What is parapertussis?

Pertussis is the proper medical term for whooping cough. Whooping cough is a nasty choking cough that often goes on for 3 weeks or more. The paroxysms of coughing are exhausting and there may be 12 episodes a day. Most cases are in teens and adults nowadays but infants are most susceptible and can die from it.

There are 3 kinds that affect humans. They are Bordetella pertussis, the commonest, Bordetella parapertussis, and the rarest which is Bordetella holmesii. Generally the only one that gets attention is the first as it had been responsible for most cases of whooping cough for at least a century.

The covid pandemic caused a general reduction in respiratory diseases including whooping cough but numbers have been creeping back up over the last 9 months. That is not a surprise, but what is surprising is that Germany and France are discovering that the predominant organism causing whooping cough is B. parapertussis.

If this turns out to be a pattern that is repeated in other countries it raises some issues that need to be better known generally.

  1. The good news is that is considered less serious than B. pertussis possibly because it does not produce pertussis toxin which is just one of the toxins Bordetella can produce. This may make it less serious for infants who are very susceptible to its damage.
  2. One of the standard tests for whooping cough is a blood or oral fluid test for pertussis toxin antibodies. Clearly they will be negative for whooping cough if parapertussis is the cause as it does not produce this toxin, leading to a negative diagnosis when it is really positive.
  3. Immunisation against B.pertussis, which is standard is thought to be ineffective or poorly effective against B. parapertussis.

It is not possible to predict what will happen. What is most important to know is that these bacteria are circulating all the time and rarely cause serious illness. Most of us have been exposed to them at some time during our life and probably developed some immunity without ever knowing it was happening. And every time we come across it subsequently we are likely to get boosted again if our immunity has dropped. Perhaps with only the symptoms of a mild cold or cough. To get a fully blown infection we might have to be invaded by a massive number of bacteria, such as when somebody with it coughs in our face or lives in the same house, or perhaps when we are already debilitated by a heavy cold.

There are so many variable factors that it makes it impossible to judge susceptibility, and most of the factors are not yet known. It parapertussis really gets hold we will quickly learn an awful lot more. That is science. That is life. 


Retired GP who is an expert on clinical whooping cough