Lassa Fever – Guinea, World Health Organization, May 2022

Lassa Fever – Guinea, World Health Organization, May 2022

Organization: World Health Organization

Type of publication: Rapport

Date de publication: 13 May 2022

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Situation at a glance

On 22 April 2022, the Ministry of Health and Public Hygiene of Guinea declared a Lassa fever outbreak following the laboratory confirmation of two cases from the Guéckédou prefecture in the southeast of Guinea. Lassa fever is endemic in several countries in West Africa and Guinea has previously reported outbreaks as well as sporadic cases. Given that the Guinean health system has been overwhelmed due to several concurrent emerging and re-emerging infectious disease outbreaks since last year, this current outbreak may have a serious public health impact. To date, no deaths have been reported.

Description of the case

On 20 April 2022, local health authorities were notified of a suspected case of hemorrhagic fever in Guéckédou prefecture, southeast Guinea (Figure 1). The case was a 17-year-old female who experienced fever and loss of appetite on 12 April. From 16 to 17 April, the case additionally reported chest pain and physical weakness. On 18 April, the case sought medical care, and was admitted to a hospital on 19 April. The case received home care for five days since symptom onset and consulted two health facilities, which resulted in 141 reported contacts.

On 20 April, a blood sample was collected from the suspected case, and reverse transcriptase polymerase chain reaction (RT-PCR) analyses were performed at the Guéckédou hemorrhagic fever laboratory for Ebola, Marburg and Lassa fever. The case tested negative for Ebola and Marburg on 20 April but was confirmed positive for Lassa fever on 21 April. On 22 April, a second test was conducted at the reference laboratory in Conakry, which tested positive again. On the same day, the Minister of Health and Public Hygiene declared a Lassa fever outbreak. The case is currently receiving care at a health facility in Guéckédou.

On 28 April, a second confirmed case of Lassa fever, with no known epidemiological link to the first case, was reported in Guéckédou prefecture. The case was a 24-year-old male. On 16 April, he presented with chest pain and insomnia and sought care at a private clinic on 18 April. On 28 April, he sought care at the provincial hospital for symptoms including fever, headache, vomiting, thoracic pain and bloody stools. On 29 April, he was confirmed positive for Lassa fever by laboratory testing in a treatment facility in Guéckédou. Epidemiological investigations are underway to determine the source of the infection.


Lassa fever is an acute viral hemorrhagic disease caused by the Lassa virus. It is primarily transmitted to humans either through direct contact with infected Mastomys rodents, or through food or household items contaminated with the urine or faeces of infected rodents. Although to a lesser extent, transmission can also occur from human-to-human through direct contact with blood or bodily fluids of an infected person, mainly in a hospital setting, due to the lack of adequate infection prevention and control measures.

Most cases (approximately 80%) are asymptomatic or mild, but the virus can cause severe disease in the remaining 20% of patients with a case fatality ratio (CFR) of approximately 15% among severely ill patients.

Early supportive care for patients is critical and improves survival. There is currently no vaccine that protects against Lassa fever.

Lassa fever is endemic in the West African countries of Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, and Nigeria, and is likely to be present in other West African countries as well. In Guinea, Lassa fever was first diagnosed in October 2011. Since then, outbreaks and sporadic cases have been reported in Guinea. The last reported outbreak of Lassa fever in Guinea was in 2021, with 8 cases and 7 deaths (88% CFR) reported in the prefectures of N’Zérékoré, Beyla, Guéckédou and Yomou.

Public health response

The Ministry of Health and Public Hygiene, in collaboration with WHO and other partners, has responded to the outbreak by strengthening prevention activities in the region. The Ministry of Health and Public Hygiene has:

  • Developed a response plan and is mobilizing funds to finance it.
  • Delivered drugs and case management supplies to the field.
  • Deployed a rapid response team to support the response activities.
  • Implemented standard interventions, including isolation of suspected cases, laboratory confirmation, infection prevention and control in health facilities, and social mobilization and community engagement.

WHO risk assessment

The risk for this outbreak at the national level is considered high, because Lassa virus is endemic in the country associated with the presence of the animal host reservoir, Mastomys rats. In addition, there are limited financial, human and logistical resources and the Guinean health system has been severely overwhelmed since last year. In 2021, Guinea experienced several concurrent emerging and re-emerging infectious diseases such as Ebola, Marburg, Lassa fever, measles, meningitis, yellow fever, vaccine-derived polio type 1, and COVID-19. This outbreak could have a serious impact on public health due to the already fragile health system.

The results of preliminary epidemiological investigations suggest that there is a risk of nosocomial and community transmission from the first case.

At the regional and global level, the risk of spread is considered low due to the primary mode of transmission of the disease, being the exposure to rodents. Although Guéckédou is located in proximity to the international borders with Liberia and Sierra Leone, the risk of cross-border transmission of cases can be considered low. However, since Lassa fever is endemic in Liberia and Sierra Leone due to the presence of Mastomys rodents, the risk of exposure is present in these two countries.