What is it?
Pertussis, also known as whooping cough, is a very contagious bacterial disease. Symptoms usually begin with those of the common cold, and proceed to weeks of coughing fits. The severity of the cough is illustrated by the fact that it is not uncommon to vomit, get hemorrhages in the eyes, or break ribs from the effort. Infants often have periods of not breathing instead of a cough. The name whooping cough originates from the “whoop” sound young children make, as they try to inhale after a fit (in older people this turns into a gasp).
WHO has estimated that in 2008, 16 million cases of pertussis occurred, 195 000 children died from it, and 95% of all cases happened in developing countries.
What causes it?
Pertussis is caused by the infection of a species of bacteria. It resides in the respiratory tracts, so it easily spreads through the air when an infected person coughs or sneezes.
What happens during it?
There are lots of microbes and other potentially harmful things in the air that we breathe. One way our body handles this is by producing mucus in the respiratory tracts. The mucus traps particles and also helps to keep the surfaces moist.The mucus is processed in the digestive tracts and needs to be swallowed, which is, for obvious reasons, a more complicated process in the lungs than in, for example, the nose. The lungs have an outer layer of cells that have hair-resembling projections called cilia on them. The job of the cilia is to produce movement that slowly pushes the mucus out from the lungs to the throat so that it can be swallowed.
The pertussis bacteria anchor themselves to these cells and produce toxins that disable them. Mucus is not transported away from the lungs. When the body realizes this, it tries to come up with an alternative solution to get rid of the things that have accumulated in the lungs: making the person cough violently.
The pertussis bacteria also produce a toxin that inhibits the immune system from reacting normally to the presence of the bacteria. The toxin essentially causes a type of immune cell to release too much energy too quickly, which leads to the disablement of its functions and, consequentially, its ability to fight the infection.
How can it be treated?
Pertussis isn’t nearly as big a problem in the developed world as it used to be, thanks to the vaccine invented in the 20th century. Our bodies have sophisticated immune systems, and one of their peculiarities is that they remember pathogens they have been exposed to. When the body is first infected with something, it takes time for it to figure out what to do: but when it is infected with that same thing again, it remembers what to do and the response is much quicker and more effective. Vaccines work by introducing a pathogen safely to the body so that it can create a memory of it while not being under immediate attack. They are important to individual health, but absolutely essential in preventing the spread of a disease in the population.
Very ill individuals can be hospitalized. Infections in children under the age of 1 is particularly fatal: in the US, 1.6% of hospitalized infants younger than this die. Antibiotics can be used in the first weeks of the illness, and while they rarely help much with symptoms, they reduce the risk of spreading the disease. Resting and drinking lots of fluids is useful, but cough medicines are unlikely to be of any benefit.
Sources: https://en.wikipedia.org/wiki/Pertussis, http://www.who.int/immunization/topics/pertussis/en/, https://en.wikipedia.org/wiki/Bordetella_pertussis, https://en.wikipedia.org/wiki/Tracheal_cytotoxin#Mechanism_of_Pathogenesis, https://en.wikipedia.org/wiki/Mucociliary_clearance, https://en.wikipedia.org/wiki/Cilium, http://www.nhs.uk/Conditions/Whooping-cough/Pages/Introduction.aspx