Introduction

Marburg virus is a highly virulent and deadly pathogen. It is classified as a Group 4 pathogen by the World Health Organisation (WHO), indicating that it presents a high risk at individual and community levels.¹ It causes Marburg Virus Disease, a rare disease with a high death rate.² 

Overview of marburg virus

History and epidemiology

The Marburg virus was first detected in 1967 during its outbreak in Germany (Marburg and Frankfurt) and Belgrade, Serbia. Workers at a laboratory became infected after handling African green monkeys imported from Uganda. The incident marked the first documented appearance of the virus, which took its name from the German city of Marburg. Since then, sporadic outbreaks have occurred worldwide, primarily in sub-Saharan Africa.² In September 2024, widespread outbreaks of the virus in Rwanda made headlines. In September alone, 26 confirmed cases, including eight deaths, were reported from different regions of this African country.

Structure and transmission  

The Marburg virus belongs to the Filoviridae family of viruses. It is the same group of viruses that includes the Ebola virus. It is an enveloped, single-stranded, negative-sense RNA virus, and its structure has many similarities with the Ebola virus.² 

The virus is a zoonotic pathogen that originates in animals and can spread to humans. Fruit bats of the Pteropodidae family, specifically the Egyptian fruit bat (Rousettus aegyptiacus), are the natural hosts of the Marburg virus. These bats harbour the virus without showing symptoms, but they can transmit it to other animals and humans. Transmission from bats to humans occurs through direct contact with bats, such as when people enter caves or mines where infected bats live or if humans consume a fruit contaminated by a Marburg virus-infected bat.²

Once a human is infected, the virus can spread from person to person through:²

• Direct contact with the infected person or bodily fluids (saliva, blood, etc.) of a person infected with the virus
• Contact with surfaces and materials contaminated with the fluids of an infected person, such as clothing, needles, medical equipment, etc
• Transmission can occur in hospitals through healthcare workers, especially if proper infection control measures are not followed

Clinical presentation

The incubation period for the Marburg virus ranges from 3 to 21 days. The infection begins with nonspecific symptoms and can progress to severe haemorrhagic fever, multi-organ failure, and death in many cases. The clinical course is divided into three phases:  initial generalisation phase, early organ phase, and late organ phase or convalescence phase. Each phase is characterised by specific clinical signs, which include:²

Initial generalisation phase

• Sudden onset of high fever
• Chills
• Myalgias (muscle pains)
• Joint pain
• Headache
• Malaise (feeling of being generally unwell)
• Nausea
• Vomiting
• Skin rash

Early organ phase

• Conjunctivitis (redness of the eyes)
• Fluctuating high and low body temperatures
• Agitation
• Seizures
• Confusion
• Haemorrhagic fever symptoms-
  • Mucosal bleeding: Bleeding from mucous membranes such as the gums and nose.
  • Hematemesis: Vomiting of blood
  • Haematochezia: Rectal bleeding
  • Petechiae: Small red or purple spots caused by bleeding under the skin
  • Bleeding from venipuncture sites: Patients begin to bleed from sites where intravenous (IV) lines or blood draws are performed

Late organ phase/convalescence phase

During this phase, the extent of organ involvement becomes evident, and the risk of multi-organ failure is highest. In this phase, the infection can become extremely severe, potentially leading to death. Alternatively, in survivors, this phase is the beginning of recovery (convalescence).

Diagnosis of marburg viral infection in a clinical setting

Diagnosis of Marburg infection is based on a combination of clinical evaluation, patient history, and laboratory confirmation.

Medical history and clinical evaluation

In a clinical setting, the diagnosis of Marburg viral infection begins with a clinical evaluation and detailed patient history. Patients are assessed for clinical signs such as the sudden onset of high fever, chills, muscle aches, headache, and joint pain, progressing to haemorrhagic symptoms.

These clinical symptoms are evaluated against the patient’s history. This involves determining if the patient has come in contact with possible risk factors. Important considerations include:²

• Recent travel to endemic areas
• Contact with infected individuals
• Occupational exposure, particularly individuals involved in mining or caving, where bats are found. 

Laboratory testing methods

The definitive method for diagnosing the Marburg virus is through laboratory testing. Laboratory methods include:^2,3

Reverse transcriptase-polymerase chain reaction (RT-PCR)

RT-PCR is a molecular technique that is the most widely used and reliable laboratory diagnostic method for detecting Marburg virus infection.

Procedure

• A sample (such as blood, saliva, urine, etc.) is collected from a patient suspected of having a Marburg virus infection. The sample is collected using safe and proper procedures, such as using personal protective equipment (PPE) to avoid exposure.
• The RNA in the sample is converted into complementary DNA (cDNA) through reverse transcription.
• The cDNA is then amplified using PCR, with primers specific to the Marburg virus genome.
• Detection is achieved through fluorescence-based methods, such as real-time PCR. 

Advantages

• High sensitivity and specificity: It can detect even small quantities of viral RNA in a sample, making it highly sensitive. RT-PCR has high specificity because it uses primers specific to the Marburg virus genome
• Early detection: It can detect the virus during the early phase of the infection

Limitations

• Requires specialised equipment, which is not necessarily available in resource-limited regions
• It is more expensive than other diagnostic tests due to the need for specific equipment

Enzyme-linked Immunosorbent Assay (ELISA)

Enzyme-linked immunosorbent assays are used to detect Marburg virus-specific antibodies or viral antigens in blood or other bodily fluids.

Types of ELISA Test

• There are two main types of ELISA used: antigen-capture ELISA and IgG/IgM-capture ELISA
• Antigen-capture ELISA and IgM-capture ELISA are used for diagnosis during the early phase of infection
• IgG-capture ELISA is used for diagnosis in the later phase of infection

Procedure

• It involves coating an ELISA plate with viral antigens or antibodies and adding patient samples (such as blood and bodily fluids)
• Then, enzyme-linked antibodies are added, which bind to the target antigens or antibodies
• The results are determined by measuring a colour change, indicating the presence of a virus

Advantages

• It is easy and simple to perform and suitable for large-scale testing
• Used in research in vaccine development and immunology studies

Limitations

• Possible cross-reactivity with other filoviruses (e.g., Ebola virus)
• Less sensitive than RT-PCR, particularly in early-phase infections

Virus isolation

It is not routinely used in clinical settings due to the need for Biosafety Level 4 (BSL-4) laboratories. Virus isolation confirms Marburg virus infection by growing the virus in cell cultures. This method is mainly used in research. 

Differential diagnosis

Since the symptoms of Marburg virus infection resemble those of many other infectious diseases, it is necessary to rule out other conditions that have similar clinical presentations. The differential diagnosis includes:² 

• Ebola virus disease
• Lassa fever
• Dengue
• Malaria
• Typhoid fever
• Rickettsial disease
• Shigella infection
• Meningitis 

Challenges in diagnosing marburg virus

Various factors make the timely and accurate diagnosis of Marburg virus a significant challenge, especially in resource-limited regions. These include:

• Diagnosis of Marburg virus is particularly challenging because its early symptoms, such as fever, headache, and muscle aches, are nonspecific and resemble those of many other common infections, like malaria, typhoid fever, or flu. This makes it difficult to differentiate Marburg virus infection from other diseases
• Confirming the virus requires advanced and specialised laboratory diagnostic methods, such as Reverse transcriptase-polymerase chain reaction (RT-PCR) tests, enzyme-linked immunosorbent assays (ELISA), etc. However, in many outbreak-prone regions, especially in rural or low-resource areas, these advanced tools are often unavailable, leading to delayed diagnosis
• The virus’s long incubation period, which ranges from 3 to 21 days, complicates the detection process, as individuals remain asymptomatic for long periods, unknowingly spreading the virus

Treatment and preventive measures

There are no specific antiviral drugs or vaccines approved for Marburg virus disease. Treatment is limited to supportive care, which involves rehydration therapy with intravenous fluids, pain management, and blood transfusions for managing severe bleeding.² 

Preventive measures include practising strict infection control during outbreaks, such as:²

• Isolation of patients
• Using proper personal protective equipment (PPE)
• Using disposable medical equipment
• Avoiding procedures that generate aerosol
• Maintaining hygiene protocols such as regular handwashing and surface disinfection

Summary

Marburg virus infection is a severe and highly infectious disease that leads to severe haemorrhagic fever. It has high death rates. The virus is primarily transmitted to humans through contact with infected fruit bats and can spread between humans through bodily fluids. Diagnosis of Marburg virus is difficult due to the virus's initial nonspecific symptoms. Diagnostic procedures such as RT-PCR, ELISA, and viral isolation are used to confirm the virus. Treatment is mainly supportive. Strict preventive measures, such as infection control protocols, quarantine, and community awareness, are practised to reduce transmission during outbreaks. Ongoing research on antiviral therapies and vaccines is paving the way for more effective management in the future. Continued research and development of diagnostic tools and treatments are necessary for improving outcomes for those affected by Marburg virus infection and preparedness for future outbreaks.