Situation at a glance

On 21 March 2023, the Ministry of Health (MoH) of the United Republic of Tanzania declared an outbreak of Marburg virus disease (MVD) in the country. As of 22 March, a total of eight cases, including five deaths (case fatality ratio [CFR]: 62.5%) have been reported from two villages in Bukoba district, Kagera region, United Republic of Tanzania. Two of these cases were healthcare workers, one of whom has died. This is the first Marburg virus disease outbreak reported in the country.

As response measures, Rapid Response Teams have been deployed to investigate and implement interventions in the affected areas, including contact tracing and risk communication activities. WHO assesses the risk of spread as very high at the national level, high at the subregional level, and moderate at the regional level due to cross-border movements between Kagera region and bordering countries including Uganda in the north, Rwanda and Burundi in the west. The risk at the global level is assessed to be low.

Description of the situation

On 16 March 2023, the MoH of the United Republic of Tanzania announced that seven cases and five deaths from an unknown disease had been reported in two villages in Bukoba district, Kagera region, northern Tanzania. The cases were later confirmed as Marburg virus infection by reverse transcriptase-polymerase chain reaction (RT-PCR) at the National Public Health Laboratory, Tanzania. On 21 March 2023, the MoH officially declared the first MVD outbreak in the country.

As of 22 March, eight cases, including five deaths (case fatality ratio [CFR]: 62.5%) have been reported from Kagera region. The remaining three patients are currently undergoing treatment. As of 22 March, no cases have been reported from outside the Bukoba district of Kagera Region.

The first identified case reported travel history from Goziba Island in Lake Victoria in Tanzania and developed symptoms after returning to his village in Bukoba. The case died in the community. Four additional cases were identified from the same family as this index case. Further, two cases were reported among healthcare workers who treated them, one of whom died. No information is available on the eighth case; investigations are ongoing. Reported symptoms of the patients were fever, diarrhoea, vomiting, bleeding from various sites, and kidney failure. Samples from both deceased and live cases were taken and confirmed for Marburg virus by the National Public Health Laboratory.

Epidemiology of Marburg virus disease

Marburg virus disease is an epidemic-prone disease associated with high case-fatality rates (CFR 24-90%). It is caused by the same family of viruses (Filoviridae) as Ebola virus disease and is clinically similar. The current CFR for this outbreak is relatively high, at 62.5%.

Marburg virus infection often results from prolonged exposure to mines or caves inhabited by Rousettus bat colonies. Once an individual is infected with the virus, it can spread through human-to-human transmission via direct contact with the blood, secretions or other body fluids of infected or deceased people. Healthcare workers have previously been infected while treating patients with suspected or confirmed MVD. Burial ceremonies that involve direct contact with the body of the deceased can also contribute to the transmission of Marburg.

The incubation period varies from two to 21 days. Illness caused by Marburg virus begins abruptly, with high fever, severe headache, and severe malaise. Severe watery diarrhoea, abdominal pain and cramping, nausea, and vomiting can begin around the third day. Severe haemorrhagic manifestations may appear between five and seven days from symptom onset, and fatal cases usually have some form of bleeding, often from multiple areas. In fatal cases, death occurs most often between eight and nine days after symptom onset, usually preceded by severe blood loss and shock.

Clinical diagnosis of MVD is difficult in the early phase as symptoms are similar to other febrile illnesses. The differential diagnosis for MVD may include other filovirus diseases, Lassa fever, malaria, typhoid fever, dengue, rickettsial infections, leptospirosis and plague.

Laboratory confirmation is primarily made by RT-PCR. Other tests can be used such as antibody-capture enzyme-linked immunosorbent assay (ELISA), antigen-capture detection tests, serum neutralization tests, electron microscopy, and virus isolation by cell culture.

Although there are no vaccines or antiviral treatments for MVD, supportive care – such as rehydration with oral or intravenous fluids – and treatment of specific symptoms improve survival. A range of potential treatments are being evaluated, including blood products, immune therapies, and drug therapies.

This is the first time that Tanzania has reported an outbreak of MVD. Even though there is an ongoing outbreak of MVD in Equatorial Guinea (for more details, please see the Disease outbreak news published on 22 March), so far there is no evidence of an epidemiological link between the two outbreaks. Other MVD outbreaks have been previously reported in Ghana (2022), Guinea (2021), Uganda (2017, 2014, 2012, 2007), Angola (2004-2005), the Democratic Republic of the Congo (1998 and 2000), Kenya (1990, 1987, 1980) and South Africa (1975).

Public health response

• Regional and district-level Rapid Response Teams have been deployed to investigate and implement response measures.
• Contact tracing activities have been implemented to monitor people with similar symptoms in the community and at health facilities, including contacts of the known cases. A total of 161 contacts have been identified and 140 have been followed up and monitored by health professionals on 21 March.
• Risk communication activities have also been initiated in the Kagera Region to provide health awareness education and prevention messages.

WHO risk assessment

The United Republic of Tanzania has reported its first outbreak of MVD, which is a highly virulent disease, with a fatality ratio of up to 90%. The affected region, Kagera, borders three countries (Uganda to the north, and Rwanda and Burundi to the west) and Lake Victoria, and cross-border population movements may increase the risk of disease spread. In addition, Marburg virus has been isolated from fruit bats (Roussettus aegyptiacus) in Tanzania and countries neighboring the affected Kagera region, therefore, the same bat species may carry the virus in this region.

Due to the high CFR and existing risk of spread of the outbreak to other areas of the country, inadequate human, financial and material resources to implement response interventions, and the likelihood of existing capacities being overwhelmed if the cases increase, the risk at the national level is assessed as very high.

Following the recent Ebola virus outbreaks in the Democratic Republic of the Congo from 23 April - 3 July 2022 and from 21 August - 27 September 2022, and Sudan ebolavirus outbreak in Uganda from 20 September 2022 to 11 January 2023, neighbouring countries in the subregion, including the United Republic of Tanzania, have been building preparedness capacities against filovirus diseases. In the West African region, an outbreak of MVD was declared on 13 February 2023 in Equatorial Guinea and is ongoing.

Based on the available information, the risk is considered as high at the subregional level, moderate at the regional level and low at the global level.

WHO advice

Human-to-human transmission of Marburg virus is primarily associated with direct contact with the blood and/or other bodily fluids of infected people. Marburg virus transmission associated with health care services has been reported in previous outbreaks when appropriate infection control measures were not or were inadequately implemented.

Healthcare workers caring for patients with confirmed or suspected MVD should apply additional infection prevention and control  measures in addition to standard precautions, to avoid contact with patients' blood and other body fluids and with contaminated surfaces and objects.

Surveillance and detection activities, including contact tracing and active case finding, should be strengthened in all affected health zones. Measures to contain outbreaks of MVD include prompt safe and dignified burial of the deceased, identification of people who may have been in contact with someone infected with Marburg virus and monitoring their condition for 21 days, separation of healthy and sick people to prevent further transmission and care for confirmed patients, and maintenance of good hygiene and a clean environment.

Raising awareness of the risk factors for Marburg infection and the protective measures that individuals can take to reduce human exposure to the virus are key measures to reduce human infections and deaths.

WHO encourages all countries to ship samples (positive or negative) to a WHO Collaborating Center for confirmation.

Based on the current risk assessment, WHO advises against any travel and trade restrictions with the United Republic of Tanzania.