What do green monkeys, fruit bats, and python caves all have in common? All have been implicated in outbreaks as transmission sources of the rare but deadly Marburg virus. Marburg virus is in the same Filoviridae family of highly pathogenic RNA viruses as Ebola virus, and similarly can cause a rapidly progressive and fatal viral hemorrhagic fever.
In the first reported Marburg outbreak in 1967, laboratory workers in Marburg and Frankfurt, Germany, and in Belgrade, Yugoslavia, developed severe febrile illnesses with massive hemorrhage and multiorgan system dysfunction after contact with infected African green monkeys imported from Uganda.
The majority of MVD outbreaks have occurred in sub-Saharan Africa, and primarily in three African countries: Angola, the Democratic Republic of Congo, and Uganda. In sub-Saharan Africa, these sporadic outbreaks have had high case fatality rates (up to 80%-90%) and been linked to human exposure to the oral secretions or urinary/fecal droppings of Egyptian fruit bats (Rousettus aegyptiacus), the animal reservoir for Marburg virus. These exposures have primarily occurred among miners or tourists frequenting bat-infested mines or caves, including Uganda’s python cave, where Centers for Disease Control and Prevention investigators have conducted ecological studies on Marburg-infected bats. Person-to-person transmission occurs from direct contact with the blood or bodily fluids of an infected person or contact with a contaminated object (for example, unsterilized needles and syringes in a large nosocomial outbreak in Angola).
On April 6, 2023, the CDC issued a Health Advisory for U.S. clinicians and public health departments regarding two separate MVD outbreaks in Equatorial Guinea and Tanzania. These first-ever MVD outbreaks in both West and East African countries appear to be epidemiologically unrelated. As of March 24, 2023, in Equatorial Guinea, a total of 15 confirmed cases, including 11 deaths, and 23 probable cases, all deceased, have been identified in multiple districts since the outbreak declaration in February 2023. In Tanzania, a total of eight cases, including five deaths, have been reported among villagers in a northwest region since the outbreak declaration in March 2023. While so far cases in the Tanzania MVD outbreak have been epidemiologically linked, in Equatorial Guinea some cases have no identified epidemiological links, raising concern for ongoing community spread.
To date, no cases in these outbreaks have been reported in the United States or outside the affected countries. Overall, the risk of MVD in nonendemic countries, like the United States, is low but there is still a risk of importation. As of May 2, 2023, CDC has issued a Level 2 travel alert (practice enhanced precautions) for Marburg in Equatorial Guinea and a Level 1 travel watch (practice usual precautions) for Marburg in Tanzania. Travelers to these countries are advised to avoid nonessential travel to areas with active outbreaks and practice preventative measures, including avoiding contact with sick people, blood and bodily fluids, dead bodies, fruit bats, and nonhuman primates. International travelers returning to the United States from these countries are advised to self-monitor for Marburg symptoms during travel and for 21 days after country departure. Travelers who develop signs or symptoms of MVD should immediately self-isolate and contact their local health department or clinician.
So, how should clinicians manage such return travelers? In the setting of these new MVD outbreaks in sub-Saharan Africa, what do U.S. clinicians need to know? Clinicians should consider MVD in the differential diagnosis of ill patients with a compatible exposure history and clinical presentation. A detailed exposure history should be obtained to determine if patients have been to an area with an active MVD outbreak during their incubation period (in the past 21 days), had concerning epidemiologic risk factors (for example, presence at funerals, health care facilities, in mines/caves) while in the affected area, and/or had contact with a suspected or confirmed MVD case.
Clinical diagnosis of MVD is challenging as the initial dry symptoms of infection are nonspecific (fever, influenza-like illness, malaise, anorexia, etc.) and can resemble other febrile infectious illnesses. Similarly, presenting alternative or concurrent infections, particularly in febrile return travelers, include malaria, Lassa fever, typhoid, and measles. From these nonspecific symptoms, patients with MVD can then progress to the more severe wet symptoms (for example, vomiting, diarrhea, and bleeding). Common clinical features of MVD have been described based on the clinical presentation and course of cases in MVD outbreaks. Notably, in the original Marburg outbreak, maculopapular rash and conjunctival injection were early patient symptoms and most patient deaths occurred during the second week of illness progression.
Supportive care, including aggressive fluid replacement, is the mainstay of therapy for MVD. Currently, there are no Food and Drug Administration–approved antiviral treatments or vaccines for Marburg virus. Despite their viral similarities, vaccines against Ebola virus have not been shown to be protective against Marburg virus. Marburg virus vaccine development is ongoing, with a few promising candidate vaccines in early phase 1 and 2 clinical trials. In 2022, in response to MVD outbreaks in Ghana and Guinea, the World Health Organization convened an international Marburg virus vaccine consortium which is working to promote global research collaboration for more rapid vaccine development.
In the absence of definitive therapies, early identification of patients with suspected MVD is critical for preventing the spread of infection to close contacts. Like Ebola virus–infected patients, only symptomatic MVD patients are infectious and all patients with suspected MVD should be isolated in a private room and cared for in accordance with infection control procedures. As MVD is a nationally notifiable disease, suspected cases should be reported to local or state health departments as per jurisdictional requirements. Clinicians should also consult with their local or state health department and CDC for guidance on testing patients with suspected MVD and consider prompt evaluation for other infectious etiologies in the patient’s differential diagnosis. Comprehensive guidance for clinicians on screening and diagnosing patients with MVD is available on the CDC website at https://www.cdc.gov/vhf/marburg/index.html.
Dr. Appiah (she/her) is a medical epidemiologist in the division of global migration and quarantine at the CDC. Dr. Appiah holds adjunct faculty appointment in the division of infectious diseases at Emory University, Atlanta. She also holds a commission in the U.S. Public Health Service and is a resident advisor, Uganda, U.S. President’s Malaria Initiative, at the CDC.