You’ve probably heard of the Ebola virus, one of the most well-known hemorrhagic fever viruses. But, there are actually several more. There are three main viral hemorrhagic fevers caused by the following viruses: Ebola, Marburg, and Lassa. All of these viruses are classified as Biosafety level 4 agents because of their high mortality and lack of effective prevention or treatment measures. However, not all hemorrhagic fever viruses are the same. Let’s take a look at each one and see what the similarities and differences are.
Transmission
Lassa Fever
The natural reservoir is the multimammate rat, one of the most common rodents in West Africa.
The virus is shed in the rodent’s urine and feces, which can be aerosolized and inhaled. Inhalation is the most common way of exposure, although ingestion can also occur (in some areas in West Africa, rodents are consumed).
Lassa fever is highly contagious.
Marburg Virus Disease
Fruit bats are the original reservoir.
Originally, human infection occurred as a result of inhaling bat droppings in mines.
Human-to-human transmission occurs very quickly, particularly through bodily fluids
Ebola Virus Disease
Fruit bats are also the original reservoir.
Ebola virus is introduced into the human population through close contact with the bodily fluids of infected animals such as primates, fruit bats, forest antelope and porcupines, found ill or dead or in the rainforest.
Burial ceremonies in which mourners have direct contact with the body of the deceased person also play a role in the transmission.
Epidemiology
Lassa Fever
Common in West Africa with seasonal fluctuation.
80% of patients are asymptomatic
In 2016 the “Lassa season” generated more cases than usual, with a case mortality unusually above 50%. This could be due to better detection but genetic sequencing showed a new lineage of the Lassa virus.
Increasing outbreaks may also be due to increasing urbanization and to climatic conditions favoring the rat.
Marburg Virus Disease
MVD is a much rarer disease than either Lassa fever or Ebola virus disease. However, it is clinically very similar to Ebola virus disease.
Most outbreaks of Marburg have been in single figures. Sporadic outbreaks have occurred since the 1967 outbreak.
Ebola Virus Disease
Prior to the 2014-2016 West African Ebola epidemic, outbreaks primarily occurred in remote villages close to tropical rainforests in Equatorial Africa.
Confirmed cases have been reported in the Democratic Republic of the Congo, Sudan, Gabon, Uganda, the Republic of the Congo and the Côte d'Ivoire.
In the 2014-2016 epidemic in West Africa, around 40% died. This was the largest Ebola outbreak the world had seen.
Pathophysiology
Lassa Fever
Unlike Marburg and Ebola, Lassa fever has a lower mortality and higher prevalence.
Even though this is true, vascular damage still occurs, hence making it a hemorrhagic fever virus.
In severe cases, the Lassa virus prevents the immune system from developing enough response to contain the replication of the virus.
Microscopic Image of Lassa Virus
Marburg and Ebola Virus Diseases
Infected cells migrate to the regional lymph nodes, the liver and the spleen, which spreads infection.
Monocytes, macrophages, and dendritic cells are the preferred replication sites for filoviruses upon initial infection.
Severe disease spectrum occurs when the virus triggers expression of pro-inflammatory cytokines, including interferons, interleukins and TNF-alpha. This affects vascular integrity and triggers coagulopathy and hypotension.
Prognosis
For all three viruses, severe disease is most often fatal. Mortality rates for Marburg and Ebola virus diseases are much higher than that of Lassa fever.
Lassa Fever
A large number of mild or asymptomatic cases go undiagnosed.
20% of patients present with severe disease. Around 15% of these patients die.
Deafness occurs in 25% of patients who survive severe disease. In half of these, hearing returns partially.
After recovery, the virus remains in body fluids for long periods of time. It is excreted in urine for three to nine weeks after infection and in semen for up to three months.
Ebola Treatment Unit in Uganda in 2022
Marburg Virus Disease
The mortality of MVD has been around 80%, although confirmed case numbers are relatively small. There is little available information on long-term complications.
Ebola Virus Disease
The West African 2014-2016 outbreak of EVD had an overall mortality of around 40%.
The mental health effects on survivors are profound.
Ebola virus may persist for many weeks in bodily fluids bringing risk of renewed transmission.
Survivors of Ebola virus infection develop antibodies that last for at least 10 years. However it is unknown if they can become infected with a different variant of Ebola.
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Sources: https://patient.info/doctor/lassa-fever-marburg-and-ebola-virus
Image Sources: https://commons.wikimedia.org/wiki/Help:Public_domain / https://www.alamy.com/licenses-and-pricing?v=2 / https://www.bloomberg.com/news/articles/2022-10-06/us-to-direct-uganda-travelers-to-5-airports-for-ebola-screening#xj4y7vzkg