Whooping Cough – the disease that takes your breath away

Bordetella pertussis is the bacteria responsible for Pertussis, more commonly known as Whooping Cough and recently responsible for keeping a good proportion of my in-laws quarantined.

B. pertussis is a pathogen that resides in the respiratory tract of susceptible hosts after inhalation of aerosol from someone else who is infected. This is the nice way of saying “breathing in someone else’s spit and mucous after they have coughed or sneezed” which is why the characteristic cough was thought to play a very important role in pathogenesis for the organism allowing it to spread effectively from one person to another. In fact, and as with most diseases, the time period where you are infectious to others is generally very early in the infection often before symptoms develop. In the case of Pertussis this is also true, if you have the cough you are probably no longer infectious, doesn’t do much for you though because that cough is less than fun.

Whoop-it (cough) Whoop-it good (Devo inspired heading 🙂 )

Coughing Child
Infant with Pertussis cough. Courtesy of the Pennsylvania Chapter of the American Academy of Pediatrics

The name ‘Whooping Cough” was attributed to Pertussis infections in the 1640’s presumably after hearing suffers of the disease during a coughing fit. The actual ‘whoop’ is horrible to have to listen too and becomes audible during coughing fits as the patient runs out of air to cough with. They quickly take a deep breath in making the characteristic ‘whoop’ sound. You can try this yourself at home by exhaling as much as possible then trying to inhale as much air as quickly as possible, just don’t do it whilst eating or drinking please, we wouldn’t want you to choke because then you might sue us, then we’d have to pay up and I don’t have any money alright so JUST BACK OFF!!!!!

Sorry about that, shall we continue?

Despite being first diagnosed in the mid 16th century formal identification of the infectious agent took a few hundred years until a man named Bordet isolated Bordetella pertussis from samples in the Institut Pasteur in 1906. He also did some other stuff like describe phagocytosis (the process where specialised cells of your immune system engulf and destroy foreign objects – like bacteria and viruses) and discovered complement (a component of your blood that is vital in fighting disease) which comprised major advancements in the field of immunology. When you achieve these sorts of things, they tend to give out Nobel Prizes. He got his in 1919 (specifically for his work on the immune system) and they named the bacteria he discovered after him as well.

Off topic thought: Would you really want to have your name immortalised as a bacteria that remains the primary cause of death by bacterial infection in infants less than 2 months old? Maybe you do, as long as you have a legacy I guess…

B. pertussis is known to only exist in humans but other Bordetella species can cause infections in other animals. The most common is in dogs called ‘kennel cough’ as it is acquired most often in dog boarding centres and spreads quickly.

Bordet Plate
He gets a bacteria, a Nobel Prize AND a personalised agar plates! That’s it I’m making Thomas and I our own plates!

Pathogenesis of disease or “what the frig is happening?”

The course of disease is actually quite simple. After inhalation of aerosol the bacteria adhere to the respiratory tract. After burrowing through the mucous to the actual skin layer of the respiratory system the bacteria begin to multiply. This damages the outermost layer of skin (called the epithelium) which the body senses and in response does two things, increases mucous production and sends in the cavalry (immune system) resulting in significant inflammation.

However, B. pertussis is crafty. To prevent its removal in the mucous the bacteria adheres more strongly to cilia, hair like structures on the lung epithelial surface, and so is able to persist in the lung. The cilia’s role is similar to that of turnstile, except it doesn’t rotate, it only moves back and forward. As the turnstile moves it pushes people along. Cilia move together to push mucous along and up the respiratory tract to the top of the throat where the mucous is swallowed. The bacteria stick to the cilia like bubblegum to the turnstile so that even though the cilia move the bacteria will not. This allows the tissue damage to continue to increase and the body’s response to continue to increase in response.

Initially the symptoms are very similar to a cold or flu, but, as the disease progresses, the patient continues to degenerate. Both the mucous and the inflammation are responsible for the cough that gets worse as the damaged area increases and the bacteria continue to multiply. It can reach a point where the coughing fits become so intense that they can induce vomiting causing the patient to begin to suffer the effects of malnutrition.

The disease is particularly bad for infants. Due to the coughing and vomiting, infants struggle to develop normally and can die due to associated complications. Infants can present with symptoms as extreme as cerebral hypoxia (low oxygen levels in the brain), hypertension, sub-conjunctival haemorrhage (burst blood vessels in the eye) and rectal prolapse (the lowest part of the bowel is turned inside out and is pushed through the anus). Pneumonia is also common particularly in infants less than one month old.

Older children (>10 years) and adults may not present with the typical cough but those that do can also develop the same symptoms as the infants listed above. Interestingly if the cough does develop in this group it is often seen only at night.

Treatment and Prevention

As parents are normally concerned about every pop, sneeze or whistle to come out of a newborn, early intervention is possible and this can help the treatment of the disease. Antibiotics are administered upon diagnosis but have been found to not impact greatly on the time course of disease. Instead there use is important to prevent spread of the infection. In infants <6 months old  hospitalisation is often recommended as infants can deteriorate quickly and may need extra assistance due to feeding difficulties and hypoxia (low oxygen levels).

Adults are a little different as they know what’s best for them, always, and they are never wrong. As mentioned above, the initial symptoms are quite mild so most adults put off seeing a doctor during the time that early intervention is useful but are also given antibiotics to reduce spread of disease.

Prevention has been possible since the 1920’s and continual development has enabled us, over the years, to improve the efficacy of the vaccine. Despite the years of development the current vaccines do not last forever but instead have been designed to last through the majority of childhood where exposure and risk are at their highest levels.

Administration of the vaccine happens alongside vaccination for tetanus and diphtheria hence the vaccines name, the DTP vaccine. The B. pertussis vaccine component is made by taking whole cells and inactivating them such that they cannot multiply and cause disease. Despite this there has always been controversy surrounding this vaccine and particularly its use as a booster in children.

The controversy surrounds very rare side effects that can lead to local (at the site of vaccination), systemic (throughout the whole body) or external site diseases (not at the site of vaccination) after delivery of the vaccine. During the 1970’s and 80’s alongside a growing suspicion of the side effects of MMR vaccination (Measles, Mumps and Rubella) questions were raised regarding a suspected link between DTP vaccination and brain development issues. This led Japanese researcher Yuji Sato to develop a vaccine that does not contain whole B. pertussis cells but instead just contained a number of components important for immune system recognition. DTP vaccines that contain Sato’s mix are called DTaP vaccines or Diphtheria, Tetanus and acellular Pertussis vaccine.

Multiple studies have since disproven any link between brain development issues and DTP vaccination and in fact the World Health Organisation still purchase the DTP style vaccine for use in the third world as it costs significantly less.

We do not, in anyway, endorse this product – its just an example of a packet of medicine with ‘pertussis’ written on the front

…and in conclusion

Whooping cough remains common enough to require vaccination but over the years has become less and less common due to the development of improved sanitary conditions and treatment options. We are continuing to look at ways to develop safer and more effective vaccines that last longer, negating the need for constant booster shots to maintain protection. But no matter how effective the current treatment and vaccine cohort is it will not change the fact that disease most often occurs before vaccination is possible. Until we develop new strategies for dealing with pre-vaccination disease, B. pertussis will continue to remain an issue for new parents into the future.

In regards to my in-laws quarantine mentioned at the start, they are all fine. Their ‘quarantine’ is simply a precaution to prevent community spread and limit disease severity if it should develop which, with all the variables considered, probably won’t.

References

Preston A. (2005). “Bordetella pertussis: the intersection of genomics and pathobiology” Journal of Medical Chemistry V137 (1)

Wood N and McIntyre P. (2008). “Pertussis: review of epidemiology, diagnosis, management and prevention” Paediatric Respiratory Reviews V9

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