Whooping cough: an unwelcome return?

 

Whooping cough, or pertussis, is a respiratory illness caused by a bacterium called Bordetella pertussis. During an infection, these bacteria multiply in the airways, causing a build up of mucus, which is difficult to clear, and inflammation of the airways.. Prior to the first availability of a vaccine in the 1957, it was common for many children to  acquire the disease in childhood; however the incidence declined rapidly soon after introduction, and whooping cough soon got ‘consigned to the trash heap of history’ (or so we thought).

 

Vaccination for pertussis is currently given as a part of the ‘5-in1’ vaccine (covering diphtheria, tetanus, and pertussis [DTap], along with polio [IPV] and haemophilus influenzae [Hib, a form of pneumonia]). This is given to babies at two, three, and four months old, and a pre-school booster vaccine is given before children start school. Immunisation is effective  for about 5-10 years and covers the childhood period, during which time children are most at risk. The effect of the immunisation wears off over time and thus adults who were immunised as children may not be protected, and may be vulnerable to whooping cough. In the UK the incidence of whooping cough in older age groups is currently very high, which has become a source of some concern.

 

The original vaccine for whooping cough was called DTP, and this contained inactivated, whole, Bordetella pertussis bacterium, allowing the body to build up immunity without contracting the disease. This is in comparison with the current DTaP vaccine which doesn’t contain the bacterium but instead contains cell surface proteins which allow immunity to develop, but with fewer side effects. As of 2006, most of the developed world use the DTaP vaccination, however, much of the developing world continues to use DTP. It is thought that the use of DTaP, as opposed to DTP, could be contributing to the current peak in cases, due to the less long-lasting immunity conferred by it. A third vaccine has been developed called Tdap, with lower concentrations of the pertussis bacterium, for use in adults as a booster.

 

A recent report by the Health Protection Agency published data showing that so far in 2012, provisionally, there had been in excess of 2460 confirmed cases of whooping cough in England and Wales as compared to 322 at the same stage in 2008. Whilst the incidence of pertussis peaks every 3-4 years, as it a cyclical disease, previous years rises have been in keeping with projected increases. Although an element of this of course could be put down to increased awareness and reporting by health care professionals; it is thought that a major contributory factor is decreased levels of immunity.

 

The main symptoms of pertussis are similar to a cold, with a night-time cough, runny nose and mild fever. This can progress over about 10 days to fits of coughing which may be accompanied by vomiting or choking, this often comes in short burst and is followed by the characteristic gasp for air (whooping noise). This can often be followed by exhaustion and the feeling of not being able to catch your breath. Because there is more mucus in the airways, and consequentially damage to the airways, one of the major complications of whooping cough is pneumonia, as the bacteria are more likely to invade the body. There are also other complications that may or may not occur. Whooping cough is now treated by a short (5-day course) of antibiotics, but historically could have lasted up to about 3 months and thus was called the 100 day cough.

 

So what are the implications of the ‘epidemic’? The government is currently in talks with the Health Protection Agency and the Joint Committee of Vaccination and Immunization to work out whether offering the booster to teens and pregnant mothers would help control the epidemic. This could be because it is thought that mothers can pass on their immunity to their newborns via the placenta. It has also been proposed that Tdap boosters should be given to health care workers who are directly in contact with neonates. The interventions would be put in place to protect children from contracting whooping cough, as they are the most vulnerable group... A major consideration, of course, is the cost of vaccinating.

The USA already recommends that all pregnant women, all people in close contact with children under 12 months and all health care professionals receive a one-time dose of Tdap, and it is mandatory that all children of secondary school age receive the Tdap booster before starting school to protect them from whooping cough. The Joint Committee of Vaccination and Immunization and the HPA are waiting to receive more information about the routes of transmission and burden of disease before they come to the decision about what will be right strategy for the UK.

 

This article is based on a news item on the BBC which can be read here

 

References

 

 

 

 

By Aiysha Puri bsi@immunology.org