What's up, Doc? Marburg virus can overwhelm the immune system
Q: Is the Marburg virus that's causing the present outbreak in Africa the same thing as Ebola?
A: The Marburg virus (MV) is different from the Ebola virus (EV), but they're both in the family Filoviridae (which are single-stranded negative-sense RNA viruses) and have many similarities, including being one of 30-plus different types of viruses that can cause viral hemorrhagic fevers (VHFs). VHFs differ in many ways, including the specific viruses that cause them (when caused by MV, the disease is called Marburg hemorrhagic fever), the way they're transmitted, the animal reservoirs that may harbor them and the prognosis for infected people.
Marburg hemorrhagic fever (MHF) was identified in 1967 during an outbreak in Germany (in the town of Marburg, hence the name) and Serbia (then part of Yugoslavia), when African green monkeys imported from Uganda for the pharmaceutical industry passed the disease on to humans. Since then, several sporadic outbreaks of MHF have occurred in Eastern Africa, and a recent outbreak has been reported with cases in Equatorial Guinea and Tanzania.
MV invades macrophages and other components of the immune system (including the lymph nodes, the reticuloendothelial system and others), then potentially spreads to other organs. The speed at which the MV virus multiplies may overwhelm the body’s immune system, preventing an adequate response; this contributes to the virulence of the disease.
After an incubation period of 2 to 21 days (the average is 5 to 9), the first phase of MHF starts with non-specific flu-like symptoms of a very high fever (up to 104 degrees Fahrenheit or more), severe headache, chills, body aches and malaise. Many patients also develop gastrointestinal symptoms of abdominal pain, nausea, vomiting and/or diarrhea. Symptoms can also include a sore throat, conjunctivitis, rash and others.
Over the next 5 to 14 days, the patient’s condition may worsen as they develop early organ involvement leading to shortness of breath, edema (excess fluid buildup in body tissues), easy bleeding (spontaneously from the gastrointestinal tract or other places, or from small skin punctures such as when an IV is started; this is often dramatically featured in unrealistic ways in movies and TV shows), kidney, pancreas, liver and/or other organ compromise. Some patients recover at this phase and do not progress to the late organ involvement phase.
Two to three weeks after initial symptoms, the late organ involvement phase may begin, often causing critical illness that may include seizures, severe metabolic imbalances, diffuse bleeding, multiorgan failure, shock, coma and/or other complications. Most patients who die from the infection do so during this phase.
MHF is diagnosed based on suspicion from the symptoms and a risk of exposure to the virus. Specialized blood tests are typically done to confirm a diagnosis.
The mortality rate for MHF is overall thought to be about 50%; in the original outbreak in Germany-Yugoslavia, the mortality rate was 22%. But in some of the subsequent identified outbreaks in Africa, a mortality rate of as high as 80% to 90% has been noted.
As with the Ebola virus, one of the mysteries of the Marburg virus is where it is harbored between outbreaks. Although not certain, there is some evidence that bats are a potential reservoir for it.
Once a person is infected with Marburg, the virus may be transmitted from patient to person via direct contact with the infected patient’s body fluids. Insects do not spread MV; if they did, the disease would be much more widespread. Just look at how widespread malaria (which is spread by mosquitoes) is.
Presently, there are no specific treatments approved for MV infection. There is also no approved vaccination to prevent it. However, research to address both of these unmet needs is being done.
For now, treatment of MHF patients revolves around supportive care to help stabilize them while their immune system tries to combat the infection. The virulence of this disease limits the success rate of this strategy and mortality rates are still extremely high. Quarantine of infected individuals and rigorous infection control measures need to be utilized to help minimize the spread of this disease.
Jeff Hersh, Ph.D., M.D., can be reached at DrHersh@juno.com.
This article originally appeared on MetroWest Daily News: Marburg virus' speed can overwhelm the body's immune system
