By Edward K. Chapnick

Ebola is a zoonotic disease, which means that it occurs naturally in animals but that it can be transmitted to humans. Researchers aren’t sure yet which animal(s) are the hosts, but the frontrunner is the fruit bat. One of the biggest reasons that determining the host has been so difficult is that Ebola outbreaks ebb and flow, suggesting a rare species might be the host.

Some virus particles have a spherical shape, but the Ebola’s particles are filament-like in structure, which gives them more surface area to potentially attack a greater number of cells. Filo is Latin for filament, which describes the shape of the virus.

[Credit: CDC Public Health Image Library]
Credit: CDC Public Health Image Library

All viruses have attachment proteins, also referred to as glycoproteins. Part of what makes Ebola so infectious is that its long, filament-shaped virus particle is completely covered by these glycoproteins. The glycoproteins find a healthy cell, attach to it (that connection point is called a receptor site), and then the Ebola virus can enter the cell and the immune system, replicating itself as it goes.

Just like other viruses, after Ebola infects a person’s cells, it triggers the release of a bunch of different types of chemicals within the person’s body. These chemicals and cells are actually the immune response to the infection. If this response isn’t properly modulated, it can cause serious disease or death from infection. Sepsis refers to the systemic inflammatory (or immune) response to infection, which can be fatal.

In addition to the virus having a ton of glycoproteins, it’s also fairly impartial and will infect a wide range of cell types in the human body. Early on in the disease, Ebola typically invades a certain type of white blood cells associated with the immune system called T cells (short for t lymphocyte). After that early infection, it travels to the lymph nodes, spleen, and liver through the blood.

The time it takes for a person to show symptoms after the Ebola virus has initially attacked her system can be anywhere from 2 to 21 days, which is called the incubation period. On average, people start showing symptoms within eight to ten days.

Many factors influence how quickly symptoms progress and the immune system deteriorates, so the earlier a person identifies her symptoms and gets treated, the better her chances of recovery are.