Pertussis is a contagious infection caused by the bacteria Bordetella pertussis, which causes violent coughing spells, called paroxysms, which make it difficult to breathe.
When it is finally possible to breathe in, air is drawn in through partially closed, swollen airways and that creates a whooping noise which gives pertussis its other name, whooping cough.
Bordetella pertussis is a gram negative coccobacilli - meaning that it looks like a short pink rod on a gram stain.
It transmits from one person to another through a sneeze or cough, when that happens thousands of bacteria-filled droplets spray out about two meters or six feet away.
These droplets can land in the mouths or noses of nearby people, or get directly inhaled into the lungs.
The bacteria can also survive for several days on dry surfaces, so it’s also possible to get the bacteria by touching a surface, like a contaminated doorknob, and then touching your own eyes, nose, or mouth.
Bordetella pertussis releases toxins which are proteins that help the bacteria in various ways to attach to and damage the respiratory epithelial cells.
It starts with three toxins: Filamentous hemagglutinin, pertactin, and agglutinogen - all of which help to anchor Bordetella pertussis to the epithelia where it remains during an infection.
Next there’s the tracheal cytotoxin which paralyzes the cilia that are the little hairy projections on the epithelial cells so they can’t sweep back and forth anymore.
Normally these cilia sweep away mucus and any bacteria stuck in the mucus, so paralyzing the cilia allows pertussis to stay snugly attached to the epithelia.
This also means that mucus starts building up which triggers a violent cough reflex to clear the airway starting up those coughing fits.
Another toxin is pertussis toxin which also helps with anchoring pertussis to the epithelia as well.
In addition to this, though, pertussis toxin causes an increase in the absolute lymphocyte level in the blood, specifically an increase in the population of T cells floating around through a few mechanisms.