New research fights the deadly hack of whooping cough

It’s a diagnosis you can make while the patient is still in the waiting room. A characteristic repetitive hacking cough, typically with a “whoop” sound heard as the person breathes in. In children it is unmistakable; among adults the coughing sound may be less dramatic but is severe and prolonged; patients will often tell you they cough until they are blue in the face.

Whooping cough, also called pertussis, is an infectious disease caused by the bacteria Bordetella pertussis which, despite the availability of a vaccine, is increasing in developed countries including Ireland.

It is spread by coughing and sneezing, and is highly infectious. The bug is sensitive to the antibiotic erythromycin, but treatment within seven days of the onset of symptoms is required if a prolonged cough is to be avoided.

After an incubation period of about 10 days, symptoms of an upper respiratory infection such as a runny nose, sneezing and a fever develop.

About two weeks later comes the characteristic whooping phase, which lasts for four weeks or even longer. Recovery can take up to 16 weeks.

Vaccine

So why is whooping cough on the march if there is a vaccine available to prevent it? The main reason is the discovery that, compared with other vaccinations, pertussis wears off after about 10 years or so. A vaccine composed of whole bacteria was first introduced in the 1940s. However, side effects associated with its use led to the development of a new, “cleaner” vaccine made from distinct components of the bacteria.

The new vaccine, called the acellular pertussis vaccine, was introduced to the routine vaccination schedule for infants and children here in the mid-1990s.

But it has now emerged that the antibody stimulation by the childhood acellular pertussis vaccination schedule does not last. How to develop a more robust vaccine is among the topics being discussed at an international Bordatella conference at Trinity College Dublin this week.

A major goal of the conference will be to try to explain and respond to the increased incidence of whooping cough in children and adults and to discuss proposals for developing an improved vaccine, according to Kingston Mills, professor of experimental immunology at TCD.

“This meeting will provide an ideal forum for scientists, clinicians, healthcare officials and industry to discuss the recent outbreaks of whooping cough and how research in basic science may help to provide a better vaccine,” he says.

This year, Mill’s research team at the school of immunology and biochemistry made novel discoveries concerning the current vaccine against whooping cough. Most vaccines include a component called an adjuvant to boost immune responses to the bacterial or viral antigens in the vaccine; the acellular pertussis vaccine uses an aluminium salt, called alum. However, the team has shown that the vaccine could be improved further through the use of a different adjuvant.

Last year, the number of cases of pertussis reported to the Health Protection Surveillance Centre had doubled since 2011.

In 2012, the UK had nearly 10,000 cases and 10 deaths in infants under three months. Some 90 per cent of pertussis-related deaths occur in those less than six months. Babies under two months cannot be vaccinated and are reliant on the rest of the population having adequate antibodies to prevent them getting the infection.

Pertussis can do unpleasant things to immature brains: it can cause brain damage because of a lack of oxygen getting to the brain. And it also damages developing lungs by causing pneumonia in almost one in four children who are hospitalised with whooping cough. A condition called bronchiectasis, in which the bronchi in the lungs are abnormally widened, allowing mucus to collect in the lungs, can develop in adults who experienced a severe bout of whooping cough as a child.

Whooping cough is an unpleasant illness for grown children and adults. But for babies it can be fatal, which is why we need this week's conference to find ways to develop a new and more potent vaccine against Bordetella.

Dr Muiris Houston is a specialist in general practice and occupational medicine and a medical education consultant. mhouston@irishtimes.com | muirishouston.com