed through laboratory testing (CFR: 53.9%). The cases were reported from 23 states in Nigeria.

    Since August 2015, ten health care workers (HCW) have been infected with Lassa fever virus, of which two have died. Of these ten cases, four were nosocomial infections.

    As of 17 May 2016, 8 states are currently reporting Lassa fever cases (suspected, probable, and confirmed), deaths and/or following of contacts for the maximum 21-day incubation period. Currently, 248 contacts are being followed up in the country. The other 15 previously affected states have completed the 42-day period following last known possible transmission.

    Public health response

    Currently, two national laboratories are supporting the laboratory confirmation of Lassa fever cases by polymerase chain reaction (PCR) tests. All the samples were also tested for Ebola, Dengue, Yellow fever and so far have tested negative. The two laboratories that are currently operational are:

    • Virology laboratory, Lagos University Teaching Hospital
    • Lassa fever research and control centre, Irrua specialist hospital

    Along with other key partners, WHO is supporting ministry of health in surveillance and response of Lassa fever outbreaks including contacts tracing, follow up and community mobilization. One of a concern since the onset of Lassa fever outbreaks is the high proportion of deaths among the cases that is still under investigation.

    WHO Risk Assessment

    Overall, the Lassa fever outbreak in Nigeria shows a declining trend. Considering the seasonal peaks in previous years, improvements in community and health care worker awareness, preparedness and general response activities, the risk of a larger-scale outbreak is low. Nevertheless, close monitoring, active case search, contact tracing, laboratory support and disease awareness (both in community in general and specific training for health care workers) should continue.

    WHO Advice

    Considering the seasonal flare ups of cases during this time of the year, countries in West Africa that are endemic for Lassa fever are encouraged to strengthen their related surveillance systems.

    Health-care workers caring for patients with suspected or confirmed Lassa fever should apply extra infection control measures to prevent contact with the patient’s blood and body fluids and contaminated surfaces or materials such as clothing and bedding. When in close contact (within 1 metre) of patients with Lassa fever, health-care workers should wear face protection (a face shield or a medical mask and goggles), a clean, non-sterile long-sleeved gown, and gloves (sterile gloves for some procedures).

    Laboratory workers are also at risk. Samples taken from humans and animals for investigation of Lassa virus infection should be handled by trained staff and processed in suitably equipped laboratories under maximum biological containment conditions.

    The diagnosis of Lassa fever should be considered in febrile patients returning from areas where Lassa fever is endemic. Health-care workers seeing a patient suspected to have Lassa fever should immediately contact local and national experts for advice and to arrange for laboratory testing.

    WHO does not recommend any travel or trade restriction to Nigeria based on the current information available.

     

    Related links

     

     

    Lassa Fever – Liberia

    Lassa Fever – Liberia

    Disease outbreak news 
    18 May 2016

    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:

    • 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.

    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.

    Public health response

    To 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 assessment

    Lassa 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.

    WHO advice

    Considering the seasonal flare ups of cases during this time of the year, countries in West Africa that are endemic for Lassa fever are encouraged to strengthen their related surveillance systems.

    Health-care workers caring for patients with suspected or confirmed Lassa fever should apply extra infection control measures to prevent contact with the patient’s blood and body fluids and contaminated surfaces or materials such as clothing and bedding. When in close contact (within 1 metre) of patients with Lassa fever, health-care workers should wear face protection (a face shield or a medical mask and goggles), a clean, non-sterile long-sleeved gown, and gloves (sterile gloves for some procedures).

    Laboratory workers are also at risk. Samples taken from humans and animals for investigation of Lassa virus infection should be handled by trained staff and processed in suitably equipped laboratories under maximum biological containment conditions.

    The diagnosis of Lassa fever should be considered in febrile patients returning from areas where Lassa fever is endemic. Health-care workers seeing a patient suspected to have Lassa fever should immediately contact local and national experts for advice and to arrange for laboratory testing.

    WHO does not recommend any travel or trade restriction to Liberia based on the current information available.

     

    Background

    Though first described in the 1950s, the virus causing Lassa disease was not identified until 1969. The virus is a single-stranded RNA virus belonging to the virus family Arenaviridae.

    About 80% of people who become infected with Lassa virus have no symptoms. 1 in 5 infections result in severe disease, where the virus affects several organs such as the liver, spleen and kidneys.

    Lassa fever is a zoonotic disease, meaning that humans become infected from contact with infected animals. The animal reservoir, or host, of Lassa virus is a rodent of the genus Mastomys, commonly known as the “multimammate rat.” Mastomys rats infected with Lassa virus do not become ill, but they can shed the virus in their urine and faeces.

    Because the clinical course of the disease is so variable, detection of the disease in affected patients has been difficult. When presence of the disease is confirmed in a community, however, prompt isolation of affected patients, good infection prevention and control practices, and rigorous contact tracing can stop outbreaks.

    Lassa fever is known to be endemic in Benin (where it was diagnosed for the first time in November 2014), Ghana (diagnosed for the first time in October 2011), Guinea, Liberia, Mali (diagnosed for the first time in February 2009), Sierra Leone, and Nigeria, but probably exists in other West African countries as well.

    Symptoms of Lassa fever

    The incubation period of Lassa fever ranges from 6–21 days. The onset of the disease, when it is symptomatic, is usually gradual, starting with fever, general weakness, and malaise. After a few days, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhoea, cough, and abdominal pain may follow. In severe cases facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina or gastrointestinal tract and low blood pressure may develop.

    Protein may be noted in the urine. Shock, seizures, tremor, disorientation, and coma may be seen in the later stages. Deafness occurs in 25% of patients who survive the disease. In half of these cases, hearing returns partially after 1–3 months. Transient hair loss and gait disturbance may occur during recovery.

    Death usually occurs within 14 days of onset in fatal cases. The disease is especially severe late in pregnancy, with maternal death and/or fetal loss occurring in more than 80% of cases during the third trimester.

    Transmission

    Humans usually become infected with Lassa virus from exposure to urine or faeces of infected Mastomys rats. Lassa virus may also be spread between humans through direct contact with the blood, urine, faeces, or other bodily secretions of a person infected with Lassa fever. There is no epidemiological evidence supporting airborne spread between humans. Person-to-person transmission occurs in both community and health-care settings, where the virus may be spread by contaminated medical equipment, such as re-used needles. Sexual transmission of Lassa virus has been reported.

    Lassa fever occurs in all age groups and both sexes. Persons at greatest risk are those living in rural areas where Mastomys are usually found, especially in communities with poor sanitation or crowded living conditions. Health workers are at risk if caring for Lassa fever patients in the absence of proper barrier nursing and infection prevention and control practices.

    Diagnosis

    Because the symptoms of Lassa fever are so varied and non-specific, clinical diagnosis is often difficult, especially early in the course of the disease. Lassa fever is difficult to distinguish from other viral haemorrhagic fevers such as Ebola virus disease as well as other diseases that cause fever, including malaria, shigellosis, typhoid fever and yellow fever.

    Definitive diagnosis requires testing that is available only in reference laboratories. Laboratory specimens may be hazardous and must be handled with extreme care. Lassa virus infections can only be diagnosed definitively in the laboratory using the following tests:

    • reverse transcriptase polymerase chain reaction (RT-PCR) assay
    • antibody enzyme-linked immunosorbent assay (ELISA)
    • antigen detection tests
    • virus isolation by cell culture.
    Treatment and prophylaxis

    The antiviral drug ribavirin seems to be an effective treatment for Lassa fever if given early on in the course of clinical illness. There is no evidence to support the role of ribavirin as post-exposure prophylactic treatment for Lassa fever.

    There is currently no vaccine that protects against Lassa fever.

    Prevention and control

    Prevention of Lassa fever relies on promoting good “community hygiene” to discourage rodents from entering homes. Effective measures include storing grain and other foodstuffs in rodent-proof containers, disposing of garbage far from the home, maintaining clean households and keeping cats. Because Mastomys are so abundant in endemic areas, it is not possible to completely eliminate them from the environment. Family members should always be careful to avoid contact with blood and body fluids while caring for sick persons.

    In health-care settings, staff should always apply standard infection prevention and control precautions when caring for patients, regardless of their presumed diagnosis. These include basic hand hygiene, respiratory hygiene, use of personal protective equipment (to block splashes or other contact with infected materials), safe injection practices and safe burial practices.

    Health-care workers caring for patients with suspected or confirmed Lassa fever should apply extra infection control measures to prevent contact with the patient’s blood and body fluids and contaminated surfaces or materials such as clothing and bedding. When in close contact (within 1 metre) of patients with Lassa fever, health-care workers should wear face protection (a face shield or a medical mask and goggles), a clean, non-sterile long-sleeved gown, and gloves (sterile gloves for some procedures).

    Laboratory workers are also at risk. Samples taken from humans and animals for investigation of Lassa virus infection should be handled by trained staff and processed in suitably equipped laboratories under maximum biological containment conditions.

    On rare occasions, travellers from areas where Lassa fever is endemic export the disease to other countries. Although malaria, typhoid fever, and many other tropical infections are much more common, the diagnosis of Lassa fever should be considered in febrile patients returning from West Africa, especially if they have had exposures in rural areas or hospitals in countries where Lassa fever is known to be endemic. Health-care workers seeing a patient suspected to have Lassa fever should immediately contact local and national experts for advice and to arrange for laboratory testing.

    WHO response

    The Ministries of Health of Guinea, Liberia and Sierra Leone, WHO, the Office of United States Foreign Disaster Assistance, the United Nations, and other partners have worked together to establish the Mano River Union Lassa Fever Network. The programme supports these 3 countries in developing national prevention strategies and enhancing laboratory diagnostics for Lassa fever and other dangerous diseases. Training in laboratory diagnosis, clinical management, and environmental control is also included.

    Multimedia

    Lassa Fever in Sierra Leone