Disease Outbreak News: Lassa fever - Togo (24 March 2022)


Outbreak at a glance

WHO was notified of an outbreak of Lassa fever in Togo following the confirmation of a case on 26 February 2022. Active case finding, and contact tracing was conducted. The risk of transmission for this outbreak is assessed as low at the national and regional level given the experience of national authorities with past outbreaks and the cross-border communication with neighboring countries.

Description of outbreak

On 26 February 2022, the national authorities in Togo notified WHO of an outbreak of Lassa fever after a case, a 35-year-old female, from Takpamba town, Oti-South district, Savanes region was laboratory confirmed. The town borders Ghana and is located 96 kilometres from Dapaong - the capital city of the Savanes region. The case was previously living in a village in the Save commune in Benin, four kilometers from the Nigerian border, and arrived in Takpamba town, Togo, on 4 February prior to their symptom onset.

On 11 February, the case developed symptoms including fever, abdominal pain and cough, and consulted the local health care facility on 14 February. Following three days of oral treatment and no improvement, the case was taken to another health centre where she was hospitalised for 24 hours and was later referred to a hospital where she was managed as an outpatient. On 22 February, the case returned to the previously visited hospital following persistence of symptoms as well as having developed vomiting and bloody diarrhea. As a result of her clinical picture, Lassa fever was suspected, and the individual was isolated and notified to the health authorities. A sample was taken for laboratory analysis at the National Institute of Hygiene, Togo, and tested positive for Lassa fever on 26 February. The case died the same day, and a safe and dignified burial was performed.

A total of 26 contacts were identified from two health districts of the Savanes region, including 10 health care workers, one of which was symptomatic and isolated. The symptomatic health care worker was exposed through direct contact with the case but upon testing was negative for Lassa fever. As of 23 March, all contacts have completed the follow-up period, and none developed Lassa fever.

No outbreak has been reported from Benin or Ghana associated with this reported outbreak in Togo. There is an ongoing outbreak in Nigeria (for more details, please see the Disease outbreak news published on Lassa fever in Nigeria on 14 February 2022) , however, no epidemiological links have been elucidated as part of this investigation.

Epidemiology of Lassa fever

Lassa fever is an acute viral haemorrhagic fever that is primarily transmitted to humans through direct or indirect contact with food or household items contaminated with infected Mastomys rodents’ urine or faeces. Though to a lesser extent, person-to-person infections can occur during the acute febrile phase through virus particles present in blood and bodily fluids of the infected person. This includes transmission in the health care facility and laboratory; thus, health care workers should be among the risk groups targeted for prevention. Overall, the case fatality ratio is around 15% among hospitalized patients with severe presentation.

The incubation period of Lassa fever ranges from 6 to 21 days. The onset of the disease, when symptomatic, is 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.

The antiviral drug, ribavirin has been given as treatment for Lassa fever in recent years, however, recent systematic reviews showed there is no strong evidence about the efficacy of ribavirin treatment on the outcome of patients with Lassa fever as well as optimal dosing regimens, highlighting the need for further research, particularly in the form of randomized clinical trials. Therefore, if the decision is to use ribavirin, it should be made under clinical trial protocol to evaluate safety and efficacy of the drug and the dosage. There is currently no approved vaccine for Lassa fever, however, optimized supportive care provided as early as possible with rehydration and symptomatic treatment can increase the chance of survival.

Lassa fever is endemic in West Africa with cases frequently reported from Benin, Ghana, Guinea, Liberia, Mali, Nigeria and Sierra Leone. Togo is affected to a lesser extent, however, since 2016, outbreaks and sporadic cases have been reported in the country every few years. Notable Lassa fever outbreaks have occurred in Togo in 2016, 2017, and the most recent was in January 2019 when two imported cases from Nigeria were reported in the Central and Kara regions of Togo. No further cases were identified, and the Ministry of Health declared an end to the outbreak in February 2019.

Outbreaks of Lassa fever in Togo have involved importation and exportation of cases at various times to nearby countries requiring the need for cross-border communication. In both endemic regions and areas with sporadic cases in West Africa, the majority of cases are reported during the dry season from December to April.

Public health response

WHO is supporting the response activities in the country and assisted in conducting the safe and dignified burial of the patient.

Active case-finding and contact tracing activities are ongoing at the household and the affected health facilities. If contacts experience any Lassa fever symptoms, case management teams have been trained to ensure that these suspected cases receive adequate care in a dedicated ward.

Other response measures undertaken include sensitization of health care workers, taking stock inventory of ribavirin, preparing a minimum capacity for case management at district level, providing risk communication messages to the public, and reinforcing infection prevention and control measures in health facilities.

WHO risk assessment

The country has proven to have adequate response capacity to Lassa fever outbreaks in the past, however, several challenges including lack of resources for case management such as insufficient number of isolation rooms, stock shortages of antiviral treatment and supportive therapy, lack of reinforcement of infection prevention and control measures in health facilities, as well as delays in sample testing turnaround times have been noted in the country during the current outbreak.

Additionally, the borders are very porous in this area with constant cross-border movement which poses a risk for transmission to neighbouring countries. However, given the management of past outbreaks and the experience with cross-border communication between national health ministries regarding Lassa fever outbreaks, the risk of transmission remains low at the national and regional level.

WHO advice

Prevention: Prevention of Lassa fever in endemic countries relies on community engagement and promoting hygienic conditions to discourage rodents from entering homes. Family members and health care workers should always be careful to avoid contact with blood and body fluids while caring for sick individuals.

Infection prevention and control:

  • In health care settings, staff should consistently implement standard infection prevention and control (IPC) measures when caring for patients, regardless of their presumed diagnosis to prevent healthcare-acquired infections.

  • Standard infection and control precautions comprise appropriate hand hygiene, rational use of personal protective equipment (PPE), environmental cleaning, isolation and safe injections practices.

  • In order to avoid any direct contact with blood and body fluids and/or splashes onto facial mucosa (eyes, nose, mouth) when providing direct care for a patient with suspected or confirmed Lassa virus, personal protective equipment should include:

    • clean non-sterile gloves;

    • clean, non-sterile fluid resistant gown; and

    • protection of facial mucosa against splashes (mask and eye protection, or a face shield).

International travel and trade:

  • WHO advises against the application of any travel or trade restrictions on Togo based on the currently available information on this outbreak.

  • Exportation of Lassa fever can occur via travellers from areas where the disease is endemic to non-affected areas. The diagnosis of Lassa fever should be considered in febrile patients who have travelled within West Africa, especially if they have been in rural areas or hospitals in countries where Lassa fever is endemic.