For the past three months we've been following several outbreaks of Lassa fever in West Africa, starting in Nigeria (see Nigeria: Lassa Fever Outbreak With 40 Fatalities), and then flaring up in both Benin and Togo (see ECDC: Rapid Risk Assessment On Lassa Fever In Nigeria, Benin, Togo, Germany & USA) with exported cases to Germany and an Air Evac'd case to the United States.
Lassa is a Viral Hemorrhagic Fever (VHF), although not as deadly as Marburg or Ebola. 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, and roughly 80% who are infected only experience mild symptoms.
The overall mortality rate is believed to be in the 1%-2% range, although it runs much higher (15%-20%) among those sick enough to be hospitalized.That said, the reported case fatality rate has been unusually high in Nigeria this year, running over 50% among lab confirmed cases.
Like many other hemorrhagic fevers, person-to-person transmission may occur with exposure to the blood, tissue, secretions, or excretions of an individual, although the CDC reassures:
Casual contact (including skin-to-skin contact without exchange of body fluids) does not spread Lassa virus. Person-to-person transmission is common in health care settings (called nosocomial transmission) where proper personal protective equipment (PPE) is not available or not used. Lassa virus may be spread in contaminated medical equipment, such as reused needles.
Last month at least one secondary infection occurred in a contact of Germany's imported case from Togo, and earlier this week we saw media reports of another imported case - this time in Sweden.
Today the World Health Organization has posted the following update on Sweden's imported case, along with advice for increased surveillance in West Africa, and infection control vigilance among those who may be called upon to treat febrile patients returning from areas where Lassa fever is endemic
On 1 April 2016, the National IHR Focal Point for Sweden notified WHO of an imported case of Lassa fever infection.
The case is a 73-year-old woman returning to Sweden after travelling for 6 weeks across Liberia. She spent her first week in Monrovia. She then stayed for a week in Yekeba. During her third week in Liberia, the patient was in Voinjama where she was exposed to rodents. The patient spent the remaining weeks in Foya Kamara. She returned to Sweden on 2 March. Around 8 March, the patient developed symptoms (fever, chills, joint pain, headache and diarrhoea) and, on 17 March, was admitted to hospital. Medical investigations showed signs of encephalitis.
On 1 April, Lassa fever was laboratory confirmed at the Public Health Agency of Sweden by serology, polymerase chain reaction (PCR) and sequencing. The patient gradually recovered during her hospitalization but her hearing deteriorated. To prevent secondary transmission, she was transported to a specialized treatment centre and placed in an isolation unit.
Public health responseContact tracing among health care workers and family members has been completed. A total of 74 contacts are currently under observation. The follow-up period (21 days) for the last identified contact will be over on 22 April.
WHO risk assessmentCases of Lassa fever have already been imported from West Africa to Europe. Data from recent imported cases in Western countries show that secondary transmission of Lassa is rare when standard infection control precautions are observed but might occur. Therefore, the risk for further transmission of Lassa fever in Sweden cannot be excluded but it is currently considered to be low. WHO continues to monitor the epidemiological situation and conduct risk assessments based on the latest available information.
WHO adviceConsidering 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 Sweden nor Liberia based on the current information available.